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• Mixed convection for a viscoelastic fluid within a square enclosure containing a rotating cylinder was numerically simulated. • The Phan-Thien-Tanner (PTT) model was used to describe the viscoelastic fluid behavior via the OpenFOAM software. • The numerical divergence at high Weissenberg numbers was addressed using a log-conformation approach. • Elevating the Weissenberg number reduced the frictional torque by 54 % and raised the Nusselt number from −1.33 to 3.32. • As the Weissenberg number increased from 1 to 100, there was a significant decline in the tangential normal stress. This paper for the first time conducted numerical simulations for the mixed convective flow and heat transfer with a viscoelastic fluid within a square enclosure containing a rotating cylinder. The flow regime was considered laminar, two-dimensional, and transient, and the Phan-Thien-Tanner (PTT) model, recognized as one of the most accurate nonlinear models for viscoelastic fluids, was used to describe the viscoelastic fluid behavior, mathematically. Solving nonlinear fluid equations, predicting the complex properties of viscoelastic fluids using the constitutive equation of the PTT model, and considering viscous dissipation were the challenges of this research. Additionally, the paper addressed the numerical divergence at high Weissenberg numbers using a log-conformation approach based on a logarithmic variable change in the polymer stress equation. The effects of the Richardson, Weissenberg, and Brinkman numbers and the ratio of polymeric viscosity to total viscosity on fluid flow and heat transfer were investigated by solving the nonlinear equations via the finite volume method. This was accomplished using the rheoHeatFoam solver within the OpenFOAM software. Local and average heat transfer characteristics around the rotating cylinder were fully studied. The results showed that elevating the Weissenberg number enhances the shear-thinning effect and diminishes the effective viscosity of the fluid by 63 %, resulting in a 54 % reduction in both the shear stress around the cylinder and the frictional torque applied to it, as well as a decrease in the viscous dissipation. Furthermore, increasing the Weissenberg number raised the Nusselt number from -1.33 to 3.32, signifying a complete reversal in the direction of heat transfer. However, the shear-thinning effect became negligible when the Weissenberg number exceeded 100. Moreover, the tangential normal stress significantly increased with an increase in the Weissenberg number up to one. However, as the Weissenberg number increased from 1 to 100, there was a significant decline in the tangential normal stress. Consequently, at very high Weissenberg numbers, the tangential normal stress approached zero, resembling a Newtonian fluid. [ABSTRACT FROM AUTHOR]

• The outdoor air relative humidity also has an impact on the threshold temperature of frost accumulation. • Under certain conditions, higher efficiency of heat recovery may be safer in terms of frost risk. • The largest ' frost ' accumulation area is formed for the middle values of the return air relative humidity (in analyzed case RH 2 i =38.5 %). In this paper, a process of frost accumulation inside the non-hygroscopic rotary heat exchanger depending on operating conditions is investigated. The study was based on the results of the numerical simulations conducted in the original computer program. The analysis considers both the threshold conditions of frost accumulation and the conditions of frost layer growth. For this purpose, three indicators related to frost accumulation were distinguished: a frost accumulation limit temperature, a surface of the matrix covered with the accumulated frost layer, a maximum thickness of the accumulated frost layer. The analyzes assessed the influence of operating parameters on these indicators, focusing on the return air relative humidity. It was revealed that the highest values of this parameter cause the greater thickness of the frost layer. However, the largest ' frost ' accumulation area was created in the range of average return air relative humidity values – in the analyzed cases it was RH 2 i =38.5 %. The paper also includes a detailed analysis of the threshold temperature of frost accumulation. These limits of outdoor air temperature were determined for a wide range of operating parameters' values: both airstream relative humidity and nominal temperature effectiveness. Additionally, eight probable configurations of active heat and mass transfer areas within rotary heat exchanger channels were revealed, which are related to the initiation of frost accumulation. Consequently, the locations of the initial ' frost ' accumulation area were predicted. It was also found that the greatest impact on the frost accumulation threshold temperature has the return air relative humidity RH 2 i , although this influence is not unequivocal. The most unfavorable conditions regarding nominal temperature effectiveness in terms of frost accumulation are also unclear. In some cases, it was even demonstrated that an increase in the effectiveness can eliminate the ' frost ' accumulation area. [ABSTRACT FROM AUTHOR]

• LaplacianFoam in OpenFOAM® solves the scalar diffusion equation. • Thermal diffusivity may be often incorrectly used in heat conduction problems. • It is tempting to make just a little change from a constant to a scalar field. • To correctly model heat conduction in heterogeneous media, ρ , c p and λ is needed. In the paper "Numerical study with OpenFOAM on heat conduction problems in heterogeneous media" by K. Zhang, C.-A. Wang, J.-Y. Tan, International Journal of Heat and Mass Transfer, Vol. 124 (2018) 1156–1162 the authors modify laplacianFoam from open-source CFD package OpenFOAM® to solve heat conduction problems in heterogeneous media by changing the diffusion coefficient from a constant value to a scalar field. Their paper clearly demonstrates a fundamental, overlooked, and common mistake in rearranging the heat conduction equation, which cannot be replaced with the temperature diffusion equation. In this comment, we provide clear evidence through mathematical derivations and numerical examples calculated in OpenFOAM®. [ABSTRACT FROM AUTHOR]

• A comprehensive review on numerical simulations of boiling heat transfer from atomistic to mesoscopic and macroscopic scales is presented. • Critical issues related to nanoscale bubble nucleation mechanisms, pool boiling, and flow boiling are highlighted. • Potential solutions and future research in the field of boiling heat transfer using the MDS, LB and CFD methods are proposed. Boiling is an efficient heat transfer mode with significant potential for thermal management in high-power electronic equipment. However, a comprehensive understanding of the boiling process, which encompasses bubble nucleation, growth, coalescence, slipping, and detachment across various scales, remains challenging. Molecular dynamics simulation, lattice Boltzmann, and computational fluid dynamics methods are popular and powerful tools for investigating boiling heat transfer phenomena at microscopic, mesoscopic, and macroscopic scales. These methods enable researchers to uncover the underlying boiling mechanisms and propose heat transfer enhancement techniques. Therefore, this paper provides a comprehensive review of boiling heat transfer, spanning from atomistic to mesoscopic and macroscopic scales, utilizing these three numerical methods. It addresses critical issues related to nanoscale bubble nucleation mechanisms, pool boiling, and flow boiling, and proposes potential solutions and future researches, supplementing our previous review [Some advances in numerical simulations of multiscale heat transfer problems and particularly for boiling heat transfer, Annu. Rev. Heat Transf., 6 (2022) 217–269]. Besides, by shedding light on the characteristics of these numerical methods in studying boiling heat transfer, this paper aims to foster their development and advance enhanced heat transfer technologies. [ABSTRACT FROM AUTHOR]

• Local condensation heat transfer in smooth channels and pin fin array is presented. • The effect of operating parameters on the heat transfer characteristics was analyzed. • Sensitivity analysis is performed of heat transfer to identify the critical parameters. • Condensation heat transfer increases with heat flux in the range of vapor quality above 0.4. In this paper, an experimental study of flow condensation was carried out of R134a in a multiport mini channel and a mini channel with pin fin array. The former comprised 20 parallel rectangular channels with an equivalent diameter of 0.64 mm. The latter is a narrow rectangular mini channel containing 10 rows of diamond pin fins with a staggered configuration, and height and longitudinal/transverse pitch of 0.5 mm and 2 mm respectively. To acquire the local value of heat flux and heat transfer coefficient, air jet impingement cooling devices were adopted to condense the vapor of refrigerants. The effects of vapor quality, mass flux, heat flux, and saturation pressure on flow condensation heat transfer coefficient were investigated with the operating conditions: vapor quality from 1 to 0, mass flux from 160 to 450 kg/(m2s), heat flux from 10.0 to 39.8 kW/m2, and saturation pressure from 600 to 1500 kPa. The experimental results indicated that the pin fin array significantly improves the condensation heat transfer coefficient up to nearly 186 % compared to the multiport mini channel in the high vapor quality region. For both channels, the local heat transfer coefficient increases with an increase in vapor quality, mass flux, and heat flux whereas decreases with increase in saturation pressure. The influence of heat flux and mass flux on heat transfer coefficient was more pronounced in the high vapor quality region than in the low vapor quality region. A sensitivity analysis was performed at different vapor quality levels. The most influential parameters in the smooth channel and the pin fin array are saturation pressure and mass flux, respectively. The relative contribution of heat flux is more obvious in the high vapor quality region. Some of the existing correlations have good prediction performance for the smooth channel experimental data in this paper, and the corresponding MAD is within 20 %. However, their deviations are much greater for the applications of pin fin array. [ABSTRACT FROM AUTHOR]

• The liquid metal cross flow tube bundle under pulsation condition is simulated. • The effect of different pulsation frequency and amplitude are analyzed. • Circumferential flow field and temperature field of the single tube are analyzed. • The vortex characteristics and turbulent structure are analyzed with PSD and CWT. Liquid metal has a broad application prospect in tube bundle heat exchangers because of its excellent thermal conductivity. However, conventional in-line tube bundle arrangements often exhibit limited secondary flow, so new methods are urgently needed to improve heat transfer. The topic of this paper is to combine two methods, liquid metal cross flow tube bundle and pulsating flow, to improve the heat transfer performance in-line tube bundles. Firstly, the applicability of the model was validated through experimental data from existing literature, encompassing overall flow dynamics, heat transfer performance, and circumferential pressure distribution around the tubes. Subsequently, numerical simulations are conducted involving liquid metal cross flow in-line tube bundles at varying pulsating frequencies, amplitudes, and Reynolds numbers. Circumferential pressure distributions and temperature profiles for individual tubes were analyzed and compared. The amplitude of reduction in thermal resistance compared to the no-oscillation condition increases gradually from a minimum of 8 % in the first row to a maximum of 40 % in the third row, while the reduction in the rear row of tubes is similar to that of the third row. Remarkably, a reversal in the trend of thermal resistance for the first three rows of tubes under pulsating flow were observed, contrasting conventional flow except for the case with an amplitude of 0.1. By analyzing the local transient flow field distribution near single tube and the corresponding circumferential heat transfer performance, the influence of the vortex evolution characteristics on the heat transfer performance at different phases of the pulsating velocity is revealed, which transient Nu is up to three times that of flow with no pulsating. Finally, a series of coherence analyses reveal that as frequency rises, turbulence exhibits a richer spectrum of small-scale vortex structures, intricately linked to enhanced energy cascade efficiency. Amplitude augmentation intensifies velocity fluctuations, particularly at high amplitudes, resulting in substantial energy peak amplification. The integrated heat transfer performance PEC factor varies in the range of 1.25 to 1.51 for all the conditions simulated in this paper, which indicates that the liquid metal coupled pulsating flow approach can significantly increase the comprehensive performance of the tube bundle heat exchangers. These findings hold significant promise for advancing heat exchanger design and enhancing thermal efficiency, with implications for various engineering applications. [ABSTRACT FROM AUTHOR]

• Optimize the thermosyphon loop thermal performance by controlling loop wettability. • Long-term effective hydrophilic and hydrophobic modification method was determined. • The optimum wall wettability under different filling ratios was clarified. • The optimized R loop is reduced by 6.9% to 53.5% under different filling ratios. The behavior of vapor-liquid two-phase transport within the riser of the two-phase thermosyphon loop significantly impacts the heat transfer process from the evaporation to the condensation, as well as the circulation velocity, thus playing a crucial role in the heat transfer performance. However, existing research has predominantly focused on optimizing the performance of the evaporator, overlooking the optimization of vapor-liquid two-phase flow patterns and transport characteristics within the loop. This paper aims to optimize the heat transfer performance of the two-phase thermosyphon loop by controlling the wall wettability of the loop. The strategy employed involves modifying the wettability of the riser to regulate the two-phase flow within the loop, while visualization techniques are utilized to investigate the influence of riser wettability on the vapor-liquid two-phase distribution and heat transfer performance of the two-phase thermosyphon loop. The findings reveal that the impact of wall wettability on flow behavior and heat transfer performance within the loop varies significantly with changes in the filling ratio. This paper sheds some light on the riser wettability of two-phase thermosyphon loops to optimize the thermal performance. [ABSTRACT FROM AUTHOR]

• The modified Murray's law distributes branching microchannels evenly under heat source. • The TLMHS-Ms exhibit the better thermal performance except for Nussle number. • With the same branching level, all TLMHS-Ms can afford the higher heat flux than TLMHS-Cs. • The higher branching levels can dissipate more heat flux in the TLMHSs. Based on the traditional Murray's law, the tree-like microchannel heat sinks (TLMHSs) cannot distribute the branching microchannels in given heat source region, so they cannot fully match exactly with the chips. This causes that their heat dissipation capacity is not very outstanding among various heat dissipation methods, and cannot be employed as a cooling method for chips with high heat flux. This paper improves the Murray's law and enables high-level branching microchannels to cover the whole region of heat source. Based on the modified Murray's law, the TLMHSs with evenly-distributed high-level microchannels (TLMHS-Ms) are proposed and their flow and heat transfer characteristics are analyzed numerically using the commercial software Fluent. The results indicate that the improved Murray's law can avoid obvious non-branching region found in the conventional TLMHSs (TLMHS-Cs). Compared with the TLMHS-Cs, the TLMHS-Ms possess the lower maximal temperature, temperature difference and thermal resistance. Depending on the aforementioned superior heat dissipation properties, the TLMHS-Ms can afford the higher heat flow under the same conditions. It is also found that the higher branching levels in the TLMHSs tend to reduce the maximal temperature, temperature difference, thermal resistance, Nusselt number and pressure drop, but the higher coefficient of performance. Among all TLMHSs, the TLMHS-Ms with k max =6 can afford the largest heat flux of 264 W/cm2. This work can provide a novel TLMHS with evenly-distributed high-level microchannels for cooling the chips with high heat flux. [ABSTRACT FROM AUTHOR]

• An efficient solver in the OpenFOAM software was developed. • The level-set model was adopted for high-precision and high-quality capturing of the fouling front. • The dynamic evolution of the fouling front and its sophisticated interactions with hydrodynamics were examined. • The relatively slight supersaturation prolonged the fouling time to several months. • The velocity increase had a smaller impact on reducing the deposit's asymptotic resistance. Most heat exchangers in wastewater treatment systems and the thermal desalination industry experience the deposition of unwanted materials on their surfaces. One of the primary causes is the supersaturation of salts with inverse solubility near the heat exchanger's heated surfaces. In this paper, a long-term simulation of the crystallization fouling of calcium carbonate by developing an efficient solver in the OpenFOAM software is proposed. The k-ω SST model was used to simulate turbulence, and the level-set model was adopted for high-precision and high-quality capturing of the fouling front inside the heat transfer tubes of a forced circulation crystallizer. The results demonstrated that the developed solver is a promising tool for accurately predicting moving boundary conjugate heat transfer. Upon validation of the results, the dynamic evolution of the fouling front and its sophisticated interactions with hydrodynamics were examined. The crystallization fouling was found to be under reaction control. Furthermore, the relatively slight supersaturation caused delayed front growth, which prolonged the fouling time to several months. Besides, findings demonstrated that the intensive competition between removal and deposition mechanisms at higher inlet velocities resulted in decreased asymptotic thermal resistance. Additionally, the velocity increase had a smaller impact on reducing the deposit's asymptotic resistance. [ABSTRACT FROM AUTHOR]

• The TF model based on FLUENT undergoes secondary development. By loading UDFs, the DTF model is applied on FLUENT to simulate turbulent combustion. • LES-DTF method coupled with the skeletal mechanism of kerosene is used to investigate the influence in ignition process under low-temperature inlet. • The key factors that influence the ignition process in the cold flow field are analyzed. • The reasons why low-temperature inlet and high oil gas ratio affect the ignition process are discussed. Radiation significantly influences turbulent combustion. This paper investigates the impact of radiative heat transfer on the ignition process in a multi-staged model combustor. The ignition process is simulated both without and with consideration of radiation. Large Eddy Simulations based on the Euler-Lagrange description of the liquid spray and the Dynamic Thickened Flame model coupled with a skeletal chemical reaction mechanism are employed. The Weighted Sum of Gray Gases method are employed to solve the spectral properties and the Discrete Ordinates method is employed to solve the radiative transfer equation. The results indicate that radiative heat transfer influences the flame structure during the ignition process. In the flame propagation phase, both the total heat transfer and the exit average temperature are higher, with the radiative heat transfer during ignition being less than 15% of the total heat transfer. During the kernel generation phase, radiative heat transfer leads to a 7.24% increase in the maximum temperature of the flame kernel, a 7.74% expansion of the flame surface area, and outward movement of the position of the maximum heat release rate. Additionally, the ignition delay time extends by 14.91%. In the flame propagation phase, the flame transfers heat to the mixed gas and droplets near the flame surface through radiation, promoting flame spread. [ABSTRACT FROM AUTHOR]

• Distinct bubbly flow regimes of refrigerant R452B in vertical microchannel are visualized. • Flow boiling sequence is simulated to estimate heat transfer coefficients and pressure drops. • Effects of mass flux, heat flux and vapor quality on thermal and frictional outcomes are analyzed. • Fluid properties and two-phase flow patterns can notably affect heat transfer performance. • Bertsch/Sun and Mishima correlations can suitably calculate thermo/friction characteristics. Energy management efficiency is crucial for the increasingly severe global energy challenges. Low global warming potential (GWP) refrigerant R452B used in air conditioning and refrigeration systems could reduce the global warming effect for applications. The objective of this paper is to conduct the numerical and experimental studies for examining the thermal fluid behaviors of flow boiling evolution of refrigerant R452B in the vertical microchannels. In the experimental approach, a gear pump and a programmable DC power supply are employed to regulate the mass flux and heat flux for determining the heat transfer and pressure drop outcomes across the microchannel at varied vapor qualities. A high-speed camera with a LED fiber optical light source is used to observe the close-up optical images over the complex flow boiling process. Theoretically, the volume-of- fluid (VOF) method built in the computational fluid dynamics (CFD) software ANSYS/Fluent® is employed to simulate the progression of bubble nucleation processes for resolving the distributions of velocity, pressure, temperature and liquid volume fraction in the microchannel. The predictions are compared against the measured heat transfer coefficients and pressure drops for the CFD model validation. The time sequences of vapor volume fraction contours are also simulated to characterize the evolving vapor-liquid interfaces for better grasping the detailed behaviors of nucleation, growth, departure, coalescence of bubbles and the transformations of dominant flow patterns. The measured results estimate the average heat transfer coefficients and pressure drops up to 14.1 kW/m2K and 76.5 kPa at a mass flux of 600 kg/m2s in the microchannel. This research further conducts the performance assessments by testing the popular correlations, and thereby reveals the effectiveness of Bertsch as well as Sun and Mishima correlations to reasonably calculate the heat transfer coefficients and pressure drops of R452B refrigerant, involving the mean absolute errors of 12.5 % and 22.6 %, respectively. [ABSTRACT FROM AUTHOR]

• The effect of filling pressures on a gravity-assisted cryogenic loop heat pipe was experimentally studied. • Filling pressures were determined based on the presumption of vapor-liquid distribution. • Heat transfer behavior and hysteresis phenomena under different filling pressures were investigated. • Test results show a good agreement with the presumptions regarding vapor-liquid distribution. This paper investigated the effect of filling pressure on the operating characteristics of a gravity-assisted cryogenic loop heat pipe(CLHP) for use in gravity environments such as terrestrial and lunar environments. The CLHP wick is made of sintered stainless-steel fibers with a pore radius of 1.56 μm and designed with a heat transport distance of 2.05 m. The experiments were conducted under gravity-assisted conditions (the condenser was placed 0.1 m higher than the evaporator). Notably, the filling pressure originated from the assumed vapor-liquid distribution in the CLHP under steady-state conditions. The filling pressure was varied from 2.9 MPa to 3.4 MPa in 0.1 MPa increments for six different conditions. Specifically, (1) 2.9 MPa and (2) 3.0 MPa are conditions where the heat leakage due to the vapor phase in the evaporator core is large, while (3) 3.1 MPa and (4) 3.2 MPa are conditions where there is no vapor phase in the evaporator core and the surplus vapor phase escapes to the CC. In general, this condition is considered to be the optimum amount of working fluid for room-temperature LHPs when designing. (5) 3.3 MPa and (6) 3.4 MPa are overfilling conditions that cause the CC to be filled with liquid. The results revealed that the higher the filling pressure, the more obvious the variation in operating temperature caused by the transition of drive modes. The maximum heat transfer capability reached 25 W in cases (1)-(4). In cases (5) and (6), the heat transfer capabilities increased to 30 W, although the operating temperature was higher. Furthermore, the hysteresis effect under different filling pressure conditions was newly confirmed. The power cycling experiments demonstrated that hysteresis in the operating temperature occurred at high heat loads and showed a similar trend to the room-temperature LHP. [ABSTRACT FROM AUTHOR]

· The heat transfer characteristics in the concentration polarization zone are analyzed. · IUT, Nusselt number and Field synergy angle are applied for heat transfer performance evaluation. · Cooling capacity is improved by increasing the twists and turns in the cooling flow field. Heat management plays a vital role in the efficient and stable operation of proton exchange membrane fuel cells (PEMFCs), especially at high current densities, which is directly related to the cooling flow field (CFF). In this paper, a non-isothermal electrochemical model coupled with CFF of PEMFC is developed, and the effects of CFF structures on the water and heat transfer performance enhancement of PEMFC at high current densities are studied. In addition, an Evaluation Criteria is expected to be applied to evaluate the heat transfer capacity of CFFs. The results indicate that high temperatures effectively alleviate PEMFC concentration polarization. Due to the twists and turns design within the channel, the heat transfer capability of the Wave CFF performs well, Nusselt number and field synergy angle values respectively 35.7 % higher and 3.34 % lower than those of Parallel CFF. Additionally, the heat transfer performance factor is used to evaluate the heat transfer capability of different cooling flow field structures. The performance factor of the Wave CFF reaches 1.44 at a coolant temperature difference of 1 K. [ABSTRACT FROM AUTHOR]

• Experimental study on spray cooling with microencapsulated phase change suspension. • Latent heat of suspension improves spray cooling by up to 33.9 % relative to water. • Excessive suspension concentration results in the deterioration of spray cooling. • Optimal spray rate or height exists when liquid-film exactly covers heat surface. • Optimal inlet temperature is 10 °C lower than melting peak temperature of particle. This paper reveals the spray cooling heat transfer mechanism with the microencapsulated phase change suspension as the working fluid based on an experimental investigation. The heat transfer performances between the spray cooling and jet impinging with suspension are compared. A series of key parameters affecting the heat transfer are analyzed, including suspension concentration, nozzle diameter, spray height, inlet temperature, and spray inclined angle. It concludes that the spray cooling of suspension has a stronger heat transfer capability relative to the jet impinging, but the pressure loss is correspondingly larger. Compared with the water, the spray cooling heat transfer of phase change suspension is superior owing to the latent heat ability of particle core, and the maximum improvement in the current tests is 33.9 %. However, excessive suspension concentration can result in the deterioration of heat transfer because of the larger viscosity. There is an optimal volumetric flow rate and an optimal spray height for the spray cooling, where a suitable spray cone angle is present so that the heating surface may be exactly covered by the liquid-film. The latent heat absorption characteristic of phase change core leads to the existence of an optimal spray inlet temperature, which is about 10 °C lower than the melting peak temperature of the particle core. For the cases of incomplete-coverage, the decrease of the spray inclined angle may enlarge the liquid-film covering area and thence improve the heat transfer. A theoretical analysis indicates that the suspension in current tests has a high complete-melting rate (σ ≥ 93.7 %) when using in the spray cooling. The results may provide the beneficial support for the potential application of spray with phase change suspension for the cooling of electronic devices. [ABSTRACT FROM AUTHOR]

• The heat transfer characteristics of different horizontal wires immersed in both liquid and supercritical carbon dioxide were studied by visualization experiments with a schlieren system. • Pseudo film boiling shown the similar heat transfer characteristics and near-wall flow field structure with subcritical film boiling. A correlation based on an integral mean Raleigh number predicted the Nusselt number well. • Experiments with various metal wires revealed distinct self-propagating transition phenomena in boiling modes, driven by the axial heat conduction characteristics. Near-critical and supercritical fluid heat transfer exhibits unique heat transfer characteristics. Pool heat transfer experiments circumvent the drawbacks of traditional flow heat transfer experiments, characterized by numerous factors and challenges in observation, and can offer new insights for the study of heat transfer mechanisms. In this paper, the heat transfer characteristics of different horizontal wires immersed in both liquid and supercritical carbon dioxide were studied by visualization experiments with a schlieren system. The study showed that as approaching the critical point, the pool boiling weakened, resulting in a decrease in the peak heat transfer coefficient. In supercritical cases, heat transfer with low heat flux maintained natural convection, while the cases with high heat flux exhibited similar heat transfer laws and near-wall flow field structures with subcritical film boiling. Meanwhile, experiments with various metal wires revealed distinct self-propagating transition phenomena in boiling modes, driven by the axial heat conduction characteristics. Based on the experiments, a pool heat transfer mechanism of the near-critical and supercritical fluids was proposed. [ABSTRACT FROM AUTHOR]

• There are 226 s to prevent TRP within the same layer. • 596 s can be used to prevent TRP between layers. • HR duration and peak temperature are different in the three modes. • TR triggered at the battery bottom is more hazardous than the top. Currently, the transportation industry, especially shipping, is still accompanied by serious carbon emissions and pollution. Electric ships are the most promising way to solve this problem. However, the application of electric ships in maritime affairs also faces many technical difficulties. This paper studies the heat generation and heat transfer in electric Marine battery cabinets (EMBC). Based on the Multi-Scale and Multi-Domain (MSMD) solution method, this study uses the Newman, Tiedemann, Gu, and Kim (NTGK) battery model to solve the thermal runaway propagation (TRP) of the EMBC, and then makes a visual analysis of the TRP of the EMBC with the three-layer Battery module (BM) structure. Furthermore, the TRP of the three-layer BM is compared based on three different triggering modes. Through analysis and comparison, it is found that among the three TR triggering modes: single battery heating, heat source at the bottom of the module, and heat source at the top. The first mode corresponds to a maximum heat release (HR) of 214.7 GJ, while the third mode exhibits a minimum HR of 212.3 GJ. Furthermore, the maximum temperature reached by the battery under the third mode is 1568 K, which is lower than that achieved in the other two modes. Additionally, it should be noted that the second mode has a higher maximum HR rate of 5772 GW/m3 compared to the third mode. The TR hazard resulting from heating at the bottom of the battery module outweighs that caused by heating at the top, without taking into account human-induced heating factors. The propagation of TR triggered by a single heat source throughout the EMBC can be inhibited within 226 s in the same layer, and prevented from spreading to the remaining layers for up to 596 s. In the present study, a new insight is presented to reveal the TR characteristics of the EMBC under different triggering modes, and quantify the TR duration. [Display omitted] [ABSTRACT FROM AUTHOR]

• Effects of persistent trapped vortex ring on the impingement heat transfer was revealed. • The tunable Generalized k - ω model was used to calibrate the jet dynamics. • Heat transfer characteristics of the steady jet and sweeping jet impingement were compared. Jet impingement-based heat transfer enhancement is widely employed due to the significant mass, momentum, and energy it accompanied. While the steady jet with high energy flux is commonly favored, it still exhibit few defects, including heat transfer deterioration away from the stagnation point and mutual flow interference in the jet arrays, which are particularly critical in demanding applications. Recently, the sweeping jet has been proposed to resolve the above challenges owing to its self-excited and self-sustaining unsteady oscillation. However, current research predominately focuses on impinging on the flat surface, neglecting impinging on the concave surface, such as internal cooling at the gas turbine blade leading-edge as well as the hot gas de-icing at the aircraft wing leading-edge. Understanding the heat transfer characteristics in these scenarios is crucial as they notably differ from those on flat surfaces. Therefore, this paper investigates the heat transfer characteristics and the related essential flow dynamics of a sweeping jet with a Reynolds number of 2577 impinging on a concave surface, and those of a steady jet under the same conditions are compared. The jet-to-wall distance and the curvature of the impingement surface are 4 and 10 times the jet's hydraulic diameter, respectively. To correctly capture the three-dimensional characteristics of the sweeping jet, this research employs the Reynolds stress model for turbulence modeling and the Generalized k - ω (GEKO) model for better calibration of the jet's spreading and dissipation rates, as well as the characteristics of trapped vortex generated due to the confined concave flow channel. The study initially focuses on the average Nusselt number on the impingement surface, revealing a 15.2 % increase in heat transfer intensity of the sweeping jet compared to the steady jet, and the sweeping jet covers a larger area with enhanced uniformity. Subsequent analysis on streamlines in two perpendicular planes and Q criterion iso-surfaces in the spatial domain shows the formation of a trapped vortex ring with a constant location around the jet, restricting the effective cooling range to its inner side and thus resulting in a steep temperature rise on the two lateral sides of the vortex ring. The stability of the trapped vortex is enhanced by the curved impingement wall in the oscillation plane, which on the one hand forces the high-temperature fluid that has exchanged heat with the wall to repeatedly wash the same location, and on the other hand significantly reduces the jet oscillation angle compared to a free sweeping jet. Consequently, the heat transfer intensity of the sweeping jet is lower in the main oscillation plane than in the non-oscillation plane. Analysis of the near-wall flow parameters indicates that the sweeping jet generates higher velocity and turbulence kinetic energy in the wall jet zone far away from the stagnation point compared to the steady jet, which results in a higher local heat transfer intensity. The unsteady transverse oscillation of the sweeping jet disturbs the wall jet zone and disrupts the formation of the wall boundary layer, causing a higher velocity gradient at the wall and hence the lower thicknesses of the velocity boundary layer and the thermal boundary layer than those of the steady jet. In conclusion, this study reveals the flow and heat transfer features of the sweeping jet impingement on confined concave surface, with the influence of the trapped vortex ring mattering significantly. The findings provide a reference for designing a more effective jet arrangement. Future work will focus on investigating the effects of jet Reynolds number and impingement distance variations on the trapped vortex ring, and how to mitigate the adverse effects of the trapped vortex ring on impingement heat transfer. [ABSTRACT FROM AUTHOR]

In this paper, we present a theoretical study aimed at investigating the rate-limiting factors in thin-film evaporative heat transfer processes, considering the finite-rate evaporation kinetics. The problems of evaporation of a flat thin-film in either pure vapours or vapour-inert-gas mixtures are analysed based on the non-dimensionalised macroscopic transport equations for continuum fluids, coupled with out-of-equilibrium kinetic boundary conditions. Both the full numerical solutions and asymptotic analytical solutions at slow evaporation limit are provided and applied to analyse thin water film evaporation. Existing solutions, assuming negligible heat transfer in the gas domain, or negligible temperature jump across the non-equilibrium kinetic layer, or more boldly a thermodynamically equilibrial interface (i.e. its temperature is at the saturation temperature), can be fully recovered from the more general solutions presented here. Our results show that while these assumptions hold in special cases, they can lead to significant errors in many conditions, especially when the film thickness δ is reduced to a few micrometers or thinner. We show that the conventional views that the rate-limiting factors in thin-film evaporative heat transfer is either the heat diffusion through the liquid film or the mass transfer in the gas domain only apply to thick film (i.e. δ ≫ λ where λ is the mean free path in the vapour phase). As δ decreases to a few micrometer or smaller (more precisely when the Knudsen number Kn increases beyond O (1) in an pure vapour environment or when the kinetic Peclet number Pe is reduced below O (1) in inert gases), the interfacial thermal resistance due to the evaporation kinetics can be on the same orders of magnitude as the thermal resistance in the liquid film. The analysis also allow us to compare the heat transfer processes during the evaporation of a thin-film in pure vapours to those in inert gases, providing deeper insight into the effectiveness of various strategies for exploring the evaporation process in practical thermal management. • Analysis of thin-film evaporation counting for finite-rate evaporation kinetics. • Provision of both dimensionless numerical and analytical asymptotic solutions. • Significant thermal resistance due to kinetics observed in micrometers or thinner films. • Limitations and conditions for existing assumptions to hold are identified. [ABSTRACT FROM AUTHOR]

• The model treats the frost layer as a heterogeneous porous medium. • This model was validated with some experimental data in the literature. • A multistep ascending growth pattern is found for both frost thickness and porosity. • The higher the frost porosity is, the lower the effective frost thermal conductivity is. The frost formation process is involved with many factors which lead to complex morphology. A two-dimensional model to simulate the early-stage frost formation on a cold flat plate is proposed in this paper based on the finite difference and cellular automata method. The concentration diffusion equation is used to constrain the diffusion of water molecules and the mass transfer equation is applied to relate the frost growth to the water vapor concentration and temperature. Furthermore, the temperature distribution during the growth process is obtained by solving the energy conservation equation. With the simulation, a heterogeneous porous medium consisting of ice crystals and air can be obtained and treated as a whole. Then, the physical properties of the frost layer like the frost thickness, the frost porosity and the effective thermal conductivity are calculated and analyzed. Results show that temperature is relatively uniform in the region where ice crystals are concentrated, and the frost surface temperature increases with the frost thickness as the frost grows. A multiple-step ascending growth pattern is observed both for the frost thickness and the frost porosity. The effective thermal conductivity of the frost layer correlates closely with the frost porosity and a higher frost porosity value results in lower thermal conductivity. Besides, the initial crystal nuclei distribution has a great influence on the morphologies of the frost layer, while the initial water vapor supersaturation has more impact on the growth speed of the frost thickness. [ABSTRACT FROM AUTHOR]

• The single effect of deposited nanoparticles and the integral effect of deposition and suspension were quantitatively investigated under saturated pool boiling. • With a mass concentration ranging from 0.001 % to 0.005 % and a heat flux range of 60–130 kW/m2, a pool boiling model with error margin within 30 % was produced through the investigation of bubble dynamics. • The major influence of deposited nanoparticles on boiling heat transfer was determined based on the theoretical model. Currently, the majority of research indicates that nanofluids have superior heat transfer capabilities. On the impact of nanofluids on the boiling heat transfer, there is debate. It is still challenging to predict the boiling heat transfer of nanofluids. Based on bubble behavior, the impact of nanoparticles on boiling heat transfer is investigated in this paper. Furthermore, a comparison is made between the percentages of deposited and suspended nanoparticles that influence on boiling heat transfer. According to the findings, deposited nanoparticles improve wettability whereas suspended nanoparticles diminish it. The number of active nucleate sites and the frequency of bubble detachment increase as a result of the influence of suspended and deposited nanoparticles, whereas the diameter of the bubble decreases. This is similar to the trend of the effect of deposited nanoparticles on bubble behavior. Based on the effect of nanoparticles on wettability, predictive models for boiling heat transfer and bubble behavior were proposed, with a range of mass concentrations between 0.001 % and 0.005 % and heat flux between 60 and 130 kW/m2. Less than 30 % was found to be the error between the experimental data and the predictive equations. It was discovered that the influence of deposited nanoparticles on boiling heat transfer was usually dominant, according to the predictions made by theoretical models. [ABSTRACT FROM AUTHOR]

• Supercritical CO 2 heat transfer in lattice structure channel is numerically studied. • Effects of key parameters of lattice on flow and heat transfer are evaluated. • Buoyancy effect and flow acceleration affected by lattice structure is analyzed. • Vortices induced by lattice structure can suppress the heat transfer deterioration. This study numerically explores the fluid flow and heat transfer features of supercritical carbon dioxide (CO 2) in lattice structure array channel. The mitigation mechanism of the miniature cylindrical lattice structure array on heat transfer deterioration (HTD) of supercritical CO 2 in vertically upward heated channel is studied. This paper evaluates the effect of several key influential parameters (length, diameter, pitch and number) of cylindrical lattice structure array on fluid flow field involving vortex structures, heat transfer coefficient, buoyancy effect and accelerated effect. The results indicate that the lattice structure can effectively suppress the HTD by generating the vortex structure which promoting the turbulent mixing effect and enhancing the turbulent kinetic energy (TKE) of the fluid. Compared with the smooth channel, the peak wall temperature of the lattice structure channel is reduced by about 50 °C, with a corresponding increase in the heat transfer coefficient of about 140 %. The average heat transfer coefficient of the channel is increased by more than 1/3. Furthermore, by increasing lattice length can reduce flow layer stratification and by increasing lattice diameter can creating a composite vortex, which enhance flow mixing strength. The larger the lattice pitch, the worse the overall suppression effect. A denser lattice arrangement produces more temperature valleys, thereby increasing the heat transfer coefficient. The conclusions in this study could provide the main theory support for security and stability of supercritical CO 2 heat exchangers in power system. [ABSTRACT FROM AUTHOR]

• A novel method for bubble departure promotion is proposed by inducing elastic plates. • Boiling heat transfer coefficient with elastic plates increased by 55.8 %. • Pumping effect is induced by the plate oscillation. • Bubble departure diameter decreases with the decreasing bending rigidity. • The method proposed opened up a new research direction for thermal design. Boiling heat transfer enhancement is essential for energy utilization. Traditional passive boiling enhancement methods aiming at bubble departure promotion usually depend on the modulation of surface tension force by surface modification. However, the limited driven force which benefits bubble departure cannot help the further improvement of heat transfer performance facing the increased heat dissipation amounts. In this paper, a novel boiling enhancement method using a pair of elastic plates (i.e., flexible parallel plates made of stainless steel) which promotes bubble departure by its swing effect for boiling on Pt wire in confined space is proposed and investigated. Compared to boiling with a pair of rigid plates (the thickness of 0.5 mm and the length of 12 mm), the heat transfer coefficient (HTC) is improved by 55.8% of those with elastic plates (the thickness of 0.01 mm and the length of 12 mm).Periodic expansion and recovery process of plates coupling bubble dynamics is observed and studied. Experimental results indicate that elastic plates enhance boiling heat transfer performance significantly by smaller bubble departure diameter and lower wall superheat at the same wall heat flux. A correlation for bubble departure diameter prediction in elastic channel is proposed which matches well with experimental results. It is found that the stronger pumping effect induced by higher swing rate of plates enhance HTC significantly. The mechanism where expansion process of plates promotes bubble departure while its subsequent recovery process benefits the supply of the cold liquid is verified by simulation. This study proposes a new approach for boiling heat transfer enhancement by inducing the energy exchange between bubbles and elastic plates, and provides theoretical and technical support for boiling study based on flexible materials. [ABSTRACT FROM AUTHOR]

• The v shape pressure reflects interaction relations among 3 thermodynamic mechanisms. • FFC reflect the intensity and rate of progress of flash at unique start stage. • The factors influencing flash rate and intensity are analyzed. • FFC rises with initial temperature and valve opening degree at unique start stage. • Expanders with larger outlet area or higher working temperature have larger flash intensity. Our experiments showed that a V shape pressure drop appeared at start stage of non-equilibrium flash. V shape pressure drop firstly denoted the generating of superheat degree, which should be the starting force driving the non-equilibrium flash. Then evaporated vapor made up the pressure drop. Finally, a dynamic equilibrium was reached between the flash rate and the outflow rate, and the pressure behaved decreasing gradually. However, few published references focus on this start stage of the non-equilibrium flash. In this paper, experiments of the flash were conducted to investigate the heat and mass characteristics during V shape start stage. Dimensionless flash conversion coefficient (FCC) was proposed to normalize the flash with different initial liquid mass at start stage. The effects of initial temperature and the valve opening degree on the heat and mass characteristics of flash during the V drop start stage were studied. The results showed that the pressure of the working fluid changed dramatically during the V drop start stage. The peak of instant liquid superheat was proportional to the opening degree of the valve, which controlled the outflow rate. The flash rate increased with increasing initial temperature and valve opening degree, which had an approximately linear relationship with the flash time. FCC increased with valve opening degree. It could be deduced that flash intensity or flash rate would be higher for an expander with larger outlet area or higher working temperature. [ABSTRACT FROM AUTHOR]

• A new model for radiation calculation to any horizontal surfaces from localized fire. • The new model is based on classic fire plume theory and radiation theory of participating medium. • The mean relative deviations of the model against experimental and numerical data are within ± 30 %. Fire is the most frequent hazard to buildings. The current design methods for predicting the temperatures of structures in fire are originally developed for the standard fire that assumes a uniform gas temperature field and are invalid for natural fires with high non-uniform gas temperature fields. Localized fire is a typical natural fire with high non-uniform gas temperature field, which is often considered in fire safety design. There are currently no validated simple general models for calculating the heat transfer from localized fire to exposed structures. To address the need of design method, this paper develops a refined cylinder fire model for calculating the incident radiant heat fluxes on horizontal structural members inside and outside the flame region of a localized fire. The model uses a cylinder, centered at the fire plume axis, to represent the localized fire. The height of the cylinder is not fixed, different to any other fire models. The temperatures in the cylinder are highly non-uniform in three dimensions and are determined based on the classic fire plume theory. For radiation calculation, the cylinder is evenly divided into several elements along the radius and height. Each element is assumed to be a homogenous, isotropic, and absorbing-emitting (participating) graybody. By careful consideration of the spatial gas temperature distribution, the radiation properties (emissivity and transmissivity) of the elementary graybody, and the configuration factor between the elementary graybody and the horizontal target surface, the model can get relatively accurate and conservative incident radiant heat flux. The relative deviations against both the experiment data and numerical results are within ± 30 %. The model introduces a new concept of calculating the heat fluxes from fire to structures, is a relatively simple general model (compared with the sophisticated computational fluid dynamics models), and is more precise and accurate than other simple ones. The model is recommended for use in performance-based fire safety design. [ABSTRACT FROM AUTHOR]

• Numerical and experimental results for air-cooled PV roof tile were compared. • SST k-ω turbulence model and Discrete Ordinates radiation model were used. • Greater heat recovery was obtained for the air flow duct with a lower height. • The maximum increase in generated power relative to the uncooled module was 11.63 %. • The highest received heat flux was 330 W/m2 at solar irradiance equal to 900 W/m2. Among renewable energy sources, Building-Integrated Photovoltaic/Thermal (BIPV/T) systems are gaining increasing interest. To improve their economic competitiveness, technologies that increase their efficiency are searched for. The paper is devoted to evaluating the impact of various air-cooling configurations on the thermal and electrical performance of a photovoltaic roof tile. A numerical model of the own experimental system was developed in the ANSYS Fluent software for a wide range of input variables. The original approach based on the SST k-ω turbulence model, Discrete Ordinates radiation model, and the use of Solar Load module were proposed. Such a numerical model allows representation of semi-transparent layers and variable solar irradiance, which is a unique realization of real system modelling. Numerous analyses conducted indicate a higher heat recovery potential for an airflow duct with a height of 25 mm for all configurations analysed. The highest value of recovered heat flux was approximately 330 W/m2 under conditions of a volumetric air flow rate of 7.5 m3/h and solar irradiance equal to 900 W/m2. Good agreement of the results of the multivariant CFD simulations with new experimental ones was confirmed. Insight into the flow phenomena behind the achieved thermal results supplemented the knowledge. The highest electrical efficiency obtained experimentally was 5.76 % for a channel with a height of 50 mm, volumetric flow rate equal to 7.5 m3/h and solar irradiance equal to 600 W/m2. The presented methodology and the results obtained can be useful in research devoted to optimising BIPV/T air-based cooling systems, which will then be tested in-situ. Moreover, new experimental data collection can be used for the verification of numerical models. [ABSTRACT FROM AUTHOR]

• Analyze the variation of heat transfer as a function of diameter and temperature. • Investigate heat transfer mechanism by crucial direct parameters. • Explore internal mechanism by phonon density of state and phonon overlap energy. Carbyne is a sp1 linear carbon chain (LCC) with characteristics of strong chemical reactivity and extreme instability under environmental conditions, which has become an obstacle to the application of LCC with high thermal and electrical conductivity. Utilizing CNT as a container to store LCC is one of the most feasible ways to realize LCC applications. However, current research of LCC encapsulated in CNT (LCC@CNT) focuses on its preparation and lacks of in-depth exploration of the intrinsic heat transfer mechanism. This paper reports the high axis thermal conductivity of LCC@CNT, explore the thermal transport enhancement degree of LCC@CNT under a wide temperature range and multiple diameters, and analyzed the underling mechanism through crucial thermal parameters and phonon theory. When LCC is loaded in CNT, the axial thermal conductivity of CNT is further increased by 15 %. Moreover, LCC@CNT shows the lower sensitivity diameter than pristine CNT. This work is expected to provide data support for the application of LCC, the lower production standard of CNT, and also attempt the higher efficient one-dimensional thermal energy transfer micro devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• An enhanced heat transfer structure is proposed, which can improve efficiency by 29 %. • The performance of the new structure was investigated by numerical simulation. • Experimental tests were conducted to prove the effectiveness of the new structure. To enhance the heat transfer efficiency of the helically coiled tubes heat exchangers, this paper proposes a double shell-passes structure designed for a multi-layer helically coiled tubes heat exchanger. Numerical simulation is employed to investigate the performance of the Double Shell-passes Multi-layer Helically Coiled Tubes Heat Exchanger (DSMHCTHE). Furthermore, an experimental test system is constructed to validate the simulation results, exploring the performance under different operating conditions. A comparative analysis is conducted with the traditional Multi-Layer Helical Tube Heat Exchanger (MHCTHE). The results indicate that, under identical experimental conditions, the heat transfer rate and thermal effectiveness of DSMHCTHE increased by 5.1 % to 12.9 %. The overall heat transfer coefficient showed an improvement ranging from 21.5 % to 29.0 %, while the shell-side heat transfer coefficient increased by 36.2 % to 47.5 %. However, the shell-side pressure drop increased by 60.7 % to 83.4 %. Utilizing the heat exchanger's comprehensive performance as the evaluation criterion, it was observed that DSMHCTHE exhibited superior comprehensive performance. In comparison to MHCTHE, the comprehensive performance of DSMHCTHE improved by 12 %. The design of the double shell-passes configuration has shown significant enhancements in both convective heat transfer and overall performance, highlighting the superior application potential of DSMHCTHE. [ABSTRACT FROM AUTHOR]

• HFE-7100 boiling curves from the onset of boiling to dry-out, in a vertical and rectangular mini-channel. • Local heat transfer coefficient (HTC) calculated with an inverse heat conduction method. • Influence of subcooling and pressure on heat transfer, pressure drop and flow patterns. • Increasing pressure improves the critical heat flux (CHF) and HTC, delays the dry-out, and reduces pressure drops. • Increasing subcooling improves CHF and HTC, delays the dry-out, and modifies the flow pattern. The background of this study is the problem of thermal runaway in the battery cells of electric vehicles. Increasingly powerful and compact battery packs require highly efficient thermal management. One potential solution is the direct liquid cooling of lithium-ion battery cells using a dielectric liquid which boils over a safety limit temperature. This approach intends to prevent in a first step the cell thermal runaway and if it fails in a second step its propagation to its neighbors: the liquid boiling helps to mitigate the cell temperature rise and to transport and spread the heat. The arrangement of the cells in the pack and their close spacing induce a scientific problem of convective boiling in a mini-channel. To enhance designs using this solution, a comprehensive understanding of flow boiling and a precise local heat transfer quantification is essential. The HFE-7100 has been selected as a working fluid for its attractive thermophysical properties and a suitable saturation temperature. The present paper introduces new experimental results of flow boiling dielectric fluid, the HFE-7100, in a vertical rectangular mini-channel. Measurements are carried out from start of boiling to dry-out. Boiling curves are obtained for a mass flux of 391 kg/(m².s), at different pressures (0.7, 1, 1.5 bar) and at different subcoolings (Δ T s u b = 0 ; 15 ; 30 ; 45 ∘ C). The test section is an aluminum block instrumented with three lines of five K-type thermocouples located all along the flow. The visualization of the flow is achieved through a glass pane with a high-speed camera to identify different flow patterns. The local heat transfer coefficient is calculated by a resolution of a 2D inverse heat conduction method. The experiment mainly aims at determining the heat transfer coefficient, the critical heat flux (CHF) and the pressure drop and at characterizing both the flow regimes and the dry-out phenomenon. The influence of subcooling and pressure on flow boiling is analyzed. An increase in subcooling enhances the CHF and the heat transfer coefficient, and delays the dry-out. Subcooling has an impact on the flow pattern and modifies the type of CHF. In the operating conditions tested, a decrease in pressure enhances CHF and delays dry-out. On the other hand, the heat transfer coefficient increases with rising pressure. Similarly, pressure drops are lower with higher pressure. [ABSTRACT FROM AUTHOR]

• The mathematical model can accurately predict the melting heat transfer process of PCMs. • The Rayleigh number increased with the heat flux, and the higher the heat flux, the larger the amplitude. • Increasing the heat flux improved the integrated heat transfer coefficient and thermal storage performance of the CPCMs. • Conduction was the primary heat transfer mechanism; however, the proportion of natural convection increased with the heat flux. To investigate the effect of heat flux on the enhanced heat transfer in phase change materials (PCMs) composed of copper metal foam (CMF) and paraffin wax (PX), a semi-cylindrical visualized heat storage device with a varied heat flux of 7.3 kW/m2, 8.5 kW/m2, 9.7 kW/m2, and 10.9 kW/m2 was established in this paper. Moreover, a 3-D mathematical model of composite phase change materials (CPCMs) was established using hybrid grid to study the temperature distribution, imbalance effect, flow, heat transfer mechanisms, and heat storage performance during the melting process. The results showed that the melting time of the CPCMs decreased as the heat flux increased. Compared with a heat flux of 7.3 kW/m2, the melting time was shortened by 10.05 %, 20.71 %, and 27.21 %, respectively. In addition, the Rayleigh number (Ra) increased with the increase in heat flux, and the amplitudes of Ra were 1.45×108,1.54×108,1.61×108, and 1.74×108, respectively, which indicated that the higher the heat flux, the larger the amplitudes. Moreover, the heat transfer mechanism during the melting process was dominated by conduction; however, with the increase in heat flux, the maximum flow velocity of the liquid paraffin increased, which caused the proportion of natural convection to increase from 27.80 % to 31.30 %. Hence, the integrated heat transfer coefficient of CPCMs increased from 5.69 W/(m·K) to 5.81 W/(m·K). However, the temperature imbalance effect of the CPCMs was exacerbated, as evidenced by the increased maximum temperature difference in the vertical direction of the center of the CPCMs from 24.7 K to 35.6 K. Besides, the heat storage performance was enhanced. Compared with a heat flux of 7.3 kW/m2, the heat storage capacities of the CPCMs increased by 4.21%, 9.46%, and 12.66 % with increasing heat flux, and the heat storage rates of the CPCMs increased by 15.3 %, 34.9 %, and 52.3 %, respectively. Furthermore, the relative error of the overall melting time was 3.4 %, indicating that the model provided reasonable predictions. [ABSTRACT FROM AUTHOR]

• 1 Flow and boiling heat transfer in a 5 mm tube were studied experimentally. • 2 Heat transfer enhancement is obviously founded in the region where x e < 0.05. • 3 New empirical correlations are developed based on the experimental data. • 4 New correlations have higher prediction accuracy than the existing correlations. Experimental investigation on flow boiling heat transfer in a small tube under high system pressure has been conducted in this study. The test-section is constructed with a 316L stainless steel tube. The inner diameter and heated length of the test-section are 5 mm and 930 mm, respectively. The working fluid is deionized water. The operating conditions of the experiments are as follows, the mass flux from 548 to 978 kg/(m2·s), the wall heat flux from 136 to 238 kW/m2, and the system pressure from 1.0 to 2.9 MPa. The experimental results showed that the inlet subcooling mainly affects the onset of nucleate boiling, but its impact on the heat transfer coefficient at the same vapor quality is almost negligible. The heat transfer coefficient increases with the increase of mass flux and wall heat flux, especially in the region where x e < 0.02. The average heat transfer coefficient is higher under high system pressure owing to the variation of the thermophysical properties. Additionally, the existing flow and heat transfer correlations cannot predict the flow boiling heat transfer coefficient and frictional pressure drop in the experiments accurately enough. Therefore, the new flow and heat transfer correlations are developed based on the experimental data in this paper, and the mean absolute deviation of the flow boiling heat transfer correlation and frictional pressure drop correlation are 13.3% and 12.1%, respectively. [ABSTRACT FROM AUTHOR]

• Bionic method developed to solve the issue of large melting dead zones of TES units. • The lotus root-inspired structure significantly enhanced the heat transfer. • Shorter melting time and higher power density achieved without reducing PCM volume. • A design complying with industrial standards optimized for low-cost mass production. Thermal energy storage (TES) is crucial in the efficient utilization and stable supply of renewable energy. This study aims to enhance the performance of shell-and-tube latent heat thermal energy storage (LHTES) units, particularly addressing the issue of the significant melting dead zones at the bottom, which are responsible for the long charging time. This paper proposed a new heat transfer enhancement technique inspired by the air channel distribution inside the root of the lotus. Numerical simulations are used to explore its melting behavior and heat storage performance, and a comparison is made with conventional shell-and-tube TES units. The results indicate that compared to the single-tube type, the bionic-lotus root type reduced the total melting time by 89.1 %, increased the average temperature by 13.2 °C, and enhanced the average effective power density by 7.6 times. Subsequently, multi-objective optimization was conducted based on response surface methodology, and an industrial standard type was constructed according to existing pipeline products to meet the manufacturing standards for mass production. The melting time was further decreased by 5.8 %, and the average effective power density increased by 6.6 %. The results of this study provide a promising and prospective solution for enhancing shell-and-tube LHTES units, with the potential to increase the efficiency, reduce the footprint and manufacturing costs of energy systems equipped with TES. [Display omitted] [ABSTRACT FROM AUTHOR]

• Algorithm for PLIC-based interfacial area concentration on 3D non-orthogonal grids. • Thermal phase change model with geometrical basis and free of empirical input. • Oscillating behavior of GOX jet plume in LOX crossflow is reproduced in simulation. • Imbalance between the mass transfer rate and the supply causes the oscillation. • Methodology developed is verified by the Stefan problem and the bubble experiment. In order to enhance the physical basis of the mass transfer model in numerical simulation of gas-liquid direct contact condensation and improve the fidelity, a set of methods and models are developed. Based on the concept of the piecewise-linear interface calculation (PLIC), an interface reconstruction algorithm is proposed to calculate the interfacial area concentration in three-dimensional non-orthogonal structured grids. The actual interface in the cell is replaced by a plane, whose position is determined iteratively to satisfy the local volume fraction and orientation of the actual interface. The area of the polygonal cut by the plane is taken as the interfacial area in the cell. The proposed algorithm is validated by calculating the surface area of a series of basic geometries. Obvious superiority of the proposed algorithm over the traditional models (gradient model and algebraic model) is seen. Then, the reconstructed area is used to determine the interfacial area concentration in the thermal phase change model. The process is implemented by ANSYS Fluent user-defined functions. The Stefan problem and steam bubble condensation experiment are used to test the performance of the developed methods and models. The simulation results agree well with the theoretical and experimental results with the quantitative relative errors no more than 4.3 % and 15 %, respectively. The oxygen jets condensation experiments are also used as test cases. The primary dominant frequencies predicted by the simulations are 163.01 Hz and 131.65 Hz, which agree well with the 139.72 Hz and 125.75 Hz in the experiments. The relative errors are only 17 % and 4.7 %. The unstable flow pattern of oxygen jet in liquid oxygen crossflow is explained based on the dynamic characteristics of turbulence, heat and mass transfer. The periodic variation of mass transfer rate is considered as the cause of condensation oscillation. The method for calculating the interfacial area proposed in this paper can serve as an optional and practical improvement to the numerical simulation of direct contact condensation. [ABSTRACT FROM AUTHOR]

• The dynamics of the thermal runaway front in large-scale Li-ion batteries are deduced theoretically. • The velocity of the front yields a 1/2 power relationship between the thermal conductivity and reaction rate. • Freezing thermal runaway front is possible in theory and validated by experiments. • Heat dissipation enlarged by heat transfer time delay is critical for the freeze. Large-scale lithium-ion batteries are favored in electric vehicles and energy storage stations; for instance, BYD blade batteries and CATL Kirin batteries are popular. A tiny defect will trigger thermal runaway from a local point towards the other parts of the battery, and the boundary between the failure region and the intact region is called the "thermal runaway front," of which the dynamics are still unclear. Herein, this paper deduces two formulas for the moving speed (v TR) of the thermal runaway front by applying the principles of energy conservation (Formula I) and flame front (Formula II); formulas for the thermal runaway front velocity (v TR) are derived. The velocity v TR conforms to the 1/2 power of the heat conductivity and reaction rate in both formulas. Data regression for the experimental data demonstrated that the overall estimation error was 10 % using Formula I and 25 % using Formula II. As the zero velocity value indicates the termination of thermal runaway propagation, further derivations reveal that forced cooling can suppress thermal runaway as long as the heat dissipation power is higher than the heat generation power. Sufficient heat dissipation time is achieved by the time delay of heat transfer in the long run of thermal runaway propagation. The formula for the dynamics of thermal runaway propagation universally applies to various large-scale lithium-ion batteries, assisting the safe design of high-energy batteries and providing new insights into suppressing battery thermal runaway by the heat transfer delay effect. [ABSTRACT FROM AUTHOR]

• A Bayesian optimization is conducted utilizing an automated framework to enhance the trade-off between heat transfer and pressure drop using spline-based two-dimensional pin-fin arrays. • The optimization objectives include minimization of pressure drop, maximization of heat transfer, and maximization of efficiency. • The maximization of efficiency optimization yields designs which balanced aerodynamic characteristics with total surface area, leading to enhanced thermal performance. • Pin-fin arrays using four splines outperform all other geometries due to the symmetric nature of the shape generation. Pin-fin arrays are crucial in the cooling of aerospace components. Specifically, pin-fins find extensive usage in the trailing edge of turbine blades, primarily due to the harsh operating conditions these blades experience. With the development of additive manufacturing, complex internal geometries that were previously too expensive to manufacture are now feasible. This advancement has created a new pin-fin design space to be explored. In this paper, Bayesian optimization (BO) is conducted to find the pin-fin array that optimizes the trade-off between heat transfer and pressure drop in a two-dimensional channel. The complexity of the pin-fin geometry varies, and is controlled by the number of connecting piece-wise cubic splines used to close the shape. Different designs are obtained using 3-, 4-, 5-, and 6-splines in a staggered pin-fin array orientation. The optimization objectives included the minimization of pressure drop, the maximization of heat transfer, and the maximization of efficiency. It is found that the pin-fins which utilize 4-splines outperform all others due to their symmetric characteristics. The performances of the pin-fin array plateaus after increasing the complexity beyond 5-splines. It is concluded that the optimization objective significantly influences the final shape characteristics and behavior. As expected, the pressure drop minimization finds aerodynamic shapes while heat transfer maximization increases the total surface area in the channel. The maximization of efficiency results in a balance of aerodynamic shapes and total surface area. [ABSTRACT FROM AUTHOR]

• A Reference-Standard-Volume optimization method is proposed to improve CESPB. • The best aspect ratio of CESPB is 2–4 considering efficiencies and pressure drop. • The volume multiple is given at 1.1 with the highest exergy efficiency of 63.72 %. • The thermal and exergy efficiencies are increased by 2.03 % and 3.65 %, respectively. Cryogenic liquids (e.g., liquid air, liquid hydrogen, liquid carbon dioxide) have gained popularity in electricity storage due to their high energy density, no geographical constraints, and environmental friendliness. The cryogenic energy storage packed bed (CESPB) is widely employed as a cold recovery device to enhance the round-trip efficiency of cryogenic energy storage systems. Nonetheless, the cycle efficiencies of CESPB remain relatively low, with limited research investigating efficient methods for determining the design parameters. To address this, a novel optimization method named as the Reference-Standard-Volume (RSV) approach is introduced to enhance the thermodynamic performance of CESPB. In this paper, the complete optimization process of CESPB is illustrated, presenting the optimization outcomes in the view of heat and mass transfer. The findings reveal that a larger aspect ratio leads to the higher efficiencies but increased pressure drops. An optimal aspect ratio of 3 and a volume multiple of 1.1 is identified, achieving the highest exergy efficiency of 63.72 %. Meanwhile, increasing charging/discharging time enhances heat transfer in CESPB, however, it leads to an increase in external cold dissipation, which gives an optimal charging/discharging time of 3/3 h. By implementing the RSV optimization method, the percentage increase of discharging efficiency, thermal efficiency, and exergy efficiency of CESPB is 2.08 %, 2.03 %, and 3.65 %, respectively. These research outcomes offer valuable reference and guidance for future CESPB design and research. [ABSTRACT FROM AUTHOR]

• The new BTMS has two heat transfer paths, including OHP and liquid cooling plate. • Pulsating flow improves OHP stability through periodic enhanced thermal loads. • Optimal OHP stability lies in 38% or 62% duty cycles, 0.03–0.05 Hz frequencies. • Stably operating OHP enhances the new system's heat transfer performance. After a comprehensive review of oscillating heat pipe (OHP) based on battery thermal management system (BTMS), a novel battery liquid-cooling system with a ⊥-shaped OHP is presented to increase the volume utilization efficiency of battery module and the total amount of heat dissipation. The new system retains the heat transfer path of the OHP while incorporating an additional heat dissipation route where the liquid cooling plate is in direct contact with the cells. In this paper, pulsating flow is used to tackle the problem of the OHP failing to operate stably due to the insufficient heat load achieved in the new system. The parametric effects of pulsating flow frequencies, cooling initiation temperatures, and duty cycles on the operational performance of the OHP and the average surface temperature of the battery module ( T b ) within the new system were investigated. The results indicate that pulsating flow periodically elevates the heat load on the battery surface, enhancing the OHP working properly. The smaller the pulsating flow frequency, the greater the impact on the temperature fluctuations of the new system. The T b is lowest when the pulsating flow frequencies range from 0.03 Hz to 0.05 Hz. Beyond a frequency of 0.06 Hz, the OHP cannot operate stably. Additionally, moderately increasing the cooling initiation temperature is beneficial for enhancing the average temperature oscillation amplitude of the OHP. The cooling initiation temperature between 45 °C and 47 °C results in a better T b . Both pulsating flow duty cycles of 38% and 62% contribute to OHP running effectively. The new system with OHP under optimum pulsating flow condition has the optimal T b , eventually rising by 17.5 °C, which is a 9.8% decrease in temperature rise compared to the system without OHP. And the battery module's surface temperature uniformity has been improved through a reduction of 1.3 °C in the maximum temperature difference ( ΔT max ), amounting to a 17.8% decrease. It has been proved that the improved thermal performance of the new system under pulsating flow is attributed to the stable operation of the OHP. [ABSTRACT FROM AUTHOR]

• A reservoir-assisted loop thermosyphon with a micro-grooved evaporator (MGTPLT) was fabricated. • Micro-grooved structures allowed faster startup and more stable operation of the MGTPLT. • The convection heat transfer ratio was proposed to evaluate the heat transfer enhancement. • The MGTPLT reduced evaporator temperatures and achieved thermal performance enhancement. The two-phase loop thermosyphon (TPLT) offers significant advantages in high-efficiency and long-distance heat transport for various thermal and energy-related applications without external power consumption. In this paper, the startup and heat transfer characteristics of a reservoir-assisted loop thermosyphon with a micro-grooved evaporator (MGTPLT) were experimentally investigated and compared with a loop thermosyphon having a smooth-tube evaporator (STPLT). R245fa was used as a working fluid at volumetric filling ratios of 50–80 %. The results demonstrated that the additional microgrooves allowed a shorter startup time characterized by a lower maximum temperature with respect to the temperature overshoot. Compared to the STPLT, the MGTPLT exhibited lower evaporator temperatures and better temperature uniformities; the micro-grooved structures could alleviate local intermittent dry-out at moderate and high levels of power input for filling ratios of 50 and 60 %. The addition of micro-grooved structures enhanced the heat transfer performance of the TPLT characterized by lower thermal resistances. The convection heat transfer ratio (CHTR) was proposed to evaluate the enhancement of the convection heat transfer within the evaporator region after using microgrooves. The CHTR showed a decreasing tend with increasing the power input. At moderate filling ratios, the value of the CHRT was greater than 1.1, and an approximately 18 % increase in the convection heat transfer was achieved under the combined condition of 60 % filling ratio and 250 W power input. The fundamental mechanism of heat transfer performance enhancement with the aid of micro-grooved structures was analyzed and elucidated. [ABSTRACT FROM AUTHOR]

• Analysis of single and double pass solar air heater-phase change material. • Evaluation based of PCM thickness to length ratio. • Improved outlet temperature during non-sunshine hours. • Improvement in useful energy during discharging period. • System's maximum efficiency of 63.34% achieved during PCM discharging. This paper presents a two-dimensional transient model for a solar air heater with phase change material (SAH-PCM), focusing on the thickness-to-length ratio (t/L) of the PCM container. Verified through experiments, the model considers single (SP) and double pass (DP) flow configurations, assessing liquid fraction, dead length, outlet temperature, energy, exergy, and system efficiency during PCM charging and discharging. Increasing the t/L ratio improves peak liquid fraction, reduces dead length, and delays PCM discharge in both configurations, enhancing system energy and exergy efficiencies. In a SP flow system, optimizing t/L at 0.042 yields a peak liquid fraction of 0.928, a 92.28% dead length reduction, and a 2 h and 22 min delay for PCM discharge (base-case t/L ratio: 0.0182), achieving a highest discharging efficiency of 39.1%. For a DP flow system, the optimized t/L ratio of 0.058 results in a peak liquid fraction of 0.976 and a 1 hour and 34 min delay for PCM discharge, attaining the highest discharging efficiency of 63.34%. Moreover, an improvement in the energy payback time (EPBT) is observed for both SP and DP flow as the t/L is increased. For the DP flow, a minimum EPBT of 0.68 years (energy basis) and 6.55 years (exergy basis) is observed at a t/L ratio of 0.058. In terms of energy cost, SP flow reaches a minimum of Rs. 20.824 Rs/kWh at a t/L ratio of 0.042. For DP flow, the minimum energy cost is 13.033 Rs/kWh at a t/L ratio of 0.058, representing a noTable 37.42% improvement compared to SP flow. These findings underscore the critical role of optimizing system parameters, specifically the t/L ratio, for enhanced energy and exergy performance, and economic viability of SAH-PCM. [ABSTRACT FROM AUTHOR]

• Thermal behavior of rectangular fins located within a square cavity were analyzed. • Inverse CFD method and experimental data were adopted for heat transfer prediction. • Suitable turbulence model based on the RMSE of the flow model were selected. • Effect of fin geometry on the flow and heat transfer within a cavity was evaluated. • Effect of PCM heat sink on the flow and heat transfer within a cavity was studied. This study examines the fluid flow and heat transfer characteristics of rectangular fins positioned within a square cavity through the use of the inverse three-dimensional computational fluid dynamics (CFD) method, experimental analysis, and the constant heat transfer rate assumption. This paper proposes a heat sink that uses a phase change material (PCM) made of paraffin within a small cavity. The inverse CFD method, combined with the least squares method, root mean square error, and excessive experimental data, is adopted to predict the unknown heat transfer rate Q and absorption heat Q ab. One of the objectives of this study is to investigate the effect of the PCM heat sink on fluid flow and heat transfer characteristics within a cavity. A sequence of tests on various flow models indicates that employing the RNG k-ε turbulence model with the standard wall function is the most suitable choice for all scenarios in the three-fin model. Conversely, the zero-equation model proved to be a more adequate fit for the PCM heat sink. Another objective of this study is to study the effect of the height of the PCM heat sink on Q and Q ab. The incorporation of a PCM heat sink results in a further improvement in the efficiency of heat dissipation. Part of the heat created is absorbed by the PCM heat sink, which absorbs 22.5 % of the thermal energy. Under the same volume, the PCM heat sink with a lower height (H p = 0.012 m) absorbs 14 % more heat compared to H p = 0.02 m. Thus, a lower-height PCM heat sink has a better heat dissipation effect. [ABSTRACT FROM AUTHOR]

• Verified rivulet behavior during dropwise condensation on vertical surface • Identified effects of surface length and rivulet flow on heat transfer • Related rivulet-covered area and dropwise condensation heat transfer Due to its superior heat transfer performance, dropwise condensation has been studied for industrial applications. This paper experimentally reports the effects of vertical length on dropwise condnsation in the presence of noncondensable gas. The formation of rivulet flows, which reduce heat transfer due to droplet coalescence, was observed. Compared to the upper side, rivulet flows on the lower side of the condensing surface were faster and more frequent. Lower heat flux was also measured on the lower side, indicating a correlation between heat transfer and rivulet flow parameters during dropwise condensation on the vertical surface. These findings represent the first study of the effects of rivulet flows on dropwise condensation heat transfer, and they can be applied to evaluate condensation heat transfer on long vertical surfaces, such as those found in small modular reactor containment systems as well as large containment building with passive containment cooling systems. [ABSTRACT FROM AUTHOR]

• A new wall boiling heat transfer model is developed to offer a fresh approach for CFD simulations within the Eulerian two-fluid framework. • Each parameter within the new model is calculated based on local physical properties and macroscopic parameters at cell level. • The new model reasonably predicts the wall temperature in flow boiling cases. • The sensitivity of the coefficients introduced in the proposed model are analyzed. Accurate prediction of flow boiling heat transfer is prominently dependent on the modeling of wall heat flux partitioning. In this paper, a new wall boiling heat transfer model was developed for three-dimensional Computational Fluid Dynamics (CFD) code to predict the wall heat flux and wall temperature. The proposed model partitioned the wall heat flux into convective heat flux and nucleate boiling heat flux, which were further modified by two correction factors. The key feature is that the new wall boiling heat transfer model was derived from bubble growth mechanism, incorporating reasonable assumptions, and each parameter within the model was calculated based on local physical properties and macroscopic parameters at the cell level. On this basis, the new wall boiling heat transfer model was coupled into ANSYS-Fluent and validated against various public experiments as well as the KIMOF experiments conducted under different conditions. Simulation results indicated that the proposed model could predict reasonable results for wall temperature and cross-section average void fraction. Finally, a comprehensive investigation was carried out to assess the sensitivity of the computational grids and the coefficients introduced in the new model. [ABSTRACT FROM AUTHOR]

· Different change rate of cross-sections along the flow field is investigated. · Microchannel condenser is used in loop heat pipe. · Effects of operating height situation and microchannel structure are studied. · Smooth operation and anti-gravity performance are effectively improved with the help of tapered channel. The microchannel condenser has the advantages of high condensation efficiency and low flow resistance. The vapor can liquefy and return to the evaporator rapidly, and the heat transfer performance and the smooth operation of the loop heat pipe can be improved. Suitable change rate of the cross-section along the microchannel flow field can adjust the pressure drop and flow rate of working fluid, and improve the anti-gravity performance of the loop heat pipe. In this paper, microchannels with different change rates of cross-section along the flow field, including 0.5 mm straight channel, 1 mm straight channel, divergent channel, and tapered channel, are designed and applied as condensers in loop heat pipes. The entrance size of the gradient microchannel is 0.5 mm or 1 mm, which uniformly expands to 1 mm or shrinks to 0.5 mm along the flow field. The vapor and cooling water form a countercurrent direction of motion in the microchannel, and the heat exchange is carried out through the bottom of the channel. The influence of the microchannel condenser structure and operating height situation between the evaporator and condenser on the heat transfer performance of the loop heat pipe are experimentally investigated. The results show that the loop heat pipe achieves an extremely low thermal resistance of 0.004℃/W with gravity assist. Under the gravity-free operation situation, the maximum evaporator temperature of the loop heat pipe with 0.5 mm straight channel and 1000 W heat load is 128.1 °C, and the vapor pressure drop fluctuated is in the range of -1000 ∼ 2500 Pa. Under the anti-gravity operation, the loop heat pipe with the tapered channel has effective transfer performance at 500 W, and the influence factor is only 28.1 %. [ABSTRACT FROM AUTHOR]

• Presents an analytical solution for thermal spreading in a cylindrical body with spatially varying side wall cooling. • A series solution is derived, with coefficients shown to be the solution of a set of linear algebraic equations. • Impact of key non-dimensional parameters on temperature field and thermal resistance is investigated. • Results are shown to be in excellent agreement with past work for special cases. • Results are of relevance for edge cooling of microprocessor chips as well as batteries. Thermal spreading and constriction resistance play an important role in thermal management of a variety of engineering systems, including semiconductor devices. Moreover, thermal contact resistance at interfaces between materials is also governed by spreading and constriction processes. Most of the past literature on theoretical modeling of thermal spreading from a source into a larger body assumes an adiabatic side wall, whereas several recent thermal management problems involve active cooling at the side wall. This work addresses such scenarios by solving the thermal spreading problem in a finite thickness cylinder with spatially varying convective heat transfer on the side wall. An eigenfunction-based series solution for the temperature field is written, the coefficients of which are shown to be governed by a set of coupled algebraic equations. Results are shown to agree well with past work for special cases of the general analysis presented here. Thermal spreading resistance is computed for a number of practical scenarios, including step function, periodic and sinusoidal convective cooling on the side wall. In each case, it is shown that the temperature distribution is consistent with the nature of the spatially varying boundary condition. A key theoretical insight from this work is that under certain conditions, the classical definition of thermal spreading resistance may become negative due to the presence of two heat sinks in the problem. Therefore, analysis based on total resistance may be more appropriate. This work offers a significant generalization of past papers, making it possible to analyze realistic thermal management problems, in which, side wall cooling plays an important role. [ABSTRACT FROM AUTHOR]

In this paper, we perform a detailed numerical study of the linear dynamics of Rayleigh–Bénard convection in a fluid layer confined in a Hele–Shaw cell and subjected to a temperature gradient with a stationary and a periodic time-dependent component. Using Floquet theory for time and the spectral method for space, we show that the system exhibits three classes of time-dependent solutions, namely harmonic, sub-harmonic and quasi-periodic instabilities. These compete into the primary bifurcation driven by two different mechanisms depending on the modulation amplitude. Indeed, harmonic convective rolls, driven by the stationary thermal gradient, arise below critical modulation amplitudes beyond which the well-known parametric resonance mechanism is responsible for the development of convective rolls. In addition, it is revealed that the convective flow reversal could identify this exchange of instability mechanisms occurring via either bicritical states with codimension-two bifurcation points between harmonic and subharmonic modes or via displacement of Floquet multipliers in the Floquet-complex plane. This latter scenario sets in between subharmonic and quasiperiodic instability modes in the high frequency limit by varying the phase-lag between the temperatures of the lower and upper boundaries. Moreover, it is shown that the nature of the instability mechanism alters considerably the heat transfer dynamics of the system. • A Floquet-based analysis on time-modulated Rayleigh-Bénard convection in a Hele-Shaw cell is presented. • Three classes of time-dependent instability modes are found namely harmonic, subharmonic and quasiperiodic instabilities. • Flow reversal is used to identify the primary bifurcation mechanism. • The effect of the instability mechanism on the heat transfer of the system is also presented. [ABSTRACT FROM AUTHOR]

• Heat transfer coefficient of highly subcooled water during flow boiling. • Challenges in minichannels during subcooled flow boiling. • Wall temperature distribution of mini and conventional channels during flow boiling. • Temporal temperature variations in minichannel at near to zero vapor quality. • Wall temperature fluctuations in minichannel for bo > 1.76 × 10−4. Channels of different sizes are employed in diverse engineering applications to enhance the efficiency of heat transfer system. Minichannels are preferred for their compactness, enhanced heat transfer, larger surface area to volume ratio, and high heat transfer coefficient values. There is a dearth of literature addressing flow boiling in minichannels with highly subcooled water at atmospheric system pressure. This research paper analyses the flow boiling phenomenon in a 2 mm diameter minichannel, comparing it with conventional 4 mm and 11.7 mm diameter tubes while maintaining a constant length to diameter ratio of 150. The analysis investigates the wall temperature distribution, local heat transfer coefficient, and temporal heat transfer fluctuations at a mass flux of 150 – 2400 kg/m2s and 109 – 1080 kW/m2 heat flux. The study explores the impact of boiling number on wall temperature fluctuations. Results reveal that mass flux doesn't impact heat transfer in subcooled flow boiling but does in saturated flow boiling in conventional channel. There are no significant temporal fluctuations of wall temperature in a 4 mm tube. However, vapor bubble size affects the circumferential area of minichannels, leading to abrupt flow disturbance. Wall temperature fluctuations occur in the minichannel for the boiling number exceeding 1.76 × 10−4. Temperature fluctuations in minichannel increase with boiling number, but decrease as mass flux is increased. Delving into the depths of minichannel heat transfer, this intriguing study unveils the pivotal role of the boiling number in ensuring process stability. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of the anomalous diffusive effects caused by micro-scale heterogeneity and kinetic and inertial thermal relaxations on the optically induced thermoelastic bending component of the photoacoustic response. We calculated the temperature distribution for a one-dimensional heat transfer problem with planar and periodic excitation, neglecting the influence of thermoelastic strains on the temperature profile. Thermoelastic bending was evaluated using a theoretical approximation of a thin plate, while pressure fluctuations in the photoacoustic cell were obtained by assuming adiabatic changes in the closed air. The model analysis shows that the relaxation processes could significantly affect the mechanical piston component of the photoacoustic response at frequencies higher than the minima of the inverse of two thermal relaxation times, while the influence of micro-scale heterogeneity is observable in the whole frequency range. • The hyperbolic DPL model enhances accuracy of thermoelastic effect at higher frequencies. • Sensitivity to fractional order of DPL model emphasizes precision in TE control. • Anomalous DPL heat diffusion shifts and attenuates the peak of the hyperbolic result. • Maximum damping occurs to identical kinetic and thermal relaxation times. [ABSTRACT FROM AUTHOR]

• The process of melting-reconsolidation of the frost layer is considered. • Improvement of the existing Eulerian multiphase flow model of frost formation. • The whole process of frost layer growth under prolonged periods of time was studied. • Changes of ice-phase volume fraction and melt-reconsolidation region with time are discussed. Frost growth is a complex heat and mass transfer process, which involves the vapor-liquid-solid three-phase interconversion problem, and the investigation of the frost growth process helps to understand the mechanism of frost growth. In this paper, frost model is considered, taking into account the role of the frost layer melting-reconsolidation. The aim is to improve the existing Eulerian multiphase flow model. Using the improved frost model, the whole process of the frost layer growth is simulated. In addition, an investigation is presented dealing with, the frost layer growth in various stages of the ice phase volume fraction and melting-reconsolidation area, considering the change and the proportion of the situation. The results showed that the volume fraction of the ice phase increased with time. Additionally, the melting-reconsolidation process starts from the front area of the frost layer surface and then gradually spreads to the whole surface. Moreover, it is shown that the proportion of the melting area increases and then decreases with time before attaining a constant value. On the other hand, the proportion of the solidifying area increases with time and finally tends to 0. [ABSTRACT FROM AUTHOR]

• An equivalent interface thin layer temperature field model (ETTM) is proposed considering the effect of TCR. • ETTM can describe the temperature gradient caused by rough contact interfaces. • The validity of the TCC model and ETTM is verified by comparing the model proposed with the previous research findings and ANSYS analysis results. • The effects of multiple factors on thermal contact conductivity, equivalent thin layer parameters and temperature field are analyzed. Improving the accuracy and efficiency of predicting the temperature field is a crucial requirement for iteratively calculating and online monitoring the temperature field, particularly for combined structures. The heat flow movement is impeded by incomplete interface contact, resulting in a temperature jump. To address this, the equivalent thin-layer temperature field model (ETTM) is proposed to replace the interface thermal contact conductance (TCC) model. Firstly, the fractal TCC model of a bolt connection is derived based on fractal geometry. Subsequently, the contact surface of the circumferential bolt connection is considered to be the parallel connection of multiple bolt thermal resistances. The TCC of the equivalent thin-layer is obtained. Building on this, the ETTM of the built-up rotor structure is developed. Finally, a temperature field model of the bolted rotor is derived. The validity of models is verified by comparing the model proposed in this paper with the previous research findings and ANSYS analysis results. Numerical simulation results reveal that TCC is influenced by several factors: contact pressure, the nominal contact area within the fractal domain, fractal dimension, fractal roughness, and the root mean square (RMS) height. Furthermore, the effects of the thickness of the thin layer model and the thermal conductivity of the material on heat transfer are examined. Ultimately, the findings indicate that heat transfer at the interface is significantly impeded by thermal contact resistance across various temperature boundary conditions. Notably, lower contact pressure intensifies this impedance. [ABSTRACT FROM AUTHOR]

• A compact jet impingement boiling heat transfer device achieves a high-powder cooling power of 1532 w. • The variation trends of critical heat flux, heat transfer coefficient and pressure drop with mass flux, saturated pressure and liquid subcooling are obtained. • Compared with smooth surface, a micro-pin-finned surface can increase CHF and HTC by up to 60 % and 32 %, while only increasing a pressure drop of 14 %. In this paper, jet impingement boiling heat transfer performance was studied using a novel new environmentally friendly refrigerant medium (HP-1) based on a high-power chip heat sink. A series of experimental investigations of jet impingement boiling were conducted on smooth and micro-pin-finned surfaces (PF0.5–0.5–1, PF0.5–0.5–2 and PF0.3–0.3–1). Heat transfer performances were evaluated over the saturated pressures from 450 to 590 kPa, liquid subcoolings from 2 to 15 K, nozzle sizes from 1 to 2 mm, mass fluxes from 71 to 858 kg/(m2s). The results show that critical heat flux (CHF) and heat transfer coefficient (HTC) increases with the increase of mass flux and saturated pressure. At ΔT sub =15 K, the CHF of the micro-pin-finned surfaces can be increased by 63 % compared with smooth surface, in which the CHF of PF0.5–0.5–2 surface is up to 1532 kW/m2. Boiling heat transfer coefficient first increases and then decreases with the increase of heat flux. Due to the increase of the inlet liquid subcooling, leading to a large temperature difference, so the heat transfer coefficient is smaller at a high liquid subcooling. Several factors, such as mass flux, saturated pressure and liquid subcooling, have a great impact on pressure drop. With the increase of vapor quality, the shear action between the vapor-liquid phase is enhanced, and the pressure drop will gradually increase. Bubble behaviors have also been captured by a high-speed camera to help analyze the mechanism of jet impingement boiling heat transfer in a confined space for high-power chips. [ABSTRACT FROM AUTHOR]

• Physics-Informed neural networks (PINNs) are used for single and two-phase flows. • The study investigates the rising bubble problem with and without heat transfer. • The pertinent physics of wake interaction and thermal boundary layer are discussed. • Physics-Informed neural networks are agnostic to geometry and fluid properties. • The maximum error in the position of the centre of mass by PINN is less than 2.8 %. This paper presents data-driven simulations of two-phase fluid processes with heat transfer. A Physics-Informed Neural Network (PINN) was applied to capture the behaviour of phase interfaces in two-phase flows and model the hydrodynamics and heat transfer of flow configurations representative of established numerical test cases. The developed PINN approach was trained on simulation data derived from physically based Computational Fluid Dynamics (CFD) simulations with interface capturing. The present study considers fundamental problems, including tracking the rise of a single gas bubble in a denser fluid and exploring the heat transfer in the wake of a bubble rising close to a heated wall. Tracking of a rising bubble phase interface of fluids with disparate properties was performed, revealing a maximum error of only 5.2% at the interface edge and a maximum error of 2.8% at the position of the centre of mass. Inferred (hidden variable) flows are studied in addition to a purely extrapolative inverse isothermal bubble case. When no velocity data was supplied, velocity field predictions remained accurate. Rise of an inferred isothermal bubble with unseen fluid properties was found to produce a maximum mean-squared error of 0.28 and centre of mass error of 1.25%. For the case of the rising bubble with a hot wall, the maximum error in the temperature domain using specified boundary conditions was 6.8%, while the bubble position analysis reveals a maximum positional error of 3.6%. These results demonstrate that PINN is agnostic to geometry and fluid properties when studying the combined effects of convection and buoyancy on two-phase flows for the first time. This work serves as a starting point for PINN in multiphase cases involving heat transfer over a range of geometries. Eventually, PINN will be used in such cases to provide solutions for forward, inverse, and extrapolative cases. Each of which represent a dramatic saving in computational cost compared to traditional CFD. Contours of volume fraction (α) and temperature (T*) predicted by the CFD (Top) and PINN (Bottom) for the evolution of flow showing how the rising bubble influences the thermal boundary layer on the wall. [Display omitted] [ABSTRACT FROM AUTHOR]