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In the integrated circuit industry, heat is transferred through the contact between wafers and the chemical vapor deposited (CVD) 3C–SiC wafer susceptor. Understanding the out-plane thermal conductivity of CVD 3C–SiC is crucial in this context. The influence of grain size and grain boundary characteristics on out-plane thermal conductivity for <111>-oriented CVD 3C–SiC was discussed in this study. The out-plane thermal conductivity sharply decreases from 146.4 W/m⸱K to 122.3 W/m⸱K when the grain size approaches 11.04 μm. This paper suggests that the significant accumulation of dislocations at high-angle grain boundaries is the primary cause of this phenomenon. The substantial lattice strain impedes phonon transfer between grain boundaries, reducing overall phonon mobility. These findings suggest that manipulating the grain boundary angle is an effective means to fine-tune heat transfer in <111>-oriented CVD 3C–SiC. [ABSTRACT FROM AUTHOR]

In this paper, we propose a second-order adaptive DLN algorithm with different subdomain variable time steps for the 3D closed-loop geothermal system. Theoretically, the stability and convergence of the algorithm in the case of variable time steps are analyzed. In numerical experiments, the DLN algorithm is combined with an adaptive algorithm to verify not only its effectiveness and second-order convergence under any arbitrary sequence of time steps but also to improve computational efficiency. We overcome the difficulty of 3D programming, and verify the applicability and accuracy of the proposed algorithm by simulating the flow characteristics and heat transfer of the closed-loop geothermal system with 3D convection. [ABSTRACT FROM AUTHOR]

The Institute for Microelectronics and Microsystems of the Italian National Research Council (Italy) has designed and fabricated a water-fed MEMS vaporizing liquid microthruster (VLM) in collaboration with the University of Salento (Italy) and KU Leuven (Belgium). Previous studies have demonstrated the device's functioning and highlighted the presence of a strong thermoelectric-hydraulic coupling that severely affects the heating and propulsive efficiencies and reliability of the device. In this regard, the current work provides a preliminary experimental investigation of a pulsed heating system actively controlled by temperature using PI-D logic (proportional and integrative actions applied to the error; derivative action applied to the output). The overall performance assessment focuses on evaluating power consumption during steady-state operation and analyzing the dynamic response of the VLM undergoing such an actively controlled pulsed heating, which has been built using both manual and data-driven offline adaptive tuning of the PID parameters. Concerning the steady-state operation, results highlight a promising enhancement of the heating efficiency to values above 0.9. The dynamic response analysis shows that operating with a single set of fixed PID parameters is not feasible and that the manual tuning is a trial-and-error approach highly dependent on the operator's experience, operating conditions, and reference temperature profile. Furthermore, shorter rise and response times require a higher proportional gain, and the overshoot experienced when crossing the saturation temperature cannot be avoided. In this paper, we show that the response of the data-driven adaptive controller solves these issues, exhibiting a reduced maximum settling time from around 59 s to less than 10 s, while the overshoot is avoided thanks to the temporal adjustment of the PID parameters. • Thermoelectric-hydraulic coupling impacts VLM heating and propulsion efficiency. • PI-D controlled pulsed heating investigated for VLM propulsion. • Steady-state efficiency boosted beyond 0.9. • Adaptive controller reduces settling time. • Data-driven approach minimizes overshoot. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose an efficient numerical scheme to deal with heat transfer problems in pipe flow with a large length/diameter ratio. The generalized finite difference method (GFDM) is combined with a space stepping algorithm (SSA) for the solution. The SSA divides the solution domain into a number of overlapping sections in the length direction of the pipe. Due to the large Peclet number, the heat transport process is dominated by advection, which allows an approximate boundary condition to be applied at the downstream cross section. The problem is then solved section by section. Using the uniform distributed points, the solution matrix for each section does not change, and only the right hand side needs to be refreshed for the changing boundary conditions. This leads to a highly efficient scheme for problems with a large pipe length. To show the accuracy of the numerical scheme, a problem with available analytical solution is studied. Then the method is applied to problems of single pipe with different pipe wall temperature and flow Reynolds number, and concentric annular pipe. Numerical results confirm the stability and efficiency of the GFDM-SSA. The method can be applied to many real world transient heat transfer problems in which the pipe is heated or cooled along its length with arbitrary wall temperature for heat exchange and other purposes. [ABSTRACT FROM AUTHOR]

• A fully coupled three-dimensional THMC model (DEHydrate) is developed for simulating hydrate dissociation. • The numerical results obtained from the proposed model are in good agreement with those from other simulations. • Only a small fraction of gas produced from radial hydrate dissociation is collected from the wellbore. • The model provides an effective tool to predict the mechanical behavior during hydrate dissociation. Due to high energy density and huge reserves, many trial projects worldwide have been conducted to exploit natural gas hydrates (NGH). However, most of them did not meet the commercialization requirements because of submarine hazards, low gas production and sand production. Therefore, it is important to investigate the NGH dissociation process. In this paper, a fully coupled multiphase, strongly nonlinear three-dimensional (3D) thermal–hydro–mechanical–chemical model (DEHydrate) is developed to consider the multiphysics behaviours including solid-liquid-gas multiphase flow, heat transfer, NGH phase transition and solid deformation during hydrate dissociation. The model is solved using a fully implicit finite element method. The gas-liquid flow and heat transfer are simulated by low-order elements while the solid deformation is calculated by high- or low-order elements. The behaviours of the multiphase seepage and geomechanics are fully coupled and the physical properties of the reservoir are updated iteratively based on changes in pressure, temperature and displacement. The DEHydrate simulator provides an effective tool to predict the evolution of reservoir mechanical behavior during hydrate dissociation, including transient pressure, temperature, displacement and stress in the reservoir, as well as multiphase saturation, hydrate dissociation rate/mass and gas production rate/mass. During the NGH dissociation, the initial stage exhibits a rapid dissociation rate of up to 206.23 kg/(d·m) for NGH layer with a length of 600 m and a thickness of 22 m, which subsequently decreases to 11.64 kg/(d·m). Only a small portion of the gas generated during NGH dissociation is collected at the wellbore (approximately 35.6 % after 100 days), while the majority remains trapped in the reservoir. In addition, throughout NGH dissociation, the reservoir matrix continues to move toward the wellbore in the horizontal direction. While in the vertical direction, the reservoir matrix below the wellbore moves upwards, with decreasing displacement due to low-pressure diffusion, while the reservoir matrix above the wellbore moves downwards, with increasing displacement. The largest displacements occur near the wellbore during the early stage of NGH dissociation, while in the late stage, the largest displacements occur above the reservoir. [ABSTRACT FROM AUTHOR]

The non-Fourier heat transfer model has gained significant attention in practical engineering applications, particularly under extreme conditions. However, solving the three-dimensional non-Fourier hyperbolic heat conduction equation remains a challenge. A method for solving the three-dimensional Maxwell-Cattaneo-Vernotte hyperbolic heat conduction equation on unstructured grids is proposed, where the total diffusion term is divided into normal diffusion term and cross diffusion term, and the temperature gradient is solved by reconstruction gradient. The convergence and accuracy of this method are verified by calculating the heat transfer process of a three-dimensional hollow cylinder, and the numerical solutions are found to be consistent with existing analytical solutions. Furthermore, the effects of relaxation time on the non-Fourier heat transfer process in three-dimensional hollow cylinder and complex ceramic part are discussed. Importantly, the method presented in this paper is not influenced by the coordinate system or the shape of the calculated region, providing a theoretical reference for solving complex three-dimensional non-Fourier heat transfer problems. [ABSTRACT FROM AUTHOR]

• The present paper explores the fluid dynamics, heat and mass transmission characteristics within hexagonal enclosure with square object. • The phenomenon encompasses the interplay of various physical mechanism, including micro-rotation of fluid particles, Joule heating, thermal radiation, porous materials, and magnetic field. • The governing nonlinear partial differential equations are transformed into non-dimensional form and then investigated numerically using continuous Galerkin finite element method. The pressure component of the momentum equation is removed by employing the Penalty parameter. • The validation of findings is ensured by establishing a consensus with previous studies. Flow, heat and mass distributions are depicted using streamlines, isotherms and isoconcnetrations. • Graphical representation of average Nusslet number and Sherwood number are also provided. It is anticipated to offer novel concept for enhancing the performance of cooling systems and optimizing the energy efficiency in diverse engineering applications. The present paper explores the fluid dynamics, heat and mass transmission characteristics within hexagonal enclosure with square object. The phenomenon encompasses the interplay of various physical mechanism, including micro-rotation of fluid particles, Joule heating, thermal radiation, porous materials, and magnetic field. The governing nonlinear partial differential equations are transformed into non-dimensional form and then investigated numerically using continuous Galerkin finite element method. The pressure component of the momentum equation is removed by employing the Penalty parameter. In order to achieve the consistent solution the value of Penalty parameter is set to 10 7. The analysis includes several physical parameters, such as Buoyancy ratio (−1–1), micropolar parameter (2–6), Joule heating parameter (0–5), Richardson number (0.5–5), thermal radiation parameter (0.1 – 0.5), Lewis number (0.1–5), Darcy number (0.001–0.1) and Hartmann number (0–50). Results reveal notable trends regarding the impact of key parameters on flow behavior and thermal-solutal transfer within cavity. Increasing Darcy numbers intensify fluid motion and subsequently augments thermal and solutal transfer. The flow regime shifts from shear fricition-dominated at low Richardson number to buoyancy-induced at high Richardson numbers. For concentration-dominant counter flow, a uniform distribution pattern emerges, while aiding flow leads to increased fluid velocity, temperature, and concentration. Additionally, the micropolar parameter influences flow velocity, with varying effects on heat and mass transfer rates depending on the Hartmann number. Mass distribution expands with increasing Lewis number, while temperature rises significantly due to variations in radiation and Joule heating parameters. These findings contribute to a deeper understanding of enclosed flow dynamics and have implications for the optimization of diverse engineering systems. [ABSTRACT FROM AUTHOR]

The investigation of jump cooling performance on turbine endwall independently causes its actual cooling effectiveness to deviate from the design values. In this paper, the endwall jump cooling structure with combustor-turbine interface cavity and combustor liners is modeled. Taking the realistic combustor-turbine interface features into account, the effect of jump coolant on turbine endwall film cooling and heat transfer characteristics is numerically studied. Under different endwall misalignment modes, the aerodynamic interaction mechanisms of realistic combustor outflow profile, jump coolant jet and cascade secondary flows at turbine endwall region are revealed. The modification effects of combustor-turbine interface features on jump cooling of the endwall are investigated. The results show that the combustor outflow severely ingests into the combustor-turbine interface cavity after flowing across several steps. Two branches of cavity vortex are subsequently generated in the middle-pitch region of cascade to affect the jump coolant jet. At low coolant blowing ratio, the attachment and separation sides of cavity vortex individually result in high and low cooling regions, while the horseshoe vortex leads to a large wedge-shaped cooling region. At z / C ax < 0, the backward step leads to a higher cooling effectiveness than forward step by 0.2. The jump coolant only leads to phantom cooling effect on downstream part of the vane suction side surface. The net heat flux reduction (NHFR) between two cavity vortexes and at pressure side junction are individually 0< NHFR <0.2 and −0.2< NHFR < −0.1. At high blowing ratio, the jump coolant can cover the pressure side junction with the highest cooling effectiveness of 0.5. The jump coolant can flow across the horseshoe vortex and directly upwash the vane surface. The weak protection regions between two cavity vortexes and near the attachment line of the pressure side horseshoe vortex enlarges. Compared with the forward step, the backward step achieves a lower NHFR by up to 0.1 and a higher Nusselt number. This paper provides an in-depth analysis of the aero-thermal physics of endwall jump cooling concerning realistic combustor-turbine interface conditions. [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]

With the highly integrated development of electronic components, higher requirements are put forward for heat transfer components, there is an urgent need for high-performance heat transfer components. Oscillating heat pipe (OHP) is novel types of heat pipe with excellent heat transfer capability. However, the heat transfer limit hinders their operation and application. This paper proposes an OHP under trans-critical conditions with the working fluid of R218 and explores its operating characteristics and heat transfer capability. Visualization experiments and pressure monitoring were conducted to analyze the state changes within the OHP under trans-critical conditions. After evaporation section temperature surpassing the critical temperature of R218, the pressure increases with the temperature, once the pressure reached near the critical pressure, OHP can transcend the limitation of the critical temperature and realize efficient oscillating operation under trans-critical conditions. With stable operation, the working fluid velocity can reach up to 1.49 m/s, and the OHP under trans-critical conditions presented excellent heat transfer performance with the thermal resistance of 0.22 °C/W. This paper proves the feasibility of the OHP under trans-critical conditions and provides a basis for further research. [ABSTRACT FROM AUTHOR]

Surfactant aids boiling enhancement, but the related mechanism is not yet comprehensively understood. For mechanism investigation on surfactant molecule, most of existing studies focused on its hydrophobic part, while research on hydrophilic part is scarce. In this paper, a group of non-ionic Triton surfactants with same functional group but different hydrophilic chain lengths were experimentally tested for pool boiling on flat copper. At critical micelle concentration (CMC), long-chain Tx-405 exhibited higher heat transfer coefficient (97.4 kW/(m2·K)) than Tx-100 (77.1 kW/(m2·K)) and Tx-114 (77.4 kW/(m2·K)). Long-term test indicated a gradually deteriorating trend of heat transfer performance from days on. Solution properties and bubble dynamics were measured. At low concentration, surfactant with shorter hydrophilic chain has better heat transfer performance due to greater surface tension reduction. The increase of hydrophilic chain length improves water affinity of surfactant and thus leads to higher CMC. If there is no restriction for surfactant concentration, a longer hydrophilic chain is favorable for higher heat transfer coefficient at CMC. The results in this paper provide insights for mechanism investigation on surfactant, promote further design of new surfactant, and contribute to the prediction of heat transfer enhancement effect. • Nucleate pool boiling of Triton surfactant solutions on flat copper was experimented. • Bubble behaviors during boiling and related solution properties were measured. • At CMC, Tx-405 with longer hydrophilic chain showed higher HTC of 97.37 kW/(m2·K). • At low concentration, Tx-114 with shorter hydrophilic chain was favorable. • Heat transfer enhancement mechanism regarding hydrophilic chain length was discussed. [ABSTRACT FROM AUTHOR]

The distributed energy supply system provides a good scheme for energy supply. The micro gas turbine with a recuperator is a common power device in distributed energy supply systems. In recent years, several achievements have been made in the development of micro gas turbine recuperators. Plate-fin and primary surface recuperators have been used in mature applications. Moreover, the thermodynamic properties of the heat transfer channel have been studied in detail. Among them, the cross wavy primary surface recuperator developed by Capston Company is one of the important achievements. This paper reviews the technical development of thermodynamic performance of micro gas turbine recuperator in recent years. The micro gas turbine recuperators are divided into plate-fin and primary surface recuperators commonly. In this paper, the correlation formula, heat exchange enhancement, optimum design and the influence of recuperator on the overall machine performance are reviewed. It has been found that the plate-fin recuperators have been sufficiently studied by scholars, and the results are more comprehensive. As for the primary surface recuperators, which have just become popular in recent years, the research results are less comprehensive due to their unique structure. In the future development of micro gas turbine recuperators, this will be the future research and development trend due to the high heat exchange efficiency and the lack of comprehensive research on primary surface recuperators. [ABSTRACT FROM AUTHOR]

Micro fins on the internal surface of the tube improves its heat transfer ability. This paper investigates the thermal performance of tube flow numerically by adding axial straight micro fins (ASMF) on internal tube surfaces. The numerical method is experimentally validated using a tube featuring ASMF. The effects of fin height e , fin number N f , and fin shape of the tube with ASMF on the thermal performance are numerically studied within the range of Reynolds number (Re) from 1280 to 7687. Compared to a smooth tube, the Nusselt number (Nu) for tube with ASMF is reduced over the entire range of Re. In order to assess the performance of heat transfer, the ratio of the heat transfer coefficient (h) multiplying the heat transfer area (F) of ASMF tube (hF) to that of the smooth tube (h s F s) is utilized. Parametric studies were performed. The optimal fin height, fin number are found to be 0.0429 and 32. The optimal fin profile is found to be quadratic function profile. By combining the optimal fin height, fin number and fin profile, the maximum value of hF /(h s F s) can reach 1.32. Besides, the heat transfer enhancement mechanism induced by ASMF is also disclosed in this paper. [ABSTRACT FROM AUTHOR]

This paper is the second of a two-part series that presents experimental data and analysis on the liquid nitrogen quenching heat transfer process of a stainless-steel tube with an inner surface low-thermal conductivity thin-film coating. This paper focuses on the effects of different flow directions and two tube wall thicknesses. Additionally, this paper also provides an analysis on the chilldown thermal efficiency of the quenching process. Three flow directions with four different inner surface coating modifications, and three tube wall thicknesses were examined. The experimental data covers the Reynolds numbers ranging from 3500 to 140,000. The chilldown efficiency, along with chilldown time and LN 2 (liquid nitrogen) mass consumption were analyzed to assess the overall performance of the LN 2 line chilldown process. For thin tube wall cases, the chilldown efficiencies cover a range between 3% and 41%, and the maximum chilldown efficiency value is found for the tube with 3 L coating at Re = 5278 in the vertical up flow direction. For thick wall tube cases, the efficiencies cover a range between 4% and 52%, and the maximum chilldown efficiency value was found for the tube with 4 L coating at Re = 5308 in the vertical up flow direction. [ABSTRACT FROM AUTHOR]

This paper formulates quadrilateral elements for the NURBS-enhanced finite element method (NEFEM). The objective is to extend the application of NEFEM to problems where the use of quadrilateral elements is preferred. By leveraging a mapping, between reference and physical spaces, that encapsulates the exact boundary representation of the domain, a tight integration with computer aided design (CAD) systems is achieved. The contribution of this work is an enhanced quadrilateral finite element that incorporates the exact CAD geometry purely from the boundary representation (B-rep) from CAD and without the need for a whole volume representation (V-rep) as a NURBS entity. Numerical examples involving heat transfer and linear elastic problems are used to numerically demonstrate the optimal convergence properties of the method under mesh refinement. [Display omitted] • This paper aims to reduce the gap between CAD and analysis. • A new NEFEM bilinear superparametric element is presented. • The shape functions are redesigned and solely reside in the parametric space. • Heat transfer and elasticity problems show that NEFEM achieves higher accuracy. [ABSTRACT FROM AUTHOR]

Strip-casting is a key step among processes for manufacturing the Nd-Fe-B permanent magnets. Current research on the process parameters of the strip casting process mostly relies on the trial-and-error method. In this paper, the influence of the cooling roller speed on the strip-cast Nd-Fe-B flakes is investigated by a combination of simulation and experiment. The microstructures of the strip-cast flakes prepared at different roller speeds are observed and analyzed. The simulation is further performed by using the thermal-fluid coupling method. The temperature field and cooling water flow field of the cooling rollers at different roller speeds are obtained to explain the principle of the microstructural evolution. The temperature field distribution affects the uniformity of the columnar grains on both sides of the strip-cast flake. Higher or lower temperature can also lead to the formation of α-Fe, cluster rare earth (RE) rich phases, or ultra-fine equiaxed grains. An increase in cooling water flow rate is helpful to obtain the columnar grain with even thickness. The simulation results are consistent with the microstructural results. Furthermore, the simulated results and microstructural analyses are combined to indirectly evaluate the trend of magnetic properties of final sintered magnets from the tested strip-cast flakes. By verifying the performance of magnets prepared under the condition of only changing the roller speed during the entire process flow, the measurement results are consistent with the evaluation results, proving that the combined analysis proposed in this paper can reasonably predict the trend of magnetic properties of sintered Nd-Fe-B permanent magnet materials from the strip-cast flakes prepared at different roller speeds. This paper can provide a transferable idea and method for using numerical simulation to assist in the design and production of Nd-Fe-B flakes and sintered magnets. • Formation of the microstructure of Nd-Fe-B strip-cast magnetic flakes was explained. • Effect of roller speed on the microstructure of magnetic flakes was discussed. • Thermal-fluid coupling during strip-casting was adopted to understand heat transfer. • Simulation and microstructure were combined to predict the trend of properties. • A method based on test and simulation was proposed to help the development of magnet. [ABSTRACT FROM AUTHOR]

The selection of optimal design and the most efficient operational parameters for energy devices constitute a priority task for sustainable development and increasing energy efficiency within the net-zero emissions strategy. This is particularly important in adsorption cooling and desalination systems with poor performance due to unfavourable heat transfer conditions in conventional packed beds of adsorption chillers (ACs). Therefore, looking for additional ways of performance improvement is still challenging, especially covering different design variants and operational strategies. The existing complex, time-consuming and costly analytical, numerical and experimental methods, usually focused on a specific design and operating parameters of conventional packed adsorption beds, cannot tackle these comprehensive problems. Since artificial intelligence (AI) based models are considered tools that sometimes may overcome the shortcomings of the programmed computing approach and the experimental procedures, the paper introduces automated machine learning (AutoML) as a general approach for the design and optimization study of adsorption cooling and desalination systems. The double-effect, i.e. specific cooling capacity (SCP) and specific daily water production (SDWP) of various adsorption chillers (ACs) operating in large-, pilot- and small-scale adsorption cooling and desalination systems, is considered in the study. The paper also presents a novel big data optimization procedure for selecting the best operating and design strategy in adsorption cooling and desalination technology. Finally, a new concept of fluidized bed-type application in adsorption chillers is proposed, which allows for enhancing the performance of ACs. The presented approach can be referred to as a complementary design technique in adsorption cooling and desalination systems, besides the existing complex analytical and time-consuming numerical methods and expensive experiments. • Double-effect desalination and cooling production in adsorption chillers (AC) are evaluated • The new approach allows considering various cooling and desalination adsorption systems. • The novel concept of fluidized bed application in adsorption systems is proposed. • The developed models constitute powerful tools for optimizing ACs systems' performance. [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 current work aims to understand and model thermal runaway (TR) events in lithium-ion (LIB) 18650 cells within the context of aircraft battery applications. The primary goal is to comprehend the phenomenon and discuss strategies for mitigating its consequences during aircraft operation. TR is modeled using Arrhenius kinetic equations and is implemented in both lumped parameters (Matlab SimulinkTM), and 3D CFD simulations (Ansys FluentTM) using User Defined Functions. To validate the thermochemical model, cells are initially simulated in an oven test, where a cell is exposed to a temperature-controlled atmosphere, triggering exothermic reactions. With a strong correlation between lumped parameters and 3D models, the latter is simulated under battery module installation conditions. An internal short-circuit is then implemented within the cell to observe how thermal runaway is triggered by an internal heat source. The trigger cell is subsequently placed in a battery module assembly to assess the dominant heat transfer modes and the likelihood of TR induction from one cell to its neighbors. This work's main objective and innovation are to compare different materials in which cells are immersed while observing the main heat transfer parameters for each material. Three conditions are tested: ceramic paper fiber and G7 as solid separators, and no separator material, where air fills the gaps between cells. The analysis of heat transfer modes reveals radiation's dominance in the case of air interstice, suggesting the possibility of using a special coating to reduce the cell surface emissivity as an alternative to decrease the likelihood of TR propagation. Thus, two values of surface emissivity were tested in the case of air. Considering a cell triggered by an internal short-circuit, a thermal runaway temperature spike is not observed in any of the four cases. However, the air interstice case with regular emissivity is the most critical one, with the closest cell reaching peak temperatures as high as 136 °C in 490 s. The ceramic paper fiber is considered the best separator material, as it postpones the temperature increase in the closest cell while also being lighter than G7. The results and discussions concerning heat propagation presented herein can serve as guidelines for developing strategies to mitigate thermal runaway in battery modules. [ABSTRACT FROM AUTHOR]

Nanochannels consisting of hot and cold walls with periodic rectangular and triangular nanostructures were simulated by molecular dynamics in this paper, the periodic size dimensionless parameters φ was defined to describe the dimension of nanostructures on the wall. The results show that the addition of nanostructures leads to the variation of mass density distribution of fluid near the wall. A hot wall with nanostructures can promote the appearance of a fluid high-potential area near it. The discrepant attraction for fluid from the wall caused by the different wall conditions leads to different flow characteristics in nanochannels. Fluid velocity growth rate near the hot wall is 10.5% higher than that near the cold wall. Average velocity of the fluid near the hot wall is 5.1% higher than that of fluid near the cold wall. A wall with rectangular nanostructures at φ = 0.28 shows minimum flow resistance among rough hot walls, while a wall with triangular nanostructures at φ = 0.14 has minimum flow resistance among rough cold walls. Heat is transferred from the hot wall to the cold wall through fluid flow. Wall conditions impact the heat transfer situation of fluid in flow boundary by changing the fluid mass density contribution. The addition of nanostructures and decrease of nanostructures size is beneficial for heat transfer while unfavorable for fluid flow, convective heat transfer was influenced by their combination. For a wall with 300 K, the addition of rectangular nanostructures at φ = 0.07 has the best convective heat transfer performance. For a wall with 200 K temperature, increasing triangular nanostructures at φ = 0.14 on the wall can reach the best convective heat transfer capacity. This paper can provide a theoretical foundation for the optimization of nanochannels to achieve best convective heat transfer ability. [ABSTRACT FROM AUTHOR]

The presence of magnetic field results in a reduction in natural convective heat transfer and entropy generation in cavities. The use of nanofluids improves the performance of thermal systems. The present paper discusses the impact of uniform and non-uniform magnetic fields on the second-law performance of nanofluid-filled and porous cavities, introduces artificial intelligence (AI) approaches, and examines the applications of AI in optimizing heat transfer and entropy generated in these systems. The mathematical formulation is presented in terms of the entropy generation for natural convection in cavities. This paper demonstrates the influences of various important non-dimensional parameters on entropy generation in cavities. Besides, advances in the second-law performance of cavities and the role of AI techniques in the field are discussed and future directions are provided. [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]

In this paper, the barrel of small-caliber automatic rifle is taken as the research object. An experiment was taken on the gun barrel and an infrared thermal imager was used to measure the change of barrel temperature field during the continuous shooting, and the finite difference model of barrel heat transfer was established. The formula of the correction coefficient of heat transfer of gunpowder gas on the inner surface of the body tube was obtained by fitting with the experimental results. The barrel transient heat transfer analysis calculation software with independent intellectual property rights was developed by C++, and the characteristics of temperature field were analyzed. The experimental results show that the temperature of the outer surface of the barrel rises and then falls along the axial direction from the bottom of the barrel to the muzzle, and the rising slope will decrease in the next 30 rounds of continuous firing. The calculation results of the small-caliber barrel with chromium layer show that the temperature of the outer surface of the chromium layer of each shot rises instantaneously and then drops rapidly, in the form of pulse, and the temperature of the steel matrix rises continuously, but it is significantly lower than the peak temperature of the chromium layer, and the presence of the chromium layer provides buffer protection for the barrel matrix material. There is still an influence region in the matrix behind the interface between the chromium layer and the barrel matrix, and the temperature of the steel matrix in this region fluctuates. The thickness of the influence region is determined by analysis. The temperature of the inner surface of the barrel reaches a maximum at the tail of the barrel along the axial axis and then slowly decreases in the direction of the muzzle, the radial temperature distribution of the barrel is steeper at the tail end and the muzzle area is relatively flat. The calculation results of the model in this paper are basically consistent with the experimental results, which provides a rapid calculation model and tool for the thermal design and analysis of the gun barrel. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence (LIF) is a robust and vigorous method for non-intrusive measurement of temperature, pressure, concentration, and pH in fluids. The application of LIF for measurement is also extendable to solid and gaseous environments. In this method, the fluorescent molecules are transferred to a higher energy state by absorbing the energy of a laser beam and subsequently undergo spontaneous emission of light in the form of fluorescence during the transition to the ground. The emitted fluorescence is commonly captured using a setup consisting of a solvent, fluorescent material, detecting cameras, lenses, and filters, which enables the determination of the thermophysical parameters of the measuring environment using pertinent mathematical formulae. This method can be used for precise measurements in a wide range of engineering and medical applications. Despite the numerous studies on the utilization of LIF for measurement, there is not a comprehensive review paper with a focus on various types of LIF techniques and their applications in temperature measurement. This paper seeks to address this gap by fully discussing these approaches, demonstrating temperature measurements in different environments and circumstances, and outlining their benefits and drawbacks. Accordingly, one-dye one-color, two-dye two-color, one-dye two-color, one-dye three-color, two-dye three-color, volumetric LIF, and encapsulation techniques are fully discussed as the main LIF approaches and their applications for the temperature measurement in fluid flows, droplets, microfluidics, and gas environments. [Display omitted] • Classification of different laser induced fluorescence technique for temperature measurement. • Classification of dyes and their corresponding properties used in LIF technique. • Detailed description of LIF techniques and their application in temperature measurement. • Full description of the advantageous and disadvantageous of LIF for temperature measurement. [ABSTRACT FROM AUTHOR]

• A novel shape optimization method for reducing thermal stress of porous structures. • Introduced homogenization method considering heat conduction and thermal elasticity. • Derived the sensitivity function theoretically for a multiscale shape design problem. • Achieved smooth pore design using the H1 gradient method, a non-parametric method. • Total volume can be properly distributed into the plural microstructures. In this paper, we propose a shape optimization method to minimize the maximum thermal stress induced in the microstructures of a multiscale structure by heat conduction and thermal expansion. The weak- coupling problem is solved by applying the temperature distribution, obtained by solving the heat conduction problem, to the thermoelastic problem to find the maximum thermal stress caused by thermal expansion. The homogenization method is used to bridge the macrostructure and the porous microstructures, in which the elastic tensor, the tensor of the coefficients of thermal expansion, the thermal conductivity tensor and the thermal transfer coefficient are homogenized. The local thermal stress in the porous structure is minimized by shape optimization. The difficulty posed by non-differentiability of the local maximum stress is avoided by introducing a Kreisselmeier-Steinhauser function. It is assumed that the macrostructure consists of multiple subregions, in which the homogenized coefficients can be independently defined. This problem is formulated as a distributed-parameter optimization problem subject to a volume constraint, including all the microstructures. The shape gradient function for this design problem is derived for each subregion using the Lagrange multiplier method, the material derivative method and the adjoint method. The H1 gradient method is used to determine the optimal shape of the porous unit cell while reducing the objective function and maintaining smooth design boundaries. The effectiveness of the proposed method for minimizing the microstructural thermal stress of porous structures is confirmed by the numerical examples presented. [Display omitted] [ABSTRACT FROM AUTHOR]

Accurate heating load prediction is essential to supply-demand collaboration in district heating systems and energy sustainability. With the development of the Internet of Things technology, massive monitoring data is collected that provides abundant data sources for the prediction models. However, the missing data from equipment anomalies, network transmissions and the complexity of heat load changing cause difficulty in realizing accurate heat load prediction. Therefore, the hybrid model based on bidirectional long short-term memory network and temporal convolutional network proposed in this paper to improve the accuracy of the heat load prediction from the aspects of reconstruction of missing values and extraction of complex features. The bidirectional long short-term memory algorithm imputes missing values based on bi-directional features of existing data and provides solid data foundation for subsequent training of predictive models. The temporal convolutional network achieves high-level feature extraction and parallel computation, which contributes to the effective modeling of complex changes in heat load and the realization of accurate heat load prediction. Comparative study was conducted with four heat exchange stations of actual environment to evaluate the performance of the prediction model. The results showed the mean absolute percentage error of the hybrid model decreased to 2.47% which is lower than the State-of-the-Art models, such as long short-term memory, temporal convolutional network, and support vector regression etc. The superior results further validated the feasibility of this hybrid model in heat load prediction. • The missing values in heating system were reconstructed by deep learning model. • A hybrid heating load prediction model was proposed considering missing values. • Detailed experiments were conducted to validate the model's superiority. [ABSTRACT FROM AUTHOR]

Inverse heat transfer problems are ill-posed problems and their solution is challenging. Conventional (hard computing) solution methods were developed for this purpose in the past, but they are not well applicable in cases including phase change, which contain strong non-linearity and bring additional computational difficulties. Soft computing methods, which currently experience very rapid development, are a promising tool for the solution of such problems. This paper addresses an inverse heat transfer problem with phase change, in which the boundary heat flux is estimated. Four methods based on distinct mathematical principles are applied to this problem and thoroughly compared. These methods include a conventional Levenberg–Marquardt method (LMM), a predictive fuzzy logic (PFL)-based method, a population-based meta-heuristic method called LSHADE (a state-of-the-art differential evolution variant), and a recently developed surrogate-assisted method coupled with differential evolution, referred to as LSADE method. Furthermore, a reformulation of the problem was developed, utilising a dimension reduction scheme and a decomposition scheme that led to sub-problems with different time frames. This reformulation brought extensive computational improvements. Results of the comparison of the methods then showed that the LMM and the PFL behave well in case without phase change but their performance deteriorates substantially in case with phase change. The LSHADE and the LSADE showed superior performance in the solution of the inverse problem with the phase change. Moreover, their performance was rather stable and insensitive to the location of the temperature sensor, which was the source of data for the estimation. • Inverse heat transfer problem with and without phase change was addressed. • Boundary heat flux was inversely identified from temperature readings. • Four solution methods were investigated and compared to each other. • Levenberg–Marquardt method (LMM) suffered from low performance due to non-linearity. • LSHADE and LSADE methods significantly outperformed LMM and fuzzy logic. [ABSTRACT FROM AUTHOR]

Inverse heat transfer problems are ill-posed problems and their solution is challenging. Conventional (hard computing) solution methods were developed for this purpose in the past, but they are not well applicable in cases including phase change, which contain strong non-linearity and bring additional computational difficulties. Soft computing methods, which currently experience very rapid development, are a promising tool for the solution of such problems. This paper addresses an inverse heat transfer problem with phase change, in which the boundary heat flux is estimated. Four methods based on distinct mathematical principles are applied to this problem and thoroughly compared. These methods include a conventional Levenberg–Marquardt method (LMM), a predictive fuzzy logic (PFL)-based method, a population-based meta-heuristic method called LSHADE (a state-of-the-art differential evolution variant), and a recently developed surrogate-assisted method coupled with differential evolution, referred to as LSADE method. Furthermore, a reformulation of the problem was developed, utilising a dimension reduction scheme and a decomposition scheme that led to sub-problems with different time frames. This reformulation brought extensive computational improvements. Results of the comparison of the methods then showed that the LMM and the PFL behave well in case without phase change but their performance deteriorates substantially in case with phase change. The LSHADE and the LSADE showed superior performance in the solution of the inverse problem with the phase change. Moreover, their performance was rather stable and insensitive to the location of the temperature sensor, which was the source of data for the estimation. • Inverse heat transfer problem with and without phase change was addressed. • Boundary heat flux was inversely identified from temperature readings. • Four solution methods were investigated and compared to each other. • Levenberg–Marquardt method (LMM) suffered from low performance due to non-linearity. • LSHADE and LSADE methods significantly outperformed LMM and fuzzy logic. [ABSTRACT FROM AUTHOR]

Combustion of iron powder is a promising option for clean and sustainable generation of heat and power. However, a fundamental understanding of the flame propagation mode is missing, especially under strong convection effects. In part I of this work, we analyzed the modes of flame propagation under weak convection effects and estimated the discreteness parameter as a ratio of the particle burn time to the conduction timescale. We found that both, the selection of temperature at which thermal properties are evaluated, and the selected length scale, are critical for a reliable prediction of the transitional particle spacing indicating the transition from the continuous to the discrete mode. In this paper, we extend our previous work by studying the effect of convection on inter-particle heat and mass transfer using boundary layer resolved numerical simulations. It is shown that for increasing convection, iron flames transition from the continuous to the discrete mode at higher particle distances. Taking into account both diffusion and convection-dominated heat transfer, an extension for the scaling of transitional particle spacing of part I is proposed. Furthermore, since iron flames could experience varying ranges of particle distances at different velocities in a practical flame, a regime diagram is constructed which is based on the Péclet number and the particle spacing with a boundary separating the two modes of flame propagation. The regime diagram offers orientation for simulations of large-scale flames using Euler–Lagrange methods where boundary layers around the particles are not resolved. [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]

The electrical wire fire often occurs in the confined space, making the flame spread behavior complex and the risk increase. In this paper, experimental and theoretical study on the flame spread over three types of polyethylene (PE) electrical wires under different side-confined distances (0∼40 mm) and currents (0∼60 A) was carried out.The ratios of copper diameter to entire wire diameter were 6mm/10 mm, 8mm/12 mm, and 6mm/12 mm for type I, type II and type III, respectively. The results show that, with the increase of s, the flame width and height, and flame spread rate will firstly increase to the maximum peaks at the position of s = 5 mm with attachment wall effect, and then gradually decrease to the values of the unconfined conditions. And with the increase of current, these parameters will gradually increase to the largest at I = 40 A and then decrease for I = 60 A, as the current effect changes from preheating to dripping acceleration.The firm correlation between preheating length δ p h and pressure difference Δ P is built, which demonstrates the smallest preheating length is at s = 5 mm with the maximum promotion of heat transfer by gypsum board. On the other hand, the generated Joule heat by the current will enhance the length of preheating, making it proportional to current. Meanwhile, it is found that, the dripping frequency influenced by the dripping mass rate, will increase with the current. The heat transfer components including of the solid conduction heat flux ( q ˙ j o u l e ″ and q ˙ c ″), flame heat flux ( q ˙ ν f ″ and q ˙ r f ″) and gypsum board heat flux ( q ˙ r g ″ and q ˙ ν g ″) are quantitatively analyzed. Correspondingly, a heat transfer model over flame spread is established, which can well predict the flame spread rate.As the diameter of the wire is relatively small, the controlling heat transfer is the flame convective heat flux q ˙ ν f ″ in this research. In addition, it is illustrated that, the heat flux of gypsum board q ˙ ν g ″ + q ˙ r g ″ will decrease with the increase of copper core diameter from type I of 6 mm to type II of 8 mm.While the solid conduction heat flux of copper q ˙ c ″ + q ˙ j o u l e ″ will decrease with the increase of thickness of PE from type I of 2 mm to type III of 3 mm. These findings can well give the understanding of heat transfer of flame spread over electrical wires with the effects of sidewall and current. [ABSTRACT FROM AUTHOR]

To deal with inverse nonlinear heat transfer problems in a two-dimensional heat conduction problem, this paper presents a hybrid approach combining fuzzy logic and the extended Kalman filter (EKF). The proposed algorithm has been applied to the real-time reconstruction of the temperature field, time-varying convective heat transfer coefficient, and time-varying boundary heat flux using temperature data from a set of sensors. The effects of the covariance of the initial estimation error, the time step of data acquisition by the sensors, and the number of installed sensors on the precision and stability of the estimation results has been investigated by numerical experiments. To compare and validate the results, all these parameters were investigated using the EKF method. The results show that the adaptive fuzzy extended Kalman filter (FEKF) method for estimating temperature, convection coefficient, and heat flux at the boundaries is precise and stable. The comparison shows that the performance of the FEKF method in parameter estimation is better than the EKF method, and the highest increase in precision and stability of the results is related to the convective heat transfer coefficient. [ABSTRACT FROM AUTHOR]

Under severe accident conditions, in addition to steam and air, there may also be hydrogen produced by the reaction of zirconium alloys and steam, CO 2 produced by the molten corium concrete interaction (MCCI) and other gases in the containment. These gases, whose properties are quite different from air, can significantly affect the steam condensation process outside the tube bundle. This paper aims to investigate the effects of non-condensable gas mixtures with varying component concentrations on the steam condensation process outside a 3 × 5 tube bundle using computational fluid dynamics (CFD) methods. The thermal conditions studied are set to a pressure of 0.4 MPa, a subcooling of 40 K, and a molar concentration of steam of 0.66. The results show that CO 2 has an acceleration effect on the flow field outside the tube bundle, which promotes the diffusion of steam to the inside of the bundle, thus increasing the condensation heat transfer coefficient (CHTC) of the bundle and decreasing the difference in CHTC between different heat transfer tubes inside the bundle. Hydrogen, on the other hand, inhibits the downward flow of the gas mixture, causing a decrease in CHTC. However, at high hydrogen concentration (X H2 >0.1), the gas mixture will form a buoyant flow upward, and then the CHTC of the tube bundle will be significantly increased by up to 177%. When the two gases act together, they will weaken each other's influence on the flow field, thus reducing the CHTC of the tube bundle. [ABSTRACT FROM AUTHOR]

Heat transfer process significantly affects the life span of gun barrels as it directly associates to the thermoelastic dynamic responses, erosion, and wears of gun barrels. The previous studies regarding the heat transfer in gun barrels were developed in the realm of local theory that is expressed by partial differential equations with the condition of smoothly distributed physical fields, and have rarely studied the cracked gun barrels. However, on one hand, due to manufacturing errors, there inherently exists fractures in realistic gun barrels; on the other hand, the inner wall of the gun barrel wears due to the high-temperature and -speed burning gas generated during the interior ballistic process, as well as the high-speed friction from projectile's movement, which severely lead more cracks and damages. Therefore, it is of great importance to investigate the heat transfer in cracked gun barrels. In this paper, a non-local heat transfer model for cracked gun barrels is formulated via the bond-based peridynamics. The governing equation is presented in the manner of integration, such that the heat process with the influence of cracks can be readily captured. Numerical results show that the heat energy severely accumulates on the crack surface and as the size of horizon increases, the non-local characteristics of the heat transfer appear to be more pronounced, resulting in a stiffer thermal response. [ABSTRACT FROM AUTHOR]

• a new 3-D multi-physics coupling model is proposed for lubricated piston-liner systems. • The sub-models for mixed lubrication, spatial multibody dynamics, and heat transfer are fully coupled on a unified absolute coordinate frame. • The coupling model is discretized employing unified spatial and temporal discrete methods. • The occurrence of wear and failure on either side of the piston skirt is predicted by the model. In this paper, a new 3-D multi-physics coupling model is proposed for lubricated piston-liner systems. The sub-models for mixed lubrication, spatial multibody dynamics, and heat transfer are established and fully coupled on a unified absolute coordinate frame. The coupling model is discretized and solved using the unified spatial and temporal discrete methods. Then, an application example of a four-cylinder engine is employed to comprehensively investigate the coupling characteristics in the piston-liner system. The new coupling model reveals the presence of two distinct locations with the lowest local film thickness on either side of the piston's central axis, consequently yielding elevated local oil film pressures. This observation provides a reasonable explanation for the occurrence of wear and failure in the piston skirt on both sides. [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]

Mixing of surface microstructure and wettability is one of the future development trends. Their combination always affects the bubble motion and heat transfer coefficient under pool boiling/flow boiling, but it is difficult to distinguish their respective contributions. This work studies the combination of new microstructure and mixed wettability to improve the flow boiling heat transfer in the channel. The nucleation, growth, coalescence and departure behaviors of R134a boiling bubbles were numerically analyzed. Effects of different heights, gaps and mixed wettability of microstructures and heat fluxes on bubble emission frequency and boiling heat transfer coefficient were discussed. Results showed that this new microstructure provides the bubble with the momentum of lateral motion, which helps the bubble to merge and leave faster. The surface of the hydrophobic groove coupled with the hydrophilicity as the substrate can effectively increase the bubble emission frequency, up to 134.37%. At the same time, the heat transfer coefficient decreases with the increase of the height of the microstructure, and it also increases with the increase of the microstructure gap. Finally, the contribution of each variable was determined by analysis of variance. The research results in this paper provide a reference for heat pipe and vapor chamber. • A creative microchannels with mixed wettability was proposed and optimized. • Synergistic effect of groove microstructure and mixed wettability was studied. • Surface mixed wettability has more influence on boiling heat transfer. • Bubble emission frequency of surface-A is 134.37% higher than surface-B. [ABSTRACT FROM AUTHOR]

In the heat transfer community, one-dimensional media refers to some media where the temperature and other thermophysical properties vary along one direction. Plane-parallel, concentric cylindrical, and concentric spherical geometries are among of regular one-dimensional media. In this paper, a general ray tracing approach is presented to track the curve paths of energy particles in regular one-dimensional variable index media. The domain of interest is limited by specular sidewalls and the medium is divided into slices with constant temperature and radiative properties. Then, the path of random energy particles emitted from boundary surfaces and volume elements are traced, element by element, until they absorb by diffuse-gray surfaces or the gray medium. After counting the number of absorbed particles by each boundary surface and volume element, the Monte Carlo method is performed to simulate thermal radiation heat transfer. The results are presented for three regular geometries, including plane-parallel, concentric cylindrical, and concentric spherical media, and the effects of radiative properties are investigated by some numerical experiments. [ABSTRACT FROM AUTHOR]

In this paper, we present a comprehensive study on the heat transfer in the spiral coiled tubes, employing both numerical simulations and experimental analysis. The investigation includes an exploration of water flow at different mass flow rates, ranging from 0.025 to 0.11 kg / s , to capture a wide range of operating conditions. The numerical simulations were conducted using advanced computational fluid dynamics (CFD) techniques, providing detailed insights into the heat transfer behavior within the spiral tube. Concurrently, experimental tests were performed to validate the numerical results and compare them with existing findings from previous studies. The primary aim of our study is to establish correlations for calculating the Nusselt number and friction coefficient in the spiral coiled tubes. These correlations serve as essential tools for engineers and researchers in predicting heat transfer characteristics and pressure drop, thus facilitating the design and optimization of heat exchangers and heat recovery systems that incorporate spiral coiled tubes. Overall, the results obtained from this investigation enhance our understanding of heat transfer in spiral tubes and contribute to the development of reliable predictive models. The proposed correlations offer practical and efficient means of assessing heat transfer performance, making significant strides towards achieving more energy-efficient and sustainable industrial processes. • Fluid flow and heat transfer in a spiral coiled tube were studied. • Effects of mass flow rate of water on heat transfer in a spiral coiled tube were investigated. • Correlations for calculation of Nusselt number and friction coefficient for water flow in a spiral coiled tube were developed. [ABSTRACT FROM AUTHOR]

Cooling systems often rely on numerical calculations with precise heat transfer boundary conditions (HTBC), usually expressed as average values. The value of the average HTBC depends on the area in which they are determined. The paper presents a new approach showing the influence of the choice of the method of supplying liquid onto the surface on the non-uniformity of energy transfer from the cooled surface, which is important in the selection of the determination domain on the HTBC. The tests were carried out for two full-cone nozzles with different spray angles and two materials with different thermal properties. The local and average heat fluxes were determined for various distances of the nozzles from the surface and various liquid supply pressures. Cooling capacity, unevenness of energy transfer from the surface and quenching characteristics were evaluated and assessed using cooling curves. The study concludes that adopting HTBC based on average heat flux variation does not cause a significant error in the assessment of energy transfer during cooling with a nozzle with spray angle of 60° for EN 1.4845 steel. However, for Inconel and a nozzle with spray angle of 45°, the noticeable non-uniformity requires the application of a local HTBC. • Unevenness the spray cooling process. • Possibilities of using the average heat transfer boundary condition. • Recommendations for the use of local heat transfer boundary condition. [ABSTRACT FROM AUTHOR]

Fuel leakage and spill fires often occur during storage and transportation of liquid fuels. And the spread and burning processes of spill fires are susceptible to cross-air flows. In this paper, spill fire experiments were conducted on a fireproof glass (with or without ignition) under different wind speeds (0–2 m/s). The effects of wind on the spread process and burning behaviors were analyzed. Results showed that, for the cases without ignition, the spread length could vary in a non-linear manner with wind speed. And a spread length model was developed based on force analysis. For spill fires under small wind speeds, the burning area increased firstly, followed by a decrease before stabilization. When the wind speed exceeded a critical value, the fuel layer spread rapidly in the upwind direction after the shrinking phase. The steady stage was observed for all tests. With the wind speed increase, the quasi-steady burning area changes from being circular to elliptic first, before it gradually became circular in the end. To explain this process, a detailed heat transfer analysis was conducted. Considering the fuel layer shape and the heat transfer characteristics of spill fires, an analytical burning rate model was developed. • Wind drag force shows a significant effect on the spreading process for non-ignition continuous leakage tests. • Three typical spill fire spreading behaviors can be observed under different wind speeds. • The variation of the convective feedback with wind speed is primarily responsible for the change in the fuel layer shape. • An analytical model is developed based on the stagnant layer theory to calculate the burning rate of liquid fires. [ABSTRACT FROM AUTHOR]

This paper employs topology optimization techniques to enhance the performance of liquid-cooled plates while investigating the optimization process and its outcomes. A multilevel optimization strategy is implemented to refine the accuracy and smoothness of the optimization process. The study demonstrates that expanding the range of penalty factors and refining the granularity of penalty factors can effectively enhance the capability of multilevel optimization in suppressing the formation of intermediate densities. Furthermore, a multi-objective function is utilized to strike a balance between the heat transfer efficiency and the hydraulic performance of the liquid-cooled plate. Ultimately, after considering aspects related to heat transfer and hydraulic performance, the research finds that compared to traditional straight-channel liquid-cooled plates, liquid-cooled plates featuring streamlined multi-branched flow channels not only increase the heat transfer area but also reduce pressure drop. As a result, this design improves the temperature uniformity of the liquid-cooled plate and enhances the velocity uniformity of the cooling fluid. At different inlet velocities, the topology-optimized liquid-cooled plate exhibits a reduction in both effective thermal resistance and pumping power compared to the traditional straight-channel liquid-cooled plate. • Multi-level optimization strategy improves the smoothness and precision of the topology optimization process. • Expanding the penalty factor range and refining granularity helps to reduce the intermediate density in the topology process. • Topology-optimized liquid-cooled plates improves the uniformity of coolant velocity and temperature distribution. [ABSTRACT FROM AUTHOR]

The porous microchannel heat sink can be used to meet the increasing demand for electronic device cooling. In this paper, heat transfer is enhanced by optimizing heat flux distribution for porous microchannel heat sinks subject to an exponential heat flux. The Nusselt number, dimensionless wall temperature and thermal resistance are obtained using the semi-analytical method. The Nusselt number is found to be dependent on the product of dimensionless exponent, Reynold number, and Prandtl number. The optimal heat flux distribution is dependent on the length of the channel and it is that under constant wall temperature boundary condition in most cases. The thermal performance is assessed using the thermal resistance ratio between constant wall temperature and constant heat flux boundary conditions. An optimal length exists when the constant wall temperature condition is used to reduce the maximum wall temperature. The effects of Biot number and the ratio between effective thermal conductivities of solid and fluid phases on the minimum value of the thermal resistance ratio and the optimal length are also studied. The result shows that the thermal resistance can be reduced by about 28% by optimizing the heat flux distribution, compared with the commonly used constant heat flux boundary condition. • Heat transfer for porous heat sinks is enhanced by optimizing wall heat flux. • The optimal heat flux distribution is that for CWT conditions in most cases. • An optimal length is found when the constant temperature conditions is used. • The thermal resistance can be reduced by about 28%. [ABSTRACT FROM AUTHOR]

The inverse heat transfer problems (IHTP) have a wide range of applications in the engineering field. Bayesian methods using Markov Chain Monte Carlo (MCMC) have long been considered as a robust and effective method for solving inverse problems. However, the discretization of the problem domain by the spatio-temporal Galerkin skill, i.e., the finite element interpolation also includes the time dimension, making the scale of the unknown parameters extremely difficult for Bayesian calculations. In this paper, a fast Bayesian parallel sampling (FBPS) framework is proposed for large-scale parameter estimation of benchmark three-dimensional inverse heat transfer problems (3D-IHTP). The FBPS we developed achieves a parameter computation scale of 10 5 magnitude within minutes, through dimensionality reduction of the space-time dependent problem domain. The Hamiltonian Monte Carlo (HMC) sampler, which is proven to be more efficient for high-dimensional parameter estimation, is employed. Through several simulation tests of IHTP, it was confirmed that the solving efficiency of FBPS surpasses that of the traditional Bayesian strategy significantly. Finally, FBPS is successfully developed to estimate the unknown heat flux on the chip heat sink and pack interface effectively, given some simulated high resolution measurement data. The reliability and efficiency show that FBPS has the potential to support efficient prediction techniques for a class of IHTPs in engineering applications. • A fast Bayesian parallel sampling framework (FBPS) for 3D-IHTP is proposed. • Computation time to solve IHTP with unknown size of 105 is in minute level. • FBPS is about 55 times faster than the traditional Gibbs method. • FBPS provides reliable technical idea to solving large-scale Bayesian inverse problem. • FBPS is applied to the inverse problem of chip packaging heat dissipation. [ABSTRACT FROM AUTHOR]

• 3D numerical simulation of droplet flow in a microchannel. • Effects of surface tension, wettability and heat flux on droplet size, heat transfer and pressure. • Improved mixing and heat transfer due to recirculating flow. • liquid film thickness and droplet velocity positively affect the heat transfer rate. • Reverse relation between surface tension and heat transfer. Droplet-based microfluidics refers to the production and utilization of micrometer-sized droplets. This technology has found widespread applications in drug delivery, biotechnology, disease prevention, chemical analysis, cell research, and functional material synthesis. Cooling of high heat flux electronic systems and hot spots is another application of the droplet flow which is focused by the current work. In this paper, formation and hydrothermal performance of oil droplets in water flow in a T-junction microchannel is studied by a 3D numerical simulation. Effects of different parameters such as surface tension, wettability and heat flux on the droplet size, heat transfer rate and pressure drop are investigated. It is observed that the shear between the discrete and continuous phases results in recirculating zones in both phases which contribute to improved mixing and heat transfer rates. Liquid film thickness adjacent to the heated surface and the droplet velocity are two other factors that positively affect the heat transfer. Decreasing the surface tension is shown to enhance the heat transfer rate. Moreover, an optimum value is found for the contact angle as 135° at which a 23 % heat transfer enhancement is achieved. Results also indicate that droplet size decreases with increase of contact angle while it slightly increases with increase of the surface tension and negligibly varies with the applied heat flux. [Display omitted] [ABSTRACT FROM AUTHOR]