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Due to environmental concerns, natural refrigerants and their use in refrigeration and air conditioning systems are receiving more attention from manufacturers, end users and the scientific community. The study of heat transfer and pressure drop is essential for accurate design and more energy efficient cycles using natural refrigerants. The aim of this work is to provide an overview of the latest outcomes related to heat transfer and pressure drop correlations for ammonia, propane, isobutane and propylene and to investigate the current state of the art in terms of operating conditions. Available data on the existing correlations between heat transfer coefficients and pressure drops for natural refrigerants have been collected through a systematic search. Whenever possible, validity intervals are given for each correlation, and the error is quantified. It is the intention of the authors that this paper be a valuable support for researchers and an aid to design, with particular reference to heat pumps. A procedure based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was adopted, and the Scopus database was used to query the relevant literature. A total of 135 publications qualified for inclusion in the survey; 34 articles report experimental investigations for unusual geometric conditions. Of the 101 selected papers related to usual geometric conditions, N = 50 deal only with HTC, N = 16 deal only with pressure drop and the remainder (N = 35) analyse both HTC and pressure drop. Among the 85 HTC papers, N = 53 deal with the evaporating condition, N = 30 with condensation and only N = 2 with the heat transfer correlations under both conditions. Most of the 101 articles concern propane and isobutane. The high temperatures are less widely investigated. [ABSTRACT FROM AUTHOR]

The development of new and more effective cooling technologies is required for several high thermal power dissipation applications such as in electronics cooling or high concentrated photovoltaic panels. The present paper addresses an experimental study on the development of a microchannel based heat sink to cool photovoltaic panels. Experiments focus on the test of a microchannel, with geometry and dimensions optimized from previous work. The analysis performed here emphasizes the experimental characterization of flow boiling in the microchannel under different working conditions. The results include pressure drop and heat flux maps, obtained combining pressure sensors with high-speed imaging and time resolved thermography. The analysis performed was able to identify where nucleation sites were formed. Slug flow interfacial heat transfer could be observed and accurately described in the heat flux maps. Overall, results show the high potential of combining high-speed imaging with time resolved infrared thermography to characterize complex flows. These results also show that there is a good potential for this microchannel based flow cooling in removing the required heat fluxes for the application considered here, when compared to other liquid and air-cooling technologies. [ABSTRACT FROM AUTHOR]

Accurately predicting the thermal characteristics and heat transfer distribution of the rotating detonation engine (RDE) and acquiring a clear understanding of the performance and mechanism of the rotating detonation are of great significance for achieving the safe and reliable long-duration operation of RDEs. Using RP-3 as fuel, a long-duration experimental study is performed on a 220 mm-diameter RDC to investigate the details with respect to the thermal environment. The heat flux at the typical location and the average heat flux of both the inner and outer cylinders are measured, respectively. Meanwhile, the peak pressure of the rotating detonation wave (RDW) and specific thrust are analyzed. When the ER is between 0.5 and 1 (oxidizer 2 kg/s), the stable rotating detonation mode is obtained, and the detonation duration is set as 40 s to accurately calculate the heat released by the detonation combustion. The heat flux in the upstream region of the RDW location ranges from 2.40 × 105 W/m2 to 3.17 × 105 W/m2, and the heat flux in the downstream area of the RDW location ranges from 1.05 × 106 W/m2 to 1.28 × 106 W/m2. The results demonstrate the important role of the detonation combustion zone, and the thrust performance of RDC can be improved by making the RDW move forward along the RDC axis, which is the optimal direction of detonation combustion. Through a comparison of average heat flux under different conditions, it is found that the heat released by the RDC is directly related to its thrust. In addition, the average heat flux of the inner cylinder is about three times that of the outer cylinder for the two-phase RDC with a Tesla valve intake structure, indicating that the high-temperature combustion product is closer to the inner wall. Therefore, more thermal protection should be allocated to the inner cylinder, and a more systematic analysis of the two-phase flow field distribution in the annular combustion chamber should be carried out to improve the thrust performance. In this paper, the average heat flux of the inner and outer cylinders of the RDC as well as the typical local heat flux of the outer cylinders is quantitatively measured by means of experiments, which not only deepens the understanding of RDC flow field distribution, but also provides quantitative boundary conditions for the thermal protection design of RDCs. [ABSTRACT FROM AUTHOR]

The spiral-wound heat exchanger (SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop. These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions. [ABSTRACT FROM AUTHOR]

Circulating fluidized bed (CFB) boilers offer a technically viable and environmentally friendly means for the clean and efficient utilization of solid fuels. However, the complex gas–solid two-phase flow processes within them have hindered a thorough resolution of prediction issues related to coupled combustion, heat transfer, and pollutant generation characteristics. To address the deficiencies in scientific research, meet the practical operational needs of CFB boilers, and comply with new carbon emission policies, conducting full-scale field tests on large-scale CFB boilers is needed, so that the complex gas–solid flow, combustion, and heat transfer mechanisms in the furnace can be comprehended. In this paper, issues related to large-scale CFB boilers, including the uniformity of air distribution, secondary air injection range, spatial distribution of oxygen consumption and combustion reactions, distribution of pollutant generation, hydrodynamic and heat transfer characteristics, coal feeding distribution characteristics, coal diffusion characteristics under thermal operating conditions, and engineering research on anti-wear technology, are reviewed. By integrating practical engineering applications, the basic methods and measurement techniques used in full-scale field tests for large-scale CFB boilers are summarized, providing a practical reference for conducting engineering tests with large-scale CFB boilers. [ABSTRACT FROM AUTHOR]

In the last decades, molecular dynamics (MD) simulations established as an important tool for solving fluid flow and heat transfer problems at the nanoscale, with a significant perspective impact on a wide range of industrial and scientific applications. As usual, this happened with several scholarly papers on this topic being published in the same period. The present article provides a thorough review of molecular dynamics (MD) simulations in the domain of fluid flow and heat transfer. In the first section, a survey of the physical modelling of heat transfer phenomena by MD simulations is presented, focusing on bubble and droplet nucleation and interfacial thermal behaviours. Subsequently, MD simulations of fluid flow and heat transfer in nanochannels are discussed, including adiabatic flow, convective heat transfer, and two-phase flow. Particular emphasis was placed on critical phenomena such as evaporation and condensation, to assess the effects of confinement within nanochannels. Finally, some of the current and emerging challenges in MD simulations and suggests future research directions are discussed. [ABSTRACT FROM AUTHOR]

In this paper, the effect of magnetic field on two ephase flow of Jeffrey and non-Jeffrey fluids in an inclined medium is investigated. The flow in both medium is assumed to be set in motion by constant pressure gradient. The electrical conductivity in the non-Jeffrey fluid in phase I is considered to be zero, so that the constant magnetic field strength Bo in the transverse direction only affects the Jeffrey fluid in phase II. The equations governed the flow of the fluid were solved using perturbation method. The effect of magnetic field, Jeffrey and thermal slip parameters on the temperature and velocity profile were examined through several graphs. It is noticed that the increase in magnetic field, decreased the fluid velocity and increased the temperature profile in phase II while it has partial effect in the velocity and decreased the temperature of phase I. Also, the increase in the thermal slip parameter has no effect on the velocity of both phases but, decreased the temperature profile of the non-Jeffrey fluid in phase I and increased that of the Jeffrey fluid in phase II. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal Applied Sciences on the topic of multiphase flow and heat transfer. The special issue includes seven articles that cover various aspects of this field, including numerical simulations, experimental studies, and applications in different industries such as petroleum engineering, nuclear engineering, and energy storage. The articles discuss topics such as steam condensation, flow pattern identification, hydrodynamic fingering, porous media effects, and enhanced heat transfer. The studies aim to provide insights into the fundamental mechanisms and practical applications of multiphase flow and heat transfer, and they may inspire further research in this field. [Extracted from the article]

In recent years, electrical appliances have become an integral part of human life, and efforts have been made to improve the quality and durability of electrical boards. One of the ways to improve the life of electrical boards is using cooling methods suitable for transferring the heat generated by the boards. In this paper, three different models of Case 1, Case 2, and Case 3 have been analyzed to provide an optimal model with the highest average Nusselt number. To achieve the optimal model the effect of heat source, the characteristics of hot and cold barriers and their locations on the flow field, heat transfer between two horizontal concentric cylinders with the presence of nanofluids were investigated. The results have shown that for all volume fractions, the Nusselt number increases with rising Riley number, as well as for the inner and outer cylinder, the value of the average Nusselt number increases at a constant Riley number with rising the volume fraction from 0 to 0.8%. Therefore, the highest Nusselt number occurs in volume fraction of 0.8% and Riley number of 105. [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]

Due to environmental concerns, natural refrigerants and their use in refrigeration and air conditioning systems are receiving more attention from manufacturers, end users and the scientific community. The study of heat transfer and pressure drop is essential for accurate design and more energy efficient cycles using natural refrigerants. The aim of this work is to provide an overview of the latest outcomes related to heat transfer and pressure drop correlations for ammonia, propane, isobutane and propylene and to investigate the current state of the art in terms of operating conditions. Available data on the existing correlations between heat transfer coefficients and pressure drops for natural refrigerants have been collected through a systematic search. Whenever possible, validity intervals are given for each correlation, and the error is quantified. It is the intention of the authors that this paper be a valuable support for researchers and an aid to design, with particular reference to heat pumps. A procedure based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was adopted, and the Scopus database was used to query the relevant literature. A total of 135 publications qualified for inclusion in the survey; 34 articles report experimental investigations for unusual geometric conditions. Of the 101 selected papers related to usual geometric conditions, N = 50 deal only with HTC, N = 16 deal only with pressure drop and the remainder (N = 35) analyse both HTC and pressure drop. Among the 85 HTC papers, N = 53 deal with the evaporating condition, N = 30 with condensation and only N = 2 with the heat transfer correlations under both conditions. Most of the 101 articles concern propane and isobutane. The high temperatures are less widely investigated.

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

• 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]

• A simplified two-fluid model is proposed for critical two-phase flow in microchannels. • The model preserves precision while incorporating fewer constitutive relations. • Proposed an enhanced metastable liquid nucleation model, achieving precise predictions of nucleation pressure. • Advance the understanding of critical flow in microchannels. Critical flow phenomena are present in many chemical engineering processes, such as microchannel heat exchangers, modeling of jet pumps, nuclear safety analysis, and various industrial facilities that involve subcooled or two-phase pressurized fluids. This paper presents a simplified, reliable two-fluid model for accurately simulating critical flow in microchannels. This study develops a five-equation two-fluid model by constructing a mixed energy equation based on the assumption of metastable liquid phase and saturated gas phase. The model utilizes an improved metastable liquid nucleation model as the gas–liquid phase transition boundary to obtain a more accurate flashing inception. It also uses fewer interfacial constitutive relation equations to reduce the occurrence of unstable solutions. The improved nucleation model is validated using experimental data from previous researchers, with prediction errors controlled within 10%. Furthermore, the five-equation model demonstrates substantial improvements in numerical convergence compared to its six-equation counterpart. By comparing critical mass flux predictions, along-channel pressure variations, and interfacial transfer terms, the five-equation model effectively mitigates instability issues observed in the six-equation model while maintaining prediction accuracy. As a result, this model boasts a broader range of applicability and excels in accurately predicting critical flow, even under more complex conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A one-dimensional whole-loop CFB dynamic model was established with the flow properties. • The model explicitly depicts the solids throughput behavior at the cyclone and standpipe. • Factors affecting the dynamic characteristics of CFB boiler under load regulation were discussed. • An optimization on a 135 MW CFB boiler demonstrated a maximum load ramp rate of about 4 %/min. CFB boilers face an increasing significance for load change rate in China. However, there is currently a lack of mechanistic understanding on limitation on fast peak shaving. Based on the mass and energy balance in the full loop, this paper conducts a dynamic model to describe the coupling effect of gas–solid two-phase flow, heat transfer, and combustion processes under load regulation conditions. In particular, the material throughput pattern of cyclone and standpipe are systemically described. Finally, the model was validated by field test data in a 135 MW commercial CFB boiler. On this basis, the impact of factors such as the draining ash strategy and adding/discharging circulating ash on the load regulation characteristics of the boiler were deeply explored, and a comprehensive optimization solution was proposed. The results showed that the boiler's ramp could be maximized to about 4 %/min after adopting this solution. [ABSTRACT FROM AUTHOR]

This paper is the first 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. The experimental data covers a wide range of flow mass fluxes (43 to 1077 kg/m2s). The experiments were conducted using test tubes with four different coating thicknesses to investigate the effects of various Teflon coating thicknesses. An analysis of the chilldown time and LN 2 mass consumption data are presented to evaluate the effects of the flow mass flux, axial distance from the tube inlet, and coating layer thickness. The chilldown time decreases with increasing flow Re. However, the chilldown mass consumption increases with increasing flow Re. In general, the larger the flow Reynolds number, the lower the percentage reduction in chilldown time is observed. For the percentage reduction in the chilldown time by the coating, the minimum is 27.8% for the tube with 7-layer coating at flow of Re = 100,000 and the maximum is 61.3% for the tube with 14-layer coating at flow of Re = 10,000. The percentage reduction in mass consumption due to coating falls in the range between 35.3% and 54.1%. [ABSTRACT FROM AUTHOR]

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

• A review of experimental and CFD methods used to analyze the thermal-hydraulic characteristics of sub-channels in rod bundle geometries is presented. • Both adiabatic and boiling two-phase flow studies are examined. • The effects of the design and flow parameters on the two-phase flow hydrodynamics and heat transfer performance are summarized. • Based on previous numerical studies, a basic CFD model for two-phase flows in rod bundle geometries is proposed. Thermal-hydraulic analysis of two-phase flow plays a crucial role in the optimal design of nuclear fuel assemblies and in nuclear safety. This paper presents the state of the art in two-phase flow hydrodynamics and heat transfer in nuclear fuel assemblies. A comprehensive review of experimental and CFD methods used in the last 30 years to analyze the thermal-hydraulic characteristics of sub-channels in rod bundle geometries under different flow conditions (adiabatic and boiling two-phase flow) is presented. The effects of design parameters, e.g. rod-pitch length, mixing vane angle, and flow parameters, e.g. pressure, mass flux and heat flux, on flow hydrodynamics and heat transfer performance are summarized. In addition, the capabilities of CFD modelling of two-phase in rod bundles are discussed. Moreover, based on the existing studies, some recommendations for future studies are given. [ABSTRACT FROM AUTHOR]

• Obtained local surface temperature (T w), boiling curves and liquid loss rate (m loss). • Heat transfer rate (Q w) and m loss increase markedly at onset of nucleate boiling. • Jet outlet velocity (v) affects Q w and m loss more obviously than impact height (H). • Effects of v and H on T w are more significant at non-phase transition stage. • Growing of Q w and M loss slows down at anaphase of nucleate boiling. Combining the benefits of jet impact and phase-transition heat transfer, jet impact boiling has been widely adopted in industrial scenarios. Notably, owing to limitations of high-velocity jets, such as high impact stress and pumping pressure in liquid circuits, low-velocity jet impacting deserves more attention and explorations. In this paper, under an atmospheric environment with wall heating temperatures ranging from 36 °C to 128 °C, the two-phase flow and heat transfer characteristics (local surface temperature, boiling curves and liquid loss rate) of low-velocity jet impacting on a cylindrical surface are investigated by experiment, followed by the analysis on the effects of jet outlet velocity and impact height. The findings reveal that, with the increase of heat transfer rate, the heat transfer regimes in sequence are non-phase transition (single-phase convection and air-liquid two-phase convection) and nucleate boiling. The influences of jet impact height and outlet velocity on local surface temperatures are pronounced at non-phase transition stage. In impact region, along with average superheat, the growth rates of heat transfer rate and liquid loss rate increase significantly from non-phase transition to nucleate boiling stage, and slow down at anaphase of nucleate boiling stage. Interestingly, the increase in outlet velocity delays the onset of slowdown in growth of liquid loss rate to some extent. Overall, the heat transfer rate and liquid loss rate are significantly enhanced at higher jet outlet velocity of 0.60 m/s, but not affected significantly by impact height. [ABSTRACT FROM AUTHOR]

• A revised self-induced jet impingement device is introduced in pool boiling using R1336mzz(Z). • Liquid-vapor separation promoted by the revised device is confirmed from the visualization results. • The revised device does nearly no effort on the nucleate boiling heat transfer coefficient until a relatively high heat flux. • Parametric investigations on the characteristics of the revised device are conducted. • The revised device gains up to 69.5 % and 36.7 % in the critical heat flux and the maximum nucleate boiling heat transfer coefficient, respectively. Pool boiling performance enhancement has attracted considerable interest on high power electronic cooling. In this paper, we introduce a self-induced jet impingement device for practical boiling enhancement, achieved by integrating the guidance tube with an orifice plate. With R1336mzz(Z) as the working fluid, we conduct visualization and parametric investigations on the pool boiling performance, considering the varying characteristics of this device. Visualization snapshots confirm the liquid-vapor separation and indicate that the two-phase flow pattern in the guidance tube eventually stabilizes as a churn-annular flow. Our findings suggest that self-induced liquid jet impingement has a minimal effect on the nucleate boiling heat transfer coefficient (h NB) under a certain heat flux, around 75 % CHF of the standard pool boiling, as the single-phase heat transfer is weakened due to the low thermal conductivity of R1336mzz(Z). As the heat flux intensifies, we observe substantial enhancements in both the Critical Heat Flux (CHF) and the Maximum Nucleate Boiling Heat transfer coefficient (h MNB) resulted from the delayed onset of boiling crisis, owing to the additional liquid supply and the promotion on vapor exhausting. The parametric studies reveal that the flow rate of the liquid jet, amplified by either extending the length or the inner diameter of the guidance tube, or by increasing the number of jet holes, positively impacts the boiling performance. However, these improvements show diminishing returns. Our study shows enhancements in CHF and h MNB of up to 69.5 % and 36.7 %, respectively, compared to the standard pool boiling. [ABSTRACT FROM AUTHOR]

To solve the problem of high heat flux heat dissipation in microelectronic devices, a manifold micro-channel heat sink with corrugated bottom (CB-MMC) is proposed on the basis of the manifold microchannel heat sink (MMC). The flow and heat transfer characteristics of HFE-7100 in MMC and CB-MMC are investigated numerically. The results show that CB-MMC reduces the pressure loss and enhances the heat transfer performance in single-phase flow. The orthogonal test method is used to obtain structural design solutions with optimal thermal performance. It is observed that the temperature reduction is always at the expense of the increase of the pressure drop. In addition, the optimization parameters combination obtained through comprehensive evaluation of temperature and pressure drop through weight matrix - optimized solution 19 (wavelength A = 800 µm, amplitude B = 40 µm, channel depth C = 180 µm, outlet width D = 300 µm, channel width E = 25 µm). Its Tave has decreased by 6.89 °C, ΔP decreased by 10.27 kPa. Moreover, the subcooled boiling flow and heat transfer performance in MMC and CB-MMC are comparatively studied. The results demonstrate that the dynamic behavior of vapor bubbles causes large pressure fluctuations, which further leads to small temperature fluctuations, and thus reduces the stability of the flow and boiling heat transfer. Compared with MMC, CB-MMC exhibits more stable two-phase flow and better boiling heat transfer. [ABSTRACT FROM AUTHOR]

Introduction: A simulation model was developed by coupling a one-dimensional (1D) system code and 3D CFD software, to analyze the three-dimensional (3D) flow and heat transfer characteristics of the once-through steam generator (OTSG). Methods: The shell side of the OTSG was simulated by FLUENT, and the tube side was simulated by the system code LOCUST. Through spatial mapping, the 1D and 3D simulations were coupled along the outer wall of the OTSG's helically coiled tubes. Results and Discussion: This coupling method enabled the acquisition of highresolution flow and heat transfer characteristics of the OTSG, and the error of heat flux calculation result by the coupled model is within 15%. Through coupling simulation analysis of the prototype OTSG, it was found that the inlet and outlet temperature difference reached as high as 150°C. The unevenness of the radial temperature distribution increased along the flow direction, and the wake swing effect caused by the sweeping flow of the tube bundle at the exit position was evident. The results of this study provide reference and a coupled simulation method for the engineering design and thermal-hydraulic characteristics analysis of OTSG. [ABSTRACT FROM AUTHOR]

Energetic Semiconductor bridge (ESCB) based on reactive multilayered films (RMFs) has a promising application in the miniature and intelligence of initiator and pyrotechnics device. Understanding the ignition enhancement mechanism of RMFs on semiconductor bridge (SCB) during the ignition process is crucial for the engineering and practical application of advanced initiator and pyrotechnics devices. In this study, a one-dimensional (1D) gas-solid two-phase flow ignition model was established to study the ignition process of ESCB to charge particles based on the reactivity of Al/MoO3 RMFs. In order to fully consider the coupled exothermic between the RMFs and the SCB plasma during the ignition process, the heat release of chemical reaction in RMFs was used as an internal heat source in this model. It is found that the exothermal reaction in RMFs improved the ignition performance of SCB. In the process of plasma rapid condensation with heat release, the product of RMFs enhanced the heat transfer process between the gas phase and the solid charge particle, which accelerated the expansion of hot plasma, and heated the solid charge particle as well as gas phase region with low temperature. In addition, it made up for pressure loss in the gas phase. During the plasma dissipation process, the exothermal chemical reaction in RMFs acted as the main heating source to heat the charge particle, making the surface temperature of the charge particle, gas pressure, and gas temperature rise continuously. This result may yield significant advantages in providing a universal ignition model for miniaturized ignition devices. [ABSTRACT FROM AUTHOR]

• Different strategies are analyzed to enhanced microchannels based heat sinks. • Nanofluids to enhance heat performance of microchannel based heat sinks is analyzed. • Experiments are performed for Al 2 O 3 , Au and Ag nanoparticles at various concentrations. • The flow-boiling regimes are identified and discussed for the working conditions considered. • Two-phase flow conditions may not always be beneficial, low concentrations of nanoparticles (ϕ ≪ 1%) can have a notable impact on heat transfer mechanisms. This paper investigates the advantages and challenges associated with two-phase flows, specifically flow boiling of pure liquids and nanofluids, for cooling applications in microchannel heat sinks. The study explores various two-phase flow patterns, their related issues, and examines the potential of nanoparticles to enhance heat transfer. Alumina (Al 2 O 3), gold (Au), and silver (Ag) nanoparticles at different concentrations were tested. Experimental tests were conducted under different working conditions using various working fluids, including water, Al 2 O 3 1 wt%, Ag 1 wt%, Au 1 wt%, Au 0.75 wt%, Au 0.5 wt%. The heat fluxes used were 1.026 kW/m2, 1.696 W/m2 and 2.403 kW/m2, while the volumetric flows ranged between 0.5 mL/min and 1.5 mL/min. The observed results indicate that even for the lowest particle concentration tested, the water-Au nanofluid exhibits superior cooling performance compared to the other examined fluids. The findings suggest that although two-phase flow conditions may not yield significant benefits, even small concentrations of nanoparticles (ϕ ≪ 1%) can significantly impact heat transfer mechanisms. This approach provides a cost-effective and efficient alternative for cooling microchannel heat sinks without necessitating the use of two-phase flow conditions. [ABSTRACT FROM AUTHOR]