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Abstract The present comment concerns some doubtful results included in the above paper. [ABSTRACT FROM AUTHOR]

This comment concerns a rightful doubt involved in the above paper. In the reviewed article, a novel model without empirical constants was proposed to evaluate the effective thermal conductivity of three-phase soils, and such a model was claimed to be workable for soils with porosity ranging from 0.0349 to 0.4764 at all saturation degrees. However, sufficient reasons and pictorial explanations were given in this comment to prove its inapplicability for high degrees of saturation. Besides, the inapplicable range is constantly changing, depending on the porosity, i.e. the larger the porosity, the smaller the inapplicable saturation region. Similar issues were further discussed due to its great influence on the follow-up research in this field, i.e. whether can achieve a full coverage of the applicable saturation range [0,1] for a given porosity. [ABSTRACT FROM AUTHOR]

Two mistakes exist in [1]. [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]

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]

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]

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]

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]

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]

A numerical investigation was conducted to explore the heat transfer optimization effect of circular tube heat exchanger with L-shaped twisted tape insert and to find the optimal parameter design in this paper. For better thermohydraulic performance, the effects of twist pitch (P), inner diameter (D), tape width (W) and number of tape (N) were studied with Reynolds number ranged from 1875 to 3750. Moreover, response surface method (RSM) was employed to indicate the relationship between the Nusselt number (Nu) and these parameters. With the analysis of flow structure inside the tube, it was conducted that the twisted tape insert was helpful to transform the axial velocity of fluid to radial velocity, forming vortex in the L region. The numerical results showed that the Nu and friction factor (f) of the tube fitted with L-shaped twisted tape insert gained an 199% to 208% increase and 674% to 696% when compared with that of smooth tube respectively. Besides, an optimal parameters set was obtained with P = 65.59 mm, W = 0.95 mm, D = 8.80 mm, in which the Nu and f were increased by 204% and 704% respectively as the results of response surface method. • Effects of L-shaped twisted tapes insert on heat transfer and flow characteristics in were numerically investigated. • The influence of four geometric parameters of twisted tape insert on thermos-hydraulic performance were studied. • The enhanced thermal performance of the L-shaped twisted tapes was obtained by centrifugal force. • The effect of short side of the L-shaped on the thermal performance and flow characteristics were discussed. [ABSTRACT FROM AUTHOR]

A novel non-intrusive thermal diffusion measurement (TDM) method has been proposed for measuring the phase flowrates of gas–liquid slug flows in our previous research. Since the structure of TDM was arbitrarily designed and needed to be optimized for accurate measurement, the effect of the heat flow distribution and the thermophysical properties of the pipe wall and fluid on the wall temperature response to a rising Taylor bubble (TB) is further investigated by using the CFD tool in this paper. The wall temperature and temperature rise are used to describe the wall temperature response, and their variation rules with heat flow distribution and the thermophysical properties of the pipe wall and fluid are presented and analyzed based on heat transfer. The simulation results indicate that the optimal heating length for a large wall temperature rise and small power consumption is 0.6 D , and the optimal pipe material should be with small density and specific heat and a suitable thermal conductivity of about 15 W/(m·K). Moreover, the wall temperature response is obvious, especially for TBs moving in the liquid with large fluid thermal conductivity, density, and specific heat, and small viscosity. The paper can clarify the wall temperature response mechanism of the heated pipe wall and provide a theoretical basis for the development of the TDM method. • Local instantaneous heat transfer characteristics of a rising TB are investigated. • Wall temperature responses under different heat flow distributions are presented. • Effect of wall/fluid thermophysical properties on temperature response is analyzed. • Titanium is the optimal metal for strong temperature response in the TDM method. • Optimal heating width is 0.6 D for strong response and energy saving. [ABSTRACT FROM AUTHOR]

The energy conversion and utilization of liquid metals is becoming one of the effective ways to solve energy problems. The conversion and transfer of thermal energy from liquid metals to water are significant in advanced nuclear energy and metallurgy. It has been an urgent concern, especially in Generation IV of advanced nuclear energy systems‑lead-cooled fast reactors and the ultimate energy source for humanity-fusion engineering. In this paper, a large-scale liquid metal and water interaction test platform was developed to investigate the lead‑bismuth liquid metal and water interaction and the cover gas pressurization characteristics. Firstly, the evolution of phase behavior and water/vapor migration paths were inferred based on the transient temperature law. Secondly, the cover gas pressurization patterns above the molten pool were analyzed, and the test data showed three pressurization patterns, including two types of local vapor explosions. Additionally, this paper predicted the existence of another dangerous pressurization mode, i.e., overall vapor explosion. Finally, the cover gas pressurization rate model was established, and there is an appropriate matching between the model and test data with an average relative error of 12.6%. This paper provides an essential reference for profoundly understanding the energy conversion and thermal interactions between liquid metals and water. • A large-scale liquid metal and water interaction test platform was developed to investigate energy conversion and interaction. • Based on the transient temperature law, we discovered the gas-phase evolution characteristics during lead-water interaction. • Three different types of pressurization patterns of cover gas were identified. • A model of cover gas pressurization was developed to predict the pressurization rate. [ABSTRACT FROM AUTHOR]

Enhancing the cold load/storage (CLS) functional cemented paste backfill (CPB) technological cooling effect is crucial given the deep mine escalating heat damage. Single optimization schemes such interval boards insulation, higher emissivity, active cooling, and integrated optimization schemes of the aforementioned measures are suggested in order to improve the cooling impact of CLS functional CPB. Firstly, active cooling was implemented to isolate the heat source and protect the cooling capacity. Experiments indicate that this approach can extend the period of time that the stope temperature is maintained below the temperature threshold. Secondly, thermal insulation material is applied to the interval boards of the stope and the CLS functional CPB to decelerate the cooling transfer rate. When the stope temperature reaches the recommended upper limit, remove the insulation material. The results show that 1 mm insulation material is the most economical and environmentally friendly option. However, when the temperature difference inside the backfill is slight, the effect of the radiation coating is not significant. The best-optimized cooling method obtained in this paper is to take active cooling around the stope and CLS functional CPB, and then paste 1 mm insulation material on the interval boards. • Multi-scheme comparison and optimization. • An experimental platform was established to verify the numerical simulation results. • CFD numerical simulation is used to obtain the temperature distribution. • Multi-angle study of cold source and heat transfer process. [ABSTRACT FROM AUTHOR]

With their ability to provide substantial solid-fluid interfacial areas, porous-fin microchannels emerge as a promising solution for the thermal management of upcoming microelectronic chips. Previous investigations have substantiated the enhanced hydrodynamic performance of porous-fin microchannels compared to their solid-fin counterparts. Nevertheless, it has been found that porous fins can diminish the thermal performance of straight plate-fin microchannel heat sinks at high channel heights due to their reduced effective thermal conductivity. In this paper, semi-porous fins that replace a portion of a solid fin height with a metallic porous fin are proposed as an alternative approach to concurrently improve the thermal and hydraulic performances of microchannel heat sinks. The effect of the porous height ratio, defined as the porous fin height to the overall fin height, on the thermo-hydraulic performances of semi-porous-fin microchannel heat sinks is examined. Results revealed that the thermal resistance decreases with an increase in the porous height ratio, reaching its lowest value at a ratio of 0.5. Beyond this point, a further increase in the porous height ratio results in an increase in the thermal resistance compared to an all-solid fin design. In other words, there exists a critical porous height ratio below which the thermal resistance of the semi-porous-fin microchannels is lower than that of the solid-fin microchannel. The semi-porous-fin microchannels have up to 11.12% lower thermal resistance compared to the solid-fin microchannel. Additionally, increasing the porous height ratio decreases the pressure drop penalty across all considered operating conditions. This research reveals that semi-porous fin structures could offer new pathways to improve the cooling performance of high-power electronic chips. [Display omitted] • The thermo-hydraulic performance of semi-porous fin microchannel heat sinks is investigated. • The thermal resistance decreases with an increase in the porous height ratio. • There is an optimal value for the porous height ratio. • Semi-porous-fin microchannels have a lower pressure drop than solid-fin microchannels. [ABSTRACT FROM AUTHOR]

In this paper, the merits and demerits of endwall modification by designing micro-scale ribs onto the turbine endwall surface was examined experimentally for two aspects: cooling performance and heat transfer characteristics. The experiment was conducted on ribbed endwall with three rib directions (horizontal, vertical and tiled rib) and two rib spacings (8 mm and 10 mm) and compared with the flat endwall. The measurement of heat transfer was conducted with a high-resolution infrared thermal camera and that of cooling effectiveness (η) was conducted with pressure-sensitive paint technique. Results showed that the direction of rib and rib-induced vortex greatly affects the coverage of coolant, which the tilted and vertical ribbed endwall demonstrated positive effects on film cooling. Additionally, the heat transfer of the ribbed endwall is also connected with the layout of the rib and mainly depends on the joint influence of the rib-induced vortex and passage vortex. The Nusselt number (Nu) of the vertical rib was the smallest. In general, vertical rib with larger rib spacing shows the comprehensive performance, that an increase of 9.5% for area-averaged η than original endwall with mass flow rate of 1.0% and the least increase of Nu , which can provide guidelines for future cooling design. [ABSTRACT FROM AUTHOR]

The high temperature of PV panels during power generation not only reduces their efficiency but also leads to increased heat transfer to the room. The impact of using PV panels on the indoor thermal environment should not be overlooked. A novel roof structure is proposed in this paper, which is composed of PV panels, phase change materials (PCMs) and ventilation layer from top to bottom. The thermal performance of PV-PCM- ventilation roof room is compared with that of PV roof room and PV-PCM roof room under active and passive conditions respectively. Results show that under passive conditions: Compared to PV roof, the PV-PCM-ventilation roof internal surface temperature fluctuation decreases by 44.12%, the correlation coefficient between the back surface temperature of PV panel and outdoor air temperature decreases from 0.79 to 0.69, and the correlation coefficient with solar radiation decreases from 0.66 to 0.60. Compared to PV-PCM roof, the back surface temperature of the PV panel decreases by 3.31 °C during the day. Under active conditions, when the set temperature is 26 °C and 28 °C, the energy consumption of the PV-PCM-ventilation roof room decreases by 15.61% compared to the PV roof room. In summary, the new roof demonstrates good insulation and energy-saving performance. [ABSTRACT FROM AUTHOR]

We present a comprehensive study on heat transfer in phase-change materials (PCMs), focusing on both melting and solidification phases, different temperature scenarios, an assessment of practical implementation aspects, and Marangoni convection. The research examines heat transfer rates during the melting-solidification cycle, with a focus on gallium (Ga) and n-eicosane (C20), the latter being a candidate for the MarPCM project aboard the ISS [1]. The paper explores different temperature scenarios using Ga to optimize PCM performance. N-eicosane requires extensive computational resources due to its significant thermal time, whereas gallium allows for more efficient simulations. The most effective scenario involves switching temperatures between cold and hot walls at a certain moment, which occurs earlier than the full melting time or reaching steady state. This specific moment corresponds to the beginning of a decrease in heat extraction efficiency. The success of this scenario relies on the symmetric thermal boundary conditions and multi-cyclic temperature inversion. We suggest that the implementation of this scenario is similar to rotating the PCM body within its package while maintaining the temperature of the external walls constant. Extending the strategy to n-eicosane yields promising results. This study also highlights the importance of Marangoni convection in heat transfer mechanisms. [ABSTRACT FROM AUTHOR]

To enhance the fin-side heat transfer capability of circle tube-fin heat exchangers, a novel fin with ellipsoidal dimple-protrusion is introduced in this paper. The effect of the ellipsoidal dimple-protrusion with five different attack angles, 0°, 10°, 20°, 30° and 40°, on the flow characteristic and heat transfer performance are numerically investigated and compared with the traditional heat transfer promoting technology by vortex generators. Both the intensity of secondary flow and heat transfer capability are significantly increased by the ellipsoidal dimple-protrusion. In comparison to the smooth channel and the channel mounted with vortex generators, the secondary flow intensity increases by up to 78.62% and 41.57%, and Nu increases by a maximum of 29.01% and 19.03%, respectively, in the range of Re for 1500–5000. The values of thermal performance factor TPF can reach a maximum of 1.161, which is an improvement of 16.1% compared with the smooth channel, and of 4.89% compared with the heat transfer channel with curved vortex generators. Formulas for Nu , f and TPF with deviations less than ±2%, ±9% and ±2% are fitted. The ellipsoidal dimple-protrusion has a superior application potentiality for heat transfer enhancement in fin-side of circle tube-fin heat exchangers. • A novel fin configuration with ellipsoidal dimple-protrusion is proposed. • Thermal performance of dimple-protrusion is superior to that of vortex generators. • Se increases by 41.57% with Nu increases by 19.03% compared with vortex generators. • TPF of the dimple-protrusion is up to 1.161 which is much higher than the vortex generator. • Fitting formulas of Nu , f and TPF are provided to facilitate the engineering application. [ABSTRACT FROM AUTHOR]

Alkali metal heat pipes are the vital components within the core of heat pipe-cooled reactors. The mechanism characteristics of alkali metal heat pipes need to be further analyzed. CFD simulation with the traditional Volume of Fluid method provide an essential means to analyze the flow and heat transfer mechanism in alkali metal heat pipes. For Lee heat and mass transfer equation within the VOF method, the evaporation and condensation coefficients have significant effects on the simulation results, and their values are typically determined empirically, which results in inaccurate or even unreasonable simulation results. To establish a reasonable numerical relationship for the evaporation and condensation coefficients of the working fluid, this paper employs a multi-zone modeling approach for heat pipes and proposes an improved VOF method. During the iterative process, the temperature and pressure values in the corresponding regions are updated based on the iteration results. The mass changes caused by evaporation and condensation processes in each wick and vapor chamber region are calculated and compared with the theoretical value. To validate the proposed method, a high-temperature experimental test platform was constructed, and an 820 mm sodium heat pipe was fabricated. Furthermore, experimental research was carried out at different heat pipe inclination angles and under various heat transfer powers, with the experimental results being compared to those obtained from the model simulations. The simulated temperature values at different points of the model agree well with the experimental values at different heat transfer levels. This research provides insights into the multiphase distribution and pressure change within the heat pipe, offering important references for the optimization design of alkali metal heat pipes. [ABSTRACT FROM AUTHOR]

Surfactants have been widely used in various industrial fields. Simply adding a small amount of surfactant can greatly enhance the boiling heat transfer of water, which can improve the performance of heat exchanger and has great application prospects in industry, but its mechanism is not fully understood. Many possible factors have been proposed, but their relative importance remains to be examined. In this paper, the possible mechanisms of surfactant effects proposed in the literature are revisited, and their impacts are discussed in depth. Combined with the experimental study, it was found that when the surfactant concentration was low, the change in boiling performance was mainly due to the non-coalescence of growing bubbles on the wall rather than the change of physical properties of the solution. The underlying reason is that surfactants alter the mobility of the vapor-water interface. At high heat flux, the non-coalescence bubbles form wet foam, making it impossible for bulk water to pass through to wet the heating surface, thereby reducing CHF. At the same time, the immobility of the vapor-water interface also increases the interface resistance, making it more difficult for the vapor to escape from the wall. • The change of fluid physical properties is not the main reason for the effect of surfactant on boiling at low concentration. • Surfactant adsorption changes the surface mobility, causing bubbles not to coalesce, which boosts the HTC. • The formation of wet foam and the increase of interfacial drag resistance reduce the CHF. [ABSTRACT FROM AUTHOR]

This study presents a novel approach to evaluating the thermal-hydraulic performance of the airside of wavy-fin compact heat exchangers under wet conditions. While previous studies have predominantly focused on dry conditions, this paper extends this knowledge by exploring the effectiveness of wavy fin configurations in the presence of condensation film. Twenty configurations of wavy-finned geometries were evaluated, including 16 from the literature, and four were newly introduced. By examining the impact of condensation and geometric parameters on thermal-hydraulic performance, this research offers a deeper understanding of heat transfer behavior in wet environments. Species transport and volume of fluid (VOF) multiphase models were implemented to investigate Colburn " j " and Fanning friction coefficient " f " using ANSYS Fluent software. The results were validated against reported experimental data. Results showed that geometries G3 and G4 exhibited optimal " f " and " j " values, indicating reduced frictional losses and enhanced heat transfer performance. GF3, GF4, and G11 had higher performance if the effect of compactness was ignored, while G11, G12, and G13 did not compromise pumping power and maintained high performance. G12 outperformed other geometries at a pumping power limit of 1.35 × 1 0 14 (W / m 2). The study also suggests new correlations to predict the j - and f -factor for wet conditions in terms of geometrical parameters or dry j - and f -factor. • Condensation in wet fins of the heat exchangers was simulated using Ansys FLUENT software. • Volume of Fluid with Lee's, k-epsilon and species transport models were utilized. • Colburn " j " and Fanning friction factor " f " were assessed for 20 geometries. • Four performance metrics were evaluated for wavy fins including conventional j/f1/3. • Empirical correlations were developed to predict factors " j" and " f " for repeatability. [ABSTRACT FROM AUTHOR]

CI-DL-MHCS represents designed central impact-inlet double layered microchannel heat sinks which shows the principal heat transfer feature, and the novel bifurcation is added on upper/lower deck in CI-DL-MHCS, namely CI-DL-MHCS-UB/LB, to explore the further overall thermal advantages numerically and experimentally. The internal located bifurcation parameters including position in CI-DL-MHCS and length have been investigated in the work with the coolant velocities in the range of 0.25–1.05 m/s. The calculated models in simulation is set as symmetric boundary condition, while the assumptions including RNG k-ε turbulence flow and incompressibility dominate in the paper. Bifurcation located lower deck of CI-DL-MHCS has been shown to be effective in controlling the substrate temperature, with a reduction in peak temperature of >18 K compared to referenced CI-DL-MHCS. Numerical simulations clearly demonstrate the enhancement of heat transfer caused by impingement jets and novel located bifurcations with experimental verification. Besides, CI-DL-MHCS with bifurcation have an average Nusselt number enhancement by 4.47% higher compared with CI-DL-MHCS without bifurcation. The bifurcation inevitably occupies the space in CI-DL-MHCS, resulting in a higher pressure drop penalty than the proposed bifurcated structure CI-DL-MHCS, but this can be balanced by an increase in heat transfer considering the overall thermal performance factor. Thus, CI-DL-MHCS featured with bifurcation located in CI-DL-MHCS-LB_3 outperforms significantly in overall thermal performance and thermal uniformity on substrate among all the designed tested models. • This novel structure is a combination of double layer impact jet structure and bifurcation located in the microchannels. • In the designed composite structure, the highest substrate temperature is 17.9 K lower than CI-DL-MHCS. • The designed bifurcation structure can effectively increase the coolant flow rate and reduce the substrate temperature. • The CI-DL-MHCS-LB_3 achieves the best cooling effects because the advantage bifurcation location. [ABSTRACT FROM AUTHOR]

Critical heat flux (CHF) represents heat transfer limit for a heat sink working under flow boiling conditions. In the literature, for the first time, in micro-pin-fin heat sinks with expanding structure, this paper experimentally focusing on CHF and proposing a correlation for saturated flow boiling at quite low mass velocities. Parallel channel heat sink is evaluated as reference case. Three mass velocities (G = 45, 68, 90 kg m−2 s−1) are studied by beginning from 130 W up to boiling crisis. Test-range falls in the pure saturated boiling conditions, and inlet temperature is approximately kept constant at 60 °C. Flow mechanism is figured out over the flow images. The heat sink with expanding structure (T-2) clearly boosts CHF compared to parallel counterpart (T-1); such that, by successfully manipulating bubble dynamics, T-2 increases the CHF up to 32.9% at the lowest mass velocity (G = 45 kg m−2 s−1). For highest mass velocity (G = 90 kg m−2 s−1), T-2 provides lower wall superheat up to 89.5% against T-1. The CHF ranges from 225 to 443.31 kWm−2, even though quite low mass velocities. Regarding prediction of the experimental data, mean absolute error (MAE) of proposed correlation is 4.7%; and all those of predictions fall in ±12% error bands. [ABSTRACT FROM AUTHOR]

This paper aims to explore the utilization of machine learning techniques for the accurate prediction of rheological properties in a specific nanofluid system, ZnO(50 %)-MWCNTs (50 %)/Ethylene glycol (20 %)-water (80 %), designed for nano-refrigeration applications. The effective manipulation of the rheological behavior of nanofluids is pivotal for enhancing their heat transfer efficiency and overall performance. By harnessing the predictive power of machine learning, this study endeavors to unravel the intricate relationships governing the rheological characteristics of the nano-refrigerant, ultimately contributing to the development of advanced cooling solutions. The obtained results show that μ nf of ZnO(50%)-MWCNTs (50%)/ Ethylene glycol(20%)-water(80%) nano-refrigerant is little affected by T, and even when T varies, this result does not alter much. Also, the lowest μ nf occurs when it has the highest temperature and the lowest γ and φ. Finally, it was concluded that the best algorithm in terms of the Taylor diagram for μ nf output is the MPR algorithm and the worst is the ECR algorithm and the pattern of γ changes shows that the ideal value of γ is the biggest when μ nf levels fall in tandem with their growth. [ABSTRACT FROM AUTHOR]

To enhance the heat transfer, an innovative origami channel heat exchanger is proposed and its performance is studied experimentally and numerically. The experimental results show the maximum temperature on the origami channels' pipe wall is 2.8 °C lower than that on the flat channel with the same the heat flux of 9500 W/m2. Additionally, the temperature difference across the pipe wall of the origami channel shows a reduction of 5.7 °C compared with that across the flat channel. The simulation results show the mean heat transfer coefficient of the origami channel increases by up to 331% compared to the flat channel with the 0.012 kg/s mass flow rate. Nevertheless, the origami channel leads to an extra energy consumption penalty. To evaluate overall performances of the origami channel, this paper introduces three dimensionless efficiency factors to quantify relevant costs in terms of energy, volume and mass. It is found that the origami channel achieves much higher dimensionless mass efficiency and volume efficiency but less dimensionless energy efficiency than the flat channel. The comprehensive evaluation, which considers all the three factors, reveals that the combined efficiency factor of origami channels with folding angles ranging from 65° to 75° improves by 80% to 95% compared to the flat channel. [ABSTRACT FROM AUTHOR]

This paper employs a computational fluid dynamics numerical framework integrating the Euler-Euler two-fluid model with the particle dynamics method to analyze the heat and mass transfer characteristics of water-based graphene nanofluid slurries in helical corrugated tubes. The results indicate that, with ice crystal content ranging from 10% to 30% at the inlet, the heat transfer performance is positively correlated with the slurry concentration, and the increase in nanofluid concentration has minimal impact on the pressure drop inside the tube. The helical structure results in the maximum flow velocity occurring in the groove area. Compared to straight tubes, the increase in heat transfer area does not only promote the generation of vortices but also enhances turbulent intensity, reduces the thickness of the thermal boundary layer, and improves heat transfer efficiency. Graphene nanofluid slurries exhibit superior heat transfer capability compared to pure water slurries, with surface heat transfer coefficient increasing with graphene concentration. The maximum HTC of helical corrugated tubes is 1.4 times that of straight tubes, with an average Nusselt number (Nu) 1.44 times higher than that of straight tubes. Lastly, an empirical correlation for Nu is established to predict the thermal performance of water-based graphene nanofluid slurries flowing through helical corrugated tubes. • Pressure drop, ice crystal concentration distribution, flow velocity, temperature distribution, and heat transfer performance are discussed. • Aqueous graphene nanofluid ice slurry demonstrates outstanding flow and heat transfer performance. • Helical structure significantly influences the flow and heat transfer of the ice slurry. • The average Nu of spiral bellows is 1.44 times that of straight pipe. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the thermophysical properties and transient heat transfer characteristics of composite phase change materials (CPCMs) were investigated numerically and experimentally in details. Two kinds of microencapsulated phase change materials (MEPCMs) paraffin with melting temperatures of 28 and 37 °C, respectively, were employed in this paper. The CPCMs were fabricated by intercalating expanded graphite (EG) with average diameter of 45 m into MEPCMs. The addition amount of EG were 10%, 30%, and 50% in weight. The thermophysical properties, including density, thermal conductivity and specific heat, of the CPCMs were measured and the latent heat and specific heat were calculated from data with differential scanning calorimetry (DSC). In the experiment, the square enclosure has a cross-section dimension of 100 by 100 mm and it was 15 mm in thickness. The top side wall of the enclosure was heated with isothermal cooling on the bottom side wall while the remaining side walls were thermally insulated. The numerical model which is designed to meet the conditions of the experimental parameters was employed to examine the transient heat transfer characteristics for the CPCMs in the enclosure. Results show that MEPCMs with increasing EG would increase the thermal conductivity and the heat transfer rate. However, the specific heat of CPCMs would decrease. The numerical predictions agree well with the experimental data. In addition, the results disclose that the CPCMs could enhance the rate of heat transfer and energy storage, but minor loss in total energy storage. [ABSTRACT FROM AUTHOR]

Abstract The present study conducts a scientometric study of the journal literature of heat transfer from 1900 to 2017 based on the database of Web of Science, 2018. A total of 120,628 items resulted from topic search using "heat transfer" as the search term. The results of this work reveal that the literature on heat transfer grows exponentially with an annual growth rate of about 9.71% for the last century the first two decades of this century through the emergence of new subjects, identified through word cloud of authors' keywords. The document types, countries and languages, journal distribution, number of authors, institution productivity and paper citations are analyzed. Highly productive journals and authors and highly cited papers are identified. The results reveal that USA and China are the two most productive countries contributing 17.4% and 14.3%, respectively. About 90% of papers are published with co-authors and 73% of the paper was published with two to four authors. The author distribution follows the trend of Lotka's law, with 61.3% of the authors published only one paper, and 15.9% of the authors published two papers. International Journal of Heat and Mass Transfer is the most productive journal contributing 9.4% of the publications. Most highly cited papers are identified and found to be consist with the emergence of new subjects in heat transfer. [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]

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]

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]

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]

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]

In the thermal management of fuel cell vehicles, radiators are subjected to vibrations due to vehicle speed and road surface irregularities. However, there has been no comprehensive study of the impact of these vibrations on the heat transfer performance of radiators. Therefore, this paper employs R141b to conduct three-dimensional transient numerical simulations of flow boiling in small channels under vertical vibrations. The study reveals that the single-phase heat transfer coefficient exhibits periodic variations. At the same vibration frequency, the heat transfer frequency for the vertically oriented heating surface is twice that of the horizontally oriented surface, This is because the thermal boundary layer varies with the vibration velocity. Furthermore, as the frequency increases to 21 Hz, the time-averaged heat transfer coefficient can increase by up to 2.5 times. Following boiling onset, for horizontally oriented heating surfaces, an increase in frequency or amplitude enhances the transient heat transfer performance. Under the conditions of 28 Hz and 5 mm, the heat transfer coefficient can increase by 125.7%. However, for vertically oriented heating surfaces, when the frequency exceeds 14 Hz or the amplitude exceeds 8 mm, the heat transfer performance weakens after 7.143 s due to the promotion of bubble coalescence by the vibrations. [ABSTRACT FROM AUTHOR]

In this paper, the gas turbine blades middle double swirl cooling structure under diverse number of nozzles N are constructed to explore the heat transfer and flow behavior. The k-ω turbulence model are applied and the inlet coolant Reynolds number is 12500. The N vary by 4 to 11 and two cases are investigated. For case 1, the cross-sectional area of each nozzle is 6 mm2 for all structures. For case 2, the cross-sectional area of total nozzles stays the constant at 42mm2 when the N is varied. Results show that, in case 1, when the N increases, the area of the high heat exchange zone decreases but the distribution is more uniform. Moreover, the thermal performance factor ξ gets larger, but the average Nusselt number Nu a decreases significantly. In case 2, when the N increases, the ratio of inclination to nozzle length increases for the jet near the outlet, Nu a is almost constant but the heat transfer uniformity is improved. The best ξ is obtained when the N is 8. For case 1, as the N is increased, the Nu a decreases significantly. Therefore, heat transfer and ξ should be considered by case 2 to select the optimum N. • Middle double swirl cooling models with different nozzle numbers are established. • Effects of nozzle number on flow and heat transfer characteristics are explored by two cases. • When the nozzle number is changed, the cross-sectional area of total nozzles in case 1 is changed, but it unchanged in case 2. • The results show that case 2 is more appropriate and the optimum nozzle numbers should be selected by the way of case 2. [ABSTRACT FROM AUTHOR]

This paper outlines and discusses the thermal conductivity of 1-Butyl-3-methylimidazolium tetrafluoroborate ionic liquid, as well as three classes of nanocolloids. The [C4mim][BF4] ionic liquid was enhanced with three kinds of nanoparticles, Al 2 O 3 , ZnO and MWCNT and all fluids thermal conductivity was experimentally measured. Results discussion includes also an in-depth analysis on Prandtl number and thermal diffusivity. All the data were carefully debated in terms of state of the art advancement and these suspensions suitability for practical applications in heat transfer. It was found that the thermal conductivity increases with nanoparticles addition and this enhancement depends on nanoparticle type and temperature. Plus, the temperature influence is rather limited, while the consideration on Prandtl number and thermal diffusivity revealed that it is extremely relevant to consider all the thermophysical properties when choosing a new thermal fluid. Additionally, a comparison with well known correlations was inserted, concluding that no theory can estimate the ionic liquids nanocolloids thermal conductivity. Concluding, the thermal properties of [C4mim][BF4] ionic liquid and its nanocolloids with Al 2 O 3 , ZnO and MWCNT shows that these nanocolloids uncover great potential for heat transfer applications. • 1-Butyl-3-methylimidazolium tetrafluoroborate thermal conductivity is experimental determined. • The thermal conductivity of nanocolloids is debated in terms of nanoparticle mass fraction and temperature. • Thermal conductivity correlations are anticipated for [C4mim][BF4] and its nanocolloids. • The thermal diffusivity and Pr number of nanocolloids based on [C4mim][BF4] follow an in depth discussion. [ABSTRACT FROM AUTHOR]

Active and passive cooling are the two possible methods for removing heat. An active cooling system is the one that involves the use of energy as opposed to passive cooling that uses no energy. Passive cooling methods are cost effective and more reliable than active cooling due to the absence of moving parts. Microchannel heat sink is one of high-tech devices that have widely considered passive cooling methods especially for electronics cooling. In this paper, the use of passive cooling methods in microchannel heat sink is comprehensively discussed. This paper also present the effects of some important parameters such as the type of channel types, surface roughness, fluid additives, and Reynolds number on the rate of heat transfer in microchannel heat sink. Finally, the conclusions and important summaries were presented according to the data collected. [ABSTRACT FROM AUTHOR]

To address the issues with the multi-phase flow and heat transfer characteristics of the gas inside solid rocket motor combustor, this paper first establishes a mathematical model form that can express the heat transfer characteristics between gas and wall, and obtains the mathematical model of heat transfer by means of experiment and numerical simulation. The results show that heat transfer in the wall surface has obvious hysteresis during the actual working process of solid rocket motor, and that temperature in the wall surface will gradually reach the peak value after the motor works. The heat transfer trend between the numerical simulation results and the experimental data is relatively consistent, and the errors of heat transfer calculation in the stable working section of the motor can be controlled by 15%. It shows that the calculation model with the Sommerfeld number as the criterion selected in this paper can better reflect the heat transfer characteristics between the alumina droplet and the wall in combustor. The maximum error between the fitted value and calculated value is 9.43%, which indicates that the numerical model of heat transfer established under the state of two-phase gas and wall scouring has certain reliability. [ABSTRACT FROM AUTHOR]

The following article overviews recent studies regarding heat transfer enhancement methods, explicitly focusing on fins and coils utilization, in phase change material-based latent heat thermal energy storage systems. It discusses the influence of various geometrical and material parameters on the melting and solidification processes, as well as the orientation of the heat transfer surface within the storage tank. Additionally, the article examines the use of a range of phase change materials regarding their melting temperature. Results show that there are research gaps regarding a few ranges of phase change materials of certain previously studied melting points. This paper's main goal was to detect possible research gaps within the phase change studies field. It should be highlighted that a vast amount of numerical studies of both finned and coiled geometries is in need of experimental verification. More than 62% of analyzed studies were performed numerically, while only 37% were performed experimentally. What is more, there were only a few studies concerning experimental investigations for melting temperatures higher than 60 °C. Furthermore, the majority of experimental as well as numerical studies were concerned only with melting phenomena. This paper also advocates for more standardized studies regarding coil geometries using non-dimensional parameters. [ABSTRACT FROM AUTHOR]

This paper presents the performance investigation of a shell and helical coil type of Solution Heat Exchanger (SHX) in an ammonia–water vapour absorption system. In an absorption system, SHX is one of the major heat recovery components. The main objective of any heat exchanger design is to achieve minimum heat transfer area required for a given heat duty, as it governs the overall fixed cost content of such a system. The required surface area is decided by the overall heat transfer coefficient. Hence, the heat transfer coefficient (HTC) correlation plays a major role in optimizing the heat exchanger. In this paper, shell and helical coil type of SHX is investigated with more emphasis on the dimensionless correlation of shell side co-efficient, which decides the overall HTC and the size of heat exchanger. From the experimental study, shell side heat transfer coefficient of 510–650 W/m 2 K is obtained with the heat exchanger effectiveness of 0.84–0.9 for the tested conditions. A proposed Nusselt number correlation is compared with the experimental results. [ABSTRACT FROM AUTHOR]

The fluid flow and heat transfer behavior of liquid–liquid two phase flows have led to significantly improve the heat transfer rates in microchannels. Both numerical and experimental studies are reviewed in this paper to gain useful insights into the effect of a number of parameters such as film thickness, Peclet number, working fluid and flow geometry on hydrodynamic and thermal behavior of microchannels using liquid-liquid two phase flow. In addition, the paper summarises information about common correlations proposed to predict the pressure drop and heat transfer coefficient in the form of Nusselt number (Nu). The present study shows that there is little agreement across the literature between measured pressure drop and Nusselt number and predictions based on these correlations. Finally, the conclusions and important summaries, and some possible future development of this field are presented. [ABSTRACT FROM AUTHOR]

The paper presents the phenomena accompanying the processes of non-adiabatic transport of ice slurry with ice mass fraction values below 20% in the transport sections of the system, assuming the conditions of significant changes in hydrostatic pressure. The subject of the analysis presented herein was to indicate the influence of hydrostatic pressure values on melting and secondary recrystallisation phenomena in the case of medium expansion in a vertical shaft pipeline and a three-chamber PES distributor. The paper proposes a computational model to determine the mass fraction of ice in the downstream section of the supply system: upstream and downstream of the PES distributor. The presented calculation results indicate that a reduction in the mass fraction of ice in the range of 0.004% per 1 m of the pipeline could be observed in vertical shaft pipelines. Maximising the enthalpy flux of the slurry at the inlet to the secondary circuit and minimising the temperature of the return water to the chiller favours mixing rates in the PES three-chamber distributor below 7%, which increase as the mass fraction of ice decreases. • Ice slurry applications in central air-conditioning systems of mining plants. • Ice slurry flow and heat transfer in shaft pipelines and PES distributors. • Ice slurry melting and recrystallisation in primary and secondary circuits. [ABSTRACT FROM AUTHOR]

The traditional single-phase fluid loop (SFL) and traditioanl thermal control algorithm can barely control the temperature rapidly. Thermoelectric cooler (TEC) has been proved to be a good thermal controller because of its high reliability, liquid-free characteristics, and fast response. This paper proposes a TEC-based precooling module that resides in front of the cold plate (CP), and consists of a TEC-CP system, manifesting a high compatibility between the novel precooling module and traditional SFL. The TEC-CP system was designed, and a mathematical model of heat and mass transfer was developed to numerically investigate the effects of the geometric parameters, TEC operating conditions, and liquid cooling states of the precooling module upon payload thermal performance. Through analysis, an optimal TEC-based precooling module with optimal geometric dimensions was attained, where the coolant temperature was decreased by 13.04 K, resulting in a 28.98% reduction compared to that without the precooling module. Transient results also demonstrate that the temperature response time can be within 3 min, indicating a fast response system for temperature control. Results outlined in this paper provide structural and data references for future designs of scientific rack-level thermal control loops in space stations. • A novel thermoelectric-cooler (TEC)-based precooling module is proposed. • It provides local rapid cooling capacity for traditional space thermal management. • The precooling module is optimized in terms of thermal performance and COP. • The COP of TEC is needed to be sacrificed to obtain the optimal cooling capacity. • Compared with the traditional one, the focused temperature can be decreased by 28.98%. [ABSTRACT FROM AUTHOR]

In this paper, an extruded tube with crossed ellipsoidal dimples was proposed to achieve heat transfer enhancement. This extruded tube was produced by mechanical extrusion, and an experiment was carried out to confirm the validity and rationality of the manufacture. The experimental results revealed that the error between geometric models built by mechanical simulation and actual manufacture was less than 15%. On this basis, the thermo-hydraulic characteristics were analyzed by numerical simulations. The CFD analysis indicated that the extruded tube improves thermo-hydraulic performance because the structure of dimples promotes mixing degree and boundary layer destruction. In addition, the dimensionless number Nu / Nu 0 , f / f 0 and PEC were presented to illustrate the effects of geometry, such as dimple depth, pitch, the semi-major axis of rigid ellipsoidal blocks and dimple configuration. It was found that the maximum PEC = 2.4 was observed when D = 3 mm, P = 25 mm, a = 10 mm and the dimples configuration is cross. The range of Nu / Nu 0 , f / f 0 and PEC for ETCED is 2.1–4.2, 1.75–7.24 and 1.7–2.4. Finally, the overall performance was compared among different enhanced tubes. The results showed that the extruded tube provided better overall performance than other enhanced tubes. The achievement of this paper can be extended to engineering applications in heat transfer enhancement. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of supercritical CO 2 heat transfer deterioration (HTD) has significant importance for ensuring the safety and reliability of supercritical Brayton cycles. Therefore, the effects of mass flux, wall heat flux, and tube diameters on the heat transfer characteristics of supercritical CO 2 inside vertical tubes are studied using experimental and numerical methods. Results indicate that the heat transfer performance is positively influenced by an increase in mass flux and heat flux, as well as a decrease in tube diameter. When HTD occurs, the overall heat transfer performance is indeed significantly compromised. When the bulk fluid temperature exceeds T pc , the thermal acceleration effect amplifies the mainstream velocity, stabilizing the Kelvin-Helmholtz instability between the pseudo-two-phases, thereby causing a new type of HTD that is named Type II HTD in this paper. The so-called post-dryout HTD occurs when the bulk temperature surpasses T +, causing a complete transition from pseudo-liquid to pseudo-gas state and resulting in a pseudo-single-phase flow. The heat transfer capability of the low-density and low-thermal-conductivity pseudo-gas diminishes as the temperature rises, leading to post-dryout HTD. The present work explains the mechanisms of two types of HTD and highlights the similarities between subcritical boiling and supercritical pseudo-boiling flow structures. This study also establishes a theoretical foundation for understanding pseudo-two-phase flow patterns during pseudo-boiling. [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]

Cooling channel (CC) design is an effective measure to improve the internal thermal management of proton exchange membrane fuel cells (PEMFC). In this paper, a new elliptical dimple (EDC) cooling channel structure is proposed. The heat transfer and flow characteristics of EDC, circular dimpled cooling channel (CDC), and smooth cooling channel (SC) are compared by numerical simulation method, and the influence of elliptical dimple structural parameters on their performance is discussed. The serpentine CC with elliptical dimples is further compared with the traditional serpentine CC. The results indicate that the EDC is more effective than the other two types due to the narrow surface of the elliptical dimple, which enhances fluid flow and creates a region at the trailing edge of the vortex that promotes heat exchange. It is worth noting that lengthening the elliptical dimple leads to reduced performance, while elongating it initially improves but eventually decreases performance. This study found that the EDC with an elliptical dimple of 0.1 mm depth and 0.6 mm length outperformed the SC, resulting in a 10.6% improvement. Furthermore, the elliptical dimple serpentine cooling channel was found to enhance heat transfer and reduce pressure loss. [ABSTRACT FROM AUTHOR]