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Regenerative cooling is critical for the thermal protection of hypersonic propulsion systems, wherein the flow and heat transfer characteristics of the hydrocarbon fuel in the cooling channel are crucial. Restricted by measurement, the distribution of the fuel temperature inside the cooling channel cannot be directly detected. As a result, the measurement of the convective heat transfer coefficient is more an overall heat transfer coefficient. Furthermore, the existing overall heat transfer coefficient calculation method is derived without considering the flow state of the hydrocarbon fuel in the cooling channel, which should be taken into consideration. Therefore, a modified calculation method of the overall heat transfer coefficient is proposed in this study. The results of the characteristics of the turbulence-related parameters show that the overall heat transfer coefficient is mainly determined by the effective thermal conductivity and surface convective heat transfer coefficient, which are related to the fuel temperature and flow state. Furthermore, the existing method might overestimate the overall heat transfer coefficient. The modified method is suitable for the calculation of the overall heat transfer coefficient in the heat transfer enhancement process in a cooling channel. [ABSTRACT FROM AUTHOR]

Ensuring comfortable climatic conditions for operators in the cabin of technological machines is an important scientific and technical task affecting operator health. This article implements numerical and analytical modeling of the thermal state of the vehicle cabin, considering external airflow and internal ventilation. A method for calculating the heat transfer coefficients of a multilayer cabin wall for internal and external air under conditions of forced convective heat exchange is proposed. The cabin is located in the external aerodynamic flow to consider the speed and direction of the wind, as well as the speed of traffic. Inside the cabin, the operation of the climate system is modeled as an incoming flow of a given temperature and flow rate. The fields of velocities, pressures, and temperatures are calculated by the method of computer hydrodynamics for the averaged Navier–Stokes equations and the energy equation using the turbulence model. To verify the model, the values of the obtained heat transfer coefficients were compared with three applied theories obtained from experimental data based on dimensionless complexes for averaged velocities and calculated by a numerical method. It is shown that the use of numerical simulation considering the external air domain makes it possible to obtain more accurate results from 5% to 75% compared to applied theories, particularly in areas with large velocity gradients. This method makes it possible to get more accurate values of the heat transfer coefficients than for averaged velocities. [ABSTRACT FROM AUTHOR]

Regulations and restrictions against high global warming potential (GWP) refrigerants have been introduced to encourage the adoption of environmentally friendly refrigerants and mitigate the environmental impact of the HVAC industry. R448A, a zeotropic blend with a GWP of 1390, has recently been proposed as a drop-in replacement for R404A and R410A in commercial systems. In this study, the heat transfer coefficient and pressure drop characteristics of R448A within a multiport mini-channel tube were experimentally investigated. The experimental ranges of the mass and heat fluxes were 100 to 500 kg/(m2s) and 3–15 kW/m2, respectively. Additionally, the range of quality from 0 to 1 was considered at two fixed saturated temperatures of 3 and 6 °C. The heat transfer coefficient increased with mass flux. Under low mass flux condition, the heat flux increased the heat transfer coefficient, but there was no noticeable effect of the saturated temperature on the heat transfer coefficient. At high mass flux, heat flux had no major effect on heat transfer, while a decrease in the saturated temperature was found to increase the heat transfer coefficient. Moreover, the pressure drop increased with an increase in the mass flux and vapor quality, whereas the heat flux did not affect the pressure drop. The heat transfer coefficient and pressure drop performance of R448A was compared with that of R410A inside the same tube. Finally, correlations for heat transfer coefficient and pressure drop were proposed for the prediction of heat transfer coefficient and pressure drop in practical applications. [ABSTRACT FROM AUTHOR]

In numerous turbomachinery applications, e.g., in aero-engines with regenerators for improving specific fuel consumption (SFC), heat exchangers with low-pressure loss are required. Pil low-plate heat exchangers (PPHE) are a novel exchanger type and promising candidates for high-speed flow applications due to their smooth profiles avoiding blunt obstacles in the flow path. This work deals with the overall system behavior and gas dynamics of pillow-plate channels. A pillow-plate channel was placed in the test section of a blow-down wind tunnel working with dry air, and compressible flow phenomena were investigated utilizing conventional and focusing schlieren optics; furthermore, static and total pressure measurements were performed. The experiments supported the assumption that the system behavior can be described through a Fanno–Rayleigh flow model. Since only wavy walls with smooth profiles were involved, linearized gas dynamics was able to cover important flow features within the channel. The effects of the wavy wall structures on pressure drop and Mach number distribution within the flow path were investigated, and a good qualitative agreement with theoretical and numerical predictions was found. The present analysis demonstrates that pressure losses in pillow-plate heat exchangers are rather low, although their strong turbulent mixing enables high convective heat transfer coefficients. [ABSTRACT FROM AUTHOR]

The development of new practices in nuclear research reactor safety aspects and optimization of recent nuclear reactors needs knowledge on forced convective heat transfer within sub-channels formed between several nuclear fuel rods or heat exchanger tubes, not only in the fully developed regime but also in the developing regime or laminar flow regime. The main objective of this research was to find a new correlation equation for calculating the convective heat transfer coefficient in the vertical square sub-channels. Recently, a simulation study was conducted to find a new heat transfer correlation equation for calculating the convective heat transfer coefficient within a vertical square sub-channel in the developing regime or laminar flow regime for Reynolds number range 400 ≤ Re ≤ 1700. Simulations were carried out using a computational fluid dynamics (CFD) code and modeling already defined in the software. The novelty of the research lies in the analysis of the entrance effect for the sub-channel by proposing a new empirical correlation that can then be inserted into the STAT computer code. The surface temperature distribution around the tangential direction of the active cylinders shows that the implementation of active and dummy cylinders in the current study can simulate sub-channels that exist in a real nuclear reactor core. The current study shows that the flow simulated in this study is in its developing condition (entrance region). A new forced convective heat transfer correlation for the developing region in the form of Nu = 2.094(Gz)0.329 for the Graetz number range 161 ≤ Gz ≤ 2429 was obtained from the current study. [ABSTRACT FROM AUTHOR]

The prediction of heat transfers in Reynolds-Averaged Navier–Stokes (RANS) simulations requires corrections for rough surfaces. The turbulence models are adapted to cope with surface roughness impacting the near-wall behaviour compared to a smooth surface. These adjustments in the models correctly predict the skin friction but create a tendency to overpredict the heat transfers compared to experiments. These overpredictions require the use of an additional thermal correction model to lower the heat transfers. Finding the correct numerical parameters to best fit the experimental results is non-trivial, since roughness patterns are often irregular. The objective of this paper is to develop a methodology to calibrate the roughness parameters for a thermal correction model for a rough curved channel test case. First, the design of the experiments allows the generation of metamodels for the prediction of the heat transfer coefficients. The polynomial chaos expansion approach is used to create the metamodels. The metamodels are then successively used with a Bayesian inversion and a genetic algorithm method to estimate the best set of roughness parameters to fit the available experimental results. Both calibrations are compared to assess their strengths and weaknesses. Starting with unknown roughness parameters, this methodology allows calibrating them and obtaining between 4.7% and 10% of average discrepancy between the calibrated RANS heat transfer prediction and the experimental results. The methodology is promising, showing the ability to finely select the roughness parameters to input in the numerical model to fit the experimental heat transfer, without an a priori knowledge of the actual roughness pattern. [ABSTRACT FROM AUTHOR]

In some engineering applications, it is very desirable that the heat exchanger is as light as possible while maintaining the heat transfer rate at an acceptable level. In this context, the possibility of reducing the weight of the heat exchanger with the star-shaped fins by cutting off the thermally least efficient part of the fin was investigated. For this purpose, the rear part of the fins was trimmed to Ø28, Ø31 and Ø34 mm. Numerical analysis was used to determine the influence of each variant on the flow characteristics in the air–water heat exchanger and on heat transfer for the range of 2300 < Re < 16,000. The best results were obtained by trimming the rear part of the fin to Ø28 mm. With a 5.53% reduction in fin weight, heat transfer can be increased by up to 8.12% compared to the star-shaped fins without trimming. The pressure drop can be reduced by up to 0.92%. The trimmed fins were also compared with perforated star-shaped fins (perforation Ø2). At approximately the same weight, the trimmed fins increase the heat transfer coefficient by up to 5.75% with a reduction in pressure drop of up to 0.76% compared to the perforated fins. [ABSTRACT FROM AUTHOR]

This article reviews the heat transfer enhancement of nanofluids with non-spherical nanoparticles. We divided the non-spherical nanoparticles suspended in nanofluids into three categories based on the dimension of geometric particle structure. Based on the measured data in experimental studies, we then evaluated the shape effect of non-spherical nanoparticles on thermal conductivity and convective heat transfer enhancement of nanofluids. Recent studies explored the numerical predictions and related heat transfer mechanisms. Due to large aspect ratios, thermal conductivity is abnormally enhanced only for nanofluids with carbon nanotubes/nanofibers/nanowires. The approximate enhancement effect exerted by three types of non-spherical nanoparticles on thermal conductivity was 4.5:2.5:1. Thermal conductivity enhancement per concentration was larger for nanorods/ellipsoids with small aspect ratios. The convective heat transfer coefficient was increased by suspending non-spherical nanoparticles in the base fluid. Consequently, no significant thermohydraulic performance was discovered for convective heat transfer of non-spherical nanoparticle nanofluid flow, specifically for turbulent flows, due to increased pumping power. However, the temperature and particle concentration effect on convective heat transfer remains unclear. In addition, no perfect model for predicting the thermal conductivity and convective heat transfer of non-spherical nanoparticle nanofluids has been reported. [ABSTRACT FROM AUTHOR]

Featured Application: The presented investigation may be used for the design process of active cooling systems. Choosing the right cooling device is crucial for the proper operation of electronic equipment. A comparison of the two different cooling devices is presented in this paper: one with a standard axial fan and the other with a synthetic jet actuator. Two distinct sets of operating conditions of the fan and two different loudspeakers for the synthetic jet actuator were used. The experimental setup consisted of a radial heat sink mounted onto a round electric heater and two cooling systems: one with the axial fan and the other with a synthetic jet actuator. From the thermal balance in the specified control volume, the heat sink's thermal resistance. as well as the coefficient of performance, were determined. The highest difference between the thermal resistance of both cooling systems occurred at a low input power of P = 0.5 W. The heat sink cooled with a synthetic jet had the thermal resistance of R = 0.39 K/W, while the same heat sink cooled with a fan achieved R = 0.23 K/W. Thus, the fan cooling exhibited almost 70% better performance than synthetic jet cooling. For a higher input power of P = 7.0 W, the relative difference in the thermal resistance decreased to the value of 42%. For the input power of P = 7.0 W, the fan-cooled heat sink dissipated the thermal power of Q ˙ HS = 487   W under the temperature difference between the heat sink base and ambient air equal to 60 K. For the same input power and temperature difference, the synthetic jet cooling of the same heat sink dissipated a thermal power of Q ˙ HS = 339   W . Under natural convection, the heat sink dissipated the thermal power of Q ˙ HS = 57   W . Thus, the heat transfer enhancement with fan cooling relative to natural convection was equal to 8.5, while the enhancement with synthetic jet cooling relative to natural convection was equal to 6.0. The modified coefficient of performance and the heat transfer rate of the heat sink per unit temperature difference and unit volume of the cooling device ε are presented. The axial fan performed better in terms of both parameters under consideration. The ε of the investigated device with a fan was around four times higher than in the case of the synthetic jet actuator and eight times higher than in the case of natural convection. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted to examine, for the first time, the influences of using different designs of tube arrangements on the local heat transfer coefficient (LHTC) in a bubble column (with a diameter of 0.13 m) equipped densely with a bundle of tubes. The effect of using two different designs of tube arrangements has been examined for a broad range of gas flow rates using a sophisticated heat transfer technique. The obtained results indicate that the LHTC increases significantly with increasing the gas velocity, regardless of the design and installation of the tubes in the column. Additionally, the shape of the LHTC's profiles alters considerably by the presence of a bundle of tubes and their arrangements. Moreover, the results indicate that the square tube pitch arrangement provides uniform heat transfer profiles, which enhance the performance of the bubble column reactor by 30%. Furthermore, the heat transfer profiles were found to be varied with the axial height of the column. The new experimental results obtained in this investigation will provide experimental reference data for creating and validating a mathematical model for predicting LHTCs. In addition, this will facilitate this kind of reactor's design, scale-up, and operation. [ABSTRACT FROM AUTHOR]

With the development of hydropower, the heat problem of a rotor cannot be ignored. This paper presents a topology of an evaporative cooling system for rotors. The system seals the pole coil in a tank and immerses the coil in the insulating coolant with a suitable boiling point. The latent heat of vaporization during the boiling of coolant is used to control the temperature rise of the pole coil. After explaining the circulation principle of the system, the effectiveness of the cooling system is verified by experiments. A small-scale experimental platform has been set up to test the effectiveness of the new topology. The comparison experiment with air-cooling shows that the phase change cooling system can not only provide hundreds of times the heat transfer capacity of air-cooling, but also the temperature rise of the coil is half that of air cooling. Based on the experimental results, the calculated formula of the heat transfer coefficient of the evaporative cooling system in the rotating state was fitted, and the deviation of the calculated result could be kept at less than 25%. Thanks to the evaporative cooling system, the rotor carries a high current density. [ABSTRACT FROM AUTHOR]

China's LNG import volume in 2021 reached 121.356 million tons, which makes China the largest importer in the world. The ambient air vaporizer (AAV) for LNG vaporization is an ideal selection for minimizing the average monetary value of terminals and maximizing operating efficiency. However, the heat and mass transfer performance of real multi-component LNG is not the same as that of the pure component in AAV; what is more, deep cryogenic and multi-component characteristics of LNG could lead to the deterioration of heat-transfer performance, which may cause catastrophic consequences. Thus, this difficulty should be concerning and solved in its operation. Based on the law of conservation of energy and mass, a heat and mass transfer model was established that can calculate the coupled heat transfer from the LNG to the air-side of the AAV along its own length. Empirical correlations are proposed to predict some basic properties of the frost layer at the outside of the tube, where the internal fluid is seen as a pure component and a multi-component. The numerical results show that the root–mean–square error (RMS) of the frost thickness is 0.749 mm, and the RMS of the outlet fluid temperature is 2.06 K and 2.21 K in summer and winter, respectively. That is in good agreement with the experimental data in the previous literature. The results show that the length of the finned tube in the AAV affected by pure CH 4 was increased by 42.5%; therefore, we recommend shortening the finned tube on the basis of safety to save costs. Compared to the pure components reference experiments, when the CH 4 content of multi-component in five regions was 78.48–96.91%, it is found that the different varieties of thermodynamic dryness degree x within the two types of components is the key point for the distinct mechanisms of the heat transfer characteristics of the AAV. Additionally, compared to changing the design pressure and flow rate, it is found that varying the flow rate has a much greater impact on the heat and mass transfer performance of the AAV than changing its pressure. The calculation of the coupled heat and mass transfer of the AAV can provide a theoretical basis for subsequent engineering designs. [ABSTRACT FROM AUTHOR]

Condensation heat transfer characteristics (using R410A as the working fluid) were studied experimentally to evaluate the heat transfer performance in copper and stainless-steel heat transfer tubes (smooth and enhanced). Experiments were carried out for a mass flux that varied from 250 to 450 kg m−2 s−1, at a saturation temperature of 318 K. Single-phase heat balance verification found that the heat loss is less than 6%, and the deviation between single-phase experimental results and various prediction correlations is less than 15%. Additionally, tube side condensation flow patterns were observed and recorded. Experimental results found that the enhancement ratio of the condensation heat transfer coefficient (enhanced tube/smooth tube) of the three-dimensional surface (1EHT) tube is in the range of 1.15~1.90, while the ratio of the micro-fin (HX) tube is in the range of 1.18~1.80. Heat transfer performance is affected by material conductivity, with the thermal conductivity of the smooth tube slightly affecting the heat transfer performance; larger heat transfer enhancements are produced in the enhanced tubes. At a low mass flow rates and vapor qualities, the flow pattern is a stratified wavy flow, while at higher mass flow rates and vapor qualities, the flow pattern is an annular flow (with the area in the enhanced tube being larger than the area of a smooth tube). Flow patterns in the smooth tube are consistent with the predicted values shown in previously reported flow pattern maps. A flow pattern diagram for condensation heat transfer in enhanced tubes is presented as part of this study. The condensation heat transfer coefficient increases with an increase in mass flow. When the mass flow rate increases, the turbulence of the liquid flow increases and the liquid film becomes thinner; thermal resistance is reduced and the heat transfer coefficient increases. Heat transfer values at lower mass velocities increase slightly with increasing mass flux values; however, at higher mass flux rates the heat transfer increase is larger than that at low mass flux values. Finally, tubes produced from high thermal conductivity materials produce larger heat transfer performance gains than the gains found in smooth tubes; small diameter tubes produce larger gains than larger diameter tubes. [ABSTRACT FROM AUTHOR]

Solar air heater is considered to be the most popular and widely used solar thermal system. Solar air heater (SAH) can be used in many applications, ranging from domestic to industrial purposes. However, it seems that the viability of SAH is not feasible due to the following two reasons: (i) the low convective heat transfer coefficient at the absorber plate is the reason that causes a low heat transfer rate to the flowing air, and (ii) the high temperature of the absorber plate insists on high heat losses, thus, reducing the thermal efficiency. The convective coefficient can be augmented by placing turbulators/roughness on the absorber plate, which induces turbulence in the flow passage near the absorber plate by disrupting and destabilizing the laminar sublayer. This comprehensive review has been presented to summarize the studies on artificial roughness/turbulators geometries to enhance the heat transfer rate. Various rib configurations (such as grits, grooves, blockages, baffles, winglets, protrusions, twisted taps, dimples, and mesh wires) and distinct arrangements of rib roughness (such as inclined, transverse, V shape, with gap) have been reviewed to present heat transfer and friction characteristics. Additionally, thermal efficiency and thermohydraulic efficiency (in terms of net effective efficiency) of various artificial roughnesses and rib configurations are presented under distinct operating conditions for comparing purposes. This comparative study has been presented to assess the most desirable ribs and their configurations. On the basis of net effective efficiency, a multiarc rib with gaps is found to be the best configuration among all and have the highest thermal and net effective efficiency of around 79%. [ABSTRACT FROM AUTHOR]

This paper investigates the cryogenic heat transfer phenomena of nitrogen flowing in helically coiled tubes under the combined effects of pseudocritical conditions, buoyancy, and coil curvature. The ultimate goal was to design optimum heat exchangers for liquid air energy storage. Local heat transfer coefficients were evaluated peripherally across tube cross sections. The pressure, mass flux, and heat flux effects on the heat transfer were examined. The dual effect of buoyancy and coil curvature on heat transfer coefficients was interpreted via a dimensionless number Ψ, which denotes a ratio between the two effects. Results reveal that the heat transfer coefficients increase with increasing mass flux but decreasing pressure and heat flux. The buoyancy effect dominates the heat transfer at fluid temperatures below the pseudocritical temperature (e.g., −146.3 °C at 35 bar), while the coil curvature-induced centrifugal effect dominates at higher temperatures. The heat transfer coefficients for the helical coil were approximately 13% lower compared with those in straight tube at fluid temperatures below the pseudocritical temperature, but their difference shrinks (<±6%) at higher temperatures. The reason is that the benefits of coil curvature and improved turbulent mixing on heat transfer are counteracted by the thermophysical property variation and buoyancy effect. [ABSTRACT FROM AUTHOR]

In this study, flow and heat transfers in bidisperse gas–solid systems were numerically investigated using the computational fluid dynamics–discrete element method (CFD–DEM). Three different models to close the gas–solid heat transfer coefficient for each species of bidisperse systems were compared in the simulations. The effect of the particle diameter ratio and particle number ratio between large and small particles on the particle mean temperature and temperature distribution of each species were systematically investigated. The simulation results show that differences in the particle mean temperature and temperature distribution profiles exist among the three heat transfer models at a higher particle number ratio. The differences between the effects of three heat transfer models on heat transfer properties in bidisperse systems with particle diameter ratios of up to 4 are marginal when the particle number ratio between small and large particles is 1. [ABSTRACT FROM AUTHOR]

The paper presents the method and results of determination of heat transfer coefficient for air-atomized water spray cooling with consideration of infrastructural factors of industrial cooling conveyor, such as effect of accelerated air. The established values of heat transfer coefficient were implemented into a numerical model of cooling line, with special definition of sprayers and the movement of the part subjected to quenching. After quantitative validation on selected samples, the obtained coefficients were used for the solution of the technological problem by means of localized cooling rate enhancement, which forms a case study confirming reliability of the established water spray heat transfer functions and suitability of the determined models for design of thermomechanical controlled processing of complex-geometry parts. [ABSTRACT FROM AUTHOR]

An investigation is conducted to study the flow and heat transfer on stagnation point over an exponentially stretching/shrinking cylinder filled with nanofluid in the presence of slip at the boundary. By using the appropriate exponential similarity transformation, the governing equations are converted into nonlinear ordinary differential equations and then solved computationally using bvp4c in Matlab software. The results of skin friction coefficient, heat transfer coefficient, velocity and temperature profiles on slip parameter, curvature parameter, nanoparticles as well as nanoparticle volume fraction parameter are presented graphically. The presence of slip and curvature parameters cause the region of dual solutions to expand and at once enhance the heat transfer rate at the surface but somehow the heat transfer rate at the surface decreases rapidly when cylinder is shrunk. The aim of this paper is to investigate the effect of slip parameter on nanofluid as well as on the stretching/shrinking surface. The new findings of the effects of skin friction and heat transfer coefficient on different nanoparticles and nanoparticle volume fraction were discussed. Since there are dual solutions in the flow characteristics, we carry out a stability analysis to verify which solution is in a stable state and can be realized physically. [ABSTRACT FROM AUTHOR]

In this study, the evaporation heat transfer characteristics of an intermediate temperature of R744 in a smooth horizontal tube, when operating as an indirect refrigeration system (IRS) among hybrid cascade refrigeration systems (HCRSs), are evaluated. Studies on the characteristics of intermediate-temperature evaporation heat transfer under the operating conditions of evaporators used in actual refrigeration systems, such as IRS, cascade refrigeration systems, and HCRS, used in supermarkets are lacking. Thus, this study provides basic data on the characteristics of evaporation heat transfer of R744 in the evaporators of refrigerators used in supermarkets. The tube employed to the evaporation experiment in this study was a horizontal smooth copper tube with a length of 8000 mm and an inner diameter of 11.46 mm. The experimental variables were measured over a wide range of mass flux of 200–500 kg/(m2·s), heat flux of 10–40 kW/m2, and saturation temperature of −40–0 °C. The main results are summarized as follows: (1) The application of Kandlikar's correlation formula at an evaporation temperature of −20 °C in an IRS helps in a good prediction of the R744 evaporation heat transfer coefficient. (2) The pressure drop according to the heat and mass flux showed the same heat transfer coefficient trend, but the pressure drop at saturation temperature was different from the trend of heat transfer coefficient. [ABSTRACT FROM AUTHOR]

The aim of this work is to numerically analyse fluid flow and heat transfer characteristics in a crossflow air-to-water fin-and-tube heat exchanger (FTHEX) by implementing two configurations of delta-winglet type vortex generators at the air side: delta-winglet upstream (DWU) and delta-winglet downstream (DWD). The vortex generators are mounted on a fin surface and deployed in a "common flow up" orientation. The effects of attack angles of 15°, 30° and 45° on air-side heat transfer and pressure drop were examined. Since the implementation of the full-size model would involve large numerical resources, the computational domain is simplified by considering a small segment in the direction of water flow. The fully developed temperature and velocity boundary conditions were set at the water inlets. To validate the defined mathematical model and numerical procedure, measurements have been performed on a plain FTHEX. The air side Reynolds number, based on hydraulic diameter, was in the range of 176 ≤ ReDh ≤ 400 and water side Reynolds number, based on inner tube diameter, was constant Redi = 17,065. The results have shown that the highest increase in the Colburn factor j (by 11–27%) and reduction in the air-side thermal resistance fraction (from 78.2–76.9% for ReDh = 176 to 76–72.4% for ReDh = 400) is achieved by using the DWD configuration with attack angle 45°. In addition, the overall heat transfer coefficient is improved by up to 15.7%. The DWD configuration with the attack angle 30° provides the greatest improvement in the heat transfer to pressure loss ratio, 5.2–15.4% over the range of ReDhstudied. [ABSTRACT FROM AUTHOR]

Taking a subsea collet connector as an example, the contact characteristics of the sealing structure of the subsea connector under thermal–structural coupling were studied. Considering the heat transfer problem of the subsea connector in deep water, the heat transfer model of seawater layer between sealing structures was established, and the relationship between equivalent thermal conductivity, composite heat transfer coefficient, and temperature was determined. The steady-state temperature field distribution of the connector under the action of the internal high-temperature oil and gas and external low-temperature seawater was obtained. Considering the stress and deformation of the subsea connector under the thermal load, the thermal–structural coupling analysis model of the steady-state temperature field was established, and the thermal stress theoretical analysis and numerical simulation of the key sealing structures of the connector were compared and verified. Analysis of coupled stress calculation, for example, under a steady-state temperature field, was carried out on the sealing structure of the subsea connector. At the same time, the pressure shock mode under a steady temperature field was analyzed, which showed that the lenticular sealing gasket is sensitive to high pressure under high-temperature conditions. [ABSTRACT FROM AUTHOR]

This paper presents experimental data on shear-stress-driven liquid water films on a horizontal plate formed by the condensation of superheated steam. The experimental results were obtained in the Experimental Multi-phase Measurement Application (EMMA) at the University of Duisburg-Essen. The liquid film thickness was spatially and temporally investigated with an optical measurement system. Furthermore, the resulting local heat transfer coefficient in the case of film condensation was determined for a variety of steam velocities and temperatures. Subsequently, the presented data are compared to the results of an analytical condensation model for shear-stress-driven liquid films developed by Cess and Koh. Thus, the model is qualitatively validated, with explicable remaining disparities between the model and experiment that are further discussed. The presented results are an important contribution to the contemporary research into steady-state, single-component multiphase flow considering phase-change phenomena including heat transfer. [ABSTRACT FROM AUTHOR]

Different parameters of the circular-arc, trapezoidal and equal cross-section-shaped flow channels were analyzed, and the core volume goodness factor was used for the comparison of the three different types of flow channels. During the experiment, the Reynolds number (Re) on the air side ranged from 1200 to 5100. The results showed that the overall heat transfer performance of the three channels in this paper are circular-arc, trapezoidal and equal cross-section in order from good to bad. The overall heat transfer enhancement performance of the circular-arc flow channel is the best, which is 9–26.2% and 3.6–11.8% higher than that of the equal and trapezoidal cross-section flow channels, respectively. This showed that although the divergent flow channel structure reduces the fluid velocity in the flow process, it weakens the convective heat transfer performance in the flow channel. However, this gradually decreasing cross-sectional area improves the downstream heat transfer area and reduces the pressure drop in the flow process, thus promoting the overall heat transfer performance. With the increase in the circular radius (R), both the j and f factors increase, and the highest overall heat transfer performance is obtained at R = 300 mm. The convective heat transfer coefficient increases with the decrease in the inlet height. [ABSTRACT FROM AUTHOR]

This study experimentally explores the thermofluidic performance of a cryogenic micro-pin fin cooler with two-phase liquid nitrogen flows. The liquid nitrogen cooling system is introduced to investigate the performance of the micro-pin cooler in a cryogenic condition. The result reveals that the nominal value of the base heat transfer coefficients of the micro-pin fin cooler with liquid nitrogen flows, 240 kW/m2-K at a mass flow rate of 2.23 g/s, is an order of magnitude greater than that with FC-72 flows. The result also demonstrates that the base heat transfer coefficient of the micro-pin fin cooler is nearly three times greater than that of the micro-gap cooler, not containing any fins. This study shows the feasibility of the cryogenic micro-pin fin cooler for thermally controlling very high heat density devices such as high-power laser diode bars, of which the heat density can reach 2000 kW/m2. [ABSTRACT FROM AUTHOR]

Featured Application: The pump-assisted capillary phase-change loop overcomes the two-phase flow instability of traditional boiling heat dissipation technologies. Thus, it shows prospects for use in the heat dissipation of electronics devices and batteries on the ground and in space in applications such as datacenter cooling, and thermal management of batteries or spacecraft. To overcome the two-phase flow instability of traditional boiling heat dissipation technologies, a porous wick was used for liquid-vapor isolation, achieving efficient and stable boiling heat dissipation. A pump-assisted capillary phase-change loop with methanol as the working medium was established to study the effect of liquid-vapor pressure difference and heating power on its start-up and steady-state characteristics. The results indicated that the evaporator undergoes four heat transfer modes, including flooded, partially flooded, thin-film evaporation, and overheating. The thin-film evaporation mode was the most efficient with the shortest start-up period. In addition, heat transfer modes were determined by the liquid-vapor pressure difference and power. The heat transfer coefficient significantly improved and the thermal resistance was reduced by increasing liquid-vapor pressure as long as it did not exceed 8 kPa. However, when the liquid-vapor pressure exceeded 8 kPa, its influence on the heat transfer coefficient weakened. In addition, a two-dimensional heat transfer mode distribution diagram concerning both liquid-vapor pressure difference and power was drawn after a large number of experiments. During an engineering application, the liquid-vapor pressure difference can be controlled to maintain efficient thin-film evaporation in order to achieve the optimum heat dissipation effect. [ABSTRACT FROM AUTHOR]

The paper presents a theoretical analysis of heat transfer in a heated tube bank, based on the Nusselt number computation as one of the basic dimensionless criteria. To compute the Nusselt number based on the heat transfer coefficient, the reference temperature must be determined. Despite the value significance, the quantity has several different formulations, which leads to discrepancies in results. This paper investigates the heat transfer of the inline and staggered tube banks, made up of 20 rows, at a constant tube diameter and longitudinal and transverse pitch. Both laminar and turbulent flows up to Re = 10,000 are considered, and the effect of gravity is included as well. Several locations for the reference temperature are taken into consideration on the basis of the heretofore published research, and the results in terms of the overall Nusselt number are compared with those obtained by the experimental correlations. This paper provides the most suitable variant for a unique reference temperature, in terms of a constant value for all tube angles, and the Reynolds number ranges of 100–1000 and 1000–10,000 which are in good agreement with the most frequently used correlating equations. [ABSTRACT FROM AUTHOR]

As electrical devices become smaller, it is essential to maintain operating temperature for safety and durability. Therefore, there are efforts to improve heat transfer performance under various conditions, such as using extended surfaces and nanofluids. Among them, cooling methods using ferrofluid are drawing the attention of many researchers. This fluid can control the movement of the fluid in magnetic fields. In this study, the heat transfer performance of a fin-tube heat exchanger, using ferrofluid as a coolant, was analyzed when external magnetic fields were applied. Permanent magnets were placed outside the heat exchanger. When the magnetic fields were applied, a change in the thermal boundary layer was observed. It also formed vortexes, which affected the formation of flow patterns. The vortex causes energy exchanges in the flow field, activating thermal diffusion and improving heat transfer. A numerical analysis was used to observe the cooling performance of heat exchangers, as the strength and number of the external magnetic fields were varying. VGs (vortex generators) were also installed to create vortex fields. A convective heat transfer coefficient was calculated to determine the heat transfer rate. In addition, the comparative analysis was performed with graphical results using contours of temperature and velocity. [ABSTRACT FROM AUTHOR]

Featured Application: This research concerns the improvement of heat transfer inside the dryer due to the use of ultrasound. The results can be used in all processes where convective heat exchange occurs in the gas. The use of ultrasound is a new method to enhance convection drying. However, there is little information in the literature on the improvement of convective heat transfer caused by ultrasound. Therefore, the heat transport during ultrasound-assisted convective heating of small samples in a hybrid dryer was experimentally examined. A small Biot number regime of heat transfer was considered. The results confirmed a great enhancement of heat transfer due to the application of ultrasound. Due to the use of ultrasound, the convective heat exchange coefficient increased from 45% to almost 250%. The enhancement is a linear function of applied ultrasound power. It was shown that the energy absorption of ultrasound existed, but the thermal effect of this absorption was very small. [ABSTRACT FROM AUTHOR]

Finally, in the review paper of Kartsonakis et al. [[10]], the principles of latent heat thermal energy storage systems with PCMs are discussed. The study of Vérez et al. [[4]] examined the effect of the design of the PCM macro-encapsulation on the thermal behavior of a latent heat thermal energy storage systems during both the charging and discharging processes. An effective way for the energy systems efficiency increment is the use of latent heat thermal energy storage because of its high energy density in comparison to sensible heat storage systems. [Extracted from the article]

The wet ball milling method was used and a dispersant (gum Arabic) was added to prepare various concentrations (0.05 and 0.2 wt%) of carbon-based nanofluids (CBNFs) by a two-step synthesis method as working fluids for heat exchange. CBNFs were actually used in a tube heat exchanger (THE) for heat transfer performance experiments. The heat transfer performance of water and CBNFs was estimated under different heating powers and flow rates of working fluid. The pump power consumption (Ppe) of 0.05 wt% CBNF was found to be similar to that of water, but the Ppe of 0.2 wt% CBNF was higher than that of water. The convective heat transfer coefficient (HTC) of CBNF in the was higher than that of water, and the HTC of 0.05 wt% and 0.2 wt% CBNF was optimal at the heating power of 120 W and 80 W, respectively. The average HTC of 0.05 wt% CBNFs at 120 W heating power was about 3.33% higher than that of water, while that of 0.2 wt% CBNFs at 80 W heating power was about 4.52% higher than that of water. Considering the Ppe and HTC concomitantly, the best overall system performance was exhibited by 0.05 wt% CBNFs. [ABSTRACT FROM AUTHOR]

This paper aims to numerically investigate the thermal enhancement of a latent thermal energy storage component with mini-channels as air passages. The investigated channels in two sizes of internal air passages (channel-1 with dh = 1.6 mm and channel-2 with dh = 2.3 mm) are oriented vertically in a cuboid of 0.15 × 0.15 × 0.1 m3 with RT22 as the PCM located in the shell. The phase change is simulated with a fixed inlet temperature of air, using ANSYS Fluent 19.5, with a varying number of channels and a ranging air flow rate entering the component. The results show that the phase change power of the LTES improves with by increasing the number of channels at the cost of a decrease in the storage capacity. Given a constant air flow rate, the increase in the heat transfer surface area of the increased number of channels dominates the heat transfer coefficient, thus increasing the mean heat transfer rate (UA). A comparison of the channels shows that the thermal performance depends largely on the area to volume ratio of the channels. The channel type two (channel-2) with a slightly higher area to volume ratio has a slightly higher charging/discharging power, as compared to channel type one (channel-1), at a similar PCM packing factor. Adding fins to channel-2, doubling the surface area, improves the mean UA values by 15–31% for the studied cases. The variation in the total air flow rate from 7 to 24 L/s is found to have a considerable influence, reducing the melting time by 41–53% and increasing the mean UA values within melting by 19–52% for a packing factor range of 77.4–86.8%. With the increase in the air flow rate, channel type two is found to have considerably lower pressure drops than channel type one, which can be attributed to its higher internal hydraulic diameter, making it superior in terms of achieving a relatively similar charging/discharging power in exchange for significantly lower fan power. Such designs can further be optimized in terms of pressure drop in future work, which should also include an experimental evaluation. [ABSTRACT FROM AUTHOR]

The paper focuses on the use of holographic interferometry in the research of thermal modification and its effect on the heat transfer from the wood surface to the surrounding air. In the experiment, spruce wood samples modified at 160 °C, 180 °C, 200 °C, 220 °C and an unmodified control sample were used. A radiant heat source was placed under the sample. The top of the sample represented the boundary where the observed heat transfer occurred. The temperature fields above the sample were visualized by real-time holographic interferometry and the heat transfer coefficient α was calculated from the obtained interferograms. During the heating of the samples, a decrease of the heat transfer coefficient was observed. The heat transfer coefficient of the control unmodified sample decreased from a maximum of α = 22.66 Wm–2K–1 to a minimum of α = 8.6 Wm–2K–1. In comparison with these values, the heat transfer coefficients of the modified samples treated at 160, 180, 200 and 220 °C, respectively, decreased to 99%, 93%, 68% and 51% of the maximal control value at the beginning of experiment and to 95%, 86%, 80% and 64% of the minimal control value by the end of the experiment. Moreover, an analysis of variance was used to determine the significance of the heat treatment effect on the heat transfer coefficient. A high significance (p < 5%) was observed between the control sample and the modified samples treated at 200 °C and 220 °C. Experiments with the use of holographic interferometry produced results consistent with previous studies conducted by different methods. [ABSTRACT FROM AUTHOR]

As fluid passes through the fracture of an enhanced geothermal system, the flow direction exhibits distinct angular relationships with the geometric profile of the rough fracture. This will inevitably affect the heat transfer characteristics in the fracture. Therefore, we established a hydro-thermal coupling model to study the influence of the fluid flow direction on the heat transfer characteristics of granite single fractures and the accuracy of the numerical model was verified by experiments. Results demonstrate a strong correlation between the distribution of the local heat transfer coefficient and the fracture morphology. A change in the flow direction is likely to alter the transfer coefficient value and does not affect the distribution characteristics along the flow path. Increasing injection flow rate has an enhanced effect. Although the heat transfer capacity in the fractured increases with the flow rate, a sharp decline in the heat extraction rate and the total heat transfer coefficient is also observed. Furthermore, the model with the smooth fracture surface in the flow direction exhibits a higher heat transfer capacity compared to that of the fracture model with varying roughness. This is attributed to the presence of fluid deflection and dominant channels. [ABSTRACT FROM AUTHOR]

Featured Application: At the end of the development program, the gas turbine should be able to drive an unmanned aerial vehicle weighing a maximum of 1200 kg and generate 1.0 MW/h of electricity. The application in the civilian market of electricity generation aims to increase the financial possibilities of success of the program, where biofuel (ethanol), derived from sugar cane, will be one of the main fuels used for motor combustion. In this paper, a calculation procedure is presented to estimate the heat transfer coefficients of a single spool gas turbine designed to generate 5 kN of thrust. These heat transfer coefficients are the boundary conditions which govern the heat interaction between the solid parts and the working fluid in the gas turbine. However, the calculation of these heat transfer coefficients is not a trivial task, since it depends on complex fluid flow conditions. Empirical correlations and assumptions have been used to find convective heat transfer coefficients over most components, including stator vanes, rotor blades, disc faces, and disc platforms. After defining the heat transfer coefficients, the finite element method was used to determine the temperature distribution in one eighth section of the gas turbine making use of the problem cyclic symmetry. Both static and rotating assemblies have been modeled. The results allowed the prediction of the thermal expansion behavior of the whole single spool gas turbine with special attention to the safety margin of clearances. Furthermore, having the temperature distribution defined, it is possible to calculate the thermal stresses in any mechanical component. Additionally, it is possible to specify suitable metallic alloys for achieving appropriate performance in every case. The structural integrity of all components was then assured with the temperature distribution and thermal expansion behavior under knowledge. Thus, the mechanical drawings could be released to manufacturing. [ABSTRACT FROM AUTHOR]

A ground source heat pump system is a highly efficient renewable heating, cooling, and ventilation system that utilizes the ground as a heat source or sink via ground heat exchangers. Energy pile is an energy geotechnical structure that couples a ground heat exchanger with a geotechnical structure, leading to low capital cost. The design of energy piles can be challengeable due to their complicated geometries and the requirement of mechanical load. This study focuses on the heat transfer across the concrete–soil interface of energy piles in urban areas. Case studies from two projects, the Lambeth College and Shell Centre projects, are presented and discussed. The back analysis of two energy pile cases illustrated that the heat transfer coefficient at the pile–soil interface can differ between the cooling mode and the heating mode. It can be concluded that the difference in the heat transfer coefficient is influenced by a number of factors such as soil properties, concrete (grout) properties, and the installation method. [ABSTRACT FROM AUTHOR]

Lithium (Li)-ion battery thermal management systems play an important role in electric vehicles because the performance and lifespan of the batteries are affected by the battery temperature. This study proposes a framework to establish equivalent circuit models (ECMs) that can reproduce the multi-physics phenomenon of Li-ion battery packs, which includes liquid cooling systems with a unified method. We also demonstrate its utility by establishing an ECM of the thermal management systems of the actual battery packs. Experiments simulating the liquid cooling of a battery pack are performed, and a three-dimensional (3D) model is established. The 3D model reproduces the heat generated by the battery and the heat transfer to the coolant. The results of the 3D model agree well with the experimental data. Further, the relationship between the flow rate and pressure drop or between the flow rate and heat transfer coefficients is predicted with the 3D model, and the data are used for the ECM, which is established using MATLAB Simulink. This investigation confirmed that the ECM's accuracy is as high as the 3D model even though its computational costs are 96% lower than the 3D model. [ABSTRACT FROM AUTHOR]

Latent Heat Energy Storage (LHES) using Phase Change Materials (PCM) is considered a promising Thermal Energy Storage (TES) approach as it can allow for high levels of compactness, and execution of the charging and discharging processes at defined, constant temperature levels. These inherent characteristics make LHES particularly attractive for applications that profit from high energy density or precise temperature control. Many novel, promising heat exchanger designs and concepts have emerged as a way to circumvent heat transfer limitations of LHES. However, the extensive range of experimental conditions used to characterize these technologies in literature make it difficult to directly compare them as solutions for high thermal power applications. A methodology is presented that aims to enable the comparison of LHES designs with respect to their compactness and heat transfer performance even when largely disparate experimental data are available in literature. Thus, a pair of key performance indicators (KPI), Φ P C M representing the compactness degree and NHTPC, the normalized heat transfer performance coefficient, are defined, which are minimally influenced by the utilized experimental conditions. The evaluation procedure is presented and applied on various LHES designs. The most promising designs are identified and discussed. The proposed evaluation method is expected to open new paths in the community of LHES research by allowing the leveled-ground contrast of technologies among different studies, and facilitating the evaluation and selection of the most suitable design for a specific application. [ABSTRACT FROM AUTHOR]

The curved geometry of a coiled flow inverter (CFI) promotes chaotic mixing through a combination of coils and bends. Besides the heat exchanger geometry, the heat transfer can be enhanced by improving the thermophysical properties of the working fluid. In this work, aqueous solutions of dispersed TiO2 nanometer-sized particles (i.e., nanofluids) were prepared and characterized, and their effects on heat transfer were experimentally investigated in a CFI heat exchanger inserted in a forced convective thermal loop. The physical and transport properties of the nanofluids were measured within the temperature and volume concentration domains. The convective heat transfer coefficients were obtained at Reynolds numbers (NRe) and TiO2 nanoparticle volume concentrations ranging from 1400 to 9500 and 0–1.5 v/v%, respectively. The Nusselt number (NNu) in the CFI containing 1.0 v/v% nanofluid was 41–52% higher than in the CFI containing pure base fluid (i.e., water), while the 1.5 v/v% nanofluid increased the NNu by 4–8% compared to water. Two new correlations to predict the NNu of TiO2–water nanofluids in the CFI at Reynolds numbers of 1400 ≤ NRe ≤ 9500 and nanoparticle volume concentrations ranges of 0.2–1.0 v/v% and 0.2–1.5 v/v% are proposed. [ABSTRACT FROM AUTHOR]

Featured Application: After a long period of use, the solar collector has to be cleaned due to the serious blocking and efficiency decline. In this work, we prepared ternary Ni-W-P coating to inhibit the fouling deposition. Also, the thermal conductivity of ternary Ni-W-P coating and heat transfer coefficient of composite material were analyzed to make identification of the heat transfer performance of a matrix with and without the ternary Ni-W-P coating after flow fouling experiment. This work can provide a reference for using anti-fouling coating to prolong the life cycle and cleaning period of equipment. Since the formation of fouling reduces heat transfer efficiency and causes energy loss, anti-fouling is desirable and may be achieved by coating. In this work, a nickel-tungsten-phosphorus (Ni-W-P) coating was prepared on the mild steel (1015) substrate using electroless plating by varying sodium tungstate concentration to improve its anti-fouling property. Surface morphology, microstructure, fouling behavior, and heat transfer performance of coatings were further reported. Also, the reaction path, transition state, and energy gradient change of calcite, aragonite, and vaterite were also calculated. During the deposition process, as the W and P elements were solids dissolved in the Ni crystal cell, the content of Ni element was obviously higher than that of the other two elements. Globular morphology was evenly covered on the surface. Consequently, the thermal conductivity of ternary Ni-W-P coating decreases from 8.48 W/m·K to 8.19 W/m·K with the increase of W content. Additionally, it goes up to 8.93 W/m·K with the increase of heat source temperature 343 K. Oxidation products are always accompanied by deposits of calcite-phase CaCO3 fouling. Due to the low surface energy of Ni-W-P coating, Ca2+ and [CO3]2− are prone to cross the transition state with a low energy barrier of 0.10 eV, resulting in the more formation of aragonite-phase CaCO3 fouling on ternary Ni-W-P coating. Nevertheless, because of the interaction of high surface energy and oxidation products on the bare matrix or Ni-W-P coating with superior W content, free Ca2+ and [CO3]2− can be easy to nucleate into calcite. As time goes on, the heat transfer efficiency of material with Ni-W-P coating is superior to the bare surface. [ABSTRACT FROM AUTHOR]

Falling film evaporators are gaining popularity as substitutes to typical flooded evaporators because of their low refrigerant charge. It is important to form and keep a thin liquid film on the heat transfer surface to ensure their high heat transfer performance. In this study, as a heat transfer enhancement surface, a fine porous surface processed using thermal spray coating was applied to a smooth copper tube with an outer diameter of 19.05 mm. Heat transfer coefficients of falling film evaporation on a single horizontal tube were experimentally evaluated using the HFC-134a refrigerant. The experiments were performed at a saturation temperature of 20 °C with the heat flux ranging from 10 to 85 kW·m−2 and for film Reynolds numbers up to 673. The study aimed to clarify the effect of the coating on the heat transfer characteristics of falling film evaporation. The results revealed that the coating could suppress partial dry out and enhance nucleate boiling in the falling film. The maximum heat transfer enhancement factor was 5.2 in the experimental range. It was further noted that the effect of the coating was especially strong under a low heat flux condition. [ABSTRACT FROM AUTHOR]

This paper mainly studies the heat transfer performance of backplane micro-channel heat pipes by establishing a steady-state numerical model. Compared with the experimental data, the heat transfer characteristics under different structure parameters and operating parameters were studied, and the change of heat transfer coefficient inside the system, the air outlet temperature of the back plate and the influence of different environmental factors on the heat transfer performance of the system were analyzed. The results show that the overall error between simulation results and experimental data is less than 10%. In the range of the optimal filling rate (FR = 64.40%–73.60%), the outlet temperature at the lowest point and the highest point of the evaporation section is 22.46 °C and 19.60 °C, the temperature difference does not exceed 3 °C, and the distribution gradient in vertical height is small and the air outlet temperature is uniform. The heat transfer coefficient between the evaporator and the condenser is larger than the heat transfer coefficient under the conditions of low and high liquid charge rate. It increases gradually along the flow direction, and decreases gradually with the flow rate of the condenser. When the width of the flat tube of the evaporator increases from 20 mm to 28 mm, the internal pressure drop of the evaporator decreases by 45.83% and the heat exchange increases by 18.34%. When the number of evaporator slices increases from 16 to 24, the heat transfer increases first and then decreases, with an overall decrease of 2.86% and an increase of 87.67% in the internal pressure drop of the evaporator. The inclination angle of the corrugation changes from 30° to 60°, and the heat transfer capacity and pressure drop increase. After the inclination angle is greater than 60°, the heat transfer capacity and resistance decrease. The results are of great significance to system optimization design and engineering practical application. [ABSTRACT FROM AUTHOR]

The vacuum tube transportation (VTT) system has been a promising direction of future transportation. Within this system, a high-speed maglev travels in a low-vacuum environment to reduce aerodynamic drag. However, the heat dissipation of on-board heating devices will be compromised under low-vacuum conditions, and the device performance may thus be lowered. This study investigates the low-vacuum conjugate heat transfer characteristic of a levitation electromagnet module of a maglev using an experimentally verified numerical method. During the heating process, the surface temperature distribution of the levitation electromagnet, and the temperature and velocity characteristics of the flow field are examined. It is found that, as the vacuum level increases from 1.0 atm to 0.1 atm, the total heat dissipating from the levitation electromagnet module is decreased by 49% at 60 min, the contribution of convection heat flux over the total heat flux is decreased from 49% to 17%, and the convection heat transfer coefficient of the levitation electromagnet is decreased by 89%. This study can provide an efficient numerical model for low-vacuum heat transfer study on a VTT system as well as help the evaluation and optimization of low-vacuum maglev thermal management systems. [ABSTRACT FROM AUTHOR]

The effects of Reynolds number and nanoparticles on the connector were also studied, revealing that introducing Fe SB 3 sb O SB 4 sb nanoparticles increased overall thermal conductivity and the heat transfer coefficient. Lv et al. [[2]] developed a novel approach to enhance the thermal conductivity of graphene papers by depositing AgNWs on graphene sheets, resulting in a highly promising TIM with a cross-plane thermal conductivity of up to 7.48 W m SP -1 sp K SP -1 sp . Jiang et al. [[4]] investigated the issue of lattice thermal conductivity calculations for two-dimensional (2D) materials and found that hydrodynamic phonon transport plays a crucial role in predicting thermal conductivity in 2D materials such as graphene and silicene. [Extracted from the article]

At present, there are many applications of nanofluids whose research results are fruitful. Nanofluids can enhance the critical heat flux, but the effect on boiling heat transfer performance still has disagreement. Base liquids with higher viscosity improve the boiling heat transfer performance of nanofluids. When the base liquid is a multicomponent solution, the relative movement between the different solutions enhances the microscopic movement of the nanoparticles due to the different evaporation order during the boiling process, so that the boiling heat transfer performance is enhanced. Compared with the thermal conductivity of the heated surface, the deposition of the low thermal conductivity nanoparticles reduces the heat dissipation rate of the heated surface and improves the wall superheat. Then the enhancement of the boiling heat transfer coefficient should be attributed to the thermal conductivity improvement of base fluid and the bubble disturbance resulted from the nanoparticle's microscopic motion. [ABSTRACT FROM AUTHOR]

This study was made to investigate the condensation local heat transfer and adiabatic pressure drop of R134a inside a 2.5 mm outside diameter smooth and microfin tube at low mass flux condition. Data were measured for mass fluxes from 50 to 300 kg m−2s−1, vapor qualities from 0 to 1 and saturation temperatures from 20 to 30 °C. The effects of mass flux, vapor quality, saturation temperature, microfin and diameter of test tube were analyzed. The pressure drop of the microfin tube was about 1.5 times higher than that of the smooth tube at mass flux 50 kg m−2s−1. The heat transfer coefficient of the microfin tube was about 2–5 times higher than that of the smooth tube at mass flux 100 kg m−2s−1. Experimental results were also compared with typical correlations. For the microfin tube, however, all the existing correlations do not adequately predict the present data. Poor predictions may be attributed to the lack of the small diameter microfin tube with low mass flux data in their database. Hence, it is essential to develop a condensation and pressure drop correlation for the small diameter microfin tube at low mass flux condition. [ABSTRACT FROM AUTHOR]

This study investigated the heat problems that occur during the operation of power batteries, especially thermal runaway, which usually take place in high temperature environments. The study was conducted on a ternary polymer lithium-ion battery. In addition, a lumped parameter thermal model was established to analyze the thermal behavior of the electric bus battery system under the operation conditions of the driving cycles of the Harbin city electric buses. Moreover, the quantitative relationship between the optimum heat transfer coefficient of the battery and the ambient temperature was investigated. The relationship between the temperature rise (Tr), the number of cycles (c), and the heat transfer coefficient (h) under three Harbin bus cycles have been investigated at 30 °C, because it can provide a basis for the design of the battery thermal management system. The results indicated that the heat transfer coefficient that meets the requirements of the battery thermal management system is the cubic power function of the ambient temperature. Therefore, if the ambient temperature is 30 °C, the heat transfer coefficient should be at least 12 W/m2K in the regular bus lines, 22 W/m2K in the bus rapid transit lines, and 32 W/m2K in the suburban lines. [ABSTRACT FROM AUTHOR]

The thermal characteristics of a motorized spindle are the main determinants of its performance, and influence the machining accuracy of computer numerical control machine tools. It is important to accurately predict the thermal field of a motorized spindle during its operation to improve its thermal characteristics. This paper proposes a model to predict the temperature field of a high-speed and high-precision motorized spindle under different working conditions using a finite element model and test data. The finite element model considers the influence of the parameters of the cooling system and the lubrication system, and that of environmental conditions on the coefficient of heat transfer based on test data for the surface temperature of the motorized spindle. A genetic algorithm is used to optimize the coefficient of heat transfer of the spindle, and its temperature field is predicted using a three-dimensional model that employs this optimal coefficient. A prediction model of the 170MD30 temperature field of the motorized spindle is created and simulation data for the temperature field are compared with the test data. The results show that when the speed of the spindle is 10,000 rpm, the relative mean prediction error is 1.5%, and when its speed is 15,000 rpm, the prediction error is 3.6%. Therefore, the proposed prediction model can predict the temperature field of the motorized spindle with high accuracy. [ABSTRACT FROM AUTHOR]

The air-side thermal-hydraulic performance of multi-louvered aluminium fin heat exchangers is investigated. A systematic numerical study has been performed to analyze the air-sde thermal hydraulic characteristics over a wide range of Reynolds number i.e., from 30 to 500. Air-side heat transfer coefficient and pressure drop were calculated and validated over the mentioned band of Reynolds numbers. The critical Reynolds number was determined numerically; and also the variation of flow pattern along with the air-side heat transfer coefficient and pressure drop in a multi-louvered heat exchanger associated with Recri has been reported. Moreover, a parametric study of the multi-louvered aluminium fin heat exchangers was also performed for 36 heat exchanger configurations with the louver angles (19-31°); fin pitches (1.0, 1.2, 1.4 mm) and flow depths (16, 20, 24 mm); and the geometric configuration exhibiting the highest air-side heat transfer coefficient was reported. The air-side heat transfer coefficient and pressure drop results for different geometrical configurations were presented in terms of Colburn j factor and Fanning friction factor f ; as a function of Reynolds number based on louver pitch. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of understanding the relationship between fluid flow and heat transfer in industrial quenching systems. It also presents an efficient analysis to design or optimize long standing quenching tanks to increase productivity. The study case is automotive leaf springs quenched in an oil-tank agitated with submerged jets. This analysis combined an efficient numerical prediction of the detailed isothermal flow field in the whole tank with the thermal characterization of steel probes in plant and laboratory during quenching. These measurements were used to determine the heat flow by solving the inverse heat conduction problem. Differences between laboratory and plant heat flux results were attributed to the difference in surface area size between samples. A proposed correlation between isothermal wall shear stress and heat flux at the surface of the steel component, based on the Reynolds-Colburn analogy, provided the connection between thermal characterization and computed isothermal fluid flow. The present approach allowed the identification of the potential benefits of changes in the tank design and the evaluation of operating conditions while using a much shorter computing time and storage memory than full-domain fluid flow calculations. [ABSTRACT FROM AUTHOR]