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To further improve the cooling performance and operation stability of system, the gas-liquid separator enhanced loop thermosyphon/vapor compression hybrid system was proposed. In the thermosyphon mode, the separator was used to reduce the pressure drop of fluid in the two-phase tube for improving the performance of steady-state heat transfer and start-up and the operation stability of system. In the vapor compression mode, the separator was used to make the saturated vapor into the condenser for increasing the mass flow rate in the condenser and enhancing the system coefficient of performance (COP). The simulation model of the hybrid system was developed to investigate the impact of structural parameters on thermosyphon mode performance. The difference of refrigeration performance between the new system and the conventional system in vapor compression mode was comparatively analyzed under the given structural condition of system. The results show that the system performance is the best when the inner diameters of two-phase tube and gas tube are respective 10 mm and 9 mm with separator height and total system height of respective 1.05 m and 1.45 m. Compared with the conventional system, the new system can achieve better performance under any operating condition, and the maximum COP of the new system is improved by 19. 70％. [ABSTRACT FROM AUTHOR]

The mechanical vapor compression system (MVC) coupled with the evaporative-cooling condenser is an effective method to improve its high temperature adaptability. However, this hybrid systems typically use an evaporative cooler as a single-stage pre-cooling unit of condenser and is mainly designed for hot–dry climates. In this paper, based on conventional evaporative-cooling condenser configuration, three two-stage evaporative-cooling condenser systems (MVC-TSEC(A), MVC-TSEC(B) and MVC-TSEC(C)) were proposed. The MVC-TSEC(A) consists of one condenser and an indirect/direct evaporative-cooler. The MVC-TSEC(B) and MVC-TSEC(C) have two condensers (in series), which are coupled with a two-stage evaporative cooling system. The refrigerant in the MVC-TSEC(C) forms a counter-flow configuration with the outdoor air, while it is concurrent flow in MVC-TSEC(B). Subsequently, the effects of the ambient parameters and outdoor air flowrate on the three two-stage hybrid systems were analyzed comparatively based on detailed numerical models. Finally, the application potential of these hybrid systems was evaluated comprehensively in hot–humid climates. The results showed that the seasonal COP and energy-saving rate for the MVC-TSEC(C) are reached by 4.2–4.7 and 12.7–21.1 %, respectively. Moreover, the static equipment payback period of the three two-stage hybrid systems are 3.8, 3.3 and 3.0 years, respectively. [ABSTRACT FROM AUTHOR]

Microchannel heat exchangers are characterized by high heat transfer efficiency and compact volume. The accuracy of microchannel wall temperature measurement directly affects the measurement result of the heat transfer coefficient. The water bath can control the heat flux in the microchannel heat transfer experiment with good uniformity of heat flux distribution and small heat dissipation. However, there is no suitable enough method to accurately measure the wall temperature of the microchannel under the water bath method and bilateral fluid. This paper uses the CFD method to carry out the fluid–solid coupled heat transfer. The measurement errors of six wall temperature measurement schemes in the Reynolds number range from 2400 to 7200 are investigated. The flow field distribution, pressure drop, and turbulent kinetic energy characteristics of different wall temperature measurement schemes are studied. The method of measuring microchannel flat tube wall surface temperature is optimized to solve the problem under a flowing water bath with a traditional resistance temperature detector. The results show that the measurement error of wall temperature caused by the layout method can be reduced to 0.0137 K. The pressure drop and turbulent specific kinetic energy are smaller using the optimal design. [ABSTRACT FROM AUTHOR]

Enhancement of heat transfer characteristics in helical condenser coils by modifying the coil shape has been reported by many researchers. While the influence of different types of condenser coil designs on the operating performance of refrigeration machines for hot water production unit is available in the literature, there exists no published numerical or experimental analysis of the impact of geometric parameter of immersed helical condenser coil on heat transfer characteristics and water velocity distribution during water heating process, which is the subject of our article. With using CFD methodology, a numerical study was carried out to present the water velocity distribution with varying coil parameters such as pipe diameter, tube pitch, and turns number. After validating the numerical model by the experimental ones, the effect of coil parameters on water velocity distribution was examined. The results confirm that by reducing the coil pitch and increasing the tube diameter, an increase of the water velocity and a higher natural convection is obtained. On the other hand, the results indicate that with reducing the turns number, the water velocity and the heat transfer coefficient is also increasing. Indeed, the average water velocity of condenser coil with N = 11 turns is higher than the other two condenser coil structures, which presents 21.34% and 63.56% higher than that of N = 13 turns and N = 15 turns, respectively. Thus, this investigation could provide some guidance to obtain the optimum condenser coil structure for water heating process. [ABSTRACT FROM AUTHOR]

A floatation nozzle can effectively transfer heat and dry without touching the substrate, and serves as a vital component for heat transfer to the substrate. Enhancing the heat transfer performance, and reducing its heat transfer unevenness to the substrate play an important role in improving product quality and reducing thermal stress. In this work, the effects of key structural parameters of the floatation nozzle on the heat transfer mechanism are systematically investigated by means of a numerical simulation of computational fluid dynamics. The findings demonstrate that the secondary vortex structure induced by the floatation nozzle with effusion holes increases heat transfer performance by 254.3% compared with the nozzle without effusion holes. The turbulent kinetic energy and temperature distribution between the jet and the target surface are affected by the jet angle and slit width respectively, which change the heat transfer performance of the float nozzle in different degrees. Furthermore, to improve the comprehensive heat transfer performance of the floatation nozzle structure, taking into account the average heat transfer capability and heat transfer uniformity, the floatation nozzle's design is optimized by the application of the response surface method. The comprehensive heat transfer performance is increased by 26.48% with the optimized design parameters. Our work is of practical value for the design of floatation nozzles with high heat transfer performance to improve product quality in industrial systems. [ABSTRACT FROM AUTHOR]

The VOF model was employed to simulate the pool boiling under typical engineoperating temperature conditions and was experimentally validated. A trapezoidal raised surface morphology with a hydrophilic-hydrophobic combination was designed, and the heat transfer ability and bubble evolution phenomena on the surface were analyzed. Then the variance contribution of each structural parameter of the trapezoidal raised surface to the average surface temperature rise and the average surface heat transfer was evaluated. Finally, the NSGA-II algorithm was used to optimize the structural design of the designed trapezoidal raised surface with the optimization objectives of minimizing the average temperature rise and maximizing the average heat transfer coefficient. Specifically, compared with the hydrophilic smooth surface, the optimized structure showed an increase in the average heat transfer coefficient by 194.5% and a decrease in the maximum average temperature rise, AT, by 33.9%. [ABSTRACT FROM AUTHOR]

A prototype of a multistage cooling system with a cooling capacity of 20 kW is assembled and studied. The traditional single-stage system is split into two sub-systems according to the temperature level, which reduces the temperature difference and irreversible heat transfer loss, and further improves the system's energy efficiency. The system mainly features three modes including free-air cooling, refrigeration-based cooling and waste heat recovery, which can achieve efficient cooling while capable of recovering the waste heat to the surrounding heat users. The efficiency of the proposed cooling and heat recovery system was assessed by measuring its energy reuse effectiveness (ERE). The energy savings and environmental benefits of the system were analyzed across five cities in China, each representing different climates. Results indicate that the system achieved an ERE of 0.91 in Beijing, 38.9 % lower than the national average of the city. Additionally, an economic analysis showed a payback period of less than two years for the proposed system across all climates considered, which is 30 % shorter than that of a single-stage cooling system. • A multi-stage data center cooling system with waste heat recovery is proposed. • Temperature gradation reduces heat transfer temperature difference and irreversible loss. • Heat transfer performance of a 20 kW scale system is experimented and analyzed. • Energy Reuse Effectiveness in Beijing is 0.91, and payback period is within 2 years. [ABSTRACT FROM AUTHOR]

Weaire-Phelan (thereafter W-P) structures, as a foam-liked structures, were widely used in the field of flow and heat transfer. The effect of various methods for removing connecting struts on the flow and heat transfer characteristics of W-P structures was investigated, while maintaining constant porosity for all structures. Furthermore, the influence of porosity on the optimal strut removal scheme for W-P structures was examined. Computational fluid dynamics (CFD) was employed to analyse the flow and heat transfer characteristics of these structures. Additionally, four representative structures were created through 3D printing technology to experimentally validate the results. The effects of geometric structure parameters on the flow resistance and heat transfer characteristics of different structures were also analysed in depth. The findings indicate that all the proposed methods for removing connecting struts result in a reduction in pressure drop of up to 20.2 %. However, the most overall heat transfer performance (OHTP) was achieved when only the symmetry direction connecting struts were removed. Furthermore, as porosity decreases, the improvement in OHTP with the strut removal scheme becomes more significant compared to the original W-P. This study provides ideas for the optimisation of complex strut structures. [ABSTRACT FROM AUTHOR]

• A micro-liquid cooling system with direct integration of the piezoelectric micropump and heat sink is proposed. • The influence of the copper electrode-to-PZT ratio affected on the performance of the piezoelectric micropump was investigated. • The guidance structure with the fish scale shape is designed and optimized based on the diffuser/nozzle principle. • A simulation model incorporating many physics is developed for piezoelectric micropump cooler(PMC). • Investigations are conducted into PMC's cooling capabilities and operating limit. Micro-liquid cooling is highly effective for the thermal management of electronic chips. However, it is challenging to apply to high heat flux and compact electronic devices because of the limited cooling power and large pump volume. To address this issue, a compact piezoelectric micropump cooler (PMC) integrating a parallel piezoelectric micropump (PPMP) and a heat sink with a fluid guidance structure is designed. The flow and heat transfer performance of the PMC is theoretically optimized through a numerical coupling model considering mechanics, flow-solid heat transfer, and piezoelectric effect. Simulation results suggest that a copper electrode-PZT ratio of 1.4 increases the output flow rate of the PMC, and the design of five fluid guidance structures enhances its heat dissipation effectiveness. Based on the optimized results, the PMC prototype is manufactured employing 3D printing technology. Experimental results show that the flow rate maximum is 62 mL/min with a precision of 0.07 mL/V·min. When the flow rate of PMC increases to 50 mL/min, the temperature of a heat source with 50 W/cm2 can be reduced to 57 °C, which is comparable with the simulation value. The developed model accurately characterizes the heat transfer properties of the PMC thermal management approach, providing a valuable reference for future research. The proposed PMC is characterized by its compact size, high level of integration, and exceptional cooling performance, making it suitable for electronic cooling applications with high heat flux. [Display omitted] [ABSTRACT FROM AUTHOR]

With the application of microdevices in the building engineering, aerospace industry, electronic devices, nuclear energy, and so on, the dissipation of high heat flux has become an urgent problem to be solved. Microchannel heat sinks have become an effective means of thermal management for microdevices and enhancements for equipment due to their higher heat transfer and small scale. However, because of the increasing requirements of microdevices for thermal load and temperature control and energy savings, high efficiency heat exchangers, especially microchannels are receiving more and more attention. To further improve the performance of microchannels, optimizing the channel geometry has become a very important passive technology to effectively enhance the heat transfer of the microchannel heat sink. Therefore, in this paper, the microchannel geometry characteristics of previous studies are reviewed, classified and summarized. The review is mainly focused on microchannel geometry features and structural design to strengthen the effect of heat transfer and pressure drop. In addition, the correlation between boiling heat transfer and geometric characteristics of microchannel flow is also presented, and the future research direction of microchannel geometry design is discussed. [ABSTRACT FROM AUTHOR]

This paper discusses the heat transfer process for a typical stator–rotor machinery-hydrodynamic retarder from the perspective of computational fluid dynamics and experimental means. Fluid cooling is an essential step in the working process of hydrodynamic retarders, and changes in viscosity along with temperature rise will affect the performance of braking. To investigate the heat transfer process of stator–rotor machinery, a novel computational fluid dynamics (CFD) method, combined with a dynamic thermophysical property transfer algorithm, is proposed. A heat-flow coupling numerical method with experimental verification is proposed, in which the density and the viscosity are variable with the temperature in an effectiveness–number of transfer units (P-NTU) method. The results show that the numerical results are in good agreement with the experimental data, with a 0.1–2.5% error. The influence of an asymmetric structure on heat transfer characteristics is discussed. The results show that the optimal braking performance, along with the liquid cooling performance, is achieved under outlets with an inlet passage set as 90 degrees. [ABSTRACT FROM AUTHOR]

Latent heat storage technology is widely used in solar power generation. Aiming to enhance the energy utilization rate to a greater extent, an innovative fan-shaped structure has been proposed to construct the metal fins of the shell-and-tube thermal storage device. The enthalpy method is used to simulate the heat storage process and focuses on the influence of inlet conditions on heat transfer. The influence of the fin structure on the melting properties of phase change material has been studied. The results show that increasing inlet temperature and inlet flow rate is a convenient and effective way to improve energy efficiency. As the inlet temperature is increased from 343 K to 358 K, the total heat storage and energy efficiency are improved by 13.4% and 10.2%, respectively, and the melting time is reduced by 36.2%. As the flow rate is increased from 3 L/min to 9 L/min, the complete melting time is reduced by 33.4%. Energy efficiency peaks at a flow rate of 5 L/min. Reasonable optimization of the fin structure can enhance the natural convection circulation during the melting process and further improve the energy efficiency. The research results can guide the design and structural optimization of the finned tube heat storage device. [ABSTRACT FROM AUTHOR]

As the dynamic random access memory (DRAM) chip tends to the larger storage capacity by die stacking, the 3D die stacking requires thermal modeling for fast temperature predicting and initial design. This work presents a theoretical model capable of fast calculating and optimizing the temperature of each die. The improved thermal network defines equivalent shape correction parameters to improve the calculation accuracy of the thermal network. The 3D die sacking derives a novel topology of improved thermal network through the division of the heat transfer path inside DRAM. The analysis demonstrates that the calculating results of improved thermal network show good consistency with the finite element method in steady and transient states thermal analysis. Beyond this, the effect of size and thermal power is discussed in the calculation accuracy. The improved thermal network is used in the optimization design of DRAM with eight-dies vertical stacking. The maximum temperature increment is reduced by 15% after optimization. • The improved thermal network of DRAM considers all heat transfer paths in the 3D die stacking. • The shape correction parameters are defined to improve the calculation accuracy of the improved thermal network. • The effects of size and thermal power on the calculation accuracy of the improved thermal network are analyzed. • The model effectiveness is verified by an optimization design of DRAM with eight-die stacking. [ABSTRACT FROM AUTHOR]

A new coupled numerical model of the overall vapor-compression cycle and water heater was developed in order to analyze the influence of condenser coil designs on the heat transfer process of a helical coil heat exchanger immersed in a storage tank. The model was developed using the CFD code ANSYS Fluent. In the numerical simulation, the helical condenser coil was treated as an internal heat source and the initial heat flux was obtained from experimental results and delivered to each coil element in the CFD model as boundary condition. The coupled model was validated with experimental results and showed that the numerical results of the proposed model are in good agreement with the experimental data with the deviation of ± 1.6%. Then, the impact of the main representative geometrical parameter on the overall heat transfer coefficient and water temperature distribution was investigated. The results indicated that the temperature distribution and overall heat transfer coefficient increase with the increase of the pipe turns of a helically coiled tube heat exchanger. [ABSTRACT FROM AUTHOR]

In this study, a high voltage heater system with a size of 310 mm × 210 mm × 60 mm has been numerically studied and experimentally verified to explore the influence of the cavity structure on the flow and heat transfer performance. The response surface model and analysis of variance are used to determine the influence of the length of the mainstream area of the inlet, Lin, the length of the mainstream area of the outlet, Lout, the length of the parallel flow channel, Lch, and the single channel width, W, on the flow heat transfer, and ultimately find the best structural plan. The results show that the structural parameters of the parallel flow channel are significantly more important than those of the mainstream area, with the width and length of the parallel single channel being the primary and secondary structural parameters, respectively. The optimization scheme obtained by the NGSA-II algorithm can simultaneously meet the requirements of heat transfer and flow uniformity. Specifically, compared with the original model, the flow distribution uniformity coefficient, S, and the inlet/outlet pressure drop, Ptotal, decreased by 53.49% and 19.52%, respectively, while the average heat transfer coefficient increased by 28.05%. [ABSTRACT FROM AUTHOR]

• Radiator models with different dry ice inlet and outlet positions are proposed. • Dry Ice with low temperature and sublimation latent heat is used as a coolant. • Influence of radiators on the temperature field, speed field and cooling time are Simulated. • A radiator model with optimum coupling of velocity and heat transfer is obtained. Based on the cooling characteristics of dry ice on high heat flux chip, a variety of radiator models with different dry ice inlet and outlet positions are proposed in the present study. The influence of these radiator models on temperature field, velocity field, dry ice distribution and chip cooling time are analyzed. The results demonstrate that when the diameter of inlet and outlet is 12 mm and the chip power P 0 = 95W, the average temperature of all models' chip bottom has reached below 50 °C when t = 70 s. The inlet of Model g is located in the center of the upper surface of the radiator and the outlet is located in the center of the side surface, the chip overall temperature of Model g is the most uniform distribution with 90% of the area temperature at 25 °C. Model g combines the advantages of the phase change heat transfer and the jet impingement heat transfer, which can realize the optimal coupling of the flow rate and the heat transfer, ensuring the safety and reliability of the chip more effectively. Moreover, the results of simulation and optimization are in good agreement with the relevant experiments, laying a foundation for further optimization of the structural scale of the radiator and better coupling of the heat flow field of the dry ice cooling system. [ABSTRACT FROM AUTHOR]

With the application of microdevices in the building engineering, aerospace industry, electronic devices, nuclear energy, and so on, the dissipation of high heat flux has become an urgent problem to be solved. Microchannel heat sinks have become an effective means of thermal management for microdevices and enhancements for equipment due to their higher heat transfer and small scale. However, because of the increasing requirements of microdevices for thermal load and temperature control and energy savings, high efficiency heat exchangers, especially microchannels are receiving more and more attention. To further improve the performance of microchannels, optimizing the channel geometry has become a very important passive technology to effectively enhance the heat transfer of the microchannel heat sink. Therefore, in this paper, the microchannel geometry characteristics of previous studies are reviewed, classified and summarized. The review is mainly focused on microchannel geometry features and structural design to strengthen the effect of heat transfer and pressure drop. In addition, the correlation between boiling heat transfer and geometric characteristics of microchannel flow is also presented, and the future research direction of microchannel geometry design is discussed.

[Display omitted] • A review of the structural optimization of RCP (radiant cooling panel) was conducted. • Systematically analyzed the status of heat transfer performance parameters of RCP. • Comprehensive introduction and mechanism analysis of RCP structural optimization methods. • The adaptability and engineering prospects of the optimization methods were assessed and justified. Radiant cooling, as an energy-saving, thermal comfort-enhancing, and noise-free air conditioning technology, has garnered increasing attention in recent years. But the risk of condensation and the resulting issue of insufficient cooling capacity becomes prominent when applied in high-heat and humidity regions such as East Asia. Structure optimization of radiant cooling panels is a crucial approach to address these issues, and many scholars have conducted research on the past decade. However, it is rarely comprehensive reports on those optimization methods due to the independently researched and innovated by different paths. This paper provides a comprehensive review of various optimization methods for radiant cooling panels including enhanced heat transfer design, surface treatment, and material selection, and then analyzes the implementation mechanisms, as well as the advantages and disadvantages of its engineering applications. Finally, an analysis of the future development of radiant cooling panels was presented from a practical application perspective. It is intended to support the research on the optimization of radiant cooling panels and the increasing applications of radiant cooling systems worldwide. [ABSTRACT FROM AUTHOR]

Based on innovative design, a liquid–vapor separation plate condenser with excellent heat transfer performance is invented. It takes less time to discharge condensate from the refrigerant channel and get a thinner liquid film in condensing channel with the new-type condenser than with the conventional one. The evaluation of the heat transfer performance of the liquid–vapor separation plate condenser and the optimization of its structure design is realized with a validated mathematical model. In this numerical simulation, the performance evaluation criterion and penalty factor are used to assess the refrigerant side performance, while the exergy efficiency is used to evaluate the overall performance, which includes the water-side performance. According to the simulation results, the optimal structure of the liquid–vapor separation plate condenser is achieved when altitude ratio is equal to 0.6 and length ratio is equal to 0.5. In this structure, when the condensation temperature of refrigerant R410A is 20 °C, the heat flux is kW m−2, the mass flux is 50 kg m−2 s−1, the performance evaluation criterion is at 1.13, the penalty factor is at 0.89, and the exergy efficiency is at 0.34. All these values outperform those of conventional plate condenser. Compared with conventional one, the heat transfer coefficients of refrigerant of liquid–vapor separation plate condenser increase by 15.98%, and its the pressure drop increases by 16.45% under the setting conditions. [ABSTRACT FROM AUTHOR]

• The critical dimensions of various types of GHEs have been counted and analyzed in recent years. • The effect of structurally optimized new types of GHEs on heat transfer is presented. • New refrigerants in heat pumps are introduced. • The application of backfill materials in recent years is analyzed. With its ability to accomplish heat transfer, the ground heat exchanger (GHE) is a crucial component of a ground source heat pump system. Numerous research on various kinds of GHEs have been conducted recently, which has substantially increased their ability to transmit heat. This study aims to present an extensive overview of current research on the newest advancements in GHE technology. A brief description of the various forms of GHEs is given, along with a tally of the actual sizes of Helical coil type and u-type GHEs installed in recent years. The impact on the heat transfer effect of many novel forms of GHEs with optimized structures is discussed. It has been demonstrated that the structure-optimized GHE significantly improves heat transmission. The idea is to improve the GHE's thermal performance by expanding the heat transfer area while keeping the traditional drilling depth. The use of backfill materials, including controlled low strength materials (CLSM), graphite, and bentonite, is examined, and a brief overview of the most current developments in backfill materials is provided. The impact of altering the ratios and adding new materials to the backfill on the heat transmission of buried pipes is examined. Furthermore, different modes of operation of GHEs are investigated and assessed, and the employment of various types of novel refrigerants in the cooling and heating cycles of ground source heat pumps is discussed. Lastly, future prospects, ideas, and recommendations for GHE research are discussed. [ABSTRACT FROM AUTHOR]

The heat transmission properties of the cooling stave were examined using a numerical simulation approach and compared with copper cooling stave and copper steel composite cooling stave under different furnace conditions and different structures. It is found that the existence of the steel layer greatly raises the maximum temperature of the cooling stave when no slag is present, and its hot surface temperature is 152 °C greater than that of the copper cooling stave. However, under typical operating conditions, the hot surface temperature of the steel layer is still below its limit working temperature of 470 °C. The temperature of the cooling stave rises with the temperature of the gas and the temperature of the inlet water and reduces with increasing water inlet velocity and slag thickness. To efficiently lower the temperature of the hot surface steel layer, the operation should ensure that the hot surface gas temperature is kept within 1300 °C, the cooling water speed is raised to 2.4 m/s, and the slag thickness should be set to 15 mm or higher. The optimal construction for a steel-copper-steel composite cooling stave is to keep the thickness of the steel layer at 11.9 mm and the thermal conductivity around 40 W/(m·K). [ABSTRACT FROM AUTHOR]

Aiming at the heat sink with dual insulated gate bipolar transistor (IGBT) modules in a direct current to direct current (DC‐DC) converter, the calculation of the temperature field of the cooling structure with low power consumption is completed by using Icepak simulation software, and analysis of the influence of the two IGBT module installation distance on the maximum temperature. The simulation results show that the maximum temperature of two heat sources decreases with the installation distance, but the maximum decline is not more than 0.5 °C. Based on field synergy theory, it is found that the local structure of the heat sink is not conducive to the natural convection heat transfer. Therefore, the improved measures of slotting the plate are proposed, and the effectiveness of this measure to reduce the heat source temperature is verified by simulation analysis and experiment. The influence of slot size on the maximum temperature of heat source is analyzed: the maximum temperature of heat source decreases with the increase of slot size. When the slot size is 16 mm, the cooling effect is obvious, and the maximum temperature drop is up to 6 °C compared with that before the slotting. Besides, the slot processing can also reduce the heat sink material and reduce the weight. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In agricultural equipment, heat exchangers are mainly used for heat exchange and full utilization. Based on the theory of enhanced heat transfer, we establish a reasonable mathematical model and physical model for the multi-degree-of-freedom spiral plate type agricultural machinery heat exchanger, and use the FLUENT numerical simulation software to add the spiral disturbing fluid to the spiral plate heat exchanger flow channel. Numerical simulation and further optimization simulation of the fluid-conducting conditions with poor heat transfer effect were carried out, and an optimal arrangement of two kinds of spiral-shaped turbulent fluids with constant curvature and variable curvature was determined. The heat transfer effect of the fixed-curvature spiral-shaped disturbing fluid is superior. Further optimize the structure of the disturbing fluid. When the diameter of the disturbing fluid increases, the heat transfer can be enhanced; thus, the diameter of the disturbing fluid plays an important role in enhancing the heat transfer effect. [ABSTRACT FROM AUTHOR]

Based on the volume of fluid algorithm and user-defined function, the flow and heat transfer of falling film on an elliptical transverse tube with different axis ratios was numerically studied. Simulation results are discussed based on the velocity, pressure, and temperature distribution of the liquid. According to the results, the liquid film pattern, heat and mass transfer of the liquid film are affected by the axis ratios: the liquid flow rate of the film outside the elliptical tube was faster compared with a circular tube; the simulated wall pressure gradually decreased along the flow direction and then rapidly recovered, and the position of the minimum pressure moved backwards with the increase of the axis ratio. Also, the distribution of local Nu along the wall was similar to the pressure distribution with the minimum value of X = 0.90. In general, the heat transfer of an elliptical tube performs best when the axis ratio is e = 1.65. The simulated Nu number distribution and film thickness were compared with published experimental data, which showed acceptable consistency. [ABSTRACT FROM AUTHOR]

In order to optimize the structure of heating system and improve heating efficiency， a numerical model was built to study heating transfer in vacuum carburizing furnace using COMSOL finite element software. The effects of key structural parameters such as number， length and distribution radius of graphite heating tube on the heat flux of workpiece surface and the temperature distribution of effective heating zone were studied. The results show that when the number， length and distribution radius of heating tubes decrease， the heat flux density increases and the heating efficiency improves. Moreover， when setting the number of heating tubes into even， decreasing the length and increasing the distribution radius can improve the temperature uniformity in effective heating zone. The findings can provide guidelines to optimize the structure of heating system in vacuum carburizing furnace. [ABSTRACT FROM AUTHOR]

The thermal deformation has a significant effect on the processing precision of the machine tool. In this paper, a simulation model and an experimental method of the thermal performance were proposed for a roll grinder. The calculation methods of thermal boundary conditions including the heat power caused by the spindle motor with water cooling, headstock motor with air cooling and hydrodynamic bearings, the convective heat transfer coefficients of the rotating surface at different spindle speeds, and machine tool contact resistance were provided to establish a high-precision FEM model. Based on the achieved key temperature points in the simulation, thermal characteristic experiments were carried out at different spindle speeds with 18 temperature sensors and three displacement sensors. The experimental results of the temperature field and thermal displacement were then compared with the simulation results to verify the effectiveness of the constructed finite element model. Finally, three kinds of optimization schemes of the roll grinder structure were discussed to further improve the thermal performance. The simulation results indicated that the thermal deformation of the spindle decreased in the X- and Y-axis directions. [ABSTRACT FROM AUTHOR]

In order to address the instability of the fixation in the temperature controlled quartz crystal microbalance (QCM), a new sensor structure was proposed and evaluated under different dew point conditions. The QCM was fixed by two O-ring thermal gaskets placed on both sides symmetrically with the constraining forces. Simulations by finite-element modeling were performed to determine the O-ring thermal gasket dimensions and the constraining forces. Results showed that the QCM structure had steady vibration properties with high heat transfer rates, when the constraining force value was less than 0.06 N, and the O-ring thermal gasket width ranged from 0.6 to 1.0 mm with a thickness of 0.5 mm. Experiments were carried out to evaluate the accuracy, stability, and repeatability of the sensor and results showed that the designed sensor had good performances compared with the standard instrument. [ABSTRACT FROM PUBLISHER]

To accurately evaluate the heat transfer effect and ensure the safe and stable operation of heat exchanger, a new heat transfer evaluation index η was proposed, which was equal to the ratio of convection heat transfer coefficient to the one-third power of pressure drop. With special consideration of the effect of pressure drop on heat exchange, the baffle structure was simulated and optimized by CFD software. The optimized baffle spacing was determined, and the optimized baffle cut height was then determined. The results show that with the increasing of baffle spacing and cut height, fluid velocity, pressure drop and convection heat transfer coefficient are decreased, while heat transfer evaluation index is decreased with latter increasing. The heat transfer effect is dependent on convection heat transfer coefficient and pressure drop. For the specific heat exchanger with the length of 1 632 mm, the optimal heat transfer effect was obtained under the conditions with baffle spacing of 350 mm and baffle cut height of 0.375D. The simulation results are in good agreement with the results of the baffle structure of heat exchanger in atmospheric-vacuum distillation unit of a refinery. [ABSTRACT FROM AUTHOR]

Thermal error is one of the main errors in ultra-precision machine tools. This paper presents a thermodynamics-based structure optimization method to reduce the thermal displacements of machine tools during operation. The method makes use of the thermal-structure coupled model to analyze the thermal behavior considering the thermal contact resistance and the temperature rise of the oil film in hydrostatic spindle. The structure of the motor link, spindle, and headstock of grinder are optimized by setting appropriate gaps in the contact region of two neighboring parts to change the heat transfer distribution and minimize the thermal displacement of the spindle center position. The proposed method is validated by an equivalent thermal conductivity-based simulation method and experiment on an ultra-precision grinding machine tool. Experimental results show that the proposed method can provide an important instruction on how to reduce the thermal error for the design of the precision machine tools, especially for those with key parts placed near the heat sources. [ABSTRACT FROM AUTHOR]

• The entransy dissipation rate model and the flow resistance model were developed. • The objective function was established based on the linear programming method. • The comprehensive performance of the optimized structure has been improved by 30%. • The smaller the number of branching levels, the better the comprehensive performance. The heat transfer performance and flow performance of microchannel convective heat transfer processes are usually mutually constrained. However, we expect microchannel heat sinks to have both excellent heat transfer and good fluidity. In order to achieve a balance between heat transfer and fluidity, we established an optimization objective function of a complex network structure based on the linear programming method. This composite objective function included both the entransy dissipation rate model to express the heat transfer performance of the fractal microchannel heat sink and the pump power model to express its flow performance. Under the same initial values and constraints, we optimized the objective function. Finally, the comprehensive performance of the optimized structure (OPTS) and the randomly designed initial structure was compared through experiments. The experimental results show that the comprehensive performance of the OPTS was always better than the initial design structure (INDS) under any conditions, and the performance of the optimized structure with fewer fractal levels was better. Within the scope of the study, the average comprehensive performance of the OPTS was improved by a minimum of 14% and a maximum of 30% relative to the INDS. This validates the rationality of the optimization method proposed in this study. We have theoretically and experimentally solved the active optimization problem of how many levels of fractal structure should be designed in a constant space and what the channel size of each level is when the heat sink has optimal performance. [ABSTRACT FROM AUTHOR]

• The guide vane is added to the air inlet chamber of the intercooler. • An end-to-end model of the intercooler guide vane based on PSO-SVR algorithm. • Structure parameters of guide vane are optimized using genetic algorithm. In order to fundamentally solve the problem of poor air flow uniformity in the cooling pipe of the heavy-duty vehicle intercooler, which leads to poor heat exchange effect, this paper innovatively proposes to add a guide vane in the air chamber of the intercooler. The air flow uniformity in the cooling pipe of the heavy-duty vehicle intercooler is investigated under different structural parameters of guide vane based on the established end-to-end model. In fact, the end-to-end prediction model is innovatively proposed to characterize the relationship between the structural parameters of guide vane and performance parameters without conducting the high-cost and long-term experiments or numerical simulation. Besides, structure parameters of guide vane with the optimal airflow uniformity coefficient are obtained using genetic algorithm (GA), that is, the diversion angle (α) is 18°, the width of rectangular holes in the guide vane (L) is 6 mm and the number of rectangular holes in the guide vane (N) is 3. To demonstrate the effectiveness of the proposed method, the optimized intercooler is validated and it is found that the airflow uniformity coefficient of the optimized intercooler is 0.983, which is 5.25% higher than the original structure, the outlet temperature is reduced by 8.2 °C. [ABSTRACT FROM AUTHOR]

The thermal performance enhancement of pin-fin structures for IGBT cooling in high voltage heater (HVH) system is numerically investigated and experimentally verified in this study. The results revealed that there may be a risk of thermal failure of the IGBT in existing HVH systems. Additionally, a new heat exchanger was designed with pin-fin structures to enhance heat transfer for cooling the IGBT component. To analyze the influence of pin-fin parameters on the cooling effect, a L16(4̂5) orthogonal array was selected to identify the main and secondary parameters, then the optimal combination scheme was found. The sensitivity analysis result showed that the diameter of the pin-fin had the greatest influence on the amount of heat transfer, and the height of pin-fin is the second. For cooling uniformity, height is the most important parameter and the diameter is the second. The optimization scheme obtained by orthogonal design could simultaneously meet the requirements of heat transfer and cooling uniformity. Compared with the original model, the maximum temperature and the maximum difference of the average temperatures of the IGBT chip layer decreased 9.4% and 14.6%, respectively. [ABSTRACT FROM AUTHOR]

The multi-chamber arc-extinguishing structure (MAS), which consists of a lot of semi-closed short-gap arc-extinguishing chambers (SSAC) in series, can be used in parallel gap lightning protection devices to improve the ability to extinguish power frequency follow current. The arc-extinguishing ability of single SSAC directly affects the arc-extinguishing performance of the whole MAS. Therefore, the arc-extinguishing performance of MAS can be improved by optimizing single SSACs. A two-dimensional model of the arc plasma in a SSAC is built based on the magneto-hydrodynamic (MHD) theory. The motion characteristics of an arc in the SSAC are simulated and analyzed. An optimization method of the SSAC structure is proposed. Finally, an impact test platform is built to verify the effectiveness of the optimized SSAC structure. Results show that the short-gap arc forms a high-speed airflow in the SSAC and the arc plasma sprays rapidly to the outlet until the arc is extinguished at its current zero-crossing point. The amplitude of airflow velocity in the optimized structure can be increased to about 8-fold the velocity in the basic structure. Experiments also show that the dissipation time of an arc in the optimized SSAC is 79.2 μs, which is much less than that in the original structure (422.4 μs). [ABSTRACT FROM AUTHOR]