With the rapid development of energy storage, traditional thermal management technologies cannot meet the lightweight and high-efficiency development needs of energy storage systems. Therefore, this paper focuses on the application of direct cooling thermal management technology in energy storage systems, aiming to reveal the temperature regulation laws of direct cooling on energy storage systems under different ambient temperatures and solve the problems of high-temperature overheating and uneven temperature distribution. First, the study established an experimental system and a numerical calculation method (with an error of only 3.2 % between the experimental and numerical results). Then, it used the collaborative method of "multi-condition experiments and numerical calculations" to explore the influence and action mechanism of different ambient temperatures on the temperature field of the energy storage system. It also tested the improvement effect of changing the subcooling degree of the direct cooling system on temperature uniformity performance, and finally reconstructed the system architecture to optimize performance. The results show that in a high-temperature environment, due to factors such as gravity and the outlet superheat of the expansion valve, the liquid phase proportion of the upper battery pack drops sharply by 50 %, leading to excessive temperature rise and temperature difference that exceed the standard, and the improvement effect of adjusting the subcooling degree is poor. To address this, the "dual-core phase-separated intelligent direct cooling system" is proposed. Through the collaboration of dual compressors, phase separation by dual gas-liquid separators, and regulation by bidirectional stop valves, uniform distribution of refrigerant is achieved (with a flow deviation of <= 1.02 % for each battery pack). Under high temperature, the maximum temperature of the energy storage system is 309.3 K, and the temperature difference is only 4.7 K, significantly improving temperature uniformity under high temperatures. Different from previous studies focusing on power batteries, this study takes more complex energy storage systems as the research object, establishes and verifies a numerical model, explores the temperature influence mechanism of direct cooling on the full temperature range of energy storage systems and the effect of subcooling degree. It also breaks through the traditional single-component optimization framework, solves the problem of uneven distribution with a system-level phase-separated architecture, and reduces the complexity and failure risks of both thermal management and energy storage systems.

The heat transfer performance of the thermal management system plays a crucial role in the hydrogen-powered aviation engine cycle. As an exceptional fuel, the thermophysical parameters of hydrogen change drastically with temperature in the trans-critical state. While previous studies on heat transfer enhancement mainly focused on changing the geometrical structure, few studies have been conducted on realizing heat transfer enhancement based on the properties of the fluid itself. Utilizing the drastic changes in thermophysical parameters of hydrogen in the trans-critical state to achieve heat transfer enhancement could greatly contribute to the thermal management system of the hydrogen-powered cycle. In this study, a trans-critical process control method for heat transfer enhancement based on multidirectional impact flow distribution is proposed. The distributions and variation patterns of temperature, density, specific heat capacity, and equivalent thermal conductivity along the flow directions were investigated, the flow and heat transfer performance of the channel optimized by the proposed method was numerically simulated, and the control of the trans-critical process and the mechanism of heat transfer enhancement were analyzed. The effects of the key design parameters such as flow distribution ratio, number, and spacing of gaps on the flow and heat transfer performance of the heat transfer unit were comparatively analyzed by taking various factors into account, and finally, a relatively optimal combination of key design parameters was obtained.

Gradual overheating of the engine accessories occurs as the speed of the aircraft increases. In order to establish an efficient accessory thermal management system (TMS), this paper carries out a comprehensive integrated study of the cabin's thermal environment, accessory thermal protection and accessory system thermal management based on five typical accessories in the cabin of a specific high-speed turbine engine. This study is based on an experimentally validated numerical method for simulating the cabin thermal environment. Firstly, the study investigates the thermal characteristics of the cabin, heat load distribution among the accessories, and the underlying causes of accessory over-temperature. The findings reveal that the thermal protection requirements for the five accessories vary according to their heat source sizes. Specifically, accessories with larger heat sources require cooling via lubricating oil, while smaller heat source accessories can benefit from the addition of aerogel to further lower surface temperatures. For accessories with high thermal loads, the integration of RAF-89 wing fins in the flow path can save up to 69.2% of the minimum lubricating oil flow required for cooling. Additionally, various flow path layouts for the accessories were designed and evaluated through a thermal protection evaluation model to determine the optimal combinations of protection strategies, the corresponding temperatures of accessories 1 to 5 are 335.0 K, 340.7 K, 361.1 K, 393.3 K, and 399.8 K, respectively, which meet the requirement that the accessory temperatures do not exceed 400 K. Lastly, a thermal management optimization model is developed, incorporating multiple performance indexes, including liquid nitrogen demand, cooling capacity utilization, cost of TMS, fuel compensation losses, and energy utilization efficiency. The model is applied to optimize the initial TMS, resulting in a 10 % improvement in overall system performance.

Recent experiments have indicated that employing nanostructures can enhance interfacial heat transport, but the mechanism by which different structural morphologies and dimensions contribute to the full-spectrum phonon interfacial transport remains unclear. In this paper, a multiscale method to study the thermal transfer at nanostructured interfaces is developed by combining the density functional calculation, Monte Carlo simulation, and diffuse mismatch method. The changes in the transport paths and contributions to the thermal conductance of different frequency phonons caused by the changes in the nanostructure morphology and size are investigated. The results show that, compared to the triangular and trapezoidal nanostructures, rectangular nanostructures are more beneficial in enhancing the probability of the reflected phonons encountering the interface and, thus, the phonon interfacial transmittance. The nanostructure makes the interfacial heat flow extremely heterogeneous, with significant transverse heat flow occurring at the sidewalls, resulting in a new thermal conduction pathway. The phenomena of multiple reflections and double transmission together lead to the existence of the optimal dimension that maximizes the nanostructure’s enhancement effect on interfacial heat transfer. The optimal nanostructure width is 100 nm when the height is 100 nm and the maximum interfacial thermal conductance enhancement ratio is 1.31. These results can guide the design of heat transfer enhancement structures at the interface of the actual high-power chips.

High temperature thermal contact conductance is a crucial parameter affecting the performance of thermal control and thermal protection systems in many engineering applications under extreme conditions. In this paper, the rough surface of high temperature Inconel 718 alloy (HTA) was characterized and reconstructed based on fractal theory satisfied with a three-dimensional W-M function. The mechanical deformation of contact model was estimated in considering three types of mechanics at the contact points: elastic, elastoplastic, and plastic. The heat transfer between contact surfaces was analyzed account for the conduction of contact points and the radiation between rough surfaces under high temperature conditions. The effects of pressure (0.1-0.6 MPa), temperature (650-1100 K), and fractal parameters on thermal contact conductance were studied through the proposed model. The results show that the contribution of solid conduction and radiation to total thermal contact conductance increases from 45% to 73% and from 14% to 27% with increasing pressure and temperature, respectively. Also, the thermal contact conductance increases with decreasing and increasing the fractal parameter of D and G, respectively, due to the simulated surface becomes smoother. And the variation tendency is more significant at higher interface pressure. Additionally, the accuracy of the thermal contact resistance prediction model was validated by comparing the predicted results with experimental data.

Heat transfer enhancement of N-Ga-Al semiconductor heterostructure interfaces is critical for the heat dissipation in GaN-based electronic devices, while the effect of the AlxGa(1-x)N transition layer component concentration and thickness on the heat transfer mechanism at the GaN-AlN interface is unclear. In this paper, using molecular dynamics simulations based on machine learning potentials, the interfacial thermal conductance (ITC) between GaN-AlxGa(1-x)N, AlN-AlxGa(1-x)N and GaN-AlxGa(1-x)N-AlN heterostructure interfaces are calculated for different transition layer thicknesses with different concentrations of Al fractions, and the reasons for the change of ITC and its heat transfer mechanism were explained by the phonon density of states and the spectral heat current. GaN-AlN heterostructure ITC at 300 K is calculated to be 557 MW/(m2K), and the ITCs of GaN-Al0.5Ga0.5N and AlN-Al0.5Ga0.5N are improved by 128% and 229% compared to GaN-AlN, whereas the ITCs of GaN-Al0.7Ga0.3N-AlN containing a 0.5 nm transition layer improved by 27.6%. This is because elemental doping enhances phonon scattering near the interface thereby promoting phonon energy redistribution, but the bulk thermal resistance of the AlxGa(1-x)N layer also increases rapidly with increasing doping ratio, and ITC is affected by a combination of these two factors. This work aims to understand the mechanism of transition layer component concentration and thickness on the heat transfer at the GaN-AlN contact interface, which provides a useful guide for better thermal design of the GaN-AlN heterostructure interface.

The use of modeling and simulation methods for engines is considered an important part of the aircraft design process. However, the traditional approach is complicated and time-consuming. In this work, a facile, novel engine dynamic simulation method was proposed, combining the effects of mass and energy flow accumulation based on the thermodynamics of the variable mass system. The typical twin-spool axis flow turbojet engine was selected as the simulation model and the dynamic simulation of the three-stage aircraft flight process was further carried out. The simulation results confirm that the new approach can greatly enhance simulation speed and is about 28 times faster than the traditional method. Besides simulation speed, accuracy has also been improved compared with the current simulation approaches. For example, during a 9 s acceleration process in which the Mach number increases from 0.6 to 0.8, errors of up to 0.473 s in time delay and up to 0.66% in energy were eliminated. During a 6 s acceleration process, 0.624 s of the time delay error was eliminated. This work plays a positive role in the accurate and rapid simulation of aircraft engines and, more importantly, lays the foundation for the simulation of other systems involving mass and energy flow.

Printed circuit heat exchanger (PCHE) is a type of micro-channel heat exchanger with high performance, which has a broad application in microelectronics, solar energy, and aerospace. Airfoil fins are widely recognized due to their exceptional thermo-hydraulic performance, but there are few studies on their shape adjustment in three dimensions. In this study, a novel twisted airfoil fin was proposed and applied to the heat exchanger. The heat transfer and flow resistance of the twisted airfoil fin PCHE with the traditional PCHE are compared using the numerical simulation method, and the influence of the twist angle, fin spacing, and arrangement is investigated. The results show that the new fins have excellent flow and heat transfer performance. Under the multiple Re number conditions, the Nu number is improved up to 52%, and the performance evaluation criteria is increased up to 16%. Also, increasing the twist angle of the fins, decreasing the fin spacing, and staggering the fins according to diverse twist directions can improve the performance of the heat exchanger.

Negative inclination angle can cause performance degradation for freezing start and decrease the capillary force, leading to the failure or burning of large diameter high temperature heat pipes (LDHTHPs) in the application process. In this paper, we studied the start-up behaviors and temperature uniformity of the prepared LDHTHP at negative inclination angles and the relevant influencing factors. The results showed that the LDHTHP could start normally and reached a steady state in the inclination angle range of −45°. The temperature difference between the evaporating section and the condensation section at −45° was lower than that of the positive inclination angle, leading to a more sufficient start-up. Furthermore, more working liquid would aggregate at the condensation section at −45° obviously increasing the vapor volume and temperature at the condensation section. The condensation section start-up time, start-up performance, gravity resistance, and the average temperature would be reduced with the increase of the heating power and condensation area when the LDHTHP was at an inclination of −45°. And the axial temperature uniformity and equivalent thermal conductivity of the LDHTHP tended to decrease when the condensation area increased. Further, the LDHTHP was mainly limited by the capillary limit at negative inclinations. However, the overall temperature uniformity and equivalent thermal conductivity of the LDHTHP wouldn't be changed significantly when the heating power increased. In consequence, the LDHTHP showed excellent anti-gravity characteristics.

Thermal contact resistance is a crucial parameter for the thermal management of electronic devices, as it directly impacts the heat dissipation efficiency across densely packed component interfaces. This paper proposes a finite element modeling approach to predict thermal contact resistance. The model is based on the optically measured surface topography of Al6061 alloy pairs using a white light interferometer. A mechanical-thermal sequential coupling approach is developed to simulate the contact area and temperature distribution of the contact model. Elastic-plastic deformable mechanics and interface heat transfer in terms of spots and gap conduction are incorporated into the approach. The research indicates that the pressure between longitudinal surfaces significantly influences heat transfer preceding the solid contact point. At an upper surface load pressure of 0.15MPa, the thermal contact resistance is 329mm²·K/W. With a gradual increase in load up to 0.6MPa, the thermal resistance decreases to 244mm²·K/W. Moreover, the transition of interstitial gas from free molecules to a continuous state results in decreased thermal conductivity. Specifically, at gas pressures of 5Pa and 1atm, the thermal contact resistance reduces from 557mm²·K/W to 270mm²·K/W. Furthermore, the numerical results, when compared to experimental data under different gas pressures, exhibit a discrepancy of less than 15%. This outcome effectively validates the accuracy of the proposed method.

Electric Vertical Takeoff and Landing (eVTOL) aircraft, as a highly promising future transportation mode, offers new possibilities for solving traffic congestion. Its unique flight mode and high power requirements present significant challenges for battery thermal management system design. Compared to electric vehicles, eVTOLs have totally different usage scenarios and operating conditions, leading to the fact that the thermal management system of conventional electric vehicles does not apply to eVTOLs. This paper proposes a battery thermal management design method for eVTOLs. The energy and power requirements for a short-distance eVTOL flight are determined through theoretical calculations. Additionally, experimental studies explore the thermal characteristics of a 61.5Ah lithium-ion battery under flight discharge conditions. Moreover, a battery thermal management system, which combines flat heat pipes and ram air, is analyzed through numerical simulations. Furthermore, this study investigates the effects of various air temperatures, air inlet mass flow rates, and fin spacing on the performance of the thermal management system. Finally, under the flight discharge cycle of a 61.5 Ah lithium-ion battery, with the environment temperature of 20 degrees C, the temperature can be controlled within 38.46 degrees C. The temperature difference can be cooled within 3.85 degrees C by the passive cooling system. Even at an extreme environment temperature of 40 degrees C, the battery temperature can still meet the standard. Meanwhile, comparing from multiple dimensions, this solution has a better overall performance than the traditional liquid cooling solution, which provides a foundation for designing a battery thermal management system for eVTOLs.

A design for a turbine pre-swirl system with impeller cavity is proposed to improve the quality of cooling air supplied to the turbine blades of an aeroengine. Impeller cavity is analyzed in order to increase the system pressure ratio with a low system power consumption at the system outlet. Theoretical and numerical investigation are used to investigate the flow characteristics in an impeller cavity pre-swirl system. The conclusions in this study indicate that the impeller structure can increases the pressure ratio by changing the power consumption and distribution of the absolute velocity in the impeller cavity and system outlet. To obtain high pressure ratio and low power consumption, the impeller should have a structure with a high outlet installation radius and low outlet angle. The highest increase in the pressure ratio compared with the empty cavity pre-swirl system is 6.4% and the corresponding increase in the power consumption is 2620 W.

An investigation has been carried out through experimental and simulation analyses to evaluate the cold flow field and combustion performance of a novel trapped vortex combustor that incorporates swirling motion. The cavity is an annular region, and the swirling flow (swirl number is 0.0, 0.6, 0.8, 1.0, and 1.2) is in the central axis of the cavity region. The technique of particle image velocimetry (PIV) is employed to investigate the flow field, with a specific focus on the swirling flow configurations within cavities. Additionally, it serves as a reference point for verifying and enhancing simulation methods. Methane is being subjected to combustion experiments at atmospheric pressure, where the fuel is only introduced into the cavity region and the air used is at a temperature of 300 K. The results show that: the cavity vortices are squeezed due to the swirl jet dumping into the cavity region as a result of the overwhelmingly increased centrifugal forces with the strong swirling flow. Additionally, the vortices' tangential velocity within the cavity area undergoes a significant rise under the influence of swirling flow, ultimately leading to a prolonged residence time. A significant increase in turbulence intensity of cavity vortices is also achieved when the swirl number is increased. For combustion results, the average temperature of the cavity increases with an increase in the cavity rear flow equivalence ratio (Φr); as the Φr further increases, the temperature reduces. The maximum temperature is approximately 1600 K for the mainstream with a swirling flow, and it is about 1200 K for no swirling flow. Finally, the rich/lean blowout limit is extended when the swirl number increases.

Recently, there has been growing interest and attention towards daytime radiative cooling. This cooling technology is considered a potentially significant alternative to traditional cooling methods because of its neither energy consumption nor harmful gas emission during operation. In this paper, a daytime radiative cooling emitter (DRCE) consisting of polydimethylsiloxane, silicon dioxide, and aluminum nitride from top to bottom on a silver-silicon substrate was designed by a machine learning method (MLM) and genetic algorithm to achieve daytime radiative cooling. The optimal DRCE had 94.43% average total hemispherical emissivity in the atmospheric window wavelength band and 98.25% average total hemispherical reflectivity in the solar radiation wavelength band. When the ambient temperature was 30°C, and the power of solar radiation was about 900W/m 2, the net cooling power of the optimal DRCE could achieve 140.38W/m 2. The steady-state temperature of that could be approximately 9.08°C lower than the ambient temperature. This paper provides a general research strategy for MLM-driven design of DRCE.

Although high-power devices have experienced rapid development, they still suffer from several limitations in terms of traditional interconnecting materials. This paper describes the preparation of nano-silver paste through liquid-phase chemical reduction using PVP/12-3-12 type gemini quaternary ammonium salt as the mixed stabilizing agent. The high-thermal-conductivity multilayer graphene was mixed into the nano-silver paste to improve the interfacial heat-transfer performance of power devices. The nano-silver paste was sintered at a low temperature (270°C), and its thermal properties were tested. The experimental results show that the thermal resistance of the sintered layers of different pastes decreases linearly with an increase in the loading of multilayer graphene under no-pressure sintering. When the loading of the multilayer graphene was 1

Ice accretion on surfaces of the aircraft and engine is a serious threat to the flight safety. In this paper, a novel hot air anti-icing method is proposed based on the porous foam. Taking the NACA0012 airfoil as an example, the traditional thermal protection structure is proved to exist the deficiency in balancing the heat exchange caused by route loss of the heat. By dividing the hot chamber into multiple regions to fill with various foam metal, flow resistance characteristics and heat transfer characteristics for this protection mode are analyzed in order to derive the maximized benefit in anti-icing process. The calculation results reveal that, under the same condition, the region filled with foamed copper not only improves the temperature uniformity on the anti-icing area, but also achieves a better protection effect for enhancing heat transfer between the tube and the hot gas, averagely above 20 °C higher than it without porous foam filling in surface temperature. Additionally, the minimum mass flow rate of the protection hot air is reduced by 16.7%. The gratifying efficiency of the porous filler in fortifying heat transfer confirms the potential of replacing the efficient but complex heat transfer design with simple structure filled with foam metal.

Thermal management has become a significant concern in the design of advanced air vehicles. However, an effective evaluation method is needed when designers need to evaluate aircraft thermal management systems comprehensively. This paper proposes an evaluation method in which several evaluation directions concerned with thermal management systems (TMSs) are put forward to form an evaluation index system. The effect of temperature control, heat sink utilization efficiency, energy utilization efficiency, flight performance penalty, thermal endurance, space occupancy ratio, and economy are chosen as the direction of evaluation for TMS, considering its primary function, system performance, and impact on aerial vehicles. This method is comprehensive, intuitive, and user-friendly, along with the intensely subjective user-defined weight parameters, which provide rational metrics for thermal management techniques involved in aerial vehicles. The evaluation method could potentially be helpful for designers to comprehensively analyze the performance of aircraft thermal management systems and provide a basis for practical application. Two examples are provided to demonstrate the application of the method to evaluating TMS comprehensively.