An electric vertical take-off and landing flying vehicle (eVTOL) is a potential technology for future urban air mobility. A major challenge for thermal management systems is the high cooling requirement and the variable application scenarios. To overcome this challenge, a multi-scene eVTOL-integrated thermal management system was developed. In this study, an eVTOL thermal management simulation platform based on Amesim simulation software was developed to investigate the effects of flight conditions on thermal management and range. The simulation results show that increasing the cruise altitude can reduce the thermal management energy consumption when the ground temperature is high. The maximum reduction of energy consumption for thermal management energy is 4 kW when the cruising temperature ranges from 10 ℃ to 26 ℃. When the hovering rescue duration is more than 150 s during the emergency rescue operation, the temperature difference inside the battery becomes too pronounced. A reduced payload improves the range, with the unloaded range being 1.33 times greater than the fully loaded range.

As a clean energy source, LH₂ is poised to play a pivotal role in future energy supplies. Currently, international hydrogen liquefaction facilities suffer from high energy consumption, high liquefaction costs, and low exergy efficiencies. In contrast, the development of cryogenic hydrogen liquefaction technologies and equipment in China is still in its infancy, significantly lagging behind advanced global standards. Against this backdrop, this paper summarizes the recent research advancements in hydrogen liquefaction technology, encompassing both process design and practical facilities. It delves into the latest developments in steady-state process simulation and dynamic characteristic studies, evaluating performance metrics across various liquefaction processes. Additionally, this paper provides an overview of the technical features and equipment layouts of large-scale hydrogen liquefaction plants and small-scale laboratory setups. Finally, it consolidates the key development priorities and future directions for hydrogen liquefaction technology, aiming to provide valuable guidance for technological progress and accelerate the widespread adoption of hydrogen energy.

R1270 and R290 are alternative refrigerants with great potential. In this study, the influence of the refrigerant charge on the performance of the heat-pump water heater with R1270 and R290, the temperature distribution of the heat transfer fluids in the condenser, and the feasibility of replacing R22 with natural refrigerants were investigated. The results indicate that the refrigerant charge has a considerable influence on the cycle performance and the temperature distribution of the heat-transfer fluids in both systems. At the same optimal charge (0.90 kg), the R1270 and R290 systems achieved a maximum coefficient of performance (COP) of 4.443 and 4.317, respectively. At different refrigerant charges, two heat transfer pinch points and two maximum heat transfer temperature differences occurred in the condensers of both systems, and the locations of the first pinch point and the second maximum temperature difference point showed similar migrations with changes in refrigerant charge. Compared with the R22 system, both the R1270 and R290 systems, at optimal charge, achieved significantly better COP and discharge temperatures, exhibited relatively equivalent discharge pressures, and their heating capacities increased by 7.05% and decreased by 10.65%, respectively. Hence, R1270 can be preferred over R290 for replacing R22 in a heat-pump water heater.

Heat pump technology is an energy-saving solution that could potentially combat global warming and reduce carbon emissions. Industrial heat pumps recover waste heat from the heating process to heat water or air, thereby reducing electricity consumption and carbon emissions. Industrial heat pumps are energy-saving, environmentally friendly, and provide stable heating. They have been widely used at all stages of production and life. This study analyzes the compressor types and characteristics of domestic and international high-temperature heat pumps (HTHP) that recover industrial waste heat and analyzes their application and technical status with a focus on twin-screw and centrifugal compressors. Twin-screw heat pump compressors should adopt an open structure when the evaporation temperature is high, and high-speed and oil-free design can be used when the condensation temperature is high. In addition, centrifugal heat pump compressors should prioritize highly efficient impellers, high-temperature-resistant motors, and oil-free lubricated bearings. Screw steam compressors need to solve the problems of rotor thermal deformation and shaft seal, and target for large temperature lifts.

Microchannel cooling, with its high heat transfer efficiency, low thermal resistance, and light weight advantages, is one of the most effective technologies for solving the problem of heat dissipation with high heat flux; however, it faces the issue of increased pressure drop. The microchannel structure determines the thermal-hydraulic performance. This study describes the research progress on single-phase liquid-cooled microchannel heat sinks in terms of domestic and international structural design to address this problem. Among them, single-phase heat dissipation structures are divided into variable cross-sectionals, flow disruption, pin-fin, double-layered, bionic, and hybrid-reinforced structures. The advantages and disadvantages of the heat transfer coefficient, pressure drop, comprehensive performance, and temperature uniformity were analyzed based on the principle of enhancing heat transfer in various structures. A cost analysis of the commonly used matrix materials and processing methods for microchannel heat sinks was conducted. Finally, we provided the prospect and development direction of microchannel heat sinks from an application perspective. The application of composite structures, integration of simulation and experimentation, advances in material science and processing technology, and the nexus of disciplines are noted as the focus of future structural research.

In cryogenic hydrogen storage systems, an accurate calculation method for the heat release from different ortho-para hydrogen catalytic conversions is important to determine the load of hydrogen storage systems. The objective of this study is to present a precise calculation method for the conversion heat of ortho-para hydrogen. By establishing a conversion model, the methods of using a smoothing spline curve to fit the experimental data and energy balance calculations are used to derive the released heat in adiabatic conversion multistage converters and the released heat during continuous conversion. The heat release properties of different conversion methods are analyzed in this study. Notably, the heat release amount of continuous conversion is the smallest, that of isothermal conversion is the largest, and the conversion heat of adiabatic conversion is in between, which is related to the number of conversion stages. In addition, a specific method and procedure are programmed to solve the implicit differential formula for continuous conversion. Finally, the calculation results of the different methods are consistent with a maximum deviation of only 0.22%, indicating that the calculations in this study are valid and accurate.

The high redundancy of the measured data from heating, ventilation, and air conditioning (HVAC) systems significantly reduces the computational efficiency of model calibration. To address this challenge, a model calibration method based on mining feature operating conditions and a priori probability guidance was introduced in this study. Correlation analysis was conducted on the operational data for mining feature operating conditions. Feature variables related to HVAC system operation were selected, and a grid sampling technique based on these characteristic variables was employed to obtain representative operating conditions, enhancing the efficiency of the model calculations. Additionally, a prior probability model was established for the parameters to be calibrated during the model calibration process. A priori interval estimation was then performed, and the objective function was improved based on the prior probability to guide the model towards faster convergence. The proposed method was validated using a one-month operational dataset from a cooling plant in an industrial building located in Wuhan, China. The results indicated that the proposed method achieved significant improvements in performance metrics. Specifically, mean absolute percentage error (MAPE) and cross-validated root mean square error (CV-RMSE) were reduced by 16.0% and 12.0%, respectively, compared to the K-means clustering-based method, and by 20.9% and 15.2%, respectively, compared to the baseline data-based method. Furthermore, the normalized mean bias error (NMBE) was closer to zero, and the coefficient of determination (R²) increased by 4.7% and 8.5%, respectively, compared to the two aforementioned methods. Additionally, our method enhanced the computational efficiency by approximately 39.3%. This method provides technical guidance and data support for achieving an efficient and accurate modeling of HVAC systems.

Hydrogen energy, as a carbon-free energy source and a pivotal technology for attaining the goals of "carbon peaking and carbon neutrality", has attracted considerable global interest in recent years. The storage of liquid hydrogen offers several advantages owing to its high hydrogen storage density, low storage pressure, and high energy density. However, the industrial development of hydrogen energy still faces many problems. Technologies for large-scale, long-term storage and long-distance transportation are crucial problems in the utilization of liquid hydrogen. Therefore, it is necessary to develop efficient technologies for storing and transporting liquid hydrogen and to build large liquid hydrogen storage tanks with good thermal insulation performance. In this paper, the development status of large liquid hydrogen storage tank storage technology at home and abroad is reviewed, and key problems such as cryogenic insulation and material thermal stress in liquid hydrogen storage are analyzed. The difficulties associated with hydrogen storage and transportation are highlighted, and the development direction of liquid hydrogen storage technology is examined.

This study investigates the in-orbit liquid hydrogen management capability of screen channel tanks in cryogenic propulsion systems by developing a three-dimensional multiphysics model that integrates filling ratios (5%-50%) and microgravity disturbances (10^-3 g). The competition mechanism between capillary and inertial forces, as well as the fluid retention stability during tank reorientation, was systematically analyzed. The key findings include the following. The fluid retention capability was attributed to the structural synergy between liquid collection channels and tank walls, ensuring continuous liquid coverage at the channel inlets under all operating conditions. At low filling ratios, surface tension dominated the phase distribution with a quasi-static interfacial evolution. Increased filling enhanced inertial forces, inducing phase oscillations via momentum transport. The directional sensitivity analysis revealed that bottom acceleration induced the largest centroid depression, top acceleration had a minimal impact on the relative centroid height, and lateral disturbances caused larger centroid oscillation amplitudes and higher frequencies than oblique lateral disturbances.

Ortho-para hydrogen conversion in the hydrogen liquefaction process is significant for the long-term storage and long-distance transportation of liquid hydrogen. This paper outlines the differences in the properties of orthohydrogen and parahydrogen, reviews the research progress on the physical mechanisms and reaction kinetic models of the ortho-para hydrogen catalytic conversion process, and summarizes the performance of common catalysts. Finally, three mainstream schemes for ortho-para hydrogen conversion are compared. Research on the internal physical mechanisms and reaction kinetic models explores the conversion process from microscopic and macroscopic perspectives, respectively. Owing to the lack of experimental data, scholars have not yet formed a unified explanation for the surface characteristics of catalysts, which must be quantitatively validated. Furthermore, although nickel-based catalysts have higher catalytic efficiency, iron hydroxides and oxide catalysts are the main catalyst choices for ortho-para hydrogen conversion, considering the preparation, activation, and deactivation of catalysts and the characteristics of the liquefier. Among the three mainstream ortho-para hydrogen conversion schemes, the hydrogen liquefaction process with continuous conversion has the lowest energy consumption and is the future direction. Relevant research in China is still in its early stages and has great potential for development. This study provides theoretical guidance for the design and construction of ortho-para hydrogen catalytic conversion test benches.