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.

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.

To investigate electrostatic accumulation induced by cryogenic liquid hydrogen (LH₂) flow in pipelines, a test system was constructed with LH₂ as the primary working medium. Using vacuum insulation, insulated connections, electrostatic shielding, and other measures, as well as the application of the leakage charge method, safe and accurate measurement of extremely low-level charge quantities generated by LH₂ flow under cryogenic conditions was achieved. The charge accumulation characteristics under multiple flow conditions with Reynolds numbers (Re) below 2×10⁵ were analyzed. The experimental results indicated that notable flow charging phenomena occurred during LH₂ flow with extremely low electrical conductivity in pipelines. Furthermore, charge accumulation demonstrated a linear growth during the test period. Within the range of pipe lengths and Reynolds numbers covered by the experiment, the average charge density decreased with an increase in the flow velocity; however, the rate of decrease gradually diminished. The average charge density of flow decreased with increasing pipe diameter. The developed electrostatic accumulation test system for low-temperature LH₂ pipe flow provided an important platform support for conducting LH₂ electrostatic tests. This study validated the feasibility of the electrostatic measurement method for LH₂, providing design guidance for exploring the electrostatic laws of LH₂ and the boundary of safe flow velocity.

In this study, an experimental platform for cryo-adsorption and hydrogen storage systems was constructed to investigate the cryo-adsorption hydrogen storage law in the system and explore the kinetic and thermodynamic properties of cryo-adsorption hydrogen storage and the hydrogen storage performance of the entire system. The experimental results demonstrated that the adsorbent material exhibited an excellent hydrogen storage capacity under liquid nitrogen temperature zone conditions, and the adsorbent material demonstrated a high hydrogen storage capacity reaching mass-weight ratio of 5.02%, equivalent to the total hydrogen storage density of 16.63 kg/m³ under a charging pressure of 5 MPa and final storage pressure of 3.04 MPa. Through experimental research, the key factors affecting the hydrogen storage performance were revealed. These factors include the microstructural properties of the adsorbent materials, thermodynamic effects during the adsorption process, and experimental operating conditions. This experimental basis provides a foundation for optimizing the performance of hydrogen storage systems.

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.

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.

Mechanical vapor compression (MVC) systems are energy-saving technologies that recover and reuse low-temperature waste heat resources, achieving energy conservation and carbon reduction. As the core equipment in MVC systems, the compressor directly affects the overall performance of the system. This article primarily reviews the thermodynamic and structural performance of vapor compressors, proposes relevant enhancement suggestions and improvement ideas, and provides a reference and assistance for the subsequent optimization of vapor compressor performance.

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.

Existing thermal management schemes struggle to actively and efficiently create a low-temperature heat sink in a limited enclosed space. Hence, a composite thermoelectric refrigeration thermal management system based on flat heat pipes is proposed in this study. A numerical simulation model of the composite system was developed, and an experimental platform for the composite thermoelectric refrigeration thermal management system was established to verify the accuracy of the model. The results showed that the proposed composite thermal management system provided a low-temperature heat sink for the entire thermal management system in a limited space and solved the problem of heat accumulation at the hot end of the thermoelectric refrigeration module by coupling with the plate heat pipe. The thermoelectric refrigeration system based on a flat-plate heat pipe was considerably better than that based on aluminum fins in terms of 1-12 A working current. The cooling capacity and COP (coefficient of performance) of a single thermoelectric module plate were effectively increased by 38.35% and 14.81%, respectively, under the best working conditions.

Quantitative research on the industrial application of direct cooling ice makers is limited, resulting in a lack of clarity in control mechanisms and inadequate heat transfer capability and uniformity in ice making. A mathematical model focusing on the refrigerant side of the ice mold evaporator was established, and a MATLAB simulation model was used to analyze the changes in heat transfer and flow parameters in the flow direction throughout the ice-making process, with comparisons drawn between the experimental data and the simulation results. The heat transfer rate before water icing was approximately 30% higher than that after water icing, and the refrigerant flow rates were significantly different. The heat flux in the superheat region decreased by 40.9% compared to that in the two-phase region, and reducing the superheat section can significantly enhance heat transfer and improve temperature uniformity. The thermal resistances of the water and ice sides accounted for 93.4% and 91.7% of the total resistance, respectively. Thus, the heat transfer of the water side or ice side should first be improved to optimize heat transfer. The simulation model can predict the change in the flow rate and simulate the superheat section, which provides a theoretical basis and practical guidance for the design and operation control of an ice-making machine and helps to improve the product performance and accelerate the ice-making process.