Cryogenic liquid fuel launch vehicles encounter longitudinal unstable vibrations during flight, which is a serious threat to the normal operation of rockets. Such vibrations exhibit typical low-frequency characteristics and often occur during the jet condensation of cryogenic liquid oxygen in propellant pipelines. To solve this problem at the source, the characteristics of the jet condensation oscillation and flow pattern transition must be investigated. Based on the height function method, a modified mass transfer model was used to dynamically capture the interfacial curvature. The relationship between the condensation pulsation frequency and two-phase interfacial curvature was established, and the frequency of the pressure oscillation was found to be 9.8-10.6 Hz. The results indicated that three typical types of jet condensation oscillations exist: stable pulsation, gas plume oscillation, and suck-back flow. The pressure amplitude of the suck-back and oscillation flows was up to 130 kPa, whereas that of the stable pulsation was only 1-3 kPa. From the dimensional analysis, the transition threshold of the flow pattern was Jc^*=7.3 when dimensionless structure parameter L^*=2.2. When Jc^*>7.3, a suck-back oscillating flow pattern appeared. The dimensionless criterion could precisely predict the condensation flow pattern. This provides a theoretical basis and technical support for the design of cryogenic liquid fuel rockets.

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.

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.

Improving indoor air quality in homes requires fresh air; however, this is a strain on air conditioning systems. To address this issue, the use of energy-efficient fresh air units equipped with exhaust air heat recovery is recommended. These units include both passive and active types, with prominent examples being air-to-air enthalpy heat exchangers and heat pump units. Currently, the evaluation of the energy efficiency in fresh air units predominantly revolves around air-to-air enthalpy heat exchangers, rendering the commonly used heat exchange efficiency inapplicable to heat pump units. The concept of exhaust air heat recovery is perplexing and contradictory. Furthermore, the assessment of fresh air units primarily focuses on the units themselves, without considering their impact on air conditioning units and the overall system performance once combined. This study aims to establish a unified definition of exhaust air heat recovery for fresh air units, elucidating its intrinsic meaning. Additionally, it proposes a comprehensive energy efficiency evaluation method for a combined fresh air and air conditioning system. Through a case study of seven existing fresh air unit types, the necessity of exhaust air heat recovery is highlighted, and the energy efficiency levels of different unit types are compared.

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.

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.

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.

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.

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.

A high-efficiency condensation dehumidification system utilizing copper foam driven by a Stirling refrigerator was developed to address the demands for high-efficiency heat transfer and a compact lightweight design in space stations. An experimental study was conducted to investigate its heat and mass transfer characteristics under various conditions. The experimental parameters were set as follows: air inlet temperature ranging from 20 ℃ to 30 ℃, relative humidity between 50% and 80%, cold plate temperature from 8 ℃ to 13 ℃, and inlet wind speed from 0.4 m/s to 1.4 m/s. The results indicated a positive correlation between the increase in the air inlet temperature and the enhancement of both the heat and mass transfer coefficients. Specifically, when the air inlet temperature increased from 20 ℃ to 30 ℃, the heat transfer coefficient increased by 10.5%, whereas the mass transfer coefficient exhibited a more substantial increase of 57.1%. Furthermore, variations in the relative humidity of the air inlet distinctly affected the heat and mass transfer coefficients: the heat transfer coefficient decreased by 31.6% with an increase in the relative humidity, whereas the mass transfer coefficient increased by 11.4%. Although reducing the temperature of the cold plate can effectively improve heat transfer, it leads to the accumulation of condensate water and reduces the efficiency of heat and mass transfer. Therefore, an appropriate cold plate temperature must be selected. Additionally, the efficiency of heat and mass transfer was markedly enhanced with increasing inlet wind speed. However, a continuous increase in wind speed resulted in higher system energy consumption. Thus, a balance between efficient heat transfer and high system energy consumption was essential. Based on extensive experimental data, the heat transfer model was refined using regression analysis. The standard deviation between the theoretical and experimental values was 8.21%, and the maximum deviation was 19.76%, demonstrating the strong predictive accuracy of the model.