Refrigerants exhibit different diffusion and distribution characteristics when they encounter obstacles after leaking into confined spaces. The influence of the thermophysical parameters of refrigerants on their diffusion and distribution after encountering obstacles thus needs to be analyzed to facilitate the prediction of flammable areas during the leakage of flammable refrigerant. In this study, R717, R290, R32, and R1234yf were selected. The diffusion and distribution characteristics of the refrigerants encountering high and low obstacles in a confined space were investigated, and the influence of the thermophysical parameters of the refrigerants on the diffusion process and flammable area were analyzed in detail. The results indicated different patterns of rigid collision when the refrigerants encountered a high obstacle after leakage. Refrigerant with lower densities diffused rapidly in the direction opposite to the leakage direction and gathered at the top of the space, whereas refrigerants with higher densities diffused along the surface of the obstacle to the ground. As the height of the measurement point decreased, the mass concentration of R717 decreased from 2.04% to 0.024%, and the mass concentration of R1234yf increased from 0.192% to 1.64%. The mass concentrations of R290 and R744 below the leakage hole were 0.92% and 1.27%, respectively. When the densities of the refrigerants were similar, the refrigerant with a higher viscosity had a higher mass concentration. The flammable area was primarily located above the high obstacle, and as the refrigerant leakage increased, the flammable area in the y-z section of the space gradually extended to the ground. When refrigerants encountered low obstacles after leakage, they accumulated below the leakage hole and gradually diffused to other low mass concentration areas of the space along the surface of the low obstacle. The distribution of refrigerants with lower densities was more uniform. As the densities of refrigerants increased, they accumulated significantly below the leakage hole. As the height of the measurement point decreased, the mass concentrations of R1234yf and R717 increased from 0.066% and 1% to 2.12% and 1.14%, respectively. The flammable area was mainly located in the corner surrounded by the low obstacle and the wall below the leakage hole. With an increase in refrigerant leakage, the flammable area extended to the ground along the surface of the obstacle.

With the continued miniaturization and high integration of electronic devices, the challenge of heat dissipation caused by the excessive power consumption of electronic devices needs to be resolved urgently. An effective thermal management solution is proposed for heat dissipation in high-power electronic devices using flat heat pipes with excellent temperature uniformity and high heat dissipation efficiency. However, with the increasingly diverse heat dissipation requirements, the creation of an efficient flat heat pipe to suit the heat dissipation demands of emerging electronic equipment remains an important research topic. Therefore, based on expounding the working principle and structural characteristics of the flat heat pipes, the heat transfer performance of the flat heat pipe, the factors that affect the heat transfer performance (capillary wick structure, cavity thickness, working medium, liquid filling rate, inclination angle, and heat source), the measures to strengthen the heat transfer performance of the flat heat pipe (different wettability surfaces and support column structure, etc.), and its application in miniature electronic equipment (IGBT, LED and battery pack) are systematically reviewed. By evaluating the internal flow and heat transfer characteristics of flat heat pipes under different capillary wick structures and cavity thicknesses, the mechanism and comprehensive optimization method of heat dissipation performance, and the design of a flat heat pipe with strong space adaptability and high heat dissipation performance compatible to different electronic device heat management requirements are still key technologies to be further developed. A valuable reference is provided for further research and optimization of flat heat pipes in cooling electronic devices.

HP-1 is an eco-friendly hydrofluoroolefin (HFO) refrigerant with favorable thermodynamic and environmental properties. The critical parameters and saturated vapor pressure of HP-1 are similar to those of R245fa, with HP-1 serving as a potential replacement for R245fa, which has a high global warming potential (GWP) in high-temperature heat pumps. The flammability, solubility, and material compatibility of HP-1 were mainly determined experimentally, with the results demonstrating that HP-1 has a flammability range of 9.75%-16.1%, exhibiting excellent solubility with MK220 lubricating oil at elevated temperatures, and good compatibility with materials used in high-temperature heat pump systems. When HP-1 is applied to high-temperature heat pump units, the condensing temperature of the unit can reach up to 125 ℃ when the evaporating temperature ranges between 50 ℃ and 70 ℃, with a heating capacity of 99.27-153.14 kW and a coefficient of performance (COP) of 2.25-4.85.

Battery thermal management systems are crucial components of pure electric vehicles. The promising application of liquid immersion technology in electronic equipment has also garnered increasing attention for its potential in battery thermal management. Power battery immersion liquid-cooling technology involves directly immersing the battery in dielectric liquid to dissipate heat through convection or phase-change heat transfer. This study analyzes the impact of temperature on battery performance and compares the advantages and limitations of different thermal management systems. The importance of immersion-based battery thermal management is emphasized. Key technical challenges and recent research advancements are reviewed in detail, including coolant selection, module design, and considerations for battery life and safety. Finally, commercially developed immersion cooling products for demonstration and exploration are introduced.

Unnecessary or delayed defrosting results in increased energy consumption, reduced stability, and increased failure rates in refrigeration and heat pump units. Accurately identifying the frost status and timely defrosting are important for improving the performance of refrigeration and heat pumps. Frost status identification methods based on digital and intelligent technologies have shown significant potential. However, existing technologies have significantly reduced accuracy in complex real-world conditions and require urgent improvement. In this paper, we proposed an intelligent recognition method based on the texture features of evaporator surface images. We used a gray-level co-occurrence matrix to extract texture features and combine them with the extreme learning machine optimized by the sparrow algorithm for classification. This is expected to mitigate the impact of external conditions, such as shooting angles and light intensity, thereby achieving strong adaptability. An experimental setup was established to collect 4125 images of the evaporator in three different frost states under complex working conditions, and the proposed method was validated and compared. The results showed that the accuracy of the method in identifying different conditions can reach 95%, which is significantly higher than that of existing methods by 5-35%. Furthermore, this method has high stability and low cost thereby demonstrating great potential for practical applications.