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The power density of electronic components grows continuously, and the subsequent heat accumulation and temperature increase inevitably affect electronic equipment’s stability, reliability and service life. Therefore, achieving efficient cooling in limited space has become a key problem in updating electronic devices with high performance and high integration. Two-phase immersion is a novel cooling method. The computational fluid dynamics (CFD) method is used to investigate the cooling performance of two-phase immersion cooling on high-power electronics. The two-dimensional CFD model is utilized by the volume of fluid (VOF) method and Reynolds Stress Model. Lee’s model was employed to calculate the phase change rate. The heat transfer coefficient along the heated walls and the shear-lift force on bubbles are calculated. The simulation data are verified with the literature results. The cooling performance of different coolants has been studied. The results indicate that the boiling heat transfer coefficient can be enhanced by using a low boiling point coolant. The methanol is used as the cooling medium for further research. In addition, the mass flow rate and inlet temperature are investigated to assess the thermal performance of twophase immersion cooling. The average temperature of the high-power electronics is 80°C, and the temperature difference can be constrained to 8°C. Meanwhile, the convective heat transfer coefficient reaches 2740 W/(m2·°C) when the inlet temperature is 50°C, and the mass flow rate is 0.3 kg/s. In conclusion, the results demonstrated that two-phase immersion cooling has provided an effective method for the thermal management of high-power electronics. [ABSTRACT FROM AUTHOR]

The safety and stability of high-speed trains are easily affected by subgrade settlement and deformation. Serious subgrade settlement may cause the following settlement of ballastless track, which will aggravate wheel-rail interaction, affect ride comfort and even lead to vehicle derailment. In order to study the influence of different types of uneven settlement of subgrade on the dynamic performance of high-speed trains, this paper established a vehicle-track-subgrade coupling dynamic analysis model based on finite element software, considering the effects of dead weight load of track structure and geometric irregularity of track, and analyzed the influence of different settlement types, driving speed, settlement amplitude and settlement wavelength on vehicle running stability, safety and dynamic action of track structure, and put forward the reference limit of subgrade settlement based on the evaluation indexes in relevant codes. The results show that the dynamic performance of high-speed trains is influenced by the type of uneven settlement, the running speed, the value of subsidence and the wavelength of subsidence. The increase of driving speed and subsidence will aggravate the influence of uneven settlement of subgrade on vehicles; Try to avoid cosine type uneven settlement with settlement wavelength less than 10 m; For the driving speed of 300 km/h and 400 km/h, the subsidence of staggered subgrade should be less than 20 mm and 10 mm respectively, and the subsidence of cosine subgrade with a settlement wavelength of 20 m should be less than 30 mm and 20 mm respectively. The control index of subgrade settlement should be based on the requirements of train running stability and vehicle wheel load. [ABSTRACT FROM AUTHOR]