Benefiting from its high thermal conductivity, simple structure, and light weight, the pulsating heat pipe (PHP) can meet the requirements for high efficiency, flexibility, and low cost in industrial heat transfer applications such as aerospace detector cooling and vehicle thermal management. Compared to a PHP working at room temperature, the mechanism of a PHP with hydrogen as the working fluid differs significantly due to the unique thermal properties of hydrogen. In this paper, a two-dimensional model of a hydrogen PHP with a filling ratio of 51% was established to study the flow characteristics and thermal performance. The volume of fluid (VOF) method was used to capture the phase distribution and interface dynamics, and the Lee model was employed to account for phase change. To validate the model, a comparison was conducted between the simulation results and experimental data obtained in our laboratory. The simulation results show that the pressure and temperature errors were within 25% and 5%, respectively. Throughout a pressure oscillation cycle, the occurrence of uniform flow velocity, acceleration, and flow reversal can be attributed to the changes in the vapor–liquid phase distribution resulting from the effect of condensation and evaporation. In addition, when the fluid velocity was greater than 0.6 m/s, dynamic contact angle hysteresis was observed in the condenser. The results contribute to a deeper understanding of the flow and heat transfer mechanism of the hydrogen PHPs, which have not been yet achieved through visualization experiments.

In this study, by assuming a small bottom slope, asymptotic solutions were developed to discuss natural convection within rooted emergent vegetation in response to different heating and cooling mechanisms. Based upon the maximum water depth in comparison to the penetration depth of solar radiation, two scenarios in shallow and deep waters were examined. The temperature structures showed that isotherms in shallows are near vertical but become stable stratified layers (horizontal isotherms) in deep regions. In shallow regions, horizontal velocity profiles perform classic cubic shapes, while the horizontal velocity in deep regions is constant near the surface, and a local upslope flow occurs near the bottom. In shallow water, viscous effects are dominant to shape the velocity profiles, whereas vegetation drag becomes more important in deep regions. By using turbulent parameters, horizontal exchange flowrates and velocities predicted by the asymptotic solutions show good agreements with the existing measurements.