Simulation of medium-temperature cesium heat pipes using the pressure-modified Capillary Wick model

Accurately simulating the flow of the working fluid within capillary wicks and the corresponding circulation dynamics in heat pipes presents a significant challenge. In this study, a pressure-modified Capillary Wick model is proposed based on molecular dynamics simulations. By customizing the momentum source term to generate a high-pressure region adjacent to the wall, the capillary pumping effect is precisely simulated. Concurrently, more physically consistent distributions of pressure and saturation temperature are achieved, with the nucleation site migrating from the inner wall of capillary wick structure to its outer surface. These improvements suppress velocity fluctuations of the condensate film and eliminate the unphysical entrainment limit phenomenon at low heating powers, along with the associated overheating of the evaporator. In comparison with the Wall Adhesion model, the vapor dryness fraction of the condenser increases from 0.436 to 0.609. Furthermore, the maximum temperature deviation of the evaporator decreases from 121.46 K to 20.38 K with a 83.22 % reduction, while the average temperature deviation of the evaporator decreases from 40.07 K to 9.08 K, with the relative error decreasing from 5.78 % to 1.31 %. Correspondingly, the overall thermal resistance of the heat pipe is reduced from 3.818 K·kW^-1 to 1.941 K·kW^-1, representing a 49.14 % reduction and thereby bringing the simulation results into closer agreement with experimental data.