Numerical Study on the Vapor–Liquid Interface in the Evaporator of Loop Heat Pipes with Multiscale Wicks Using Pore Network Simulation

This study numerically and experimentally investigated the maximum heat transfer rate of the evaporator in loop heat pipes (LHPs) using a pore network simulation that considers the vapor–liquid interface within the evaporator wick under high heat flux conditions. The numerical model was validated with previous results. Based on the validated model, the boundary conditions were modified to consider high heat flux conditions. Also, a porous medium approach was applied to predict the working fluid flow in multiscale wicks, which were fabricated by sintering micro-sized SAC305 particles onto conventional screen mesh wicks. The effective pore radius and permeability of multiscale wicks were experimentally measured using the rate-of-rise method. Using the modified numerical model and experimental results, a parametric study was conducted on sintered weight fraction (SWF), fin ratio, and wick thickness to evaluate their effects on the maximum heat transfer rate of the LHP evaporator. As a result, the maximum heat transfer rate increased with higher SWF and thicker wicks due to improved capillary performance and greater vapor growth space, while a higher fin ratio reduced the maximum heat transfer rate by decreasing the vapor groove area. Under optimal conditions, a maximum heat flux of 800 W/cm2 was achieved.