RÉSUMÉ

A mathematical model of the hydrodynamics and heat transfer in a U-shaped PHP involving one liquid plug and two vapor bubbles is presented. The vapor bubble governing equations and liquid plug energy equation are solved numerically by the explicit finite difference method and explicit IOCV method based on the Lagrangian approach, respectively. Unlike other models, the vapor bubble state is checked, if superheated, the pressure is calculated from the ideal gas equation, otherwise saturation pressure is found from the curve fitted equation. Film thickness is calculated using correlation. The metastable state of a vapor bubble is incorporated by the modified latent heat term. The heat transfer coefficient is calculated by film thickness and spatial film thickness variation which is found by considering evaporation from a liquid film and vapor interface. The model studies different parameters like the plug velocity, bubble temperature and pressure, driving pressure, thermal conductance, and heat transfer. It is observed that film thickness variations are very small in the range from 1 to 3% of the initial thickness due to the higher oscillation frequency in the range from 11 to 13 Hz. The latent heat transfer is 7% of the total heat transfer, in the case of 2-mm ID, water as a working fluid with 80 and 20°C for the evaporator and condenser temperatures, respectively. The heat transfer rate and thermal conductance increase with the temperature difference between the evaporator and condenser, but decrease with decrease in the operating temperature for a given temperature difference between the evaporator and condenser. The vapor sensible heat has significant effects on the vapor bubble temperature.