Investigation of startup behaviors of a loop heat pipe

The results of ground experiments on startup behaviors of a loop heat pipe are presented. One objective is to investigate the effects of working conditions on the startup of loop heat pipes. Startup behaviors as functions of various parameters, including the vapor/liquid distribution in the evaporator, startup heat load, sink temperature, and adverse elevation are described and explained. The physical process of startup is described, and the explanation that pressure transfer leads to the saturated temperature rise in the compensation chamber during startup is discussed. The other objective is to investigate the effect of startup on the steady-state operation of loop heat pipes. Test results indicate that evaporation inside the wick tends to occur at low startup heat loads when the evaporator, including the vapor grooves and the evaporator core, is flooded with liquid. Some peculiar phenomena, including evaporation inside the wick, temperature oscillation at the condenser inlet, and reverse flow equilibrium, which lead to higher operating temperatures, were observed during startup.