Ding Ting

Investigation On 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.

Development and Test Results of a Dual Compensation Chamber Loop Heat Pipe

A dual compensation chamber loop heat pipe is developed to solve the problem of the relative orientation limit between the evaporator and the compensation chambers. The construction of the evaporator and the compensation chambers is presented. The concurrent design method of the working fluid charge mass and the compensation chamber volumes, that can realize the objectives where, within a certain temperature range, the dual compensation chamber loop heat pipe cannot only start up and operate normally at any orientation, but can also avoid the most difficult startup situation, is introduced. The operation and the thermal control characteristics of the dual compensation chamber loop heat pipe are investigated. Test results indicate that in some heat load regions, the operating temperatures vary with the relative orientation between the evaporator and the compensation chambers. This is explained by the thermal equilibrium of the compensation chamber and the usage efficiency of the return liquid subcooling. The test results and discussion of the dual compensation chamber loop heat pipe suggest that part of the return liquid subcooling that cools the liquid to be locally subcooled must be considered in the mathematical modeling of the loop heat pipe.