Modeling of room-temperature heat pipe startup from the frozen state

An analytical investigation was conducted to examine the effects of noncondensible gas charging on restart from the frozen state for room-temperature heat pipes. The model utilized regional energy balances and assumed uniform regional temperatures, independent movement of the vapor/gas front and the liquid melt front, and working fluid sublimation in the frozen state. The model compared well with experimental data for a uniformly distributed working fluid along with negligible noncondensible gas loading and for sufficient gas charging to result in a gas-controlled restart condition. The analysis showed that for negligible noncondensible gas charges up to 90% of the evaporator heat addition may be carried out of the evaporator by sublimating quid, thus leaving insufficient heat addition to thaw the heat pipe. For high levels of noncondensible gases, restart was easily accomplished and was gas controlled.