STUDY OF STARTUP REGIMES OF HIGH-TEMPERATURE HEAT PIPES.

An experimental study is described of the startup regimes of heat pipes. The experiments were carried out with a short as well as long pipe in two specially designed facilites. It was determined that best startup conditions are attained by preheating the pipe to 400-500C. It was found further that, barring wick dryout, the sonic limit on the amount of heat to be transferred is overcome under any startup conditions. This makes it desirable to select a wick structure such that the heat transfer limit governed by the pressure drop be much higher than the sonic limit at starting temperature. This, in turn, is attainable by maintaining the maximum evaporator temperature at the 600C level. Experimental results are represented graphically.