High Temperature Heat Pipe Furnaces for Material Processing

A heat pipe furnace development was carried out to demonstrate the potential of the heat pipe heating technique at temperatures up to 1500°C for future material processing purposes and for process temperature control in a microgravity environment. Two different types of heat pipes were developed, viz. a variable conductance heat pipe and a specially modified constant conductance heat pipe. Both types utilizing molybdenum 41 wt% rhenium and lithium as containment material and working fluid, respectively, were successfully operated in the temperature range 900°C to 1500°C. The variable conductance heat pipe employing a gas buffering technique provides an excellent temporal temperature stability of less than 80 mK at temperatures of 1300°C and above and a very good temperature measurement accuracy by means of working fluid vapour pressure measurement. The constant conductance heat pipe equipped with special provisions for vapour pressure measurement provides the furnace with a temporal temperature stability of .4K in the temperature range 900°C to 1500°C and a temperature measurement accuracy like that of the variable conductance heat pipe.