Testing of ceramic-radiant-tube heating system. Topical report, March-September 1990

Questions concerning the feasibility and performance of a gas-fired ceramic radiant tube heating system to heat a 2350F vacuum chamber were answered in a test program. Permeability tests run up to 2250F on reaction bonded SiC showed the material to be substantially impermeable to gas exchange with the furnace environment. An upper limit of flue gas leakage was placed at 3.8 x 10 to the power of -8 SCFH per square inch of tube surface. The thermal efficiency of the tube/burner systems was found to range from 75% to 65% as the furnace temperature ranged from 1500F to 2350F. SiC radiant tubes were exposed to thermal gradients and mechanical loading at least as severe as those expected in industrial applications. No indication of tube failure resulting from these conditions were indicated. Tube failures were seen at the closed end of some tubes as a result of overheating. Solutions involving burner design and operation were identified. A developed concept of horizontal tube mounting and sealing was successfully tested.