PERFORMANCE TESTING OF A TWO-PHASE INTERFACE HEAT EXCHANGER 891462

This paper describes the design and performance testing of a heat exchanger which interfaces separate two-phase ammonia thermal loops. The basic design involves a tube-in-tube concept, with boiling occurring in the inner tube and condensation in the outer tube. Eight such tubes arc arranged in parallel. Ammonia vapor enters the outer set of heat exchanger tubes, while subcooled liquid ammonia, at a saturation temperature lower than that of the vapor, enters the inner tubes in counter flow with the vapor. Heat is transferred from the vapor to the liquid through the aluminum heat exchanger tube wall. Both liquid and vapor channels are spiraled at an angle of 11 degrees along the length of the eight heat exchanger lubes in order to promote belterflow distribution. Testing has demonstrated that up to 8.2 KW of heat may be transferred across the heat exchanger when the saturation temperature difference between the systems is 5 C. Performance of the heat exchanger is affected primarily by the mass flow rate of ammonia in the liquid supply loop. When the quality of the ammonia exiting the heat exchanger in this loop exceeds 30%, vapor occupies the entire heat transfer area on the vapor supply side of the heat exchanger. This occurs regardless of the total heat load or loop saturation temperature differences. The limitation may be the result of flow mal distribution between the parallel tubes caused by the design of the heat exchanger's inlet manifold.