Influence of Oil Contamination on the Nucleate Pool-Boiling Behavior of R-114 from a Structured Surface

摘要

The U.S. Navy currently uses refrigerant R-114 in centrifugal chilled-water air-conditioning plants aboard submarines and surface ships. The Navy hopes to reduce the size of these units and increase their performance by using enhanced evaporator and condenser surfaces. The external nucleate pool-boiling heat-transfer coefficient of a horizontal smooth copper tube in R-114-oil mixtures (0 to 10 percent oil) was measured for heat fluxes from 1 to 100 kW/sq m at two different saturation temperatures (-2.2 C and 6.7 C). A copper-nickel tube coated with the Union Carbide 'High Flux' coating was similiarly tested. The High Flux coating was found to improve the heat-transfer coefficient by at least a factor of 7 in oil-free R-114. Oil resulted in about 20 percent reduction of the heat transfer coefficient of the High Flux surface at heat fluxes less than 30 kW/sq m and up to an 80 percent reduction at heat fluxes above 30 kW/sq m with greater than 6 percent oil. Under all conditions, the High Flux coated tube outperformed the smooth copper tube.