Enhanced Tube Bundles Research Articles

Nucleate pool boiling of R-114 and R-114-oil mixtures from smooth and enhanced surfaces—II. Tube bundles

Measurements of pool boiling heat-transfer coefficients in pure R-114 and R-114-oil mixtures are reported for a bundle of smooth tubes and three enhanced tube bundles (finned, structured and porous). Each bundle contained 15 electrically heated tubes (five of which were instrumented) in a staggered triangular-pitch layout. Tests were carried out at atmospheric pressure while decreasing the heat flux. For pure refrigerant, the structured and porous bundles provide the highest average enhancements of between 4 and 6. For all but the porous bundle, the bundle effect is only significant at low heat fluxes: the porous tube bundle exhibits no bundle effect. With addition of oil, the performance of the smooth and finned tube bundles at first increases before dropping off slightly. For the structured and porous bundles, oil addition leads to a steady decrease in performance, especially for the porous bundle at high heat fluxes.