NUCLEATE POOL BOILING OF R-114 AND R-114-OIL MIXTURES FROM SMOOTH ANDENHANCED SURFACES .1. SINGLE TUBES

Measurements of pool-boiling heat-transfer coefficients in pure R-114 and R-114-oil mixtures are reported for a smooth tube and eight enhanc ed tubes (five finned and three re-entrant cavity). Tests were carried out at atmospheric pressure while decreasing the heat flux. For pure refrigerant, the finned tubes typically provide enhancements of betwee n 3 and 4, whilst the re-entrant cavity tubes provide enhancements of more than 10 at low heat fluxes, decreasing to around 4 at high heat f luxes. With addition of oil, performance of the finned tubes at first increases (with 3% oil) before dropping off. For the reentrant cavity tubes, addition of oil causes a steady drop-off in performance; especi ally for the porous tube where heat transfer rates similar to that of the smooth tube were obtained.