Heat transfer enhancement by metal foam during nucleate pool boiling of refrigerant/oil mixture at a wide range of oil concentration

Abstract

Nucleate pool boiling heat transfer characteristics of refrigerant/oil mixtures on metal foam covers were experimentally investigated at a wide range of oil concentrations. The refrigerant and oil are R113 and VG68, respectively; and the oil concentration varies from 0% to 40%. The copper foams have pores per inch (ppi) of 10 and 20 and porosity from 90% to 98%. Experimental conditions include a saturation pressure of 101 kPa (14.696 psi), and heat flux from 30 to 137 kW m−2 (2.6417 to 12.064 Btu s−1 ft−2). The experimental results indicate that the nucleate pool boiling heat transfer coefficients on copper foam covers are larger than those on a plain heating surface by a maximum of 450%; the presence of oil deteriorates the nucleate pool boiling heat transfer on copper foam covers by a maximum of 90%. With the increase of oil concentration, the deterioration effect on high ppi metal foams is more obvious than that for low ppi. A correlation for predicting the nucleate pool boiling heat transfer coefficient of refrigerant/oil mixtures on metal foam covers is developed, and it agrees with 90% of the experimental data within a deviation of ±30%.