EXPERIMENTAL-STUDY ON FORCED CONVECTIVE BOILING HEAT-TRANSFER OF PUREREFRIGERANTS AND REFRIGERANT MIXTURES IN A HORIZONTAL TUBE

Convective boiling heat transfer coefficients of pure refrigerants (R2 2, R32, R134a, R290, and R600a) and refrigerant mixtures (R32/R134a, R 290/R600a, and R32/R125) are measured experimentally and compared with Gungor and Winterton correlation. The test section is made of a seaml ess stainless steel tube with an inner diameter of 7.7 mm and is unifo rmly heated by applying electric current directly to the tube. The exi t temperature of the test section was kept at 12 degrees C +/- 0.5 deg rees C for all refrigerants in this study. Heat fluxes are varied from 10 to 30 kW m(-2) and mass fluxes are set to the discrete values in t he range of 424-742 kg m(-2) s(-1) for R22, R32, R134a, R32/R134a, and R32/R125; 265-583 kg m(-2) s(-1) for R290, R600a, and R290/R600a. Hea t transfer coefficients depend strongly on heat flux at a low quality region and become independent as quality increases, The Gungor and Win terton correlation for pure substances and the Thome-Shakil modificati on of this correlation for refrigerant mixtures overpredicts the heat transfer coefficients measured in this study. (C) 1997 Elsevier Scienc e Ltd and IIR.