Experimental Heat Transfer Coefficient and Pressure Drop during Condensation of R-134a and R-410A in Horizontal Micro-fin Tubes

Condensation heat transfer coefficients and pressure drops of HFC refrigerants R-134a and R-410A have been investigated experimentally in smooth and micro-fin tubes (helix angles 18 degrees and 15 degrees) of outer diameter 9.52 mm at mass fluxes from 200 to 600 kg/m(2).s, vapor qualities between 0.1 and 0.9 and at saturation temperatures of 35 degrees C and 40 degrees C. Results showed that the heat transfer coefficients of R-134a and R-410A inside micro-fin tubes were 1.21-1.82 and 1.15-1.47 times higher and frictional pressure drops were 2.11-2.56 and 1.62-2.12 times higher than those of smooth tubes. These experimental results are compared with the existing heat transfer and frictional pressure drop correlations proposed by different researchers. The comparison showed fairly good agreement with these existing correlations within +/- 30%. A new correlation has also been proposed for predicting heat transfer coefficient in micro-fin tubes. The oil concentrations measured for refrigerants R-134a and R-410A varied in the range of 1.3-1.5%, respectively.