Pool boiling heat transfer on a plain tube in saturated R-134a and R-410A

The present paper presents the results of an experimental investigation on nucleate pool boiling heat transfer of pure fluid R-134a and environmentally harmless azeotropic refrigerant mixtures R32/R125 (R-410A) on a plain horizontal copper tube. The experiment has been carried out at saturation temperatures of 5, 10, 15 and 20 degrees C for heat fluxes ranging from 10 to 70 kW/m(2) with an interval of 10 kW/m(2) in the increasing order of heat flux. The diameter of the test tube was 25.4 mm and an effective length of 130 mm. From experimental results, it is found that the boiling heat transfer coefficient increases with increasing the heat flux and also found that the heat transfer coefficient of refrigerant R-134a was 20-39% lower than that of refrigerant R-410A. Experimental data were compared with empirical correlations available in the literature. The Jung and Gorenflo correlations were well balanced with the present data of both refrigerants at given saturation temperatures. The Jung correlation over-estimates the experimental data of R-134a by 19% and 23% for R-410A where as Gorenflo correlation overpredics the present data of refrigerants R-134a and R-410A about 20% and 50% respectively. The thermal performance of a plain tube was correlated in terms of non-dimensional form having different dimensionless numbers to evaluate the pool boiling heat transfer coefficients of R-134a and R-410A. This correlation showed a good agreement with measured data within an error of +/- 12 percent.