AUGMENTATION OF HEAT TRANSFER DURING POOL BOILING OF REFRIGERANT

Abstract

One of the necessary features for the successful operation of a refrigeration unit is that the heat transfer performance of the refrigerant within the evaporator. The optimum design of the evaporator depends on the right analysis of the nucleate boiling and also the convective contributions to heat transfer. Nucleate boiling heat transfer is a widespread industrial process. The importance of nucleate boiling arises from its ability to get rid of huge quantities of heat per unit time and area from the hot surface with a comparatively low thermal temperature difference. Suggest that a tremendous reduction in heat exchanger surface is likely by means of nucleate boiling. The thesis describes the results of an experimental investigation on nucleate pool boiling heat transfer of pure fluid R-134a and new environmentally harmless azeotropic refrigerant mixtures of R-125, R-143a, and R-134a (R-404a) on a plain horizontal copper Tube. The experiment has been carried out at saturation temperatures of 21oC and heat fluxes from 5 to 40kW/m2 with an interval of 5kW/m2 in the increasing order of heat flux. The diameter of the test tube was 25.4 mm (1 in.) and had an effective length of 130 mm. Experimental data were compared with some empirical correlations available in the literature. The Jung, Cooper and Gorenflo correlations were well balanced with the present data of both refrigerants at given saturation temperatures. The Jung correlation under-predicts the experimental data with a maximum mean error of 11% for R-134 and 20-25% for R-404a while Cooper‟s under predicted the data of R-134a by 11% and 15% for R-404a