Experimental study on film condensation heat transfer characteristics of R134a, R1234ze(E) and R1233zd(E) over condensation tube with enhanced surfaces

This paper presents an experimental study on the film condensation heat transfer characteristics of a horizontal smooth tube and an enhanced tube using R134a, R1233zd(E) and R1234ze(E). The objectives of this paper are to develop experimental correlations of heat transfer for enhanced tubes used in a film type condenser and to provide a guideline for design of the film type condenser. Tests are performed on a horizontally smooth tube with a 19.05 mm diameter and three enhanced tubes. The temperature of the saturated vapor inside the condenser is 38 degrees C. In the case of the horizontal smooth tube, the film condensation heat transfer coefficients of R1234ze(E) and R1233zd(E) were approximately 10.97% and 10.04% lower than those of R134a, respectively. The experimental values obtained from the horizontal smooth tube agreed well with the theoretical value of Nusselt's film which were within the +/- 10% error range. In the enhanced tubes experiment, the film condensation heat transfer characteristics according to the number of knurling and Fin per inch were examined. The enhanced tubes E.T(C)-1 and E.T(C)-3 exhibit a fin per inch number value of 55 and 85 and 107, respectively. Moreover, the fin per inch and knurling number of E.T(C)-5 are 60 and 117, respectively. As a result, the film condensation heat transfer coefficient was found to decrease with increasing heat flux, and E.T (C) -5 showed the highest average film condensation heat transfer coefficient for all refrigerants. Based on the experimental results, the effect of the fin per inch number on the heat transfer coefficient outside the tube is greater than that of the knurling number. In this study, the equations for film condensation heat transfer coefficient for each refrigerant and each enhanced were derived tube according to the heat flux, and a total of nine correlations were observed to have an accuracy of +/- 10% within the experimental range.