EHD-Enhanced Condensation of Alternative Refrigerants in Smooth and Corrugated Tubes

Abstract

An experimental study of EHD-enhanced in-tube condensation of alternative refrigerants is presented. The refrigerants tested were the single-component refrigerant R-134a, the zeotropic mixture R-407c, and the near-azeotrope R-404a. Tests for R-404a and R-407c were performed in smooth and corrugated tubes, whereas R-134a tests were performed only in corrugated tubes, with smooth tube data extracted from Singh (1995). The tests were performed with internally mounted cylindrical electrodes. It was found that, in general, all three refrigerants respond remarkably well to the EHD enhancement. The heat transfer performance of near-azeotrope R-404a is enhanced 18.8-fold in the smooth tube at the highest applied voltage of 18 kV, with a corresponding pressure drop penalty of 11.8-fold, and the maximum enhancement inside corrugated tube is 5.8-fold for the range of conditions tested in this study. R-134a has a maximum heat transfer enhancement of 8.3-fold, with a corresponding pressure drop penalty of 20.8-fold at an applied voltage of 18 kV inside the corrugated tube. Among the three refrigerants tested, R-407c shows the lowest heat transfer enhancement, with a 3.9-fold maximum enhancement at an applied EHD voltage of 18 kV inside the smooth tube, and a maximum enhancement of 2.9-fold inside the corrugated tube.