Enhancement in heat transfer during condensation of an HFO refrigerant on a horizontal tube with 3D fins

Abstract

In this work, heat transfer coefficients during condensation of an environment-friendly hydro-fluoro-olefin (HFO) refrigerant R1233zd(e) on the outside surface of two horizontal tubes are separately measured. The cooling water flows inside the tubes and provides cooling to the vapor refrigerant. One tube is a plain tube (commercially smooth both inside and outside) while the other tube is an enhanced tube, with the inside surface having 2D helical ridges and the outside surface having 3D extruded fins. The tests were conducted at the saturation temperature 36.1 °C. The condensation heat transfer degrades with an increase in the condensation temperature difference; the degree of degradation is the nearly the same for the two tubes. Compared with the plain surface, the condensation heat transfer from the enhanced surface is approximately 10.8 times as high. In addition to the area increase due to the extruded fins, the enhancement in the condensation heat transfer is partly attributed to more effective condensate draining mechanism of the 3D fins where surface tension plays an important role. Further analysis reveals that heat transfer during the condensation process on the tube with 3D fins follows the Nusselt correlation with a multiplier that accounts for the enhancement in heat transfer, which is desirably simple approach to modeling condensation heat transfer on the complex 3D enhanced surfaces. This work provides more insights into the physical mechanisms underlying the complex condensation process on tubes with 3D fins.