Dropwise Condensation on Surfaces Having Different Thermal Conductivities

Abstract

Heat flux and vapor-to-surface temperature difference measurements have been made for dropwise condensation of steam on copper, bronze, copper-plated bronze, and ptfe-coated copper surfaces. Except in the case of the ptfe surface the promoter used was dioctadecyl disulphide. Tests were carried out at various pressures ranging from atmospheric down to about 12 kPa. Care was taken to insure that the apparatus was leak-tight and a local venting technique was used to obviate the effects of traces of non-condensing gases. The heat flux and surface temperature were obtained from temperatures indicated by fine-wire thermocouples accurately located at different distances from the condensing surface. In order to randomize the error in the extrapolated surface temperature for the bronze plate, the thermocouples were repeatedly removed and re-installed. Tests were carried out using a total of six different thermocouple installations. The results for the copper and bronze surfaces were in close agreement with each other and with earlier results for dioctadecyl disulphide-promoted copper surfaces. For the ptfe-coated copper surface, when the ptfe layer resistance was accounted for on the basis of simple one-dimensional steady conduction, the residual vapor-to-(ptfe) surface temperature differences were found to be very close to those obtained for the dioctadecyl disulphide-promoted copper surface.