Film condensing heat transfer of R134a on single horizontal tube coated with open cell copper foam

Abstract

Film condensing of refrigerant R134a on single horizontal tube coated with open cell copper foam was investigated at saturation pressures of 10.1 Bar and 8.87 Bar. Two foam thicknesses of 1.6 and 2.5 mm, three pore densities of 40, 80 and 130 PPI(Pores per inch) as well as the porosity of 90%, characterize the six tubes in the experiment. Heat flux in this work ranges from 10 to 60 kW/m2. It is found that saturation vapor pressure within the measurement range has almost no effect on the condensing heat transfer in the range of 8.87–10.1 Bar. Film condensing depends much on foam thickness with the pore density of 40 PPI, compared with 80 PPI and 130 PPI. The heat transfer coefficient generally ranges from 2 to 6 kW/m2 K for the six tubes, which decreases linearly up to the heat flux of 60 kW/m2 on a log–log plot. The enhanced ratio of all the coated tubes compared with that of the plain tube ranges from 2 to 3. Minor increment of the enhanced ratio is observed as the increment of heat flux.