Optimum fin density of low fin tubes for the condensers of building chillers with HCFC123

In this study, external condensation heat transfer coefficients on a horizontal plain tube and four low fin tubes of 19.0 mm outside diameter are measured for an alternative refrigerant of HCFC123 used widely in building chillers. For ease of surface temperature measurement, thick wall test tubes are manufactured with fin specifications similar to the commercial tubes. Heat transfer measurements are carried out for the vapor temperature of 39 °C with the wall subcooling of 3–8 °C to determine the optimum fin density of the low fin tubes. Tests results show that HTCs obtained on the low fin tubes are up to 5.8 times higher than those on the plain tube. Especially, the enhancement was high at low wall subcooling. HTCs increase up to the fin density of 28 fpi but decrease sharply beyond that density. For four low fin tubes tested, the 28 fpi tube showed the highest HTCs for three refrigerants including HCFC123.