The influence of return bends on the downstream pressure drop and condensation heat transfer in tubes

Abstract

The influence of return bends on the downstream pressure drop and heat transfer coefficient of condensing refrigerant R-12 was studied experimentally. Flow patterns in glass return bends of 1/2 to 1 in. radius and 0.315 in. I. D. were examined visually and photographically using a high frequency xenon light source. Local pressure drop and heat transfer measurements were made along a horizontal 14 1/2 ft. test section immediately following the return bend. The refrigerant mass flux ranged from 1.32 X 105 to 4.58 X 105 lbm/hr-ft 2, saturation temperature from 90 to 107*F, and return bend quality from 0.24 to 1.0. The pressure drop and heat transfer data were compared to previous data for condensation without return bends. Effects on the downstream pressure drop and heat transfer were found to be small, if not negligible.