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

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.Sponsored by Technical Committee 1.3, American Society of Heating, Refrigeration, and Air Conditioning Engineers DSR Projec

Forced-convection condensation inside tubes

High vapor velocity condensation inside a tube was studied analytically. The von Karman universal velocity distribution was applied to the condensate flow, pressure drops were calculated using the Lockhart- Martinelli method, and heat transfer coefficients were calculated from the momentum and heat transfer analogy. Subsequently, the analysis was reduced to an accurate, but simplified form, to facilitate calculations. Experimental data for refrigerants R-12 and R-22 condensing in a 0.315 in. I. D. tube were obtained for mass fluxes from 1.2 x 105 to 11.3 x 105 lbm/hr-ft 2, qualities from 0.02 to 0.96, and saturation temperatures from 75 to 140*F. On the basis of the data and analysis, a simplified non-dimensional presentation of the results evolved. The agreement between the majority of the data and the analysis was within + 15 percent.Sponsored by Technical Committee 1.3, American Society of Heating, Refrigeration, and Air Conditioning Engineers DSR Projec