An improved correlation for two-phase pressure drop of R-22 and R-410A in 180° return bends

Abstract

A correlation for two-phase flow pressure drop in 180° return bends is proposed based on a total of 241 experimental data points for R-22 and R-410A from two independent studies. The data span smooth tubes with inner diameters ( D) from 3.3 mm to 11.6 mm, bend radiuses ( R) from 6.4 mm to 37.3 mm, and curvature ratios (2 R/ D) from 2.3 to 8.2. The correlation consists of a two-phase pressure drop for straight-tubes and a multiplier that accounts for the bend curvature. The Buckinham-PI Theorem was used to formulate the curvature multiplier in terms of refrigerant properties, flow characteristics, and bend geometry. The correlation predicts all data with a RMS deviation of 25%, and 75% of the data fall within ±25% error bands.