Frictional performance of R-22 and R-410A inside a 5.0 mm wavy diameter tube

The influence of return bend on the frictional performance of R-410A and R-22 in a 5-mm diameter tube is examined with a curvature ratio of 6.63. The existing single-phase correlations give fairly good agreements with the present single-phase data, but the existing two-phase correlations of the return bend fail to predict the present two-phase data. For test results of the twophase flow at G>=200 kg m^-2 s^-1, ((dP/dz)c/(dP/dz)s) is approximately equal to 1.8 and is relatively independent of the vapor quality x. However, at a smaller mass flux of 100 kg m^-2 s^-1, ((dP/dz)c/(dP/dz)s) decreases with x, reaching approximately 5 for x=0.1. The significant increase of this ratio for G increased from 100 to 200 kg m^-2 s^-1 may be attributed to the change of the two-phase flow pattern.