Abstract
The influence of return bend on the frictional performance of R-410A and R-22 in a 5-mm diameter wavy tube is examined in this study with a curvature ratio of 6. 63. For the single-phase results, the existing correlations give fairly good agreements with the present data. Conversely, the existing two-phase correlations of the return bend fail to predict the present data. For test results of the two-phase flow at G≥200 kg m-2s-1, the ratio of (dPc/dz)/(dPs/ dz) is approximately equal to 2 and is relatively independent of the vapor quality. However, the ratio of (dPc/dz)/(dPs/ dz) decreases with the increase of quality when x is less than 0.3 for a smaller mass flux of 100 kg m-2s-1. The value of (dPc/dz)/(dPs/ dz) reaches approximately 5 for x = 0.1 that may be attributed to the change of the two-phase flow pattern. The frictional two-phase multiplier in U bend can be fairly correlated by using the Chisholm correlation. By introducing the Martinelli parameter to the Chisholm correlation, a new correlation could be obtained to describe the present φ2B,L data if more experimental data are available.
