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�Cthe existing correlations give fairly good agreements with the present data.Conversely�Cthe existing two-phase correlations of the return bend fail to predict the present data. For test results of the two-phase flow at G�†200kgm^-2s^-1�C the ratio of�idP_c/dz�j�^�idPs/dz�jis approximately equal to 2 and is relatively independent of the vapor quality.
However�Cthe ratio of�idPc/dz�j�^�idPs/dz�jdecreases with the increase of quality when x is less than 0.3 for a smaller mass flux of 100 kgm^-2s^-1�D
The value of�idPc/dz�j/�idPs/dz�jreaches approximately 5 for x��0.1 that may be at tributed 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�D By introducing the Martinelliparameter to the Chisholm correlation�C a new correlation could be obtained to describe the present ƒ³²_B,Ldata if more expenmental data are available.