Prediction of the Transition Criterion to Annular Flow in Two-Phase Flow Pattern of Refrigerants

Two-phase flow pattern data during horizontal in-tube flow boiling are presented for pure and mixed refrigerants of R134a and R123. The flow pattern is observed through tubular sight glasses located at inlet and outlet of the test section, which is made of a stainless steel tube, 2 m long with 10 mm I.D., 1.5 mm wall thickness. The obtained results are compared to the available various correlations for flow pattern. The flow pattern map of Hashizume was very well agreement with the present data except the region of low mass velocity. Weisman flow pattern map was also known to satisfactorily predict data for refrigerants in the region of annular flow. In order to establish the transition quality to annular flow in this study, flow pattern are simply classified into two groups; stratified (including intermittent, stratified and stratified-wavy) flow and unstratified (annular) flow. The transition quality from stratified to unstratified flow was obtained by modifying the liquid Froude number.