Two-Phase Flow Analyses During Throttling Processes

This study presents an experimental investigation of the throttling process of saturated fluorocarbon refrigerants (such as R116, R218, and R610) inside capillary tubes. For the detailed two-phase flow analyses, refrigerant R218 was selected. A divided capillary tube was prepared with a set of precise pressure and temperature sensors providing detailed information about the refrigerant flow behavior inside the tube. The metastable flow regions of the superheated liquid and of the two-phase vapor-liquid mixture were clearly detected. A correlation for the ‘underpressure’ of vaporization applicable for capillary flow of fluorocarbon refrigerants was determined. New experimental data were compared with a modified numerical model simulating all four capillary flow regions. A negative effect of non-condensing gases present within the cooling circuit on the overall capillary tube performance was experimentally noted.