New Insights into the Behavior of the Metastable Region of an Operating Capillary Tube

Abstract

This study examines the mass flow rate of R-22 in an adiabatic capillary tube, with an emphasis on the nature of the metastable region. The metastable region of an operating capillary tube was found to be much more predictable than previously reported in the literature. A new data acquisition technique, which takes the history of the system into account, revealed a hysteresis effect in the mass flow rate as the level of inlet subcooling is increased and decreased. This result is attributed to the fact that, as the inlet level of subcooling is decreasing, it is possible to create and lengthen a metastable region in which liquid flow exists where it might otherwise be two phase. It is predicted that this finding will have an impact on the future of capillary tube data acquisition, modeling efforts, and the fundamental understanding of capillary tube flow.