Two-phase fluid flow through nozzles and abrupt enlargements

The behavior of a fluid undergoing a phase change from liquid to vapor while flowing through a duct is of interest to engineers in many practical situations. For the case of interest to us, geothermal hot water flowing through various channels (well bores, surface pipes, equipment, etc.) may reach its flash point and choke point under appropriate conditions. The proper design of energy conversion systems depends on the ability of the engineer to predict this behavior with an acceptable degree of accuracy. The present study was in part motivated by the task of designing the blow-down, two-phase fluid flow test facility at Brown University. In that facility, a refrigerant (dichlorotetrafluoroethane or R-114) is boosted to a selected stagnation state and allowed to flow through a nozzle orifice into a long straight tube. The operation relies on the fluid being choked at the inlet section, and under certain circumstances, at the downstream section as well. A simple schematic of the test section is shown. This paper treats the problem generically and analytically, making use of the basic laws of fluid mechanics and thermodynamics. Specific calculations have been performed using R-114 as the flowing medium. They attempt to identify and describe all possible flow conditions in and downstream of the nozzle for all possible stagnation conditions