Flashing Flow Discharge of Initially Subcooled Liquid in Pipes

The release rates of hot fluids stored under pressure during a pipe break or valve failure are a pertinent consideration in source term modeling as part of the environmental health and safety issue. This technical brief presents an analytical treatment for flashing discharge of a hot liquid in a pipe from a high pressure reservoir. Specifically, the liquid is initially subcooled relative to stagnation condition but superheated relative to ambient pressure. The effect of inlet subcooling, pipe length-to-diameter ratio, and physical property groups of the fluid can be readily assessed by the present generalized model. A criterion related to the amount of ''limiting'' subcooling is found where the discharge rate can be evaluated using a form similar to the incompressible pipe flow formula. Unlike other previously published works, the present solution yields a smooth transition from saturated inlet to subcooled conditions and reduces exactly to the nozzle flow limit at zero pipe length.