Some basic physics of evaporating two-phase flow obtained through a two-fluid model

Document Type

Conference Proceeding

Publication Date

12-1-1990

Abstract

A two-fluid model is used as a basis for the development of simple mixture equations governing evaporating two-phase flow. Characteristic flow parameters such as the Reynolds, Froude and Mach numbers are rationally defined in the context of this model, and their relative importance throughout the evolution of the flow from flashing to choking is discussed. The definition of the local two-phase Mach number emerges from a critical flow analysis which is briefly described. The compressibility induced by phase-change is shown to play a very significant role on the flow development. Away from the neighborhood of the flash horizon pressure-drop and kinetic energy changes are theoretically shown to scale with similar local Mach functions as those of single-phase compressible flow. After making some simplifying assumptions limiting expressions for the pressure, specific volume and slip-ratio gradients in the neighborhood of the flash horizon are derived from the governing equations. The pressure gradient is shown to increase discontinuously across the flash horizon because of compressibility effects. Existing experimental data from vertical-upwards two-phase flow in pipes indicate good agreement with the theoretical guidelines and predictions.

Publication Source (Journal or Book title)

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED

First Page

481

Last Page

487

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