Two-Phase Flow During Transient Boiling of Hydrogen and Determination of Nonequilibrium Vapor Fractions
In a nuclear rocket propulsion system using a propellant stored in the liquid state, the existence of two-phase flow of the working fluid is of critical concern during start-up. It is generally required that the quality of the fluid at certain locations be predicted. But the behavior of single-component, nonisothermal two-phase flow is not well understood. Moreover, fluid flow and heat transfer data under these conditions are practically nonexistent. An experimental program was undertaken to study forced convection, transient boiling heat transfer to hydrogen during cool-down of a metal test section. It was recognized that a knowledge of the vapor fraction is of primary importance to the understanding of two-phase flow and boiling heat transfer; however, a reliable instrument f or the determination of vapor fractions does not exist at the present time. Isbin et al.  used a. gamma-ray attenuation method to measure the void fractions for steam-water in annular flow, but the calculated qualities were based on the assumption of vapor-liquid equilibrium. Hooker and Popper  have studied the method and concluded that the gamma-ray technique is unsatisfactory for nonhomogeneous flow. Cook  and Egen  reported errors as large as 93% in annular flow. Neal and Bankoff  proposed an electrical resistivity probe for the determination of void fractions. These investigators studied a mercury-nitrogen system in which a large electrical conductivity differential existed between the two phases.
KeywordsTest Section Void Fraction Boiling Heat Transfer Slug Flow Bubbly Flow
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