Experimental and theoretical investigation of adiabatic bubbly flow and subcooled boiling flow in an annulus
Abstract
The two-fluid model is the most advanced thermal hydraulic model for the analysis of nuclear reactor systems. One of the closure relations for this model is the interfacial area transport equation. Subcooled boiling is of considerable interest to boiling water reactor safety. A robust mechanistic model does not exist yet for subcooled boiling. To develop a mechanistical constitutive relation for the subcooled boiling condition, a better understanding of the physical phenomenon and a solid, extensive database are essential. This thesis focuses on experimental and theoretical investigations on adiabatic bubbly flow and subcooled boiling flow in a BWR-scaled annular flow channel. A database of flow parameters and data sets of the liquid velocity are established for the adiabatic bubbly flow. Databases of flow parameters and boundary parameters, such as active nucleation site density, bubble lift-off diameter, and bubble lift-off frequency, are also obtained for subcooled convective boiling in the annular test section. The one-dimensional, one-group interfacial area transport equation is evaluated based on the experimental data in the adiabatic bubbly flow. The correlation of distribution parameter, drift velocity, and Sauter mean diameter are evaluated from data in both adiabatic bubbly flow and subcooled boiling flow. A bubble-layer thickness model is proposed to avoid various covariances in the cross-sectional area averaged interfacial area transport equation in the subcooled boiling flow. The newly-developed model can predict the bubble-layer thickness as well as the void fraction profile by assuming a square void peak in the bubble-layer region. In addition, the constitutive equation for the distribution parameter in the drift-flux model for boiling flow of an internally heated annulus is also developed based from the measured data. A constitutive relation for the bubble lift-off size is developed based on a force balance and turbulence analysis. The comparisons between the constitutive relation and the experimental data show good agreements. In addition, a preliminary constitutive relation of the bubble lift-off frequency is also obtained. The achievements will be used for the development of the interfacial area transport equation. This will provide a true, mechanistic model of the transfer mechanisms in subcooled convective boiling.
Degree
Ph.D.
Advisors
Ishii, Purdue University.
Subject Area
Nuclear physics
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