Two-phase choking flow at low pressure and low quality

Ho Jun Yoon, Purdue University

Abstract

The prediction of two-phase choking flow at low pressure is much more difficult than at relatively higher pressure (>1MPa). This is due to the large density ratio and relatively large thermal and mechanical non-equilibrium between the phases at low pressure. For low pressure blow down or choking flow, currently available models are not reliable and satisfactory. In view of these, separate effect tests were conducted to systematically investigate the effects of mechanical and thermal non-equilibrium on the two-phase choking flow in a pipe at low pressure. The mechanical non-equilibrium effects were studied with air-water choking flow. Subcooled water, saturated water and steam-water two-phase choking flow were studied to identify the degree of mechanical and thermal non-equilibrium effects. A typical nozzle and orifice were used as the choking flow section to evaluate the degree of non-equilibrium due to geometrical effects. Experimental data were compared with RELAP5 and TRAC-M code predictions. The code predictions in general were not in agreement with the air-water choking flow test data. This indicated that the mechanical non-equilibrium effects were not properly modeled in the codes. Because of the above mentioned shortcomings, the mechanistic model which considers the mechanical and thermal non-equilibrium for the two-phase choking flow is developed. This model is compared with the air-water experimental data as the two-phase two-component flow and subcooled water and steam-water data as the two-phase one-component flow. The comparison of predicted choking model for mechanical non-equilibrium with other experimental in high quality region (up to 80%) is quite reasonable with small error. (Abstract shortened by UMI.)

Degree

Ph.D.

Advisors

Ishii, Purdue University.

Subject Area

Nuclear physics|Mechanical engineering

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