Interfacial area transport equation and measurement of local interfacial characteristics

Seungjin Kim, Purdue University

Abstract

The motivation of the present study originated from the necessity of the closure relation for the interfacial area concentration in the application of the two-fluid model. Considering that the two-fluid model describes a two-phase flow most accurately, the constitutive relation for the interfacial area concentration is indispensable in the accurate safety assessment of the nuclear reactor system. In the present study, the interfacial area transport equation applicable to a wide range in bubbly flow conditions was developed in view of establishing the constitutive relation for the interfacial area concentration. In the transport equation, the source and sink terms were established through mechanistic modeling of the major fluid particle interactions. In the course of modeling efforts, the large bubble interactions were also studied. Noting furthermore that the available data basis for the local two-phase parameters was quite limited, the state-of-the-art local measurement technique was developed based on the previous conductivity probe technique. Significant improvements were made in both the probe design and the signal processing, which enabled the newly developed probe to be applicable to a wide range of two-phase flow regimes. In the present experiment, detailed local two-phase flow parameters were acquired at three axial locations in the adiabatic rectangular vertical air-water loop under atmospheric pressure for 9 different flow conditions in bubbly, dispersed-bubbly, and distorted-bubbly flow conditions. With the acquired data, the theoretical model was evaluated. In view of this, the one-dimensional steady-state one-group interfacial area transport equation was formulated by applying the Eulerian area-average to the local formulation. The overall agreement between the data and the model prediction was good within ±10% difference. In the sensitivity analysis of the individual contributions from different interaction mechanisms, active fluid particle interactions were clearly demonstrated and the dominant mechanism varied depending on the flow conditions. In general, the turbulent impact break-up and the random collision coalescence mechanisms were dominant in the highly turbulent flow conditions, whereas the bubble expansion and the wake induced coalescence mechanisms were dominant in the bubbly or bubbly to cap-bubbly flow transition conditions.

Degree

Ph.D.

Advisors

Ishii, Purdue University.

Subject Area

Nuclear physics|Mechanical engineering

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