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Measurements of Void Concentration Parameters in the Drift-Flux Model
윤병조,박군철,정창현,Yun, B.J.,Park, G.C.,Chung, C.H. Korean Nuclear Society 1993 Nuclear Engineering and Technology Vol.25 No.1
가압경수로형 원자로의 정상 비정상 운전시의 열수력학적 거동을 예측하기 위해서는 원자로내기포계수의 분포를 정확히 계산하는 것이 필수적이다. 이러한 기포계수의 정확한 예측을 위하여 많은 모델들이 제시되었다. 이중 drift-flux모델은 그 계산의 정확성과 간결성에 의하여 널리 사용되고 있다. 이러한 drift-flux 모델을 사용하여 보다 더 정확한 기포계수를 예측하기 위해서는 각 상간의 슬립률과 flow regime 에 따른 기포의 운동의 변화가 정확히 고려되어야 한다. Drift-flux 모델에서는 이러한 두 가지 요소가 drift-flux parameter인 $C_{o}$ 와 (equation omitted), 에서 고려된다. 본 연구에서는 이러한 $C_{o}$ 의 실험적 결정을 위하여 원자로 노심을 모사한 4개의 전열봉이 있는 비등이 발생하는 수직사각 유로를 구성하였으며, 완성된 유로내에서 기포계수의 분포 및 기포속도의 분포를 측정하였다. 국부적 기포계수 및 기포속도 분포의 측정에 사용된 방법은 이중탐침법이며 측정이 이루어진 유로내의 유동 상태는 유속이 비교적 느린 low flow rate condition이며 유로내 압력은 3기압 이하이다. 본 실험에서는 액상의 속도는 측정되지 않았으며, 따라서 $C_{o}$ 의 계산을 위하여 (equation omitted)의 실험 상관관계식을 사용하여 유로내 평균 기포계수의 함수로 나타내었다. To predict accurately the thermal hydraulic behavior of light water reactors during normal or abnormal operation, the accurate estimation of the void distribution is required. Up to date, many techniques for predicting void fraction of two-phase flow systems have been suggested. Among these techniques, the drift-flux model is widely used because of its exact calculation ability and simplicity. However, to get more accurate prediction of void fraction using drift-flux model, slip and flow regime effects must be considered more properly In the drift-flux method, these two effects are accounted for by two drift-flux parameters ; $C_{o}$ and (equation omitted). At earlier stage, $C_{o}$ is measured in a circular tube. In this study, $C_{o}$ is experimentally determined by measuring local void fraction and vapor velocity distribution in a rectangular subchannel having 4 heating rods which simulates nuclear subchannels. The measurements are peformed with two-electrical conductivity probes which are known to be adequate for measuring local parameters. The experiments are performed at low flow rate and the system pressure less than 3 atmo spheric pressure. In this experiment, (equation omitted), is not measured, but quoted from well-known empirical correlation to formulate $C_{o}$. Finally, $C_{o}$ is expressed as a function of channel averaged void fraction. fraction.
미포화 비등 이상유동 내 국소 기포 인자에 대한 실험적 연구
배병언(B.U. Bae),윤병조(B.J. Yun),박원만(W.M. Park),송철화(C.H. Song),박군철(G.C. Park) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Subcooled boiling test was carried out in the SUBO (Subcooled boiling) test facility to extend a database for a code benchmark. The test section is a vertical annulus with a heater rod at the channel center. For the measurement of local bubble parameters, double optical fiber sensors were applied at the six elevations. Total six test matrixes are chosen for the parametric study of the heat flux, mass flux and inlet subcooling. Void fraction, interfacial area concentration and bubble velocity were measured at 12 radial locations at each elevation. The local bubble parameters show well the characteristics and propagation of a void fraction and an interfacial area concentration along the test section in the subcooled boiling flow. The present data will be suitable for the benchmark, verification and model development for the CFD style codes or existing safety analysis codes.
미포화 비등 유동에 대한 Bubble lift-off model 개발 및 1군 계면면적 수송방정식 해석
배병언(B.U. Bae),윤병조(B.J. Yun),윤한영(H.Y. Yoon),송철화(C.H. Song),박군철(G.C. Park) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
The interfacial area transport equation for the subcooled boiling flow was developed with a mechanistic model for the wall boiling source term. It included the bubble lift-off diameter model and lift-off frequency reduction factor model. Those models took into account the bubble's sliding on the heated wall after a departure from the nucleate site and the coalescences of sliding bubbles. To implement the model, the two-phase flow CFD code was developed, which was named as EAGLE (Elaborated Analysis of Gas-Liquid Evolution). The developed model and EAGLE code was validated the experimental data of SUBO (Subcooled Boiling) facility. The computational analysis revealed that the interfacial area transport equation with the bubble lift-off diameter model agreed well with the experimental results. It presents that the source term for the wall nucleation enhanced the prediction capability for a multi-dimensional behavior of void fraction or interfacial area concentration.