Flow regime transition and heat transfer model at low mass flux condition in a post-dryout region = 포스트-드라이아웃 영역에서의 유동형태 천이와 저유량 조건에서의 열전달 모델

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The post-dryout flow regime transition criterion from inverted annular flow (IAF) to agitated inverted annular flow (AIAF) is suggested based on the hyperbolicity breaking concept. The hyperbolicity breaking represents a bifurcation point where a sudden flow transition occurs. The hyperbolicity breaking concept is applied to describe the flow regime transition from IAF to AIAF by the growth of disturbance on liquid core surface. The resultant correlation has the similar form to Takenaka``s empirical one. To validate the proposed model, it is applied to predict Takenake``s experimental results using R-113 refrigerant with four different tube diameters of 3, 5, 7 and 10 mm. The proposed model gives accurate predictions for the tube diameters of 7 and 10 mm. As the tube diameter decreases, the differences between the predictions and the experimental results slightly increase. The flow regime transition from AIAF to dispersed flow (DF) is described by the drift flux model. It is shown that the transition criterion can be well predicted if the droplet sizes in dispersed flow are evaluated appropriately. Existing mechanistic post-dryout models result in fairly good predictions when the mass flux is high or when the film dryout occurs. However, the predictions by these models become poor at low mass flux at which the flow regime before dryout is believed to be churn-turbulent. This is because the constitutive relations and/or the imposed assumptions used in the models become erroneous at low mass flux. The droplet size predicted by the correlation used in the model becomes unrealistically large. In addition, the single phase vapor heat transfer correlation becomes invalid at low mass flux condition. To develop a mechanistic post-dryout model which is available at low mass flux condition, the entrainment mechanisms and the entrained droplet sizes with relation to the flow regimes are investigated. Through the analysis of many experimental post-dryout data, it is show...
No, Hee-Cheonresearcher노희천researcher
한국과학기술원 : 원자력공학과,
Issue Date
108785/325007 / 000895469

학위논문(박사) - 한국과학기술원 : 원자력공학과, 1996.8, [ xvi, 163 p. ]


Post-dryout heat transfer; Dispersed flow; Flow regime transition; Inverted annular flow; Droplet size; 액적크기; 포스트-드라이아웃 열전달; 분산유동; 유동형태천이; 역환상유동

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