Two-group interfacial area transport equation coupled with void transport equation in adiabatic steam water flows

Abstract

The two-group coupled model with IATE is benchmarked with the recently available adiabatic phase-change flow datasets. The current state of adiabatic phase-change data is extensively discussed, followed by a thorough review of the two-group two-fluid model and the two-group IATE. The interfacial mass generation models from RELAP5/MOD3.3 are benchmarked and are observed to underpredict the group-2 interfacial mass generation rate which then causes underprediction of void fraction under flashing conditions. A new group-2 interfacial mass generation model is proposed using the mass-energy balance approach where slug bubbles are assumed as a cylinder with a constant width that only grows in the lengthwise direction. The proposed model is implemented to the two-group coupled model with IATE and benchmarked with the flashing datasets where the accuracy of the predicted values is significantly improved. Similar benchmark is carried out for flashing conditions with a near-zero initial void faction and adiabatic phase-change flows with an initial condensing phase followed by a flashing phase. It is observed that due to the lack of interfacial area concentration, the interfacial mass generation model is unable to produce a significant enough interfacial mass generation rate to allow the growth of bubbles. Bubble generation models are implemented to the simulations at flashing inception where improved results are obtained.