VOF Calculations of Countercurrent Gas-Liquid Flow in a PWR Hot Leg

We improved the computational grid and schemes in the VOF (volume of fluid) method with the standard k - epsilon turbulent model in our previous study to evaluate CCFL (countercurrent flow limitation) characteristics in a full-scale PWR hot leg (750 mm diameter), and the calculated CCFL characteristics agreed well with the UPTF data at 1.5 MPa. In this paper, therefore, to evaluate applicability of the VOF method to different fluid properties and a different scale, we did numerical simulations for full-scale air-water conditions and the 1/15-scale air-water tests (50 mm diameter), respectively. The results calculated for full-scale conditions agreed well with CCFL data and showed that CCFL characteristics in the Wallis diagram were mitigated under 1.5 MPa steam-water conditions comparing with air-water flows. However, the results calculated for the 1/15-scale air-water tests greatly underestimated the falling water flow rates in calculations with the standard k - epsilon turbulent model, but agreed well with the CCFL data in calculations with a laminar flow model. This indicated that suitable calculation models and conditions should be selected to get good agreement with data for each scale.