Numerical Calculations for Air-Water Tests on CCFL in Different-Scale Models of a PWR Hot Leg

Air-water CCFL (countercurrent flow limitation) tests using the 1/5^th scale rectangular channel and 1/15^th scale circular tube simulating a PWR hot leg and both air-water and steam-water CCFL tests using the 1/3^rd scale rectangular channel were previously carried out at Kobe University and Forschungszentrum Dresden-Rossendorf (FZD), respectively. In this paper, numerical calculations for the air-water CCFL tests at FZD using FLUENT6.3.26 are presented and compared with the experimental data at Kobe University and FZD. In the calculations, the VOF (volume of fluid) model or two-fluid (2F) model was used. Major results were as follows: (1) the calculated CCFL characteristics using the 2F model for the FZD tests agreed well with the 1/15^th scale circular tube data obtained at Kobe University and the calculated results for full-scale PWR conditions, which supported the validity of the 1/3^rd scale rectangular channel to simulate CCFL in circular tubes; and (2) comparison with the FZD data showed that the calculations using the 2F and VOF models overestimated the falling water flow rates.