Effects of liquid properties on CCFL in a scaled-down model of a PWR hot leg

This paper describes the effects of liquid properties on countercurrent flow limitation (CCFL) in a PWR hot leg. CCFL experiments were conducted in a 1/15th scaled-down model of the hot leg using air/water and air/glycerol-water solutions as working fluids. The experimental results revealed that an increase in the liquid viscosity did not change the zero liquid penetration point but did increase the slope of the CCFL curves on the Wallis diagram, which indicated that the increase in liquid viscosity from that of water did not affect the interfacial drag force but did influence the wall friction force. Numerical simulations of the experiments were carried out using a two-fluid model implemented in the CFD software FLUENT 6.3.26, and it was confirmed that the two-fluid model simulations properly evaluated the effects of liquid viscosity on the CCFL characteristics in the hot leg. Numerical simulations were also carried out to compare a low viscosity liquid to water. The predicted CCFL characteristics for low viscosity liquid showed no significant difference from those for water, which indicated that the decrease in liquid viscosity from that of water affected neither the interfacial force nor the wall friction force. (author)