Wall Friction and Void Fraction in a 3×3 Rod Bundle under Stagnant Liquid Conditions

Abstract

The wall friction term in a one-dimensional model vanishes under the stagnant liquid conditions (i.e. the liquid volume flux J_L = 0). Hence void fraction α_G(ΔP) in rod bundles have been evaluated using measured pressure gradients dP/dz. However, effects of the wall friction term on α_G(ΔP) have not been quantitatively evaluated. In this study, we therefore carried out air-water experiments using a 3×3 rod bundle under the conditions of J_L = 0, and measured dP/dz and α_G,exp with the closing valve method. We obtained the dimensionless wall friction force F_w^* (= α_G(ΔP)－α_G,exp) from the measured dP/dz and α_G,exp. The F_w^* values were expressed by using the gas volume flux J_G, because the liquid flow field was induced by the gas flow (i.e. J_G). The difference between α_G,exp and α_G(ΔP) was reduced by half after α_G(ΔP) was corrected using the obtained correlation for F_w^*. The F_w^* correlation was applied to existing α_G(ΔP) data for 4×4 and 8×8 bundles, and effects of F_w^* on the α_G(ΔP) values were confirmed to be small in a large rod bundle due to the small wall area per unit fluid volume.