Natural circulation flow resistance correlations in a rod bundle channel under vertical, inclined and rolling motion conditions

Abstract

Flow resistance characteristics in a 3 × 3 rod bundle channel are investigated under static vertical, inclined and rolling motion conditions. The circulation mode hardly influences the frictional and local resistance and the transition Reynolds number under forced and natural circulation conditions are both around 800. Correlations are proposed to predict the frictional and local resistance coefficients. Under inclined conditions, the friction factors are slightly larger than vertical values due to the radial convection and increase with the inclination angles for the same Reynolds number. Since the flow resistance increases clearly in the laminar regime, a correlation allowing for the inclination angles is proposed to predict the friction factors in the laminar regime under inclined conditions. The spacer grid local resistance is barely influenced by the inclination instead. The natural circulation flowrate and pressure drop fluctuations are quite different from the forced circulation results in previous studies. The amplitude is much larger and no obvious phase difference is observed under natural circulation conditions. The friction factor variation rules are different from the forced circulation results as well. A new correlation is proposed considering the rolling parameters through dimensionless numbers and rolling Reynolds number. It is tested with a mass of experimental data and applicable to friction factors prediction under given conditions.