AbstractMixed convection flow for parallel vertical channels connected at upper and lower plenums is studied. The one-dimensional conservation equations are formulated in dimensionless form using channel integral parameters. Based on this formulation, expressions are derived for stable flow and reversal of channel flow. The equations are then used to calculate the flow redistribution within a liquid-metal reactor core during natural circulation primary loop flow. A channel/plenum interaction phenomenon, which limits the applicability of using one-dimensional formulations, is modeled, and a correlation is formulated utilizing measured results to predict the onset of this behavior. Finally, the reversal of a heated channel from upflow to downflow, which cannot be predicted with a onedimensional analysis, is described, and the channel/plenum interaction previously modeled is proposed as the mechanism that initiates this flow reversal.