An Evaluation of the RPI Model for the Prediction of the Wall Heat Flux Partitioning in Subcooled Boiling Flows

Subcooled boiling flows are encountered in most nuclear reactor configurations. Wall heat flux partitioning models form an integral part of the subcooled boiling formulations in CFD codes. These models attempt to describe the flow of heat from the wall into the fluid by dividing it according to several mechanisms of heat transfer. This work presents a one-dimensional evaluation of the wall heat flux partitioning model of Kurul and Podowski, also referred to commonly as the RPI model, which is used in the state-of-the-art codes of today. This model was assessed against the measurements of Okawa et al. for a vertically upward subcooled boiling flow of water at near atmospheric pressure. Although the predictions showed good agreement with the measured wall temperatures, significant discrepancies were observed in the predictions of the constituent sub-models that comprised the overall model. Prospects for improvement are discussed.