A Method of Predicting CHF in Interconnected Subchannels

Abstract

The paper describes a method to predict the Critical Heat Flux (CHF) in subchannel-shaped geometries, and to assess the effects of a simulated misalignment. CHF data obtained at the downstream end of a "Three-Equal-Subchannel" test section were used in this study. The subchannel geometry was achieved by placing a shaped insert inside a tube. The CHF data for the conditions of interest were compared with predictions from the "CHF-Table of Groeneveld et al." The ratios of measured and predicted CHF were correlated with the local thermalhydraulic parameters. The derived correlations were then used to predict the CHF in subchannels of different geometry. Experimentally, these geometries were achieved by placing the insert eccentrically using different spacer heights. Also, the prediction method was applied to the original geometry, where the insert was divided lengthwise in three sections that were rotated by 60" with respect to each other. This created an upstream misalignment, which caused an increase in the turbulence level. The method predicted the misaligned subchannel data well, indicating that the turbulence generated at the point of misalignment had decayed 50 cm downstream. The method overpredicted the CHF in subchannels with a smaller hydraulic diameter, indicating the effect of enthalpy maldistribution.