Comparison of Heat-Flux and Wall-Temperature Based Correlations for Predicting Post-Dryout Surface Temperature in Tubes

Abstract

Two correlations for predicting the post-dryout surface temperature have been assessed against a set of experimental data obtained in 12.6-mm inside diameter tubes of two different heated lengths. The first correlation for post-dryout heat-transfer coefficient is expressed in terms of the surface heat flux, while the second correlation is based on the wall superheat. These correlations consist of two components covering the fully developed post-dryout heat transfer and the developing post-dryout region. The fully developed post-dryout heat-transfer coefficient is evaluated from look-up tables, and the developing post-dryout heat transfer is expressed as modification factors that were derived from a large experimental database for tubes. Wall-temperature distributions along these uniformly heated tubes were established using a semi-analytical scheme and compared against the measurements. Both correlations have been shown to provide good wall-temperature predictions. However, the overall prediction accuracy for the heat-flux-based correlation appears to be slightly better than that for the wall-superheatbased correlation. Furthermore, the heat-flux-based correlation follows closely the developing post- dryout region as compared to the wall-superheat-based correlation.