Separate Effects on Film-Boiling Heat Transfer

Correlations for effects of geometry, spacing devices and vapour-film development on film-boiling heat transfer have been derived and assessed using experimental data obtained with several types of channel. Only limited sets of data covering a narrowrang e of flowconditions were used in the development of these correlations because most data consist of a combination of effects rather than a single separate effect. In the assessment, the predicted surface-temperature values based on these correlations were compared against measurements of various experiments. These measurements covered either a single separate effect or a combination of effects. They were obtained with simple tubes, an annulus, an annulus-type channel with three equal subchannels, and a 25-rod bundle. Overall, the assessment showed that fully developed film-boiling correlations overpredict the surface-temperature measurements (hence underpredict the heat-transfer rate) that are affected by these separate effects. Furthermore, the parametric trend of the predictions deviates considerably from the experimental data. Implementation of these correlations for various separate effects has led to an improved agreement, in both magnitude and trend, between predictions and data.