Technique for Determining Local Nucleate and Film Boiling Correlations for Large Diameter Tubes

Abstract The boiling behaviour on the surface of large diameter tubes is known to be strongly dependent on the local orientation of the surface around the circumference. Understanding such local variations in boiling behaviour is of particular interest in the CANDU® nuclear industry, where part of the heat removal path for cooling the fuel under postulated accident conditions is via pool-boiling on the surface of the 132 mm diameter calandria tube that is immersed in a pool of the heavy water moderator. While the average pool boiling behaviour of the calandria tubes has been well studied with integrated experiments, local boiling correlations have not been developed for prototypical diameter calandria tubes. Local boiling correlations will allow for more detailed modelling of postulated accident scenarios and better quantification of safety margins. In this study, the nucleate and film pool-boiling characteristics of a large diameter Zircaloy-2 CANDU® calandria tube were tested in a pool of subcooled water. A novel technique is developed to derive the local boiling curve along the circumference of the tube, involving the local heating, measurement of the wall temperature, and heat flux. The adequacy of the technique is determined by comparing the local boiling curves with previous experiments in which averaged pool boiling characteristics were obtained.