A new criterion for the onset of heat transfer deterioration to supercritical water in vertically-upward smooth tubes

The heat transfer characteristics of supercritical water, Deteriorated Heat Transfer (DHT) in particular, is crucial to the safety of supercritical devices. It became imperative to develop a new criterion with extensive applicability and high prediction accuracy, to determine whether the operating conditions are safe. To achieve this, a broad-based review was conducted to collect experimental heat transfer data of supercritical water flowing in vertically-upward smooth tubes. The experimental data base consisted of 9705 data points, and the numbers of the Non-DHT and DHT cases were 109 and 64, respectively. Based on the data base, 8 criteria for predicting critical heat flux causing the onset of the DHT (q(dht)) were assessed and compared thoroughly. It was observed that Yamagata's criterion showed the best prediction accuracy among the existing criteria. However, Yamagata's criterion was still insufficient in predicting the DHT conditions. For improvement, further analyses were conducted and the author believed that increasing pressure and decreasing the tube diameter might suppress the occurrence of the DHT under the same conditions, and lead to an increase in q(dht). However, the effects of mass flux, pressure and tube diameter on qdht were not considered simultaneously by the earlier researchers. Thus, this paper recognized the need and developed a new criterion which considered the effects of mass flux, tube diameter, and pressure comprehensively. The prediction accuracy of this new criterion for the Non-DHT and DHT were both higher than 90%, and the overall prediction accuracy was 94.25% which was higher than that of existing criteria.