Prediction of “critical heat flux” for supercritical water and CO2 flowing upward in vertical heated tubes

Abstract

The prediction method for the occurrence of supercritical critical heat flux (CHF) is investigated both theoretically and statistically. The supercritical CHF is defined as the lowest heat flux that causes the wall temperature (Tw) peak to occur. The new definition is helpful to avoid the confusion caused by different definitions of the heat transfer deterioration (HTD) in supercritical flow. A new theory to explain supercritical CHF mechanisms is proposed, which considers the rupture of flow stability between the liquid-like and vapor-like layers of the supercritical flow in a heated tube as the main reason for supercritical CHF phenomena. From this theory, a general mathematical model for supercritical CHF identification for upward vertical flow is derived. To substantiate the general mathematical model, two databases for supercritical CHF of water and CO2 flowing upward in vertical circular tubes are compiled from the available literature, based on which the general model is reduced to a practical correlation applicable to both supercritical water and supercritical CO2 for CHF occurring before the pseudo-critical point. The new correlation differentiates the CHF cases from the non-CHF ones very well, and it has much higher prediction accuracy than any existing counterpart.