A new correlation for the limiting quality of critical heat flux at low mass fluxes and low pressures

Abstract

The limiting quality (or limiting critical quality) was studied experimentally. We used a test section made of Inconel-600 with 8 mm OD, 170 mm length and I turn wall thickness. The experiments were carried out with water at up flow for mass fluxes from 100 to 400 kg m(-1) s(-1), at low pressures (1.0-7.0 bar) and subcoolings (up to 70 K). The limiting quality is characterized by a sharp drop of the critical heat flux (CHF) in a diagram CHF versus critical quality with fixed values of pressure and mass flux and with change of the inlet subcooling. It was observed that the limiting quality appeared in our experimental results. There is a disagreement in the literature on how this phenomenon occurs. According to the present study the limiting quality phenomenon takes place due to a change of CHF mechanisms between DNB and dryout in agreement with Doroshchuk's findings. Existent correlations from literature have been compared with the experimental data. However, no correlations agree with our data because of their different validity ranges. Therefore a new correlation for the limiting quality phenomenon is developed for a large range of pressure. Furthermore the critical heat flux is calculated via a heat balance in which the value of the limiting quality is included. Copyright (C) 2004 John Wiley Sons, Ltd.