Critical heat flux under zero flow conditions in vertical annulus with uniformly and non-uniformly heated sections

The experimental study of water CHF (critical heat flux) under zero how con ditions has been carried out in an annulus flow channel with uniformly and non-uniformly heated sections over a pressure range of 0.52-14.96 MPa. In t he present boiling system, the CHFs occur in the upper region of the heated section, in contrast to the results in the experiments for boiling tubes c onducted by several investigators. The general trend of the CHF with pressu re is that the CHF increases up to a medium pressure of about 6-8 MPa and d ecreases as the pressure is further increased. A comparison of the present data with the existing flooding CHF correlations shows that the correlation s depend greatly on the effect of the heat flux distribution. When the corr ection terms with the density ratio and the effect of the heat flux distrib ution proposed in the present work are used with the CHF correlation based on the Wallis flooding correlation, it predicts the measured flooding CHF w ithin an RMS error of 9.0%. (C) 2001 Elsevier Science B.V. All rights reser ved.