Prediction of critical heat flux (CHF) for vertical round tubes with uniform heat flux in medium pressure regime
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The description of critical heat flux (CHF) phenomena under medium pressure (10 bar≤P≤70.81 bar) regime is complex due to the large specific volume of vapor and the effect of buoyancy that are inherent in the conditions. In this study, a total of 2,562 data points of CHF in uniformly heated round vertical tube for water were collected from 5 different published sources. The data consisted of the following parameter ranges: 93.7≤G (mass flux)≤18,580 kg/m2s, 0.00114≤D (diameter)≤0.03747 m, 0.008≤L (length)≤5 m, 0.26≤qc (CHF)≤9.72MW/m2, and-0.21≤L (exit qualities)≤1.09. A comparative analysis is made on available correlations, and a new correlation is presented. The new CHF correlation is comprised of local variables, namely, “true” mass quality, mass flux, tube diameter, and two parameters as a function of pressure only. This study reveals that by incorporating “true” mass quality in a modified local condition hypothesis, the prediction of CHF under these conditions can be obtained quite accurately, overcoming the difficulties of flow instability and buoyancy effects. The new correlation predicts the CHF data are significantly better than those currently available correlations, with average error 2.5% and rms error 11.5% by the heat balance method.
Key wordsCHF (Critical Heat Flux) Dryout Burnout Heat Transfer Equipment
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