Abstract
The critical heat flux look-up table was applied to a large diameter tube, namely 67 mm inside diameter tube, to predict the occurrence of the phenomenon for both vertical and horizontal uniformly heated tubes. Water was considered as coolant. For the vertical tube, a diameter correction factor was directly applied to the 1995 critical heat flux look-up table. To predict the occurrence of critical heat flux in horizontal tube, an extra correction factor to account for flow stratification was applied. Both derived tables were used to predict the effect of high heat flux and tube blockage on critical heat flux occurrence in boiler tubes. Moreover, the horizontal tube look-up table was used to predict the safety limits of the operation of boiler for 50% allowable heat flux.
Highlights
Critical heat flux (CHF) is a phenomenon corresponding to the point where a continuous liquid contact cannot be maintained at the heated surface
CHF results in sudden drop in heat transfer rate between the heated surface and the coolant
Beyond CHF, a small increase in heat flux leads to large increase in surface temperature for a heat-flux-controlled surface, and a small increase in surface temperature leads to decrease in heat flux for a temperature-controlled surface
Summary
Critical heat flux (CHF) is a phenomenon corresponding to the point where a continuous liquid contact cannot be maintained at the heated surface. Beyond CHF, a small increase in heat flux leads to large increase in surface temperature for a heat-flux-controlled surface (e.g., electric heaters), and a small increase in surface temperature leads to decrease in heat flux for a temperature-controlled surface (e.g., steam condensers). The earliest prediction methods were primarily empirical [1, 2] These crude empirical correlations lacked any physical basis and had a limited range of application. Since most empirical CHF correlations and models have a limited range of application, the need for a more generalized technique is obvious. The CHF-LUTs for 67 mm diameter tubes were generated in this work covering wide range of flow conditions of pressure, mass flux, and thermodynamic quality
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