Critical Heat Flux Prediction for Pool Boiling of Binary Mixtures

Abstract

The model of binary mixtures boiling crisis presented here develops the previous approach of the author to the problem. The boiling crisis is considered to be a result of irreversible increase of the area of dry spots at the heated surface. Very small dry spots always exist as nucleation sites in nucleate boiling and very high peak heat fluxes have been observed at their boundaries. In the near-critical regime the dry spots become larger and the heat flux averaged over a dry spot becomes comparable to the average heat flux at the heated wall. The equality of these heat fluxes is assumed to be the boiling crisis condition. As the liquid flow rate to the dry spot boundary is assumed to be controlled by the capillary pressure gradient, an additional effect of surface tension gradient in mixture boiling is naturally involved in the analysis. A simple correction factor to the earlier developed equation for critical heat flux in pure component boiling is derived. The resulting equation is shown to be in rather good agreement with the available experimental data on critical heat flux for boiling of binary mixtures.