CRITICAL HEAT-FLUX OF BINARY-MIXTURES IN POOL BOILING AND ITS CORRELATION IN TERMS OF MARANGONI NUMBER

Critical heat flux (CHF) in nucleate pool boiling of binary mixtures w as newly measured with a horizontal platinum wire, 0.5 mm in diameter, and heated by DC, over the full range of concentrations. Seven mixtur es were selected with the intent to cover various types of mixtures: m ethanol/water, ethanol/water, methanol/ethanol, ethanol/n-butanol, met hanol/benzene, benzene/n-heptane and water/ethylene glycol, each in th e saturated state at atmospheric pressure. Total 311 raw CHF data were obtained at 75 concentrations including pure components. Aqueous mixt ures of methanol and ethanol revealed significant increase of CHF comp ared to either CHF linearly interpolated between pure components or CH F predicted from a single component correlation with use of the mixtur e properties. Three organic mixtures showed more or less the same leve l as an interpolated CHF, while the remaining two mixtures of methanol /benzene and water/ethylene glycol gave the reduced CHF by 20% and 50% at most, respectively. Marangoni number was introduced as a controlli ng variable to explain the observed increased, invariable, or reduced CHF, and an empirical correlation was developed. (C) 1998 Elsevier Sci ence Ltd and IIR.