The critical- and minimum-heat flux points conditions in a boiling curve are important because they are the hinge points for the nucleate, transition, and film boiling regimes. However, these boiling characteristics of binary mixtures have seldom been reported. In this work, boiling curves for ethanol/water and n-propanol/water binary mixtures were systematically obtained by quenching a sphere from high temperature in the saturated liquids. Pool boiling critical-heat-flux (CHF)-point condition (q_(CHF), #triangle openT_(CHF) and minimum-heat-flux (MHF)-point condition (q_(MHF), triangle openT_(MHF)) values were therafter determined from these boiling curves. Significant variations of q_(CHF), triangle openT_(CHF), q_(MHF) and triangle openT_(MHF) with the composition of the binary mixtures were evidenced. The two equations of Ded and Lienhard(1972) and Gunnerson and Cronenberg(1980), which were derived for single component fluids based on hydrodynamic instability theories, are shown to ill-predict the CHF and MHF, respectively, for a binary mixture. I is postulated that the mass diffusion in liquid mixture is basically responsible for the deviation in CHF and MHF of binary mixtures from those evaluated for an equivalent pure fluid(EPF), which is an ideal pure substance with exactly the same physical properties as the mixture. Other possible effects of binary mixtures in explanation of the observed boiling phenomena are also examined and discussed.
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