Critical heat flux on flow boiling of ethanol–water mixtures in a diverging microchannel with artificial cavities

Abstract

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.This study investigates experimentally the convective boiling heat transfer and the critical heat flux (CHF) of ethanol–water mixtures in a diverging microchannel with artificial cavities. Experimental results show that the boiling heat transfer and the CHF are significantly influenced by the molar fraction (xm) as well as the mass flux. The CHF increases from xm=0 to 0.1, and then decreases rapidly from xm=0.1 to 1 at a given mass flux of 175 kg/m2s. The maximum CHF is reached at xm=0.1 due to the Marangoni effect, indicating that small additions of ethanol into water could significantly increase the CHF. On the other hand, the CHF increases with increasing the mass flux at a given molar fraction of 0.1. None of existing correlations for the CHF on flow boiling of pure component in a microchannel could present the correct trend as the CHF data on flow boiling of ethanol–water mixtures, and none of those correlations could predict the CHF precisely. However, the experimental results of the CHF show an excellent agreement with an empirical correlation for the CHF prediction of flow boiling of the mixtures, proposed by Lin et al. [1]. That, the overall mean absolute error of this correlation is 8.49% and more than 80% of the experimental data are predicted within a ±15% error band, confirms the correlation may accurately catch the Marangoni effect on the CHF of ethanol–water mixtures (present study) as well as methanol– water mixtures (our previous study [1]), and it is expected that this correlation may be applied for other convective boiling of binary mixtures.