In this present work, bubble dynamics of subcooled flow boiling in water–ethanol mixture is investigated through visualization using a high-speed camera in horizontal rectangular channels. The heat transfer coefficient of water–ethanol mixture during subcooled flow boiling is determined for various parameters like heat flux, mass flux, and channel inlet temperature. The effect of bubble departure diameter on heat transfer coefficient is discussed. A correlation is developed for subcooled flow boiling Nusselt number of water–ethanol mixture. The parameters considered for correlation are grouped as dimensionless numbers by Buckingham π-theorem. The present correlation is compared with the experimental data. The mean absolute error (MAE) of Nusselt number of water–ethanol mixture calculated from the experimental data and those predicted from the present correlation is 10.39%. The present correlation is also compared with the available literature correlations developed for water. The MAE of Nusselt number of water predicted from the present correlation and those predicted with Papel, Badiuzzaman, Moles–Shaw, and Baburajan correlations is 41%, 19.61%, 29.9%, and 43.1%, respectively.

In the present study, heat transfer coefficient of water-ethanol mixture in the subcooled boiling region is determined in a rectangular conventional channel (Channel size ≥3 mm). When the heat flux and mass flux increase it is observed that heat transfer coefficient increases. But the effect of heat flux is significant when compared with that of mass flux in the subcooled boiling region. It is found that maximum and minimum heat transfer coefficient are observed for mixture with 25% Ethanol volume fraction and 75% Ethanol volume fraction respectively. Wall heat flux partitioning analyses is carried out for mixture with different ethanol volume to determine the contribution of heat flux towards convection, agitation and evaporation. It is also found that heat flux due to convection decreases with increase in heat flux at partial and fully developed nucleate boiling heat regions for all volume fractions. The heat flux determined from the partitioning analysis are lower than the experimentally determined heat flux values at the partial nucleate boiling region and are higher at the fully developed boiling region.

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