Heat Transfer and Boiling Crisis at Droplets Evaporation of Ethanol Water Solution

Abstract

Droplets evaporation and boiling crisis of ethanol water solution were studied experimentally. At intensive nucleate boiling within a droplet, most evaporation relates to an increase in the area of the wetting droplet surface and only 10–20% of evaporation relates to the effect of diffusion and a change in the thermal–physical coefficients. In alcohol solution with mass salt concentration C0 = 25–35%, maximal instability of the bubble microlayer is observed. The critical heat flux behaves nonmonotonously due to changes in mass alcohol concentration in the solution, and there are two extrema. The maximal value of sustainability coefficient at droplets evaporation of ethanol solution corresponds to C0 of 25–30%. The heat transfer coefficient of ethanol water solution of droplet in the suspended state decreases with a rise of wall overheating and spheroid diameter. Experimental dependence of the vapor layer height on wall overheating at boiling crisis was observed. The height of this layer at Leidenfrost temperature was many times higher than the surface microroughness value. The liquid–vapor interface oscillates, and this extends the transitional temperature zone associated with a droplet's boiling crisis.