Chemical Industry and Chemical Engineering Quarterly 2012 Volume 18, Issue 2, Pages: 315-327
https://doi.org/10.2298/CICEQ111020008S
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Subcooled flow boiling heat transfer of ethanol aqueous solutions in vertical annulus space
Sarafraz M.M. (Young Researchers Club, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran)
Peyghambarzadeh S.M. (Chemical Engineering Department, Islamic Azad University, Mahshahr Branch, Mahshahr, Iran)
Vaeli N. (Chemical Engineering Department Islamic Azad University, Shahrreza Branch, Isfahan, Iran)
The subcooled flow boiling heat-transfer characteristics of water and ethanol
solutions in a vertical annulus have been investigated up to heat flux
132kW/m2. The variations in the effects of heat flux and fluid velocity, and
concentration of ethanol on the observed heat-transfer coefficients over a
range of ethanol concentrations implied an enhanced contribution of nucleate
boiling heat transfer in flow boiling, where both forced convection and
nucleate boiling heat transfer occurred. Increasing the ethanol concentration
led to a significant deterioration in the observed heat-transfer coefficient
because of a mixture effect, that resulted in a local rise in the saturation
temperature of ethanol/water solution at the vapor-liquid interface. The
reduction in the heat-transfer coefficient with increasing ethanol
concentration is also attributed to changes in the fluid properties (for
example, viscosity and heat capacity) of tested solutions with different
ethanol content. The experimental data were compared with some
well-established existing correlations. Results of comparisons indicate
existing correlations are unable to obtain the acceptable values. Therefore a
modified correlation based on Gnielinski correlation has been proposed that
predicts the heat transfer coefficient for ethanol/water solution with
uncertainty about 8% that is the least in comparison to other well-known
existing correlations.
Keywords: Flow boiling, Heat transfer, Ethanol, Water, Gnielinski correlation, Bubble generation