Experimental Description of the Convective Heat Transfer Coefficient for Pool Boiling of Binary Mixtures on Porous Heating Surfaces

This work presents the experimental results of the effect of porous heating surfaces, and the Marangoni effect on the convective heat transfer coefficient for pool boiling, h. The porous heating surfaces fabricated for these experiments, and the interfacial tension gradients in the binary mixtures reduced the bubbles’ size and their coalescence in the proximity of the heating surface. The convective heat transfer coefficient was calculated for the boiling of pure water and three aqueous mixtures with 12, 16, and 20% weight of ethanol on five different porous coverings on the heating element. Some combinations of these variables were studied in a 3² factorial design, and represented by the response surface calculated. The maximum h for boiling of pure water on the bare surface of the heating element was 50 kW/m² °C. Using the porous coverings, the maximum h value was 180 kW/m² °C. For boiling the binary mixtures on the smooth heating element surface the maximum h value was 65 kW/m² °C, while on the porous coverings the values of h attained a maximum of 220 kW/m² °C. The maximum values of h correspond to the composition of 16% ethanol, and a porous covering with the smallest porous diameter.