Experimental and theoretical studies on non-filmwise condensation techniques for enhancing heat transfer in the process of steam condensation

The current research discusses the various techniques used for enhancing heat transfer rate in the process of steam condensation both experimentally and theoretically. Two different types of hydrophobic coatings have been analyzed experimentally for their ability to promote dropwise condensation (DWC). Solutions of n-octadecyl mercaptan (defined as SAM-1 in the results) and stearic acid solution (defined as SAM-2 in the results) were used to form ultra thin organic hydrophobic films on the surface. An oxide layer was initially formed on the substrate surface before coating the surface with mono-layers. The oxide layer formed on the substrate surface tends to improve the bonding between the substrate and the mono-layers which eventually improves the longevity of the coating.; When compared to complete filmwise condensation, n-octadecyl mercaptan (SAM-1) coated surface increased the condensation heat transfer rate by a factor of 3 for copper alloy surfaces, under vacuum condition (33.86 kPa) and to about 8 times when operated under atmospheric condition (101 kPa) after 100 hrs of experimentation.; In the current research experiments were carried out using self assembled mono-layers SAM-1 (n-octadecyl mercaptan) coating increased the condensation heat transfer coefficient by a factor of approximately 3 after 100 hrs of experimentation and by a factor of approximately 1.6 after 3,600 hrs of experimentation for copper alloy surfaces, under vacuum condition (33.86 kPa). Lifetime of maintaining dropwise condensation is greatly dependent on the bonding of SAM coating to the condensing surface, from the experimental investigation it was evident that n-octadecyl mercaptan showed good DWC due to its covalent bonding with the substrate surface when compared to that of stearic acid which is bonded to the substrate surface by hydrogen bonding. Contact angles were measured for all the SAM coated surfaces before and after experimentation respectively.; In the current research we try to explain the surface tension effect for enhancing heat transfer rate in steam condensation using effective heat transfer additives. The surface tension induced stress at the liquid vapor interface due to the condensing steam combined with that of the heat transfer additive plays an important role in causing the breaking of the liquid film and producing a dropwise-like condensation. (Abstract shortened by UMI.)...