Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : condensation

Experimental Analysis of Heat Transfer with Dropwise and Filmwise Condensation on Inclined Double Tubes Heat Exchanger

Abdulhassan A. Karamallah; Assim H. Yousif; Ban M. Mohammed

Engineering and Technology Journal, 2014, Volume 32, Issue 7, Pages 1640-1654

Dropwise condensation provides larger heat transfer coefficients compared to filmwise condensation, as discovered in the year 1930 by Schmid et al. Dropwise condensation can be described as a phenomenon of the incomplete wettability of a surface.
The wettability of the surface is responsible for the formation of the respective type of condensation and has a very strong effect on the performance of the heat transfer process. Likewise, the wettability of the surface has a very strong effect on the subcooling of the condensate, for constant cooling performance.
Although the conditions necessary for promoting dropwise condensation are well known since several decades, and experiments with coatings as promoters have been carried out successfully, at least in part, the application of dropwise condensation is still today in a testing phase.
The main problems in the realization of dropwise condensation are the insufficiency of the theoretical description of working boundary surface phenomena, such as complete or incomplete wettability and their strong dependence on influences caused in the practical operation by contamination, oxidation of the surface, adsorption layers, and gas enclosures.

Effect of Exit Pressure of Steam Turbine Last Stage Cascade Blade on Two Phases of Saturated Vapor and Water Droplet

Assim H. Yousif; Amer M. Al-Dabbagh; Reyadh Ch. Mahawi

Engineering and Technology Journal, 2013, Volume 31, Issue 2, Pages 235-244

Experimental investigation was carried out in low pressure steam turbine cascade to determine the effect of exit pressure on two phases of saturated vapor and fine water droplet. Numerical investigation was also presented by assuming the flow is two dimensional, compressible, turbulent, viscous, with the aid of the classical nucleation model applied for the mass transfer in the transonic conditions to predict the two phases behavior in the cascade. Comparison between experimental and theoretical results for the cascade flow was found to be fairly acceptable. Experimentally it was found that the most important influence of rapid condensation on the pressure distribution is on the suction surface. Also when the outlet is termed supersonic the heat release causes a pressure rise in the zone of rapid condensation, therefore the term "condensation shock" for this feature is misleading. In the numerical approach when the flow is regard subsonic the rapid condensation zone occurs downstream the throat and not accompanied by a pressure rise, while in the experimental test for the same case there is no sign of this condensation.