لقمان محمدپور

Condensation occurs on a solid wall when the surface temperature falls below the local saturation temperature of the adjacent vapor. On specially treated surfaces, liquid droplets will appear at specific nucleation sites. As condensation proceeds, these droplets grow, coalesce with neighboring drops, and may fall off or start to slide down the wall. The process is cyclic and drop instability will prevent the formation of a liquid film. Such a phase-change process, termed dropwise condensation, is heterogeneous, in which vapor condenses in the form of discrete liquid drops on or underneath a cold solid substrate. dro‎pwise condensation can be sustained only on specially textured surfaces. The subject is of interest because of specific features of this mode of condensation. The heat transfer coefficient during dropwise condensation can be quite high, for example, up to 30 times greater than the filmwise mode, when tested with Langmuir-Blodgett surfaces, and 5–20 times better when a promoter layer is. Therefore, dropwise condensation has the potential to diminish the size of heat exchange equipment used in thermal and nuclear power plants. We used Surface Evolver an interactive program for the study of surfaces shaped by surface tension and other energies to for modeling a single droplet on the desired surfaces. The Evolver evolves the surface toward minimal energy by a gradient descent method. After simulating the models using SE, we analysised the ruslets in Ansys Fluent. For the first step the effect of increasing the droplet volume on the heat transfer had been studied and the results has been showing that by increasing the droplet volume the rate of heat transfer passing through the droplet will decrease. By studying the of effect of an inclined surface on the rate of the heat transfer passing through the droplet we noticed that in droplets with small volume, by increasing the inclination angle the rate of the heat transfer will not have a noticeable change. And finally we noticed that the rate of the heat transfer through a droplet on a surface with casey roughness is much higher than than a smooth and wenzel roughness.