چكيده به لاتين
Condensation on a solid surface is divided into two categories: layer condensation and droplet condensation. Various studies have shown that droplet condensation has a very high heat transfer coefficient compared to layer condensation. Drowise condensation can exist on a surface that has a low surface energy. In recent years, to lower the surface energy, researchers have focused on roughening the surface in different ways and using a hydrophobic coating on these roughnesses. If the condensed liquid droplets are located above the roughness and do not penetrate into the roughness, the Cassie state occurs, and if these droplets penetrate into the roughness and fill the space between the roughness, the Wenzel state occurs. Unlike the Wenzel mode, Cassie mode droplets have higher mobility due to less contact with the surface, which is a factor of increasing heat transfer, but due to the presence of steam between the roughnesses, unlike the Wenzel mode, which is filled with condensed liquid, it has a higher thermal resistance. This thesis has tried to obtain mathematical modeling of condensation on hydrophilic and hydrophobic mixed surfaces by considering Marangoni displacement in three states, smooth, Cassie and Wenzel, in order to obtain a better understanding of the functions of Cassie and Wenzel in different conditions. In this report, Cassie and Wenzel have been modeled on a smooth surface. After the mathematical modeling, the modeling results were compared with the laboratory test on the vertical circular surface that was made hydrophobic and hydrophilic by Teflon and laser in specific strips. In this research, Teflon and 1-octadecyl mercaptan were used as water repellants. Also, in this research, CFD simulation of single droplet condensation considering Marangoni displacement in equilibrium for surfaces with Cassie and Wenzel micro-nanostructures and smooth surface, mathematical modeling of condensation on a pipe with a combined hydrophobic and hydrophilic surface and experimental testing on a horizontal pipe with a mixed surface which were made hydrophobic and hydrophilic by 1-octadecyl mercaptan and tool (thread) was investigated. From the obtained results, we can point out the following: the heat transfer ratio of condensation on a combined hydrophilic and hydrophobic surface to full dropwise condensation at a fixed contact angle on a vertical surface, there is an optimal width for the hydrophobic area, which makes this ratio greater than unity. Also, this phenomenon is dominant for the Marangoni number greater than 2204. Therefore, the effect of Marangoni displacement was also investigated in mathematical modeling.
