چكيده به لاتين
Condensation phenomenon occurring on the surfaces appears in two modes including filmwise condensation (FWC) and dropwise condensation (DWC). It is well-known that dropwise condensation (DWC) has considerably higher heat transfer than filmwise condensation.
Dropwise condensation can exist on surface with low surface energy. Recent years many research studies have focused on using micro/nano-structured SH surfaces for DWC purposes. If droplet stays on roughness and cannot penetrate between the roughness it is Cassie state and if it penetrates between the roughness it is called Wenzel state. Unlike Wenzel state, Cassie state droplets have high mobility because of its less interface with surface. In the other hand Cassie state droplets have higher thermal resistance than Wenzel state because of trapped vapor between the pillars. In this study both Cassie and Wenzel state droplets in DWC are studied numerically. As well as, effects of surface roughness shapes on heat transfer of DWC is studied. To do this, two fundamental roughness shapes including semi-conical and semi-pyramidal and their limit states including prismatic and cylindrical roughness have been considered. The results of different roughness shapes are extracted at same solid fraction and roughness factor.
The results show that Wenzel or Cassie droplets are not generally the best morphology in DWC from heat transfer point of view. In fact, the surface conditions such as surface energy, roughness geometry and roughness arrangement determines the best morphology. DWC heat transfer can be enhanced by adjusting roughness geometry and at constant roughness factor and solid fraction, pyramidal and conical roughnesses are better than prismatic and cylindrical roughness from heat transfer point of view.
Keywords: Dropwise condensation, Numerical modeling, Heat transfer, Cassie and Wenzel, Roughed surfaces
