Dropwise Condensation Essay

MATHEMATICAL MODELING ON DROPWISE CONDENSATION
1Mr.Shivaji S.Parihar,2Prof. PrashnatT.Borlepwar,
12Mechanical Department,Maharashtra Institute Of Technology,
Aurangabad, M.S. India.
,

Abstract:-The phenomenon of dropwise condensation, in which the condensate forms into dropsrather than covering the entire cooling surface with a continuous film.Dropwise condensation produces heattransfercoefficients as much as 2 to 10 times greater than those produced by filmwisecondensation.Hence dropwise condensation is always desirable as it is more effective method of heat transfer than filmwisecondensation.Dropwise condensation can be promoted by applying (i) Suitable organic promoter (ii) Thin layer of special metal (iii) Coating with polymer film

If condensate tends to wet the surface and there by forms a liquid film, then processes of condensation is known as film wise condensation & on the other hand if condensate does not tends to wet the surface, the condensate forms the droplets on the surface and every time fresh surface is exposed to the vapour. By specially treating the condensing surface the contact angle can be changed & the surface become ‘non – wettable’.Very high heat transfer rate are reported in dropwise processes due to the good contact between the vapour and surface.[1] Condensation is the change of phase from the vapour state to the liquid or solid state.Condensation plays a major role in the heat rejection parts which generally involve pure substances. The random nucleation, growth and departure of droplets results in a certain size distribution of droplets on the condenser surface.[2] The drop size distribution and the heat transfer through the individual droplets must be known in order to calculate the heat flux with dropwise condensation. Dropwise condensation has been obtained on these types of surface by one of three methodsi) Coating the surface with certain chemical substances called promotersii) Coating the surface with a solid hydrophobic non-metallic materialiii) Coating the surface with a noble metal.The thickness of the promoter layer on the condensation surface also affects the type of condensation, if the layer is too thin filmwise condensation occurs whereas excessive amounts of promoter increases the wettability of the