Presentation on Filmwise and Dropwise Condensation

Presentation on Filmwise and Dropwise Condensation

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  PRESENTATION ON FILMWISEAND DROPWISE CONDENSATION BY: KRISHNA KHANDELWAL(10BEM0083)
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  WHAT IS CONDENSATION? Occurs when the temperature of vapour is reduced below its saturation temperature(Tsat).  Saturation temperature is the temperature at which vapour change into liquid.  This is done by bringing the vapour into contact with solid surface whose temperature(Ts)is below the saturation temperature of the vapour.
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  TYPES OF CONDENSATION DROPWISE CONDENSATION .  FILMWISE CONDENSATION.
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  DROPWISE CONDENSATION  Thecondensed vapor forms droplet on the surface instead of continuous film.  The small droplets that forms at the nucleation sites on the surface grow as a result of continued condesation,coalesce into large droplets and slide down when the reach the certain size.  The surface is covered by countless droplets of varying diameter.
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   Observed tooccur either on highly polished surfaces. Or on surfaces contaminated with impurities like organic compounds.  It is achieved by adding a promoting chemical into the vapour ,treating the surface with a promoter chemical or coating the surface with a polymer(teflon) or a noble metal(Ag,Pt,Au).  The promoters used are wax ,fatty acid like oleic ,linoic acid.  Dropwise condensation didn’t last long and converted to film condensation after sometime
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  FILMWISE CONDENSATION  Thecondensate tends to wet the surface and thereby forms a liquid film.  The liquid flows down the cooling surface under the action of gravity.  The thickness of the film increases in the flow direction as more vapor condenses on the film.
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  DIFFERENCE BETWEEN FILMWISEAND DROPWISE CONDENSATION  Heat transfer at in dropwise is 10 times larger than in filmwise .  In dropwise a large area of solid surface is directly exposed to vapour .  Dropwise condensation occurs on nonwettable surface while filmwise occurs on wettable surfaces.
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