CONDENSATION MECHANISM

What is condensation?

When the temperature of vapour is reduced below its saturation temperature, condensate occurs.(In which vapour is converted into liquid.)

Film wise condensation

          ·          Most heat transfer surface on a heat exchanger are made of wettable materials.

          ·          During condensation, a film of condensate spreads over these surfaces. As the more vapour condensation on the outside of the film its thickness increases and under the action of gravity the film flows continuously over the surface.

          ·          A thermal gradient exists in the film and as a result it acts as a resistance to heat transfer .

          ·          Film condensation is generally characteristic of clean uncontaminated surface.

Drop wise condensation

·       If the heat transfer surface are treated to become 'non-wettable' the condensate that forms, on the surface will be shaped like spherical beads.

·       Here the vapour condenses into small liquid droplets of varying sizes.

·       These drops may ultimately get detached from the surface and eventually fall down.

·       Drop wise condensation is highly preferred to film wise condensation, it is extremely difficult to achieve or maintain it. This is because the condensate has a greater tendency to wet the surface.