4.2 Dropwise Condensation

In dropwise condensation the surface is not fully covered by the liquid and exposed to the vapor for the condensation. Therefore, the heat transfer coefficient will be higher for dropwise condensation. Thus the dropwise condensation is preferred over the film condensation. However, the dropwise condensation is not practically easy to achieve. We have to put some coating on the surface or we have to add some additive to the vapor to have dropwise condensation.

  • If traces of oil are present in steam and the condensing surface is highly polished, the condensate film breaks into droplets. The droplets grow, coalesce, and runoff the surface, leaving a greater portion of the condensing surface freely exposed incoming steam.

  • Since the entire condensing surface is not covered with a continuous layer of liquid film, the heat transfer for ideal dropwise condensation of steam is much higher than that filmwise condensation of steam. The heat transfer coefficients may be 5 to 10 times greater.

  • Steam is the only pure vapor known to condense in a dropwise manner, and special conditions are required for its occurrence.