Question

Drop wise condensation usually occurs on:

• A. Oily surface
• B. Glazed surface
• C. Smooth surface
• D. Coated surface

Hint:

Drop-wise condensation offers 5–10 times higher heat transfer than film-wise and usually occurs on hydrophobic, oily, or treated surfaces.

Answer 1

The Correct Option is A

Condensation of vapor on a surface can occur in two forms: film-wise and drop-wise condensation.
Film-wise condensation occurs when the condensate wets the surface and forms a continuous liquid film. This film acts as a resistance to heat transfer.
In contrast, drop-wise condensation occurs when the surface does not allow the liquid to spread, leading to the formation of discrete droplets that roll off the surface, allowing continuous fresh surface exposure. This results in much higher heat transfer rates.
Drop-wise condensation is promoted on non-wettable surfaces, especially those that are hydrophobic or coated with substances like oil.
An oily surface resists wetting, which encourages the formation of individual droplets instead of a film. Hence, it is the most favorable for drop-wise condensation.
Option analysis:
- Glazed surface: Though relatively smooth, it does not prevent wetting effectively.
- Smooth surface: Not necessarily non-wettable, can still support film formation.
- Coated surface: Vague term; unless specifically oil-coated, it doesn't imply drop-wise condensation.
Therefore, drop-wise condensation is best achieved on an oily surface.