Does Coating Change Condensate Drainage?
Key facts
| Surface behaviour | Effect on a wet cooling coil |
|---|---|
| Hydrophilic (water spreads) | Thin film drains down the fins; lower wet pressure drop |
| Hydrophobic (water beads) | Droplets may bridge fins or carry over at high velocity |
| Bridged fins from coating | Water held between fins; higher pressure drop |
| Under-cured film | May soften when wet for long periods |
Why surface matters
Condensate forms on a cooling coil as droplets or a film, depending on how easily water wets the surface. Hydrophilic fin stock is used on evaporators because it spreads water into a film that drains. A post-fabrication coating replaces that surface with its own.
Carry-over
Droplets that bridge the gaps between fins are pushed downstream by the airflow. At higher face velocities they can be blown off the coil into the unit, a problem known as carry-over. Manufacturers set face-velocity limits for this reason.
What to check
Ask how the coating behaves wet, check the manufacturer’s face-velocity limit for the coil, and look for bridging in the batch QC. Pressure-drop tests on a wet coil show the combined effect.
What this means for your project
For evaporators and AHU cooling coils, tell us the design face velocity. Thin films applied by dip are the default for wet coils.
