Does Coating Increase Air-Side Pressure Drop?
Key facts
| Cause | Effect on pressure drop |
|---|---|
| Thin even film (5–15 μm) | Very small — the gap narrows by twice the film thickness |
| Thick film (20–40 μm and above) | Larger, especially at high fin density |
| Bridged fins | Blocked passages; the largest effect |
| Corroded uncoated fins | Deposits and collapsed fins also raise pressure drop over time |
Where pressure drop comes from
Air flowing through a coil loses pressure as it passes between the fins and around the tubes. Anything that narrows the passages raises the pressure drop; the fan then either uses more power or delivers less air.
How much a film narrows the gap
A film on both faces of neighbouring fins narrows the gap by twice its thickness. At 18 fins per inch the gap is about 1.3 mm, so a 10 μm film takes up under 2% of it, while a 40 μm film takes up about 6%.
Bridging is the real risk
When coating spans the gap between two fins, that passage is blocked entirely. A few bridged areas on a face can raise pressure drop more than the film on the whole coil.
What this means for your project
For high-density fins and microchannel coils, specify a thin-film system applied by dip, a bridging check on both faces in the batch QC, and a pressure-drop result from a before-and-after test.
