Duct pressure loss — Darcy–Weisbach — Sim your flow

Duct pressure loss with Reynolds number, Swamee–Jain and fittings. Results in Pa, mmH₂O and inH₂O.

Where the fan loses its strength

Every metre of duct and every bend costs pressure. That is why a 400 m³/h fan often delivers far less in real life. Take this into the operating point, and visualize the delivered flow — not the box rating.

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