EngineerBenchRelating dust-collection airflow and duct size
Airflow equals duct cross-sectional area multiplied by air velocity. For the same airflow, a smaller round duct gives a higher velocity. The calculator can solve for airflow, velocity, or diameter and estimate pressure loss along the entered duct run.
Use actual inside diameter and run losses
Inside diameter determines flow area; nominal duct size may not describe every fitting or flexible section. Enter a friction factor and fitting-loss total appropriate to the run. The pressure calculation does not automatically include the hood, separator, filter, or losses elsewhere in the system.
A fan's advertised airflow is not the operating flow
Actual airflow depends on the fan curve and the complete system's resistance. Add the other losses before comparing with a fan curve. Capture at the machine and transport of the particular dust need suitable equipment guidance; this single-run calculation is not a branched-network or dust-hazard design.
Comparing velocity and pressure loss
For a fixed airflow, reducing duct diameter reduces area and increases velocity. Higher velocity also increases the velocity-pressure term used in the loss calculation. The resulting pressure loss is not determined by diameter alone: run length, friction factor, fittings, and air density all contribute. A short smooth run and a long flexible run can behave differently at the same nominal size.
The worksheet solves one represented run, not the balance of several branches with gates in different positions. Use inside diameter and an appropriate fitting-loss sum, then add losses for the capture hood, separator, filter, and other components before comparing with the fan curve. A fan's free-air rating occurs under a different resistance condition and is not automatically the flow delivered at the machine. Required capture and transport conditions depend on the process and dust. The calculated velocity cannot establish that hazardous dust is controlled, that a hood captures emissions, or that a system meets fire and explosion protection requirements.
Formula
Q = vπD²/4. Darcy-Weisbach run loss = (fL/D + ΣK)ρv²/2.