Engineering calculators / Geometry & flow
Net Open Area Velocity Calculator
Calculate average velocity through known open passages, or the flow corresponding to a selected opening velocity. Use actual volumetric flow at operating conditions.
Example inputs demonstrate arithmetic only. Unit changes convert existing values.
Formula and assumptions
Aopen = Agross × f − Ablocked; vopen = Qactual / Aopen; Qactual = vselected × Aopen
The percentage must describe geometric opening area on the same surface basis as the gross area. Subtract only openings actually blocked, without repeating edge deductions already included in the percentage. Porosity of sintered media is not a projected opening percentage. This average opening velocity is not media face velocity, interstitial velocity in a tortuous porous network, local peak velocity, pressure drop or filtration efficiency. No recommended velocity is supplied.
Frequently asked questions
Can I enter normal or standard gas flow?
No. Convert it to actual volumetric flow at the operating pressure and temperature first.
Does a 60% sintered-media porosity mean 60% open area?
No. Total pore volume fraction is different from a measured projected opening-area ratio.
Should I subtract the entire support-rib area?
Only subtract known opening area actually obscured. Do not automatically subtract the whole projected support-rib area or repeat previously included losses.
What does the reverse flow result mean?
It is the arithmetic flow corresponding to the velocity you supplied. It does not establish rated flow capacity.
Unit definitions: NIST SI conversion factors. Geometry is calculated from the explicit model above.
