Free Area Ratio

An easy way to represent a perforated plate or a baffle that has a known open (free) area is to use a free area ratio.

The free area ratio is the ratio of the open area to the total area of the plate or baffle:

To input a free area ratio:

Example showing creation of a Free Area Ratio Resistance

The relationship between loss coefficient, K, and free area ratio, FAR, is given as:

Note: This equation is valid for flow with Reynolds number greater than 105. The ratio of the flat portion of the hole length, l, to hydraulic diameter, Dh, is between 0 and 0.015: