What is CFM, and how do you measure it in relation to something familiar

Cubic Feet per Minute. It is a measure of the volume of air flow.

It is used to rate fans etc.

CFM means cubic feet per minute and is a measurement of air flow. This can be done using a number of methods like an anemometer, a wind gauge, or even by a measuring the amount of time it takes for a puff of smoke to travel a premeasured distance. CFM also depends on the dimensions of the area in which it is measured.

For horizontal fluid flow, an increase in the velocity of flow will result in a decrease in the static pressure. The equation describing this effect is known as Bernoulli is law. The most practical example of this is in the action of an airfoil. The shape of an airplane wing is such that air flowing over the top of the wing must travel faster than the air flowing under the wing, & so there is less pressure on the top than on the bottom, resulting in lift.

Bernoulli is law describes the behavior of a fluid under varying conditions of flow & height. It states

P + ½ pv² + pgh = [constant]


where P is the static pressure (in Newtons per square meter), is the fluid density (in kg per cubic meter), v is the velocity of fluid flow (in meters per second) & h is the height above a reference surface. The second term in this equation is known as the dynamic pressure. The effect described by this law is called the Bernoulli effect, & is sometimes known as Bernoulli is equation.