Determine the capture velocity for a particular pollutant by using the equation Q = VH x (10 D^2 + A). "A" represents fume hood area; "D" is the distance from the hood where the pollutant is released (assume 12 inches); VH is recommended hood capture velocity for a pollutant (300 feet per minute); and Q is the volumetric flow rate. Solving for Q specifies the volumetric flow rate required to achieve a capture velocity within a distance D inches from the hood opening. Rearrange the equation to solve for VH and you can determine the capture velocity for your hood at D inches from the hood opening. VH = Q / (10D^2 + A) with the variables plugged into the equation yields a capture velocity, VH for your hood, is the volumetric flow rate of exhaust divided by 1640 for the values in this example. The value of VH is not dependent on the shape of the hood but only on the particular pollutant released. The volumetric flow rate of the hood will determine the exhausting ability of the hood for pollutants in the laboratory.
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