29.921 in. Hg

101.325 kPa


70°F (529.7°R)

21 °C (294.2°K)


0 %

0 %


0.075 lbm/ft3

fluid passing through the fan per unit of time. Since air or gas is compressible, the volumetric flow rate will vary depending on the location at which it is measured. The volumetric flow rate at the fan inlet is equal to the mass flow rate divided by the gas density.

The same static and dynamic head or pressure components that exist with pumps are present in compressible flow applications. Pressure gauges are calibrated in inches

(in.) of water (the pressure exerted by a column of water 1 in. high) or in. of mercury (Hg) for higher ranges at 60°F (15.55°C). One in. of water equals 0.036 psi and 1 in. of mercury equals 13.6 in. of water. In SI units, 1 millimeter (mm) of Hg equals 13.6 mm of water and 0.133 Pa.

Head (h) is the ratio of pressure (p) and fluid density (p), expressed as follows:

Guide to Alternative Fuels

Guide to Alternative Fuels

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