Pressure Tube Anemometer Measurement Equation

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Pressure Tube Anemometer Measurement Equation

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Pressure Tube Anemometer Air Flow Measurement Equation

The tube anemometer which uses the air flow pressure to measure the velocity. This works on the principle that, the air flow passing through the tube creates pressure where as the flow across a tube results in suction. Consider two tubes as shown in the Fig. 1 The pressure in the tube
parallel to the wind is the sum of atmospheric pressure and the wind pressure.

Tube Anemometer Figure 1

The drag force of a non-moving cup Anemometer is given by

Eq. 1
P₁ = P_A + 0.5 · C₁ · ρ _a · V²

Similarly in the tube perpendicular to the wind, the pressure is

Eq. 2
P₂ = P_A - 0.5 · C₂ · ρ _a · V²

where P_A is the atmospheric pressure and C₁ and C₂ are coefficients. Subtracting P₂ from P₁ and solving for V, we get

Eq. 3
V = [ 2 ( P₁ - P₂ ) / ( ρ _a · ( C₁ + C₂ ) ) ]^0.5

Thus, by measuring the difference in pressure inside the two tubes, the wind velocity can be estimated. Values of C₁ and C₂ are available with the instrument. The pressure is measured using standard manometers or pressure transducers. The major advantage of pressure tube anemometer is that it does not have any moving parts. This anemometer has limited application in the open field measurements as the presence of dust, moisture and insects can affect its accuracy.

Source:

Sathyajith Mathew
Wind Energy Fundamentals, Resource Analysis and Economics