E4.6 Orifice - Gas Flow

Example 4.6: Air is flowing through an orifice meter and water manometer reads 1 in. What is the expansion factor of this meter? The density of air under the operating conditions is 0.075 lb/ft³. Nominal diameters of orifice are 3 in and 2 in. Use the following information:

Heat capacity ratio, k = 1.4, density of water = 62.43 lb/ft³, density of air = 0.075 lb/ft³

Inlet pressure of air, P₁ = 14.7 psi.

Solution

Pressure drop, ΔP (Equation 4.1)

Final pressure, P₂:

P₂ = P₁ - ΔP = 2116.2 - 5.2 = 2111 lb_f/ft²

Pressure ratio, r (Equation 4.8):

r = P₂/P₁ = 2111/2116.2 = 0.998

Diameter ratio, β (Equation 4.6)

d₂ = 0.622 in, d₁ = 3.068 in

β = d₂/d₁ = 0.622/3.068 = 0.203.

Expansion factor, Y (Equation 4.10).