Reference: Elementary Fluid Mechanics, 1940, John Wiley & Sons, Inc., John K. Vennard, page 163 “Illustrative Problem”


Pipe Flow Expert File: Case_24_Air_Through_Horizontal_Pipe.pfe


Problem Description:  

Air is pumped from a reservoir at 50 psi.a through a clean horizontal smooth pipe 3” in diameter and 2000 ft long.

The conditions of flow are isothermal and the temperature of the gas is 100 degrees F.  

With a flow rate of 40 lb/min what is the pressure 2000 ft downstream? 


The calculation method used for the published data was the Simplified version of the Complete Isothermal Equation, which neglects the term 2*ln(V2/V1) since this is normally small compared to f*(L/D).


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Fluid Data: Air at 100 °F, 0.0 psi.g, density 0.071 lb/ft3, viscosity 0.0191 centipoise.

Pipe Data: Internal diameter 3 inches, roughness 0.000001 inches.

Calculation Method: Complete Isothermal Flow equation, Node Adjust Method.

Standard Atmospheric Model: 68 °F, 14.696 psi absolute.

Gas Physical Model: Ideal Gas Law


Result Comparison: 


Data Item

Published data

Pipe Flow Expert

Pressure 2000 feet downstream

39.3 psi.a

38.96 psi.a

Friction factor

0.0145

0.014818


Commentary:

The published data and the calculated results compare well.


The published result was calculated using a friction factor of 0.0145 (which was read from a plot).

Pipe Flow Expert used a pipe roughness of 0.000001 inches, calculating a friction factor of 0.0148.