Pipe Flow Expert Software Non Compressible Results Verification - Case 39: Air - Isothermal Flow Through a Pipe

Reference:  Theory and Problems of Fluid Mechanics and Hydraulics, 1993, McGraw-Hill, R V Giles, Jack B. Evett, Ph. D., Cheng Liu, M.S., Page 237, Example problem 11.1

Pipe Flow Expert File: Case_39_Air_Isothermal_Flow_Through_A_Pipe.pfe

Problem Description: 

Air at temperature of 65°F flows through a pipe with 6” internal diameter.

The pipe surface is smooth and the flow is isothermal.

The pressure at the start of a 550 ft long horizontal pipe section is 82 psia (67.3 psig) the pressure at the end of the section is 65 psia (50.3 psig).

Calculate the weight flow rate of the air.

Note: This case is solved here using Pipe Flow Expert’s non-compressible calculation engine. See the commentary below for more details. 

This case has also been solved using Pipe Flow Expert’s compressible calculation engine and the results are reported in the separate Compressible Results Verification document (Case 01).

Fluid Data: Air at 65°F at an average density of 73.5 psia (58.8 psig)

Result Comparison: 

Commentary: 

The published data and the calculated results compare well.

The published text assumes an initial friction factor of 0.0095 and this is then used to estimate the weight of flow as 14.5 lb/sec. The weight of flow is then used to recalculate the friction factor as 0.0097.

The new friction factor is compared to the initial assumed friction factor value and is taken as confirmation of the previously calculated weight of flow.

The Pipe Flow Expert program uses the Darcy-Weisbach equation to determine flow rates and pressure loss in pipes.  

Where the system includes compressible fluids and the pressure loss is greater than 10% of the entering pressure the calculations need to be carried out using the average fluid density to obtain an accurate result.

The average density of the air in the pipe has been used in the Pipe Flow Expert Calculation.

Normally Pipe Flow Expert would be used with the Compressible Flow calculation engine to analyze this system.