Gas Flow from an Open PipeVolumetric flow from an open-ended pipe

What this calculates

This spreadsheet determines the flow rate of a gas through an open-ended in a pipe.

How to use it

Determine the pressure drop across the pipe (usually the regulator pressure) and enter it in inches WC in cell C5. Enter the INNER diameter of the pipe in cell C6. Enter the length of the pipe in cell C7 and the specific gravity of the gas in cell C8.

The spreadsheet will convert the items entered in cells C5,6,7 to the appropriate metric units before the calculation is done.

The gas flow rate is provided in m3/hour (cell C10) and in cubic feet per minute (cell C11).

Variables

Q: Gas flow rate [m³/hr]
ΔP: Pressure drop along the pipe length [mbar]
d: Internal pipe diameter [mm]
L: Pipe length [m]
Sg: Specific gravity of gas (relative to air) [—]

Equations

$$ Q = 0.00403 \, \left( \dfrac{ \Delta P \cdot d^{\,4.8} }{ Sg^{\,0.8} \cdot L } \right)^{\!0.555} $$Volumetric flow rate (Harris 1983)

Discussion

This equation is good for gas flow through open pipe ends, but not small leaks or punctures. Specific gravity of the gas can generally be obtained from the gas company for that region or from any number of reference books. This spreadsheet is not specific to any one type of gas.

Worked example

Example

A pipe with an inner diameter of 0.404 inches is opened up at a location 20 feet from the regulator, which is set at 12 inches WC. The gas in the pipe was propane, with a specific gravity of 1.5. What is the rate of flow through the open end of the pipe?

Enter the pressure setting of 12 in cell C3. Enter the inner diameter of 0.404 in cell C6. Enter the length of 20 feet in cell C7. Enter the specific gravity of 15 in cell C8.

The answer should be 4.02 m3/hr, or 2.36 cfm.

References

Harris, R. J. — The Investigation and Control of Gas Explosions in Buildings and Heat Plant, 1983.