ACFM air to ACFM natural gas 1

TedHy,
In the natural gas industry, we usually refer gas volumes to standard conditions. You can do the conversion in two steps, first you can convert the air flow to standard conditions and then you can calculate the equivalent gas flow.

To correct to standard flow rate, Q[sub]s[/sub], you need to correct the flowing temperature T[sub]a[/sub] and pressure P[sub]a[/sub] to standard T - P conditions using the combined gas laws:

P[sub]s[/sub]Q[sub]s[/sub]/T[sub]s[/sub]Z[sub]s[/sub] = P[sub]a[/sub]Q[sub]a[/sub]/T[sub]a[/sub]Z[sub]a[/sub]

where the subscript a refers to actual conditions and the subscript s refers to standard conditions, Z is the compressibility.

Solving for Q[sub]s[/sub] and noting that Z[sub]s[/sub]=1 for P[sub]s[/sub] << 100 psia

Q[sub]s[/sub] = T[sub]s[/sub] P[sub]a[/sub]Q[sub]a[/sub]/T[sub]a[/sub]Z[sub]a[/sub] P[sub]s[/sub]

Now, you can work out an equivalent gas flow by using a simple valve equation. You can write,
Q[sub]s-gas[/sub] = C[sub]v[/sub] [&radic;][ (P[sub]a[/sub][&Delta;]P)/ (T[sub]a[/sub]G[sub]gas[/sub] Z[sub]gas[/sub])]
Q[sub]s-air[/sub] = C[sub]v[/sub] [&radic;][ (P[sub]a[/sub][&Delta;]P)/ (T[sub]a[/sub]G[sub]air[/sub] Z[sub]air[/sub])]

C[sub]v[/sub] , P[sub]a[/sub] , [&Delta;]P , and T[sub]a[/sub] cancel out when you take the ratio Q[sub]s-gas[/sub] / Q[sub]s-air[/sub]. Also note that the flow is assumed to be turbulent so that viscosity does not come into play.

Q[sub]s-gas[/sub] / Q[sub]s-air[/sub]= [&radic;][1/(G[sub]gas[/sub] Z[sub]gas[/sub])] / [&radic;][1/(G[sub]air[/sub] Z[sub]air[/sub])]

Q[sub]s-gas[/sub] / Q[sub]s-air[/sub]= [&radic;][(G[sub]air[/sub] Z[sub]air[/sub])/(G[sub]gas[/sub] Z[sub]gas[/sub])]

G[sub]air[/sub]=1 by definition. If P[sub]a[/sub] << 100 psia then Z[sub]air[/sub] and Z[sub]gas[/sub] can be taken as 1.0 and

Q[sub]s-gas[/sub] = Q[sub]s-air[/sub] [&radic;][1/G[sub]gas[/sub]]

Nomenclature:
Q[sub]s[/sub] = Volumetric flow rate at standard conditions.
P[sub]s[/sub] = Standard pressure.
T[sub]s[/sub] = Standard temperature.
Z[sub]s[/sub] = Compressibility at standard conditions.
Q[sub]a[/sub] = Volumetric flow rate at actual conditions.
P[sub]a[/sub] = Actual pressure.
T[sub]a[/sub] = Actual temperature.
Z[sub]a[/sub] = Compressibility at actual conditions.
Z[sub]air[/sub] = Compressibility of air at actual conditions.
Z[sub]gas[/sub] = Compressibility of gas at actual conditions.
Q[sub] s-gas [/sub] = Volumetric flow rate of gas at standard conditions.
Q[sub] s-air [/sub] = Volumetric flow rate of air at standard conditions.
Q[sub] a-gas [/sub] = Volumetric flow rate of gas at actual conditions.
Q[sub] a-air [/sub] = Volumetric flow rate of air at actual conditions.
C[sub]v[/sub] = Valve constant
[&Delta;]P = Pressure drop across the component.
G[sub]gas[/sub] = Specific gravity of gas (density gas/density air).
G[sub]air[/sub] = Specific gravity of air (density air/density air = 1.0).

Thank you for the information.

For the purpose of determining energy/BTU usage, would I use SCFM or ACFM?

TH

The energy content of natural gas is normally given at standard conditions, BTU/SCF, BTU/SCCF, BTU/SMCF.