AGA 10

Speed of Sound in Natural Gas and Other Related Hydrocarbon Gases

This standard calculates several thermodynamic and physical properties including the speed of sound in the gas at flowing conditions.


Composition Limits


The table below lists the composition limits for both the Gross (Normal Range) and Detailed (Extended Range) methods.


Component Extended Range
Min.% Max.%
Methane 0 100
Ethane 0 100
Propane 0 12
iButane 0 6
nButane 0 6
iPentane 0 4
nPentane 0 4
neo-Pentane 0 4
nHexane 0 100
nHeptane 0 100
nOctane 0 100
nNonane 0 0.2
nDecane 0 100
Hydrogen 0 100
Nitrogen 0 100
Carbon Dioxide 0 100
Hydrogen Sulphide 0 100
Water 0 100
Helium 0 3
Oxygen 0 21
Carbon Monoxide 0 3
Argon 0 1

Procedure

The general procedure for computing the speed of sound at the flowing or operating conditions is as follows:


Step 1. Input the operating temperature (T), the operating pressure (P) and the gas composition
Step 2. Calculate the molar mass of the mixture
Step 3. Calculate the compression factor and density of the fluid at the operating conditions
Step 4. Calculate the ideal gas constant pressure heat capacity at the operating temperature
Step 5. Calculate the real gas constant volume heat capacity at the operating conditions
Step 6. Calculate the real gas constant pressure heat capacity at the operating conditions
Step 7. Calculate the ratio of heat capacities, cp/cv, at the operating conditions
Step 8. Calculate the speed of sound based on the results of the preceding steps
Step 9. Calculate the isentropic exponent, k.

Upstream Compression Factor


The upstream density is determined from gas compression factor at upstream conditions for temperature and pressure. The compression factor is calculated using the detail characterisation method defined in American Gas Association Report No.10 2003.

Upstream Density


The upstream density and gas compression factor are related as follows:
Upstream Density

Symbol Description Units
ρ1 Density at the upstream pressure point P1 kg/m3
m Gas molar mass kg/kmol
p1 Upstream pressure bar a
z1 Compression factor at upstream conditions -
t1 Upstream temperature K

Constant Description Value Units
R Universal Gas Constant 8.314510e-3 kJ/mol/K

Standard Compression Factor


The standard density is determined from gas compression factor at standard conditions for temperature and pressure. The compression factor is calculated ising the detail characterisation method defined in American Gas Association Report No.10 2003.

Standard Density


The standard density and gas compression factor are related as follows:
Standard Density

Symbol Description Units
ρb Density at standard conditions kg/Sm3
m Gas molar mass kg/kmol
pb Standard pressure bar a
z1 Compression factor at standard conditions -
tb Standard temperature K

Constant Description Value Units
R Universal Gas Constant 8.314510e-3 kJ/mol/K

Speed of Sound


The speed of sound can be calculated as follows:
AGA10_SpeedofSound

Symbol Description Units
W Speed of sound m/s
CP Constant pressure heat capacity J/kg-mol.K
CV Constant volume heat capacity J/kg-mol.K
T Stream temperature K
Mr Molar mass of the mixture kg/kmol
Z Upstream compression factor -
ρ Stream density kg/m3
∂Z/∂ρ Partial derivative of Z with respect to ρ -


Constant Description Value Units
R Universal Gas Constant 8.314510e-3 kJ/mol/K

References