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Gas sonic velocity calculation
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1. Introduction
2. Sonic Velocity Calculation
3. Critical pressure ratio
1. Introduction
Calculating the sonic velocity is necessary for different design activities. It is also handy to be able to determine under which pressure drop a gas flow will reach sonic conditions.
2. Sonic Velocity Calculation
How to calculate a gas sonic velocity ?
Gas sonic velocity = Vs
= (K g R T)0.5
With :
Vs = Sonic velocity (ft/s)
K = Cp/Cv around 1.4 for most diatomic gases
g = 32.2 ft/s2
R = 1544 / M
T = Absolute temperature (°R)
The formula can also be expressed in SI units :
Gas sonic velocity = Vs
= (K.R.T)0.5
With :
Vs = Sonic velocity (m/s)
K = Cp/Cv around 1.4 for most diatomic gases
R = 8134/M (J/kg/K)
T = Absolute temperature (°K)
3. Critical pressure ratio
How to calculate the critical pressure ratio for a nozzle or orifice ?
Critical pressure ratio = [2/(K+1)]K/(K-1)
K = Cp/Cv around 1.4 for most diatomic gases
Source
[1] Rules of Thumbs for Chemical Engineers, Brannan,
Gulf, 2005
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