Gas viscosity¶
Gas viscosity as a function of temperature can be calculated from the following equation:
where coefficients A, B, C, and D are obtained from tables in the Yaws’ Handbook for inorganic and organic compounds. The Chemics function supports 372 inorganic gas species and 7,031 organic gas species. At a minimum, the function requires the formula name and temperature as input parameters; however, the CAS number may be needed as an input if more than one form of a species exists.
Viscosity of a gas mixture can be estimated as a weighted mean using the mixture function. Note that for a gas mixture, the sum of the components must equal 1.
Nomenclature¶
Source code¶

chemics.gas_viscosity.
mu_gas
(formula, temp, cas=None, full=False)[source]¶ Viscosity of gas as a function of temperature. Results calculated from coefficients in Yaws’ Critical Property Data for Chemical Engineers and Chemists 1. CAS (Chemical Abstracts Service) number may be required for some species.
 Parameters
formula (str) – Molecular formula of the gas.
temp (float) – Temperature of the gas [K]
cas (str, optional) – CAS number of the gas, required for some species []
full (bool, optional) – When set to
False
(default) just gas viscosity is returned. When set toTrue
then return gas viscosity and other information.
 Returns
mu_gas (float) – Viscosity of gas [micropoise]
mu_gas, cas, tmin, tmax, a, b, c, d (tuple) – Additional values are only returned when keyword
full=True
.mu_gas  Viscosity of gas [micropoise]cas  CAS number []tmin, tmax  Temperature range at which results are applicable [K]a, b, c, d  Values for regression coefficients []
 Raises
ValueError – If gas formula is not found in csv data file.
ValueError – If gas temperature is not in range between tmin and tmax.
Examples
>>> mu_gas('CH4', 810) 234.21
>>> mu_gas('C2Cl2F4', 900, cas='374072') 314.90
>>> mu_gas('H2', 404) 113.18
>>> mu_gas('N2', 773) 363.82
>>> mu_gas('N2', 773, full=True) (363.82, '7727379', 63.15, 1970.0, 4.46, 0.63, 0.00026, 5.41e08)
References
 1
Carl L. Yaws. Viscosity Gas Tables 80 and 81 in Yaws’ Critical Property Data for Chemical Engineers and Chemists. Published by Knovel, 2014.

chemics.gas_viscosity.
mu_graham
(mus, xs)[source]¶ Calculate viscosity of a gas mixture using Graham’s method 2. Formula presented here is based on Equation 1 from the Davidson report 3.
\[\mu_{mix} = \sum (x_i \cdot \mu_i)\]where \(\mu_{mix}\) is viscosity of the gas mixture, \(x_i\) is mole fraction [] of each component, and \(\mu_i\) is gas viscosity of each component.
 Parameters
mus (list, tuple, or array) – Viscosity of each gas component.
xs (list, tuple, or array) – Mole fraction of each gas component []
 Returns
mu (float) – Gas viscosity of the mixture. Units are same as input viscosity.
 Raises
ValueError – If sum of mole fractions does not equal 1.0
Example
>>> mu_h2 = cm.mu_gas('H2', 773.15) ... mu_n2 = cm.mu_gas('N2', 773.15) ... mu_graham([mu_h2, mu_n2], [0.85, 0.15]) 207.37
References
 2
Thomas Graham. On the Motion of Gases. Philosophical Transactions of the Royal Society of London, vol. 136, pp. 573631, 1846.
 3
Thomas Davidson. A Simple and Accurate Method for Calculating Viscosity of Gaseous Mixtures. United States Department of the Interior: Report of Investigations 9456, 1993.

chemics.gas_viscosity.
mu_herning
(mus, mws, xs)[source]¶ Calculate viscosity of a gas mixture using the approach by Herning and Zipperer 4. Formula presented here is based on Equation 1 from the Davidson report 5.
\[\mu_{mix} = \frac{\sum (\mu_i \cdot x_i \cdot \sqrt{MW_i})}{\sum (x_i \cdot \sqrt{MW_i})}\]where \(\mu_{mix}\) is viscosity of the gas mixture, \(x_i\) is mole fraction [] of each component, \(\mu_i\) is gas viscosity of each component, and \(MW_i\) is the molecular weight [g/mol] of each component.
 Parameters
mus (list, tuple, or array) – Viscosity of each gas component.
mws (list, tuple, or array) – Molecular weight of each gas component [g/mol]
xs (list, tuple, or array) – Mole fraction of each gas component []
 Returns
mu (float) – Gas viscosity of the mixture. Units are same as input viscosity.
 Raises
ValueError – If sum of mole fractions does not equal 1.0
Example
>>> mu_h2 = cm.mu_gas('H2', 773.15) ... mu_n2 = cm.mu_gas('N2', 773.15) ... mw_h2 = cm.mw('H2') ... mw_n2 = cm.mw('N2') ... mu_herning([mu_h2, mu_n2], [mw_h2, mw_n2], [0.85, 0.15]) 252.81
References
 4
F. Herning and L. Zipperer. Calculation of the Viscosity of Technical Gas Mixtures From the Viscosity of the Individual Gases. Gasund Wasserfach, vol. 79, pp. 6973, 1936.
 5
Thomas Davidson. A Simple and Accurate Method for Calculating Viscosity of Gaseous Mixtures. United States Department of the Interior: Report of Investigations 9456, 1993.