its in gas viscosity calculation:
oC=degrees Celsius, K=Kelvin, oF=degrees Fahrenheit, oR=degrees Rankine, lb-s/ft2=pound-second per square foot, slug/ft-s=slug per foot per second, N-s/m2=Newton-second per square meter, kg/m-s=kilogram per meter per second, SG=specific gravity

The viscosity on this page is the dynamic (absolute) viscosity. Dynamic viscosity of gases is primarily a function of temperature. This variation is provided in Crane (1988) as a graph for hydrocarbon vapors and natural gases, and as an equation for other common gases. The impact of pressure is minor and the viscosity correction for pressure is less than 10% for the gases in our calculation for pressures up to 500 psi (34.5 bar) (Crane, 1988).

Hydrocarbon vapors and natural gases
The LMNO Engineering calculation takes the user input temperature and extracts viscosity from the graph on page A-5 in Crane (1988), performing linear interpolation if needed. The input temperature is restricted to the range 0 < temperature < 1000oF.

Other gases
Gas viscosity is computed using Sutherland's formula (Crane, 1988):

    μ = μo*(a/b)*(T/To)3/2

    a = 0.555To + C
    b = 0.555T + C

    μ  = viscosity in centipoise at input temperature T
    μo = reference viscosity in centipoise at reference temperature To
    T   = input temperature in degrees Rankine
    To = reference temperature in degrees Rankine
    C  = Sutherland's constant

The following table gives the values of Sutherland's constant and the reference temperature and viscosity for the gases used in the LMNO Engineering calculation. Values of Sutherland's constant are from Crane (1988, p.A-5). The reference temperatures and viscosities were selected from CRC (1984, pp.F-42-44).