Theory

In Sutherland's law, equation (1), $T_s$ sets how fast the growth of the viscosity with temperature levels off: well above $T_s$ the viscosity grows like $T^{1/2}$ , well below it like $T^{3/2}$ . For air $T_s$ = 110.4 K, so at exhaust temperatures the viscosity rises roughly with the square root of the temperature (air: 1.81e-5 Pa s at 20 °C, 4.09e-5 Pa s at 700 °C).

Equations

\mu(T) = \frac{A_s\,T^{3/2}}{T + T_s}

(1)

where	meaning	unit
$\mu$	Dynamic viscosity	Pa s
$A_s$	Sutherland coefficient	kg/(m s K^0.5)
$T_s$	Sutherland temperature (this setting)	K
$T$	Temperature	K

Default and rule

Default: 110.4 K (air)
Rule: 110.4 K.
Source: Sutherland's law (Sutherland, 1893); the air constant is that of the standard atmosphere (U.S. Standard Atmosphere, 1976).

Valid range > 0

Values

Positive. Change it only for a gas other than air or exhaust gas.

References 2

Sutherland, W. (1893). The viscosity of gases and molecular force. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 36(223), 507-531. DOI 10.1080/14786449308620508
NOAA, NASA and USAF (1976). U.S. Standard Atmosphere, 1976. NOAA-S/T-76-1562, NASA-TM-X-74335. Web page

Theory

Equations

Default and rule

Valid range > 0

Related 3

References 2