Any phenomena based on exponentials and or logarithms is inherently Non-Linear
Some Models for kinematic viscosity
The effect of temperature on the
kinematic viscosity is described by a number of
empirical equations.
The
Walther formula is typically written in the form
In lubricant specifications, normally only two temperatures are specified, in which case a standard value of
= 0.7 is normally assumed, and
and
are empirical parameters specific to each liquid.
The
Wright model has the form
is often a polynomial fit to experimental data, has been added to the Walther formula, and
and
are empirical parameters specific to each liquid.
The
Seeton model is based on
curve fitting the viscosity dependence of many liquids (
refrigerants, hydrocarbons and
lubricants) versus temperature and applies over a large temperature and viscosity range:
is the zero order modified
Bessel function of the second kind, and
and
are empirical parameters specific to each liquid. [Seeton, Christopher J. (2006), "Viscosity-temperature correlation for liquids",
Tribology Letters,
22: 67–78,
doi:
10.1007/s11249-006-9071-2]
"Handbook of Physics and Chemistry"