2. Definitions of transport properties

We say that each transport property is defined by a gradient law of proportionality between a flow and a gradient.

If the gas is subjected to a velocity gradient (du /dy ), this results in a flow of momentum which translates into a shear stressτ : $\tau =\eta \frac{\text{d}u}{\text{d}y}$

The dynamic viscosityη (in Pl or Pa · s) is the coefficient of proportionality between τ (in N · m ^{– 2} ) and du /dy (in s ^{– 1} ).

The thermal conductivityλ (W · m ^–1 · K ^–1 ) is the coefficient...