ABSTRACT
We can say that the flux of particles, the number of particles moving per unit time, per unit area, is a function of this gradient:
Flux = f(Gradient) (2.1)
This functionality may be quite complex, especially for systems composed of many different components or in systems where many state variables are changing simultaneously. Fortunately, for most engineering purposes, the fluxes can be approximated quite accurately by making them linearly proportional to gradients in the state variables. The constants of proportionality in the relationships we call the transport properties of the material.
