Inhomogeneous Systems Postulate of Quasi-Equilibrium for Physically Small Volumes

Inhomogeneous Systems Postulate of Quasi-Equilibrium for Physically Small Volumes 

In most cases, nonequilibrium systems are spatially inhomogeneous. For the entropy of such systems to be determined, the approximation of local quasi-equiHbrium [2, 4] should be realized as the basic one. To be exact, divide the inhomogeneous system into physically small volumes (sites) having the following properties  

1) The size of the site Ax is less than the characteristic inhomogeneity length over the considered property (for example. Ax T/ gradr ). 

2) The relaxation time of the site to equilibrium at external parameters being fixed is less than the characteristic time for a nonequiHbrium process (for example, T r/ ar/9t ). 

3) The site contains many more bulk atoms when compared to the number of surface atoms this separates it from other sites (which provides additivity of energy and entropy). 

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