Classification according to scale degree of physical detail

Classification according to scale (degree of physical detail) 

Physicochemical models based on the degree of internal detail of the system encompassed by the model are classified in Table 2.2. The degree of detail about a process decreases as we proceed down the table. 

The most fundamental description of processes, in the present context, would be based on molecular considerations. A molecular description is distinguished by the fact that it treats an arbitrary system as if it were composed of individual entities, each of which obeys certain rules. Consequently, the properties and state variables of the system are obtained by summing over all of the entities. Quantum mechanics, equihbrium and non-equilibrium statistical mechanics, and classical mechanics are typical methods of analysis, by which the properties and responses of the system can be calculated. 

A microscopic description assumes that a process acts as a continuum and that the mass, momentum, and energy balances can be written in the form of phenomenological equations. This is the usual level of transport phenomena where detailed molecular 

Rgure 2.5. Concept of representative elementary volume for a fluid (a) and a porous medium (b), respectively. 

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