Energy conservation in open systems

The convectional and diffiisional parts of the flow can be made explicit by using (15.3.6) in (15.3.4)  

By virtue of their definitions, the nonconvective flows J must obey the relation 

In the absence of convection, the flow is entirely J. We then have 

In the presence of an external field, such as a static electric field, may have a part that depends on the field. When no field is present, is entirely due to diffusion in Chapters 18 and 19 we shall study such dijfusion-reaction systems under far-from-equilibrium conditions in some detail. 

In Chapter 2 we saw the foundations of the concept of energy and its conservation. We have also noted how this conservation law must be local. We can express the local form of the law in a differential form. The total energy density e is a sum of the kinetic and the internal energies  

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