Entropy Generation Cause and Effect

In Section 3.3, we have shown that the entropy generation rate in the case of heat transfer in a heat exchanger is simply the product of the thermodynamic driving force X = A(l/T), the natural cause, and its effect, the resultant flow / = Q, a velocity or rate. Selected monographs on irreversible thermodynamics, see, for example, [1], show how entropy generation also has roots in other driving forces such as chemical potential differences or affinities. 

We have taken over this name for lack of a better one in order to distinguish between the effects caused by differences of entropy demands and those caused by entropy generation. In Eq. (8.25), the expression on the left represents the latent molar reaction entropy and the one on the right, the generated molar reaction... 

In phenomenological description (comparable to a kind of wanted poster ), the entropy appears as a kind of stufF which is distributed in space, can be stored or transferred, collected or distributed, soaked up or squeezed out, concentrated or dispersed. It is involved in aU thermal effects and can be considered their actual cause. Without it, there would be no hot and no cold. It can be easily generated, if the required energy is available, but it cannot be destroyed. Actually, entropy can be easily recognized by these effects. This direct understanding of the quantity S is deepened by a simplified molecular kinetic interpretation. 

An increase of U can be effected by heat dQ flowing into the system from the outside or by mechanical work dW done onto the system. The change of entropy may be split up into a portion —d S which is equal to dQ/T and into the internal entropy production d S caused by irreversible processes as for instance by stress relaxation or generation of heat through friction ... 

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