Entropy-generation analysis

An alternative to the lost-work or entropy-generation analysis is a work analysis. This is based on Eq. (4-366), written... 

A work aiialysis here expresses each of the individual work terms on the right as a fraction of tV,. A work analysis cannot be carried out in the case where a process is so inefficient that vVideal is positive, indicating ihat the process should produce work, but Ws is negative, indicating that the process in fact requires work. A lost-work or entropy-generation analysis is always possible. 

Thus, an analysis of the lost work, made by calculation of the fraction that each individual lost-work term represents of the total lost work, is the same as an analysis of the rate of entropy generation, made by expressing each individual entropy-generation term as a fraclion of the sum of all entropy-generation terms. 

The reader is referred to the original papers for detailed analysis, where the various components of entropy generation and irreversibility are defined. The advantage of this work is not only that it involves less approximation but also that it is revealing in terms of the basic thermodynamics. It should also be used by designers who should be able to see how design changes relate to increased or decreased local loss. 

Analysis of the process with respect to entropy generation is shown in the following table ... 

The theory treating near-equilibrium phenomena is called the linear nonequilibrium thermodynamics. It is based on the local equilibrium assumption in the system and phenomenological equations that linearly relate forces and flows of the processes of interest. Application of classical thermodynamics to nonequilibrium systems is valid for systems not too far from equilibrium. This condition does not prove excessively restrictive as many systems and phenomena can be found within the vicinity of equilibrium. Therefore equations for property changes between equilibrium states, such as the Gibbs relationship, can be utilized to express the entropy generation in nonequilibrium systems in terms of variables that are used in the transport and rate processes. The second law analysis determines the thermodynamic optimality of a physical process by determining the rate of entropy generation due to the irreversible process in the system for a required task. 

MicroChannel heat sinks, such as a microchannel of square cross section with internal longitudinal fins, are an integral part of most devices used for thermal management in electronic equipment cooling. A thermodynamic analysis may help optimize the height of fin and thermophysical parameters, based on the minimizing the entropy generation rates due to heat transfer and fluid flow within the microchannel. 

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