Second-law analysis

The second law of thermodynamics is applicable to all physical, chemical, and biological processes, as well as to heat and work conversions. The second law can quantify the thermodynamic equivalence of heat to work through exergy 

Second-law analysis can determine the level of energy dissipation from the rate of entropy production in the system. The entropy production approach is especially important in terms of process optimality since it allows the entropy production of each process to be determined separately. The map of the volumetric entropy production rate identifies the regions within the system where excessive entropy production occurs due to irreversible processes. Minimizing of excessive irreversibilities allows a thermodynamic optimum to be achieved for a required task. Estimation of the trade-offs between the various contributions to the rate of entropy production may be helpful for attaining thermodynamically optimum design and operation. 

In every nonequilibrium system, an entropy effect exists either within the system or through the boundary of the system. Entropy is an extensive property, and if a system consists of several parts, the total entropy is equal to the sum of the entropies of each part. Entropy balance is 

Change in total entropy = Total entropy in Total entropy out + Total entropy produced Entropy balance in the rate form is given by 

The general entropy balance relations for a control volume are given in terms of the rate of entropy change due to the heat transfer, mass flow, and entropy production 

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Second-law analysis looks at the individual components of an overall process to define the causes of lost work. Sometimes it focuses on the efficiency of a step and ratios the theoretical work needed to accomplish a change, eg, a separation, to that actually used. 

Typically, the biggest lost that occurs in chemical processes is in the combustion step (6). One-third of the work potential of natural gas is lost when it is burned with unpreheated air. Eigure 3 shows a conventional and a second law heat balance. The conventional analysis only points to recovery of heat from the stack as an energy improvement. Second law analysis shows that other losses are much greater. 

Meunier, F., Second law analysis of a solid adsorption heat pump operating on reversible cascade cycles application to the zeolite-water pair. Heat Recovery Systems, 1985, 5, 133 141. 

El-Masri. M.A. (1986b), On thermodynamics of gas turbine cycles Part I second law analysis of combined cycles, ASME J. Engng Power Gas Turbines 107, 880-889. 

Adebiyi, G.A., and Russell, L.D., 1987, A second law analysis of phase change thermal energy storage systems, ASME HTD 80 9—20. 

An earlier book, ACS Symposium Series No. 122, Thermodynamics Second Law Analysis, is an introduction to the direct application of the second law of thermodynamics to (1) process efficiency analysis and (2) cost accounting in energy conversion systems and chemical/metallurgic processes. Since the publication of that volume, there has been a steady growth in the interest in applying these methods, and hence, more applications that encompass a greater realm of processes have surfaced. The purpose of this sequel is to present these new applications—in particular those that shed additional light on the theory and practice of the subject. The reader may wish to refer... 

For any conversion, the theoretical upper limit of rin is 100%, which corresponds to the ideal case with no dissipations. To approach this limit in practice requires the investment of greater and greater capital and/or time. The tradeoff, then, is the classical one operating costs (for fuel) versus capital (for equipment and time). The important point here is that attainment of the optimal, economic design can be greatly facilitated by the application of Second-Law analysis (i.e., exergy analyses) to processes, devices, and systems. 

Wepfer, W.J. and Gaggioli, R.A., "Reference Datums for Available Energy", Thermodynamics Second Law Analysis, A.C.S. Symposium Series, 122, 77-92, 1980. 

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