Out of equilibrium with the environment

We turn to Figure 6.2, which shows a specific mass, let us say 1 mol, of air that is out of equilibrium with the environment only with respect to its temperature T, which has been chosen to be larger than T0, the temperature of the environment. As has been shown before in this chapter, Equation 6.11, thermodynamics allows us to calculate the minimum amount of work required to bring this mass out of equilibrium with the environment Weired Weired... 

Physical exergy out of equilibrium with the environment in temperature. 

In Figure 6.2, we studied an arbitrary mass of air that was out of equilibrium with its environment because its temperature T > T0. We mentioned that thermodynamics allows us to calculate the minimum amount of work, Wr " / that it takes to create this nonequilibrium situation. Well considered, this amount of air creates a structure within its environment, in which a different... 

Recall that exergy values reflect the extent to which a compound or mixture is out of equilibrium with our environment. Examples are differences in pressure and temperature with the environment. Differences in temperature lead to heat transfer, while differences in pressure lead to mass flow. Chapter 6 shows that the physical exergy represents the maximum amount of work that can be obtained from a system by converting a system s pressure and temperature to those of our environment. 

Linear polarization instruments provide an instantaneous corrosion-rate data, by utilizing polarization phenomena. These instruments are commercially available as two-electrode Corrater and three electrode Pairmeter (Figure 4-472). The instruments are portable, with probes that can be utilized at several locations in the drilling fluid circulatory systems. In both Corrater and Pairmeter, the technique involves monitoring electrical potential of one of the electrodes with respect to one of the other electrodes as a small electrical current is applied. The amount of applied current necessary to change potential (no more than 10 to 20 mV) is proportional to corrosion intensity. The electronic meter converts the amount of current to read out a number that represents the corrosion rate in mpy. Before recording the data, sufficient time should be allowed for the electrodes to reach equilibrium with the environment. The corrosion-rate reading obtained by these instruments is due to corrosion of the probe element at that instant [184]. 

The use of wood in long-life products, such as buildings, ensures that this sequestered carbon is held in a materials pool for a longer time. If the use of renewables is encouraged, then more carbon is stored in this manner. Eventually, of course, such systems will establish equilibrium with the environment, as the materials flow into the pool equals the materials flow out into the environment. The use of wood in this way intervenes in a natural cycle, so that wood use and ultimate disposal replaces the natural cycle of wood decay in the forest (Figure 1.5). 

A third possibility is that mineral ions leak out of tissue in the presence of phenolic acids, not because membrane permeability is altered, but rather because the driving force that maintains high ion concentrations in cells (i.e. PD) is dissipated by the chemicals. Without an electrical potential, ions would distribute solely according to their chemical concentrations. Thus, most ions would leak out of cells to reach chemical equilibrium with the external environment. 

Precipitation usually occurs when the concentration of a compound in solution exceeds the equilibrium solubility, although slow reaction kinetics may result in supersaturated solutions. For organic wastes in the deep-well environment, precipitation is not generally a significant partitioning process in certain circumstances, however, it may need to be considered. For example, pentach-lorophenol precipitates out of solution when the solution has a pH of <5,35,36 and polychlorophenols form insoluble precipitates in water high in Mg2+ and Ca2+ ions.37 Also, organic anions react with such elements as Ca2+, Fe2+, and Al3+ to form slowly soluble to nearly insoluble compounds. 

The second law of thermodynamics asserts that the total entropy 5 of a system may change in time because of exchanges with its environment and internal entropy production which is vanishing at equilibrium and positive out of equilibrium [5]... 

Equation 13.17 explicitly mentions the useful exergy flows coming out of the process because exergy can be lost in two different ways. First, exergy is lost in any real process as a result of irreversibility in the process itself, and such losses are called internal exergy losses. Second, exergy can be lost via waste streams that are not yet at equilibrium with the natural environment. 

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