Exergy-releasing process

Fig. 11.8. Schematic exergy vector diagrams for exergy transfer between an exergy-absorbing process and an exergy-releasing process (a) the combined process is not feasible, (b) the combined process is feasible.

In the case shown in Fig. 11.8(a) where the composite vector, that is the vector sum of the two component vectors of the exergy-absorbing and exergy-releasing processes 1 and 2, points in the direction of exergy increase (AE > 0), the resultant process of the coupled and coupling processes is thermodynamically impossible to occur in the system under consideration. On the other hand, in the case shown in Fig. 11.8(b) where the composite vector points in the... 

Examples of such external exergy losses are the release of hot flue gases or high-pressure gas to the atmosphere. Both the internal and the external exergy losses are in principle inefficiencies, and the exergy used efficiently in the process is therefore only the exergy of products and the exergy of waste products, provided they are made useful in other processes. 

The fall in temperature from 7 to the environmental temperature T0 releases an amount of enthalpy (A - h0), of which however only the exergy part can be used for the available and transformable energy to obtain useful work or products by means of reversible processes. We then define the energy availability A of a high temperature substance as in Eq. 10.14 ... 

In contrast to isentropy, the process of isothermal compression-expansion, which is accompanied by heat release or heat absorption, is represented by an exergy vector with the slope of < 1 in the regimes of heat absorption and heat release as shown in Fig. 11.10(a). 

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