(158e) Energy Requirement and Available Energy Consumption

Today, ?energy consumption? is popularly uttered or printed; nevertheless, caution should be exercised for its continued use, especially in the instruction of not only thermodynamics but also various other courses in Engineering, including those in Chemical Engineering. The first law of thermodynamics teaches that energy is always conserved in an isolated (or closed) system; it is neither created nor destroyed by any process, system, or phenomenon. In contrast, the available energy analysis, which is the combination of the first and second laws, indicates that the available energy is never conserved even in an isolated (or closed) system in the real world, even though it is only theoretically conserved in the ideal circumstances; it is incessantly consumed, or dissipated, by any process, system, or phenomenon. The consumption of available energy, or exergy, is accompanied by an increase in entropy, signifying the dissipation of available energy, or exergy, to the surrounding environments. The available energy, or exergy, dissipation reduces its potential or availability to perform useful work. With the aid of a deceptively simple example, it has been unequivocally demonstrated that energy is conserved, i.e., never consumed; what is always consumed, or dissipated, is available energy (exergy), which is the essence of this brief contribution. This simple example also succinctly indicates that an attempt to rigorously assess the sustainability of any process or system should be based firmly on the thermodynamics, in general, and the evaluation of the system's second-law efficiency based on available energy (exergy), in particular, as practiced in the EU community and the Canton of Geneva in Swaziland.