Exergy is a more accurate representation of energy usage in open systems than entropy. It represents the amount of energy available for useful work, which is used up and contributes to the overall entropy of the universe. Exergy analysis is a method of describing the energy available in a system that can do work. Calculating exergy development can be done with a variety of mathematical formulas. The increase in exergy and entropy are both considered to be definitive examples of how any increased order brought to matter will eventually be undone. However, if the universe is an open system, then the ascending order can be continued indefinitely.
Exergy is a concept in the physics of thermodynamics that has come to replace entropy as the more accurate representation of what happens to energy when it is used in an open system, such as in industrial or biological processes on Earth. Simply put, exergy represents the amount of energy in a system that is available for useful work. As the system performs its function, exergy is used up in the process and can never be recovered.
In this sense, the use of exergy contributes to the overall entropy of the universe itself. This is because entropy represents a trend towards a maximum distribution of energy to the point where change is no longer possible to occur, which is more succinctly referred to as heat death. The concept of heat death represents a period in the distant future for the entire universe, which is considered a closed system in which external energy never enters. Ultimately, energy in the fundamental form of heat is expected to be equally distributed in space, creating a completely homogeneous environment in which life itself would be impossible. An exergy energy analysis is, therefore, a method of taking the natural, pervasive process of entropy and looking at it at a smaller local scale for machines or any orderly process or creature that consumes energy to function or live in a state highest of order.
Measuring chemical exergy can be important as it is a way of representing the consumption of natural resources and the inevitable loss of some of the mass of these resources on Earth as they are converted into heat, which is lost to space. An automobile engine is a good example of a system that consumes energy to work. As the energy in the fuel burned by the engine is converted into heat and pressure in the engine, this energy is released into the external environment in waste heat and mechanical motion, which is eventually carried out into space and is no longer recoverable for useful work.
Exergy in this way respects the second law of thermodynamics, which states that the different energy levels between systems or bodies have a tendency to equalize over time. Even the first law of thermodynamics is consistent with the principle, where it states that matter can neither be created nor destroyed. Since exergy analysis is a method of describing the energy available in a system that can do work, it does not claim that the energy has been destroyed, merely that it has reached a state in which the system can no longer make use of it.
Calculating the exergy development for a system can be done with a variety of mathematical formulas. They depend on the use that the energy is put into the system, whether to produce exergy heat, pressure, sound, light, or other forms of useful energy-based work. One formula used in an attempt to represent all factors is:
Ε = U – Ueq + po(V -Veq) – Τo(S – Seq) – Σμo(ni – nieq)i.
In the formula, U, V, S and ni all represent factors within an ordered system such as a machine or life form which include its internal energy level, mass per volume and intrinsic entropy. Its size measured by its molecular weight. The values represented by po, To, and uo are placeholders for the external environment, including pressure, temperature, and chemical interactions. The value of eq stands for thermodynamic equilibrium, towards which all systems tend with their surroundings.
While the increase in exergy and entropy are both considered to be definitive examples of how any increased order brought to matter will eventually be undone, that concept is based on the idea that the universe is a closed system. Like a clock that is gradually running out, all ordered processes are considered to be heading towards a state of maximum entropy and randomness. If the universe, however, is an open system into which external energy enters as energy from the Sun continually enters the Earth, then the ascending order can be continued indefinitely. Both physical theories postulating the presence of a multiverse of multiple interacting parallel universes, or that of a higher power overseeing the cosmos, suggest that the universe could be an open system where energy enters from outside and the exergy is replenished.
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