Editing Second law of thermodynamics (section)

=== Generalized conceptual statement of the second law principle ===
Second law analysis is valuable in scientific and engineering analysis in that it provides a number of benefits over energy analysis alone, including the basis for determining energy quality (exergy content<ref>{{Cite journal |last1=Wright |first1=S.E. |last2=Rosen |first2=M.A. |last3=Scott |first3=D.S. |last4=Haddow |first4=J.B. |date=January 2002 |title=The exergy flux of radiative heat transfer for the special case of blackbody radiation |url=http://dx.doi.org/10.1016/s1164-0235(01)00040-1 |journal=Exergy |volume=2 |issue=1 |pages=24–33 |doi=10.1016/s1164-0235(01)00040-1 |issn=1164-0235}}</ref><ref>{{Cite journal |last1=Wright |first1=S.E. |last2=Rosen |first2=M.A. |last3=Scott |first3=D.S. |last4=Haddow |first4=J.B. |date=January 2002 |title=The exergy flux of radiative heat transfer with an arbitrary spectrum |url=http://dx.doi.org/10.1016/s1164-0235(01)00041-3 |journal=Exergy |volume=2 |issue=2 |pages=69–77 |doi=10.1016/s1164-0235(01)00041-3 |issn=1164-0235}}</ref><ref>{{Cite journal |last1=Wright |first1=Sean E. |last2=Rosen |first2=Marc A. |date=2004-02-01 |title=Exergetic Efficiencies and the Exergy Content of Terrestrial Solar Radiation |url=http://dx.doi.org/10.1115/1.1636796 |journal=Journal of Solar Energy Engineering |volume=126 |issue=1 |pages=673–676 |doi=10.1115/1.1636796 |issn=0199-6231}}</ref>), understanding fundamental physical phenomena, and improving performance evaluation and optimization. As a result, a conceptual statement of the principle is very useful in engineering analysis. Thermodynamic systems can be categorized by the four combinations of either entropy (S) up or down, and uniformity (Y) – between system and its environment – up or down. This 'special' category of processes, category IV, is characterized by movement in the direction of low disorder and low uniformity, counteracting the second law tendency towards uniformity and disorder.<ref name="Wright 12–18">{{Cite journal |last=Wright |first=S.E. |date=February 2017 |title=A generalized and explicit conceptual statement of the principle of the second law of thermodynamics |url=http://dx.doi.org/10.1016/j.ijengsci.2016.11.002 |journal=International Journal of Engineering Science |volume=111 |pages=12–18 |doi=10.1016/j.ijengsci.2016.11.002 |issn=0020-7225}}</ref>
[[File:Exergysun1.png|thumb|Four categories of processes given entropy up or down and uniformity up or down]]

The second law can be conceptually stated<ref name="Wright 12–18"/> as follows: Matter and energy have the tendency to reach a state of uniformity or internal and external equilibrium, a state of maximum disorder (entropy). Real non-equilibrium processes always produce entropy, causing increased disorder in the universe, while idealized reversible processes produce no entropy and no process is known to exist that destroys entropy. The tendency of a system to approach uniformity may be counteracted, and the system may become more ordered or complex, by the combination of two things, a work or exergy source and some form of instruction or intelligence. Where 'exergy' is the thermal, mechanical, electric or chemical work potential of an energy source or flow, and 'instruction or intelligence', although subjective, is in the context of the set of category IV processes.

Consider a category IV example of robotic manufacturing and assembly of vehicles in a factory. The robotic machinery requires electrical work input and instructions, but when completed, the manufactured products have less uniformity with their surroundings, or more complexity (higher order) relative to the raw materials they were made from. Thus, system entropy or disorder decreases while the tendency towards uniformity between the system and its environment is counteracted. In this example, the instructions, as well as the source of work may be internal or external to the system, and they may or may not cross the system boundary. To illustrate, the instructions may be pre-coded and the electrical work may be stored in an energy storage system on-site. Alternatively, the control of the machinery may be by remote operation over a communications network, while the electric work is supplied to the factory from the local electric grid. In addition, humans may directly play, in whole or in part, the role that the robotic machinery plays in manufacturing. In this case, instructions may be involved, but intelligence is either directly responsible, or indirectly responsible, for the direction or application of work in such a way as to counteract the tendency towards disorder and uniformity.

There are also situations where the entropy spontaneously decreases by means of energy and entropy transfer. When thermodynamic constraints are not present, spontaneously energy or mass, as well as accompanying entropy, may be transferred out of a system in a progress to reach external equilibrium or uniformity in intensive properties of the system with its surroundings. This occurs spontaneously because the energy or mass transferred from the system to its surroundings results in a higher entropy in the surroundings, that is, it results in higher overall entropy of the system plus its surroundings. Note that this transfer of entropy requires dis-equilibrium in properties, such as a temperature difference. One example of this is the cooling crystallization of water that can occur when the system's surroundings are below freezing temperatures. Unconstrained heat transfer can spontaneously occur, leading to water molecules freezing into a crystallized structure of reduced disorder (sticking together in a certain order due to molecular attraction). The entropy of the system decreases, but the system approaches uniformity with its surroundings (category III).

On the other hand, consider the refrigeration of water in a warm environment. Due to refrigeration, as heat is extracted from the water, the temperature and entropy of the water decreases, as the system moves further away from uniformity with its warm surroundings or environment (category IV). The main point, take-away, is that refrigeration not only requires a source of work, it requires designed equipment, as well as pre-coded or direct operational intelligence or instructions to achieve the desired refrigeration effect.