Technology & Engineering
Entropy Gradient
Entropy gradient refers to the difference in entropy between two points in a system. In engineering, it is used to describe the flow of energy or matter from areas of high entropy to areas of low entropy, which is a natural tendency in physical systems. Understanding and managing entropy gradients is important in designing efficient and effective systems.
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4 Key excerpts on "Entropy Gradient"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Orange Apple(Publisher)
Energy dispersal The concept of entropy can be described qualitatively as a measure of energy dispersal at a specific temperature. Similar terms have been in use from early in the history of classical thermodynamics, and with the development of statistical thermodynamics and quantum theory, entropy changes have been described in terms of the mixing or spreading of the total energy of each constituent of a system over its particular quantized energy levels. Ambiguities in the terms disorder and chaos , which usually have meanings directly opposed to equilibrium, contribute to widespread confusion and hamper comprehension of entropy for most students. As the second law of thermodynamics shows, in an isolated system internal portions at different temperatures will tend to adjust to a single uniform temperature and thus produce equilibrium. A recently developed educational approach ________________________ WORLD TECHNOLOGIES ________________________ avoids ambiguous terms and describes such spreading out of energy as dispersal, which leads to loss of the differentials required for work even though the total energy remains constant in accordance with the first law of thermodynamics (compare discussion in next section). Physical chemist Peter Atkins, for example, who previously wrote of dispersal leading to a disordered state, now writes that spontaneous changes are always accompanied by a dispersal of energy. Relating entropy to energy usefulness Following on from the above, it is possible (in a thermal context) to regard entropy as an indicator or measure of the effectiveness or usefulness of a particular quantity of energy. This is because energy supplied at a high temperature (i.e. with low entropy) tends to be more useful than the same amount of energy available at room temperature. Mixing a hot parcel of a fluid with a cold one produces a parcel of intermediate temperature, in which the overall increase in entropy represents a “loss” which can never be replaced.
eBook - PDF- Lokesh Pandey(Author)
- 2020(Publication Date)
- Arcler Press(Publisher)
2. Entropy is a non-conserved property, and there is no such thing as the conservation of entropy. Therefore, the entropy of universe is continuously increasing. 3. The performance of engineering systems is degraded by the presence of irreversibility. The entropy generation is a measure of the magnitudes of the irreversibilities present during the process. 3.2. TERMS RELATED TO ENTROPY 3.2.1. Entropy Balance Entropy is a measure of molecular disorder or randomness of a system, and the second law states that entropy can be created but it cannot be destroyed. Entropy and Entropy Components 59 The increase of entropy principle is expressed as Entropy change = Entropy transfer + Entropy generation ∆S system = ∆S transfer + ∆S gen This principle is commonly known as the entropy balance. 3.2.2. Entropy Change The entropy balance is easier to apply that energy balance, since unlike energy (which has many forms such as heat and work) entropy has only one form. The entropy change for a system during a process is: Entropy change = Entropy at final state - Entropy at initial state ∆S system = ∆S final – ∆S initial Therefore, the entropy change of a system is zero if the state of the system does not change during the process. For example, entropy change of steady flow devices such as nozzles, compressors, turbines, pumps, and heat exchangers are zero during steady operation. 3.2.3. Mechanisms of Entropy Transfer Entropy can be transferred to or from a system in two forms: heat transfer and mass flow. Thus, the entropy transfer for an adiabatic closed system is zero. Heat Transfer : Heat is a form of energy that is not organized and some disorganization (entropy) will flow with heat. Heat rejection is the only way that the entropy of a fixed mass can be decreased. The ratio of the heat transfer Q/ T (absolute temperature) at a location is called entropy flow or entropy transfer.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
______________________________ WORLD TECHNOLOGIES ______________________________ Thermodynamic entropy is a non-conserved state function that is of great importance in the sciences of physics and chemistry. Historically, the concept of entropy evolved in order to explain why some processes are spontaneous and others are not; systems tend to progress in the direction of increasing entropy. Entropy is as such a function of a system's tendency towards spontaneous change. For isolated systems, entropy never decreases. This fact has several important consequences in science: first, it prohibits perpetual motion machines; and second, it suggests an arrow of time. Increases in entropy correspond to irreversible changes in a system, because some energy must be expended as waste heat, limiting the amount of work a system can do. In statistical mechanics, entropy is essentially a measure of the number of ways in which a system may be arranged, often taken to be a measure of disorder (the higher the entropy, the higher the disorder). Specifically, this definition describes the entropy as being proportional to the logarithm of the number of possible microscopic configurations of the individual atoms and molecules of the system (microstates) which could give rise to the observed macroscopic state (macrostate) of the system. The constant of proportionality is the Boltzmann constant. The second law of thermodynamics The second law of thermodynamics states that in general the total entropy of any system will not decrease other than by increasing the entropy of some other system. Hence, in a system isolated from its environment, the entropy of that system will tend not to decrease. It follows that heat will not flow from a colder body to a hotter body without the application of work (the imposition of order) to the colder body.
eBook - PDFUnearthed
The Economic Roots of Our Environmental Crisis
- Kenneth M. Sayre(Author)
- 2010(Publication Date)
- University of Notre Dame Press(Publisher)
A mathematical (thus quantitative) measure of order in operating systems is explained in the appendix to this chapter. Its purpose, as al-ready indicated, is to show that entropy in the form of degraded struc-ture or disorder is subject to quantitative measurement no less than entropy in the form of degraded energy. Readers not concerned with this matter may pass over the appendix without losing track of the continu-ing discussion. 2.6 Entropy and Randomness Discussion of entropy in chapter 1 was confined to expended energy, which is energy no longer capable of work. Work is done when physical occurrences are brought about by other physical occurrences rather than occurring randomly (section 1.2). A standard example of energy incapable of further work is the low-grade heat expended by metabolic activity (e.g., the body heat of living animals). Another conception of entropy was introduced into the discussion at the beginning of the present chapter. This second conception equates entropy with disorder. In photosynthesis, solar energy is expended in creating biomass that provides chemical energy to plant-eating or-ganisms. The highly ordered wave structure of sunlight is converted into chemical structure, which then is further degraded into the waste Ent ropy and Disorder 23 products of metabolic activity. This process of increasing degradation culminates in the nondirectional wave structure of black-body radiation by which fully expended energy from the sun is eventually returned to space. The conceptions of entropy as expended energy and as structural disorder can be further integrated in terms of a third conception equat-ing entropy with randomness. This conception was implied in our dis-cussion of orderliness in the preceding section but needs to be more explicitly articulated. On one hand, random events are events whose oc-currence exhibits no particular order. The entropy present in disorder thus is equivalent to that present in random occurrences.
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