Entropy unit12/5/2023 ![]() (i) the tendency to acquire a state of minimum energy, and The overall tendency of a process to occur can be expressed on the resultant of two tendencies namely: Thus, this concept of entropy (measure of randomness) has led to the conclusion that all substances in their normal crystalline state at absolute zero temperature would be in the condition of maximum orderly arrangement, because all motion has essentially ceased at ‘0 K.’ In other words, entropy of a substance at 0 K is minimum. ![]() When two gases are mixed, the molecules of the gases intermix to achieve more randomness. The process of vaporisation produces an increase in randomness in the distribution of molecules, hence an increase in entropy. For example, when a solid changes to a liquid, an increase in entropy takes place, because with the breaking of the orderly arrangement of the molecules in the crystal to the less orderly liquid state, the randomness increases. Conversely, if the change is one in which there is an increase in orderliness, there is a decrease in entropy. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 2-4.Physical significance: Entropy has been regarded as a measure of disorder or randomness of a system. Thus when a system goes from a more orderly to less orderly state, there is an increase in its randomness and hence entropy of the system increases. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 3-2. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 9-4. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 3-2. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993. Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.Physics of Nuclear Kinetics. Addison-Wesley Pub. Nuclear and Particle Physics. Clarendon Press 1 edition, 1991, ISBN: 978-0198520467 Nuclear Reactor Engineering: Reactor Systems Engineering, Springer 4th edition, 1994, ISBN: 978-0412985317 Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 8-1. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983). The fact that the absolute value of specific entropy is unknown is not a problem, however, because it is the change in specific entropy (∆s) and not the absolute value that is important in practical problems. For example, the specific entropy of water or steam is given using the reference that the specific entropy of water is zero at 0.01☌ and normal atmospheric pressure, where s = 0.00 kJ/kg. Normally, the entropy of a substance is given with respect to some reference value. ![]() In general, specific entropy is a property of a substance, like pressure, temperature, and volume, but it cannot be measured directly. Because entropy tells so much about the usefulness of an amount of heat transferred in performing work, the steam tables include values of specific entropy (s = S/m) as part of the information tabulated. ![]() M = mass (kg) T-s diagram of Rankine CycleĮntropy quantifies the energy of a substance that is no longer available to perform useful work. It equals to the total entropy (S) divided by the total mass (m). The specific entropy (s) of a substance is its entropy per unit mass. Engineers use the specific entropy in thermodynamic analysis more than the entropy itself. The entropy can be made into an intensive, or specific, variable by dividing by the mass. ![]()
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