![]() ![]() Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 2-4. 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. The units of entropy are commonly referred to as bits, but entropy is also measured in shannons, nats, or hartleys, depending on the base of the logarithm used to define it. 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 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 for 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 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. Entropy itself is traditionally described with the units of J/K.The entropy can be made into an intensive or specific variable by dividing by the mass. Standard entropies of formation are given in molar quantities because they assume the process is taking place to create 1 mole of the substance. But the magnitude of the change is related to the amount of energy the system currently has (which is directly related to its temperature in kelvin). We associate adding heat with an increase in entropy. where p is the pressure and V is the volume of the gas. Substituting for the definition of work for a gas. where E is the internal energy and W is the work done by the system. We begin by using the first law of thermodynamics: dE dQ - dW. If you want to think conceptually, think what adding heat will do to the system. For gases, there are two possible ways to evaluate the change in entropy. So we look at the amount of heat in joules and compare that to the temperature where we applied the heat. So this allows us to measure $ \Delta S$ directly by looking at how much heat we apply to cause this process to proceed. At 273 K ice and liquid water are in a state of equilibrium, but if we apply heat we can cause ice to melt. So if you take for example ice melting at 273 K, this process is thermodynamically reversible. ![]() Entropy doesn't depend on the pathway that we take. The best explanation I can give is that in order to measure entropy for a process we can exploit the fact that it's a state function. ![]()
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