Is it possible to have reversible adiabatic process in practical? because if it is a reversible process than we allowing it to exchange heat with surroundings. If it is in insulation than either we some external will conduct process or system will. if system itself itself is doing it than is temperature or some other thermodynamic parameter may change . Can anyone give me any example?
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3$\begingroup$ An irreversible adiabatic cycle is impossible, and this statement is almost equivalent to the 2nd law thermodynamics. Furthermore "When a reversible and adiabatic process resumes the initial values of the generalized displacements, it has completed a cycle." This means that not only the mechanical/electrical/magnetic, etc., coordinates but its thermal (temperature, energy, energy) coordinates must return to their original value. See, "Didactic remarks on the Sears-Kestin statement of the second law of thermodynamics" by Pau-Chang Lu, Am. J. Phys. 50(3), March 1982. $\endgroup$– hyportnexCommented Dec 23, 2016 at 17:03
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1$\begingroup$ Yes, an adiabatic reversible process is possible. In such a process, both the temperature and the volume of the gas change. The effects of both of these on entropy cancel one another. So the change in entropy is zero, even though the temperature changes. $\endgroup$– Chet MillerCommented Dec 23, 2016 at 17:50
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$\begingroup$ Yet it sounds like the question is if it is possible in practice. So the answer to that could easily be no, any change to a system should come with some heat transfer, as perfect insulation should be impossible. However, of course the concept of an adiabatic change is just a theoretical idea and a very useful one. So it is, in practice, useful to think about the concept of adiabatic reversible processes. $\endgroup$– Ken GCommented Dec 23, 2016 at 19:00
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$\begingroup$ In practice, is it possible to have a reversible process at all? $\endgroup$– DeepCommented Dec 24, 2016 at 14:35
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1$\begingroup$ Is it only me who is having some trouble understanding the body of this question? $\endgroup$– valerioCommented Jan 17, 2018 at 12:23
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2 Answers
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A process is said to be reversible if the system can be brought back to its initial state without leaving any changes in the surroundings, i.e, the system and the surroundings can be brought back to their initial states. There are no conditions on it concerning the existence of heat exchange, so there is no problem in having an adiabatic or a non adiabatic reversible process (theoretically).
However, in practice, reversible processes themselves are impossible. Just as a frictionless surface in mechanics and a wire with zero resistance in electricity, a reversible process is an ideal case used to simplify problems, but doesn't exist in reality.
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1$\begingroup$ Superconducting wires are a thing. $\endgroup$– MauricioCommented May 31, 2018 at 16:03
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An example of a reversible adiabatic process is compressing/expanding a gas so rapidly that there is no time for heat transfer to the surroundings, but below the speed of sound so that uneven pressure distributions don't build up in the gas.
The compression/expansion must also be frictionless.
The second law is:
$$ \Delta S = \sum\frac{Q}{T} + S_{gen}$$
If the process is adiabatic (or so fast that negligible heat transfer occurs), then $Q=0$.
If the process is frictionless, then $S_{gen} = 0$.
For a compression, this means $\Delta S=0$, and we could quickly expand after the compression to reach the same state again. It's therefore a reversible process.
answered May 11, 2019 at 15:16