Abstract
Irreversibility plays an important role in evaluating thermodynamic processes. In case friction occurs, a system can not be operated reversibly. This has been treated in Chap. : A wire pendulum for instance does not reach its initial, starting position after a number of oscillations. The amplitude decreases by time until the pendulum finally stops in its rest position. This is due to dissipation, i.e. friction at the mounting point as well as due to interactions between environment and pendulum. Consequently, kinetic energy is dissipated and transferred to the environment from where it can not be gained back into the system. Consequently, the state value entropy in such a case rises due to dissipation. It has been shown, that the rate of generation of entropy is a quantitive measure for the degree of irreversibility.
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- 1.
Due to the perfect thermal contact, the pendulum itself always possesses ambient temperature as well.
- 2.
Mind, that the internal energy is an extensive state value, thus it can be superimposed as well!
- 3.
Everyday experience shows, that a house needs a heating system in order to compensate the heat being released to environment!
- 4.
Comparable to the pressure compensation in Problem 14.2.
- 5.
See Theorem 14.3.
- 6.
In this case \(\delta S_{\mathrm {a, total}}\) is zero, since the entire system shall be adiabatic to the environment.
- 7.
This equation is derived in the lecture Heat and Mass Transfer.
- 8.
This can be in open as well as in closed systems.
- 9.
Pressure, temperature and chemical potential.
- 10.
A car does not re-climb a hill without external impact, once it has reached its rest position. A cup of tea does not heat up, once it has reached ambient temperature. Components in a gaseous mixture do not segregate once they are perfectly mixed.
- 11.
The heat reservoir is huge!
- 12.
See Fig. 13.13!
- 13.
Hence, its state is constant!
- 14.
Due to its homogeneity, the outer edge of the environment has no temperature gradients, so that no heat is transferred. Furthermore, \(Q_{12}\) is within the system, i.e. it does not occur at the system boundary!
- 15.
Due to the large heat transfer area, that allows heat transfer with \(\Delta T\rightarrow 0\).
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Schmidt, A. (2019). Transient Processes. In: Technical Thermodynamics for Engineers. Springer, Cham. https://doi.org/10.1007/978-3-030-20397-9_14
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DOI: https://doi.org/10.1007/978-3-030-20397-9_14
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