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2022 | OriginalPaper | Buchkapitel

7. Changes of State

verfasst von : Achim Schmidt

Erschienen in: Technical Thermodynamics for Engineers

Verlag: Springer International Publishing

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Abstract

So far, thermodynamic systems have been discussed and state values categorised to quantify the internal state of systems.

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Vorheriges Kapitel Thermal Equation of State

Nächstes Kapitel Thermodynamic Processes

Or rather chemical potential.

See Theorem 6.4.

Key to solving problems in thermodynamics is understanding the path a change of state takes!

The gas as part of the system under investigation can also be in equilibrium, although it is not in thermal equilibrium with the external environment. In this case, the gas is adiabatically isolated and is not influenced by the environment. In this case, the temperature inside the cylinder is constant and uniform in time!

The experiments performed by Boyle-Mariotte as well as by Gay-Lussac, see Chap. 6, have been conducted under the premise of thermodynamic equilibrium.

The system would drive itself into thermal, mechanical as well as chemical equilibrium!

The pressure is assumed to be homogeneous. Thus, the gravitational effect has been ignored, see Sect. 7.1.1!

Imagine you are taking photos of a car that is accelerating. If your camera has a very short exposure time, each of the many photos looks like static, all the images are sharp. In this very short period of time, the movement of the car is negligible. If the shutter speed is too slow, the pictures will not look static at all, because the movement will result in blurred pictures.

As well as chemical potentials.

In the following Sect. 7.2.2, it is investigated what too high means!

Mass fractions \(\xi _{i}\) are introduced in Part II though.

And thus a homogeneous phase!

Later on, internal friction is called dissipation!

To cope with this example a knowledge of first and second law of thermodynamics is required.

The system is going to be further discussed later in Problem 11.4!

Benefit of a differential notation is, that it shows what is ongoing inbetween initial and final equilibrium state.

The term friction \(\Psi _{\text {fric.}}\) is explained in Sect. 9.2.5.

If the gas inside the cylinder expands, i.e. \(\text {d}V>0\), work is released by the system to the environment. Thus, \(\delta W_{\text {12,env}}\), as assumed in the sketch, is negative. The related work can be calculated easily since the ambient pressure is constant.

For a technical application, mathematical functions for \(\psi _{\text {12,G}}\) and \(\psi _{\text {fric.}}\) are needed. These functions must correlate the specific dissipation with the distance moved and the velocity of a system. A detailed example is given with Problem 11.5.

With the mass of the gas still ignored.

To cope with this problem a knowledge of first and second law of thermodynamics is required.

Titel: Changes of State
verfasst von: Achim Schmidt
Verlag: Springer International Publishing
Buch: Technical Thermodynamics for Engineers
Print ISBN: 978-3-030-97149-6

Electronic ISBN: 978-3-030-97150-2

Copyright-Jahr: 2022
DOI: https://doi.org/10.1007/978-3-030-97150-2_7

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