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2022 | OriginalPaper | Buchkapitel

9. Process Values Heat and Work

verfasst von : Achim Schmidt

Erschienen in: Technical Thermodynamics for Engineers

Verlag: Springer International Publishing

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Abstract

In the previous chapters, the internal state of a system has been described. A thermodynamic system can change its state and several possible changes of state have been discussed. For further understanding, it is essential to be familiar with the concepts of reversibility/irreversibility as well as with the idea of a quasi-static change of state.

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Vorheriges Kapitel Thermodynamic Processes

Nächstes Kapitel State Value Versus Process Value

Imagine a gas turbine in a stationary state: It does not emit a single portion of heat, but it does emit heat permanently.

This approach is also applicable to the work later on!

Be aware that the drawing convention in this book is always from the point of view of the system!

In case of steady state!

Which refers to the change in the centre of gravity of a system.

A detailed explanation is going to follow in Sect. 11.3.4!

Sir George Gabriel Stokes (

https://static-content.springer.com/image/chp%3A10.1007%2F978-3-030-97150-2_9/MediaObjects/482881_2_En_9_Figa_HTML.gif

13 August 1819 in Skreen, County Sligo,

https://static-content.springer.com/image/chp%3A10.1007%2F978-3-030-97150-2_9/MediaObjects/482881_2_En_9_Figb_HTML.gif

1 February 1903 in Cambridge).

Actually, the force F acting from the outside is infinitesimally greater than pA.

Cf. the following three scenarios.

Force is pointing into the system.

Force is pointing out of the system.

Isochoric change of state.

Although the outer atmosphere can expand or can be compressed, the ambient pressure is constant due to the size of the environment.

The negative sign results from the sign convention. In this differential step \(\text {d}x\), the pressure p is assumed to be constant.

E.g. work by an impeller, cf Sect. 9.2.7.

Isochoric means there is no volume work.

The cylinder is supposed to be horizontal, so that the potential energy of the gas does not have an impact.

For this section the knowledge of the first law of thermodynamics is required.

See Sect. 13.5.

I.e. kinetic and potential energies.

Dissipation consumes energy.

Solids are supposed to be incompressible, i.e. no volume work occurs.

For a solid there is no distinction between \(c_{v}\) and \(c_{p}\), see Sect. 12.4.2.

The following equations are introduced and explained in Chap. 11ff.

According to Example 7.6 the requirements for an isobaric change of state are fulfilled.

While doing so, the piston’s potential energy rises.

The piston’s potential energy decreases. Its energy is transferred to the gas.

(E)\(\rightarrow \)(1) as well as (2)\(\rightarrow \)(A) are isobaric.

Titel: Process Values HeatHeat and WorkWork
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_9

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