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2019 | OriginalPaper | Chapter

17. Components and Thermodynamic Cycles

Author : Achim Schmidt

Published in: Technical Thermodynamics for Engineers

Publisher: Springer International Publishing

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Abstract

Although many technical components, that are required to run energy conversion processes, have already been discussed previously, the focus in this chapter is on thermal turbo-machines as well as on heat exchangers. However, in this chapter the technical components are treated in steady state operation. In order to quantify the efficiency of turbine and compressor the so-called isentropic efficiency is defined. In addition, relevant thermodynamic cycles are introduced and discussed. Cyclic processes have been discussed in the previous chapters as well, but mostly in a black-box notation. A distinction has been made between clockwise cycles, i.e. thermal engines, and counterclockwise cycles, i.e. cooling machines respectively heat pumps. This chapter concludes the first part of this book.

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Footnotes
1
Such as adiabatic throttle, compressor and turbine.
 
2
Except for the Carnot-cycle, i.e. the technical benchmark, whose underlying changes of state, i.e. isentropic, isothermal, isentropic, isothermal, have been introduced as well.
 
3
Following, that the energy flux in is balanced by the energy flux out in steady state!
 
4
Entropy flux in is balanced by entropy flux out.
 
5
Exergy flux in is balanced by exergy flux out.
 
6
Thus, no dissipation or any other imperfections that cause generation of entropy.
 
7
Following, that the energy flux in is balanced by the energy flux out in steady state!
 
8
Entropy flux in is balanced by entropy flux out.
 
9
Exergy flux in is balanced by exergy flux out.
 
10
Thus, no dissipation or any other imperfections that cause generation of entropy.
 
11
There are no mechanical/electrical parts within the component, that exchange work with the environment.
 
12
Outer energies are ignored!
 
13
Kinetic and potential energies ignored.
 
14
Systems A and B are supposed to be homogeneous.
 
15
Generation of entropy in system C is caused by heat transfer, not by dissipation!
 
16
Since every single change of state is reversible, the entire process is reversible as well!
 
17
This is due to no dissipation occurs and outer energies are ignored.
 
18
Mind, that the area beneath a change of state in a T, s-diagram is the summation of specific heat and specific dissipation.
 
19
As long, as potential and kinetic energies are ignored! Anyhow, the entire heat exchanger generates entropy, since a temperature gradient is required to transfer heat. However, the T, s-diagram just shows the fluid, operated in the cycle. This fluid is supplied with heat, no matter regarding the source of the heat. The only cause for dissipation in the fluid is due to a (mechanical) pressure loss. Mind, that generation of entropy at heat transfer is at the interface of the two systems, i.e. imperfection in the wall caused by \(\Delta T>0\).
 
20
As long, as potential and kinetic energies are ignored!
 
21
This is called sensible heat.
 
22
This is called latent heat.
 
23
As will be seen at the end of the cycle!
 
24
The notation of the applied first law of thermodynamics is, that the sign is taken into account by balancing in and out. This requires, that each energy is counted as absolute value. Thus, the heat release \(q_{0}\), which is negative, needs to be taken as absolute value but on the side of the leaving energy.
 
25
Liquid and vapour occur at the same time!
 
26
In case kinetic and potential energies are ignored.
 
27
Since there is no information regarding potential and kinetic energy, both are neglected. Relevant information for the kinetic energy could be a volume flow rate in combination with a tube’s cross section for instance.
 
28
Energy in is balanced by energy out in steady state!
 
29
Hence, the enthalpy of water is purely a function of temperature.
 
30
Without pressure loss!
 
31
Mind, that \(T_{\text {m}}\) is the thermodynamic mean temperature of the water!
 
32
Entropy in is balanced by entropy out. There is no generation of entropy, since no pressure loss occurs for the water!
 
33
The partial energy equation for the tank reads as \(W_{12}=0=W_{\text {12,V}}+W_{\text {12,mech}}+\Psi _{12}\). Since there is no volume work respectively mechanical work, there is no dissipation and no generation of entropy within the tank!
 
34
Again in differential notation, since the temperature in the tank is not constant! In this extended system there is dissipation due to the heat transfer, that is now part of the system boundary!
 
Metadata
Title
Components and Thermodynamic Cycles
Author
Achim Schmidt
Copyright Year
2019
Book
Technical Thermodynamics for Engineers

Print ISBN: 978-3-030-20396-2

Electronic ISBN: 978-3-030-20397-9

Copyright Year: 2019

DOI
https://doi.org/10.1007/978-3-030-20397-9_17

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