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2022 | 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 required for the operation of energy conversion processes have been discussed previously, the focus in this chapter is on thermal turbomachinery as well as on heat exchangers. However, in this chapter the technical components are addressed in steady state operation.

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previous chapter Exergy
next chapter Single-Component FluidsFluidssingle-Component
Footnotes
1
Such as adiabatic throttle, compressor and turbine.
 
2
With the exception of the Carnot cycle, i.e. the technical benchmark, whose underlying changes of state, i.e. isentropic, isothermal, isothermal, have also been introduced, see Sect. 15.​3.
 
3
It applies that the energy flux in and the energy flux out are in equilibrium.
 
4
Entropy flux in is balanced by entropy flux out.
 
5
Exergy flux in is balanced by exergy flux out.
 
6
So there is no dissipation or other imperfections that lead to the generation of entropy.
 
7
Such a definition ensures that the efficiency is always less than 1.
 
8
It applies that the energy flux in and the energy flux out are in equilibrium.
 
9
Entropy flux in is balanced by entropy flux out.
 
10
Exergy flux in is balanced by exergy flux out.
 
11
So there is no dissipation or other imperfections that lead to the generation of entropy.
 
12
Such a definition ensures that the efficiency is always less than 1.
 
13
There are no mechanical/electrical parts within the component, that exchange work with the environment.
 
14
Outer energies are ignored.
 
15
Such a disequilibrium causes a transient balancing process.
 
16
Kinetic and potential energies are not considered.
 
17
Thus, it is \(\frac{\text {d}S_{\text {A}}}{\text {d}t}=0\).
 
18
Systems A and B are homogenised by their thermodynamic mean temperatures.
 
19
Generation of entropy in system C is caused by heat transfer, not by dissipation.
 
20
An exception is the Carnot process, which has already been discussed in detail.
 
21
Since each individual change of state is reversible, the entire process is also reversible.
 
22
This is due to the fact that no dissipation occurs and outer energies are ignored.
 
23
Note that the area beneath a change of state in a T, s-diagram is the summation of specific heat and specific dissipation.
 
24
As long as potential and kinetic energies are ignored. Nevertheless, the entire heat exchanger generates entropy because a temperature gradient is required for heat transfer. However, the T, s-diagram only shows the fluid being circulated. Heat is supplied to the fluid, regardless of where the heat comes from. The only cause of dissipation in the fluid is a (mechanical) pressure loss. Note that the entropy generation during heat transfer occurs at the interface of the two systems, i.e. at the imperfection in the wall caused by \(\Delta T>0\).
 
25
As long, as potential and kinetic energies are ignored.
 
26
This is called sensible heat.
 
27
This is called latent heat.
 
28
Potential energies do not play a role in a horizontal arrangement. The system is considered to be at rest at the end of each change of state, i.e. kinetic energies are not relevant.
 
29
As will be seen at the end of the cycle.
 
30
The notation of the first law of thermodynamics applied here states that the sign is taken into account by balancing the inputs and outputs. This requires that each energy is counted as an absolute value. Thus, the heat release \(q_{0}\), which actually is negative, must be taken as an absolute positive value but accounted for on the outgoing energy side.
 
31
Liquid and vapour occur at the same time.
 
32
In case kinetic and potential energies are ignored.
 
33
In case kinetic and potential energies are ignored.
 
34
Since there is no information about potential and kinetic energy, both are neglected. Relevant information for kinetic energy could be, for example, a volume flow in combination with the cross-section of a pipe.
 
35
Energy in is balanced by energy out in steady state.
 
36
Hence, the enthalpy of water is purely a function of temperature.
 
37
Without pressure loss.
 
38
Note that \(T_{\text {m}}\) is the thermodynamic mean temperature of the water.
 
39
Entropy in is balanced by entropy out. There is no generation of entropy, since no pressure loss occurs for the water.
 
40
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 entropy generation in the tank. For dissipation to occur, the fluid would have to be in motion.
 
41
Again in differential notation, since the temperature in the tank is not constant. In this extended system there is entropy generation due to the heat transfer, that is now part of the system boundary.
 
Metadata
Title
Components and Thermodynamic Cycles
Author
Achim Schmidt
Copyright Year
2022
Book
Technical Thermodynamics for Engineers

Print ISBN: 978-3-030-97149-6

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

Copyright Year: 2022

DOI
https://doi.org/10.1007/978-3-030-97150-2_17

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