🔑 Key Issues
Key issues are the most important concepts for fully leveraging the book. Below is the complete list organized by chapter, with corresponding self-assessment activities.
Chapter 2: Components, Functions, and Reference Processes
B2.1 KEY ISSUES: Architecture and operation of basic cycles
In this chapter, we have introduced the cycles of the three simplest and most popular energy technologies.
It is important that you understand their architecture, how they work and know the names of their components.
These self-assessment activities will allow you to test your knowledge on these topics:
- Architecture of a steam plant, gfe
- Architecture of a steam power plant, ddi
- Mechanical energy in a simple steam plant, quiz
- Architecture of a gas turbine, gfe
- Architecture of a gas turbine, ddi
- Mechanical energy in a simple gas turbine, quiz
- Architecture of a refrigeration plant, gfe
- Architecture of a refrigeration cycle, ddi
- Heat exchanges in a refrigeration machine, gfe
Self-Assessment Activities: 9
B2.2 KEY ISSUES: Four basic functions
The first key concept is that only four functionalities are sufficient to describe the functioning of the machines we have studied:
- compressions can be carried out with the fluid being liquid or gaseous. In the first case the component is a pump, in the second a compressor;
- expansion with work production is generally carried out in turbines;
- expansion without work production (throttling) takes place in valves or filters;
- heating can be carried out either in combustion chambers or boilers, or in heat exchangers. Cooling is generally done in heat exchangers.
We have also stated a very general observation: in all power cycles, the working fluid is successively compressed, heated, expanded and cooled or released in the atmosphere, and, in all refrigeration machines, it is compressed, cooled, expanded and heated or released in the atmosphere.
The following self-assessment activities will allow you to check your understanding of these concepts:
- Functions in a steam plant cycle, ddi
- Functions in a gas turbine cycle, ddi
- Functions in a refrigeration cycle, ddi
Self-Assessment Activities: 3
B2.3 KEY ISSUES: Basic notions
These self-assessment activities will allow you to test your understanding of these concepts:
Self-Assessment Activities: 2
B2.4 KEY ISSUES: First law, energies put into play in processes
Another key concept is a direct application of the First Law of thermodynamics: For components that can be modeled in an open system, the variation in enthalpy of the fluid passing through them is sufficient to determine the energy put into play in the elementary processes corresponding to each of these functions.
- Compression and expansion with work: W = Δh
- Heat exchanges, combustion chambers, boilers: Q = Δh
- expansion without work: valves, filters: Δh = 0
This self-assessment activity will allow you to test your understanding of the First Law:
Self-Assessment Activities: 1
B2.5 KEY ISSUES: Reference processes, imperfection factors
Two other key concepts play a fundamental role, that of reference processes and imperfection factors.
The reference processes correspond to the functioning of components which would be perfect, for which a well-chosen variable or state function remains constant and to which we know how to associate a simple evolution equation.
It is then possible to characterize the real process by introducing an imperfection factor, often called effectiveness or efficiency, which expresses its performance compared to that of the reference process.
The reference process and imperfection factor couples that we have introduced are:
- Compression and expansion with work: perfect or reversible adiabatic, isentropic efficiency
- Heat exchanges, combustion chambers, boilers: isobaric, pressure drops
- Expansion without work: valves, filters: isenthalpic (no imperfection factor)
This self-assessment activity will allow you to test your understanding of reference processes:
Self-Assessment Activities: 1
Chapter 3: Modeling of Simple Cycles
B3.1 KEY ISSUES: Fluid properties
The different states of fluids and gas modeling must be well understood before studying their representation in diagrams.
This self-assessment activitiy will allow you to test your knowledge on this topic:
Self-Assessment Activities: 1
B3.2 KEY ISSUES: Thermodynamic charts
The different states of fluids and gas modeling must be well understood before studying their representation in diagrams.
These self-assessment activities will allow you to test your knowledge on these topics:
- (h, ln (P)) chart of a gas, gfe
- (h, ln (P)) chart of a vapor, gfe
- Zones of a (h, ln (P)) condensable vapor chart, ddi
- Curves of a (h, ln (P)) condensable vapor chart, ddi
- Placement of points in a (h, ln (P)) condensable vapor chart, ddi
- Placement of points in a (h, ln (P)) ideal gas chart, ddi
Self-Assessment Activities: 6
B3.3 KEY ISSUES: Efficiencies
We will frequently use two concepts which must be well understood, that of isentropic efficiency and overall cycle efficiency.
These self-assessment activities will allow you to test your knowledge on these topics:
Self-Assessment Activities: 2
B3.4 KEY ISSUES: Identification of basic cycles in (h, ln (P)) charts
We will frequently use two concepts which must be well understood, that of isentropic efficiency and overall cycle efficiency.
These self-assessment activities will allow you to test your knowledge on these topics:
- Identification of a steam plant cycle in a (h, ln (P)) chart, ddi
- Identification of a gas turbine cycle in a (h, ln (P)) chart, ddi
- Identification of a refrigeration cycle in a (h, ln (P)) chart, ddi
Self-Assessment Activities: 3
Chapter 4: Combustion and Heat Exchangers
B4.1 KEY ISSUES: Main difference between diesel and gasoline engines
An important difference between a gasoline engine and a diesel engine is not in the mode of introducing fuel, which in modern gasoline engines is also injected, but when the fuel is introduced, which determines the nature of gas when the reaction starts and the type of combustion which takes place inside the engine, as will be explained in detail in Chapter 9.
In the gasoline engine, fuel is introduced well in advance so that the cylinder is full, when ignition occurs, of a substantially homogeneous gaseous mixture. In the diesel engine, fuel is injected at the last moment and burned as fine liquid droplets as and when it is introduced (diffusion flame).
Self-Assessment Activities: —
B4.2 KEY ISSUES: Fundamental combustion notions
The fundamentals you should make sure to understand are the following: stoichiometry, air factor λ, CO₂ dissociation, quenching temperature and differences between higher heating value HHV and lower heating value LHV.
The following self-assessment activities will allow you to check your understanding of stoichiometric and non stoichiometric combustion:
Self-Assessment Activities: 2
B4.4 KEY ISSUES: Effectiveness-NTU method
The following self-assessment activity will allow you to check your understanding of the Effectiveness-NTU method:
Self-Assessment Activities: 1
B4.6 KEY ISSUES: Fundamental heat exchanger notions
A heat exchanger can be modeled by the number of transfer units NTU method. While it is perfectly appropriate for studying the insertion of a heat exchanger in a thermodynamic cycle, such a phenomenological model, however, only gives access to the heat exchanger UA product, while the assessment of U can be particularly complex, as indicated. The success of this model is such that it is often used as a behavior model for a particular heat exchanger by adding a UA evolution law, function for example of fluid flows through the exchanger.
The concepts you should make sure you understand are UA, effectiveness ε and number of transfer units NTU, as well as pinch.
Self-Assessment Activities: —
Chapter 5: Steam Cycle Components
B5.1 KEY ISSUES: Architecture and configuration of a boiler
The following self-assessment activities will allow you to check your understanding of boilers:
Self-Assessment Activities: 2
Chapter 6: Second Law, Entropy, Exergy
B6.2 KEY ISSUES: Entropy chart
The following self-assessment activities will allow you to check your understanding of the entropy chart:
- Placement of points in a (T,s) entropy ideal gas chart, ddi
- Placement of points in a (T,s) entropy condensable vapor chart, ddi
Self-Assessment Activities: 2
B6.6 KEY ISSUES: Exergy balance spreadsheet
For simple cycles, establishing an exergy balance poses no particular difficulty but needs to be done very carefully otherwise errors can be committed.
To facilitate this task, a spreadsheet, named ExerBalanceThopt.xls has been prepared for you. Downloadable from the Thermoptim-UNIT portal, it gathers a number of worksheets related to the examples illustrating Thermoptim use. It is complemented by a detailed methodological note which explains how to use Thermoptim result files.
In addition, the Diapason e-learning module S06, which deals specifically with exergy balances, will guide you through your first steps, and modules S23, S28 and S32 will help you build the exergy balance of a gas turbine, a steam plant or a vapor compression refrigeration machine.
Self-Assessment Activities: —
Chapter 8: Variants of Steam Power Plants
B8.2 KEY ISSUES: Practical Difference Between Isentropic and Polytropic Approaches
Although they can be to a large extent considered as equivalent in a large number of cases, the polytropic approach is generally preferred to model the compression or the expansion in a multistage turbomachine, as the polytropic efficiency can be considered as an elementary stage isentropic efficiency.
It is particularly appropriate to do so if you make sensitivity analyses varying the compression or expansion ratio.
This is why gas turbine compressors and turbines are generally modeled using the polytropic reference in the examples provided with this book.
The following self-assessment activity will allow you to check your understanding of the polytropic efficiency:
Self-Assessment Activities: 0
Chapter 9: Conventional Internal Combustion Engines
B9.6 KEY ISSUES: Reciprocating internal combustion engines
The following self-assessment activities will allow you to check your understanding of reciprocating internal combustion engines:
- General mode of operation of a reciprocating internal combustion engine, gfe
- Differences between gasoline and diesel engine, gfe
- Locating a gasoline engine cycle in a Watt diagram, ddi
- Locating a Diesel engine cycle in a Watt diagram, ddi
Self-Assessment Activities: 4
Chapter 11: Compression Refrigeration Cycles
B11.2 KEY ISSUES: Ejectors
The following self-assessment activity will allow you to check your understanding of ejectors:
Self-Assessment Activities: 1
Chapter 13: Advanced Topics
B13.1 KEY ISSUE: CTP Lib thermodynamic properties server
CTP Lib is the library for calculating thermodynamic properties of the Center for Process Thermodynamics of Mines ParisTech.
Coupled to Thermoptim, it can calculate the properties of mixtures of real fluids, which the software cannot do itself. Access to CTPLib
Self-Assessment Activities: —
B13.2 KEY ISSUES: Modeling of the pair LiBr-H₂O
The ASHRAE equations giving the properties of the pair LiBr-H₂O, have been implemented in Thermoptim as an external substance.
It is thus possible to model absorption refrigeration machines using this pair.
Results obtained are given in several sections of this book and the associated models are available on the portal:
- Trigeneration by micro-turbine and absorption cycle, Chapter 10, whose absorber is presented below;
- Single effect LiBr-H₂O absorption cycle, below.
Self-Assessment Activities: —
© Renaud Gicquel, 2021.2
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