1. outline define terms and conventions introduce 1 st law of thermodynamics contrast state and...
TRANSCRIPT
![Page 1: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/1.jpg)
1
![Page 2: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/2.jpg)
2
Outline
• Define terms and conventions• Introduce 1st law of thermodynamics• Contrast state and non-state properties• Describe the Carnot cycle
![Page 3: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/3.jpg)
3
System and environment
• System = what we wish to study– View as control mass or control volume
• Control mass (CM)– Define some mass, hold fixed, follow it around
• Control volume (CV)– Define and monitor a physical space
• Environment = everything else that may interact with the system
![Page 4: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/4.jpg)
4
System states
• Systems may be open or closed to mass– Open systems permit mass exchange across system
boundaries– Our CVs are usually open– Strictly speaking, a CM is closed
• Closed systems may be isolated or nonisolated– Isolated systems do not permit energy transfer with
environment– Closed, isolated system = environment doesn’t
matter
![Page 5: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/5.jpg)
5
Lagrangian vs. Eulerian
• CM is the Lagrangian viewpoint– Powerful, desirable but often impractical– Total derivatives– Freeway example
• CV is the Eulerian viewpoint– Observe flow through volume– Partial derivatives
![Page 6: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/6.jpg)
6
Air parcel
• Our most frequently used system• CM (usually!) – Lagrangian concept• Monitor how T, p, and V change as we follow it
around
![Page 7: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/7.jpg)
7
Conventions
• We often use CAPITAL letters for extensive quantities, and lower case for specific quantities– Specific = per unit mass
• Example:– U is internal energy, in Joules– u is specific internal energy, in J/kg– Unfortunately, “u” is also zonal wind velocity
• Exceptions:– Temperature T is essentially specific, but capitalized (and isn’t
per unit mass anyway)– Pressure p is fundamentally extensive, but lower case
![Page 8: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/8.jpg)
8
Energy and the 1st law
• Total energy = KE + PE + IE– Conserved in absence of sources and sinks
• Our main use of 1st law: monitor changes in internal energy (IE or u) owing to sources and sinks
• How do we change system u? With energy transfer via– heat Q or q– work W or w
• Caveat: w is also vertical velocity, and q will be reused (briefly) for water vapor specific humidity
![Page 9: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/9.jpg)
9
Work
• Work = force applied over a distance– Force: N, distance: m– Work: Nm = J = energy
• Our principal interest: CM volume compression or expansion (dV) in presence of external pressure (p)
• W > 0 if dV > 0
![Page 10: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/10.jpg)
10
Work
W > 0 when system expands againstenvironment
![Page 11: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/11.jpg)
11
Heat
• Diabatic heat– Diabatic: Greek for “passable, to be passed
through”– Internal energy exchanged between system and
environment– q > 0 when energy flow is INTO system
• Adiabatic = system is isolated– Adiabatic: impassable, not to be passed through
![Page 12: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/12.jpg)
12
Caution on nomenclature
• We should use diabatic when the energy exchange is between system and environment
• But, what if the heat source or sink is inside the system?– That’s adiabatic, but q ≠ 0– Our interior heat source will be water changing phase
• Dry adiabatic: q = 0– No heat source, outside OR inside– “dry” really means no water phase changes
• Moist adiabatic: q ≠ 0, but heat source/sink is inside system– “moist” implies water phase change– Synonyms include “saturated adiabatic” and “wet adiabatic”– Can also be referred to as “diabatic”!
![Page 13: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/13.jpg)
13
1st law
• In the absence of ∆KE and ∆PE
• Other ways of writing this
Most of my examples will be per unit mass.
![Page 14: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/14.jpg)
14
State properties
• Internal energy u is a state property• Changes in state properties are not path-
dependent
• Other state properties include m, T, p, r, V, etc.
![Page 15: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/15.jpg)
15
State properties
![Page 16: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/16.jpg)
16
Path-dependence
• Work and heat are path-dependent
![Page 17: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/17.jpg)
17
Path-dependence
• A cyclic process starts and ends with the same state property values
• … but the cyclic process can have net heat exchange and do net work
![Page 18: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/18.jpg)
18
Path-dependence
![Page 19: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/19.jpg)
19
Path-dependence
![Page 20: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/20.jpg)
20
Carnot cycle
• 4-step piston cycle on a CM• 2 steps of volume expansion, 2 of volume
compression• 2 steps are isothermal, 2 are (dry) adiabatic• Warm and cold thermal reservoirs external to
system• Start and end with temperature T1 and volume
V1
![Page 21: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/21.jpg)
21
Carnot – Step 1
Isothermal volume expansion
Add heat QA from warmreservoir
T2 = T1
V2 > V1
![Page 22: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/22.jpg)
22
Carnot – Step 2
Adiabatic volume expansion
No heat exchange
T3 < T2
V3 > V2
![Page 23: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/23.jpg)
23
Carnot – Step 3
Isothermal volume compression
Lose heat QB to cold thermalreservoir
T4 = T3
V4 < V3
![Page 24: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/24.jpg)
24
Carnot – Step 4
Adiabatic volume compression
No heat exchange
T1 > T4
V1 < V4
Returned to original state T1, V1.Cycle is complete.
![Page 25: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/25.jpg)
25
![Page 26: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/26.jpg)
26
Apply 1st law
![Page 27: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/27.jpg)
27
Carnot on T-V diagram
![Page 28: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/28.jpg)
28
Carnot on T-V diagram
![Page 29: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/29.jpg)
29
Carnot on T-V diagram
![Page 30: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/30.jpg)
30
Carnot on T-V diagram
![Page 31: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/31.jpg)
31
Carnot on T-V diagram
![Page 32: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/32.jpg)
32
Carnot on T-V diagram
![Page 33: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/33.jpg)
33
Carnot on T-V diagram
No net ∆VBut did net W
![Page 34: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/34.jpg)
34
Conceptual summary
Heat flow divertedto do work
![Page 35: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/35.jpg)
35
Question for thought #1
The isothermal expansion (QA) occurred at a higher temperature than the Isothermal compression (QB).
What does this imply for the work?
QB is waste heat. What does this imply for the efficiency of this heat engine?
Is there a limit to efficiency?Is the limit found in the 1st law?
![Page 36: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/36.jpg)
36
Question for thought #2
Can you design a cyclic process that does no net work?
What would it look like on a T-V diagram?
![Page 37: 1. Outline Define terms and conventions Introduce 1 st law of thermodynamics Contrast state and non-state properties Describe the Carnot cycle 2](https://reader035.vdocument.in/reader035/viewer/2022070306/55199bb65503463d068b49f0/html5/thumbnails/37.jpg)
37
Summary
• 1st law says, in essence, if you can’t take the heat, you can’t do the work
• Work and heat are path-dependent• Carnot cycle illustrates isothermal and (dry)
adiabatic processes– Heat diverted to do work, but some is wasted
W = QA - QB