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THERMAL PHYSICS
Содержание
- 1. THERMAL PHYSICS
- 2. Scan to read the message!
- 3. Learning Objectivesunderstand and describe principles of work of heat enginesrecall and apply
- 4. 2nd Law of ThermodynamicsA heat engine is
- 5. Reversible and Irreversible ProcessThermodynamic processes that occur
- 6. Reversible and Irreversible ProcessThe flow of heat
- 7. Reversible and Irreversible ProcessA system that undergoes
- 8. Reversible and Irreversible ProcessReversible processes are thus
- 9. Reversible and Irreversible Process
- 10. Reversible and Irreversible Process
- 11. Efficiency of Heat EngineThe efficiency (e or
- 12. Efficiency of Heat Engine
- 13. Carnot EngineTo see how to increase efficiency,
- 14. Carnot EngineNo Carnot engine actually exists but
- 15. Carnot EngineFor animation, please visit:http://science.sbcc.edu/~physics/flash/heatengines/Carnot%20cycle.htmlCarnot cycle explanation by Glen Research Center (NASA) please visit:http://www.grc.nasa.gov/WWW/K-12/airplane/carnot.html
- 16. Слайд 16
- 17. Carnot EngineThe first process performed on the
- 18. Carnot EngineThe second process performed on the
- 19. Carnot EngineThe third process performed on the
- 20. Carnot EngineThe fourth process performed on the
- 21. Слайд 21
- 22. Слайд 22
- 23. Carnot EngineCarnot showed that for an ideal
- 24. Sample ProblemAn automobile engine has an efficiency
- 25. Слайд 25
- 26. Sample ProblemA steam engine operates between 500
- 27. Слайд 27
- 28. Sample ProblemAn engine manufacturer makes the following
- 29. Слайд 29
- 30. Sample ProblemA heat engine exhausts 8200 J
- 31. Слайд 31
- 32. Sample ProblemA heat engine does 9000 J
- 33. Слайд 33
- 34. Sample ProblemWhat is the maximum efficiency of
- 35. Слайд 35
- 36. Sample ProblemThe exhaust temperature of a heat
- 37. Слайд 37
- 38. Sample ProblemA nuclear power plant operates at
- 39. Слайд 39
- 40. Sample ProblemIt is not necessary that a
- 41. Слайд 41
- 42. Sample ProblemA Carnot engine performs work at
- 43. Слайд 43
- 44. Sample ProblemA Carnot engine’s operating temperatures are
- 45. Слайд 45
- 46. Sample ProblemA heat engine utilizes a heat
- 47. Слайд 47
- 48. Sample ProblemAt a steam power plant, steam
- 49. Слайд 49
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Слайды и текст этой презентации
Слайд 3Learning Objectives
understand and describe principles of work of heat engines
recall
and apply
Слайд 42nd Law of Thermodynamics
A heat engine is any device that
changes thermal energy into mechanical work, such as steam engines
and automobile engines.
Слайд 5Reversible and Irreversible Process
Thermodynamic processes that occur in nature are
all irreversible process. These are processes that proceed spontaneously in
one direction but not the other.
Слайд 6Reversible and Irreversible Process
The flow of heat from a hot
body to a cooler body is irreversible.
Sliding a book across
a table converts mechanical energy into heat by friction; this is irreversible, for no one has ever observe the reverse process.
Слайд 7Reversible and Irreversible Process
A system that undergoes an “idealized” reversible
process is always very close to being in thermodynamic equilibrium
within itself and with its surroundings.
Слайд 8Reversible and Irreversible Process
Reversible processes are thus equilibrium processes, with
the system always in thermodynamic equilibrium.
A reversible process is an
idealization that can never be precisely attained in real world.
Слайд 11Efficiency of Heat Engine
The efficiency (e or η) of any
heat engine can be identified as the ratio of the
work (W) it does to the heat input at the high temperature (QH or Q1).
Слайд 13Carnot Engine
To see how to increase efficiency, the French scientist
Sadi Carnot (1796 – 1832) examined the characteristics of an
ideal engine (now called Carnot Engine).
Слайд 14Carnot Engine
No Carnot engine actually exists but as a theoretical
idea it played an important role in the development of
thermodynamics.The idealized Carnot engine consisted of four (4) processes done in a cycle, two of which are adiabatic (Q = 0) and two are isothermal (ΔT = 0).
Слайд 15Carnot Engine
For animation, please visit:
http://science.sbcc.edu/~physics/flash/heatengines/Carnot%20cycle.html
Carnot cycle explanation by Glen Research
Center (NASA) please visit:
http://www.grc.nasa.gov/WWW/K-12/airplane/carnot.html
Слайд 17Carnot Engine
The first process performed on the gas is an
isothermal expansion.
The 300 degree heat source is brought into contact
with the cylinder, and weight is removed, which lowers the pressure in the gas.The temperature remains constant, but the volume increases.
During the process from State 1 to State 2 heat is transferred from the source to the gas to maintain the temperature. We will note the heat transfer by Q1 into the gas.
Слайд 18Carnot Engine
The second process performed on the gas is an
adiabatic expansion.
During an adiabatic process no heat is transferred to
the gas.Weight is removed, which lowers the pressure in the gas.
The temperature decreases and the volume increases as the gas expands to fill the volume. During the process from State 2 to State 3 no heat is transferred.
Слайд 19Carnot Engine
The third process performed on the gas is an
isothermal compression.
The 200 degree heat source is brought into contact
with the cylinder, and weight is added, which raises the pressure in the gas.The temperature remains constant, but the volume decreases.
During the process from State 3 to State 4 heat is transferred from the gas to heat source to maintain the temperature. We will note the heat transfer by Q2 away from the gas.
Слайд 20Carnot Engine
The fourth process performed on the gas is an
adiabatic compression.
Weight is added, which raises the pressure in the
gas.The temperature increases and the volume decreases as the gas is compressed.
During the process from State 4 to State 1 no heat is transferred.
Слайд 23Carnot Engine
Carnot showed that for an ideal reversible engine, the
heat Q1 (QH) and Q2 (QL) are proportional to the
operating temperatures T1 (TH) and T2 (TL) in Kelvins, so the efficiency can be written as
Слайд 24Sample Problem
An automobile engine has an efficiency of 20% and
produces an average of 23000 J of mechanical work per
second during operation. (a) How much heat input is required, and (b) how much heat is discharged as waste heat from this engine, per second?
Слайд 26Sample Problem
A steam engine operates between 500 ⁰C and 270
⁰C. What is the maximum possible efficiency of this engine?
Слайд 28Sample Problem
An engine manufacturer makes the following claims: An engine’s
heat input per second is 9.0 kJ at 435 K.
The heat output per second is 4.0 kJ at 285 K. Do you believe these claims?
Слайд 30Sample Problem
A heat engine exhausts 8200 J of heat while
performing 3200 J of useful work. What is the efficiency
of this engine?
Слайд 32Sample Problem
A heat engine does 9000 J of work per
cycle while absorbing 22.0 kCal of heat from a high-temperature
reservoir. What is the efficiency of this engine?
Слайд 34Sample Problem
What is the maximum efficiency of a heat engine
whose operating temperatures are 580 ⁰C and 380 ⁰C?
Слайд 36Sample Problem
The exhaust temperature of a heat engine is 230
⁰C. What must be the high temperature if the Carnot
efficiency is to be 28%?
Слайд 38Sample Problem
A nuclear power plant operates at 75% of its
maximum theoretical (Carnot) efficiency between temperatures 626 C and 350
C. If the plant produces electric energy at the rate of 1.3 GW (gigaWatts), how much exhaust heat is discharged per hour?
Слайд 40Sample Problem
It is not necessary that a heat engine’s hot
environment be hotter than ambient temperature. Liquid nitrogen (77 K)
is about as cheap as bottled water. What should be the efficiency of an engine that made use of heat transferred from air at room temperature (293 K) to the liquid nitrogen fuel?
Слайд 42Sample Problem
A Carnot engine performs work at the rate of
440 kW while using 680 kCal of heat per second.
If the temperature of the heat source is 570 ⁰C, at what temperature is the waste heat exhausted?
Слайд 44Sample Problem
A Carnot engine’s operating temperatures are 210 ⁰C and
45 ⁰ C. The engine’s power output is 950 W.
Calculate the rate of heat output.
Слайд 46Sample Problem
A heat engine utilizes a heat source of 550
C and has an ideal (Carnot) efficiency of 28%. To
increase the ideal efficiency to 35%, what must be the temperature of the heat source?
Слайд 48Sample Problem
At a steam power plant, steam engines work in
pairs, the output of heat from one being the approximate
heat input of the second. The operating temperatures of the first are 670 C and 440 C, and of the second 430 C and 290 C. If the heat of combustion of coal is 2.8 ×107 J/kg, at what rate must coal be burned if the plant is to put out 1100 MW of power? Assume the efficiency of the engines is 60% of the ideal efficiency.
