Lecture 5 GEOS24705 Thermodynamics of heat...
Transcript of Lecture 5 GEOS24705 Thermodynamics of heat...
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Lecture 5 GEOS24705
Thermodynamics of heat engines
Copyright E. Moyer 2011
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What is a “heat engine”?
A device that generates converts thermal energy to mechanical work by exploi8ng a temperature gradient
• Makes something more ordered: random mo8ons of molecules ordered mo8on of en8re body
• Makes something less ordered: degrades a temperature gradient (transfers heat from hot to cold)
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The two technological leaps of the Industrial Revolu?on that bring in the modern energy era
1. “Heat to Work” Chemical energy mechanical work via mechanical device Use a temperature gradient to drive mo8on Allows use of stored energy in fossil fuels Late 1700’s: commercial adop8on of steam engine
2. Efficient transport of energy: electrifica;on Mechanical work electrical energy mech. work Allows central genera8on of power Late 1800s: rise of electrical companies
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Newcomen’s design is state of the art for 60+ years
First true steam engine:
Thomas Newcomen, 1712, blacksmith
Copy of Papin’s engine of design of 1690, with piston falling as steam cooled, drawn down by the low pressure generated
First reciproca;ng engine: force transmiOed by mo8on of piston
Can pump water to arbitrary height.
Force only on downstroke of piston
Very low efficiency: 0.5%
IntermiOent force transmission
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Newcomen’s design is state of the art for 60+ years
First true steam engine:
Thomas Newcomen, 1712, blacksmith
Copy of Papin’s engine of design of 1690, with piston falling as steam cooled, drawn down by the low pressure generated
First reciproca;ng engine: force transmiOed by mo8on of piston
Can pump water to arbitrary height.
Force only on downstroke of piston
Very low efficiency: 0.5%
IntermiOent force transmission
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First modern steam engine:
James WaO, 1769 (patent), 1774 (prod.) Higher efficiency than Newcomen by introducing separate condense Reduces wasted heat by not requiring hea8ng and cooling en8re cylinder
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First modern steam engine:
James WaO, 1769 (patent), 1774 (prod.) Higher efficiency than Newcomen by introducing separate condenser
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First modern steam engine:
James WaO, 1769 patent (1774 produc8on model)
Like Newcomen engine only with separate condenser Higher efficiency: 2%
Force only on downstroke of piston
IntermiOent force transmission
No rota8onal mo8on
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Improved Wa> steam engine:
James WaO, 1783 model Albion Mill, London
Separate condenser Higher efficiency: ca. 3%
Force on both up-‐ and downstroke
Con8nuous force transmission
Rota8onal mo8on (sun and planet gearing)
Engine speed regulator
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Steam engines got more powerful AND more efficient over Dme
From V. Smil
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How were both accomplished?
POWER • More pressure • Bigger cylinders • More cylinders
EFFICIENCY • Removing obvious losses • Higher temperatures
Pressure and temperature are related for steam
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Prince Consort Beam engine (world’s largest steam engine)
Prince Consort Beam engine
Beam engine train (see 6:20)
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Double-‐acDon steam engine:
Why use suc8on to pull the piston down – why not just push it down with another injec8on of steam?
Piston pushed by steam on both up-‐ and down-‐stroke.
No more need for a condenser. Steam is simply vented at high temperature
slide valve alternates input & exhaust
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Double-‐acDon steam engine:
slide valve alternates input & exhaust
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Double-‐acDon steam engine:
primary use: transportation
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Indicator diagrams told engineers how much work a cylinder put out on each stroke