A Stirling Engine Primer.pdf

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Stirling.ppt
A Stirling
Stirling Engine Primer
Engine Primer
Mario Paolo Giordani
Università degli Studi di
Mario Paolo Giordani
Udine
mario.paolo. giordani@ud
giordani@ud .infn.it
.infn.it
Facoltà di
di Ingegneria
Ingegneria — CCS
CCS Ingegneria Meccanica
Ingegneria Meccanica
June 18, 2008
18, 2008
A
Università degli Studi di Udine
mario.paolo.
Facoltà
June
94818839.006.png
Basic idea: Stirling
Stirling cycle
cycle
Four-phase thermodynamic process on working fluid
1 2 isothermal expansion at
2 isothermal expansion at T h
2 3 isometric (isochoric) cooling
3 isometric (isochoric) cooling
3 4 isothermal compression at
4 isothermal compression at T k
4 1 isometric heating
1 isometric heating
Heat exchanged in all phases
Heat exchanged in all phases
two constant-temperature heat sources
two constant-temperature heat sources
multiple (infinite) sources with
multiple (infinite) sources with T k TT h
however, for
however, for a source
a source with (
with ( T,T+
T,T+ d T )
in ( T )= nC
nC V d T=
T= d Q out
out ( T )
heat recycling:
heat absorbed in 4
returned in 2 3
no net heat absorbed in isometric
is returned in 2
no net heat absorbed in isometric phases
phases
Two heat sources (heater at T h , cooler at
, cooler at T k ) +
) + “ regenerator
regenerator”
regenerator is a reversible (two-way) heat exchanger
is a reversible (two-way) heat exchanger
18.06.2008
Mario Paolo Giordani
2
Basic idea:
Four-phase thermodynamic process on working fluid
d Q in
heat recycling:
heat absorbed in 4 1 is
Two heat sources (heater at
regenerator
94818839.007.png 94818839.008.png
Stirling efficiency
efficiency
Definition of efficiency for a thermodynamics cycle:
W
Q in
= Q in Q out
Q in
= 1 Q out
Q in
Heat exchanged in isothermal transformations involving ideal gases:
Q isoth = P d V
= nRT
f
d V
V
= nRT ln V f
(
)
i
T
i
V i
Ideal Stirling
Stirling cycle efficiency:
cycle efficiency:
= 1 T k
T h
= C
Stirling cycle achieves maximum theoretical efficiency (
cycle achieves maximum theoretical efficiency ( Carnot
Carnot’ s
s theorem)
theorem)
Definitely a good reason to study!
18.06.2008
Mario Paolo Giordani
3
Stirling
f
Ideal
Stirling
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Stirling engines
engines
Not exactly a new idea
first prototypes date 1826
first prototypes date 1826
first scientific analysis in 1871
first scientific analysis in 1871
External combustion engine
External combustion engine
with respect to most internal combustion engines
with respect to most internal combustion engines
relatively simple design (few parts in motion, no valves)
relatively simple design (few parts in motion, no valves)
quiet running
quiet running
can run with any heat (or even cold!) source
can run with any heat (or even cold!) source
either low or no
emissions (for instance, solar power)
closed cycle (working fluid sealed inside engine)
closed cycle (working fluid sealed inside engine)
low power per cycle, low rpm
low power per cycle, low rpm
high peak stresses on bearings and other components
high peak stresses on bearings and other components
complicated thermal insulation, regenerator issues
complicated thermal insulation, regenerator issues
Despite being
Despite being conceptually simple...
conceptually simple...
"the various 'ideal' cycles are neither physically realizable nor representative of the
"the various 'ideal' cycles are neither physically realizable nor representative of the
Stirling
Stirling cycle
cycle” — Dr.
Dr. I.
I. Urieli
Urieli (Ohio
(Ohio University)
University)
18.06.2008
Mario Paolo Giordani
4
Stirling
Not exactly a new idea
either low or no emissions (for instance, solar power)
94818839.001.png
Mechanical configurations
& separate cylinders
cylinders connected in series
cylinders connected in series with heater, regenerator and cooler
with heater, regenerator and cooler
Gamma engines: piston-displacer arrangements
displacer: loosely-fit piston
cycles working fluid between hot and cold ends
Beta engine: in-line piston-displacer
which cycles working fluid between hot and cold ends
Beta engine: in-line piston-displacer
Gamma engine: separate cylinders for power piston and displacer
piston and displacer
18.06.2008
Mario Paolo Giordani
5
Alpha engines: two pistons & separate cylinders
Alpha engines: two pistons
Beta & Gamma engines: piston-displacer arrangements
Beta &
displacer: loosely-fit piston which
Gamma engine: separate cylinders for power
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