How it Works:
Stirling
Cycle: As stated before, there are several types of
Stirling engines, but they all use the Stirling Cycle. The
Stirling Cycle
has four stages: compression,
expansion, heat added, heat removed. The cycle goes as such:
Isothermal compression:
In
the cold end the gas transfers it's heat to it's surroundings to keep
the same temperature during
compression from the piston.
Constant-Volume Heat
Addition: The compressed air is heated and thus pressure
on the
piston increases.
Isothermal Expansion:
The
gas expands as heat is added in order to maintain temperature.
Constant-Volume Heated
Rejected: The air has expanded as far as the piston can
move
back, volume can no longer increase so the
air must now lose heat.[1]
The
Stirling Cycle was derived from Gay-Lussac gas law: (P1V1)/T1=(P2V2)/T2=nR
where P=pressure V=volume T=temperature n=number
of moles of gas R=universal
gas constant
Efficiency:
The Stirling engine is a heat engine meaning it runs off of a fluid's
expansion and contraction from heat (combustion
engines(cars) and steam
engines(power plants/old-time trains) are also examples of heat
engines). Thanks to French physicist,
Nicolas
Leonard
Sadi
Carnot (1796-1832), we have an equation to tell us the
maximum possible efficiency a heat engine can have. His equation
shows the hotter
your hot end and the
colder your cold end the greater
your maximum possible efficiency.
Carnot's
equation: (1 - (Tcold/Thot))
x 100= % efficiency T=Temperature
in Kelvin
Example: So if
the temperature at your cold end was the
freezing point of water (~273 kelvin) and your hot end was at the
boiling point of water
(~373 kelvin) you would have a maximum possible
efficiency of:
(1-(273k/373k)) x 100 =26.8% efficiency
