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1. Find Carnot cycle efficiency
The thermal efficiency of the cycle is given by
where
2. Carnot cycle diagram
Process 1: Isothermal expansion at high temperature. As the gas
expands, it does work.
Expansion sends the temperature down and to keep the same
temperature, the gas
absorbs heat from its surroundings.
Process 2: Adiabatic expansion. As the gas expands, it does work
and sends thetemperature down. Because it's adiabatic, no heat is
absorbed or ejected.
Process 3: Isothermal compression at low temperature. As the gas
contracts, work is
done on the gas and sends the temperature up. To keep the same
temperature, the gas
ejects heat into its surroundings.
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7/29/2019 Satellite Assignment 2 Carnot
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Process 4: Adiabatic compression. As the gas contracts, work is
done on the gas and
sends the temperature up. Because it's adiabatic, no heat is
absorbed or ejected.
.
3. Define the temperature involved. Pick one real example and
elaborate
Carnot cycle is applied in cylinder piston engine (reciprocating
engine). In the beginning,
the system is at temperature Thot at state a. The cylinder head
is brought in contact with
a heat reservoir which is a constant temperature source. Then,
the gas is allowed to
expand slowly, doing work on the surroundings. As a result, the
system then undergoes
an isothermal expansion from a to b, with heat absorbed but
keeps the same
temperature. At state b, the cylinder head is removed from
contact with the heat
reservoir and then let expand to c. During this expansion the
temperature decreases to
lowest temperature Tcold (temperature of cold reservoir). The
heat exchanged during this
part of the cycle is zero. At state c, the cylinder head is
brought in contact with a heat
reservoir at temperature Tcold. It is then compressed to state
d, rejecting heat in the
process. Finally, the system is compressed adiabatically back to
the initial state a. The
heat exchange is zero. To increase the efficiency of Carnot heat
engine, the temperature
of hot reservoir Thot should be increased while the temperature
of cold reservoir T cold
should be decreased. The thermal efficiency of actual heat
engines can be maximized
by supplying heat to the engine at the highest possible
temperature and rejecting heat
from the engine at the lowest possible.
4. What is the significant of Carnot cycle?
Carnot cycle is significant at its reversibility. No heat engine
can have a higher efficiency
than a reversible heat engine operating between the same
high-and-low temperature
reservoirs. The Carnot heat engine is the most efficient of all
heat engines operating
between the same high-and-low temperature reservoirs. Carnot
cycles efficiency is
determined by the temperatures of the hot and cold reservoirs
between which it works
and by the properties of the working substance used.
REFERENCES
1. Cengel, Yunus A. and Michael A. Boles. (2001).
Thermodynamics: An. Engineering
Approach, 4th ed. New York: McGraw-Hill.
