Transcript Slide 1

THERMODYNAMICS
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Conservation of Energy Principle
Energy can neither be
created nor destroyed
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Energy Transfer
Work
air
Heat
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Work is force acting through a
distance
W
Unit, kJ
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Work done per unit time is
POWER
Power =
(unit kJ/s or kW)
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There will be work when there is movement.
If there is no movement, no work is done
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Calculate the amount of work that has to
be done to lift a 10-pound bag of
groceries a distance of 2.5 feet from the
floor to the top of the kitchen counter
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Moving Boundary Work
δW = Fds = PAds = PdV
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Moving Boundary Work
Total boundary work from initial state to final state
2
W 
 PdV
1
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Work
air
Compression process
- dV –ve, ∴W
air
Expansion process
- dV +ve, ∴W
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Area under curve = PdV=Work
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Isochoric Process
Constant Volume
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A rigid tank contains air at 500 kPa
and 150°C. As a result of heat transfer
to the surroundings, T and P drop to
65°C and 400 kPa. Determine the
boundary work done during this
process.
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Solution
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Isobaric Process
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Consider a cylinder containing gas at
P = 200 kPa and V= 0.04 m3. The
cylinder is fitted with a piston on which
a number of small weights are placed.
Heat is added to the system until the
volume increased to 0.1m3 while the
pressure remains constant. What is
the work done during this process.
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Solution
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Polytropic Process
A process which occurs with an interchange of
both heat and work between the system and its
surroundings. The nonadiabatic expansion or
compression of a fluid is an example of a
polytropic process.
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Polytropic Process
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Polytropic Process
Work,
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Consider a cylinder containing gas at
P = 200 kPa and V= 0.04 m3 but at the
same time the heat is under the
cylinder and the piston is rising,
weights are removed at such a rate
that the expression PV1.3= constant
describes the relations between P and
V. Determine the work done.
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Solution
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Isothermal Process
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Isothermal Process
V2
Work ,W  P1V1 ln
V1
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A piston–cylinder device initially
contains 0.4 m3 of air at 100 kPa and
80°C.The air is now compressed to
0.1 m3 in such a way that the
temperature inside the cylinder
remains constant. Determine the work
done during this process.
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Solution
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Other Mechanical Forms of Work
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Gravitational work
Acceleration work
Shaft work
Spring work
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Non Mechanical Forms of Work
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Electrical work
Magnetic work
Electrical Polarization work
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