power cycle thermodynamics

1. POWER AND REFRIGERATION
CYCLES

2. Steam power plant
Heat (Qin) is transferred to the steam in the boiler from a
furnace, which is the energy source.
The turbine produces work (Wout ) when steam passes
through it.
A condenser transfers the waste heat (Qout) from steam
to the energy sink, such as the atmosphere.
A pump is used to carry the water from the condenser
back to the boiler. Work (Win) is required to compress
water to boiler pressure.
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3. The net work output from this power plant is the difference between the work output
and the work input.
Wnet, out = Wout - Win
From the energy balance of the cycle, the net work output is
Wnet, out = Qin - Qout
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4. Example:
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6. Example: A car engine with a power output of 90kW has a thermal efficiency of 28%. Determine
the rate of fuel consumption if the heating value of fuel is 44000kJ/kg (44000kJ of energy is
released for 1kgof fuel burned).
= 90/0.28
= 321.4 kJ/s
Fuel consumption rate =321.4/44000
= 7*10^-3 kg/s
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7. The transfer of heat from a low-temperature
medium to a high-temperature one requires
special devices called refrigerators (Ex:
Household refrigerator, Air conditioners) and
cycle works on called refrigeration cycle.
The working fluid used in the refrigeration cycle
is called a refrigerant.
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2. Refrigeration Cycle

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10. Coefficient of Performance
The efficiency of a refrigerator is expressed in terms of
the coefficient of performance (COP), denoted by
COPR.
The objective of a refrigerator is to remove heat (QL)
from the refrigerated space. To accomplish this
objective, it requires a work input of Wnet,in.
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11. • Heat pump is another device that transfers heat
from a low-temperature medium to a high-
temperature.
• Refrigerators and heat pumps operate on the same
cycle but differ in their objectives.
• The objective of a refrigerator is to maintain the
refrigerated space at a low temperature by
removing heat from it.
• The objective of a heat pump, however, is to
maintain a heated space at a high temperature.
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3. Heat pump Cycle

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13. The measure of performance of a heat pump is also expressed in terms of the coefficient
of performance,
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