Download - Refrigeration Heat Pumps Air Conditioning
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REFRIGERATION
&
HEAT PUMPS
Anjana Tharanga
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Evaporative Cooling
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Is used to reduce the temperature ofcooling water.
Water to be cooled is sprayed into the topof the tower.
And then it is allowed to flow down a fill ofmaterial
Ambient air stream is flown in counter
flow manner
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Vapour compression refrigeration
Highly compressed fluids at a certain temperaturetend to get colder when they are allowed toexpand.
fluid is used to cool a low temperatureenvironment and reject the heat to a hightemperature environment
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Thermo-dynamics aspect of
refrigeration The 1st law of thermodynamics says heat flow
occurs from a hot source to a cooler sink.
So energy in the form of work must be added tothe process to get heat to flow from a lowtemperature region to a hot temperature region.
The Carnot cycle can serve as the initial model ofthe ideal refrigeration cycle.
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The choice of refrigerant and the requiredcooling temperature and load determine thechoice of compressor, as well as the design of
the condenser, evaporator, and otherauxiliaries.
Additional factors such as ease ofmaintenance, physical space requirementsand availability of utilities for auxiliaries(water, power, etc.) also influence componentselection.
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Vapour absorption refrigeration
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Absorption refrigeration systems that use Li-Br-water as a refrigerant have a CoefficientofPerformance (COP) in the range of 0.65 -0.70
and can provide chilled water at 6.7 oC with acooling water temperature of 30 oC. Systems
capable of providing chilled water at 3 oC arealso available.
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How cooling efficiency is
expressed
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Energy flows through a cooling
machine
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EFFICIENCY IS DEFINED AS
USEFUL ENERGY OUTPUT DIVIDED
BY TOTAL ENERGY INPUT.
But for chillers we cant apply it.
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COEFFICIENT OF PERFORMANCE
(COP)
COP is dimensionless.
The higher the COP, the more efficient
the heat pump.
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COOLING MACHINE
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COEFFICIENT OF PERFORMANCE
(COP)
The cooling process with the maximum possible efficiency is theCarnot cycle.
The COP of a cooling machine using the Carnot cycle is;
Where THot
and Tcold
are the absolute temperatures of the hot andcold heat reservoirs respectively.
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The COP of any machine
depends strongly on the
temperature difference againstwhich it operates.
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Heat Pump
Similar to the refrigeration cycle but theenergy released in the condenser isconsidered instead of the energy absorbed inthe evaporater.