Download - Effect of compressor heating and cooling
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R.PANDIYAN,
M.E, 1ST YEAR,
R&AC DEPARTMENT.
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COMPRESSOR WORK
πΎ =π
π β ππ·π½π
π·ππ·π
πβππ
β π
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COMPRESSOR WORK
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COMPRESSOR CYLINDER HEATING,COOLING
AND FRICTION
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COMPRESSOR CYLINDER HEATING
High pressure compression.
Heat due to friction.
High ambient condition.
Improper selection of capillary and expansion
devices.
High load on evaporator.
Suction line not insulated properly.
Inefficiency of condenser.
Thermal losses from motor windings.
CAUSES:
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COMPRESSOR CYLINDER HEATING
TEMPERATURE
VOLUME OFREFRIGERANT VAPOUR
Hence PRESSURE RATIO
Due to thisCOMPRESSION WORK
TEMPERATURE
VOLUME OFREFRIGERANT VAPOUR
HenceVOLUMETRIC EFFICIENCY
Due to thisMASS FLOW RATE andREFRIGERANT CAPACITY
πΌπ½ = π + πͺ β πͺπ·π
π·π
π
π
where,
πͺ =π½π
π½π β π½π
π»ππ»π
=π·ππ·π
πβππ
EFFECTS:
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COMPRESSOR CYLINDER HEATING
At high temperature,
-Breakdown of lubricating oil occurs,
-Results in wear and Reduced life of
compressor valve.
At high temperature,
-Undesirable chemical reactions occurs
-In presence of water damage the
compressor.
High discharge temperature,
-In hermetic compressor it affects motor
insulation.
EFFECTS:
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CHEMICAL REACTION IN COMPRESSOR
Mineral oil will start to decompose at approximately350ΒΊF (400ΒΊF for POE oil).
First the oil is transformedinto a dark thick oil, then a sludge, and finallya solid powder.
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RECTIFICATION:
INTERCOOLER or FLASH CHAMBER Provided in Multistage Air compressor System.
COMPRESSOR CYLINDER HEATING
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INTERCOOLER
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INSULATION of Suction line, Motor Winding and
Compressor Side is must be provided like in
Hermetic Compressor.
THERMOSTAT VALVE is used to Cut-Off the
compressor at the Time Of Over Loading.
SUB-COOLING after condenser reduced the
temperature of refrigerant.
Reduced the discharge pressure by proper
designing of condenser and evaporator.
RECTIFICATION:
COMPRESSOR CYLINDER HEATING
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CYLINDER OVERCOOLING
CAUSES:
Overcooling of compressor by Intercooler and
Flash chamber.
Wet Compression.
Moisture present in Refrigerant.
Load in the evaporator Decreases.
Overcharging.
Insufficient heat transfer of dirty Evaporator.
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EFFECTS:
πΎ =π
π β ππ·ππ½π
π·ππ·π
πβππ
+π·ππ·π
πβππ
β π
COMPRESSOR CYLINDER COOLING
Intercooling in compressor P-V Diagram
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COMPRESSOR CYLINDER COOLING
R-134a Refrigerant at 29*C
EFFECTS:
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EFFECTS:
If the cooling is sufficiently provided to cylinder means volume of refrigerant vapour decreases so that Ξ·v increases.
Due to that work of compression work and power consumption decreases hence RE and COP increases.
If Excessive cooling produced, the condensationmay occurs inside the cylinder. Liquid is not compressed by compressor.
Because of Hydraulic pressure developed in the cylinder make liquid slugging can damage the compressor body, crankshaft, connecting rods, piston, valves.
CYLINDER OVERCOOLING
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EFFECTS:If the condensation allowed inside the cylinder
means, it dilute the lubricating oil and the lubrication at compressor parts are tend to lesser.
Moisture reacts with lubricant to form the acidsand failure of compressor possible.
The maximum permissible moisture amount inside the cylinder is 50 mg/m2.
CYLINDER OVERCOOLING
Effect of acid Formation
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RECTIFICATIONS:
Receiver with thermostat as a regulator to control the flow of refrigerant depending upon the load.
Thermostat used as a cylinder ON-OFF control i.e., if the compressor temperature increases and decreases than set temperature the thermostat switches of the compressor.
Built a combination of condensate separator and trapper after cooler.
Avoid overcharging and using cut-off in low load condition.
Drier or suction line accumulator should be used after the evaporator.
CYLINDER OVERCOOLING
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CAUSES:
Lubrication oil may lack the viscosity of oil
due to overheating and overcooling.
More moving parts.
Lack of lubrication oil.
Discharge pressure increases.
Instability and Immiscibility of oil.
Copper plating, Metallic contaminants cause
the friction.
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CYLINDER FRICTION
EFFECTS:
Noise Production
Pressure drop occurs in the cylinder.
Thermal heat added to the Refrigerant and itβs
discharge temperature increases.
Over wear and tear damage the inside parts of
cylinder and that the compressor life is reduced.
Chemical reaction may produced due to
overheating and inner parts are corroded.
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Loss of Lubrication:
CYLINDER FRICTION
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CYLINDER FRICTION
RECTIFICATION:
Sufficient lubrication must be provided.
Heating and cooling of cylinder is provided as
required level.
Lubricant should have high chemical and
thermal stability.
It should have good miscible characteristics
with refrigerant.
Metallic contaminants should be cleared
properly.
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Short term return of mass of
liquid refrigerant, oil or both to
the compressor cylinder..
In water cooler when thermostat
cuts of 70% of refrigerant will
store in the evaporator.
Once the thermostat cuts in
slugging will occur.
Hydraulic compression produce
tremendous load on the
compressor.
2.FLOOD BACK1.SLUGGING
Continuous return of liquid
refrigerant in the suction side
of compressor.
Insufficient expansion allow
more refrigerants to flow low
sides of the system.
It washes the oil of the
lubricated surfaces.
This causes typical foaming
in the compressor crank case
and oil out in a minute.
May damage valves, gaskets,
piston and bearing.
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3.ELECTRICAL PROBLEMS:
If the proper voltage maintenance, the compressor is fail
to start cause a locked rotor situation which brings on
overheating of start windings and rapid failure.
Normal Rotor winding Burned Rotor winding
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4.CONTAMINATION:(i) Moisture(ii) Air and other condensable gases:- It form thick film in inner surface of the condenser may
decreasing overall heat transfer and building discharge pressure. It increases power consumption, temperature and decreases the
efficiency of the compressor. Carbonization of oil on discharge valve, valve plates and cylinder
heads.Effect of carbonization
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(iii)Copper plating : The formation of thin film of corroded copper on the surface of
the components in compressor is copper plating. In this Copper converted into invisible copper oxide which
deposit can interfere the proper operation of compressor. (iv)Metallic Contaminants: Dirt, Metal chips, Brazing material, flux wear out cylinders,
bearing, valve plates etc. It blocks the capillary, strainers.
Effect of Copper Plating Effect of Metallic Contaminants
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5.HIGH OPERATING TEMPERATURES.
6.TRANSPORT PROBLEMS:
Noise due to breakage of suspension of spring
using for pump mounting inside the cell.
breakage of suspension
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Compressor Failure
CAUSES EFFECTS
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