effect of compressor heating and cooling

R.PANDIYAN,

M.E, 1ST YEAR,

R&AC DEPARTMENT.

COMPRESSOR WORK

𝑾 =𝒏

𝒏 − 𝟏𝑷𝑽𝟏

𝑷𝟐𝑷𝟏

𝒏−𝟏𝒏

− 𝟏

COMPRESSOR WORK

COMPRESSOR CYLINDER HEATING,COOLING

AND FRICTION

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:

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

𝜼𝑽 = 𝟏 + 𝑪 − 𝑪𝑷𝟐

𝑷𝟏

𝟏

𝒏

where,

𝑪 =𝑽𝟑

𝑽𝟏 − 𝑽𝟑

𝑻𝟐𝑻𝟏

=𝑷𝟐𝑷𝟏

𝒏−𝟏𝒏

EFFECTS:

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:

CHEMICAL REACTION IN COMPRESSOR

Mineral oil will start to decompose at approximately350ºF (400ºF for POE oil).

First the oil is transformedinto a dark thick oil, then a sludge, and finallya solid powder.

RECTIFICATION:

INTERCOOLER or FLASH CHAMBER Provided in Multistage Air compressor System.

COMPRESSOR CYLINDER HEATING

INTERCOOLER

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

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.

EFFECTS:

𝑾 =𝒏

𝒏 − 𝟏𝑷𝟏𝑽𝟏

𝑷𝟐𝑷𝟏

𝒏−𝟏𝒏

+𝑷𝟑𝑷𝟐

𝒏−𝟏𝒏

− 𝟐

COMPRESSOR CYLINDER COOLING

Intercooling in compressor P-V Diagram

COMPRESSOR CYLINDER COOLING

R-134a Refrigerant at 29*C

EFFECTS:

EFFECTS:

If the cooling is sufficiently provided to cylinder means volume of refrigerant vapour decreases so that ηv 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

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

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

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.

CYLINDER FRICTION

EFFECTS:

Noise Production

Pressure drop occurs in the cylinder.

Thermal heat added to the Refrigerant and it’s

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.

Loss of Lubrication:

CYLINDER FRICTION

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.

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.

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

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

(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

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

Compressor Failure

CAUSES EFFECTS