Understanding Refrigerations

UNDERSTANDING REFRIGERATIONS

RELATED PHYSICS IN REFRIGERATIONS

REFRIGERATIONS 

Process of reducing and maintain the temperature

REFRIGERATIONS EXCHANGE

OF HEAT TRANSFER OF HEAT FROM A SPACE TO REFRIGERANT AND VICE VERSA

LE SYSTEME INTERNATIONAL d’UNITES (SI) 

Mass - amount of material in a substance measure in grams or kilograms

SI 

Force - a push or pull

Weight - measure of the force exerted on the body by the gravitational pull of the earth

SI 



Kilogram force (kgf) - the force of gravity of an object having a mass of 1 kg Newton - mass 1kg, acceleration 1 m/s2

gravity = 9.807 m/s2

SI 

Pressure - force per unit area P = f/a

PRESSURE kgf/cm2  Pascal (Pa)  Pound per square inch (psi) 

PRESSURE The deeper the more pressure  The pressure is the weight of column of water above the diver 

PRESSURE Atmospheric pressure – layer of gas around the earth about 20km thickness  Agreed unit of pressure is Pascal (Pa) or bar  0 meter, 1bar=1atm 

MANIFOLD GAUGE 

A device for measuring:

– pressure – temperature

GAUGE Pressure  Temperature  Refrigerant 

0 b = 1atm  absolute pressure = gauge pressure + atmospheric pressure 

QUIZ 

If atmospheric pressure is 1 b, why is the gauge show 0 at rest?



relative pressure or gauge pressure

THE PRESSURE-TEMPERATURE RELATIONSHIP 

In a balloon there is two pressure:

– Internal pressure – External pressure or atmospheric pressure

Pressure-Temperature At atmospheric pressure the internal and external pressure is equivalent  Pressure uniformly distributed 

Pressure-Temperature Increase the internal pressure and the water start to boil  At 1 b pressure, the temperature is 100 °C 

Pressure-Temperature External pressure smaller – 0.7 b  The internal pressure need less pressure to overcome external pressure  At 0.7 b external, water boil at 90°C 

CONCLUSION

CONCLUSION  Every

time the pressure changes, the temperature also changes  At every pressure, there is a corresponding boiling point  This

is call pressure-temperature relationship

CONVERSIONS

CONVERSIONS

HEAT A

SENSATION OF TEMPERATURE DIFFERENTS  BRAIN IS MAKING COMPARISON BETWEEN THE LEVEL OF HEAT  The

palm of our hand is between 30°C~33°C

UNIT OF HEAT  Calorie

(cal) -1g water, 1°C = 1 cal  Joule (J) - 1g water, 1°C = 4.187J  British thermal unit (Btu) - 1lb, 1°F = 1Btu

CONVERSIONS

HEAT TRANSFER 

Water and air “touch” indirectly



Heat passes from hotter to colder

HEAT TRANSFER 

The amount of heat gained by the air is exactly equal to that lost by the water

HEAT TRANSFER 





Only if there is temperature difference Heat always flows from the hotter body to the colder body In financial industry, the rich didn’t always give to the poor

BOILING OF WATER 

Water boil at 100°C



If we keep boiling, temperature of water will stabilizes

BOILING OF WATER CHANGE OF STATE  Liquid state to gaseous state (steam)  The water vaporizes 

The temperature does not increase further…

BOILING OF WATER 

Temperature increase from t0 – t2

BOILING OF WATER 

At t2-t3, the temperature is 100°C



Changing from liquid to vapor



When liquid evaporates, it absorb heat- latent heat of vaporization

0°C 0°C, Ice melting  Temperature constant - fusion 

0°C 0°C, Ice melting  t0-t1 – solid state to liquid state 

0°C No more ice  Temperature start to increase 

0°C - 100°C Temperature t2 =100 °C  Latent heat of fusion –solid to liquid 

CONCLUSION  Water

changes from solid to liquid at constant temperature 0°C by absorbing heat – LATENT HEAT OF FUSION  Water changes from liquid to vapor at constant temperature 100°C by absorbing heat – LATENT HEAT OF VAPORISATION

CONCLUSION  To

evaporate, water needs energy (heat)

AMOUNT OF HEAT

AMOUNT OF HEAT 2

and 4 - latent heat  1,3 and 5 - sensible heat

REFRIGERANTS

REFRIGERANT A

heat carrier  Working fluid to vaporizes and condenses as it absorb/gives off heat  Types of refrigerant - primary - secondary

PRIMARY REFRIGERANT Refrigerant used in vapor compression systems  Halocarbon - contain chlorine, fluorine and bromine 

PRIMARY REFRIGERANT 

Inorganic compound - an early refrigerants

PRIMARY REFRIGERANT 

Hydrocarbon - suitable for petroleum and petrochemical industry

REFRIGERANT 22 FREON 22  FORANE 22  SUVA 22  Monochlorodifluoromethane CHCLF2 



Whatever the names is, R22 evaporates at -42°C at atmospheric pressure

REFRIGERANT 22  CHCLF2

– 2 atoms of fluorine - 1 atoms of hydrogen + 1

CCL2F2 - 2 atoms of fluorine - 0 atoms of hydrogen + 1 - R 12

REFRIGERANT 22

REFRIGERANT 22

QUIZ 

Why do you think the R22 gauge reads -42°C at 0 bar?



At atmospherics pressure R22 evaporates at -42°C

DANGER!

REFRIGERANTS 

Selection - inexpensive - nonpoisonous - non corrosive - non flammable - stable - high latent heat of vaporization - easy to condense and vaporize - easy to detect leaks

SELECTIONS

REPLACEMENT ODP  GWP  Compositions 

REPLACEMENT

SECONDARY REFRIGERANTS  Fluid

that carry heat from a substance being cooled to the evaporator  Change in temperature but does not change phase  Water  Brines  Anti freezes – solution of water and glycol or calcium chloride

REFRIGERATING MACHINE & CYCLE

HEAT TRANSFER

REFRIGERATION CYCLE  1.

Evaporator  2. Compressor  3. Condenser  4. Expansion device

Evaporator Evaporate the refrigerant in the tube  Changes from liquid to vapor  Absorbed heat from the surrounding  Cooling 

Evaporator 1. evaporator inlet  2. evaporator outlet  3. tube  4. fin 



An evaporator must be exposed to the space to absorbed heat

Compressor 

To compress the refrigerant



Increase pressure and temperature



Lp - cold



Hp - hot

Condenser 

The condenser is hotter than the ambient temperature



Hotter temperature always give up heat

Condenser 

1. condenser inlet



2. condenser outlet



3. tube



4. fin



Vapor to liquid

Expansion device 

Connect condenser and evaporator



Drop the pressure from hp to lp thus dropping the temperature

Expansion device 

Capillary tube



Thin copper tube



Interior diameter and length is fixed

REFRIGERATION CYCLE refrigerator

REFRIGERATION CYCLE refrigerator

REFRIGERATION CYCLE refrigerator

REFRIGERATION CYCLE refrigerator

REFRIGERATION CYCLE operation

R22 enter evaporator as liquid  Room heat will “evaporates” the R22 



Room will become colder

REFRIGERATION CYCLE operation



R22 is vaporize by the interior room heat



R22 vapor then “suct” by the compressor

REFRIGERATION CYCLE operation

R22 enter condenser as hp vapor  Hot R22 gives up heat to the ambient – “condensation” 

REFRIGERATION CYCLE operation



At condenser outlet vapor had turn to liquid



Hp liquid will enter the expansion valve

WINDOW UNIT

WINDOW UNIT

WINDOW UNIT

SPLIT UNIT

SPLIT UNIT - internal

SPLIT UNIT - external

SPLIT UNIT

OPERATING CONDITION - hp 

High pressure 16.3b



High temperature 45°C

OPERATING CONDITION - lp 

Low pressure 4.8b



Low temperature 5°C

NORMAL OPERATING CONDITION

REFRIGERATION COMPONENTS & ACCESSORIES

the role of COMPRESSOR 

A temperature of a trapped compress air in a bicycle pump will increase



Compression of a gas causes an increase in pressure and temperature

COMPRESSOR 1. intake – lp  2. outlet – hp  3. lp valve  4. hp valve  5. piston  6. cylinder  7. connecting rod  8. eccentric crank 

COMPRESSOR A. bdc  B. piston move up to compress 

COMPRESSOR 9. valve plate  Pressure stable 

COMPRESSOR pressure at 6 is greater than hp  Compression 

COMPRESSION



The valves are controlled by the refrigerant itself

COMPRESSION B-C. piston rises  when the pressure in the cylinder is greater than hp, the valve open 

COMPRESSION D. tdc  The pressure at hp is equal to the cylinder  Valve close 



Note: clearance space is the gap between tdc and the piston head so that the piston will not knock the valve

COMPRESSION

The piston move up and down  The compression continues lp to hp 

COMPRESSOR - rotary 

Advantages - compact and light - less vibration and noise - low power consumption

- high durability  Disadvantages - advanced processing technology is required - an accumulator required

COMPRESSOR - scroll 

Advantages - little fluctuation of torque - low vibration and noise - less gas leak and high efficiency - no suction and discharge, high durability



Disadvantages - advanced processing technology is required; accuracy of few micron units - more components than rotary

COMPRESSOR - reciprocating 

Advantages - no accumulator is required - vibration are not transmitted outside - rotation of both side possible



Disadvantages - heavy weight - large volume

ROTARY

SCROLL

RECIPROCATING

SCREW 

Male and female gears



Three step; - suction - compress - discharge

CENTRIFUGAL Impeller and volute  High speed ±10000rpm  Centrifugal force change the gaseous refrigerant into speed energy, then converted to pressure energy for compression 

HEAT EXCHANGER

HEAT EXCHANGER – slit fins High heat radiation efficiency  Compact and light  Low resistance to airflow, reduce noise 

HEAT EXCHANGER – corrugated fins Simple structure  Low cost 

HEAT EXCHANGER – spine fins High reliability against gas leak with less brazing sections  Condenser can be design freely 

TUBE - hairpin 

Smooth pipe



Spiral pipe

METERING DEVICES Hand expansion valve  Automatic expansion valve  Thermostatic expansion valve  Capillary tube  High pressure float  Low pressure float 

Expansion device – capillary tube 

1 and 2 same length



2 is smaller



1 and 3 same diameter



3 is longer

Expansion device – capillary tube 

Pressure at 1 is low



Pressure at 2 is greater





The flow depend on – dimension and length Pressure different between hp and lp

Expansion device – capillary tube

Expansion device – capillary tube

Expansion device – capillary tube 

Compression is increasing the pressure and temperature



Expansion is decreasing the pressure and temperature

REFRIGERANT PIPE Discharge line - normally the same size of liquid line - any increase of pressure drop will be a penalty to the compressor  Liquid line - carry liquid - smaller size  Suction line - bigger size - carry vapor to compressor 

LIQUID RECEIVER  





Between condenser and expansion valve Act as a liquid supply to the expansion valve and storage Quiz; Do not use lr in capillary systems. Why? During off cycle, liquid will travel to evaporator through cap tube – when start up, liquid compression

FILTER DRYER 

Remove moisture and particles of foreign object

Quiz; Why moisture?  Cap tube stopped up by ice  Hydrochloric acid will corrodes metal  Copper plating 

ACCUMULATOR Prevent liquid from entering the compressor  The refrigerant oil will return through small hole at the bottom of the suction pipe 

MUFFLER At discharge line  To break up pressure pulses that create noise 

SOLENOID VALVE 

Use to open or close by energizing on and off

CHECK VALVE 

Allow refrigerant to flow in one direction only

HIGH PRESSURE SWITCH  

 

Install at discharge pipe Stop when there is abnormal high pressure Bellow Diaphragm

LOW PRESSURE SWITCH Install at suction pipe  Stop when there is abnormal low pressure 