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