ME– VII SEM Refrigeration & Air Conditioning Manav Rachna College of Engg.
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ME– VII SEM Refrigeration & Air Conditioning M a n a v R a c h n a C o l l e g e o f E n g g .
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DEFINITION Refrigeration may be defined as the process of removing heat from a body or enclosed space so that its temperature is first lowered and then maintained at a level below the temperature of surroundings. The system maintained at the lower temperature is known as refrigerated system while equipment used to maintain this lower temperature is known as refrigerating equipment. Work is required to transfer heat from lower temperature body to higher temperature body. Amount of heat removed by refrigerating equipment from refrigerated system is known as refrigerating effect. Manav Rachna College of Engg.
Transcript of ME– VII SEM Refrigeration & Air Conditioning Manav Rachna College of Engg.
ME– VII SEM
Refrigeration &
Air Conditioning
Manav Rachna College of Engg.
OBJECTIVES
To Learn Basic operation of refrigeration and AC systems. Principle components of refrigeration and AC systems. Thermodynamic principles of refrigeration cycle. Safety considerations.
Manav Rachna College of Engg.
Uses of SystemsUses of Systems
Cooling of food stores, buildings and cargo.Cooling of electronic spaces and equipment.
CIC, Radar, Sonar, Radio, Computers etc. Air conditioning for Aero plane, Space ships, Naval Ships, Train, Bus, Car etc.
DEFINITION Refrigeration may be defined as the process of
removing heat from a body or enclosed space so that its temperature is first lowered and then maintained at a level below the temperature of surroundings. The system maintained at the lower temperature is known as refrigerated system while equipment used to maintain this lower temperature is known as refrigerating equipment.
Work is required to transfer heat from lower temperature body to higher temperature body. Amount of heat removed by refrigerating equipment from refrigerated system is known as refrigerating effect.
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UNIT OF REFRIGERATION
The unit of refrigeration is ton of refrigeration or simply ton denoted by TR.
One ton of refrigeration means amount of heat required to remove from one ton of water at 00C to produce ice at 00C in 24 hours.
The latent heat of ice is 334.9 kJ/Kg and one tons water equals to 907.18 kg therefore 1 ton of refrigeration equals to,
1 TR = (334.9 x 907.18) / (24 x 3600) = 3.516 kW
COEFFICIENT OF PERFORMANCE (COP) The performance of refrigerators and heat pumps is expressed
in terms of coefficient of performance (COP), defined as
COP QW
COPQW
RL
net in
HPH
net in
Desired outputRequired input
Cooling effectWork input
Desired outputRequired input
Heating effectWork input
,
,
COPHP is larger than COPR . Under the same operating conditions, the COPs are related by
COP COPHP R 1
REFRIGERATION CYCLE
Refrigeration - Cooling of an object and maintenance of its temperature below that of surroundings.
Working substance must alternate b/t colder and hotter regions.
Most common: vapor compressionReverse of power cycleHeat absorbed in low temp region and released
in high temp region
GENERIC REFRIGERATION CYCLEM
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THERMODYNAMIC CYCLEM
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COMPONENTS
Refrigerant Evaporator/Chiller Compressor Condenser Receiver Thermostatic expansion valve
(TXV)
REFRIGERANT
Definition:- It is a heat carrying medium which during their
cycle compress, condense, expense and evaporate.
It absorb heat from a low temperature system and discard the heat to higher temperature system.
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HISTORY OF REFRIGERANTS
• 1830s - Jacob Perkins - Vapor Compression (ether) • 1851 - John Gorie - Patent for Vapor Compression Cycle • 1859 R-717 / R-718 (Ammonia / Water) • 1866 CO2 - Naval Applications • 1873 - R-717 (Ammonia) Commercial Refrigeration – Karl Linde • 1875 - R-764 (Sulfur dioxide) • 1920s -R-600a (Isobutane) & R-290 (Propane) • 1922 - Willis Carrier - R-1130 (Dielene) • 1926 - R-30 (Methylene Chloride)
PROPERTIES OF REFRIGERANTS
Desirable properties:High latent heat of vaporization – max. coolingNon-toxicity (No health hazard)Desirable saturation temp (For operating
pressure)Chemical stability (Non-flammable/non-
explosive)Ease of leak detectionLow costReadily available
Commonly use FREON (R-12, R-114, etc.)
EVAPORATOR/CHILLER
Located in space to be refrigerated Cooling coil acts as an indirect heat exchanger Absorbs heat from surroundings and vaporizes
Latent Heat of VaporizationSensible Heat of surroundings
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Slightly superheated (10°F) - Ensures no liquid carryover into compressor
COMPRESSOR
Superheated Vapor:Enters as low pressr., low tempr. Vapor.Exits as high pressr., high tempr. Vapor.
Tempr. creates differential (ΔT) promotes heat transfer. Increase in energy provides the driving force to
circulate refrigerant through the system
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CONDENSER
Refrigerant rejects latent heat to cooling medium. Latent heat of condensation (LHC). Condenser used may be air cooled or water cooled.
RECEIVERRECEIVER
Temporary storage space & surge volume for the sub-cooled refrigerant.Serves as a vapor seal to prevent vapor from entering the expansion valve.
EXPANSION DEVICE
Thermostatic Expansion Valve (TXV) Liquid Freon enters the expansion valve at high
pressure and leaves as a low pressure wet vapor. (vapor forms as refrigerant enters saturation region).
Controls:Pressure reductionAmount of refrigerant entering evaporator
controls capacity.
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AIR CONDITIONING
Purpose: Maintain the atmosphere of an enclosed space at a required temp, humidity and purity.
Refrigeration system is at heart of AC system.
Types Used: Self-contained Refrigerant circulating Chill water circulating
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AC SYSTEM TYPES
Self-Contained SystemAdd-on to ships that originally did not have AC
plantsNot located in ventilation system (window unit)
Refrigerant circulating systemHot air passed over refrigerant cooling coils
directly Chilled water circulating system
Refrigerant cools chill waterHot air passes over chill water cooling coils
Basic AC System
The vapor compression refrigeration cycle is a common method for transferring heat from a low temperature to a high temperature.
REVERSED CARNOT REFRIGERATOR AND HEAT PUMP
Shown below are the cyclic refrigeration device operating between two constant temperature reservoirs and the T-s diagram for the working fluid when the reversed Carnot cycle is used. Recall that in the Carnot cycle heat transfers take place at constant temperature. If our interest is the cooling load, the cycle is called the Carnot refrigerator. If our interest is the heat load, the cycle is called the Carnot heat pump.
CONT…
CONT…
The standard of comparison for refrigeration cycles is the reversed Carnot cycle. A refrigerator or heat pump that operates on the reversed Carnot cycle is called a Carnot refrigerator or a Carnot heat pump, and their COPs are
COPT T
TT T
COPT T
TT T
R CarnotH L
L
H L
HP CarnotL H
H
H L
,
,
/
/
11
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CLASSIFICATION OF REFRIGERANTS
This text is based on the American standard ANSI/ASHRAE 34 published in 2001 and entitled “Designation and Safety Classification of Refrigerants”.
This classification makes it possible to designate all refrigerants used in a clear and internationally recognized manner by classifying them according to their chemical composition.
Main types 1. Primary 2.Secondary
Primary: They are directly take part in refrigeration. 1.Helo Carbon Refrigerant 2. Azeotrope Refrigerant 3.Inorganic Refrigerant 4.Hydro carbon Refrigerant
Secondary:- They first cool primary refrigerant and
than used for cooling purpose. 1. Water 2. Brine 3. Inhibited Glycols
CLASSIFICATION OF REFRIGERANTS CONT..
NOMENCLATURE OF REFRIGERANTS
Refrigerants are denotes by ‘ R’ followed by certain number as R-11, R-12, R-114
1. For saturated Hydrocarbon:- Cm + Hn + Fp + Clq , n +p
+q=2m+2 m- No .of carbon atoms n- No .of hydrogen atoms p- No .of fluorine atoms q- No .of chlorine atoms
Nomenclature- R(m-1)(n+1)(p)
NOMENCLATURE OF REFRIGERANTS
1. For Unsaturated Compounds:-
n + p + q = 2m Nomenclature - R1(m-1)(n+1)(p)
Eco friendly Refrigerants 1.Hfcs 2. Hcfc-123 3. Hfc-134a
INTRODUCTION TO CRYOGENICS Cryogenics is the study of how to get to low
temperatures and of how materials behave when they get there. Besides the familiar temperature scales of Fahrenheit and Celsius (Centigrade), cryogenicists use other temperature scales, the Kelvin and Rankine temperature scales.
OR
Cryogenics may be defined as the branch of physics which deals with the production of very low temperature and their effect on matter. It may also be defined as the science and technology of temperatures below 1200 K. The word “cryo” is derived from a Greek word “kruos” which means cold.
ADVANTAGES OF CRYOGENIC PROCESSING
Advantages of Cryogenic Processing: The following properties are attained to the materials
treated:- Increases wear resistance, Increases corrosion resistance ,Good dimensionality ,high strength, Good quality Cost reduction in the material manufactured, lower stress corrosion etc. Cryogenic heat treatment helps to reduce the stored stress in the metal by creating a unified bond between the crystals.
CONT…
Cryogenics are also used to treat many types of sports equipment, the most common being golf clubs. Because cryogenics increases the molecular density of treated materials, it improves the distribution of energy (in this case kinetic energy) through the object. The treatment also increases the rigidity of the metal, which in this case might affect the shaft of the golf club. Combined, the increases in kinetic energy distribution and rigidity of the shaft make for a longer and straighter drive.
CONT…
Cryogenics can be applied to almost everywhere in every field. It finds its application in military, tooling industry, agricultural industry, aerospace, medical, recycling, household, automobile industry, cryogenics is found to improve the grain structure of everything treated be it metal or plastic or coils or engines or musical instruments or fiber. This field could be put to many other applications in various fields. Its reaches in the mentioned industries hold a good chance of extension. Hence Cryogenics proves to be very promising for the future in this world of materials.
END OF UNIT IST
