Transcript
IGN
OU Introduction to
Refrigeration and
Air-conditioning
Presentation by
Dr. Subhasis Maji
SCHOOL OF ENGINEERING AND TECHNOLOGYIndira Gandhi National Open University
Maidan Garhi, New Delhi – 110 068
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OU Application of
RefrigerationPreserving fresh food
To store medicines, vaccines, blood plasma
To store cut flowers to preserve.
Ice Plants use refrigeration machines.
Industries use refrigeration for producing frozen fruit juice, ice creams, chemicals.
Manufacturing industries use refrigeration.
Refrigeration is used for chilling oil to remove wax in oil refineries.
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OU Refrigerants
The common refrigerants available at reasonable costs are ammonia, carbon di-oxide and freon – 12. Freon – 12 condenses at moderate pressure and under normal atmospheric temperature conditions. This property makes the refrigerant suitable for most refrigeration application.
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OU Refrigerant
• Desirable properties:– High latent heat of vaporization - max cooling– Non-toxicity (no health hazard)– Desirable saturation temp (for operating pressure)– Chemical stability (non-flammable/non-explosive)– Ease of leak detection– Low cost– Readily available
• Commonly use FREON (R-12, R-114, etc.)
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OU Type of RefrigerationType of Refrigeration
Vapour Compression Refrigeration
Type of refrigerant
• Refrigerant determined by the required cooling temperature
• Chlorinated fluorocarbons (CFCs) or freons: R-11, R-12, R-21, R-22 and R-502
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OU Type of RefrigerationType of Refrigeration
Vapour Compression Refrigeration
Choice of compressor, design of condenser, evaporator determined by
• Refrigerant
• Required cooling
• Load
• Ease of maintenance
• Physical space requirements
• Availability of utilities (water, power)
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OU Type of RefrigerationType of Refrigeration
Vapour Absorption Refrigeration
Condenser Generator
Evaporator
AbsorberCold Side
Hot Side
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Air Conditioning
The process of conditioning the surrounding air according to the human comfort and desire is called as Air-Conditioning.
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OU Application of Air Conditioning
Restaurants, Hotels, Home, Hospitals, Airplanes, Offices etc.Air conditioning helps control moisture in printing press.In business and industry, air conditioning improves efficiency.Manufacturing of Tools and Instruments.Textile Mills.Pharmaceutical, Chemical Plants and Food industries.
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Working of a Air Conditioning system
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OU Advantages of the Window Air Conditioner
A separate temperature control is provided in each room in which the unit is installed.
Ducts are not required for air distribution.
Disadvantages of the window Air conditioner
The unit has a fixed air quantity.The installation must be made only on the outside wall.
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OU IntroductionIntroduction
How does it work?
High Temperature Reservoir
Low Temperature Reservoir
R Work Input
Heat Absorbed
Heat Rejected
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OU IntroductionIntroduction
AC options / combinations:
AC Systems
• Air Conditioning (for comfort / machine)
• Split air conditioners
• Fan coil units in a larger system
• Air handling units in a larger system
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OU IntroductionIntroduction
• Small capacity modular units of direct expansion type (50 Tons of Refrigeration)
• Centralized chilled water plants with chilled water as a secondary coolant (50 – 250 TR)
• Brine plants with brines as lower temperature, secondary coolant (>250 TR)
Refrigeration systems for industrial processes
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OU Types of RefrigerationTypes of Refrigeration
• Vapour Compression Refrigeration (VCR): uses mechanical energy
• Vapour Absorption Refrigeration (VAR): uses thermal energy
Refrigeration systems
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OU Type of RefrigerationType of Refrigeration
Vapour Compression Refrigeration
Two advantages
• Lot of heat can be removed (lot of thermal energy to change liquid to vapour)
• Heat transfer rate remains high (temperature of working fluid much lower than what is being cooled)
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It is the rate at which heat can be extracted from cold body, (i.e.) the rate at which refrigeration can be produced. It is defined as the Quantity of Heat removed ( refrigerating effect) to freeze one ton of water at 00C to ice at 00C in 24 hours.
One ton of refrigeration = 12,600 kJ /hr. = 210 kJ / min. = 3.5 kJ / sec.
Capacity of refrigerator
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OU Coefficient of
PerformanceCOP of a refrigeration system is defined as the ratio of heat extracted in a given time (refrigerating effect) to the work input to the system.
doneWork
extractedHeatCOP
workCompressor
effectingRefrigeratCOP
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RefrigeratorQ
1!
S
Evaporator
Exp. Device
Condenser
Compressor WC
Q2
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OU Type of Type of RefrigerationRefrigeration
Vapour Compression Refrigeration
Refrigeration cycle
Condenser
Evaporator
High Pressure
Side
Low Pressure
Side
CompressorExpansion Device
1 2
3
4
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OU Generic Refrigeration Cycle
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OU Thermodynamic Cycle
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TypicalRefrigeration
Cycle
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OU Components
• Refrigerant
• Evaporator/Chiller
• Compressor
• Condenser
• Receiver
• Thermostatic expansion valve (TXV)
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OU 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 Vaporization– Sensible Heat of surroundings
• Slightly superheated (10°F) - ensures no liquid carryover into compressor
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• Superheated Vapor:– Enters as low press, low temp vapor– Exits as high press, high temp vapor
• Temp: creates differential (T) promotes heat transfer
• Press: Tsat allows for condensation at warmer temps
• Increase in energy provides the driving force to circulate refrigerant through the system
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OU Condenser
• Refrigerant rejects latent heat to cooling medium
• Latent heat of condensation (LHC)
• Indirect heat exchanger: seawater absorbs the heat and discharges it overboard
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OU 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 reduction– Amount of refrigerant entering evaporator
controls capacity
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OU 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
• Heaters in ventilation system
• Types Used:• Self-contained
• Refrigerant circulating
• Chill water circulating
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OU WQ
CWQQ 21
CW
Q2fRe)COP(
Or
Coefficient of Performance
Calculations
CWQQ 21
)()COP(
21
2fRe QQ
Q
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OU Heat Pump
21
11hp)COP(
Q
W
Q
C
fhp COPCOP Re)(1)(
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41 hhQ2 12W hh 43 hh
12
41
h
h)(
h
hCOP
4132
41
hhhh
hh
PH
PL
TH
TL
T
1
23
4
s
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TH
TL
PH
PL
P
1
23
4
h
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OU Refrigerating Effect
kj/kghheffectRef. 41
Capacity of the VCRS
kWhhCapacity 41
.
m
Compressor Power
kWhhPower 12
.
m
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OU Heat Engine
Direct Heat Engine
t!
E W
t2
t! > t2
Q!
Q2
t!
E
W
t2
Q!
Q2
Reversed Heat Engine
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OU Exercise
A reversible heat engine is operating between –130C and 370C. Find its COP as (a) heat pump and (b) refrigerator.
T2
T1
Q2
Q1
12
1
12
11fRe)COP(
TT
T
Q
W
Q
W
E
2.550
260)COP( fRe
2.612.5)COP( .p.h
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OU Exercise
An ideal wet compression refrigeration cycle, with R– 12 as the refrigerant, operates between an evaporator temperature of –100C and a condenser temperature of 400C. Calculate the following: Refrigerating effect, Compressor work, and COP.
kg/kJ05.203h2
kg/kJ53.74hh 34
kg/kJ53.74h3
kg/kJ9.177h1
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OU Refrigerating Effect
kg/kJ37.103heffect.fRe 4 1h
Compressor Work
kg/kJ15.25hwork.Comp 12 h
Coefficient of Performance
11.415.25
37.103
work.comp
effect.refCOP
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OU Vapour absorption refrigerators
COP
EO
E
G
OG
G
E
TT
T
T
TT
Q
Q
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OU Exercise
What is the maximum COP of an absorption refrigeration system, if it has to maintain an evaporator at –30C, while having heat transfer from a high temperature reservoir at 127oC at a place where the ambient temperature is 270C?.
K400TG K300TK,270T oE
EO
E
G
OG
TT
T
T
TTCOP
25.2270300
270
400
300400COP
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Dr. Subhasis MajiProfessor in Mechanical EngineeringSchool of Engineering & TechnologyIGNOU, Maidan Garhi, New Delhi – 110 068
E-mail : subhmaji@hotmail.com subhasis@ignou.ac.in
Telephone/Fax : 91-11-2953 4808
Contact us
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OU
Thank You !
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