Introduction to RACIntroduction to RAC

1. Introduction to Refrigeration & Air Conditioning
Dr. A.D. Badgujar
Associate Professor-Mechanical Engineering
School of Engineering & Technology
Navrachana University
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Refrigeration & Air Conditioning

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Refrigeration & Air Conditioning
Course Outline
Sr. No. Topics
1 Introduction and Applications
2 Methods of Producing Low Temperature
3 Air Cycle Refrigeration System
4 Vapor compression Refrigeration system
5 Vapor Absorption Refrigeration System
6 Refrigerant
7 Psychrometric Properties
8 Psychrometric Processes

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Refrigeration & Air Conditioning
Course Outline
Sr. No. Topics
9 Air conditioning system
10 Cooling load calculations
11 Introduction to I.C. Engines

4. Text Books:
• Stoecker, W., Refrigeration & Airconditioning, Tata Mc Graw Hill.
• Dossat, R.J., Principles of refrigeration, John Wiley & Sons.
• Arora, C.P., Refrigeration & Airconditioning, Tata Mc Graw Hill.
• R.S. Khurmi, Refrigeration & Airconditioning.
Reference Books:
• Threlkeld, J.L., Thermal Environmental Engineering, Prentice Hall.
• Ananthanarayanan, P.N, Basic refrigeration & Airconditioning, Tat
Mc Graw Hill, 2005
Refrigeration & Air Conditioning

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Refrigeration & Air Conditioning
• Refrigeration may be defined as the process of achieving
and maintaining a temperature below that of the
surroundings, the aim is to cool some product or space to
the required temperature.
• To achieve the same we need a system (Sink) at very low
temperature.
What is Refrigeration?
System - A
(Room – at 20 C)
System - B
(Sink – A/c – at -5 C)
Surrounding – 35/40 C

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Refrigeration & Air Conditioning
Applications
• One of the most important applications of refrigeration has been the
preservation of perishable food products by storing them at low
temperatures. Low temperature reduces the growth of Micro-
organism.

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Refrigeration & Air Conditioning
Applications
• Refrigeration systems are also used extensively for
providing thermal comfort to human beings by means of air
conditioning.

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Refrigeration & Air Conditioning
Applications
• Special Applications
cold treatment of metals : Heat treatment
Medical : O.T, medicine, Injections, organs
Cooling of concrete
Ice-skating
• Industrial applications
chemical processing : separation of gases, removal of heat of
reaction, condensation of gases, dehumidification of air
Manufacturing of Yarns (Textiles)
Electronics Industry, computers
Automobile

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Refrigeration & Air Conditioning
How to Achieve low Temperature
• Sensible Cooling
• Use of Phase change Processes
Phase change associated with large amount of Heat Transfer
which can be utilized for cooling of a system
High Temperature
System - A
e.g. Room
Low temperature
System - B
e.g. AC
Q = mcp(TA – TB)
0 DEG
ICE
0 DEG
WATER
100 DEG
STEAM
SYSTEM TO BE COOLED
335 2257
100 DEG
WATER
Q = m(HV – HL)

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Refrigeration & Air Conditioning
How to Achieve low Temperature
• Expansion of Liquids or Expansion of Gases
• The expansion may be Isentropic or Isenthalpic
• Isentropic expansion  Turbine  work is produced  result in
low temperature
• Isenthalpic expansion may or may not result in production low
temperature, it depends on inversion temperature of fluid being
expanded.

11. Joule – Tompson Effect
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• Mathematically,
JT
h
T
p

 

  

 
Effect
>0 Cooling
<0 Heating
=0 No effect
JT

Pressure
A
B
D
2 1
C

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Refrigeration & Air Conditioning
History of Refrigeration
• Natural Refrigeration
Nocturnal cooling
Evaporative cooling
Cooling by Salt Solutions
• Artificial Refrigeration
Vapor Compression Refrigeration System
Vapor Absorption Refrigeration System
Gas Cycle Refrigeration system
Steam Jet Refrigeration system
Thermo-electric refrigeration
Vortex tube refrigeration system
Magnetic Refrigeration

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• Nocturnal cooling
• In this method ice is made by keeping a thin layer of water in a
shallow earthen tray and then exposing the tray to the night sky.
• Insulation of about 0.3 m thickness is used.
• Water looses heat by radiation to stratosphere which is at
around -55 degC, in early morning hrs the water gets freezes.
• This was very popular in India in ancient times.

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Refrigeration & Air Conditioning
• Evaporative cooling
• Cooling of earthen pots : useful in Dry weathers, in desserts

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Refrigeration & Air Conditioning
• Cooling by Salt solutions
• Certain salts when added to water, absorbs the heat of
solution (endothermic process). This reduces temperature of
solution
• Nacl  - 20 C, Cacl2  - 37 C
• Recovery of the salt is very difficult, one time use and slow
process

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Refrigeration & Air Conditioning
Artificial Refrigeration
• Artificial Refrigeration
VCRS : Phase change process, Mech. Comp., mW to MW
VARS : Heat Energy used, mW-W
Gas Cycle Refrigeration system: sensible cooling
Steam Jet Refrigeration system : Obsolete, W-kW
Thermo-electric refrigeration : Based on Peltier Effect, mW
Vortex tube refrigeration system : Mines cooling
Magnetic Refrigeration : mW, to reach in mK range

17. Stem Jet Refrigeration System

19. Thermo-electric refrigeration
In 1834, Peltier found that an electrical current would produce
a temperature gradient at the junction of two dissimilar metals.
Temp diff of 70 C
No moving parts
No CFCs, Life – 1 Lakh hrs
Poor efficiency – 10 to 15 % of carnot efficiency
Also called a Peltier device, Peltier heat pump, solid state refrigerator,
or thermoelectric cooler (TEC)

20. • The thermoelectric semiconductor material most often used in today's TE coolers is
an alloy of Bismuth Telluride (Bi2Te3) that has been suitably doped to provide
individual blocks or elements having distinct N and P characteristics. Other
thermoelectric materials include Lead Telluride (PbTe), Silicon Germanium (SiGe),
and Bismuth-Antimony (Bi-Sb) alloys, which may be used in specific situations;
however, Bismuth Telluride is the best material in most computer cooling scenarios.
• If the polarity changed the hot side becomes cold and the cold side becomes hot.
• There are many products using thermoelectric coolers, including CCD cameras
(charge coupled device), laser diodes, microprocessors, blood analyzers and
portable and picnic coolers etc. TER is also a good option for food preservation
applications & cooling of pharmaceutical products.
Thermo-electric refrigeration

21. Vortex Tube Refrigeration
Application :
Mines cooling

22. Vortex Tube Refrigeration

23. Magnetic Refrigeration

24. Magnetic Refrigeration
Magnetic refrigeration was the first method developed for cooling below about 0.3K.
Initially magnetic field is applied adiabatically to the refrigerant material, as a result of that all the
moments will try to align along the field direction, therefore the energy of the system will
increase, as a result of that temperature of the system will increase . The extra heat can be
removed by placing the system in contact with any fluid or gas.
After removing the extra heat from the system , the system is demagnetized adiabatically ,
therefore all the moments will try to randomize themselves ,this randomization needs energy,
this energy is provided by the system, therefore the system cools after that the magnetic field is
held constant to prevent the material from reheating. Then the material is placed in thermal
contact with the environment to be refrigerated.
The material is a paramagnetic salt, such as cerium magnesium nitrate.

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Refrigeration & Air Conditioning
VCRS
VCRS : Vapor Compression Refrigeration Process
1
2
3
4

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Refrigeration & Air Conditioning
VARS
Working Principle :
Absorption capacity of fluids with great affinity
decreases with increase in temperature and
increases with decrease in temperature.

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Refrigeration & Air Conditioning
Gas Cycle Refrigeration System

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Thank You!
Refrigeration & Air Conditioning