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1- Introduction to Introduction to RAC rac
- 1. Introduction to Refrigeration & Air Conditioning Dr. A.D. Badgujar Associate Professor-Mechanical Engineering School of Engineering & Technology Navrachana University 1 Refrigeration & Air Conditioning
- 2. 2 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
- 3. 3 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
- 5. 5 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
- 6. 6 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.
- 7. 7 Refrigeration & Air Conditioning Applications • Refrigeration systems are also used extensively for providing thermal comfort to human beings by means of air conditioning.
- 8. 8 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
- 9. 9 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)
- 10. 10 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 11 • Mathematically, JT h T p Effect >0 Cooling <0 Heating =0 No effect JT Pressure A B D 2 1 C
- 12. 12 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
- 13. 13 • 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.
- 14. 14 Refrigeration & Air Conditioning • Evaporative cooling • Cooling of earthen pots : useful in Dry weathers, in desserts
- 15. 15 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
- 16. 16 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
- 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.
- 25. 25 Refrigeration & Air Conditioning VCRS VCRS : Vapor Compression Refrigeration Process 1 2 3 4
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- 27. 27 Refrigeration & Air Conditioning VARS Working Principle : Absorption capacity of fluids with great affinity decreases with increase in temperature and increases with decrease in temperature.
- 28. 28 Refrigeration & Air Conditioning Gas Cycle Refrigeration System
- 29. 29 Thank You! Refrigeration & Air Conditioning