ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Vapor Absorption Refrigeration Systems Sameer Khandekar Sir M. Visvesvaraya Chair Professor Department of Mechanical Engineering Indian Institute of Technology Kanpur Kanpur (UP) 208016 INDIA Sameer Khandekar Sameer Webpage: home.iitk.ac.in/~samkhan/ ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India In this lecture… ◉ What is an absorption system ◉ Construction ◉ Operation ◉ Comparison with vapor compression system Sameer Khandekar Sameer Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 1 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Vapor absorption refrigeration system ◉ An absorption refrigerator is a refrigerator that uses a heat source (e.g., solar energy, a fossil-fuel flame, waste heat from factories, or district heating systems) to provide the energy needed for the cooling process. ◉ In this system mechanical compression process of vapor compression cycle is replaced by a thermal compression process. ◉ The thermal compression is achieved by the following process: ○ Absorbing a fluid vapor (e.g., say: ammonia) into another carrier liquid (e.g., say water). ○ Pumping this solution to a high pressure cycle by a simple pump ○ Producing vapors from the solution by heating (thus, cooling) Sameer Khandekar Sameer ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Features ◉ ARS are often classified as heat-driven systems. They are used especially, when there is a source of inexpensive thermal energy at a temperature of 100 to 200°C. ◉ The principle can be used to air-condition buildings using available waste heat from a source. ARS are primarily used in large commercial, industrial installations or for storage in recreational vehicles. ◉ Some examples include geothermal energy, solar energy, and waste heat from cogeneration or process steam plants, and even natural gas when it is at a relatively low price. ◉ For example, using waste heat from a gas turbine makes it very efficient because it first produces electricity, then hot water, and finally, air- Sameer Khandekar Sameer conditioning (called cogeneration/trigeneration). Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 2 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Vapor absorption refrigeration cycle Thermal Compression Condenser Heating Water return via rectifier Liquid pump Heat of absorption Sameer Khandekar Sameer ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Another layout to represent the ARS Sameer Khandekar Sameer Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 3 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Requirements of the system ◉ Solubility requirement: The refrigerant should have very high solubility in the absorbent material (usually much higher than the Roult’s law applicability limits), so that a strong solution is possible. ◉ Boiling point requirement: There should be a large difference in the normal boiling point of the two substances, of the order of 150 C to 200 C. Higher the better. The absorbent should have negligible vapor pressure at the generator temperature. Thus almost absorbent free refrigerant is boiled off from the generator and the absorbent alone returns to the absorber. Sameer Khandekar Sameer ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Ammonia Absorption Refrigeration system Thermal Compression ◉ ARS involves the absorption of a refrigerant by a transport medium. ◉ Most widely used system is NH3 – H2O system, where NH3 serves as refrigerant and H2O as transport medium. ◉ Other systems include water–lithium bromide and water–lithium chloride systems, where water serves as the refrigerant. These systems are limited to applications such as A-C where the minimum temperature is above the Ammonia absorption refrigeration cycle. freezing point of water. Sameer Khandekar Sameer Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 4 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Advantages of ammonia systems ◉ Ideally fits into the concept of Integrated Energy Systems such as Cogeneration involving combined generation, heat, refrigeration and power (CHRP Plants) on various fuels like bio-mas, coal, Natural Gas, Heavy Oil, Solar, geothermal, etc. ◉ Excellent for waste heat utilization ◉ Earns carbon credits, reduces taxes, promotes sustainable development. ◉ Uses best eco-friendly refrigerant – ammonia ◉ Wide operational range + 5 C to – 55 C ◉ Low maintenance cost – no moving parts ◉ Can operate well for over 25 years Sameer Khandekar Sameer ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Equivalent thermodynamic model Sameer Khandekar Sameer Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 5 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Determination of COP of ARS ◉ The COP of actual absorption refrigeration systems is usually less than 1. ◉ Air-conditioning systems based on absorption refrigeration, called absorption chillers, perform best when the heat source can supply heat at a high temperature with little temperature drop. Sameer Khandekar Sameer ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Discussion on COP ◉ The COP depends on the main three operating temperatures: ○ Temperature of the heat source (High temperature) ○ Temperature of Condenser/ Absorber (They can be different) ○ Temperature of the refrigeration space (Low temperature) ◉ Hot source should be as high as possible ◉ Condenser/Absorber should be low ◉ Refrigeration temperature should be high. If Condenser and Absorber temperatures are different, then maximum COP is given by 푇 − 푇 푇 푂푃 = 푇 푇 − 푇 Sameer Khandekar Sameer Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 6 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Device Construction ◉ Like a standard vapor compression system, a vapor absorption system also consists of a condenser, an expansion valve and an evaporator. ◉ These three devices have exactly the same function as in the vapor compression system ◉ Instead of a mechanical compressor, the vapor absorption system achieves the compression by the application of heat – thermal compression. ◉ Hence, to achieve this it has a refrigerant absorber, a liquid pump, a heat exchanger (thermal compression), an analyzer and a rectifier (for separating the solvent from the refrigerant). Sameer Khandekar Sameer ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Operational steps ◉ Dry ammonia vapor at low pressure passes in to the absorber from the evaporator. ◉ In the absorber the dry ammonia vapor is dissolved in cold water and strong solution of ammonia is formed. ◉ Heat evolved (heat of absorption) during the absorption of ammonia in water is removed by circulating cold water