Comparative Study on Performance Analysis of Vapour Absorption Refrigeration System Usingvarious Refrigerants

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1 Comparative Study on Performance Analysis of Vapour Absorption Refrigeration System Usingvarious Refrigerants Subhash Kumar 1, Dr.R.R Arakerimath 2 1 ME Student, GHRCEM,Wagholi, Pune,Maharastra,India 2 Professor and HOD (Mech),GHRCEM, Wagholi,Pune,Maharastra,India ABSTRACT This paper focuses on the construction of a two fluid gas absorption refrigeration unit, intended to operate in an atmospheric environment. Vapour absorption systems, unlike vapour-compression systems, use a heat source to facilitate refrigeration. Two fluid gas absorption refrigerators use electric based heater installed generator and no moving parts, such as pumps and compressors, and operate at a single system pressure. Extensive analysis of the thermodynamics, heat transfer, and chemical properties of a two fluid gas absorption system was conducted to design and construct the structural model shown in this paper. In this paperwe havecompared the performance of VARS that are used for refrigeration temperatures are below atmospheric temperature. Since the most common vapour absorption refrigeration systems (VARS) workson NH3-H2O solution with H2O as the absorbent and NH3 as the refrigerant, research has been devoted for the betterment of the performance of NH3-H2O absorption refrigeration systems in recent years. In this paper the performances analysis of the NH3-H2O and possible alternative cycles as lithium bromide-water are compared in respect of the (COP) and different operating conditioning. The highest COP was found as a function of the absorber, generator, condenser, and evaporating temperature. Keywords:- Absorption refrigeration, coefficient of performance, NH3-H20, Libr-H20, VARS 1. INTRODUCTION Refrigeration has become an essential part of the way we live our life. Almost everyone has a household refrigerator, but not many know of the process required to produce the drop in temperature that we know as refrigeration. Nature works much like a heat engine, heat flows from high-temperature elements to low-temperature elements. As it does this, work is also done to its environment. Refrigeration is a process to keep a cool element or to reduce the temperature of one element below that of the other. The refrigeration process is, in essence then, a reverse heat engine, where heat is taken from a cold element to be transferred to a warmer element, generally by adding work to the system. In a heat engine, work was done by the system; so in order to do the reverse; work must be done to the system. This work input is traditionally mechanical work, but it can also be driven by magnetism, lasers, acoustics, and other means. Several different types of refrigeration systems which utilize different work input were considered for this work. They are: the vapour-compression system, and the absorption refrigeration system. In recent developments of thermal engineering, the Refrigeration technologies play an important role in today's industrial applications [7].But as far as COP of this refrigeration system is concerned; it is always a challenge to the researchers to significantly increase the COP for these systems. The most popular refrigeration and air conditioning systems at present are those based on the vapour absorption systems. These systems are popular because they are reliable, relatively inexpensive and their technology is well established. However, these systems require high-grade energy (mechanical or electrical) for their operation. Apart from this, the recent discovery that the conventional working fluids of vapour absorption systems are causing the ozone layer depletion and greenhouse effects has forced the scientific researchers to look for alternative systems for cooling applications. The natural alternative is of course the absorption system, which mainly uses heat energy for its operation. Moreover, the working fluids of these systems are environment-friendly [8]. A suitable working fluid is probably the single most important factor in any refrigeration system. The cycle efficiency and operation characteristics of an absorption refrigeration system depend on the properties of refrigerant, absorbent and their mixtures. The most important thermo-physical properties are: heat of vaporization of refrigerant, heat of solution, vapour pressure of refrigerant and absorbent, solubility of refrigerant in solvent, heat capacity of solution, viscosity of solution andsurface tension and thermal conductivity of the solution. Apart from this, the other selection criteria for the working fluids are their toxicity, chemical stability and corrosively. The ultimate objective of the strategy paper is the security of energy supply, encompassing environmental principles. The priority of the energy supply field lies in the reduction ofthe global atmosphere warming with emphasis on efficient energy use and on renewable energy sources (RES) [7]. Simultaneous heating and cooling are required in many industries such as dairy plant pharmaceuticals chemical etc. Volume 3, Issue 1, January 2015 Page 5

2 Absorption systems have been extensively paid attention in recent years due to the potential for CFC and HCFC replacements in refrigeration, heating and cooling applications [8]. Furthermore, thanks to the progressive reduction of both installation and maintenance cost and energy consumption, their employment may become more and more diffuse [9]. Most of industrial process uses lots of thermal energy by burning fossil fuel to produce steam or heat for the purpose. After the process, heat is rejected to the surrounding as a waste. This exhaust waste heat can be used as refrigeration by using a heat based refrigeration system, likeavapour absorption refrigeration cycle [10]. Despite a lower coefficient of performance (COP) as compared to the vapour compression cycle, absorption refrigeration systems are promising for using inexpensive waste energy from industrial processes, geothermal energy, solar energy etc. Thermodynamic properties of presented working fluids can be obtained from publications [7-11]. Evaluation of potential working fluid for the absorption cycle is a problem because of a lack of published thermodynamic data. The ideal absorbent-refrigerant pair does not exist, all possible combinations present advantages and disadvantages [11]. Many working fluids aresuggested in literature but for the refrigeration temperatures below 0 C the most common workingfluid is NH3-H2O. NH3-H2O system exhibits a generally low COP; that s why efforts are being madeto search for best refrigerant-absorbent pairs thatcan improve system performance.libr-h2o refrigerant-absorbent mixture can be used as second VARS system. 1.1 Objectives of the Study The objectives of the study on the subject Comparative study on Performance Analysis of Vapour Absorption Refrigeration System by Using Two Refrigerants is as follows 1. Identify the Refrigeration system with respect to VCRS. 2. Compare the key characteristics of traditional VCRS and VARS. 3. Differentiate between NH3-H2O and Libr-H2O VARS. 4. Finding the best result in the form of COP for the both the system. Figure: 1-Vapor-compression system diagram Figure: 2-Diagram with state points of a basic three fluid vapour absorption system Volume 3, Issue 1, January 2015 Page 6

3. REFRIGERANT-ABSORBENT COMBINATIONS FOR VAPOUR ABSORPTION REFRIGERATION SYSTEM (VARS) VARS are commercially available today basically in two configurations.

3 3. REFRIGERANT-ABSORBENT COMBINATIONS FOR VAPOUR ABSORPTION REFRIGERATION SYSTEM (VARS) VARS are commercially available today basically in two configurations. For applications above 50ºC (primarily airconditioning) the cycle uses LiBr/H2O. For applications below 50ºC, ammonia/water cycle, is employed withnh3 as the refrigerant and H2O as the absorbent. 3.1 Desirable Properties of Refrigerant Absorbent Mixtures: Refrigerant-absorbent mixtures for VARS should possess some desirable properties of the refrigerant should be more volatile than the absorbent, in other words the boiling point of refrigerant should be much lower than the absorbent.), so that the solution in the Generator need only to be heated to thetemperature required boiling off only the refrigerant. Thisensures that only refrigerant (pure) circulates through refrigerantcircuit (evaporator-condenser-expansion valve). The refrigerant should exhibit high solubility with solution in the absorber. The absorbent should have a strong affinity for the refrigerant. This will minimize the amount of refrigerant to be circulated. Operating pressures should be preferably low so that the walls of the shells and connecting pipes need not to be thick. It shouldnot undergo crystallization or solidification of the system. Because crystallization will block the free flow of solution in the line. The mixture should be safe, chemically stable, noncorrosive, and inexpensive and should be available easily. The refrigerant should have high heat of vaporization [12], [13]. 3.3 Refrigerant-Absorbent Pairs The two most common usedabsorbent-refrigerant pairs in commercial systems are [6]: 3.3 Water-Lithium Bromide (H2O-LiBr) System-for moderate temperatures (50ºC and above) applications specifically air conditioning. Here H2O is the refrigerant and LiBris the absorbent. 3.4 Ammonia-Water (NH3-H2O) System-for low temperature(less than 50 C) refrigeration applications with NH3 as refrigerant and H2O as absorbent. The Lithium Bromide-Water pair satisfies majority of the above-listed properties. For these reasons Li-Br and Water systems are becoming more popular. Comparison of Lithium Bromide- Water systems and Ammonia-Water Systems 3.5 Ammonia-Water Systems Since the invention of absorption refrigeration system, NH3- H2O has been widely used. Both ammonia (refrigerant) and water(absorbent) are highly stable for a wide range of operatingtemperature and pressure.nh3 has a high latent heat of vaporization and the freezing point is -77 C, which is necessary for efficient performance of the system, for that it may be used for low- temperature applications. But bothammonia and water are volatile, the cycle needs a rectifier to strip away water thatnormally evaporates with ammonia. Without a rectifier, the waterwould accumulate in the evaporator and offset the systemperformance. Otherdisadvantages of its high pressure, toxicity, and corrosive action of copper and its alloy. Ammonia/Air mixtures are barely inflammable but may be explosive in the case of high percentages of ammonia between 15.5 and 27 % by volume [14]. Figure: 3-Ammonia-Water based vapour absorption refrigeration system 3.6Lithium Bromide-Water Systems The use of LiBr-Water for VARSbegan around Two outstanding features of LiBr-Water are non-volatility absorbent of LiBr (no need of a rectifier) and extremely high heat of vaporization ofrefrigerant (water). However, using H2O as a refrigerant limits the low-temperature application to that above0 C. As H2O is the refrigerant, the system Volume 3, Issue 1, January 2015 Page 7

must be worked under vacuum conditions. At high concentrations, the solution is prone to crystallization. One way,to prevent this to happen toadd one or more extra salts e.g., ZnBr2, ZnCl2.

Hence the strong solution can be cooled in the heat exchanger to near absorber temperature without salt crystallization, thus improving the performance of the system. COP is high (0.

4 must be worked under vacuum conditions. At high concentrations, the solution is prone to crystallization. One way,to prevent this to happen toadd one or more extra salts e.g., ZnBr2, ZnCl2.The addition of the third component of the basic water-lithium bromide solution pushes the crystallization limit away from the normal operating zone. Hence the strong solution can be cooled in the heat exchanger to near absorber temperature without salt crystallization, thus improving the performance of the system. COP is high (0.7 to 0.9) as compared to (0.5 to 0.6) for Ammonia-Water systems [15]. Figure: 4-LiBr-H2O based vapour absorption refrigeration system (15) Figure: 5-Experimental setup VARS Volume 3, Issue 1, January 2015 Page 8

4.OBSERVATION TABLE AND RESULTS 4.1 Observation Table -01-NH3-H20 4.2 Result Table-01-NH3-H20 4.

5 4.OBSERVATION TABLE AND RESULTS 4.1 Observation Table -01-NH3-H Result Table-01-NH3-H Observation Table -02-LiBr-H Result Table-02-LiBr-H20 Volume 3, Issue 1, January 2015 Page 9

6 5. COOLING CAPACITY FOR CHARGE AIR COOLING The amount of cooling capacity required for charge air cooling is very much dependent on the temperature reduction of the charge air due to cooling incorporated in the system. Therefore, the energy transfer from the charge air is: ). The heat from the generator and evaporator which can be transferred to the water and the heat gain by water can be estimated from the following Qg= mcv T Where Qg is the generator heat (kw), is Water mass flow rate and Cp: specific heat at constant pressure. To find the coefficient performance of the absorption cycle From the second law of thermodynamics, Stotal= Ssystem+ Ssurrounding>_0 Where ΔS is the total change of entropy which is equal to the sum of change of entropy of the system, ΔSsysand total entropy change of the surroundings ΔS. Since the refrigeration system works in a closed cycle, thechange of entropy surr of the working fluid of the system undergoing the cycle is zero, i.e., ΔSsys=0. Thechange in entropy of the surroundings is given by: Substituting first law of thermodynamicsexpression in the above equation Neglecting solution pump work, Wp; the COP of VARS is given by: 6.COMPARATIVE GRAPHS OF NH3-H20 AND LIBR-H2O VARS Figure: 6-The effect of Generator temp on the COP Figure -7: The effect of Generator Heat on the COP Figure: 8-The effect of Evaporator Heat on the COP Figure: 9- The effect of Generator heat on the Evaporator Heat. Volume 3, Issue 1, January 2015 Page 10

7 Figure: 10- The effect of time variation on COP Figure: 11- The effect of Generator temp. on evaporator temp 7. CONCLUSION The performance of NH3-H2O, LiBr-H2O as working fluids for refrigeration temperature below atmospheric were presented in this paper. The preferable working fluid can be considered as a solution with the highest COP, lower required generator temperature and circulation ratio as low as possible. It is evident that COP strongly depends on working conditions such as generator, absorber, condenser and evaporating temperature. We observed, the range of C.O.P for the aqueous ammonia system is (0.1o - 0.8) when the generator temperature is up to 65 C and the range of LiBr-H2O system are ( ) when the generator temperature is up to 95 C.The range of minimum evaporator temperature is (10 C - 15 C). The range of NH3 and LIBR is (15% maximum). 8. SCOPE FOR FUTURE WORK This machine was designed to reduce the impact of emission mandating using HCFCs or CFCs as refrigerants to the atmosphere and to preserve perishable goods. However, the system is limited to only electrical power source. Hence, it is recommended that other sources of powering the machine (solar, waste heat, etc) should be encouraged for further studies to improve its operation and performance. It is also proposed that high aluminium pipe materials should be used as the condenser. This will increase the capacity of the generator thus speeding up the heating process of the system. REFERENCES [1] Technologies To Recover Exhaust Heat From Internal Combustion Engines R. Saidur A, M.Rezaei A, W.K.Muzammil A, M.H.Hassan A,S.Paria A, M.HasanuzzamanElsever. [2] Sreeshankar K. K, Vikas P L, Sooraj K(2013), Vapour Absorption Refrigeration System For Cold Storage & Power Generation in Automobiles Using Exhaust Gas. [3] Khaled S. 2011,Evaluation and Performance of water- Ammonia Auto Air Conditioner System Using Exhaust waste, Science-direct Energy Procedia 6 (2011) [4] S.LakshmiSowjanya 2013, Thermal Analysis of a Car Air Conditioning System Based on An Absorption Refrigeration Cycle Using Energy From Exhaust Gas Of An I.C Engine, Advanced Engineering And Applied Sciences: An International Journal ISSN [5] S.C.Pang,N,H.H.Masjuk,M.A.Kalam,M.A.Hazrat 2013, A Review on Renewable and sustainable energy reviews Liquid Absorption And Solid Absorption System For Household, Industrial And Automobile Applications: 28, [6] SohailBux, A.C. Tiwari 2014, Natural Refrigerants Based Automobile Air Conditioning System, International Journal of Emerging Science and Engineering (IJESE) ISSN: , Volume-2. [7] Poberžnik S.; Goricanec D.; Krope J.,Traditional vs. alternative energy house heating source, Proceedings of the 2 nd IASME / WSEAS International Conferenceon Energy & Environment (EE'07), Portoroz,n Slovenia, May 15-17, 2007 [8] Feng X.; Goswami D. Y., ThermodynamicProperties of ammonia-water mixtures forpower-cycle application, Energy, 24, 1999, pp [9] Mohideen S. T.; Renganarayanan S., Heat and mass transfer studies on 134 A-DMAC based falling film absorbers for absorption refrigeration system, Proceedings of the 4 th WSEAS Int. Conf. on HEAT TRANSFER,THERMAL ENGINEERING andenvironment, Elounda, Greece, August 21-23, 2006, pp [10] Romero R. J.;Guillen L.; Pilatowsky I., Monomethylamine-water vapour absorption refrigeration system, Applied Thermal Engineering, 25, 2005, pp Volume 3, Issue 1, January 2015 Page 11

8 [11] RotchanaPrapainop, K O Suen, " Effects Of Refrigerant Properties On Refrigerant Performance Comparison: A Review " International Journal Of Engineering Research AndApplications (Ijera) Vol. 2, Issue 4, July-August 2012, Pp [12] G. Ali Mansoori and Vinod Patel, "Thermodynamic Basis for the Choice of Working Fluids for Solar Absorption Cooling Systems Solar Energy, Volume 22, Issue 6, 1979, Pp [13] José A. Manrique, "A Solar Air-Cooled Water-Ammonia Absorption Chiller" 61st Ati National Congress International Session Solar Heating andcooling Pp 1-5. [14] SoterisKalogirou, George Florides, SavvasTassou, Louis Wrobel" Design and Construction of A Lithium Bromide Water Absorption Refrigerator" Clima 2000/Napoli 2001 WorldCongress Napoli (I), September 2001 [15] Manu.S, T.K., T.B.Prasad,NagendraDept.ofMech.Engg., Sri Siddhartha Institute of Technology,Tumkur Theortical Model of Absorber for Miniature LiBr-H2o Vapor Absorption Refrigeration System International Journal of Modern Engineering Research (IJMER) Vol.2, Issue.2, Mar-Apr 2012 pp ISSN: AUTHOR'S PROFILE. Subhash Kumarwas born in Koderma Jharkhand, India in He received the B.E degree in Mechanical Engineering from NMU, Jalgaon, Maharastra, India in Currently, he is working towards his M.E (Mechanical Heat Power Engineering) thesis at GHRCEM, UOP,Pune,Maharastra, India.. His area of research includes Low grade energy sources, Refrigeration systems and Performance of VARS and exhaust waste heat recovery. He is LMISTE. Dr. R.R Arakerimath Author is HOD,Dean Academics and Professor in Department of Mechanical Engineering, GHRCEM,Pune,Maharastra, India. He has 20 years of teaching experience at various levels. He has published more than 30 papers in national and international journal. He is guiding PG/and PHD students under Pune and Nagpur university. He has membership of various organisations. Volume 3, Issue 1, January 2015 Page 12

Thermodynamic Analysis of Single-Effect Lithium Bromide Water Vapour Absorption Refrigeraion System

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