e-issn 2455 1392 Volume 2 Issue 5, May 2016 pp. 108-116 Scientific Journal Impact Factor : 3.468 http://www.ijcter.com Performance Analysis of Li-Br Water Refrigeration System with Double Coil Anti-Swirl Shell and Coil Heat Exchangers (Waste Heat Recovery Mechanism - An Experimentation and Improvement ) Patil Shrinivas V. 1, Shrishrimal Chaitanya S. 2, Sonawane Swapnil B. 3, Dr. S. S. Bhavikatti 4 1 Department of Mechanical Engineering, College of Engineering Pune, patilsv12.mech@coep.ac.in 2 Department of Mechanical Engineering, College of Engineering Pune, shrishrimalcs12.mechv12@coep.ac.in, 3 Department of Mechanical Engineering, College of Engineering Pune, sonawanesb12.mech@coep.ac.in 4 Department of Mechanical Engineering, College of Engineering Pune, bhavikatti.mech@coep.ac.in Abstract Many industries use heating operations at some point or another. At the end of these operations there is exhaust gas leaving the system at very high temperature (200 250 o C) as compared to ambient temperature. These gases can take as high as 30% to 35% of the total heat and hence plants having power in MW will lose enormous amount of energy if flue gases are released without recovering the heat content which they have. However, if this energy is recovered the efficiency of the system will increase and cost will get reduced. Vapour absorption system is one such method to recover waste heat. Taking heat as input this system creates refrigeration effect which can be used for cooling purpose. This Paper analyses the results obtained for performance analysis of Li-Br Water Refrigeration System and investigates the improvement in the performance by implementing Double coiled Anti-Swirl type of Heat Exchangers for Condenser and Evaporator. Keywords Anti-Swirl, Double Helical Coil, Waste Heat Recovery, Crystallization, Corrosion Inhibitor, Vapour Absorption Refrigeration, COP (Coefficient of Performance). I. INTRODUCTION In vapour absorption refrigeration system the function of compressor is accomplished in three step process by the use of the absorber, pump and generator or reboiler as follows: a) Absorber: Absorption of the refrigerant by its weak or poor refrigerant solution in the suitable absorbent forming a strong or rich solution of the refrigerant in the absorbent. b) Pump: Pumping of the refrigerant concentrated solution to raise its pressure to condenser pressure. c) Generator: Distillation (Separation of Water Vapour from Li-Br Water concentrated solution) of the vapour from the rich solution leaving the poor solution for recycling. The pump work, W p = - v dp (for flow process) is very small as compared to the compressor work in the vapour compression system, as the specific volume of the liquid is extremely small compared to that of the vapour in Vapour Compression Refrigeration cycle. The energy consumption of the vapour absorption system is mainly in the generator in the form of heat supplied. A number of refrigerant-absorbent pairs can be used as working substances in the vapour absorption system, from which the most common ones are water-lithium bromide and ammonia-water. These two pairs offer good thermodynamic performance and they are environmentally friendly. There has been a lot of research going on in the field of Vapour Absorption Refrigeration systems. As the system poses many challenges while implementing it, many researchers have tried rigorously to overcome these challenges and get the results for performance analysis. Li-Br Water refrigeration @IJCTER-2016, All rights Reserved 108
System is used for experimentation because of following reasons - Li-Br water solution is Less hazardous for human life compared to NH 3,Copper tubes can be used hence high conductivity and rate of heat transfer and NH 3 -Cu are not compatible, Non-volatility absorbent of Li-Br (no need of a rectifier in the system), Extremely high heat of vaporization of refrigerant (water), Environment friendly compared to HCFCs, not responsible for Green House effect and Ozone layer depletion. Fig. 1 : Schematic of Li-Br Water Heat Recovery System II. EXPERIMENTAL SETUP Fig 2 : Experimental Setup The Experimental Setup consists of Shell and coil type of Generator and Absorber Heat Exchangers. Evaporator and Condenser are of Double Helical coil with Anti-Swirl; details of which are mentioned in the CAD Models of the respective parts: @IJCTER-2016, All rights Reserved 109
2.1 Cooling Water Helical Coils: Specifications of Generator and Absorber Coils in Experimental Setup: 2.1 Inner diameter of tube 13.6 mm Outer diameter of tube 15.0 mm Thickness of tube 0.7 mm Diameter of coil 120 mm Pitch of coil 23.08 mm Length of coil 300 mm Number of turns 13 Material Copper (Cu) Table 2.2 Shell of Generator and Absorber : Specifications of Generator and Absorber Helical Coils Fig 2.1 CAD model (Creo) of Cooling water Helical Coil of Generator and Absorber along with Specifications Specifications of Shell of Generator and Absorber in Setup: Inner Diameter Outer Diameter Thickness Length Material 130 mm 140 mm 5 mm 400 mm Steel Table 2.2 Specifications of Shell Fig 2.2 CAD model (Creo) of Shell of Shell and Coil type Generator and Absorber along with Specifications 2.3 Solution Pump: Specifications of Solution Pump used: Voltage 12V Current 0.3A Tabl Type DC e 2.3 Mass flow rate 1.16kg/min (70 kg/hr) Spec ifications of Solution Pump Fig 2.3 CAD model (Creo) of Solution Pump along with Specifications 2.4 Double Helical Anti-Swirl Coils of Condenser and Evaporator: @IJCTER-2016, All rights Reserved 110
Specifications of Double Helical coils of Condenser and Evaporator in Experimental Set up: T a b l e 2. 4 S p e c i Outer diameter of tube1&2 15 mm Outer diameter of plate 130 mm Inner diameter of tube1&2 13.6 mm Inner diameter of plate 121 mm Diameter of coil1 120 mm Diameter of coil2 80 mm Length of coil1&2 300 mm Length of coil3 320 mm Pitch of coil1&2 23.08 mm Number of turns of coil1&2 13 Number of turns of Anti-swirl coil 5 Material of coil1,2&3 Copper (Cu) fications of Double Helical Coil with Anti-swirl Fig. 2.4 CAD model (Creo) of Double Helical Coil with Anti-swirl used in Condenser and Evaporator 2.5 Shell and Coil Assembly for Double Helical Coil with Anti-Swirl of Condenser and Evaporator: Specifications of Shell of the Shell and Double Helical Coil Condenser and Evaporator: Inner Diameter Outer Diameter Thickness Length Material 130 mm 140 mm 5 mm 400 mm Steel Table 2.5 Specifications of Shell of Shell and Double Helical Coil with Anti-swirl Condenser and Evaporator Fig 2.5 Cross section of CAD Model (Creo) of Shell and Coil Assembly for Double Helical Coil with Anti-Swirl Helical Path for Anti-Swirl (Indicated by Green colour in Fig 2.4) in the direction opposite to the direction of coil for steam in all the shell and coil type of heat exchangers will increase the rate of phase change process due to increased rate of heat transfer due to turbulence. Also, if there are two coils/passes for the cooling water as shown above, the area of heat transfer will increase and thus there will be more rate of heat transfer. This will enhance the performance of the Vapour absorption system. @IJCTER-2016, All rights Reserved 111
III. METHODOLOGY For Experimentation and Analysis on Li-Br - water Vapour absorption system having a refrigerating capacity of 1 KW with a condenser temperature of 28 C and an absorber temperature of 37 C and the temperature of Evaporator is 10 C, the setup (shown in fig. 2) is fabricated. Heat Input required in the generator was obtained from IC Engine exhaust gases. Li-Br and water Vapour Absorption refrigeration system for the Waste Heat Recovery was to be experimented for finding out following results: (1) Coefficient of Performance of the Refrigerating System with Waste Heat Recovery Mechanism i.e. Vapour Absorption Refrigeration System (2) Improvement in the Performance of System by implementation of Double Helical Coiled Anti-Swirl type of Shell and Tube Heat Exchangers for Condenser and Evaporator 3.1. Study of Critical Parameters: For the purpose of experimentation on the designed model of Li-Br water refrigeration system, certain Critical parameters are identified which are essential to consider for enhanced performance of the system. 3.1.1 Vacuum Requirements: At Evaporator desired temperature 10 C, the pressure of water vapour is 9.21 mm of Hg (12.21 mbar i.e. 0.01221 bar), which is to be achieved using a vacuum pump. All the joints required were checked for leak-proof conditions in order to avoid infiltration of outside air so as to maintain vacuum of desired order. 3.1.2 Corrosion Inhibitors: Li-Br solution is a corrosive solution. Copper metal is naturally protected at low ph and low solution alkalinities. It is Iron that suffer under these conditions. If low ph and alkalinity are maintained in the lithium bromide solution, corrosion inhibitors are needed to protect the steel. A large amount of debris can foul pumps and reduce heat transfer. Air, specifically oxygen, is the cause of corrosion in this system; As oxygen dissolves in water, it releases free electrons into solution. These free electrons are readily consumed by metals (Iron and Copper) and corrosion takes place. The quality of the Li-Br solution decides the refrigeration performance to a large extent. Therefore, strict measures must be taken to control its quality, which should meet the following standards: Concentration of Li-Br Solution prepared 58% Alkalinity of Li- Br Solution prepared ph 10 Amount of Additives added for Corrosion inhibition during solution preparation (Li 2 MoO 4 content: 0.015%) Li 2 CrO 3 content: 02% Table 3.1.1 Details of the Li-Br Water Solution Concentration and Amount of Additives added 3.1.3 Crystallization of Li-Br in Li-Br Water solution: The concentration of the saturated Li-Br solution is about 60% at normal temperature. At a given concentration, crystals separate out from the solution when the temperature drops. And at a given temperature, crystals separate out when the concentration rises. Crystallization must be avoided during the operation and shutdown period. @IJCTER-2016, All rights Reserved 112
3.2 Observations recorded during Experimentation: 3.2.2 Condenser and Evaporator as Single Coil Shell and Coil Heat Exchangers: 1. Mass flow rate of refrigerant (Water Vapour): 0.46 Kg / min = 7.67 x 10-3 Kg / s 2. Concentration of Li - Br solution = 0.58 (580 gm Li-Br powder + 420 gm water per kg of solution) 3. Vacuum Gauge Reading = 20 mm of Hg absolute. 4. Temperatures of cooling water in shell and coil type of heat Exchangers: Temperature in o C Generator (steam / water) Condenser Single Coil and Shell (cooling water) Evaporator Single Coil and Shell (water) Absorber (Cooling water) Inlet 100.8 27.7 27.7 27.7 Outlet 96.4 39.1 21.6 31.2 Table No. 3.2.1: Temperatures of water/steam measured at different parts of system for single coil and shell condenser and evaporator 5. Mass flow Rates: Sr. No. Description Volume Measured (ml) Time (sec) 1 Condenser cooling water 620 30 0.0210 2 Evaporator water 300 24 0.0250 3 Absorber cooling water 600 25 0.0240 Mass flow rate (Kg / s) Table No. 3.2.2: Mass Flow Rates of water measured at different parts of system for single coil and shell condenser and evaporator 3.2.2 Condenser and Evaporator as Double Coil Anti-Swirl Shell and Coil Heat Exchangers: 1. Mass flow rate of refrigerant (Water Vapour): 0.52 Kg / min = 8.66 x 10-3 Kg / s 2. Concentration of Li - Br solution = 0.58 (580 gm Li-Br powder + 420 gm water per kg of solution) 3. Vacuum Gauge Reading = 20 mm of Hg absolute. 4. Temperatures of cooling water in shell and coil type of heat Exchangers: Temperature in o C Generator (steam / water) Condenser Double Coiled Anti-Swirl (cooling water) Evaporator Double Coiled Anti-Swirl (water) Absorber (Cooling water) Inlet 102.2 27.7 27.7 27.7 Outlet 95.0 42.6 20.3 30.1 Table No. 3.2.3: Temperatures of water/steam measured at different parts of system for double Anti-Swirl coil and shell condenser and evaporator @IJCTER-2016, All rights Reserved 113
5. Mass flow Rates: Sr. No. Description Volume Measured (ml) Time (sec) 1 Condenser cooling water 620 30 0.0210 2 Evaporator water 300 24 0.0250 3 Absorber cooling water 600 25 0.0240 Mass flow rate (Kg / s) Table No. 3.2.4: Mass Flow Rates of water measured at different parts of system for double Anti-Swirl coil and shell condenser and evaporator IV. RESULTS Keeping the Heat Supplied to generator same, the Performance of the two cases i.e. Single and Double coil of Condenser and Evaporator are compared. Heat supplied by steam to solution in generator = Q g = m g x C pg x ( T gi T go ) = 8.77 x (10-3 ) x 1.005 x (250 80) Q g = 1.49 kw 4.1 Performance Parameters for Single Coil and Shell Condenser and Evaporator: Heat absorbed in evaporator = Q e1 = m e x C pw x T = 0.0250 x 4.18 x (27.7-21.6) Q e1 = 0.637 kw COP of refrigeration system in Single coil and shell Evaporator case = Q e / Q g = 0.637 / 1.49 COP 1 = 0.425 Heat Rejected in Condenser = Q c1 = m c x C pw x T = 0.021 x 4.18 x (39.1-27.7) Q c1 = 1.001 kw Heat Rejected in absorber = Q a1 = m a x C pw x T = 0.024 x 4.18 x (31.2-27.7) Q a1 = 0.351 kw 4.2 Performance Parameters for Double Coil Anti-Swirl and Shell Condenser and Evaporator: Heat absorbed in evaporator = Q e2 = m e x C pw x T = 0.0250 x 4.18 x (27.7-20.3) Q e2 = 0.731 kw Heat Rejected in Condenser = Q c2 = m c x C pw x T = 0.021 x 4.18 x (42.6-27.7) Q c = 1.307 kw Heat Rejected in absorber = Q a2 = m a x C pw x T = 0.024 x 4.18 x (30.1-27.7) Q a2 = 0.2407 kw @IJCTER-2016, All rights Reserved 114
COP of refrigeration system, COP 2 = Q e2 / Q g2 = 0.731 / 1.39 COP 2 = 0.5262 4.3 Comparison of Performance parameters for Double and Single coil and Shell Heat Exchanger Refrigerator: Parameter Single Coil kw Double Coil kw Heat rejected in generator 1.49 1.49 Heat rejected in condenser 1.001 1.307 Heat rejected in absorber 0.351 0.247 Refrigerating effect 0.637 0.731 COP 0.425 0.526 Table 3.1 Comparison of Single and Double Coil and Shell Condenser and Evaporator 4.4 Performance Parameters Correlation: (A) (B) Fig. 4.4.1 (A) COP Vs Absorber Temperature ( o C) at different Generator Temperatures (B) COP Vs Evaporator Temperature ( o C) at different Generator Temperatures Graph of COP Vs Absorber Temperature and at different generator temperatures and COP Vs Generator Temperature at different Absorber temperatures is plotted using Numerical Analysis of Double Coil Anti-Swirl Shell and Coil Condenser and Evaporator using MATLAB code. The graph of COP Vs Absorber Temperature and at different generator temperatures shows that at constant absorber temperature as generator temperature increases, COP of the system also increases. For a particular generator temperature, increase in absorber temperature causes decrease in COP. The graph of COP Vs Generator Temperature at different Absorber temperatures shows that at constant generator temperature as evaporator temperature increases, COP of the system also increases. For a particular evaporator temperature, increase in generator temperature causes decrease in COP. @IJCTER-2016, All rights Reserved 115
V. CONCLUSIONS COP obtained in case of single coil and shell condenser and evaporator is 0.425 and that in case of double coil anti-swirl condenser and evaporator is 0.526. For comparison purpose generator heat supplied and mass flow rates of evaporator, condenser and absorber pumps are kept constant. Increase in COP is 23.60% which proves improvement in performance by implementation of double coil heat exchangers. REFERENCES [1] N.Hatraf and L. Merabeti, The Experimental Measurement of The Li-Br Concentration of Solar Absorption Machine. International Journal of Chemical, Moleculer, Nuclear, Materials and Metallurgical Engineering, Volume 8, No-6, 2014. [2] Subhash Kumar, Comparative Study on Performance Analysis of Vapour Absorption Refrigeration System Using various Refrigerants. PASJ International Journal of Mechanical Engineering (IIJME), Volume 3, Issue 1, January 2015. [3] Md Azhar and M. Altamush Siddiqui, Thermodynamic Analysis Of A Gas Operated Triple Effect Absorption Cycle. ISSN: 2319-8753 International Journal of Innovative Research in Science, Engineering and Technology Vol. 2, Issue 5, May 2013 [4] Atishey Mittal, Devesh Shukla and Karan Chauhan, A Refrigeration System for An Automobile Based On Vapour Absorption Refrigeration Cycle Using Waste Heat Energy From The Engine, International Journal Of Engineering Sciences & Research Technology. [5] V.D.Patel, A.J.Chaudhari and R.D.Jilte, Theoretical and Experimental Evaluation of Vapour Absorption Refrigeration System, International Journal of Engineering Research and Applications (IJERA). [6] Incropera, DeWiitt,Bergman and Nabin, Fundamentals of Heat and mass Transfer 6 th Edition,Willey Publications. [7] C. P. Arora, Refrigeration and Air Conditioning, 3 rd Edition, The McGraw Hill Publications. @IJCTER-2016, All rights Reserved 116