SEMINAR REPORT ON AUTOMOBILE AIR CONDITIONING USING ENGINE EXHAUST HEAT By
SHIV SINGH PRAJAPAT 2009UME408
Submitted to: Dr. P.K. Saxena Professor
Dr. G. Agarwal Professor
Dr. T. C. Gupta Associate Professor
DEPATEMENT OF MECHANICAL ENGINEERING MALAVIYA NATIONAL INSTITUTE OF TECHNOLOGY, JAIPUR DECEMBER 2012
I
SYNOPSIS
Major commercial refrigerant chloro fluoro carbons (CFCs) are going to be phase out shortly as part of Montreal Protocol since they caused the phenomenon called green house effect and depletion of ozone layer. Being very environment friendly amoniya water combination is the most suitable working fluid pair for vapour absorption refrigeration system. Energy from the exhaust gas of an internal combustion engine is used to power an absorption refrigeration system to air-condition an ordinary passenger car. According to a cautious estimate, approximately 10% of the energy available at the crankshaft in a diesel operated vehicle is used for operating the compressor of the vehicle’s air-conditioning system. This is a huge loss if one takes into account the fact that the thermal efficiencies of most diesel operated vehicles range from 2030% when in pristine condition. The bottom line is that a great deal of diesel is consumed to generate electricity. In addition to this, alternating current via an alternator is necessary for the operation of the conventional a/c system. The refrigerant, usually R12 or R22 leaks easily. Being a secondary refrigerant, it is also harmful to the environment. A new driving scheme is put forward in this report, in which primary exhaust heat sources is used to drive the air conditioner. There requires quite a few moving parts in this new scheme. If the low power engine is mounted in the car, additional solar energy can be combined to drive the air conditioner. The principle of the new airconditioning system and its structure are illustrated in this report. The automatic control system for this new Air-condition System driven by of Exhaust Heat of Engine and Solar Energy is described in detail as well. This new system is energy conserving, environment-protective, low-carbon, and high efficient. It has a promising application prospect. This seminar report presents a revolutionary ammonia water absorption system for air conditioning in automobiles. The cooling effect is achieved by recovering waste thermal energy from the exhaust gases. The system is cheap and easy to fabricate. The refrigerant, being water, is environment friendly.
II
Contents Synopsis Content List of figures List of tables
I II IV V
Sr. No
Page no
1. 2.
3.
4.
Chapter name Introduction 1.1 History of air conditioning 1.2 Development Conventional Vehicle air conditioning 2.1 Need for Air Conditioning 2.2 Cycle 2.3 Working 2.4 Sources Of Heat To The car 2.5 Components 2.6 Advantages 2.7 Drawbacks 2.8 Alternatives Vapour Absorption Refrigeration System 3.1VARS 3.2 Methodology 3.3Theoretical Calculation of the System 3.4 Conclusions
1 1 3 3 5 5 6 6 8 9 10 11 12 15
Vapour Absorption Refrigeration System In Automobiles
4.1 Methods Of Implementation In An Automobile 4.2 Components of VARS 4.3 Working Of The System
17 18 20
5. Comparison between VCRS and VARS 5.1 Advantages of Absorption Refrigeration over Vapor 21 Compression Refrigeration Cycle
5.2 Disadvantages of Absorption Refrigeration over
24
Vapor Compression Refrigeration Cycle
6. Case Study 6.1 Engine parameters 6.2 Waste Heat Of The Engine 6.3 Final Value 6.4 Testing of the Prototype Nissan1400
26 26 27 29
III
6.5 Conclusions 7. Indian Scenario 8. World Scenario 9. Future Prospects 10. Conclusion REFRENCES BIBLIOGRAPHY ANNEXURES
32 34 36 37 38
42 43 44
IV
List of figures
Sr No
Fig No
1.
3.1
2.
4.1
3.
4.2
4.
6.1
5.
6.2
6.
6.3
Caption
Page
Schematic diagram of vapour absorption refrigeration system Components of Absorption A/C[2]
11
Schematic diagram of three fluid vapor absorption system[7] Load variation[2]
21
The shaded and the clear areas indicate the temperature conditions before and during the road-tests respectively.[2] Averaged values for the enthalpy-concentration performance chart of the plant[2]
30
19
29
31
V
List of Tables
#
Table No
Tabe Name
page
1
Table 3.1
Properties of Ammonia (R717).
12
2
Table 3.2
3
Table 6.1
Enthalpy values on different 14 points on enthalpy entropy chart of Ammonia (R717). Results 29
Chapter-1
Introduction 1.1 History With the invention of the R-12 in 1928 by GM researchers, the dawn of the automotive air-conditioning started. The first prototype self-contained system was installed in a 1939 Cadillac. Packard Motor Company in 1939 was the first company to offer complete auto air-conditioning system for cooling in summer and heating in winter using R12 refrigerant. The first bus A/C proto developed in 1934 by a joint venture between Houde Engineering Corporation of Buffalo, NY and Career Engineering Corporation of Newark, NJ and others followed. Initial airconditioners had a number of problems as well as Second World War hampered the production/progress. In the 1953 model year, many of the problems had been resolved and General Motors and Chrysler came back with improved air conditioning and that luxury became the necessity now for a common car owner for ever Until then most of the A/C parts were placed in the trunk and took up whole space of trunk. In 1953, Harrison Radiator Division of General Motors came up with a revolutionary air conditioner that was totally spaced in the underhood and dashboard (eliminating it from the trunk). The use of desiccant material to absorb moisture in refrigerant line started in 1953. The following were the milestones of the development in the succeeding years.
In 1955, GM developed the first A/C and heating unit that was front mounted, totally pre-assembled and pre-tested. By 1957, all car makers followed this design approach. To provide the evaporator freeze protection, a hot gas bypass valve was introduced in the A/C system in 1956. In 1957, air conditioning became a standard item in Cadillac Eldorado Broughams. The average price of all air conditioners sold in 1957 was $435. The popularity of auto A/C soared and the number of installed A/C systems on the vehicle tripled from 1961 to 1964. During 1963, Ford set A/C unit price at $232. In August 1965, GM crossed the five million A/C unit production mark. GM also introduced first the Climate Control system on Cadillac. Industry wide penetration of A/C reached 70% by 1980. Due to oil embargo in 1973, the emphasis was placed on the fuel economy. Harrison Radiator Division of General Motors developed a cycling clutch orifice tube (CCOT) system replacing Frigidaire Valve-in Receiver (VIR) system that resulted in the compressor off for 1/3 of the time rather than Page | 1
continuously running, thus improving fuel economy. By 1979 all GM vehicles used this CCOT system. In 1974, world came to know the ozone depletion in stratosphere due to R12 use. Harrison Radiator analyzed nine refrigerants and by 1976 arrived at R134a as the replacement of R12 eliminating chlorine. However, there was no commercial availability of R134a then; Allied Chemicals, the major company conducting research on R134a then, would supply about 1 lb of refrigerant per week and the need was about 1000 lb per week for A/C system development work at Harrison in those days. Although the viability of R134a was proven by Harrison through wind tunnel tests on 1978 Chevrolet, the development of A/C system with R134a was discontinued due to the lack of availability of R134a till the Montreal Protocol was adopted by United Nations in September 1987. The first major revolution in the A/C system thus came starting 1990s by replacement of R-12 to R-134a to eliminate the ozone depletion in stratosphere by introducing a refrigerant having chlorine replaced by fluorine in its composition. The commercial production of R134a started with DuPont and ICI in 1990. The changeover of R12 to R134a necessitated the following changes in the A/C system: about 20% higher condensing capacity condenser (to maintain the same operating pressure so that new compressor is not needed), and change of lubricant from mineral oil to synthetic polyalkylene glycol (PAG) oil. Conversion from R12 to R134a in the USA, Europe and Japan took place during 1991-1994. The rest of the world has changed to R134a as the refrigerant for the A/C system during late 1990s and early 2000s. Global warming potential (GWP) was not an issue when changeover from R12 to R134a took place, although the global warming potential of R134a was significantly lower than R12, 1300 vs 7800; carbon dioxide is the basis for global warming potential yardstick having GWP of 1. According to the European Union F-gas regulation, the refrigerant in all new A/C systems introduced in EU must have GWP of 150 or less starting 2011
1.2 Development Automotive air-conditioning system has played an important role in human comfort and to some extent safety during vehicle driving in varied atmospheric conditions. It has become an essential part of the vehicles of all categories worldwide. Even in India, 96% of all new cars manufactured in 2005 had factory-built air conditioning. After discussing the basic operation of the A/C system, in this report, a brief summary is provided on historical development of the vehicular A/C system, refrigerant history from the inception of the A/C system to future systems: R-12, R-134a, enhanced A/C system to next generation refrigerants having Page | 2
no ozone layer depletion potential and negligible global warming potential. The discussion also includes the direct and indirectemissions from vehicles due to the use of the A/C system. This would explain why we continue to change the refrigerants in the automotive A/C system in spite of billions of dollars of the previous refrigerant change cost. The system design considerations are then outlined for minimizing the impact of A/C operation on the vehicle fuel consumption. Finally, new concept design of A/C system and vehicle heat load reduction ideas are discussed to further minimize the impact of A/C system operation on the environment without impacting the human comfort. It is anticipated that this report will provide the overall and detailed prospective of the A/C system developments and provide an opportunity to the researchers to accelerate R&D for the refrigerant changeover. According to the ASHRAE, air conditioning is the science of controlling the temperature, humidity, motion and cleanliness of the air within an enclosure. In a passenger/driver cabin of a vehicle, air conditioning means controlled and comfortable environment in the passenger cabin during summer and winter, i.e., control of temperature (for cooling or heating), control of humidity (decrease or increase), control of air circulation and ventilation (amount of air flow and fresh intake vs. partial or full recirculation), and cleaning of the air from odor, pollutants, dust, pollen, etc. before entering the cabin. While the A/C system provides comfort to the passengers in a vehicle, its operation in a vehicle has twofold impact on fuel consumption: (1) burning extra fuel to power compressor for A/C operation, and (2) carrying extra A/C component load in the vehicle all the time. In addition, the A/C running depends on the climatic condition of the concerned geographical region and the time of the year. The most important impact on the fuel economy is when the A/C is running. Clodic et al. (2005) report the additional fuel consumption due to MAC operation as 2.5 to 7.5% (in USA/Europe) considering the climatic conditions, engine type (diesel or gasoline) and user profile. Corresponding CO2 emission due to MAC operation is between 54.7 and 221.5 kg CO2 per year per vehicle. Of course, the impact on the fuel consumption is more significant when the A/C is installed in compact and sub-compact vehicles.
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Chapter -2
Conventional Vehicle air conditioning Introduction The use of refrigeration and air conditioning for transporting purpose proves to be very advantageous. Air conditioning is very much used in cars i.e. Automobiles, railways and ships. The use of air conditioning in automobiles is a luxury in India but it is commonly used in western countries to provide better human comfort. Today automobile air conditioning has acquired a growing market. The AC in automobiles is a need of persons who are suffering from the hot climate in India which may be carry about 8 to 10 months per year. The new cars are so designed as to accommodate A.C. in its cabin. Premier 118NE Contessa Classic, Tata Instat., Tata Siera, Opel Astra, Ford and Mercedes Bens are some of the models which are having A.C. system.
2.1Need for Air Conditioning Automobile air conditioning system works on the principle of vapour compression refrigeration cycle and employees R12 as refrigerant to run the system. The following factors are controlled by A.C. which leads to human comfort. 1) Heating of cabin, 2) Cooling, 3) Circulation of air, 4) Cleaning and filtering, 5) Humidity control. As per the standards the temperature at 25 0 C and humidity of 50% R.H. is maintained to provide better comfort. This can be achieved very easily in a room or office but it is very difficult to maintain such temperature and R.H. factor because of different sources of heat addition to the automobile system. This heat sources are stated later.
2.2 Cycle Vapour compression refrigeration cycle is used in the car air conditioning system. Vapour (fairly dry vapour) leaves the evaporator and enters the compressor at point 1. The vapour is compressed is entropically to point 2. During compression, the pressure and temperature increases. The temperature at point 2 should be greater than the temperature of the Condenser cooling medium. The vapour leaves the compressor in dry saturated state and enters the condenser at 2. The vapour is Page | 4
condensed and latent heat of condensation is removed in condenser. The high pressure saturated liquid leaves the condenser and enters the throttle valve at 3. Thus the flow through valve causes decrease in pressure and temperature of refrigerant and causes it to evaporate partly. This refrigerant liquid at every low temperature enters the evaporator where it absorbs heat from the space to be cooled thus producing refrigerating effect. This increases its pressure and temperature and the refrigerant is now dry vapour , which is supplied to compressor. This completes the cycle.
2.3 Working Cool refrigerant gas is drawn into the compressor from the evaporator and pumped from the compressor to the condenser under high pressure and temperature due to compression, As this gas passes through the condenser, high pressure, high temperature gas rejects etc. Heat to the outside air as the air passes over the surface of condenser. The coding of the gas causes it to condense into a liquid refrigerant. The liquid refrigerant still in high pressure passes to receiver drier (dehydrator), The receiver acts as a reservoir for refrigerant. The liquid refrigerant flows from the receiver dehydrator to the thermostat expansion valve refrigerant will loses its pressure and temperature.This low pressure low temperature liquid enters the evaporator. The evaporator coil is mounted below front dash board. As the temperature of refrigerant passing through evaporator is low„ it absorbs heat and continues to boil, drawing heat from the surface of the evaporator core warmed by the rush of air passing over the surface of the evaporator core. In addition to the warm air passing over- the evaporator rejecting its heat to the cooler surfaces of the evaporator core, any moisture in the air condenses on the cool surface of the core resulting in cool dehydrated air passing into the compartment of the car. By the time the gas leaves the evaporator, it gets completely vapourised and is slightly superheated. The pressure in evaporator is controlled by suction throttle valve. R12 vapour passing through the evaporator flows through the suction throttle valve and is returned to compressor where refrigeration cycle is repeated.
2.4 Sources Of Heat To The Car The cooling load is affected by many factors. Some of them are listed below 1) Faster the car moves, the greater amount of infiltration into the car and better rate of heat transfer . 2) The sun baking down on the blank road will raise the temp. up to 50 0 C to 60 0 C and thus increases the amount of heat transferred into the car through the floor. 3) Because of the relatively large glass areas, metal construction and the flow of air around the moving vehicle (automobile) is very large, so the air conditioning capacity is also large in comparison with A. C. installed at home. Page | 5
4) Quantity of fresh air in. 5) Number of occupants. 6) Quantity of heat directly rejected by sun on car. For all the above sources, it is necessary that capacity of automobile A.C. should be large, be capable to take overloads and operate for relatively long periods. The cooling capacity of automobile A.C. system ranges from 1 to 4 tones, which is the amount of refrigeration needed to cool a small house.
2.5 Components 1) Compressor :Compressor is a driver of the system. The construction is much rigid and the unit is semi sealed. i.e. the power to drive the compressor is directly taken from the crank shaft by means of v-belt pulley and electromagnetic clutch. The heavy-duty gaskets are provided at joint to prevent vibration, noise and leakage. A typical value arrangement is provided to suit the requirements. The high and high pressure refrigerant enters in compressor which further gets compressed causing hot vapour exit from the compressor unit, The compressor can start or stop by means of thermostat arrangements which engages or disengages the electromagnetic clutch so as to run compressor as per requirements. Lubrication oil is placed inside the chamber. The noise of compressor is very least as compared to that of engine. The vibration of compressor creats problem in Diesel air conditioning system. 2) Electromagnetic Clutch The pulley assembly contains an electrically controlled magnetic: clutch, permitting the compressor to operate only when air conditioning is actually desired. All automobile A.C. systems employs the clutch to drive the compressor on demand from the thermostat inside the car (i.e. the knob). When the compressor clutch is not engaged, the compressor shaft does not rotate, although the pulley is being rotated by belt from the engine. The clutch armature plate, which is movable member of the drive plate assembly is attached to the thrive hub through drive springs and is riveted to both driver and armature plate. The hub of this assembly is pressed over the compressor shaft is aligned with a square drive key located in the key way on the compressor shaft. The pulley assembly consist of pulley rim, pulley hub and power element ring. 3) Condenser A condenser is similar to an ordinary automobile radiator but are designed to withstand much high pressure, It contains a fan to provide forced circulation of air. This whole assembly is fitted in front of the car radiator so that it receives high volume of air.
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The high temperature and high pressure refrigerant vapour loses its heat to forced air flowing through it causing change of this phase into high pressure liquid. The fan and electromagnetic clutch are electrically coupled. Rapid condensation of refrigerant can be done by fan. This high pressure liquid refrigerant then passed to receiver drier. 4) Receiver:The purpose of receiver is to ensure a solid column of liquid refrigerant to the thermostatic expansion valve. Automobile A.C. units are more susceptible to leaks than units because of vibration. Over a period of time, small leaks will occur, which may requires addition of refrigerant,, Also the evaporator requirements vary because of the changing heat load. A small receiver is used in the system to compensate all the above variables, Refrigerant is stored in the unit untitled it is needed by the evaporator. A liquid Automobile Air Conditioning indicator or slight glass is provided at outlook pipe of receiver unit. The appearance of bubbles or foam in the slight glass indicates the shortage of refrigerant in the system. Drier part of this unit consists of sillicagel to absorb moisture if any in the system, also it traps foreign material which may have entered the system during assembly. It is temporary storage and purifying unit. 5) Expansion Valve:The expansion valve fulfils the following two functions. a. The temperature and pressure of refrigerant is reduced to such a low-level due to sudden expansion by throttling process. This is helpful to create low temperature than the evaporator. b. According to cooling load, the quantity of refrigerant supplied to evaporator can be controlled. It automatically regulates the flow of liquid refrigerant. The valve is located at the inlet to evaporator core. It consists of a (capillary bulb and tube, which are connected to an operating diaphragm (sealed within the valve). When the cooling load increases, the refrigerant evaporates at a faster rate in evaporator than the compressor can suck. As a result., the degree of superheat and pressure in evaporator increases which cause the valve to open more allowing more refrigerant to enter into the evaporator. At, the same time the increases in suction pressure also enables the compressor to deliver increased refrigerating capacity. When cooling load decreases;, the refrigerant evaporates at a slower rate than the compressor can suck, As a result the evaporator pressure drops and the degree of superheat will decrease., The valve tenets to close and the compressor delivers less refrigerant capacity. Thus this valve is capable of meeting the varying load requirements. This valve keeps the evaporator full of refrigerant, thus ensures safety to compressor. 6) Evaporator:Page | 7
Evaporator is a place where the refrigerant evaporates and absorbs heat from the air passed over it. Air is forced to flow over the evaporator with the help of blower, which is installed in the evaporator itself and cooled before distributing in seating compartment. The design of evaporator is more critical as the space limitations are very severe and worse than compact room conditioners. The evaporator is placed under dashboard of car. We can provide more ducts if the car seating capacity is more. The purpose of evaporator is to cool and dehumidify the air passing over it into passenger's cabin. The refrigerant in cooled liquid state boils immediately in evaporator when air loses its heat and moisture to it. Heat from the core surface is lost to boiling and vapourizing refrigerant, which is cooler than the core, thereby cooling the core. The moisture collected is then drained of as it may reduce the cooling effect. Dirt or other foreign matter on the core surface or in evaporator housing will restrict the airflow. A cracked or broken housing can result in insufficient air-or warm air supply to passenger’s compartment. The dirt can be removed by forcing dry air on it under pressure. 7) Controls:These units ensures safe operation of air conditioner. The thermostat is used to prevent the formation of frost on the evaporator coil. The cabin air temperature is also controlled to the desired level. Once the evaporator fins temperature approaches near freezing point, the thermostat sends signals to the thermo amplifier which in turn cuts all power supply to electromagnetic clutch, thereby A.C. operation stops temporarily.
2.6 Advantages The main advantage of this system is to travel with comfort for a long distance in any type of atmospheric conditions without tired. During summer the temperature inside the car can he maintained low and this is very necessary for comfort conditions. There may be more advantages rather than this.
2.7 Drawbacks 1) Moving parts are in the compressor. Therefore, more wear, tear and noise. 2) It uses high grade energy like Mechanical work. Engine speed, average and power will reduce due to power supplied to run A.C. system. 3) High operating cost, since fuel economy is affected, high maintenance cost, costly refrigeration. A loss in economy level of the order of 1 to 1.5 km/liter can occur due to the use A/C. 4) CFC’s (Chlorofluorocarbon) if leaks out of the system causes great damage to the ozone layer. 5) If the car’s reserve power is less, it can affect its acceleration. 6) Maintenance and initial cost of unit is high. Page | 8
2.8 AlternativesAdsorption/Absorption Air-Conditioning Using Waste Heat :- In this system the compressor is replaced by the combination of Absorber, Generator and Pump that uses a waste heat source to provide the energy needed to drive the cooling system. Adsorption - Adsorption is the phenomenon in which, the liquid or gas (refrigerant) molecules in the adsorbing pair gets deposited on the solid (adsorbent) surface without any chemical change .This is an exothermic process. For ex: the silica gel acts as an adsorbent, which adsorbs the water molecules on its surface. Absorption- The phenomenon of absorption is the mixture of a gas in a liquid, the two fluid present strong affinity, to form a solution (uptake of molecules into the interior of another substance).
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Chapter-3
Vapour Absorption Refrigeration System Introduction The vapour absorption system uses heat energy, instead of mechanical energy as in vapour compression system, in order to change the condition of the refrigerant required for the operation of the refrigeration cycle. In this system, the compressor is replaced by an absorber, a pump, a generator, and a pressure reducing valve. This complete chapter discuss about the theoretical calculations are made of different components of the systems like evaporator, absorber, condenser and pump of vapour absorption system for a capacity of 1 TR and experimentally developed and run system to validated for reducing the temperature for the free of cost of operation.
3.1VARS In the vapour absorption refrigeration (VAR) system, a physicochemical process replaces the mechanical process of the vapour compression refrigeration (VCR) system by using energy in the form of heat rather than mechanical work. The main advantage of this system lies in the possibility of utilizing waste heat energy from industrial plants or other sources and solar energy as the energy input. The VAR systems have many favourable characteristics. Typically a much smaller electrical input is required to drive the solution pump, compared to the power requirements of the compressor in the VCR systems, also, fewer moving parts means lower noise levels, higher reliability, and improved durability in the VAR systems. A vapour absorption refrigeration system is a heat operated unit which uses refrigerant (NH3) that is alternately absorbed by and liberated from the absorbent (water). The vapour absorption system uses heat energy, instead of mechanical energy as in vapour compression system, in order to change the condition of the refrigerant required for the operation of the refrigeration cycle. In this system, the compressor is replaced by an absorber, a pump, a generator, and a pressure reducing valve. These components in the system perform the same function as that of compressor in vapour compression system. The vapour refrigerant from evaporator is drawn into an absorber where it is absorbed by the weak solution of refrigerant forming a strong solution. This strong solution is pumped to the generator where it is heated by utilizing solar energy. During the heating process, the vapour refrigerant is driven off by the solution and enters into the condenser where it is liquefied. The liquid refrigerant then flows into the evaporator and thus the cycle is completed. Page | 10
3.2 Methodology Fig.1 shows the schematic diagram of a vapour absorption system. Ammonia vapour is produced in the generator at high pressure from the strong solution of NH3 by an external heating source. A solar cooker will produce the heat and generate ammonia gas. Ammonia gas then enters into the condenser. High pressure NH3 vapour is condensed in the condenser. The cooled NH3 solution is passed through a throttle valve and the pressure and temperature of the refrigerant are reduced below the temperature to be maintained in the evaporator. The low temperature refrigerant enters the evaporator and absorbs the required heat from the evaporator and leaves the evaporator as saturated vapour. Slightly superheated, low pressure NH3 vapour is absorbed by the weak solution of NH3 which is sprayed in the absorber.
Fig.3.1 Schematic diagram of vapour absorption refrigeration system [1]
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Table 3.1 Properties of Ammonia(R717).
3.3 Theoretical Calculation of the System The following specific parameters are assumed for theoretical calculation of the complete system design: Condenser pressure: 5 bar, Evaporator pressure: 2 bar, Capacity of refrigeration: 0.25 TR, i) Heat removed in condenser (Qc): The amount of heat removed in the condenser is given by: Qc = (h2-h1) kJ/kg
of NH3.
(1)
Where h is enthalpy at different points on chart. As NH3 saturated vapour enters in and NH3 saturated liquid comes out. Page | 12
ii) Heat absorbed in the evaporator (Qe): evaporator is given by: Qe = (h4-h3) kJ/kg of NH3.
The amount of heat absorbed in the
(2)
where h4 is the heat of saturated vapour at Pc and h3 is the heat of mixture of NH3 liquid and vapour at Pe or heat of NH3 liquid at points ‘2’ as 2-3 is constant enthalpy throttling process. iii) Heat removed from the absorber (Qa): When NH3 vapour at point 4 and aqua at point 10 are mixed, the resulting condition of the mixture in the absorber is represented by 7’’ and after losing the heat in the absorber (as it is cooled), the aqua comes out at condition 5. Therefore, the heat removed in the absorber is given by: Qa = (h7-h5) kJ/kg of aqua.
(3)
iv) Heat given in the generator (Qg): Qg is the heat supplied in the generator and Qd is the heat removed from the water vapour, then the heat removed per kg of aqua is given by: (Qg-Qd) = (h7’-h7) kJ/kg of aqua.
(4)
As the aqua goes in at point 7 and comes out at condition 8 and 1 which can be considered a combined condition at 7’. By extending the triangle 8-7-7’ towards right till 8-7’ cuts at 1 and 8-7 cuts at ‘a’ on y-axis then, the heat removed per kg of NH3 is given by: (Qg- Qd) = h1-ha kJ/kg of NH3.
(5)
For finding out Qd separately, extend the vertical line 7-7’ till it cuts the auxillary Pc line and mark the point ‘b’. Then draw horizontal line through ‘b’ which cuts the Pc line in (in vapour region) at point 11. Then join the points 7 and 11 and extend that line till it cuts y-axis at 12. Therefore, Qd is given by: Qd = (h12-h1) kJ/kg of NH3.
(6)
The table 2 shows the values obtained on enthalpies based on enthalpy concentration chart of Ammonia (R717).
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Table 3.2 Enthalpy values on different points on enthalpy entropy chart of Ammonia (R717).
Based on above enthalpies calculation values the following results are obtained for the design load of different component of the system. i) Mass flow rate of NH3 through evaporator (mf): mf = Cooling load/ h4 - h3 = (0.25x0.35)/(1632.462-376.722) mf = 6.968×10-4kg/s=2.51kg/h. ii) Heat rejected in absorber (Qa): Qa = mr× x× (h4-ha) = 6.968 x 10-4 x (1632.462-(-334.864)) Qa =1.371kW. iii) Heat removed in condenser (QC): QC = mr ×x× (h1- h2) = 6.968 x 10^-4 x (1632.462-376.722) QC = 0.875kW. iv) Mass of strong solution handled by pump per second (ms): Page | 14
Enthalpy balance across heat exchanger is, Heat lost by weak solution = heat gained by strong solution, mw × (h8-h9) = (mw + 1 )×(h7-h6) mw× (209.92-92.0876) = (mw+1)× (133.9456-41.858) mW = 3.6667kg/kg of NH3. Hence, mass of strong solution handled by pump (ms), ms = mr × (mw +1) = 6.968 x 10-4× (3.6667+1) Therefore, ms= 3.2517×10-3 kg/s. v) Heat supplied to generator temperature = 75°C. Qg = mr x (h12 – ha) = 6.968 x 10-4 x (1820.823-(-334.864)) Therefore, Qg = 1.502kW. vi) Design of pressure vessel for generator: At pressure 5bar, with diameter (d) =200mm, and assuming 33% overload, the design pressure,(Pd) obtained 6.65bar.Design pressure (Pd) =1.33 xP = 6.65bar. Therefore, thickness of pressure vessel as thin cylinder, [(Pd x d)/2 xt] =330N/mm2 (330N/mm2 assuming C40 as a material for pressure vessel from PSG data book). Therefore, t=8mm. vii) Design of air cooled condenser: Calculations are made and obtained LMTD (Log Mean Temperature Difference) = 42.45°C, and length of coil=1.87m.
3.4Conclusions After designing, manufacturing and run the system the achieved temperature drop of 3.5oC below ambient temperature with the time period of 32.5s as shown in Fig.3. Although the system was designed for a capacity of 0.25TR the desired capacity was not completely achieved. This was due to fact that certain parameters could not be achieved during the practical design as compared to the theoretical design as stated below. 1 Less number of turns of condenser& tube length resulted in inefficient heat rejection. This caused the hot vapour from the generator to enter the evaporator coil without changing its phase completely and thus reduced the cooling effect. Page | 15
2 The system couldn’t sustain desired pressure range. The pressure capacity of the flexible hoses used in the system limited the system pressure and thus the design pressure could not be achieved due to fear of failure. 3 Concentration of ammonia in the system design was for 50% concentration of ammonia but in the ammonia commercially available is of 25% concentration. This was also a limitation.
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Chapter-4
Vapour Absorption Refrigeration System In Automobiles
Introduction Much of an internal combustion engine’s heat from combustion is discarded out of the exhaust or carried away via the engine cooling water. All this wasted energy could be useful. The common automobile, truck or bus air conditioner uses shaft work of the engine to turn a mechanical compressor. Operating the mechanical compressor increases the load on the engine and therefore increases fuel consumption, emissions and engine operating temperature. With an absorption refrigeration system, we can utilize the exhaust heat and the heat absorbed by the engine’s cooling water. This heat, which could be considered as free energy, would be enough to drive an adsorption refrigeration. It is well known that an IC engine has an efficiency of about 35-40%, which means that only one-third of the energy in the fuel is converted into useful work and about 60-65% is wasted to environment. In which about 28-30% is lost by cooling water and lubrication losses, around 30-32% is lost in the form of exhaust gases and remainder by radiation, etc. In a Vapour Absorption Refrigeration System, a physicochemical process replaces the mechanical process of the Vapour Compression Refrigeration System by using energy in the form of heat rather than mechanical work. The heat required for running of a Vapour Absorption Refrigeration System can be obtained from the exhaust of any vehicle working with an IC engine, which would otherwise be exhausted into the atmosphere. Hence using a Vapour Absorption Refrigeration System will not only prevent the loss of power from the vehicles engine but will also produce refrigeration using the low grade energy (i,e. exhaust) from the engine. The use of a Vapour Absorption Refrigeration System will also reduce pollution by reducing the amount of fuel burned while working the conventional vapour compression refrigerating unit.
4.1 Methods Of Implementation In An Automobile For a road transport utilizing Vapour Absorption Refrigeration System heat energy can be supplied in two ways:
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1. Using heat of combustion of a separate fuel- By using a separate fuel for working the refrigeration system i,e. a fuel for example natural gas can be used for the working of a Vapour Absorption Refrigeration System. This can be achieved by burning the fuel in a separate combustion chamber and then, supplying the Generator of a Vapour Absorption Refrigeration System with the products of its combustion to produce the required refrigerating effect. However this prospect is eliminated since it requires a separate fuel and a separate combustion chamber which makes it uneconomical and the system becomes inefficient. 2. Using waste heat of the IC engine- Another method is by utilizing the heat of combustion which is wasted into the atmosphere. By designing a generator capable of extracting the waste heat of an IC engine without any decrease in engine efficiency, a Vapour Absorption Refrigeration System can be brought to work. Since this arrangement does not require any extra work expect a small amount of work required for the pump, which can be derived from the battery, this system can be used in automobiles where engine efficiency is the primary consideration.
In an IC engine, fuel (usually petrol or diesel) is combusted inside the cylinder due to which the piston moves outward and rotates the crank, and hence the engine produces work. In IC engines the combustion of the fuel produces heat, which is converted to mechanical work using the piston and crank arrangement. From the heat produced from combustion of fuel only 30% (approx) of heat is converted into useful mechanical work. The remaining heat energy is wasted into the atmosphere in the form of: (i) heat carried away by the cooling water, (ii) heat taken away by the exhaust gases, (iii) heat carried away by the lubricating oil, (iv) and, heat lost by radiation. The cooling water and exhaust gases carry away the maximum amount of heat from the engine, ie around 60% (approx). This heat is called the low grade energy of the engine.
4.2 Components of VARS
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Figure 4.1 Components of Absorption A/C [2]
4.2.1 Generator It is basically a container where the solution is maintained at constant level. The exhaust pipe is passed through it and its heat is extracted in the generator. It has two exits and an inlet. From the two exits, one is for the flow of refrigerant to the condenser and the other for the flow of solution back to absorber. The exhaust pipe passing through the generator is made of copper while the other components are made of steel. 4.2.2 Condenser Usually the condenser of an automobile is of an oval cross-section. It is made of aluminum to have easy transfer of heat from the refrigerant coming from generator to the atmosphere. A large number of fins are provided to increase the surface area and thereby increase the heat transferred from the refrigerant to the atmosphere.
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4.2.3 Expansion valve A needle valve is used to drop the pressure of the refrigerant from high pressure to low pressure side. A needle valve can be easily adjusted to obtain the required pressure within the system. 4.2.4 Evaporator The refrigerant from the expansion valve enters the evaporator where the cold refrigerant absorbs heat from the surroundings. To have maximum heat transfer from surroundings to the refrigerant the evaporator is made of copper tubes. 4.3.5 Absorber This is the container which has two inlets, one for the refrigerant coming from the evaporator while the other for the weak solution coming from the generator. The one exit is for pumping the solution to the generator. It has a perforated sheet to strain the solution coming from the generator to have a proper mixing of the weak solution with the refrigerant coming from the evaporator. Fins are provided around the container to increase the surface area, to remove the heat developed during the mixing of the refrigerant and the weak solution. 4.2.6 Pump Since the system is small the flow rate required is also small. Hence a fuel pump is used to pump solution from the absorber to the generator. The power to run the pump is derived from the engine battery. 4.2.7 Control valve This is placed in between the generator and the absorber to bring the solution pressure from high pressure to low pressure. The control valve may be another needle valve which could also be used to control the flow rate of the weak solution back to the absorber. 4.2.8 Pre-heater This is a container containing coiled tubes through which the solution passes. It is placed in between the generator and the pump of the absorber. Cooling water is passed through the container, ie it is placed in the path way of hot water flowing from the engine jacket to the radiator. The quantity of cooling water inside the pre-heater is always fixed. The coils for the flow of solution are made of copper to have maximum heat transfer fro the cooling water to the solution and the remaining parts are of cast iron.
4.3 Working Of The System Page | 20
Figure 4.2 Schematic diagram of three fluid vapor absorption system [7]
The strong solution at 35°C is pumped from the absorber to the pre-heater where the solution of the strong solution is increased to 75°C from the cooling water at 80°C. This solution then enters the generator where the refrigerant, ie water at 40°C gets vapourizes and is passed through the condenser, where the latent heat is removed from the refrigerant. This refrigerant is then passed through the expansion valve to bring the temperature to around 10°C, after which it is passed through the evaporator coil to absorb the latent heat of the refrigerant at 10°C. The vapourized refrigerant then enters the absorber where the weak solution coming from the generator gets mixed liberating heat. This formed solution is again pumped to the generator using the pump and the cycle is repeated again.
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Chapter-5
Comparison between VCRS and VARS 5.1 Advantages of Absorption Refrigeration over Vapor Compression Refrigeration Cycle 1) Method of compression of the refrigerant: One of the most important parts of any refrigeration cycle is the compression of the refrigerant since all the further operations depend on it. In the vapor compression refrigeration system the compression of the refrigerant is done by compressor which can be of reciprocating, rotating or centrifugal type. In the vapor absorption refrigeration system, the compression of the refrigerant is done by absorption of the refrigerant by the absorbent. As the refrigerant is absorbed, it gets converted from the vapor state to liquid state so its volume reduces. 2) Power consumption devices: In the vapor compression cycle the compressor is the major power consuming device while in the vapor absorption cycle the pump used for pumping refrigerant-absorbent solution is the major power consuming device. 3) The amount of power required: The compressor of the vapor compression cycle requires large quantities of power for its operation and it increases as the size of the refrigeration system increases. In case of the vapor absorption refrigeration system, the pump requires very small amount of power and it remains almost the same (or may increase slightly) even for higher capacities of refrigeration. Thus the power consumed by the vapor absorption refrigeration system is much more than that required by the vapor compression system. 4) Type of energy required: The vapor absorption system runs mainly on the waste or the extra heat in the plant. Thus one can utilize the extra steam from the boiler, or generate extra steam for the purpose and also use the hot available water. Similarly the waste heat from the diesel engine, hot water from the solar water heater, etc. can also be utilized. In case of the vapor compression refrigeration system, the compressor can be run by electric power supply only; no other types of energy can be utilized in these systems. 5) Running cost: The vapor compression refrigeration system can run only on electric power, and they require large amount of power. These days the electric power has become very expensive, hence the running cost of the vapor compression refrigeration system is very high. In case of the absorption refrigeration system only small pump requires electric power and it is quite low. In most of the process Page | 22
industries, where the absorption refrigeration is used, there is some extra steam available from the boiler, which can be used for running the system. Thus in absorption refrigeration system no extra power in the pure electric form is required and the energy that would have otherwise gone wasted is utilized in the plant. Thus the running cost of the absorption refrigeration system is much lesser than the vapor compression system. 6) Foundations required and noise: The compressor of the vapor compression system is operated at very high speeds and it makes lots of vibrations and noise. It also requires very strong foundation so that it can remain intact under vibrations and high pressures of the refrigerant. In the absorption refrigeration system there are no major moving parts hence they don’t vibrate, don’t make noise and also don’t require heavy foundations. The absorption refrigeration systems operate silently. 7) Maintenance: Compressor is the crucial part of the vapor compression cycle, and it has number of moving parts. It is very important to do the thorough lubrication of the compressor and also keep checking it regularly for any defects. The compressor also requires changing of the piston, piston rings, cylinder liner etc. from time-totime. Thus the vapor compression system requires lots of maintenance. Failure of compressor can be very expensive at times as the suction and the discharge valve of the compressor are very expensive. Even the motor of the compressor is very heavy and expensive. The compressor also requires cooling, for which special pump is required to pump the water from the cooling tower to the compressor. Since there are number of moving parts of the compressor that move at very fast speed some or the other failure occurs regularly. In the absorption refrigeration system the only moving part is the small pump that fails rarely. Thus the maintenance required by the vapor compression system is much more than that required by the vapor absorption system. 8) Capacity control of the system: In the vapor compression cycle the capacity control of the system is done from the compressor and in most of the cases stepwise capacity control is obtained. In case of the absorption refrigeration system it is possible to obtain stepless capacity control and zero capacity when there is no load on the system. Though these days compressors with stepless capacity control are available, but they will consume lots of power even if there is zero load on the refrigeration system. In absorption system, when there is zero load the power consumption is almost zero. 9) Type of refrigerant used and its cost: In ammonia-water absorption refrigeration system, ammonia is used as the refrigerant, which is easily and cheaply available. In lithium bromide system, water is used as the refrigerant, which is also available
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cheaply and easily. In case of the vapor compression refrigeration system halocarbons are used as the refrigerants, which are very expensive. 10) Leakage of the refrigerant: In the absorption refrigeration system there are no (or very few) leakages of the refrigerant and the refrigerant itself is very cheap. Thus there are almost zero refrigerant recharging costs. In case of the vapor compression systems there are lots of leakages of the refrigerant thus regular recharge of the refrigerant is required which is very expensive. 11) Greenhouse effect: Most of the halocarbon refrigerants used in the compression refrigeration system produces greenhouse effect. As per the Montreal Protocol, their use has to stop completely by the year 2020. In the absorption refrigeration system no refrigerant produces the greenhouse effect, so their use won’t be stopped in future.
5.2 Disadvantages of Absorption Refrigeration over Vapor Compression Refrigeration Cycle 1) Initial capital cost: Though the running cost of the absorption refrigeration system is much lesser than the vapor compression system, its initial capital cost is much higher. 2) Corrosive nature of lithium bromide: In the lithium bromide absorption refrigeration system, lithium bromide is corrosive in nature, which reduces the overall life of the system. In case of the ammonia system, ammonia is corrosive to copper. In the vapor compression system copper is used with the halocarbon refrigerants and they are quite safe thus ensuring long life of the refrigeration system. As such the vapor compression system with reciprocating or centrifugal compressor has longer life than the lithium bromide absorption refrigeration system. 3) Low working pressures: The working pressures of the absorption refrigeration cycle are very low. In case of the lithium bromide system these pressures are so low that even the expansion valve is not required since the drop in pressure of the refrigerant due to its flow is good enough to produce its expansion. Due to this the refrigeration system should be sealed thoroughly so that no atmospheric gases would enter the refrigeration system. As such the system of the compression refrigeration should also be packed tightly, but this is to prevent the leakage of the refrigerant to the atmosphere. 4) Coefficient of Performance (COP): The coefficient of performance of the absorption refrigeration systems is very low compared to the vapor compression systems. For instance, the COP of the two stage lithium bromide system is about 1.1, while that of the vapor compression system used for the air conditioning applications it is about 4 to 5. Thus the absorption refrigeration system becomes Page | 24
competitive only if the ratio of the electricity to fuel (oil, gas or coal used to generate the steam in the boiler) becomes more than four. If this ratio is lesser there are chances that excess fuel would be required to generate the steam. However, if there is excess steam in the industry, this ratio may not be given importance. 5) Higher heat rejection: In the absorption refrigeration heat has to be rejected from number of parts like condenser, absorber, analyzer, rectifier etc. thus heat rejection factor for absorption refrigeration system is high and it can be around 2.5. In the compression refrigeration system the heat is given up only from the condenser, so it heat rejection factor is small, which is about 1.2. Thus the cooling tower and pump capacities for pumping the cooling water have to be higher in case of the absorption refrigeration system, which leads to increase in the running cost of the system.
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Chapter 6
Case Study
Introduction Let us consider an engine of an automobile on which the vapour absorption refrigeration system is to be implemented. In this chapter we discuss about case study done on Hindustan Motors Ambassador model engine. From the heat produced from combustion of fuel only 30% (approx) of heat is converted into useful mechanical work. The remaining heat energy is wasted into the atmosphere in the form of the cooling water and exhaust gases carry away the maximum amount of heat from the engine, around 60% (approx). This heat is called the low grade energy of the engine.
6.1 Engine parameters The IC engine based on which the calculations are done is • • • • • • • •
Make - Hindustan Motors Model - Ambassador No of cylinders, n = 4. Power, P = 60 bhp at 2000 rpm. Capacity, V = 1717cc. No of strokes = 4. Fuel used = diesel. Air-fuel ratio, A/F =15:1
6.2 Waste Heat Of The Engine The main two areas through which the heat is exhausted into the atmosphere from the engine are the cooling water and the exhaust gases. It is necessary to calculate the amount of heat energy carried away by the exhaust gases and the cooling water. 6.2.1 Exhaust gas heat Volumetric efficiency of the engine, Evol = 70%. Rated speed, N = 2000 rpm Mass flow rate of air into the cylinder, ma = VN Evol /2 = 0.001717x2000x0.7/2 ma =0.02m3/s. Page | 26
Mass flow rate of fuel, mf = ma/(A/F ratio) = 0.02/15 mf =0.001335 kg/sec Total mass flow rate of exhaust gas, me= ma+mf = 0.021335 kg/s. Specific heat at constant volume of exhaust gas Cpe= l kj/kgk. Temperature available at the engine exhaust, te= 300°C. Temperature of the ambient air, ta = 40°C Heat available at exhaust pipe Qe = meCpe (te-ta) = 0.021335xlx(300-40) Qe=5.5kW 6.2.2 Cooling water heat Temperature of water entering the cooling water jacket, tcj=50°C. Temperature of water exiting the cooling water jacket, tco=80°C. Mass flow rate of water for a 4 cylinder diesel engine, mw=0.1 kg/s. Specific heat of water, Cpw=4.18 kj/kg-k Heat carried away by cooling water Qw = mwCpw(tco-tcj) = 0.1x4.18x(80-50) Qw= 12.54 kW.
6.3 Final Value Heat available at exhaust gas = 5.5 kW Heat carried by cooling water = 12.54 kW This heat can be utilized in vapour absorption refrigeration system for air conditioning of car.
6.4 Testing of the Prototype Nissan1400 A rough energy balance of the available energy in the combustion of fuel in a motor car engine shows that one third is converted into shaft work, one third is lost at the radiator and one third is wasted as heat at the exhaust system even for a relative Page | 27
small car-engine, such as for the Nissan1400, 15 kW of heat energy can be utilised from the exhaust gas. This heat is enough to power an absorption refrigeration system to produce a refrig- eration capacity of 5 kW. The standard working fluids for absorption refrigeration plants are water and ammonia, Lithium-Bromide and water, and Tetra-Ethylene Glycol Dimethyl-Ether (TEG-DME) and R-22. Of these combinations, water and ammonia is no threat to the environment and is preferable for this application for reasons listed below: •
• •
Water has the highest latent heat of vaporization at 00 C but its combination with LiBr can cause crystallization due to unstable temperature conditions caused by fluctuations of exhaust gases flow rates. Freon-22 is a well known refrigerant, but in combination with its absorbent the plant becomes uneconomical. Ammonia is highly soluble in water and this ensures low solution circulation rates. Both constituents are obtainable at minimal cost. The choice of Ammonia-water combination is not made without considering certain disadvantages: ammonia attacks copper and its alloys when it has been hydrated. Therefore, all components are made from mild steel or stainless steel.
Preliminary analysis showed that an absorption refrigeration plant with a 2 kW cooling load at 00 C and with water as a secondary fluid, is more than sufficient to air-condition the passenger space of the NISSAN 1400 truck. This cooling load is calculated from three difference heat sources: 1. Transmission of heat through the car body structure QT = 0.19 kW 2. Solar heat gain through the wind-screen and side windows QR = 0.44 kW 3. Internal heat gains QI = 0.50 kW Total QTOT = 1.13 kW Prior to installing the components in the car, the absorption plant is assembled for a laboratory test. The exhaust gas from the engine is simulated by the combustion of propane through a gas burner. The air-cooled condenser and absorber are subjected to an air draft created by air-blowers maintaining the condensate and the strong solution in the absorber at an average temperature of 35 0 C. The plant is subjected to a variation of expansion valve settings1 and its cooling capacity is established by measuring the temperature drop and rate of water circulation through the evaporator. The inlet to the evaporator is between -20 C and 00 C.
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Under these conditions, the load variation is shown in Figure 6.1, where a maximum of 2 kW cooling is obtained.
Figure 6.1 Load variation[2]
6.4.1Road test The road-test results are collected in two groups, (vehicle in motion): 1. Before opening the expansion valve 2. After opening the expansion valve. These results are depicted in the graph of Figure 5, where a drop in the temperature in the passenger’s space is clearly indicated. Table 6.1 contains the averaged results collected from the absorption plant during the entire duration of the road tests. These averaged values serve to plot the enthalpy-concentration performance chart for the plant as shown in Figure 6.3. The construction of the absorption cycle on the enthalpy-concentration diagram is according to established theory of absorption refrigeration machines. Table 6.1 Results
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With reference to the data from Figure 6.2 and Table 6.1 the diagram of Figure 6.3 is constructed and analyzed as follows: The 3bar low pressure and the 50 C evaporator’s temperature, establish points ‘5L’ and ‘5V’. At the generator and condenser, the data is not sufficient for a full evaluation. However, with the simplification that there is only a reflux condenser, instead of a distillation column to purify the generator’s vapours, point ‘1’ can be considered as the vapour in equilibrium with the generator’s solution, point ‘A’. This solution boils at 1200 C (Table 6.1) and the line A-1 is the isotherm between the liquid and its vapour. This vapour becomes the condensate at 8bar pressure and this is depicted by point ‘E’. The temperature curve through point ‘E’ is 28.4 oC, which is in agreement with the average ambient cooling temperature, about 25oC (see Figure 6.2).
Figure 6.2
The shaded and the clear areas indicate the temperature conditions before and during the road-tests respectively[2]
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Figure 6.3 Averaged values for the enthalpy-concentration performance chart of the plant[2]
The vertical line 1-E indicates the concentration of the refrigerant, y= 0.737.The line 1-E intersects the isotherm 5L-5V at point ‘D’ and the difference in enthalpy h D-hE is the Refrigeration Effect, RE=188.7kJ/kg. The absorber, at point ‘B’, is at conditions of 3 bar pressure and 28.4 oC temperature. This temperature is the same as that of the condenser at point ‘E’, because both are cooled by the same medium.
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The vertical line through point ‘B’ indicates the concentration of the strong solution, XST = 0.475. The vertical line through point ‘A’ indicates the concentration of the weak solution, XWE = 0.170. The COP value is calculated as the ratio of refrigeration effect to the generator’s heat.
The generator’s heat, however, can be reduced by the use of a regenerator, or a heat exchanger. During the road-test, there was no provision made to measure the temperature of the solution at the exit of the heat exchanger. Therefore, the following calculation of the COP is only an indication and not the real condition. From Figure 6.3
A solution heat exchanger would bring the strong solution to a higher temperature than that of the absorber, (let’s say to 54oC, point ‘10’). This would reflect to a heat saving in the generator, equivalent to the enthalpy difference h K-hC. The new COP will be in this case is
6.5 Conclusions The theoretical analysis, is verified by both laboratory and road tests through the results obtained. This work results from a prototype which will have to be improved for further development. The claim that is made from this work is that it has shown the feasibility of such a system in a positive frame. It can be concluded that: 1. In the exhaust gases of motor vehicles, there is enough heat energy that can be utilised to power an air-conditioning system. Therefore, if air-conditioning is achieved without using the engine’s mechanical output, there will be a net reduction in fuel consumption and emissions. 2. Once a secondary fluid such as water or glycol is used, the aqua-ammonia combination appears to be a good candidate as a working fluid for an absorption car air-conditioning system. This minimizes any potential hazard to the passengers. Page | 32
3. The low COP value is an indication that improvements to the cycle are necessary. A high purity refrigerant would give a higher refrigeration effect, while the incorporation of a solution heat exchanger would reduce the input heat to the generator. The present system has both a reflux condenser and a heat exchanger. However, the reflux condenser is proved inadequate to provide high purity of the refrigerant and needs to be re-addressed. The evaluation of the COP, with and without the heat exchanger also proves that unless there is a high purity refrigerant, the effect of the heat exchanger to the generator’s heat is small.
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Chapter-7
Indian Scenario In air conditioning of automobile the vapour compression refrigeration system causes the loss in economy level of the order of 1 to 1.5 km/liter can occur due to the use A/C. In India there are no automobile absorption refrigeration system which is working on the exhaust heat of the engine because following reasons. 1. Initial capital cost -Though the running cost of the absorption refrigeration system is much lesser than the vapor compression system, its initial capital cost is much higher. 2. Size -The size of this system is more than vcrs. Mainly in India there is small size of cars. The space occupied by generator is main limiting factor. 3. Coefficient of Performance (COP)- The coefficient of performance of the absorption refrigeration systems is very low compared to the vapor compression systems. 4. Lack of cooling potential in the exhaust gases at low and idling speeds. In India there is laboratory test done on this system in automobile air conditioning at SVNIT Surat by A. C. Deshpande which is currently working as a Jr. Research Fellow at SVNIT, Surat under BARC. Another college where laboratory test is done is Jawaharlal Darda Institute Of Engineering & Technology, Yavatmal. These factors affect the use of this system in automobile but in other areas like power plants and other industries where waste heat can be utilized by installing vapour absorption refrigeration system. In India Thermax Ltd working on these systems. This uses waste heat from steam, solar power, flue gases, and hot water.This serving for Bhilai steel plant Raurkela steel plant Reliance industries ltd Gas authority of India ltd.
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Products are Steam Driven Vapour Absorption MachineCapacities: From 50 to 2000 TR Steam pressure: From 0.6 to 3.5 Kg/cm² (g) Chilled water temperature: Up to 3.5ºC (0ºC for brine) Heat source: Steam
Hot Water Driven Vapour Absorption Machine Capacities: From 10 to 2000 TR Chilled water temperature: Up to 3.5ºC (0ºC for brine) Water temperature: From 75ºC to 200ºC
Exhaust Vapour Absorption MachineFrom 50 to 2000 TR, chilled water temperature Up to 3.5ºC (0ºC for brine)
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Chapter-8
World Scenario Vapour absorption refrigeration system based on exhaust heat (or waste heat from solar) is not widely used due to its limitations.
Refrigerating effect will be reduced or will be difficult to produce should the vehicle be at rest or in a very slow moving traffic condition. The refrigerating effect produced using a Vapour Absorption Refrigeration System is less compared to a Vapour compression Refrigeration System.
But still Toyota developed solar ac based on absorption refrigeration in his car in 2010 in model Toyota Prius. Nowhere is the greenhouse effect more noticeable than inside a car on a hot day. But the new Toyota Prius comes with new green technologies including cooling fans run by optional solar panels.The Prius includes a solar panel on the roof of the car, which can only provide enough power to run the ventilation system while the car is parked, to keep the interior cooler in sunny warm conditions. For the U.S. market only the Prius Two, Three, Four and Five were offered. Even when the car is off and locked, these fans whir around, so when you step back into it you don't need to crank up the power-hungry air conditioning. And the air-con system on the 2010 Prius. Nissan developed prototype in 2008 Nissan 1400 truck and the results indicate a successful prototype and encouraging prospects for future development.The developed prototype and give following results 1. In the exhaust gases of motor vehicles, there is enough heat energy that can be utilised to power an air-conditioning system. Therefore, if air-conditioning is achieved without using the engine’s mechanical output, there will be a net reduction in fuel consumption and emissions. 2. The coefficient of performance of the absorption refrigeration systems is very low compared to the vapor compression systems. The low COP value is an indication that improvements to the cycle are necessary. 3. Size -The size of this system is more than vcrs. The space occupied by generator is main limiting factor.
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Chapter-9
Future Prospects Vapour absorption refrigeration system is not widely used due to its limitations. There is need for certain developments like 1. Cop of the system – we have to improve the cop of the system. 2. Size of the Condenser, Evaporator and Generator which is reduce s the size of the system. But in future is necessary to use because of the consumption of petrol is due to use of vcrc system. A loss in economy level of the order of 1 to 1.5 km/liter can occur due to the use A/C. Day by day the price of gasoline/diesel is increasing. The source of energy is limited. Air conditioning system, compressor consumes 10% of engine output. But in container which is used for transport the goods with refrigerating system. This consume more power for providing necessary refrigeration effect. This system can be use in container where no problem for space. This system used.
The generator is design to have a capacity of 4.8kW with temperature around 90 °C and pressure of 19 bars. This component can be installed is 50 cm long, 25 cm wide and 15 cm high, which is available in containers. Amount of heat required to be rejected by the absorber to achieve good absorption process must be not less than 1739 kJ/ kg of refrigerant. Then the total heat transfer area was calculated A = 0.3978463 m 2 Which represents a tube having 6.65 meters long tube.
In automobiles there are limitations of the space so now a days these systems are not applied. But in future can be applied due to following reason if the system space can be reduces. Also in bus and containers there is solar absorption systems can be used becasued of availability of space. If there is need is more and the this system can used for some capacity and other requirements can fulfill by vapour absorption refrigeration system. This combination can reduce the engine power consumption and utilized the exhaust heat. Other reason for using in future is
Moving parts are only in the pump,which is a small element of the system. Hence operation is smooth.
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The system can work on lower evaporator pressures also without affecting the COP. No effect of reducing the load on performance. We can increase economy level of the order of 1 to 1.5 km/liter. Foundations required and noise: The compressor of the vapor compression system is operated at very high speeds and it makes lots of vibrations and noise Maintenance: No need of maintenance of this system. Capacity control of the system: In absorption system, when there is zero load the power consumption is almost zero. Type of refrigerant used and its cost: In ammonia-water absorption refrigeration system, ammonia is used as the refrigerant, which is easily and cheaply available. Leakage of the refrigerant: In the absorption refrigeration system there are no (or very few) leakages of the refrigerant and the refrigerant itself is very cheap. Thus there are almost zero refrigerant recharging costs. In case of the vapor compression systems there are lots of leakages of the refrigerant thus regular recharge of the refrigerant is required which is very expensive. Greenhouse effect: The existing system sffect the environment Most of the halocarbon refrigerants used in the compression refrigeration system produces greenhouse effect. As per the Montreal Protocol, their use has to stop completely by the year 2020. In the absorption refrigeration system no refrigerant produces the greenhouse effect, so their use won’t be stopped in future.
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Chapter-10
Conclusion Experimental study of an aqua-ammonia absorption system used for automobile air conditioning system, this system using the exhaust waste heat of an internal combustion diesel engine as energy source. The energy availability that can be used in the generator and the effect of the system on engine performance, exhaust emissions, auto air conditioning performance and fuel economy are evaluated. Because automotive air conditioning is one the most equipment that heavily uses CFC compounds and the leakage of CFCs from such air conditioners impact on the environment. The main purpose of this investigation to explore the feasibility of using waste energy to design the absorber and generation since these components are the most important components of absorption and they are directly influence the performance of the whole system. It has been found that the aqua -ammonia concentration effect the cooling capacity. The estimated cooling load for the automobile found to be within acceptable ranges which are about 1.37 ton refrigeration. The obtained results show that the coefficient of performance (COP) values directly proportional with increasing generator and evaporator temperatures but decrease with increasing condenser and absorber temperatures. Measured values for generator, absorber, and evaporator and condenser temperature were recorded and the coefficient of performance of the system varied between 0.85 and 1.04. The main components of the absorption cycle were designed and fabricated for optimal performance and could be rapidly transfer to the industry, The system was found to be applicable and ready to produce the required conditioning effect without any additional load to the engine. The proposed system decreases vehicle operating costs and environmental pollution caused by the heating system as well as causing a lower global warming. The following conclusion can be drawn
Performance of auto air conditioner using exhaust waste energy from diesel engine has been carried out in this investigation. It is evident that COP strongly depends on working conditions such as generator, absorber, condenser and evaporating temperature. The aqua-ammonia vapour absorption automobile air conditioner is an economically attractive concept for utilizing exhaust waste heat because most of the energy input comes from the heat available in the exhaust gases, with only small electric power used to operate the pump. The engine exhaust gas was confirmed as a potential power source for absorption automobile air conditioner system. In other words, the absorption refrigeration system may
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be able to take advantage of the exhaust gas power availability and provide the cooling capacity required for automotive air conditioning. Overall, carbon monoxide emission was decreased when the absorption refrigeration system was installed in the exhaust gas. So, changes in exhaust components concentration were a consequence of the major modifications in the exhaust system. The absorption cycle has the economic advantage of having few high precision components, thus reducing manufacturing costs. The low efficiency, however, is a negative economic factor. Ammonia Absorption cycle, should be considered as a viable alternative to mechanical vapor compression cycle. Appreciable cooling load reduction can be realized by modification on the automobile body and the door and windows design. With flexibility in operation, absence of compressor noise, very low maintenance and high reliability. The waste heat energy available in exhaust gas is directly proportional to the engine speed and exhaustgas flow rates. Feasibility study should made to decide the unit’s chances to be produced on commercial scales. Also, applying this project practically in Jordan, because it has many advantages from the pollution and economic point of view.
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References
1. International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 National Conference on Emerging Trends in Engineering & Technology (VNCET-30 Mar’12) V.D.Patel , A.J.Chaudhari, R.D.Jilte , Theoretical and Experimental Evaluation of Vapour Absorption Refrigeration System,2012 2. Journal of Energy in Southern Africa, G Vicatos,J Gryzagoridis, A car airconditioning system based on an absorption refrigeration cycle using energy from exhaust gas of an internal combustion engine, 2008 3. International Journal of Modern Engineering Research (IJMER) ,Manu.S, T.K.Chandrashekar, Theoritical Model of Absorber for Miniature LiBr-H2o Vapor Absorption Refrigeration System , 2012 4. Energy procedi, aKhaled AlQdah , Sameh Alsaqoor , Assem Al-Jarrah , Design and Fabrication of Auto Air Conditioner Generator Utilizing Exhaust Waste Energy from a Diesel Engine ,2011 5. Second International Conference on Emerging Trends in Engineering and Technology, ICETET-09, A C Deshpande, R M Pillai,Adsorption AirConditioning (AdAC) for Automobiles Using Waste Heat Recovered from Exhaust Gases ,2009 6. Zhong Ji-Xiang, Research on A Novel Air-condition System driven by combination of Exhaust Heat of Engine and Solar Energy,2009 7. The 2nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”, 21-23 November 2006, Bangkok, Thailand, Shah Alam, A Proposed Model for Utilizing Exhaust Heat to run Automobile Air-conditioner, The 2nd Joint International Conference on SEE,2006 8. Khaled S. AlQdah Tafila Technical University Tafila, Jordan, Performance and Evaluation of Aqua Ammonia Auto Air Conditioner System Using Exhaust Waste Energy,2011 9. Nahla Bouaziz, Ridha Ben Iffa and Lakhdar kairouani, Performance of a water ammonia absorption system operating at three pressure levels, 2011
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10. R.H.L. Eichhorn - Eindhoven University of Technology , Waste Energy Driven Air Conditioning System (WEDACS), 2009. 11. ASHARE Hand book, 2008
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Bibliography Impact of Vehicle Air-Conditioning on Fuel Economy, Tailpipe Emissions, and Electric Vehicle Range http://www.nrel.gov/docs/fy00osti/28960.pdf Eco-friendly cooling with absorption chillers http://www.thermaxindia.com/Live-at-Thermax/Eco-friendlycooling-with-absorption-chillers.aspx International Journal Of Energy Research, exergy calculation of lithium bromide–water solution and its application in the exergetic evaluation of absorption refrigeration systems LiBr-H2O, Reynaldo Palacios-Berec, 2010 Adsorption Air-Conditioning for Containerships and Vehicles Metrans Report 00-7, Craig Christy and Reza Toossi California State University ,Long Beach,August 05, 2004
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Annexures Adsorption air conditioning working http://www.youtube.com/watch?v=aMF-STB18Xo 2010 Prius: Solar Powered Ventilation System http://www.youtube.com/watch?v=CchHIy7JgvA Absorption Chiller Animation http://www.youtube.com/watch?v=vHLKKd04hfk
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