ELECTROLUX REFRIGERATION USING SOLAR HEAT
PROJECT REPORT Submitted in partial fulfillment of the requirements for the award of the Degree of Bachelor of Technology in Mechanical Engineering to the University of Kerala
Submitted by
KIRAN P R PADMAKUMAR R PRATHEESH S BABU RAMAN RAJENDRAN
Department of Mechanical Engineering College of Engineering, Thiruvananthapuram – 16 April, 2009
DEPARTMENT OF MECHANICAL ENGINEERING COLLEGE OF ENGINEERING, TRIVANDRUM – 16
CERTIFICATE
This is to certify that the project report entitled ‘ Electrolux Electrolux refrigeration refrigeration using solar heat’ submitted by KIRAN P R, PADMAKUMAR R, PRATHEESH S BABU and RAMAN RAJENDRAN to the University of Kerala in partial fulfillment of the requirement for the
award of the Degree of Bachelor of Technology in Mechanical Engineering is a bonafide work carried out under our guidance and supervision. The contents of this work in full or parts have not been submitted in any other institute or University for the award of any degree or diploma.
Dr. N. Asok Kumar Assistant Professor Dept. of Mechanical Engineering College of Engineering Trivandrum
Dr. B Anil Professor & Head Dept. of Mechanical Engineering College of Engineering Trivandrum
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ACKNOWLEDGEMENT ---------------------------------------------------------------------------------
ACKNOWLEDGEMENTS
We would like to take this opportunity to extend our gratitude to our guide Dr N. Asok Kumar for his timely advice and inputs without which we would not have been able to complete this project. The several sessions we spent with him on finding new paths regarding the direction of the project was quite educational. Any expression of gratitude cannot be deemed complete without mentioning the role played by our Head of the Department, Dr. B. Anil for giving us total freedom to make the maximum utilization of the the depa depart rtme ment ntal al reso resour urce ces. s.
We woul would d also also like like to expr expres esss our gratit gratitud udee to the
technicians at Super cold refrigeration system, Mr. Dilakan, Mr. John M.G engineer at Thermax India Ltd and Steve Hammerling, Assistant Manager of Research & Technical Services American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.(ASHRAE) for technical assistance provided during the course o f the project. We also thank our classmates and seniors for their suggestions especially our seniors Sabu Sabu V.G, V.G, Shibu Shibu K.R, K.R, Shome Shome V.S, V.S, Santho Santhosh sh K, Roby Roby Sebast Sebastian ian for valuabl valuablee ideas ideas impart imparted ed during during the format formation ion of this this projec project. t. To summar summarize, ize, it has been quite quite an experience and we extend our sincere gratitude to all those whom we have missed, for positive comments they put in and cooperation they all extended were vital for the successful completion of this project.
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REFRIGERATOR ---------------------------------------------------------------------------------
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CONTENTS ---------------------------------------------------------------------------------
CONTENTS
CHAPTER
PARTICULAR
PAGE No.
ACKNOWLEDGEMENT
1. SYNOPSIS 2. INTRODUCTION 3. REVIEW OF LITERATURE 4. BATTERY 5. THERMO ELECTRIC ZIP COOLER 6. CONDENSER 7. D.C BLOWER 8. WORKING PRINCIPLE 9. LIST OF MATERIALS 10. COST ESTIMATION 11. ADVANTAGES AND DISADVANTAGES 12. APPLICATIONS 13. CONCLUSION
APPENDIX BIBLIOGRAPHY PHOTOGRAPHY
ACKNOWLEDGEMENTS
We would like to take this opportunity to extend our gratitude to our guide Dr N. Asok Kumar for his timely advice and inputs without which we would not have been able to complete this project. The several sessions we spent with him on finding new paths regarding the direction of the project was quite educational. Any expression of gratitude cannot be deemed complete without mentioning the role played by our Head of the Department, Dr. B. Anil for giving us total freedom to make the maximum utilization of the the depa depart rtme ment ntal al reso resour urce ces. s.
We woul would d also also like like to expr expres esss our gratit gratitud udee to the
technicians at Super cold refrigeration system, Mr. Dilakan, Mr. John M.G engineer at Thermax India Ltd and Steve Hammerling, Assistant Manager of Research & Technical Services American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.(ASHRAE) for technical assistance provided during the course o f the project. We also thank our classmates and seniors for their suggestions especially our seniors Sabu Sabu V.G, V.G, Shibu Shibu K.R, K.R, Shome Shome V.S, V.S, Santho Santhosh sh K, Roby Roby Sebast Sebastian ian for valuabl valuablee ideas ideas impart imparted ed during during the format formation ion of this this projec project. t. To summar summarize, ize, it has been quite quite an experience and we extend our sincere gratitude to all those whom we have missed, for positive comments they put in and cooperation they all extended were vital for the successful completion of this project.
ABSTRACT
The project consists of an Electrolux refrigeration system using solar energy as input. This system was actually invented by two Swedish engineers, Von Platen and Carl Munters. The idea was first developed by the ‘Electrolux Company, of Luton, England, hence hence the name name ‘Elect ‘Electrol rolux ux refrig refrigera erati tion on syste system’. m’. The princi principle ple behind behind Electr Electrolu olux x refrigeration is that it uses three gases to accomplish its cooling effect namely ammonia (refrigerant) water (absorbent) and hydrogen. Ammonia is used as the refrigerant as it is easily easily availa available ble,, enviro environme nmenta ntally lly frien friendly dly and can produce produce a better better cooling cooling effect effect.. Hydrogen is used to reduce the partial pressure of ammonia vapour in the evaporator chamber so that more ammonia evaporates yielding more cooling effect. Heat input is required at the generator where aqua ammonia is heated to get ammonia vapors. In this project, an experimental setup for Electrolux refrigeration is made using solar energy to supply input heat. A double involute cusp shaped plate is used as the solar collector. Two 1” diameter pipes welded together is placed at the focal point of the involute cusp which acts as the generator pipes. Solar energy is concentrated to these pipes by the solar collector, heating the aqua ammonia solution. The rest of the system is unaltered.
CONTENTS
INTRODUCTION
If the solar energy possesses the advantage to be "clean", free and renewable, this last is probably, considered like an adapted potential solution, that answers in even time at a economi economicc preocc preoccupa upatio tion n and ecologi ecological cal proble problems. ms. Among Among the main main done curren currently tly research is the use of this free source to make operate system of refrigeration. Since among the domestic appliances used today, refrigerators consume a considerable amount of energy, using solar energy to run refrigerator is of great practical relevance nowadays.
The diffusion absorption absorption refrigerator refrigerator cycle invented in the 1920s is based on ammonia ammonia (refrigerant) and water (absorbent) as the working fluids together with hydrogen as an auxiliary inert gas. Since there are no moving parts in the unit, the diffusion absorption refrigerator system is both quiet and reliable. The system is, therefore, often used in hotel rooms and offices. The absorption diffusion refrigerating machine is designed according to the operati operation on princi principle ple of the refrig refrigera eratin ting g machin machinee mono mono pressu pressure re invent invented ed by PLATERN and MUNTER. This machine uses three operation fluids, water (absorbent), the ammonia (refrigerant) and hydrogen as an inert gas used in order to maintain the total pressure constant
LITERATURE REVIEW
1.
VAPOR ABSORPTION REFRIGERATION IN ROAD TRANSPORT
VEHICLES, J. Energy Engrg. Volume 125, Issue 2, pp. 48-58 (August 1999) Abstract
This study includes an experimental investigation into the use of vapor absorption refrigeration (VAR) systems in road transport vehicles using the waste heat in the exhaust gases of the main propulsion unit as the energy source. This would provide an alternative to the conventional vapor compression refrigeration system and its associated internal combustion engine. The performance of a VAR system fired by natural gas is compared with that of the same system driven by engine exhaust gases. This showed that the exhaust-gas-driven system produced the same performance characteristics as the gasfired system. It also suggested that, with careful design, inserting the VAR system generator into the main engine exhaust system need not impair the performance of the vehicle propulsion unit. A comparison of the capital and running costs of the conventional and proposed alternative system is made.
2.
DESIGN AND SIMULATION OF AN ABSORPTION DIFFUSION SOLAR REFRIGERATION UNIT by B. Chaouachi,
S. Gabsi (American Journal of
Applied Sciences , Feb, 2007) Abstract
The purpose of this study was the design and the simulation of an absorption diffusion refrigerator using solar as source of energy, for domestic use. The design holds account about the climatic conditions and the unit cost due to technical constraints imposed by the technology of the various components of the installation such as the solar generator, the condenser, the absorber and the evaporator. Mass and energy conservation equations
were developed for each component of the cycle and solved numerically. The obtained results showed, that the new designed mono pressure absorption cycle of ammonia was suitable well for the cold production by means of the solar energy and that with a simple plate collector we can reach a power, of the order of 900 watts sufficient for domestic use.
3
INTERNATIONAL JOURNAL OF REFRIGERATION (Volume 31, Issue 4,
June 2008, Pages 545-551 Refrigeration with Ammonia and Hydrocarbons) by Andy Pearson, Star Refrigeration Ltd., Glasgow G46 8JW, UK,
Abstract
Ammonia is widely used as a refrigerant in industrial systems for food refrigeration, distribution warehousing and process cooling. It has more recently been proposed for use in applications such as water chilling for air-conditioning systems but has not yet received widespread acceptance in this field. This review paper assesses the reasons why ammonia is so popular in industrial systems, the reasons why it is deemed less suitable for other applications and the possible benefits at local, national and international levels that might be gained by more general acceptance of ammonia as a refrigerant. The paper also considers other possible applications which might benefit from the use of ammonia as refrigerant.
4
UNDERSTANDING SOLAR ENERGY: A GENERAL OVERVIEW by
Mr. Ajay Prakash Shrivastava, President, Solar Energy Society of India (SESI).
Abstract
India is one of the few countries with long days and plenty of sunshine. This zone, having abundant solar energy available, is suitable for harnessing solar energy for a number of applications. In areas with similar intensity of solar radiation, solar energy could be easily harnessed. Solar thermal energy is being used in India for heating water for both industrial and domestic purposes. A 140 MW integrated solar power plant is to be set up in Jodhpur but the initial expense incurred is still very high. India is getting a solar irradiation of 500W/m2.
5
UNDERSTANDING SOLAR CONCENTRATORS by George M. Kaplan,
VITA Volunteer, President of KAPL Associates. Abstract
Solar thermal technology is concerned principally with the utilization of solar energy by converting it to heat. In the concentrating type of solar collector, solar energy is collected and concentrated so that higher temperatures can be obtained; the limit is the surface temperature of the sun.. Similarly, overall efficiency of energy collection, concentration, and retention, as it relates to energy cost, imposes a practical limit on temperature capability.. The cusp collector whose surface geometry is the locus of the position of the end of a string as it is unwrapped from a pipe can provide a modest concentration suitable to boil water.
6
LOW REFLECTION LOSS CUSP LIKE REFLECTOR FOR SOLAR ENERGY COLLECTOR by Raymond H.Lambert, Generic electric company, Philadelphia. (US patent 4246891, Jan 27 1981)
Abstract
There is disclosed the manner in which a reflector for a solar energy collector is designed. The absorber is a right circular cylinder and is contained in an evacuated glass shroud. The glass shroud prevents the use of the reflector design technique of the prior art, and instead calculations are performed as if an absorber having a smaller diameter were to be used.
7
REFLECTOR WITH CURVED DUAL INVOLUTE SURFACES by Fred A
Plofchan (US Patent 4843521, Jun 27 1989)
Abstract
A wide angle flash tube reflector has dual involute surfaces thereon intersecting at a cusp and bent in the horizontal to intercept light from a light source adjacent the cusp and to reflect such light in a dispersion pattern that spreads the flash coverage to match extended light coverages of lenses from a normal focal length to extreme wide angle. One light source is in the form of a bent tube having adjustable positioned cathode and anode electrodes for varying the length of a plasma arc to control the extent of the dispersion pattern reflected from the dual involute surfaces.
PROJECT OUTLINE
When we started with our project, we were planning to utilize the nonconventional energy resources like solar energy for domestic purposes. While considering the power utilization of various domestic appliances, by knowing that a major amount of power is drawn by refrigerators, we planned to make use of solar energy to drive
refrigerators
which will be more economical with less wastage of electrical power. Mostly used refrigerator systems are vapour absorption and vapour compression of which vapour absorption system is more suitable when heat is used as the energy input. Our studies about the vapour absorption system led to the conclusion that Electrolux refrigeration system is best suitable for domestic purpose as it consumes less energy. Since the Electrolux system uses no pump for its working, the only energy input is in the form of heat at the generator pipe. An Electrolux system also called Platen-Munters system uses three fluids for its operation viz Ammonia, Water and Hydrogen. Hence the system is also called Three Fluid System.
We got an old Electrolux refrigeration system from the dump yard of the heat engines lab in our college. We inspected the system with the help of a professional fridge mechanic and came to a conclusion that the existing system cannot be pressurized as its piping was totally damaged. We came to know that similar system is used as mini bar in star hotels. We managed to get an obsolete Electrolux refrigerator from Leela Kempinski Hotel, Kovalam.
Our next aim was to modify the existing system so that its running cost is zero. For this, we decided to modify the existing system by replacing the heating unit with a solar heating device (solar collector).
Experiments so far conducted show that for effective liberation of ammonia vapour from ammonium hydroxide solution, the temperature should be above 88oC. After lot of studies about various solar concentrating devices, it was found that the concentration ratio of involute cusp shaped collector is comparatively high with a wide acceptance range. Besides this, the collector has an advantage that it is non-tracking. The reflecting surface was coated with mirror plastic in order to increase the reflectivity.
The generator pipe is made of two 1” MS pipe welded together. Holes were provided for pressure gauge valve, inlet, exit and ammonia charging at appropriate positions.
The next step was to fix the position of the collector. Since the fluid circulation in Electrolux system is completely controlled by buoyancy change and gravity, the position of the generator is crucial. Thus the collector-generator assembly is fixed at the bottom of the fridge between the absorber tank and the vapour lift tube.
The charging of ammonia was done by making ammonium hydroxide solution of adequate concentration. Hydrogen was charged through the hydrogen charging line provided at the absorber tank.
REFRIGERATION
Refrigeration is the process of removing heat from an enclosed space, or from a substance, and moving it to a place where it is unobjectionable. The primary purpose of
refrigeration is lowering the temperature of the enclosed space or substance and then maintaining that lower temperature. The term cooling refers generally to any natural or artificial process by which heat is dissipated. The process of artificially producing extreme cold temperatures is referred to as cryogenics.
Cold is the absence of heat, hence in order to decrease a temperature, one "removes heat", rather than "adding cold." In order to satisfy the Second Law of Thermodynamics, some form of work must be performed to accomplish this. This work is traditionally done by mechanical work but can also be done by magnetism, laser or other means.
The first known method of artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in Scotland in 1756. Cullen used a pump to create a partial vacuum over a container of diethyl ether, which then boiled, absorbing heat from the surrounding air. The experiment even created a small amount of ice, but had no practical application at that time.
In 1805, American inventor Oliver Evans designed but never built a refrigeration system based on the vapor-compression refrigeration cycle rather than chemical solutions or volatile liquids such as ethyl ether.
In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low temperatures.
First refrigeration systems
The first known method of artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in Scotland in 1756. Cullen used a pump to create a partial vacuum over a container of diethyl ether, which then boiled, absorbing heat from the surrounding air. The experiment even created a small amount of ice, but had no practical application at that time. In 1805, American inventor Oliver Evans designed but never built a refrigeration system based on the vapor-compression refrigeration cycle rather than chemical solutions or volatile liquids such as ethyl ether. In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low temperatures. An American living in Great Britain, Jacob Perkins, obtained the first patent for a vapor-compression refrigeration system in 1834. Perkins built a prototype system and it actually worked, although it did not succeed commercially.
The first gas absorption refrigeration system using gaseous ammonia dissolved in water (referred to as "aqua ammonia") was developed by Ferdinand Carré of France in 1859 and patented in 1860. Due to the toxicity of ammonia, such systems were not developed for use in homes, but were used to manufacture ice for sale. In the United States, the consumer public at that time still used the ice box with ice brought in from commercial suppliers, many of whom were still harvesting ice and storing it in an icehouse.
Current applications of refrigeration
Probably the most widely-used current applications of refrigeration are for the airconditioning of private homes and public buildings, and the refrigeration of foodstuffs in
homes, restaurants and large storage warehouses. The use of refrigerators in our kitchens for the storage of fruits and vegetables has allowed us to add fresh salads to our diets year round, and to store fish and meats safely for long periods.
In commerce and manufacturing, there are many uses for refrigeration. Refrigeration is used to liquify gases like oxygen, nitrogen, propane and methane for example. In compressed air purification, it is used to condense water vapor from compressed air to reduce its moisture content. In oil refineries, chemical plants, and petrochemical plants, refrigeration is used to maintain certain processes at their required low temperatures (for example, in the alkylation of butenes and butane to produce a high octane gasoline component). Metal workers use refrigeration to temper steel and cutlery. In transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes and seagoing vessels, refrigeration is a necessity.
Dairy products are constantly in need of refrigeration, and it was only discovered in the past few decades that eggs needed to be refrigerated during shipment rather than waiting to be refrigerated after arrival at the grocery store. Meats, poultry and fish all must be kept in climate-controlled environments before being sold. Refrigeration also helps keep fruits and vegetables edible longer.
TERMS IN REFRIGERATION Coefficient of Performance (COP)
The coefficient of performance or COP, of a refrigeration system is the ratio of the heat removed from the cold reservoir to input work.
is the heat moved from the cold reservoir (to the hot reservoir).
•
•
is the work consumed by the heat pump.
Unit of refrigeration
Domestic and commercial refrigerators may be rated in kJ/s, or Btu/h of cooling. Commercial refrigerators in the US are mostly rated in tons of refrigeration, but elsewhere in kW. One ton of refrigeration capacity can freeze one short ton of water at 0 °C (32 °F) in 24 hours. Based on that:
Latent heat of ice (i.e., heat of fusion) = 333.55 kJ/kg ≈ 144 Btu/lb One short ton = 2000 lb Heat extracted = (2000)(144)/24 hr = 288000 Btu/24 hr = 12000 Btu/hr = 200 Btu/min 1 ton refrigeration = 200 Btu/min = 3.517 kJ/s = 3.517 kW
METHODS OF REFRIGERATION
Methods of refrigeration can be classified as non-cyclic, cyclic and thermoelectric.
Non-cyclic refrigeration
In these methods, refrigeration can be accomplished by melting ice or by subliming dry ice. These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable coolers.
Cyclic refrigeration
This consists of a refrigeration cycle, where heat is removed from a low-temperature space or source and rejected to a high-temperature sink with the help of external work, and its inverse, the thermodynamic power cycle. In the power cycle, heat is supplied from a high-temperature source to the engine, part of the heat being used to produce work and the rest being rejected to a low-temperature sink. This satisfies the thermodynamics. Heat naturally flows from hot to cold. Work is applied to cool a living space or storage volume by pumping heat from a lower temperature heat source into a higher temperature heat sink. Insulation is used to reduce the work and energy required to achieve and maintain a lower temperature in the cooled space. The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in 1824 as a heat engine.
The most common types of refrigeration systems use the reverse-Rankine vaporcompression refrigeration cycle although absorption heat pumps are used in a minority of applications.
Cyclic refrigeration can be classified as:
1. Vapor cycle, and 2. Gas cycle
Vapor cycle refrigeration can further be classified as:
1. Vapor compression refrigeration 2. Vapor absorption refrigeration
Vapor-compression cycle
The vapor-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems. Figure 1 provides a schematic diagram of the components of a typical vapor-compression refrigeration system.
The thermodynamics of the cycle can be analyzed on a diagram as shown in Figure 2. In this cycle, a circulating refrigerant such as Freon enters the compressor as a vapor. From point 1 to point 2, the vapor is compressed at constant entropy and exits the compressor superheated. From point 2 to point 3 and on to point 4, the superheated vapor travels through the condenser which first cools and removes the superheat and then condenses the vapor into a liquid by removing additional heat at constant pressure and temperature. Between points 4 and 5, the liquid refrigerant goes through the expansion valve (also called a throttle valve) where its pressure abruptly decreases, causing flash evaporation and auto-refrigeration of, typically, less than half of the liquid.
That results in a mixture of liquid and vapor at a lower temperature and pressure as shown at point 5. The cold liquid-vapor mixture then travels through the evaporator coil or tubes and is completely vaporized by cooling the warm air (from the space being refrigerated) being blown by a fan across the evaporator coil or tubes. The resulting
refrigerant vapor returns to the compressor inlet at point 1 to complete the thermodynamic cycle.
Vapor absorption cycle
In the early years of the twentieth century, the vapor absorption cycle using waterammonia systems was popular and widely used. After the development of the vapor compression cycle, the vapor absorption cycle lost much of its importance because of its low coefficient of performance (about one fifth of that of the vapor compression cycle). Today, the vapor absorption cycle is used mainly where fuel for heating is available but electricity is not, such as in recreational vehicles that carry LP gas. It's also used in industrial environments where plentiful waste heat overcomes its inefficiency.
The absorption cycle is similar to the compression cycle, except for the method of raising the pressure of the refrigerant vapor. In the absorption system, the compressor is replaced by an absorber which dissolves the refrigerant in a suitable liquid, a liquid pump which raises the pressure and a generator which, on heat addition, drives off the refrigerant vapor from the high-pressure liquid. Some work is required by the liquid pump but, for a given quantity of refrigerant, it is much smaller than needed by the compressor in the vapor compression cycle. In an absorption refrigerator, a suitable combination of refrigerant and absorbent is used. The most common combinations are ammonia (refrigerant) and water (absorber) and water (refrigerant) and lithium bromide (absorber).
Gas refrigeration cycle
When the working fluid is a gas that is compressed and expanded but doesn't change phase, the refrigeration cycle is called a gas cycle. Air is most often this working fluid. As there is no condensation and evaporation intended in a gas cycle, components corresponding to the condenser and evaporator in a vapor compression cycle are the hot and cold gas-to-gas heat exchangers in gas cycles.
The gas cycle is less efficient than the vapor compression cycle because the gas cycle works on the reverse Brayton cycle instead of the reverse Rankine cycle. As such the working fluid does not receive and reject heat at constant temperature.Because of their lower efficiency and larger bulk, air cycle coolers are not often used nowadays in terrestrial cooling devices. The air cycle machine is very common, however, on gas urbine-powered jet aircraft because compressed air is readily available from the engines' compressor sections.
Thermoelectric refrigeration
Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. This effect is commonly used in camping and portable coolers and for cooling electronic components and small instruments.
Magnetic refrigeration
Magnetic refrigeration, or adiabatic demagnetization, is a cooling technology based on the magnetocaloric effect, an intrinsic property of magnetic solids. The refrigerant is often a paramagnetic salt, such as cerium magnesium nitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms.A strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. A heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off. This increases the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the h eat sink.
Other methods
Other methods of refrigeration include the air cycle machine used in aircraft; the vortex tube used for spot cooling, when compressed air is available; and thermo-acoustic refrigeration using sound waves in a pressurised gas to drive heat transfer and heat exchange.
TYPES OF VAPOUR ABSORPTION SYSTEM
Carre’s process
Absorption cooling was invented by the French scientist Ferdinand Carre in 1858. The original design used water and sulfuric acid.The expansion device and evaporator used in this system is similar to the VCR system. Instead of a compressor, an absorber generator assembly is used with regulation valves and heat exchangers. Pressure is increased in liquid phase and hence less mechanical work is required. It is a robust technology.
Einstein refrigerator
The machine is a single-pressure absorption refrigerator, similar in design to a gas absorption refrigerator. The refrigeration cycle uses ammonia pressure-equalizing fluid, butane refrigerant, and water absorbing fluid, has no moving parts, and does not require electricity to operate, needing only a heat source, e.g. a small gas burner or electric heating element.The ammonia is introduced into the evaporator, causing the refrigerant to evaporate, taking energy from the surroundings, due to the fact that the partial pressure of the refrigerant is reduced, and the mix of gasses then passed through to a Condenser heat transfer condenser where it comes into contact with the absorption liquid. Since ammonia is soluble in water and butane is insoluble, the ammonia gas is absorbed by the water, freeing the butane. Heat is thus first given from the butane to the ammonia as the gasses mix, and then from the ammonia to the water, as the ammonia leaves the butane, taking heat with it, and dissolves into the water. The butane then assumes the pressure inside the condenser, which is enough to make it liquefy. Since butane's specific gravity is less than that of ammonia in solution in water, the liquid butane floats on top of the ammonia solution. The liquid butane then passes back to the evaporator to repeat the cycle. The
ammonia solution flows to a heat exchanger where a heat source drives it from the water as a gas again and it returns to the evaporator. The Einstein refrigerator has been described as "noiseless, inexpensive to produce and durable".
Lithium bromide – Water system
As shown in the figure, the cooling water (which acts as heat sink) flows first to absorber, extracts heat from absorber and then flows to the condenser for condenser heat extraction. This is known as series arrangement. This arrangement is advantageous as the required cooling water flow rate will be small and also by sending the cooling water first to the absorber, the condenser can be operated at a higher pressure to prevent crystallization. It is also possible to have cooling water flowing paralleling to condenser and absorber, however, the cooling water requirement in this case will be high. A refrigerant pump circulates liquid water in evaporator and the water is sprayed onto evaporator tubes for good heat and mass transfer. Heater tubes (steam or hot water or hot oil) are immersed in the strong solution pool of generator for vapour generation. Pressure drops between
evaporator and absorber and between generator and condenser are minimized, large sized vapour lines are eliminated and air leakages can also be reduced due to less number of joints.
ELECTROLUX REFRIGERATION SYSTEM History
In 1922, two young engineers, Baltzar von Platen and Carl Munters from the Royal Institute of Technology in Stockholm, submitted a degree project that gained them much attention. It was a refrigeration machine that employed a simple application of the absorption process to transform heat to cold. The heat source that initiated the process could be fueled by electricity, gas or kerosene, making the system extremely flexible.
The two inventors needed money to develop and market their product, however. By 1923, they had come as far as establishing two companies, AB Arctic and Platen-Munters Refrigeration System. Refrigerator production got under way now, albeit on a small scale, at the new Arctic factory in Motala. The absorption refrigeration machine was far from fully developed when Wenner-Gren began to take an interest in it. It was, then, a bold move when he made an offer for the two companies, which meant Electrolux's future would depend on the success of the refrigerator. In 1925, Electrolux introduced its first refrigerators on the market. Intense efforts to develop refrigeration technology were under way at a refrigeration lab that had been set up in Stockholm. The primary goal was to develop an air-cooled system. Platen-Munters' first appliance was water-cooled and had to be connected to a heat source, a water line and a drain in order to function. It was a fairly impractical solution. This was one of the reasons for bringing physicist John Tandberg to the lab. Tandberg was one of the specialists who played a key role in the development of refrigeration technology at Electrolux, making contributions to improving the control of corrosion and rust and much more.
How it works? The continuous absorption type of cooling unit is operated by the application of a limited amount of heat furnished by gas, electricity or kerosene. No moving parts are employed.
The unit consists of four main parts - the boiler, condenser, evaporator and absorber.
The unit can be run on electricity, kerosene or gas. When the unit operates on kerosene or gas the heat is supplied by a burner which is fitted underneath the central tube (A) and when the unit operates on electricity the heat is supplied by a heating element inserted in the pocket (B).The unit charge consists of a quantity of ammonia, water and hydrogen at a sufficient pressure to condense ammonia at the room temperature for which the unit is designed. When heat is supplied to the boiler system, bubbles of ammonia gas are produced which rise and carry with them quantities of weak ammonia solution through the siphon pump (C). This weak solution passes into the tube (D), whilst the ammonia vapor passes into the vapor pipe (E) and on to the water separator. Here any water vapor is condensed and runs back into the boiler system leaving the dry ammonia vapor to pass to the condenser. Air circulating over the fins of the condenser removes heat from the ammonia vapor to cause it to condense to liquid ammonia in which state it flows into the evaporator. The evaporator is supplied with hydrogen. The hydrogen passes across the surface of the ammonia and lowers the ammonia vapor pressure sufficiently to allow the liquid ammonia to evaporate. The evaporation of the ammonia extracts heat from the food storage space, as described above, thereby lowers the temperature inside the refrigerator. The mixture of ammonia and hydrogen vapor passes from the evaporator to the absorber. Entering the upper portion of the absorber is a continuous trickle of weak
ammonia solution fed by gravity from the tube (D). This weak solution, flowing down through the absorber comes into contact with the mixed ammonia and hydrogen gases which readily absorbs the ammonia from the mixture, leaving the hydrogen free to rise through the absorber coil and to return to the evaporator. The hydrogen thus circulates continuously between the absorber and the evaporator. The strong ammonia solution produced in the absorber flows down to the absorber vessel and thence to the boiler system, thus completing the full cycle of operation. The liquid circulation of the unit is purely gravitational.Heat is generated in the absorber by the process of absorption. This heat must be dissipated into the surrounding air. Heat must also be dissipated from the condenser in order to cool the ammonia vapor sufficiently for it to liquefy. Free air circulation is therefore necessary over the absorber and condenser.The whole unit operates by the heat applied to the boiler system and it is of paramount importance that this heat is kept within the necessary limits and is properly applied.
A liquid seal is required at the end of the condenser to prevent the entry of hydrogen gas into the condenser. Commercial Platen-Munters systems are made of all steel with welded joints. Additives are added to minimize corrosion and rust formation and also to improve absorption. Since there are no flared joints and if the quality of the welding is good, then these systems become extremely rugged and reliable. The Platen-Munters systems offer low COPs (of the order of 0.1 to 0.4) due to energy requirement in the bubble pump and also due to losses in the evaporator because of the presence of hydrogen gas. In addition, since the circulation of fluids inside the system is due to buoyancy and gravity, the heat and mass transfer coefficients are relatively small, further reducing the efficiency.
AMMONIA REFRIGERANT (R717)
HISTORY
Many years ago, the food and beverage industry embraced ammonia refrigeration. The economic advantages alone made it the refrigerant of choice for cold storage facilities and food processing facilities as well as the dairy and meatpacking industries. Almost all of the food on the family breakfast, lunch and dinner table passes through an ammonia refrigeration facility before reaching your grocery store including fresh fruits and vegetables, meat, poultry and fish, frozen convenience foods, milk, cheese and ice cream, and beverages such as soft drinks, beer and wine.
Ammonia was among the early refrigerants used in mechanical systems, and it's the only one of the early refrigerants to secure a lasting role as a refrigerant. Mechanical refrigeration was developed in the 1800s based on the principle of vapor compression. The first practical refrigerating machine using vapor compression was developed in 1834 and by the late 1800s refrigeration systems were being used in breweries and cold storage warehouses. The basic design of the vapor compressor refrigeration system, using ammonia as a refrigerant in a closed cycle of evaporation, compression, condensation, and expansion, has changed very little since the early 1900s.
Ammonia was first used as a refrigerant in the 1850s in France and was applied in the United States in the 1860s for artificial ice production. The first patents for ammonia refrigeration machines were filed in the 1870s. By the 1900s, ammonia refrigeration machines were being commercially installed in block ice, food processing, and chemical
production facilities. By the 1920s, ammonia refrigeration was being applied to ice rinks. During the 1930s, air conditioning markets began to develop, first for industrial applications and then for human comfort. The use of smaller units for domestic refrigerators increased substantially between 1920 and 1930
Ammonia refrigeration has been the backbone of the cold storage and food processing industries since the early 1900s. Ammonia refrigeration is the most cost effective and energy efficient method of processing and storing frozen and unfrozen foods. It is the workhorse for the post-harvest cooling of fruits and vegetables, the cooling of meat, poultry, and fish, refrigeration in the beverage industry, particularly for beer and wine, refrigeration of milk and cheese, and the freezing of ice cream. Practically all fruits, vegetables, produce and meats, as well as many beverages and juices, pass through at least one facility that uses an ammonia refrigeration system before reaching our homes. Ammonia refrigeration is also used in the chemical industry.
PROPERTIES
Ammonia is a colorless gas with a characteristic pungent smell. It is lighter than air , its density being 0.589 times that of air . It is easily liquefied due to the strong hydrogen bonding between molecules; the liquid boils at −33.3 °C, and solidifies at −77.7 °C to white crystals. Liquid ammonia possesses strong ionizing powers reflecting its high ε of 22. Liquid ammonia has a very high standard enthalpy change of vaporization (23.35 kJ/mol, cf. water 40.65 kJ/mol, methane 8.19 kJ/mol, phosphine 14.6 kJ/mol) and can therefore be used in laboratories in non-insulated vessels without additional refrigeration.
It is miscible with water. Ammonia in an aqueous solution can be expelled by boiling. The aqueous solution of ammonia is basic. The maximum concentration of ammonia in water (a saturated solution) has a density of 0.880 g /cm³ and is often known as '.880 Ammonia'. Ammonia does not burn readily or sustain combustion, except under narrow fuel-to-air mixtures of 15-25% air. When mixed with oxygen, it burns with a pale yellowish-green flame. At high temperature and in the presence of a suitable catalyst, ammonia is decomposed into its constituent elements. Ignition occurs when chlorine is passed into ammonia, forming nitrogen and hydrogen chloride; if ammonia is present in excess, then the highly explosive nitrogen trichloride (NCl3) is also formed.
CHEMICAL PROPERTIES
One of the most characteristic properties of ammonia is its basicity. It combines with acids to form salts; thus with hydrochloric acid it forms ammonium chloride (salammoniac); with nitric acid, ammonium nitrate, etc. However, perfectly dry ammonia will not combine with perfectly dry hydrogen chloride: moisture is necessary to bring about the reaction.
NH3 + HCl → NH4Cl
The salts produced by the action of ammonia on acids are known as the ammonium salts and all contain the ammonium ion (NH4+). Anhydrous ammonia is often used for the production of methamphetamine. Aqueous ammonia can be applied on the skin to lessen the effects of acidic animal poisons, such as from insect and jellyfish.
Although ammonia is well-known as a base, it can also act as an extremely weak acid. It is a protic substance and is capable of formation of amides (which contain the NH2− ion), for example lithium and ammonia react to give a solution of lithium amide:
2 Li + 2 NH3 → 2 LiNH2 + H2
Triple point
195.4 K (–77.75 °C),6.060 k Pa
Critical point
405.5 K (132.3 °C),11.300 MPa
Std enthalpy change
+5.653 kJ/mol
of fusion, ΔfusHo Std entropy change
+28.93 J/(mol·K)
of fusion, ΔfusSo Std enthalpy change
+23.35 kJ/mol at BP of –33.4 °C
of vaporization, ΔvapHo Std entropy change of vaporization ΔvapSo
, +97.41 J/(mol·K at BP of –33.4 °C
PHYSICAL PROPERTIES
Anhydrous ammonia is a clear liquid that boils at a temperature of -28°F. In refrigeration systems, the liquid is stored in closed containers under pressure. When the pressure is released, the liquid evaporates rapidly, generally forming an invisible vapor or gas. The rapid evaporation causes the temperature of the liquid to drop until it reaches the normal boiling point of -28°F, a similar effect occurs when water evaporates off the skin, thus cooling it. This is why ammonia is used in refrigeration systems. Liquid anhydrous ammonia weighs less than water. About eight gallons of ammonia weighs the same as five gallons of water. Liquid and gas ammonia expand and contract with changes in pressure and temperature. For example, if liquid anhydrous ammonia is in a partially filled, closed container it is heated from 0°F to 68°F, the volume of the liquid will increase by about 10 percent. If the tank is 90 percent full at 0°F, it will become 99 percent full at 68°F. At the same time, the pressure in the container will increase from 16 pounds per square inch (psi) to 110 psi.Liquid ammonia will expand by 850 times when evaporating: Anhydrous ammonia gas is considerably lighter than air and will rise in dry air. However, because of ammonias tremendous affinity for water, it reacts immediately with
the
humidity
in
the
air
and
may
remain
close
to
the
ground.
The odor threshold for ammonia is between 5 - 50 parts per million (ppm) of air. The permissible exposure limit (PEL) is 50 ppm averaged over an 8 hour shift. It is recommended that if an employee can smell it they ought to back off and determine if they need to be using respiratory protection.
USES OF AMMONIA
Cleaner
Household ammonia is a general purpose cleaner that can be used on many surfaces. Because ammonia results in a relatively streak-free shine, one of its most common uses is to clean glass, porcelain and stainless steel. It is also frequently used for cleaning ovens and soaking items to loosen baked-on or caked-on grime.
-As a vehicle fuel
Ammonia has been proposed as a practical alternative to fossil fuel for internal combustion engines. The calorific value of ammonia is 22.5 MJ/kg (9690 BTU/lb) which is about half that of diesel. In a normal engine, in which the water vapor is not condensed, the calorific value of ammonia will be about 21% less than this figure. It can be used in existing engines with only minor modifications to carburetors/injectors.
To meet these demands, significant capital would be required to increase present production levels. Although the second most produced chemical, the scale of ammonia production is a small fraction of world petroleum usage. It could be manufactured from renewable energy sources, as well as coal or nuclear power. It is however significantly less efficient than batteries.. If produced from coal, the CO2 can be readily sequestrated. (the combustion products are nitrogen and water). In 1981 a Canadian company converted a 1981 Chevrolet Impala to operate using ammonia as fuel.
Hazards of ammonia
Ammonia is not, strictly speaking, a poison and repeated exposure to it produces no additive (chronic) effects on the human body. However, even in small concentrations in the air it can be extremely irritating to the eyes, throat, and breathing passages. Ammonia is a corrosive, toxic gas with a very pungent odour. It is slightly lighter than air and it can mix with water vapour and become heavier than air, collecting in pockets at floor level. It is not normally flammable, but at extremely high concentrations it can create an explosive mixture with air. Ammonia is a severe irritant of the eyes, nose and throat, where airborne concentrations between 25 and 50 ppm may be irritating to the mucous membranes. Exposures in excess of the allowable limit (25ppm) can cause headaches, coughing and difficulty breathing. Prolonged exposure to high concentrations of ammonia can lead to pulmonary edema (an accumulation of fluid in the lungs) which can be fatal. Skin contact with liquid ammonia can cause burns, blisters and even frostbite. Eye contact can cause severe damage to the eye and may lead to blindness anhydrous ammonia primarily affects three areas of the body:
•
Eyes
•
Lungs
•
Skin
Eyes
Everything from mild irritation to destruction of the eye can occur depending on whether a spray or gas is involved. Ammonia penetrates the eye more rapidly than other alkalis.
Lungs
In the lungs, liquid anhydrous ammonia causes destruction of delicate respiratory tissue. Exposure to ammonia vapor may cause:
•
Convulsive coughing.
•
Difficult or painful breathing.
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Pulmonary congestion and death
Gaseous ammonia effects at various concentrations are as follows:
•
25 ppm or less - TWA
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25-50 ppm - Detectable odor; unlikely to experience adverse effects
•
50-100 ppm - Mild eye, nose, and throat irritation; may develop tolerance in 1-2 weeks with no adverse effects thereafter
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140 ppm - Moderate eye irritation; no long-term sequelae in exposures of less than 2 hours
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400 ppm - Moderate throat irritation
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500 ppm - IDLH
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700 ppm - Immediate eye injury
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1000 ppm - Directly caustic to airway
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1700 ppm - Laryngospasm
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2500 ppm - Fatality (after half-hour exposure)
•
2500-6500 ppm - Sloughing and necrosis of airway mucosa, chest pain, pulmonary edema, and bronchospasm
Skin
Skin damage depends upon the length and concentration of exposure and can range from mild irritation, to a darkened freeze-dry burn, to tissue destruction. Because liquid ammonia boils at -28°F, the expanding gas has the potential to freeze anything in its path of release, including human flesh and organs. Because water can absorb ammonia so readily, it is a factor that contributes to human toxicity. Ammonia will keep spreading across contacted skin until the chemical is diluted bys kin moisture. Alkalis effect tissue differently than acids, which tend to burn and seal off a wound. Alkalis, such as ammonia cause liquidization of tissue and turn tissue into a sticky "goo" and mix with this tissue, causing further damage. As a result, anhydrous ammonia burns keep spreading until the chemical is diluted. In addition to liquidization, super-cooled anhydrous ammonia spray causes a freeze dry effect like frost bite when it hits the skin. The spray is also capable of freezing clothing to skin so that if the clothing is removed incorrectly whole sections of skin can be torn off. High concentrations in the air can also dissolve in the moisture of the skin or perspiration and result in a corrosive action on the skin and mucous membranes.
ACCIDENTS
A number of accidental releases of ammonia have occurred from refrigeration facilities in the past. Causes of these releases include plant upsets, leading to the lifting of relief valves; leaks in rotating seals; pipeline failures; vehicular traffic hitting pipes, valves, and evaporators; and failures during ammonia delivery, such as hose leaks. Some of these releases have killed and injured workers, caused injuries off site, or resulted in evacuations. The following describes several recent incidents in more detail. A specific
incident demonstrates the need for mechanical protection to protect refrigeration equipment from impact. In a 1992 incident at a meat packing plant, a forklift struck and ruptured pipe carrying ammonia for refrigeration. Workers were evacuated when the leak was detected. A short time later, an explosion occurred that caused extensive damage, including large holes in two sides of the building. The forklift was believed to be the source of ignition. In this incident, physical barriers would have provided mechanical protection to the refrigeration system and prevented a release.
HAZARD AWARENESS
Ammonia is used widely and in large quantities for a variety of purposes. More than 80% of ammonia produced is used for agricultural purposes; less than two percent is used for refrigeration. Use of ammonia is generally safe provided appropriate maintenance and operating controls are exercised. It is important to recognize, however, that ammonia is toxic and can be a hazard to human health. It may be harmful if inhaled at high concentrations. The Occupational Safety and Health Administration (OSHA) Permissible Exposure Level (PEL) is 50 parts per million (ppm), 8-hour time-weighted average. Effects of inhalation of ammonia range from irritation to severe respiratory injuries, with possible fatality at higher concentrations. The National Institute of Occupational Safety and Health (NIOSH) has established an Immediately Dangerous to Life and Health (IDLH) level of 300 ppm for the purposes of respirator selection. Ammonia is corrosive and can burn the skin and eyes. Liquefied ammonia can cause frostbite.
WATER ABSORBENT Properties and existence
Water (H2O, HOH) is the most abundant molecule on Earth's surface, constituting about 75% of the Earth's surface in liquid, solid, and gaseous states. It is in dynamic equilibrium between the liquid and gas states at standard temperature and pressure. At room temperature, it is a nearly colorless (with a hint of blue), tasteless, and odorless liquid. Many substances dissolve in water and it is commonly referred to as the universal solvent. Water is the chemical substance with chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Water is a tasteless, odorless liquid at ambient temperature and pressure, and appears colorless in small quantities, although it has its own intrinsic very light blue hue. Ice also appears colorless, and water vapor is essentially invisible as a gas
Water has the second highest specific heat capacity of any known chemical compound, after ammonia, as well as a high heat of vaporization (40.65 kJ mol−1), both of which are a result of the extensive hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature.
The specific enthalpy of fusion of water is 333.55 kJ kg−1 at 0 °C. Of common substances, only that of ammonia is higher. This property confers resistance to melting upon the ice of glaciers and drift ice. Before the advent of mechanical refrigeration, ice was in common use to retard food spoilage.
One molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Water is a tasteless, odorless liquid at ambient temperature and pressure, and appears colorless in small quantities, although it has its own intrinsic very light blue hue. Ice also appears colorless, and water vapor is essentially invisible as a gas. Water is primarily a liquid under standard conditions, which is not predicted from its relationship to other analogous hydrides of the oxygen family in the periodic table, which are gases such as hydrogen sulfide. Also the elements surrounding oxygen in the periodic table, nitrogen, fluorine, phosphorus, sulfur and chlorine, all combine with hydrogen to produce gases under standard conditions. The reason that water forms a liquid is that it is more electronegative than all of these elements (other than fluorine). Oxygen attracts electrons much more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom. The presence of a charge on each of these atoms gives each water molecule a net dipole moment. Electrical attraction between water molecules due to this dipole pulls individual molecules closer together, making it more difficult to separate the molecules and therefore raising the boiling point. This attraction is known as hydrogen bonding. The molecules of water are constantly moving in relation to each other, and the hydrogen bonds are continually breaking and reforming at the timescales faster than 200 femtoseconds. However, this bond is strong enough to create many of the peculiar properties of water described in this article, such as the ones that make it integral to life. Water can be described as a polar liquid that slightly dissociates disproportionately into the hydronium ion (H3O+(aq)) and an associated hydroxide ion (OH−(aq)).
2 H2O (l) H3O+(aq) + OH−(aq)
Why water?
The polarity of NH3 molecules and their ability to form hydrogen bonds explains to some extent the high solubility of ammonia in water. However, a chemical reaction also occurs when ammonia dissolves in water. In aqueous solution, ammonia acts as a base, acquiring hydrogen ions from H2O to yield ammonium and hydroxide ions. NH3(aq) + H2O(l) NH4 +(aq) + OHG(aq) The production of hydroxide ions when ammonia dissolves in water gives aqueous solutions of ammonia their characteristic alkaline (basic) properties. The double arrow in the equation indicates that equilibrium is established between dissolved ammonia gas and ammonium ions. Not all of the dissolved ammonia reacts with water to form ammonium ions. A substantial fraction remains in the molecular form in solution. Water boils at 273 kelvin at 1 bar atmospheric pressure. Ammonia is readily miscible in water. Ammonium Hydroxide on slight heating easily liberates ammonia gas. Water is easily available, safe to handle and environmentally friendly. Circulation of the solution of water is easy when compared to other phases of matter. The reaction of ammonia with water is exothermic and the energy from this exothermic reaction is used for the circulation of hydrogen in the system. All these properties make it apt to be used as the absorber in our refrigeration system.
HYDROGEN – THE CARRIER GAS
Properties and existence
Hydrogen is the most abundant element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms. This element is found in great abundance in stars and gas giant planets. Molecular clouds of H2 are associated with star formation. Hydrogen plays a vital role in powering stars through proton-proton reaction and CNO cycle nuclear fusion.
Throughout the universe, hydrogen is mostly found in the atomic and plasma states whose properties are quite different from molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity and high emissivity (producing the light from the sun and other stars). The charged particles are highly influenced by magnetic and electric fields. For example, in the solar wind they interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora. Hydrogen is found in the neutral atomic state in the Interstellar medium.
Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H2 .However, hydrogen gas is very rare in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth's gravity more easily than heavier gases. However, hydrogen (in chemically combined form) is the third most abundant element on the Earth's surface. Most of the Earth's hydrogen is in the form of chemical compounds such as hydrocarbons and water . Hydrogen gas is produced by
some bacteria and algae and is a natural component of flatus. Methane is a hydrogen source of increasing importance.
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H2. With an atomic weight of 1.00794, hydrogen is the lightest element. The density of hydrogen at 273 kelvin is 0.08988g/l. The melting point is 14.02k and boiling point is 20.28k.
The most common isotope of hydrogen is protium (name rarely used) with a single proton and no neutrons. In ionic compounds it can take a positive charge (a cation composed of a bare proton) or a negative charge (an anion known as a hydride). Hydrogen forms compounds with most elements and is present in water and most organic compounds. It plays a particularly important role in acid-base chemistry with many reactions exchanging protons between soluble molecules. As the only neutral atom with an analytic solution to the Schrödinger equation, the study of the energetic and bonding of the hydrogen atom played a key role in the development of mechanics. Hydrogen gas (dihydrogen) is highly flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion for hydrogen is −286 kJ/mol:
2 H2(g) + O2(g) → 2 H2O(l) + 572 kJ (286 kJ/mol). H2 reacts with every oxidizing element. Hydrogen can react spontaneously and violently at room temperature with chlorine and fluorine to form the corresponding halides: hydrogen chloride and hydrogen fluoride.
Why hydrogen in Platen Munters system?
Hydrogen is used as the carrier gas in Platen Munters system. Hydrogen is used to reduce the partial pressure of ammonia in the evaporator. Also it keeps the total pressure of the system constant. A major volume of evaporator is filled with hydrogen so that ammonia gets less volume to expand. Thus ammonia directly evaporates without boiling in the presence of hydrogen. Also hydrogen causes an inert atmosphere to exist in the evaporator cabin for ammonia. The reason for selecting hydrogen as the gas in the evaporator is because it is the lightest gas that can occupy the maximum volume. Also it reacts neither with water nor with ammonia. Hydrogen is easily available and also is non corrosive. Another reason is that it is non-toxic. The critical temperature of hydrogen is 32.97K. Since the critical temperature is very low, it can be easily used for very low evaporator temperature.
Other carrier gas
Other similar gas which can act as a carrier gas is helium. It is the next lightest gas after hydrogen. Also it belongs to group 18 in periodic table; hence they are inert by nature. Also the critical temperature of helium is 5.2K which is an advantage for using it in refrigeration. The only drawback of helium as compared with hydrogen is that it is heavier than hydrogen and hence it is not as effective as hydrogen
ENERGY SOURCES
The main energy sources for Electrolux refrigeration are •
Solar energy
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Electric heaters
•
Waste heat
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Kerosene
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Natural gas
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Steam
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Geo thermal energy
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Bio gas
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Automobile exhaust gas
RENEWABLE ENERGY
Renewable energy is energy generated from natural resources —such as sunlight, wind, rain, tides and geothermal heat —which are renewable (naturally replenished). In 2006, about 18% of global final energy consumption came from renewables, with 13% coming from traditional biomass, such as wood-burning. Hydroelectricity was the next largest renewable source, providing 3% (15% of global electricity generation), followed by solar hot water /heating, which contributed 1.3%. Modern technologies, such as geothermal energy, wind power , solar power , and ocean energy together provided some 0.8% of final energy consumption.
Wind power is growing at the rate of 30 percent annually, with a worldwide installed capacity of over 100 GW, and is widely used in several European countries and the United States. The manufacturing output of the photovoltaic industry reached more than 2,000 MW in 2006, and photovoltaic (PV) power stations are particularly popular in Germany and Spain. Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 MW SEGS power plant in the Mojave Desert.. The world's largest geothermal power installation is The Geysers in California, with a rated capacity of 750 MW. Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18 percent of the country's automotive fuel. Ethanol fuel is also widely available in the USA.
While there are many large-scale renewable energy projects and production, renewable technologies are also suited to small off-grid applications, sometimes in rural and remote areas, where energy is often crucial in human development. Kenya has the world's
highest household solar ownership rate with roughly 30,000 small (20–100 watt) solar power systems sold per year. Renewable energy flows involve natural phenomena such as sunlight, wind, tides and geothermal heat, as the International Energy Agency explains:
"Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources."
SOLAR ENERGY
Solar energy is the radiant light and heat from the Sun that has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for most of the available renewable energy on Earth. Only a minuscule fraction of the available solar energy is used.
Solar power provides electrical generation by means of heat engines or photovoltaic. Once converted its uses are only limited by human ingenuity. A partial list of solar applications includes space heating and cooling through solar architecture, potable water via distillation and disinfection, daylighting, hot water , thermal energy for cooking, and high temperature process heat for industrial purposes.
Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute sunlight. Active solar techniques include the use of photovoltaic panels, solar thermal collectors, with electrical or mechanical equipment, to convert sunlight into useful outputs. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air .
The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.
Earth's land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived.
The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year.[12][13] Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined.
Applications of solar technology
Solar energy refers primarily to the use of solar radiation for practical ends. All other renewable energies other than geothermal and tidal derive their energy from the sun.Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.
SOLAR COLLECTOR
Definition
A solar collector is a device for extracting the energy of the sun directly into a more usable or storable form. The energy in sunlight is in the form of electromagnetic radiation from the infrared (long) to the ultraviolet (short) wavelengths. The solar energy striking the earth's surface at any one time depends on weather conditions, as well as location and orientation of the surface, but overall, it averages about 1000 watts per square meter under clear skies with the surface directly perpendicular to the sun's rays.
Efficiency
The efficiency of a solar collector is defined as the quotient of usable thermal energy versus received solar energy. Besides thermal loss there always is optical loss as well. The conversion factor or optical efficiency h0 indicates the percentage of the solar rays penetrating the transparent cover of the collector (transmission) and the percentage being
absorbed. Basically, it is the product of the rate of transmission of the cover and the absorption rate of the absorber. The heat loss is indicated by the thermal loss factor or kvalue. This is given in watt per m² collector surface and the particular temperature difference (in °C) between the absorber and its surroundings. The higher the temperature difference, the more heat is lost. Above a specific temperature difference, the amount of heat loss equals the energy yield of the collector, so that no energy at all is delivered to the solar circulation system. A good collector will have a high conversion factor and a low k-value.
Concentration ratio
Where
TYPES OF SOLAR COLLECTORS
Although the discussion that follows deals with concentrators as entities, concentrators are only a portion of an energy collection system. To be useful the concen trated rays must be directed to a target called a receiver, which converts the rays into another form of energy, heat. The concentrator and receiver must be matched for optimum performance. Frequently, the receiver is expected to impart heat to a fluid in order that the heat be utilized or dissipated. When the main purpose of the concentrator is to obtain heat effectively, then the combination of concentrator and receiver must be carefully designed to reduce stray loss of energy from either the co ncentrator or receiver.
Flat plate
Solar thermal system for water heating - these are deployed o n flat roofs.
A flat plate is the most common type of solar thermal collector, and is usually used as a solar hot water panel to generate solar hot water . A weatherproofed, insulated box containing a black metal absorber sheet with built in pipes is placed in the path of sunlight. Solar energy heats up water in the pipes causing it to circulate through the system by natural convection (thermosyphon). The water is usually passed to a storage tank located above the collector. This passive solar water heating system is generally used in hotels and homes in sunny climates such as those found in southern Europe.
For these purposes, the general practice is to use flat-plate solar energy or evacuated tube collectors with a fixed orientation (position). The highest efficiency with a fixed flat-plate collector or evacuated tube collector is obtained if it faces toward the sun and slopes at an
angle to the horizon equal to the latitude plus about 10 degrees. Solar collectors fall into two general categories: non-concentrating and concentrating.
In the non-concentrating type, the collector area (i.e. the area that intercepts the solar radiation) is the same as the absorber area (i.e., the area absorbing the radiation). In these types the whole solar panel absorbs the light.
There are many flat-plate collector designs but generally all consist of (1) a flat-plate absorber, which intercepts and absorbs the solar energy, (2) a transparent cover(s) that allows solar energy to pass through but reduces heat loss from the absorber, (3) a heattransport fluid (air, antifreeze or water) flowing through tubes to remove heat from the absorber, and (4) a heat insulating backing. One flat plate collector is designed to be evacuated, to prevent heat loss.
Evacuated tube
These collectors have multiple evacuated glass tubes which heat up solar absorbers and, ultimately, solar working fluid (water or an antifreeze mix -- typically propylene glycol) in order to heat domestic hot water, or for hydronic space heating. The vacuum within the evacuated tubes reduce convection heat losses, allowing them to reach considerably higher temperatures than most flat-plate collectors. The evacuated tubes draw their energy from the available light rather than outside temperature. For these reasons they can perform well in colder conditions. The advantage is largely lost in warmer climates, except in those cases where very hot water is desirable.
The advantage this design has over the flat-plate type is that the constant profile of the round tube means that the collector is always perpendicular to the sun's rays and therefore the energy absorbed is approximately constant over the course of a day - provided the inner collecting tube is circular in section and not of the flat fin type. The question what to do with the "lost" sun shining through the gaps between evacuated tubes (gaps which can be as wide as the tubes' absorbtive surface themselves) can be addressed either by by adding specially curved metal reflectors under the evacuated tubes or by reverting to the use of flat plate collectors which are designed not to offer any gaps in the collector's light interception profile.
Parabolic trough
This type of collector is generally used in solar power plants. A trough-shaped parabolic reflector is used to concentrate sunlight on an insulated tube (Dewar tube) or heat pipe, placed at the focal point, containing coolant which transfers heat from the collectors to the boilers in the power station. Alternatively the trough can be aligned on an east-west
axis, this reduces the overall efficiency of the collector, due to cosine loss, but only requires the trough to be aligned with the change in seasons, avoiding the need for
tracking motors. This tracking method works correctly at the spring and fall equinoxes with errors in the focusing of the light at other times during the year
Two dimensional involute cusps
The peculiar advantage of involute cusp in solar energy concentration had been recognized very early stages by Trombe and Meinel. Mathematically, the involute of any
curve is defined as a curve that intersects all its tangents at right angles. The Trombe Meinel designs a profile described by the locus of a string unwrapped from about a circular receiver. Type of Concentrator
: Cusp
Type of Focus
: Line
Lens or Mirror
: Mirror
Sun's Concentration
: 1.5-2.5
Tracking
: No
Tracking Receiver
: No
Temperature (C)
: 121
Temperature (F)
: 250
About involute curve Attach a string to a point on a curve. Extend the string so that it is tangent to the curve at the point of attachment. Then wind the string up, keeping it always taut. The locus of points traced out by the end of the string is called the involute of the original curve, and the original curve is called the evolute of its involute.
Our design
FABRICATION Double involute cusp collector
The solar concentrating device is having a shape of double involute cusp. The fabrication was done at the sheet metal shop of Industan engineering works, Karamana. The design of the collector was created with the help of CAD software. From the dimensioned figure, a template of the collector was made first on a strip of MS metal sheet of gauge 2”. Then a MS sheet of dimension 42” x 7” was cut out. The centre line is drawn on the sheet. Then the sheet was then curved with the help of hammer and roller. The entire sheet was first curved with a radius of curvature 4”. Then the cusp shape was made by keeping the sheet in between two pipes and hammering along the centre line with a straight edge chisel. After each set of hammering the design was cross checked with the template made. Any deviation from the design was rectified at each stage. Hammering was continued until the required profile was obtained. Then the surface is leveled to remove the punch marks made by hammer. The edges are hammered to get a straight edge.
The next step was fixing the generator tubes on the collector. The focus of the collector is along the centre line. A portion of the collector was cut using snippets to provide room for the pressure gauge assembly. Then the generator tube was welded on the collector using electric arc welding.
After fixing the generator tubes, again the inner surface is polished with medium course grade sand paper (grades #60 & #80). Finally fine polishing was done by using a sand paper of medium grade (#100). The polishing was done in o rder to stick the mirror plastic
paper on the surface. The mirror plastic used in our project is similar to the reflecting papers used to tint automobile glasses. In order to stick the mirror paper, an initial layer of PVC is coated over the collector surface. The colour of the PVC coating is selected white to improve the reflectivity. Then the mirror paper is fixed after spraying water over the entire surface. Water is sprayed to reduce the trapping of air bubbles in between the layer. The bottom surface of the collector was painted to reduce corrosion.
Generator tube
The generator tube was made of two 1” diameter MS tube of gauge 5mm and having a length of 1m. Using high gauge tube was to withstand even higher pressures. The initial design was to use a generator tube of 2” diameter of gauge 5mm.Using such large diameter tube will reduce the effective surface area exposed and also much time will take to heat the solution inside the generator tube. The two tubes are welded together by electric arc welding so that they form a closed loop. A hole is made at the top of the generator tube and a threaded coupling of diameter 1” is welded at the top. This is the ammonia charging line. The ammonia charging line was sealed using an end cap made of MS having diameter 1”. After that the generator tube was pressurized by pumping water into it at high pressure and kept for 4 hours to check if there is any leak. Initially leaks were detected at the welded joints. The leaks were rectified finally. After the leak check, holes were drilled for the inlet of aqua ammonia and exit of ammonia gas. Hose collars made from MS tube of quarter inch diameter was welded at the appropriate places. Also a connection was made for fixing a valve for pressure gauge.
The pressure gauge is used is a compound pressure gauge used for checking pressure of ammonia and oil. A pressure gauge must always be assembled along with a valve. This is to facilitate the replacing of pressure gauge if it went wrong. After finishing the leak check and giving options for valves and gauges, the generator tube was polished using sand paper to remove scale. Then the tubes were painted with black matte finish paint. This is done to ensure maximum absorptivity.
Hose collars
Aqua ammonia is very much corrosive to copper and its alloys as ammonia readily reacts with copper to give a green coloured cupric salt. Hose collars available in the market are either made of brass or bronze. Since both contain copper we cannot use them for making our connections. Hence hose collars of appropriate size were made from quarter inch MS tubes. The MS pipe was taper turned in a lathe to obtain the collar shape. These hose collars were welded at the appropriate places in the generator tubes as well as in the fridge. Hose collars are used as the connections were made using rubber hoses.
FRIDGE MODIFICATION Exit for aqua ammonia
The Electrolux refrigeration system obtained was modified in order to accommodate the solar collector. For this the pipe coming from the absorber tank was cut using a cutting grinder. This pipe was extended outwards using a MS pipe of quarter inch diameter. The pipe was gas welded into the system. A hose collar was fixed to the other end of the tube by gas welding. Inlet for ammonia vapour
The concentric pipe adjacent to the heating coil was cut. Another quarter inch MS pipe was inserted into the system and end was sealed by gas welding. The end of the pipe was fixed with another hose collar of same specification. Bypass for weak ammonia solution
A hole was drilled on the outer tube of the near the heating coil. The pipe which carries the weak ammonia solution coming from the rectifier is welded to this hole. Thus the weak ammonia solution is routed to the absorber coils. Hydrogen charging line
A hole was drilled on the absorber tank and a threaded MS pipe of quarter inch diameter was gas welded on it. A valve was fixed on the threaded pipe. This is the hydrogen charging line.. Connections
Connections between the generator tube and the refrigerator are made using rubber hoses with nylon reinforcement. The rubber hoses are connected on the hose collars and the made leak proof by looking them with adjustable hose clips.
CHARGING Charging the system means filling the cooling system with refrigerant at appropriate concentration, pressure and quantity. In vapour absorption system, adequate amount of refrigerant must be charged. If the amount of refrigerant charged is too high, desired cooling effect will not be obtained as there will not be adequate space for the evaporation of the refrigerant. In our system, it contains three fluids. Hence charging the system is more complex compared to VAR system. Charging of each fluid is explained below. Ammonia
Since ammonia vapour is toxic with irritating smell, it is desirable to charge aqua ammonia solution instead of charging the system with ammonia vapour. For this fresh water is taken in a bucket and ammonia vapour is allowed to pass through this water. Ammonia readily absorbs in water. It is kept as such until the solution becomes saturated. The solution begins to boil as the reaction is exothermic. Now this solution is poured into the generator tube through the coupling welded at the top of it. Three fourth of the generator tube is filled with aqua ammonia solution. Then the generator tube is closed with the end cap. Hydrogen
Hydrogen is the carrier gas in the system. it helps to keep the pressure of the system constant. The system is pressurized only after charging of hydrogen. Hydrogen line is fixed at the absorber tank. There will a small pressure rise inside the system due to the liberation of ammonia vapour. This is because the system is charged with saturated ammonium hydroxide solution. A pressure equal to the vapour pressure of ammonia
exists inside the system. if the hydrogen charging line is open, this pressurized ammonia will escape. In order to avoid this, the pressure inside the system must be reduced. For this the generator tube is covered with ice cubes. This ensures low pressure inside the system as more vapour ammonia gets dissolved into the solution. Now the level of the generator pipe is raised so that absorber tank is now fully filled with aqua ammonia solution. This is done to ensure non return of the hydrogen gas during charging.
Now by means of rubber tube, hydrogen cylinder is connected to the hydrogen charging line. By monitoring the pressure gauge fixed on the generator, adequate amount of hydrogen is charged to get the required system pressure. After charging, the valve is closed and ice cube is removed
CALCULATIONS Dimension of solar collector
From the company specifications of the Electrolux system Power required at the generator is (Pactual)
= 80 W
Solar irradiation at tropical region (I)
=500 W/m2
Effective area required to get desired power
= (Pactual)/ I =80/500 =0.16 m2
Fixing the length of generator pipe as 1 m Width of solar collector
=0.16 m
For a double involute cusp, the width of the collector
=πd
Where d is the diameter of the generating circle of the involute. Now we have, πd d
=0.16 = 0.16/π
Diameter =.0509m =5.09cm =2”
Thus an involute of 2” diameter generating circle was designed for the solar collector.
System pressure
From the specification of Electrolux refrigeration, the system pressure
= 10 Kg/cm2
Energy calculation
Amount of energy released when one mol of ammonia reacts with one mol of water NH3 (gas) + H2O (aq) <==> NH4OH(aq) Enthalpy of reaction = -50 KJ/mol This implies that an enthalpy of 50 KJ/mol is released during the formation of ammonium hydroxide. This is the net enthalpy change which includes both the enthalpy change during mixing of ammonia vapour with water and also the formation of ammonia and hydroxide ions in the solution. Since ammonium hydroxide is a weak base, the amount of hydroxide ions is very less. Hence the enthalpy of reaction can be taken as the enthalpy of reaction of ammonium hydroxide solution itself. Thus 50 KJ/mol energy is required to liberate one mole of ammonia from ammonium hydroxide solution. Time required
The solar collector is so designed to produce 80W of energy. 80W = .08 KJ/s So one minute of heating gives 80 x 60 = 4.8 KJ of energy. This implies that keeping the solar collector out in the sun for about 10 mins, 50KJ of energy can be produced. This is sufficient to release one mole of ammonia vapour from the solution.
Mass of ammonia in solution
Molar concentration of saturated ammonium hydroxide
= 17 mol/ l
Molecular mass of ammonia
= 17 g/mol
Concentration of ammonia in one liter of solution = 17 x 17 =289 g/l Volume of ammonium hydroxide solution in the system
= 3/4th volume of the generator tube
Volume of one generator tube
= (π d2)/4 x 1
Volume of ammonium hydroxide solution
= 3/4 x 2 x (πd2)/4 x100 = 760.06 cm3 = 0.76 litres
Mass of ammonia in the solution
= 289 x 0.76 = 219.64 g
Cooling load calculation
Enthalpy change in generator, QG
= mass x latent heat of vaporization = 0.219 x 1372 KJ/Kg =300.25 KJ
This is the amount of energy absorbed at the generator to liberate ammonia vapour from solution To find the theoretical temperature drop
Assuming the fridge is empty with only air inside to obtain the max temperature drop Volume of cooling cabin
= 60 litres
Hence volume of air inside the cabin
= 0.06 m3
Density of air
= 1.15 Kg/ m3 (at sea level, 30oc)
Mass of air inside the cabin
= 0.069 Kg
Specific heat of air (c p)
1.005 kJ/kg K
=
= 40 oC
Assuming ambient temperature (Tamb)
= 313 K Enthalpy change of refrigerant during evaporation = Enthalpy change of air inside cabin + Enthalpy change of ammonia vapour Assuming a theoretical COP of 0.1 COP
= QE /QG
QE
= 0.1 x 300.25 =30 KJ
This much energy is absorbed from the evaporator cabin QE
= m (air) x c p x change in temperature
30
= 0.067 x 1.005 x (313 - Te) + 0.22 x 4.75 x (313 - Te)
Te
= 286.03 K =13.03 oC
This is the theoretical temperature drop which can be obtained from the modified system.
TEST PARAMETERS
The system was tested for different test parameters like •
Orientation of solar collector
•
Incident angle of solar irradiation
•
Temperature drop inside the evaporator
•
Temperature at generator tube
•
Pressure of the system
•
COP of the system
•
Efficiency of the system
For best results, the different parameters must be as follows Orientation of solar collector
: north-south direction.
Incident angle of solar irradiation
: horizontal.
Temperature at generator tube
: 90 oC.
Pressure of the system
: 10 bar
COST ANALYSIS
The cost of manufacturing a component is mainly classified in to two types MATERIAL COST
It is the cost of material used for manufacturing the product. Item Refrigerator Generator tube (1” diameter, 1m length) Collector plate ( 50” x 20”) PVC coating (50” x 15”) Mirror paper (50” x 15”) Matte finish black paint Sand paper ( # 80 and # 100) Air master ammonia Pressure gauge K valve ( 2 point type ) Nylon reinforced Rubber hose Hose clip Ammonium hydroxide Hydrogen cylinder Ice ¼” MS pipe Total
Quantity 1 no. 2 nos. 1 no. 1 no. 1 no. 50 ml 2 nos. 1 no. 2 nos. 3m 5 nos. 1500 ml 1 no. 7 liter 3m -
Cost ( in Rs) 5,000 600 600 150 150 40 20 450 2,000 300 40 250 1,000 40 300 10,940
OVER HEAD COST
All the expenditure other than material cost is called overhead expenses. Direct charges Item Hose collar fabrication Generator tube fabrication Solar collector fabrication Leak check/ Ammonia charging Hydrogen charging Total
Indirect charges
Coast in Rs 50 2,000 600 50 300 3,000
Item Administrative expenses Traveling expenses Total
Total over head cost
Cost in Rs 350 2,000 2,350
= 2,350+ 3,000 =5,350/-
Total cost
= 10,940 + 5,350/=16,290/-
Suggestions for modification
Our project was to build a domestic refrigerator with zero running cost. But the present system cannot be used during night and also during cloudy seasons. For this another system can be attached with the system. The additional system used is called a solar adsorption system which utilizes the ice battery concept which was used in earlier times.
The adsorption system is similar to vapour absorption system in which ammonia vapour is adsorbed on calcium chloride. Ammonia reacts with calcium chloride to give ammonium chloride and calcium crystals. The reaction is a reversible one. On heating this mixture, ammonia vapour is liberated from the mixture. This vapour is passed through an air cooled condenser to liquefy ammonia. This liquid ammonia is stored in a tank. When the generator begins to cool, the valve between the condenser and the storage
tank is closed. Then the liquid ammonia is allowed to pass through the evaporator tubes. Water kept in the evaporator cabin solidifies due to the evaporation of liquid ammonia inside the evaporator coil. The ammonia vapour thus formed is directed towards the generator where this vapour recombines with calcium chloride. The ice formed in the evaporator cabin provides cooling effect during night. Incorporating the above said system in our present system, we can obtain a round the clock domestic refrigeration working at zero running cost.
Future scope
In the present scenario of energy shortage this system will be most welcoming. Different forms of solar refrigeration systems using absorption technique is widely used now a day. A group of students in San Jose State University fabricated a solar ice maker using a refrigerant other than ammonia. Research is going on to effectively utilize the renewable energy to run absorption systems which can deliver better COP.
Conclusion
The present system is having slight defects which can be rectified by proper welding of joints; modifying the design of solar collector for wide acceptance angle and making
generator tubes with material of higher thermal conductivity. Proper installation is also required to get the desired effect.
REFERENCES
1.
C.P.ARORA,
“Refrigeration
and
Air
conditioning”,
Tata
McGraw-Hill
Publishing Company limited, New Delhi 2.
Refrigeration and Air Conditioning by Stoecker and Jones
3.
Solar absorption system by Sanford A. Klein, Ph.D., Fellow ASHRAE, and Douglas T. Reindl, Ph.D., Member ASHRAE
5.
Ammonia as refrigerant by
6.
Solar Energy: Fundamentals, Design, Modeling, and Applications by G. N. Tiwari
7.
ABSORPTION REFRIGERATION Kevin D. Rafferty, P.E. Geo-Heat Center Klamath Falls.
