(##)electrolux refrigeration using solar heat (solar refrigeration)
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ELECTROLUX REFRIGERATION USING SOLAR HEAT
PROJECT REPORT
Submitted in partial fulfillment of the requirementsfor 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
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DEPARTMENT OF MECHANICAL ENGINEERING
COLLEGE OF ENGINEERING, TRIVANDRUM 16
CERTIFICATE
This is to certify that the project report entitled Electrolux 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 Dr. B Anil
Assistant Professor Professor & Head
Dept. of Mechanical Engineering Dept. of Mechanical EngineeringCollege of Engineering Trivandrum College of Engineering Trivandrum
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ACKNOWLEDGEMENT---------------------------------------------------------------------------------
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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 departmental resources. We would also like to express our gratitude 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 of the project.
We also thank our classmates and seniors for their suggestions especially our seniors
Sabu V.G, Shibu K.R, Shome V.S, Santhosh K, Roby Sebastian for valuable ideas
imparted during the formation of this project. To summarize, it has been 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
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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
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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 departmental resources. We would also like to express our gratitude 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 of the project.
We also thank our classmates and seniors for their suggestions especially our seniors
Sabu V.G, Shibu K.R, Shome V.S, Santhosh K, Roby Sebastian for valuable ideas
imparted during the formation of this project. To summarize, it has been 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
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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 the name Electrolux refrigeration system. The principle behind Electrolux
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 available, environmentally friendly and can produce a better cooling 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
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INTRODUCTION
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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
economic preoccupation and ecological problems. Among the main done currently
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 refrigerator cycle invented in the 1920s is based on 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 operation principle of the refrigerating machine mono pressure invented 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
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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 thewaste heat in the exhaust
gases of the main propulsionunit 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 gas-
fired 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. Acomparison 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
http://findarticles.com/p/search/?qa=B.%20Chaouachihttp://findarticles.com/p/search/?qa=S.%20Gabsihttp://findarticles.com/p/articles/mi_7109/http://findarticles.com/p/articles/mi_7109/http://findarticles.com/p/search/?qa=B.%20Chaouachihttp://findarticles.com/p/search/?qa=S.%20Gabsihttp://findarticles.com/p/articles/mi_7109/http://findarticles.com/p/articles/mi_7109/ -
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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
http://www.sciencedirect.com/science/journal/01407007http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235765%232008%23999689995%23691306%23FLA%23&_cdi=5765&_pubType=J&view=c&_auth=y&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=724fb91da3985a63d4909113e5e6a425http://www.sciencedirect.com/science/journal/01407007http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235765%232008%23999689995%23691306%23FLA%23&_cdi=5765&_pubType=J&view=c&_auth=y&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=724fb91da3985a63d4909113e5e6a425 -
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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)
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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
http://www.patentstorm.us/patents/4843521/description.htmlhttp://www.patentstorm.us/patents/4843521/description.html -
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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).
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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
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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 inventorOliver 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.
http://en.wikipedia.org/wiki/William_Cullenhttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Diethyl_etherhttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Heat_of_vaporizationhttp://en.wikipedia.org/wiki/Oliver_Evanshttp://en.wikipedia.org/wiki/Vapor-compression_refrigerationhttp://en.wikipedia.org/wiki/Michael_Faradayhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/William_Cullenhttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Diethyl_etherhttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Heat_of_vaporizationhttp://en.wikipedia.org/wiki/Oliver_Evanshttp://en.wikipedia.org/wiki/Vapor-compression_refrigerationhttp://en.wikipedia.org/wiki/Michael_Faradayhttp://en.wikipedia.org/wiki/Ammonia -
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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 Carr 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 air-
conditioning of private homes and public buildings, and the refrigeration of foodstuffs in
http://en.wikipedia.org/wiki/William_Cullenhttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Diethyl_etherhttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Heat_of_vaporizationhttp://en.wikipedia.org/wiki/Oliver_Evanshttp://en.wikipedia.org/wiki/Vapor-compression_refrigerationhttp://en.wikipedia.org/wiki/Michael_Faradayhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Jacob_Perkinshttp://en.wikipedia.org/wiki/Absorption_refrigerationhttp://en.wikipedia.org/wiki/Ferdinand_Carr%C3%A9http://en.wikipedia.org/wiki/Ice_boxhttp://en.wikipedia.org/wiki/Icehouse_(building)http://en.wikipedia.org/wiki/William_Cullenhttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Diethyl_etherhttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Heat_of_vaporizationhttp://en.wikipedia.org/wiki/Oliver_Evanshttp://en.wikipedia.org/wiki/Vapor-compression_refrigerationhttp://en.wikipedia.org/wiki/Michael_Faradayhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Jacob_Perkinshttp://en.wikipedia.org/wiki/Absorption_refrigerationhttp://en.wikipedia.org/wiki/Ferdinand_Carr%C3%A9http://en.wikipedia.org/wiki/Ice_boxhttp://en.wikipedia.org/wiki/Icehouse_(building) -
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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, andpetrochemical plants,
refrigeration is used to maintain certain processes at their required low temperatures (for
example, in the alkylation ofbutenes 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 sea-
going 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.
http://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Propanehttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Oil_refinerieshttp://en.wikipedia.org/wiki/Chemical_planthttp://en.wikipedia.org/wiki/Petrochemicalhttp://en.wikipedia.org/wiki/Alkylationhttp://en.wikipedia.org/wiki/Butenehttp://en.wikipedia.org/wiki/Butanehttp://en.wikipedia.org/wiki/Octane_ratinghttp://en.wikipedia.org/wiki/Heat_pumphttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Propanehttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Oil_refinerieshttp://en.wikipedia.org/wiki/Chemical_planthttp://en.wikipedia.org/wiki/Petrochemicalhttp://en.wikipedia.org/wiki/Alkylationhttp://en.wikipedia.org/wiki/Butenehttp://en.wikipedia.org/wiki/Butanehttp://en.wikipedia.org/wiki/Octane_ratinghttp://en.wikipedia.org/wiki/Heat_pump -
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is the heat moved from the cold reservoir (to the hot reservoir).
is the workconsumed 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
http://en.wikipedia.org/wiki/Mechanical_workhttp://en.wikipedia.org/wiki/Kilojoulehttp://en.wikipedia.org/wiki/British_thermal_unithttp://en.wikipedia.org/wiki/Tonhttp://en.wikipedia.org/wiki/Short_tonhttp://en.wikipedia.org/wiki/Heat_of_fusionhttp://en.wikipedia.org/wiki/Pound_(mass)http://en.wikipedia.org/wiki/Kilowatthttp://en.wikipedia.org/wiki/Mechanical_workhttp://en.wikipedia.org/wiki/Kilojoulehttp://en.wikipedia.org/wiki/British_thermal_unithttp://en.wikipedia.org/wiki/Tonhttp://en.wikipedia.org/wiki/Short_tonhttp://en.wikipedia.org/wiki/Heat_of_fusionhttp://en.wikipedia.org/wiki/Pound_(mass)http://en.wikipedia.org/wiki/Kilowatt -
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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 sublimingdry
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. Workis 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.
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The most common types of refrigeration systems use the reverse-Rankine vapor-
compression 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.
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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 compressoras 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 condenserwhich 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
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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 water-
ammonia 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.
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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. Airis 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.
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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.
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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 aparamagneticsalt, such as cerium magnesiumnitrate. The active magneticdipoles
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 heat 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.
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TYPES OF VAPOUR ABSORPTION SYSTEM
Carres 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.
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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
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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
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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.
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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.
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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
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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.
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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
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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 of
22. Liquid ammonia has a very high standard enthalpy change of vaporization
(23.35 kJ/mol, cf. water40.65 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.
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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 /cm 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 (sal-
ammoniac); 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
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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 andjellyfish.
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 ofamides (which contain the NH2 ion),
for example lithium and ammonia react to give a solution oflithium amide:
2 Li + 2 NH3 2 LiNH2 + H2
Triple point 195.4 K (77.75 C),6.060 kPa
Critical point 405.5 K (132.3 C),11.300 MPa
Std enthalpy change
of fusion, fusHo
+5.653 kJ/mol
Std entropy change
of fusion, fusSo
+28.93 J/(molK)
Std enthalpy change
of vaporization, vapHo
+23.35 kJ/mol at BP of 33.4 C
Std entropychangeof vaporization vapSo , +97.41 J/(molK at BP of 33.4 C
PHYSICAL PROPERTIES
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Anhydrous ammonia is a clear liquid that boils at a temperature of -28F. 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 -28F, 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 0F to 68F, the volume of the liquid will
increase by about 10 percent. If the tank is 90 percent full at 0F, it will become 99
percent full at 68F. 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
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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
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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
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In the lungs, liquid anhydrous ammonia causes destruction of delicate respiratory tissue.
Exposure to ammonia vapor may cause:
Convulsive coughing.
Difficult or painful breathing.
Pulmonary congestion and death
Gaseous ammonia effects at various concentrations are as follows:
25 ppm or less - TWA
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
140 ppm - Moderate eye irritation; no long-term sequelae in exposures of less
than 2 hours
400 ppm - Moderate throat irritation
500 ppm - IDLH
700 ppm - Immediate eye injury
1000 ppm - Directly caustic to airway
1700 ppm - Laryngospasm
2500 ppm - Fatality (after half-hour exposure)
2500-6500 ppm - Sloughing and necrosis of airway mucosa, chest pain,
pulmonary edema, and bronchospasm
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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 -28F, 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
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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.
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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 hydrogenatomscovalentlybonded 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,
afterammonia, as well as a high heat of vaporization (40.65 kJ mol1), 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 kg1 at 0 C. Of common
substances, only that of ammonia is higher. This property confers resistance to melting
upon the ice ofglaciers and drift ice. Before the advent of mechanical refrigeration, ice
was in common use to retard food spoilage.
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One molecule of water has two hydrogenatomscovalentlybonded 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 theperiodic table, which are gases
such as hydrogen sulfide. Also the elements surrounding oxygen in the periodic table,
nitrogen, fluorine,phosphorus, sulfurand 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 apolarliquid that slightly
dissociates disproportionately into the hydronium ion (H3O+
(aq)) and an associated
hydroxide ion (OH(aq)).
2 H2O (l) H3O+
(aq) + OH
(aq)
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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.
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HYDROGEN THE CARRIER GAS
Properties and existence
Hydrogen is the most abundant element in the universe, making up 75% ofnormal 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 throughproton-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
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