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Abstract
The job of a refrigeration plant is to cool articles or substances down to, and maintain them at a temperature lower than the ambient temperature. Refrigeration can be defined as a process that removes heat.The oldest and most well-known among refrigerants are ice, water, and water. In the beginning, the sole purpose was to conserve food. The Chinese were the first to find out that ice increased the life and improved the taste of drinks and for centuries Eskimos have conserved food by freezing it. All we are using Refrigeration system now a days because of this high heat as well as global warming.
Refrigeration is a process in which work is done to move heat from one location to another. Refrigeration has many applications, including, but not limited to: household refrigerators, industrial freezers, cryogenics, and water conditioning.
Introduction
Refrigeration is a process of producing low temperatures as compared to the surrounding temperatures. It will be possible only if heat is transferred from the low temperature region to a high temperature region. Obviously it is not possible in the natural manner because heat flows from high temperature to low temperature like fluid flows from high pressure to low pressure/ current flows from high voltage to low voltage/ gas flows from high concentration to the region of low concentration. It means in refrigeration one is trying to go against the natural process as well as against the second law of thermodynamics which states that heat cannot flow from low temperature region to a high temperature region without the use of an external agent. The external agent in refrigeration is the compressor which introduces the most common method of refrigeration.
The most commonly used closed vapour compression refrigeration system consists of six main parts namely compressor, condenser, expansion device, evaporator, piping and circulating working substance called the refrigerant.
Objectives
• To build a low cost but effective vapour compression type refrigeration system.
• To make it available for commercial use.
1.4 Methodology:
• Collection of data and technical information from the manuals of SAMSUNG,
PHILIPS, WALTON .
• Purchase of the discrete components from local market.
PRINCIPLE OF REFRIGERATION
Pressure is the force on an object that is spread over a surface area. The equation for pressure is P = F/A. Pressure can be measured for a solid is pushing on a solid, but the case of a solid pushing on a liquid or gas requires that the fluid be confined in a container. The force can also be created by the weight of an object. So that,
P=F/A Where,
P=Pressure is new tons per square meter (N/m²) or Pascal’s (Pa).
F=The force in new tons (N).
A=The area in square meters (m²).
Another common unit of pressure measure is the bar.
One bar is equal to 100000 pa or N/m².
2 Pascal’s Law:
To honour the scientist Pascal, the SI metric system uses the term "Pascal" as a unit of pressure. A Pascal is a Newton per square meter (N/ m²).A Newton is the metric unit offorce. One Newton is equal to the mass of 1 kilogram being accelerated at rate of 1 meterper second per second. Pascal low states that pressure applied upon a confined fluid is transmitted equally in all directions. It is the basis of operation of most hydraulic and pneumatic system.
Pressure gage:
A pressure gage is an instrument, which used to measure fluid (Gaseous or liquid) pressure in a closed vessel. Pressure gages commonly used in the refrigeration industry are of two principle types. Such as manometer and bourdon tube.
Atmospheric pressure:
The earth is surrounded by an envelope of atmosphere or water extends upward from the surface of the earth to a distance of some 50 miles or more. Since water has mass and is subject to the actions of gravity. It exerts a pressure that is known as the atmospheric pressure.
Absolute pressure:
Absolute Pressure is the sum of the available atmospheric pressure and the gage pressure in the pumping system.
Heat:
12Heat is a from of energy. This is evident from the fact that heat can be converted in to other forms of energy and that other forms of energy can be converted in to heat. Thermodynamically heat is the defined as energy in transit from one body to another as the result temperature difference between the two bodies. All other transfers occur as work.
Specific heat:
Specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The specific heat of water is 1 calorie / gram °C.
So that ,Q = c m dT
Where,
Q = Heat added. c = Specific heat. m = Mass. dT = Change in temperature.
Sensible heat:
Sensible heat is the heat absorbed or given off by a substance that is not in the process of changing its physical state. Sensible heat can be sensed or measured with a thermometer and the addition or removal of sensible heat will always cause a change in the temperature of the substance.
Latent heat:
Latent heat is the heat absorbed or given off by a substance while it is changing its physical state. The heat absorbed or given off does not cause a temperature change in the substance the heat is latent or hidden. In other words, sensible heat is the heat that affects the temperature of things latent heat is the heat that affects the physical state of things.
Superheat:
Once a liquid has been vaporized, the temperature of the resulting vapour can be further increased by the additional of heat. The heat added to a vapour after vaporization is the sensible heat of the vapour, more commonly called super heat.
Temperature:
Temperature is a measurement of the average kinetic energy of the molecules in an object or system and can be measured with a thermometer or a calorimeter. It is a means of determining the internal energy contained within the system.
Absolute temperature:
The temperature value relative to absolute zero. The absolute zero is the theoretical temperature at which molecular motion vanishes and a body would have no heat energy the zero point of the Kelvin and Rankin temperature scales. Absolute zero may be interpreted as the temperature at which the volume of a perfect gas vanishes or more generally as the temperature of the cold source, that would render 100% efficient.
Saturation temperature:
13Saturation temperature means boiling point. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapour phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase transition.
Thermometer:
An instrument for measuring and indicating temperature typically one consisting of a narrow hermetically sealed glass tube marked with graduations and having at one end a bulb containing mercury or alcohol that expands and contracts in the tube with heating and cooling.
Work:
Work is the transfer of energy. Otherwise work is defined (in calculus terms) as the integral of the force over a distance of displacement. The SI units for work are the joule (J) or Newton-meter (N × m), from the function.
W = F × s Where, W=Is work. F=Is force. s = Is the displacement.
Power:
Power is the time rate at which work is done or energy is transferred. In calculus terms, power is the derivative of work with respect to time. The SI unit of power is the watt (W) or joule per second (J/s). Horsepower is a unit of power in the British system of measurement. The dimension of power is energy divided by time.
Energy:
Energy is the capacity of a physical system to perform work. Energy exists in several forms such as heat, kinetic or mechanical energy, light, potential energy, electrical, or other forms. The SI unit of energy is the joule (J).
Saturation temperature:
The temperature and pressure of the atmosphere must be at that point or in an interval of values for the substance to be saturated.
Superheated vapour:
The present invention involves a system and method for superheating the refrigerant gas in a motor vehicle water conditioning system in order to minimize the amount of work required to be performed by the compressor. In an embodiment of the present invention, the refrigerant gas is diverted through the exhaust manifold immediately after passing through the compressor. As the refrigerant gas passes through the exhaust manifold. 14The surrounding hot exhaust gases thereby increasing the refrigerant gas pressure to reduce the amount of work done by the compressor superheat it. Refrigerant vapour at a temperature that is higher than its boiling point at a given pressure.
Sub cooled liquid:
A compressed fluid (also called a sub cooled fluid or sub cooled liquid) is a fluid under thermodynamic conditions that force it to be a liquid. It is a liquid at a temperature lower than the saturation temperature at a given pressure. In a plot comparing absolute pressure and specific volume (commonly called a P-v diagram), of a real gas, a compressed fluid is to the left of the liquid-vapour phase boundary; that is, it will be to the left of the vapour dome.
Vaporization:
Vaporization is the transition of matter from a solid or liquid phase into a gaseous phase. Water boiling into steam is an example of vaporization.
Evaporation:
Evaporation is the process by which water is converted from its liquid form to its vapour form and thus transferred from land and water masses to the atmosphere. Evaporation from the oceans accounts for 80% of the water delivered as precipitation with the balance occurring on land, inland waters and plant surfaces.
The cooling effect of evaporation:
Evaporation is the removal of water molecules from the surface of a liquid. If alcohol is splashed on the back of the hand, it produces a cooling effect. When a liquid evaporates, this involves a change of state from liquid to gas. This change requires heat energy called latent heat/ hidden heat. As plants transpire, water is evaporated from the leaves. Evaporation has a cooling effect in this situation as well. Plants are cooled during transpiration. Evapouration is used by the body to regulate its temperature. When the temperature of the body rises we begin to perspire more. Sweat glands in the skin will produce more sweat. This sweat evaporates and the result is a cooling effect on the skin. The rate at which the evapouration takes place depends on the rate of water over the skin and this is why we fan ourselves to speed up the process. When the surroundings are cold, the blood vessels contract, to prevent heat loss. In these circumstances the subcutaneous fat serves as insulation and is sometimes burnt to provide heat. H waters may also become erect to trap water as further insulation. In circumstances where the temperature is high, our metabolic rate falls so that less heat is generated by our body. In cold temperatures extra heat is produced by an increase of the metabolic rate, mainly of the liver and muscles. This sometimes causes rhythmical involuntary contractions of the skeletal muscles (shivering).
Condensation:
It is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of evaporation. 15When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition. Upon the slowing-down of the molecules of the material, the overall attraction forces between these prevail and bring them together at distances comparable to their sizes. Since the condensing molecules suffer from reduced degrees of freedom and ranges of motion, their prior kinetic energy must be transferred to an absorbing colder entity either a center of condensation within the gas volume or some contact surface.
Critical temperature:
The temperature at which some phase change occurs in a metal during heating or cooling, i.e. the temperature at which an arrest or critical point is shown on heating or cooling curves.
Critical pressure:
Critical pressure is the lowest pressure at which a substance can exist in the liquid sate at
its critical temperature. It is the saturation pressure at the critical temperature.
Enthalpy:
Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.
So that, H = U + p V
Where, H = Is the enthalpy of the system. U = Is the internal energy of the system. p = Is
the pressure at the boundary of the system and its environment.
V = Is the volume of the system.
Entropy:
A thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work often interpreted as the degree of disorder or randomness in the system.
Refrigeration history:
In Prehistoric times, man found that his game would last during times when food was not available if stored in the coolness of a cave or packed in snow. In China, before the first millennium, ice was harvested and stored. Hebrews, Greeks, and Romans placed largeamounts of snow into storage pits dug into the ground and insulated with wood and straw. The ancient Egyptians filled earthen jars with boiled water and put them on their roofs, thus exposing the jars to the night’s cool water. In India, evapourative cooling was employed. When a liquid vapourizes rapidly, it expands quickly. The rising molecules of vapour abruptly increase their kinetic energy and this increase is drawn from the immediate surroundings of the vapour. These surroundings are therefore cooled. The intermediate stage in the history of cooling foods was to add chemicals like sodium nitrate or potassium nitrate to water causing the temperature to fall. Cooling wine via this method was recorded in 1550, as were the words "to refrigerate”. Cooling drinks came into vogue by 1600 in France. Instead of cooling water at night people rotated long necked bottles in water in which saltpeter had been dissolved. This solution could be used to produce very low temperatures and to make ice. By the end of the 17th century, iced liquors and frozen juices were popular in French society. The first known artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in 1748.Cullen let ethyl ether boil into a partial vacuum he did not however, use the result to any practical purpose. Ice was first shipped commercially out of Canal Street in New York City to Charleston, South Carolina in 1799. Unfortunately, there was not much ice left when the shipment arrived. New Englanders Frederick Tudor and Nathaniel Wyeth saw the potential for the ice business and revolutionized the industry through their efforts in the first half of the 1800s. Tudor, who became known as the “Ice King”, focused on shipping ice to tropical climates. He experimented with insulating materials and built icehouses that decreased melting losses from 66 percent to less than 8 percent. Wyethdevised a method of quickly and cheaply cutting uniform blocks of ice that transformed the ice industry, making it possible to speed handling techniques in storage,transportation and distribution with less waste.
In 1805, an American inventor, Oliver Evans, designed the first refrigeration machine that used vapour instead of liquid. Evansnever constructed his machine, but one similar to it was built by an American physician,John Gorrie. In 1842, the American physician John Gorrie, to cool sickrooms in a Floridahospital designed and built an water-cooling apparatus for treating yellow fever patients.His basic principle that of compressing a gas, cooling it by sending it through radiatingcoils, and then expanding it to lower the temperature further is the one most often used inrefrigerators today. Giving up his medical practice to engage in time consumingexperimentation with ice making, he was granted the first U.S. patent for mechanicalrefrigeration in 1851. Commercial refrigeration is believed to have been initiated by an American businessperson, Alexander C. Twinning, in 1856. Shortly afterward an Australian, James Harrison examined the refrigerators used by Gorrie and Twinning and introduced vapour-compression refrigeration to the brewing and meatpacking industries. Ferdinand Carré of France developed a somewhat more complex system in 1859.17Unlike earlier compression machines, which used water as a coolant, Carré's equipment contained rapidly expanding ammonia (Ammonia liquefies at a much lower temperature than water and is thus able to absorb more heat.) Carré's refrigerators were widely used, and vapour compression refrigeration became and still is, the most widely used method of cooling. However, the cost, size and complexity of refrigeration systems of the time, coupled with the toxicity of their ammonia coolants prevented the general use of mechanical refrigerators in the home. Most households used iceboxes that were supplied almost daily with blocks of ice from a local refrigeration plant. Beginning in the 1840s,refrigerated cars were used to transport milk and butter. By 1860, refrigerated transportwas limited to mostly seafood and dwatery products. The refrigerated railroad car was patented by J.B. Sutherland of Detroit, Michigan in 1867. He designed an insulated car with ice bunkers in each end. Water came in on the top passed through the bunkers and circulated through the car by gravity controlled by the use of hanging flaps that created differences in water temperature. The first refrigerated car to carry fresh fruit was built in 1867 by Parker Earle of Illinois, who shipped strawberries on the Illinois Central Railroad. Each chest contained 100 pounds of ice and 200 quarts of strawberries. It wasnot until 1949 that a refrigeration system made its way into the trucking industry by way of a roof-mounted cooling device, patented by Fred Jones. Brewing was the first activity in the northern states to use mechanical refrigeration extensively, beginning with an absorption machine used by S. Liebmann’s Sons Brewing Company in Brooklyn, New York in 1870. Commercial refrigeration was primarily directed at breweries in the 1870s and by 1891, nearly every brewery was equipped with refrigerating machines. Natural ice supply became an industry unto itself. More companies entered the business, prices decreased and refrigeration using ice became more accessible. By 1879, there were 35 commercial ice plants in America, more than 200 a decade later, and 2,000 by 1909. No pond was safe from scraping for ice production not even Thoreau’s Walden Pond, where 1,000 tons of ice was extracted each day in 1847. However, as time went on ice, as a refrigeration agent, became a health problem. Says Bern Nagengast, co-author of Heat and Cold Mastering the Great Indoors (published by the American Society of Heating, Refrigeration and Water-conditioning Engineers), “Good sources were harder and harder to find. By the 1890’s, natural ice became a problem because of pollution and sewagedumping.” Signs of a problem were first evident in the brewing industry. Soon the meatpacking and dwatery industries followed with their complaints. Refrigeration technology provided the solution ice, mechanically manufactured giving birth to mechanical refrigeration. Carl (Paul Gottfried) von Linde in 1895 set up a large-scale plant for the production of liquid water. Six years later he developed a method for separating pure liquid oxygen from liquid water that resulted in widespread industrial conversion to processes utilizing oxygen (e.g., in steel manufacture). Though meatpackers were slower to adopt refrigeration than the breweries, they ultimately used refrigeration pervasively. By 1914, the machinery installed in almost all American packing plants was the ammonia compression system, which had a refrigeration capacity of well over 90,000 tons/day. Despite the inherent advantages, refrigeration had its problems. Refrigerants like sulfur dioxide and methyl chloride were causing people to die. Ammonia had an equally serious toxic effect if it leaked. Refrigeration engineers searched for acceptable substitutes until the 1920s, when a number of synthetic refrigerants called halocarbons or CFCs (chlorofluorocarbons) were developed by Frigidwatere. The best known of these substances was patented under the brand name of Freon. Chemically Freon was created by the substitution of two chlorine and two fluorine atoms for the four hydrogen atoms in methane (CH4) the result, dichlorodifluoromethane (CCl2F2) is odorless and is toxic only in extremely large doses.18Though ice, brewing, and meatpacking industries were refrigeration’s major beneficiaries, many other industries found refrigeration a boon to their business. In metal working, for instance mechanically produced cold helped temper cutlery and tools.Iron production got a boost, as refrigeration removed moisture from the water delivered to blast furnaces, increasing production.Allied fighting ships held carbon-dioxide machines to keep ammunition well below temperatures at which high explosives became unstable.In 1973, Prof. James Lovelock reported finding trace amounts of refrigerant gases in the atmosphere. In 1974, Sherwood Rowland and Mario Molina predicted that chlorofluorocarbon refrigerant gases would reach the high stratosphere and there damage the protective mantle of the oxygen allotrope, ozone. In 1985 the "ozone hole" over the Antarctic had been discovered and by 1990 Rowland and Molina's prediction was provedcorrect. The basic components of today’s modern vapour-compression refrigeration system are a compressor, a condenser, an expansion device, which can be a valve, a capillary tube, an engine, or a turbine; and an evapourator. The gas coolant is first compressed, usually by a piston, and then pushed through a tube into the condenser. In the condenser, the winding tube containing the vapour is passed through either circulating water or a bath of water, which removes some of the heat energy of the compressed gas.The cooled vapour is passed through an expansion device to an area of much lower pressure as the vapour expands, it draws the energy of its expansion from its surroundings or the medium in contact with it. Evaporators may directly cool a space by letting the vapour come into contact with the area to be chilled or they may act indirectly-i.e. by cooling a secondary medium such as water. In most domestic refrigerators, the coil containing the evaporator directly contacts the water in the food compartment. At the end of the process, the warmed gas is drawn toward the compressor.
REFRIGERATION SYSTEM
We can classification seven types of refrigeration systen from principle and operation.
1) Dry-ICE Refrigeration system.
2) Steam-Jet Refrigeration system.
3) Water cycle refrigeration system.
4) Vapour compression refrigeration system.
5) Vapour absorption refrigeration system.
6) Thermo-Electric Refrigeration system.
7) Cryogenics refrigeration system.
Dry-ICE Refrigeration system:
Dry ice is the solid carbon dioxide having the temperature of -78 degree Celsius. Dry ice converts directly from solid state to gaseous this process is called as sublimation. Dry ice can be pressed into various sizes and shapes as blocks or slabs. Dry ice is usually packed in the frozen food cartons along with the food that has to be kept frozen for long intervals of time. When the dry ice gets converted into vapour state it keeps the food frozen. The process of dry ice refrigeration is now a days being used for freezing the food in watercraft transportation.
Dry-Ice refrigeration system.
This methods of refrigeration system can be used only in places where small amount of refrigeration is required in places like laboratories, workshops, water coolers, small old drink shops, small hotels etc. In fact the ordinary ice and dry ice used for the refrigeration purposed have to be manufactured by the cyclic methods of refrigeration which we shall see in the next article. However, in the earlier days the ice used for the cooling purposes was usually harvested during the winter seasons from the ponds and lakes and stored in large insulated ice houses for the use throughout the year.
Steam jet refrigeration system:
If water is sprayed into a chamber where a low pressure is maintained a part of the water will evapourate. The enthalpy of evapouration will cool the remaining water to its saturation temperature at the pressure in the chamber. Obviously lower temperature will require lower pressure. Water freezes at 0oC hence temperature lower than 4oC cannot be obtained with water. In this system, high velocity steam is used to entrain the evapourating water vapour. High-pressure motive steam passes through either convergent or convergent-divergent nozzle where it acquires both sonic or supersonic velocity and low pressure of the order of 0.009 kPa corresponding to an evapourator temperature of
4oC. The high momentum of motive steam entrains or carries along with it the water vapour evapourating from the flash chamber. Because of its high velocity it moves the vapours against the pressure gradient up to the condenser where the pressure is 5.6 to 7.4kPa corresponding to condenser temperature of 35-45oC. The motive vapour and the evapourated vapour both are condensed and recycled. It can be seen that this system requires a good vacuum to be maintained. Sometimes booster ejector is used for this purpose. This system is driven by low- grade energy that is process steam in chemical plants or a boiler.
Schematics diagram of steam jet refrigeration system.
In 1838, the Frenchman Pelletan was granted a patent for the compression of steam by means of a jet of motive steam. Around 1900, the Englishman Charles Parsons studied the possibility of reduction of pressure by an entrainment effect from a steam jet. However, the credit for constructing the steam jet refrigeration system goes to the French engineer, Maurice Leblanc who developed the system in 1907-08. In this system, ejectors were used to produce a high velocity steam jet (≈ 1200 m/s). Based on Leblanc’s design the first commercial system was made by Westinghouse in 1909 in Paris. Even though the efficiency of the steam jet refrigeration system was low, it was still attractive as water is harmless and the system can run using exhaust steam from a steam engine. From 1910 onwards, stem jet refrigeration systems were used mainly in breweries, chemical factories, warships etc. In 1926, the French engineer Fellahin improved the machine by introducing multiple stages of vaporization and condensation of the suction steam. Between 1928-1930, there was much interest in this type of systems in USA. In USA they were mainly used for water conditioning of factories, cinema theatres, ships and even railway wagons. Several companies such as Westinghouse, Ingersoll Rand and Carrier started commercial production of these systems from 1930. However, gradually these systems were replaced by more efficient vapour absorption systems using LiBrwater. Still, some east European countries such as Czechoslovakia and Russia manufactured these systems as late as 1960s. The ejector principle can also be used to provide refrigeration using fluids other than water, i.e., refrigerants such as CFC-11, CFC-21, CFC-22, CFC-113, CFC-114 etc. The credit for first developing these closed vapour jet refrigeration systems goes to the Russian engineer, I.S. Badylkes around 1955.
Water cycle refrigeration system:
Water cycle refrigeration systems belong to the general class of gas cycle refrigeration systems in which gas is used as the working fluid. The gas does not under go any phase change during the cycle, consequently, all the internal heat transfer processes are sensible heat transfer processes. It applications in water craft cabin cooling and also in the liquefaction of various gases. Water cycle refrigeration systems use water as their refrigerant compressing it and expanding it to create heating and cooling capacity. 22Water cycle is not a new technology. Water cycle or ‘cold water machines’ were available from Companies such as J & E Hall in the early 1900s. These were used on board ships and by food producers and retailers to provide cooling for their food stores. However, the development of vapour compression cycles based initially on ethyl ether ammonia or sulphur-dioxide but superseded by chlorofluorocarbons (CFCs) led to the gradual replacement of the majority of water cycle systems except in the field of watercraft water conditioning. Environmental concerns about CFCs, ozone depletion, global warming and the resulting increasingly stringent legislation have renewed interest in alternatives to the current standard of vapour-compression refrigeration technologies. The use of water cycle is one of these offering a benign substitute for CFC refrigerants as well as reduced energy consumption and capital costs for targeted applications. Water cycle refrigeration works on the reverse Brayton or Joule cycle. Water is compressed and then heat removed this water is then expanded to a lower temperature than before it was compressed. Work must be taken out of the water during the expansion otherwise the entropy would increase. Work is taken out of the water by an expansion turbine which removes energy as the blades are driven round by the expanding water. This work can be usefully employed to run other devices such as generators or fans. Often though it is used to power a directly connected (bootstrap) compressor which elevates the compressed (hot) side pressure further without added external energy input essentially recycling the energy removed from the expanding water to compress the high pressure water further. The increase in pressure on the hot side further elevates the temperature and makes the water cycle system produce more useable heat (at a higher temperature). The cold water after the turbine can be used as a refrigerant either directly in an open system or indirectly by means of a heat exchanger in a closed system.
The efficiency of such systems limited to a great extent by the efficiencies of compression and expansion as well as those of the heat exchangers employed. Originally slow speed reciprocating compressors and expanders were used. The poor efficiency and reliability of such machinery were major factors in the replacement of such systems with vapour compression equipment. However, the development of rotary compressors and expanders (such as in car turbochargers) greatly improved the isentropic efficiency and reliability of the water cycle. Advances in turbine technology together with the development of water bearings and ceramic components offer further efficiency improvements. Combining these advances with newly available compact heat exchangers which have greatly improved heat transfer characteristics makes competition with many existing vapour compression quite feasible
Figure: Schematic of a simple watercraft refrigeration cycle.23In figure shows the schematic of a simple watercraft refrigeration system and the operating cycle on T-s diagram. This is an open system. As shown in the T-s diagram the outside low pressure and low temperature water (state 1) is compressed due to ram effect to ram pressure (state 2). During this process its temperature increases from 1 to 2. This water is compressed in the main compressor to state 3, and is cooled to state 4 in the water cooler. Its pressure is reduced to cabin pressure in the turbine (state 5), as a result its temperature drops from 4 to 5. The cold water at state 5 is supplied to the cabin. It picks up heat as it flows through the cabin providing useful cooling effect. The power output of the turbine is used to drive the fan which maintains the required water flow over the water cooler. This simple system is good for ground cooling (when the watercraft is not moving) as fan can continue to maintain water flow over the water cooler.
Vapour compression refrigeration system:
Refrigeration systems are also used for providing cooling and dehumidification in summer or personal comfort (water conditioning). The first water conditioning systems were used for industrial as well as comfort water conditioning. Eastman Kodak installed the first water conditioning system in 1891 in Rochester, New York for the storage of photographic films. An water conditioning system was installed in a printing press in 1902 and in a telephone exchange in Hamburg in 1904. Many systems were installed in tobacco and textile factories around 1900. The first domestic water conditioning system was installed in a house in Frankfurt in 1894. A private library in St Louis, USA was water conditioned in 1895, and a casino was water conditioned in Monte Carlo in 1901. Efforts have also been made to water condition passenger rail coaches using ice. The widespread development of water conditioning is attributed to the American scientist and industrialist Willis Carrier. Carrier studied the control of humidity in 1902 and designed a central water conditioning plant using water washer in 1904. Due to the pioneering efforts of Carrier and also due to simultaneous development of different components and controls water conditioning quickly became very popular especially after 1923. At present comfort water conditioning is widely used in residences, offices, commercial buildings, water ports, hospitals and in mobile applications such as rail coaches, automobiles, watercrafts etc. Industrial water conditioning is largely responsible for the growth of modern electronic, pharmaceutical, chemical industries etc. Most of the present day water conditioning systems use either a vapour compression refrigeration system or a vapour absorption refrigeration system. The capacities vary from few kilowatts to megawatts. As shown in the figure the basic system consists of an evaporator, compressor, condenser and an expansion valve.