ABSTRACT
This work investigates the result of an experimental study carried out to determine the performance of domestic refrigerator when a propane-butane mixture is liquefied petroleum gas (LPG) which is locally available and comprises 24.4% propane, 56.4% butane and 17.2% isobutene which is very from company to company. The LPG is cheaper and possesses an environmental friendly nature with no ozone depletion potential (ODP). It is used in world for cooking purposes. The various methods of refrigeration on the basis of standard refrigerant discussed. He refrigerator used in the present study is of medium size with a gross capacity of 125 litre and is designed to work on LPG. The performance parameters investigated is the refrigeration effect in certain time. The refrigerator worked efficiently when LPG was used as refrigerant instead of CFC 12. The evaporator temperature reached -5 ºC with and an ambient temperature of 12 ºC. Also from the experiment which done in atmospheric condition, we can predict the optimum value of cooling effect with the suitable operating condition of regulating valve and capillary tube of the system. The results of the present work indicate the successful use of this propane-butane mixture as an alternative refrigerant to CFC 12 in domestic refrigerant.
1
CHAPTER 1:- REFRIGERATION
1.1 INTRODUCTION The term ‘refrigeration’ in a broad sense is used for the process of removing heat (i.e. cooling) from a substance. It also includes the process of reducing and maintaining the temperature of a body below the general temperature of its surroundings. In other words, the refrigeration means a continued extraction of heat from a body, whose temperature is already below the temperature of its surroundings. For example, if some space (say in cold storage) is to be kept at -2 ºC, we must continuously extract heat which flows into it due to leakage through the walls and also the heat, which is brought into it with the articles stored after the temperature is one reduced to -2 ºC. Thus in a refrigerator, heat is virtually being pumped from a lower temperature to a higher temperature. According to second law of thermodynamics, this process can only be performed with the aid of some external work. It is thus obvious, that supply of power (say electrical motor) is regularly required to drive a refrigerator. Theoretically, the refrigerator is a reversed heat engine, or a heat pump which pumps heat from cold body and delivers to a hot body. The substance which works in a heat pump to extract heat from a cold body and to deliver it to a hot body is called refrigerant. When people hear the word refrigeration they immediately think of the refrigerator in their kitchen. However there are actually quite a few different kinds of refrigeration out three and they each have their own methods of functioning. One particular type of refrigeration is industrial refrigeration. This type of refrigeration is typically used for cold storage, food processing, and chemical processing. The equipment is very large and made of industrial stainless steel. Industrial refrigeration, which frequently uses ammonia refrigeration to maintain temperature, is
2
necessary for computer, foodstuffs, blood, vaccines, and quite a few other goods that must maintain a constant and steady temperature at all times. Temperatures that are too high or too low may spoil certain goods or ruin them. As a result industrial refrigeration is especially important maintaining temperature is as well. Since temperature is so important into industrial refrigeration companies offering this service must pay attention at all times to the temperature of the industrial refrigerators.
1.2 HISTORY OF REFRIGERATION The refrigeration system is known to the man, since the middle nineteenth century. The scientist, of the time, developed a few stray machines to achieve some pleasure. But it paved the way by inviting the attention of scientist for proper studies and research. They were able to build a reasonably reliable machine by the end of nineteenth century for the refrigeration jobs. But with the advent of efficient rotary compressors and gas turbines, the science of refrigeration reached its present height. Hebrews, Greeks, and Romans placed large amounts 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 their roofs, thus exposing the jars to the night’s cool air. In India, evaporating cooling was employed. When a liquid vaporises rapidly, it expands quickly. The rising molecules of vapour abruptly increase heir 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 above method was recorded in 1550, as were the words “to refrigerate”.
3
Cooling drinks came into vogue by 1600 in France. Instead of cooling water at night, people rotate long-necked bottles in water in which saltpetre had been dissolved. This solution could be used to produce very low temperature 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 Glasow in 1748. Beginning in the 1840, refrigerated cars were used to transport milk and butter. By 1860, refrigerated transport was limited to mostly seafood and dairy 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. Air 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 air temperature. 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 1870 and 1891, nearly every brewery was equipped with refrigerating machines. Natural ice supply became an industry unto itself. 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 health problem. Says Bern Nagengast, co-author of Heat and Cold: Mastering the Great Indoors (published by the American Society of Heating, Refrigeration and Air-conditioning Engineers), “Good sources were harder and harder to find. By the 1890’s, natural ice became a problem because of
4
pollution and sewage dumping.” Signs of a problem were first evident in the brewing industry. Soon the meatpacking and dairy 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 air. Six years later he developed a method for separating pure liquid oxygen from liquid air that resulted in widespread industrial conversion to processes utilizing oxygen (e.g. in steel manufacture).
1.3 TYPES OF REFRIGERATION The difference types of refrigeration systems are given below.
1.3.1 Cyclic Refrigeration In the cyclic process of refrigeration the heat is removed from the low temperature reservoir and is thrown to high temperature. As per the second law of thermodynamics the natural flow of heat is from the high temperature to low temperature reservoir. In the cyclic refrigeration process since the flow of heat is reversed, the external work has to be done on the system. The cyclic process of refrigeration is also reverse of the thermodynamic power cycle or Carnot cycle in which the heat flows from high temperature reservoir to low temperature reservoir; hence the cycle of refrigeration is also called as Reversed Carnot Cycle.
There are two types of cyclic process of refrigeration: »
Vapour cycle and
5
»
Gas cycle.
The vapour cycle is classified into » »
Vapour compression cycle and vapour absorption cycle.
1.3.1.1 Vapour Compression Cycle In a vapour compression system, an evaporator and a gas-liquid separator are received in a common casing, so that the gas-liquid separator and the evaporator are placed close to each other. Thus, it is possible to limit heart absorption of the liquid phase refrigerant from the atmosphere to reduce the heat loss upon discharge of the refrigerant from the gas-liquid separator. Also, it is possible to reduce pressure loss in refrigerant passage between the gas-liquid separator and the evaporator
1.3.1.2 Vapour Absorption Cycle Before the development of the vapour compression system of refrigeration, vapour absorption system was very widely used. The vapour compression system replaced vapour absorption system because it has high coefficient performance (COP). The vapour absorption system requires very less amount of electricity but large amount of heat; hence it can be used very effectively in industries where very large stocks of excessive stem are available. In such cases there is not only effective utilization of steam, but also lots of savings in electricity costs.
1.3.1.3 Gas Cycle Just as the vapour are used for cooling in the vapour compression cycle and vapour absorption cycle, the gas is used cooling in gas refrigeration cycle. When the gas is throttled from very high pressure to lower pressure in throttling valve, its
6
temperature reduces suddenly while its enthalpy remains constant. This principle is in gas refrigeration system. In the system instead of using Freon or ammonia as the refrigerant, the gas is used as the refrigerant. Throughout the cycle there are no phase changes of the gas, which are observed in the liquid refrigerant. Air is the most commonly used gas, also called as refrigerant in this case, in the gas refrigeration cycles.
1.3.2 Non Cyclic Refrigeration In these methods, refrigeration can be accomplished by melting ice or by dry ice. These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable coolers.
1.3.3 Thermoelectric Refrigeration A refrigeration effect can also be achieved without using any moving parts by simply passing a small current through a closed circuit made up of two dissimilar materials. This effect is called Peltier effect, and a refrigerator that works on this principle is called a thermoelectric refrigerator.
7
Fig : 1.1 Thermoelectric refrigeration Under steady-state operating conditions, heat will be transferred from the refrigerated space to the cold junction. The other junction will be at a temperature above the ambient, and heat will be transferred from the junction to the surrpundings.
1.3.4 Magnetic Refrigeration
Magnetic refrigeration is a cooling technology based on the magneto caloric effect. This technique can be used to attain extremely low temperatures (well below 1K), as well as the ranges used in common refrigerators, depending on the design of the system.
8
1.3.5 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.
1.4 UNITS OF REFRIGERATION Domestic and commercial refrigerators may be rated in kj/s, or Btu/h of cooling. Commercial refrigerators in the US are in tons of refrigeration, but elsewhere in kw. One ton of refrigeration capacity can freeze one short ton of water at 0 ºC (32 ºF) in 24 hours. Latent heat of ice (i.e. heat of fusion) = 333.55 kj/kg ≈ 144 Btu/lb
One short ton = 2000lb Heat extracted = (2000)*(144)/24 hr = 288000 Btu/24 hr = 12000 Btu/hr = 200 Btu/min 1 tonne of refrigeration = 200 Btu/min = 3.517 kj/s = 3.517 kw
9
The practical unit of refrigeration is expressed in terms of ‘tonne of refrigeration’ (briefly written as TR). A tonne of refrigeration is defined as the amount of refrigeration effect produced by the uniform melting of one tonne (1000 kg) of ice
from and 0 ºC in 24 hours. Since the latent heat of ice is 335 kj/kg, therefore one tonne of refrigeration, 1 TR = 1000 * 335 kj in 24 hours = (1000) * (335) / (24) * (60) = 232.6 kj/min
In actual practice, one tonne of refrigeration is taken as equivalent to 210 kj/min or 3.5 kw (i.e. 3.5 kj/s).
1.5 COEFFICIENT OF PERFORMANCE OF A REFRIGERATOR
The coefficient of performance (briefly written as C.O.P.) is the ratio of heat extracted in the refrigerator to the work done on the refrigerant. It is also known as theoretical coefficient of performance. Mathematically, Theoretically C.O.P. = Q/W Where
Q = Amount of heat extracted in the refrigerator ( or the amount of refrigeration effect produced, or the capacity of a refrigerator), and W = Amount of work done.
1.6 Application
1.6.1 Food processing, preservation and distribution
10
1. Storage of Raw Fruits and Vegetables 2. Fish 3. Meat and poultry 4. Dairy Products (a). Ice cream (b). Butter (c). Cheese (d). Buttermilk 5. Beverages 6. Candy 7. Processing and distribution of frozen food
1.6.2 Chemical and process industries 1. Separating of gases 2. Condensation of gases 3. Dehumidification of Air 4. Storage as liquid at low pressure 5. Cooling for preservation
1.6.3 Special application of refrigeration 1. Cold Treatment of Metals 2. Medical 3. Ice Skating Rinks 4. Construction
11
5. Desalination of water 6. Ice manufacturer
It is also widely used for the cooling of storage chambers in which perishable food, drinks and medicines are stored. The refrigeration also has wide applications in sub-marine ships, rockets and aircrafts.
12
CHAPTER 2 :- REFRIGERATION PROCESS
2.1 REFRIGERATOR
Refrigerator keep things cold because of the nature of the heat. Thermodynamics essentially starts that if a cold object is placed to a next to a hot object, the cold object will become warmer and the hot object will become cooler. A refrigerator does not cool items by lowering their original temperature; instead, an evaporating gas called a refrigerant draws heat away, leaving the surrounding area much colder. Refrigerators and air conditioners both work on the principle of cooling through evaporation.
Fig 2.1 : Refrigerator
13
A refrigerator consists of two storage compartment – one for frozen items and the other for items requiring refrigeration but no freezing. These compartment are surrounded by a series of heat-exchanging pipes. Near the bottom of the refrigerator unit is a heavy metal device called a compressor. The compressor is powered by an electric motor. More heat-exchanging pipes are coiled behind the refrigerator. Running through the entire system is pure ammonia, which evaporates at -27 ºF. this system is closed, which means nothing is lost or added while it is operating. Because liquid ammonia is a powerful chemical, a leaking refrigerator should be repaired or replaced immediately. The refrigeration process begins with the compressor. Ammonia compressed until it becomes very hot from the increased pressure. This heated gas flows through the coils behind the refrigerator, which allows excess heat to be released into the surrounding air. This is why users sometimes fill warm air circulating around the fridge. Eventually the ammonia cools down to the point where it become a liquid. This liquid form of ammonia is then forced through a device called an expansion valve or capillary tube. Essentially, the expansion valve has a small opening or the capillary tube has a very small diameter of copper tube that the liquid ammonia is turned into a very cold, fast-moving mist, evaporating as it travels through the coils in the freezer. As the evaporating ammonia gas absorbs more heat, its temperature rises. Coils surroundings the lower refrigerator compartment are not as compact. The cool ammonia still draws heat from the warmer objects in the fridge, but not as much as the freezer section. The ammonia gas is drawn back into the compressor, where the entire cycle of pressurization, cooling and evaporation begins anew.
2.2 REFRIGERATION CYCLE
14
The refrigeration cycle uses a fluid, a called a refrigerant, to move heat from one place to other. We will begin with the cool, liquid refrigerant entering the indoor coil, operating as the evaporating during cooling. As the name implies, refrigerant in the evaporator “evaporator”. Upon entering the evaporator, the liquid refrigerant’s temperature is between 40 and 50 ºF and without changing its temperature, it absorbs heat as it changes state from a liquid to a vapour. The heat comes from the warm, moist room air blown across the evaporator coil. As it passes over the cool coil, it gives up some of its heat and moisture may condense from it. The cooler, drier room air is re-circulated by a blower into the space to be cooled. The vapour refrigerant now moves into the compressor, which is basically a pump that raises the pressure so it will move through the system. The increased pressure from the compressor causes the temperature of the refrigerant to rise. As it leaves the compressor, the refrigerant is a hot vapour, roughly 120 to 140 º F. It now flows into the refrigerant-to-water heat exchanger, operating as the condenser during the cooling. As it condenses, it gives up heat to the loop, which is circulated by a pump
Fig 2.2 : Refrigeration Cycle .
15
As the refrigerant leaves the condenser, it is cooler, but still under pressure provided by the compressor. It then reaches the expansion valve or capillary tube. That the high pressure refrigerant to “flash” through becoming a lower pressure, cooled liquid. When pressure is reduced, as with spraying an aerosol can or a fire extinguisher, it cools. The cycle is complete as the cool, liquid refrigerant re-enters evaporator to pick up room heat.
2.3 HOW REFRIGERATOR WORKS
In the summertime, have you ever gotten out of a swimming pool and then felt very cold standing in the sun? that’s because the water on your skin is evaporating. The air carries off the water vapour, and with it being taken away from your skin. This is similar to what happens inside older refrigerators. Instead of eater, through, the refrigerator uses chemicals to do the cooling.
There are two things that need to be known for refrigeration. 1.
A gas cools on expansion.
2.
When you have two things that are difference temperature that touch or are near each other, the hotter surface cools and the colder surface warms up. This is a law of physics called the Second Law of Thermodynamics.
16
2.4 TYPES OF DOMESTIC REFRIGERATOR
There are two types of domestic refrigerator. 1. Single door fresh food refrigerator 2. Double-door refrigerator-freezer
Most domestic refrigerator are of two types – either a single door fresh food refrigerator or a two-door refrigerator-freezer combination, with the freezer compartment on the top portion of the cabinet, or a vertically split cabinet (side-byside), with the freezer compartment on the left side of the cabinet. They are completely self-contained units and are easy to install. Most refrigerators use R-22 refrigerant, normally maintaining temperatures of 0 ºF in the freezer compartment and about 35 ºF to 45 ºF in the refrigerator compartment. There are some pictures of different types of refrigerators as shown.
Fig 2.3 : Single Door
Fig 2.4 : Single Door
Refrigerator
Refrigerator
17
Fig 2.5 : Single Door Refrigerator
Fig 2.6 : Double Door Refrigerator
18
2.5 TEMPERATURTE ZONE AND RATING Some refrigerators are now divided into four zones to store different types of food:
»
-18 ºC (0 ºF) (freezer)
»
0 ºC (32 ºF) (meats)
»
5 ºC (49 ºF) (refrigerator)
»
10 ºC (50 ºF) (vegetables) The capacity of a refrigerator is measured in either litres or cubic feet (US).
Typically the volume of a combined fridge-freezer is split to 100 litres (3.53 cubic feet) for the freezer and 140 litres (4.94 cubic feet) for the refrigerator, although these values are highly variable. Temperature settings for refrigerator and freezer compartments are often given arbitrary numbers (for example, 1 through 9, warmest to coldest) by manufacturers, but generally 2 to 8 ºC (36 to 46 ºF) is idle for the refrigerator compartment and -18 ºC (0 ºF) for the freezer. Some refrigerators require a certain external temperature 16 ºC (60 ºF) to run properly. Thus can be an issue when placing a refrigerator in an unfinished area such as a garage.
2.6 REFRIGERANT
Refrigeration application
Short description
Typical HFCs used
19
Domestic Refrigeration
Appliances used for keeping food in
HFC-134a
Commercial
dwelling units. Holding and displaying frozen and fresh
R 404A, R 507,
Refrigeration food in retail outlets HFC-234a Food processing and cold Equipment to preserve, process and store R410A, storage
Industrial Refrigeration
food from its source to the wholesale
R407C,R 507,
and cooling
HFC-134a
Large equipment, typically 25 kW to 30
HFC-134a, R-
MW, used for chemical processing, cold
404A, R-507
storage, food processing and district Transport refrigeration
heating and cooling Equipment to preserve and store goods,
R410A, R407C,
primarily foodstuffs, during transport by
HFC-134A
road, rail, air and sea
2.7 VAPOUR COMPRESSION CYCLE
2.7.1 Introduction The vapour compression cycle is the mostly widely used method of refrigeration in the modern application. Your household refrigerator, water cooler, deep freezer, airconditioner etc, all run on vapour compression cycle. The cycle is called as vapour compression cycle, because the vapours of refrigerant are compressed in the compressor of the system to develop the cooling effect.
2.7.2 Working Here are the various process of vapour compression cycle (refer the figure). 20
(1)
Compression: The vapours of refrigerants enter the compressor and get compressed to high pressure and high temperature. During this process the entropy of the refrigerant ideally remains constant and it leaves in superheated state.
(2)
Condensation: The superheated refrigerant then enters the condenser where it is cooled either by air or water due to which its temperature reduces, but pressure remains constant and it gets converted into liquid state.
(3)
Expansion: The liquid refrigerant then enters the
expansion valve or
throttling valve or capillary tube when sudden expansion of the refrigerant occurs, due to which its temperature and pressure falls down. The refrigerant leaves expansion valve or capillary tube in partially liquid state and partially in gaseous state. (4)
Evaporation or cooling: The partially liquid and partially gaseous refrigerant at very low temperature enters the evaporator where the substance to be cooled is kept. It is here where the refrigeration effect is produced. The refrigerants absorbs the heat from tge substance to be cooled and gets converted into vapour state.
Fig 2.7 : Simple VCR System
T-S diagram of VCR System
21
Fig 2.8 : P-V diagram of VCR System
2.7.3 Advantages » Capable of large refrigerating loads at lower initial purchase and operating cost. » Very efficient » Very compact system for small to very large heat loads. » Cycle can be reversed for heat pump operation. 2.7.4 Disadvantages
22
» Parts can wear out. » Noise. » Potential refrigerant leaks. » Operates in limited orientation.
2.7.5 Application » Household refrigerator, » Air-conditioners, » Water coolers, » Ice and Ice cream maker, » Deep freezers, » Large industrial refrigeration and » Air-conditioning systems,
2.8 VAPOUR ABSORPTION CYCLE
2.8.1 Introduction The various processes of the vapour absorption cycle are similar to the one in vapour compression cycle, only the method of compression of the refrigerant is different. In vapour absorption system ammonia is used as the refrigerant, which has very high affinity to dissolve in water. Here are various processes of vapour absorption cycle; 2.8.2 Working
23
(1)
Compression or absorption of the refrigerant: in vapour absorption
system there is no traditional compressor, instead there is absorber. The absorber consists of water, as a absorbent, in which the refrigerant, ammonia, dissolves. This mixture of water and ammonia is then pumped and heated thus increase in temperature and pressure of the ammonia occurs. Ammonia leaves the absorber at high pressure and high temperature. Some work has to be provided to the pump and heating is carried out by the steam. The amount of electricity required by the pump is much lesser than that required by the compressor hence there is lots of saving of electricity, however, the additional source of heat in the form of steam has to be provided. (2)
Condensation: The refrigerant at pressure and temperature then enters
condenser where it is cooled by water and its temperature and pressure reduces. (3)
Expansion: Thereafter the expansion of refrigerant occurs in throttling
valve or capillary tube due to which the temperature and pressure of the ammonia refrigerant reduces drastically and suddenly. (4)
Evaporation: Finally the refrigerant enters the evaporator where it produces
the cooling effect. It leaves the evaporator in vapour state and then enters absorber, where it is absorbed by absorbent, water and compressed by the pump. This process repeats again and cycle continues. There are different types absorbents like water and lithium bromide that can be used with refrigerant ammonia. These systems are called water absorption system.
24
2.8.3 Advantages » No moving parts. » No vibration or noise on small system. » Small systems can operate without electricity using only heat, large systems require power for chemical pumps. » Can make use of waste heat.
Fig 2.9 : Vapour Absorption System
25
2.8.4 Disadvantages » Potential refrigerant leaks. » Operates under limited vibration and orientations. » Complicated and difficult to service and repair. » Stalls in a hot ambient » Very bulky. » Poor efficiency.
26
CHAPTER 3 :- LPG REFRIGERATION
3.1 INTRODUCTION
In India, more than 80% of the domestic refrigerator utilize HFC 134a as refrigerant, due to its excellent thermodynamic and thermo physical properties. But, HFC 134a has a high global warming potential (GWP) of 1300. There is a need of assess various refrigerant option considering the existing refrigerators in the field and for the future market. CFC’s are principally destroyed by ultraviolet radiations in the stratosphere; the chlorine released in the high stratosphere catalyzes the decomposition of ozone to oxygen; and ultraviolet radiations penetrates to lower altitudes. Credible calculations of the magnitude of the effect (Hoffman 1987) and his team predicted 3% global ozone emissions of 700 thousand tonnes/year after a hundred years. The ozone impact of car air conditioners also can not be ignored. Hydrofluorocarbons (HFC’s) can be thought of as a replacement, but unfortunately the radiation properties of HFC’s like R-134a make them powerful global warming agents. HFC 134a and the HC blend have been reported to be substitutes for CFC 12, but they have their own drawbacks in energy efficiency, flammability and serviceability aspects of the systems. HFC 134a is not miscible with mineral oil, and hence, polyol ester oil is recommended, which is highly hygroscopic in nature. This hygroscopicity demands stringent service practices, which otherwise results in moisture entry into the system. Thus, hydrocarbon refrigerants; particularly LPG serves as the best contender to replace CFC’s from domestic refrigerator as well as car air conditioners.
27
LPG consists mainly of propane (R-290) and butane (R-600), and LPG is available as a side product in local refineries. In Cuba for already several decades LPG is used as a drop-in refrigerant. LPG mixtures have composition of a commercial LPG mixture suitable as ‘drop-in’ replacement for R-12 was calculated crudely as 64% propane and 36% butane by mass. Liquefied petroleum gas (LPG) of 60% propane and 40% commercial butane has been tested as a drop-in suitable for R 134a in a single evaporator domestic refrigerator with a total volume of 10 ft3. The revival of LPG refrigerants in domestic and small commercial application in a happy accident (Vidal 1992). Engineers had known since the 1920’s that LPG refrigerants performed well and in the 1980s refrigerators manufacturers again tested them (Kuijpers et al. 1988). Fear of a flammability campaign from the chemical industry deterred any manufacture. In march 1989, the Institute of Hygiene in Dortmund Germany needed a new cold storage room. The young idealistic director, Dr Harry Rosin, could not consider using a CFC refrigerant and so tried propane and iso butane. Greenpeace Australia imported a Foron refrigerator in February 1993 and in December 1993 Email Ltd, Australia’s largest appliance manufacturer, displayed prototype LPG refrigerators. In 1994, German manufacturer announced one by one their intention of switch to LPG refrigerants. OZ Technology Inc, a start up company in Idaho, introduced OZ-12 a mixture of commercial propane and butane in 1992. they sold over 50,000 170 g cans the first summer. The Mobile Air-Conditioning Society made flammability hazard claims including ‘a bomb in the passenger compartment’ (Keebler 1993, MACS 1993). The US EPA refused to approve OZ-12 on flammability grounds. OZ then introduced another LPG refrigerant HC-12a, which has already sold over 100,000 cans. The US EPA may not approve this either but OZ’s petition (OZ
1994) is convincing,
comprehensive and technically sound especially on safety. Calor released Care 30 in June 1994. Care 30 is a high purity mixture of R-290 and R-600a and is a drop- in
28
replacement for R-12 and R 134a. it has been very successful in vehicle refrigeration and air-conditioning.
3.2 PROPERTIES »
Colourless.
»
Odourless. (It’s normal to odorise LPG by adding an odorant prior to supply to the user, to aid the detection of any leaks).
»
Flammable.
»
Heavier than air.
»
Approximately half the weight of water.
»
Non toxic but can cause asphyxiation.
»
LPG expands upon release and 1 litre of liquid will form approximately 250 litres
of vapour.
A good mixture : LPG is mainly Propane (C3H8), Butane (C4H10) or a mix of Propane/Butane. Since LPG has such a simple chemical structure, it is among the cleanest of any alternative fuel.
Boiling point : LPG’s boiling point ranges from -42 ºC to 0 ºC depending on its mixture percentage of Butane and Propane.
Combustion : The combustion of LPG produces carbon dioxide (CO2) and water vapour but sufficient air must be available. Inadequate appliances flueing or ventilation can result in the production of carbon monoxide which can be toxic.
29
Vapour pressure : LPG is a stored as a liquid under pressure. It is almost colourless and its weight is approximately half that of an equivalent volume of water. The pressure inside a closed container in which LPG is stored is equal to the vapour pressure of the liquid and corresponds to its temperature.
Ignition temperature : The temperature required to ignite LPG in air is around 500 ºC.
Calorific value : The calorific value of LPG is about 2.5 times higher than that of main gas so more heat is produced from the same volume of gas.
Toxicity : LPG is a colourless, odourless and non-toxic gas. It is supplied commercially with an added odorant to assist detection by smell. LPG is an excellent solvent of petroleum and rubber product and is generally non-corrosive to steel and copper alloys.
Safety : LPG is just as safe as any other fuel. In fact, it is safer than most fuels because neither LPG itself nor the end products that are produced by burning LPG in a suitable appliance, are poisonous to inhale. Since LPG cannot burn without air, there can never be a ‘Flash-back’ into the cylinder. You can feel safe with LPG as the most through precaution are taken to ensure your safety. All you have to do is to handle it correctly whilst adhering to the simple instructions provided.
30
3.3 APPLICATION
Application of LPG as refrigerant that divides in two categories: 1. Processes that uses LPG 2. Industries that uses LPG
3.3.1 Processes that use LPG LPG’s high calorific value makes it a key gas for: »
Heating appliances :- used
because
of
its case of
combustion, portability and clean burning characteristics and compatibility with almost all water and space heating appliances. The best product depends the climate. »
Propane :- suitable for use in all conditions. It is the only LPG product suitable for cold climates (such as the UK and Canada) because of its low boiling point of -43.6 ºF (-42 ºC).
»
Butane :- suitable for use in hot climate only because of its higher boiling point of 22.9 ºF (-5 ºC).
»
Propane/Butane mixtures :- suitable for use in moderate climates
»
Cooking :- preferred to electricity by professional chefs.
31
»
Oxy-Fuel application :- LPG performs well in large-scale oxy-fuel burner application.
LPG’s clean burning characteristics make it a good gas for:
»
Transport fuel :- for forklift and other trucks that operate inside warehouses and factories because it provides no noxious exhaust gases and give more power than batteries. LPG is also increasingly used as a clean automotive fuel in countries with serious air pollution problems.
»
propane and butane’s low boiling points also give them good closed cycle
refrigerants characteristics (similar to Freon’s).
3.3.2 Industries that use LPG LPG’s calorific and clean-burning characteristics are used across many industries such as: »
Automotive :- as a forklift truck fuel and in some countries as a private car or
public transport fuel. »
Hospitality and Leisure :- as a heating and cooking gas in restaurant, cafes and
mobile catering vans. »
Agriculture :- for crop drying, heating greenhouses and animal sheds and for
flame weeding and pest control.
32
»
Construction :- LPG’s portability allow its use for general space heating to enable
work on projects during winter months, and for road heating in bitumen replacement work. »
Chemicals and petrochemicals :- LPG surplus is used as feedstock when prices
are low.
3.4 THE LPG REFRIGERATION CYCLE
(1). LPG Gas Cylinder: From the LPG gas cylinder, LPG flows through the pipe and reaches to the capillary tube. LPG gas pressure is approximate 80-100 psi.
(2). Capillary Tube: As the capillary tube, capillary tube downs the pressure up to less then 1 psi.
(3). Evaporator: In the evaporator LPG is converted into the vapour from with low pressure. After passing through the evaporator low pressure and temperature LPG vapour absorbs heat from the chamber system.
(4). Gas Burner:
33
After performing the cooling effect, low pressure LPG gas goes into the burner where the burns.
3.5 PARTS OF REFRIGERATORS
3.5.1 LPG Gas Cylinder LPG is Liquefied Petroleum Gas. This is general description of Propane (C3H8) and Butane (C4H10), either stored separately or together as a mix. This is because these gases can be application
of
a
liquefied at a normal temperature by
moderate pressure increases, or at normal pressure by
application of LPG using refrigeration. LPG is used as a fuel for
domestic, drying
industrial,
processes.
LPG
horticultural,
can be used as
propellant for aerosol, in addition can
also
be
agricultural,
used
to
an
other to
through the use of pressure lanterns.
34
cooking,
automotive specialist
provide
heating fuel
applications.
or
and as LPG
lighting
3.5.2 Capillary Tube The capillary tube is the commonly used throttling device in the domestic refrigeration.
The capillary of very
tube is a copper tube of very
long length and it is coiled to
would occupy used for
the
less
space.
The
refrigeration
internal
several
internal diameter
of
diameter. It is
turns so that it the capillary tube
applications varies from 0.5
(0.020 to 0.09 inch). The capillary the
small
tube
is shown in
to 2.28 mm
picture.
When
refrigerant enters in the capillary tube, its pressure drops down suddenly due to
very small diameter. The decrease in pressure of the refrigerant through the capillary depends on the diameter of capillary and the length of capillary. Smaller is the diameter and more is the length of capillary more is the drop in pressure of the refrigerant as it passes through it.
35
3.5.3 Evaporator The evaporators are another important parts of the refrigeration systems. It through the evaporators that the cooling effect is produced in the refrigeration system.
It is in the evaporators when the actual cooling effect takes place in the refrigeration systems. For many people the evaporator is the main part of the refrigeration system, consider other part as less useful. The evaporators are heat exchanger surface that transfer the heat from the substance to be cooled to the refrigerant,
thus removing the heat from the
from
evaporators
are
of
refrigeration
used
and
for
wide variety
hence the available 36
in
the substance. The diverse application in
wide variety of shape, sizes and
designs. They are also classified in different manner depending on the method of feeding the refrigerant, construction of the evaporator, direction of air circulation around the evaporator, application and also the refrigerant control. In the domestic refrigerators the evaporators are commonly known as freezers since the ice is made in these compartment. In the evaporators the refrigerant enters at very low pressure and temperature after passing through the capillary tube. This refrigerant absorbs the
heat
from
the substance that is to be cooled so the refrigerant gets heated while the substance gets cooled. Even after cooling the substance the temperature of the refrigerant leaving the evaporator is less than the substance. In the large refrigeration plants the evaporator is used for chilling water. In such cases shell and tube type of heat exchanger are used as the evaporators. In such plants the evaporators are classified as: (1). Dry expansion type of evaporators (2). Flooded type of the evaporators The evaporators are classified based on the construction as: (1). Bare tube evaporators (2). Plate surface evaporators (3). Finned evaporators (4). Shell and tube evaporator (5). Shell and coiled evaporator, and (6). Tube-in-tube evaporator The evaporators are classified based on mode of heat transfer (1). Natural convection evaporator, and (2). Forced convection evaporator
37
The evaporators are classified based on operating conditions (1). Frosting evaporator, (2). Non-frosting evaporator, and (3). Defrosting evaporator
3.5.4 Pressure gauges
Many techniques have been developed for the measurement of pressure and vacuums. Instruments used to measure pressure are called pressure gauges or vacuum gauges.
A manometer could also referring to a pressure measuring instrument, usually limited
to measuring
pressures
near
is often used to refer specifically to liquid
Stainless steel pressure gauge
38
to atmospheric. The term manometer column
hydrostatic instruments.
Catering to the requirements of to power and allied array
of stainless
Industry, we offer
quality
steel, weatherproof pressure gauges. Renowned for offering
resistance in corrosive environments and modes, these find wide application in power generation, pollution
control equipment, chemicals
and petrochemicals
and
also exploration. These gauges are available in 63mm, 100mm, and 150mm sizes and can be customized as per client.
Bourdon gauge A Bourdon gauge uses a coiled tube, which, as it expands due to pressure increases cases a rotation of an arm connected to the tube.
39
In 1849 the Bourdon tube pressure gauge was Bourdon. The pressure sensing element is a
patented in France by Eugene
closed
coiled
tube connected
to the chamber or pipe in while the pressure is to be sensed. As pressure
increases
the
the
gauge
tube will tend to uncoil, while a reduced gauge pressure
will patented France by Eugene
Bourdon.
The pressure sensing el cause the tube to coil more tightly. This motion is transferred through a linkage to a gear train connected to an indicating needle. The needle in presented in front of a card face inscribed with the pressure indications associated with particular needle deflections. In a barometer, the Bourdon tube is sealed at both ends and the absolute pressure of the ambient atmosphere is sensed. Differentials Bourdon gauges use two Bourdon tubes and a mechanical linkage that compares the readings.
3.5.5 High Pressure pipes
The range of high pressure pipes covers most
application
where there is a
requirement to transfer gas at high pressure. They consist of a steel pipe with a steel ball fitted these
to
balls against
both
ends. Two swivelling
the seating of
connection
nipples press
the connecting hole and
thus sealing
against gas leakage.
40
»
Wide range of pipes.
»
All pipes are pressure tested to 100 M Pa (14,500 psi) over recommended working pressure.
3.6 CONSTRUCTION OF THE LPG REFRIGERATOR The LPG refrigerator shown in figure. We make the one box of the plywood. The plywood sheet size is 12mm for used the LPG refrigerator. The size of the refrigerator is 724*457*381 mm3. The evaporator is fitted on the upper portion of box inside. Inside the refrigerator, we also put the thermo-coal sheet, because of the cold air can not the transfer from inside to outside of refrigerator.
Fig 3.1 :- Construction of the LPG refrigerator
The schematically diagram of the LPG refrigeration system is shown in next page. The gas tank is connect by pipes to the capillary tube. The capillary tube is fitted with evaporator. The evaporator coiled end is connect to the stove by another gas circulation pipe. When two pressure gauge is put between capillary tube and gas tank, and another is put the end of the evaporator.
41
3.7 WORKING LPG REFRIGERATOR The basic idea behind LPG refrigeration is to use the evaporation of a LPG to absorb heat. The simple mechanism of the LPG refrigeration working is shown in figure.
Fig 3.2 Working of LPG Refrigerator »
LPG is stored in the LPG cylinder under high pressure. When the gas tank of regulators is opened then high pressure LPG passes in gas pipe. This LPG is going by high pressure gas pipe in capillary tube.
»
High pressure LPG is converted in low pressure at capillary tube with enthalpy remains constant.
»
After capillary tube, low pressure LPG is passed through evaporator. LPG is converted into low pressure and temperature vapour from and passing through the 42
evaporator which absorbs heat from the chamber. Thus the camber becomes cools down. Thus we can achieve cooling effect in refrigerator. »
After passing through the evaporator low pressure LPG is passed through pipe by burner. And we can uses the low pressure of LPG is burning processes.
3.8 CAUSES AND PRECAUTION
»
Explosion in space Any refrigerant with vapour pressure above ambient can
flash to a larger volume. The potential increase in volume is greater if combustion of lubricant or refrigerant occurs. Explosion venting may be necessary to limit pressure rise to what the space can safely withstand. 2 kPa can blow window glass off a building. »
Fire Combustible lubricant and refrigerant must be discharged safely outside a
building when a fire occurs especially it the heat of combustion exceeds 200 MJ. »
Asphyxiation or poisoning All refrigerants except air and oxygen are
asphyxiations. Ventilation must prevent serious injury or death on a sudden total release of refrigerants. The quantity of ventilation necessary varies greatly between refrigerants. »
Flying metal System must comply with piping and pressure vessels codes.
»
Corrosion or chemical reaction LPG refrigerants are non-reactive and chemically
stable at refrigeration temperature.
43
»
Chemical or cold burns Accidental contact between skin and cold metal must be
prevented by insulation. Accidental releases of liquid refrigerant must drain safely.
3.9 ADVANTAGE OF LPG
The advantages of LPG are as follows : »
Clean burning.
»
Effects of corrosions are greatly reduced.
»
Instantly control the flame temperature.
»
Avoids scaling and decarburising of parts.
»
Environmentally friendly fuel, with minimal sulphur content and sulphur-free emissions.
»
Very high efficiency with direct firing system instant heat for faster warm-up and cool-down.
»
LPG is easily liquefied and stored in pressure containers. It can be easily transported in cylinder or tanks.
44
CHAPTER 4:- ANALYSIS OF LPG REFRIGERATOR
»
Size of Refrigerator :-724*457*381 mm3
»
Atmospheric temperature :- 40 ºC
»
Initial water temperature :- 35 ºC
»
Inlet pressure of LPG :-80 psi
»
Outlet pressure of LPG :- less than 1psi
4.1 :- OBSERVATION TABLE AND CHART The experiment of this project was done on May 15, 2010 at 1.45p.m. and reading were taken under ten minute’s interval which are under as follow:
Time
Pressure
Inlet
Outlet
Water
Freezer
Chamber
in
Temp.
Temp.
Temp.
Temp.
Temp.
bar
(ºC)
(ºC)
(ºC)
(ºC)
(ºC)
1.0 -1.1 -2.0 -4.1 -6.0 -6.9 -7.5 -7.9 -8.9 -9.3
37.9 33.8 29.4 25.5 23.1 19.9 17.9 15.7 14.2 10.3
10 6.7 0.2 10 30.0 10 6.4 0.01 8.2 24.2 10 6.8 -0.09 7.6 19.7 10 6.7 -0.90 5.2 15.8 10 6.6 -1.25 4.1 11.2 10 6.7 -2.20 3.1 8.3 10 6.7 -3.74 2.2 5.1 10 6.8 -4.90 1.8 3.2 10 6.6 -5.90 1.1 1.02 10 6.7 -7.10 0.5 0.30 Chart no. 4.1 :- Freezer Temperature Vs Time Period
X axes : Time Period in minute. 45
Y axes : Freezer surface temperature in ºC.
2
0 0
20
-2
-4
-6 Chart No. 4.2 :- Water Temperature Vs Time Period X axes : Water temperature in ºC. Y axes : Time Period in minute.
-8 46
40
35
30
25
20 Chart No 4.3 :- Chamber Temperature Vs Time Period X axes : Time Period in minute. Y axes : Chamber Temperature in ºC.
15
47
40
35
30
25
4.2 ADVANTAGES
20 »
The cooling capacity of LPG is 10% higher than R-12 and the vapour pressure is appropriate.
»
LPG is naturally occurring and non-toxic.
15
48
»
Use of LPG as a refrigerant also improves the overall efficiency by 10 to 20%.
»
The ozone depletion potential (ODP) of LPG is 0 and Global warming potential (GWP) is 8 which is Significantly negligible as compared to other refrigerant.
»
Apart from environment friendly, use of also LPG gives us lot of cost advantages.
»
LPG does not form acids and thereby eliminates the problem with blocked capillaries.
»
There is 60% reduction in weight of the system due to higher density of LPG.
»
The fridge works when electricity off.
»
It is efficient to save fuel.
»
No pollution
»
The units are effectively silent in operation.
»
Running cost is zero.
»
Eliminates the compressor and condenser.
4.3 DISADVANTAGES
»
LPG is explosive in nature.
»
Do not maintain constant pressure in LPG cylinder.
49
»
Put the LPG cylinder is inverted position.
»
After the refrigeration processes, the exhaust of LPG is burn into burner. Because of the exhausted vapour LPG can not converted again liquid phase , because the this process is very costly.
»
The prevention of leakage of the LPG is the major problem in LPG
refrigeration system. Because of the LPG is highly flammable.
CHAPTER 5 :- CONCLUSION OF LPG REFRIGERATION
50
5.1 CONCLUSION After performing this project “LPG Refrigeration”, we conclude that refrigeration effect is produced with the use of LPG. From observation table, we conclude that, the regulating valve is fully open that, we achieve the chamber temperature down from 38ºC to 10ºC in a 100 minute. We achieve the evaporator temperature down from 1ºC to -9.3ºC in a same time interval. We put the water in one plastic bottle in the evaporator. The initial temperature of water is 35 ºC. From observation table, we conclude that, the condition of regulating valve is fully opened, the same time period we achieve the temperature of water is 0.30 ºC. We also conclude that, the capillary tube is maximum pressure of gas cylinder is reduces the less then of 1 psi. The capillary tube is more suitable throttling device in LPG refrigeration system. This system is cheaper in initial as well as running cost. It does not require an external energy sources to run the system and no moving part in the system so maintenance is also very low. We also conclude that, we try the burnt to the exhaust LPG, the pressure of exhaust gas is less than 1 psi, the small flame produce by the burner. This system most suitable for hotel, industries, refinery, chemical industries where consumption of LPG is very high.
Picture of Project
51
BIBLIOGRAPHY
»
http://www.hychill.com.au/pdf/pasolpgr.pdf
52
»
www.e-lpg.com
»
http://www.google.com/g
»
www.dynatempintl.com
»
www.lpgforyou.com
»
http://www.brighthub.com/engineering/mechanical.aspx
»
http://coolingdevice.net/4.html
»
http://howstuffworks.com/refrigerator.htm
»
http://www.google.com/gwt/x?site
»
www.indiamart.com
»
“A Textbook of
Refrigeration and Air Conditioning” by R.S.KHURMI &
J.K.GUPTA »
“Performance and safety of LPG Refrigerant ”, The Univercity of New South
Wales, Australia. »
“Applications of Refrigeration & Air Conditioning”, Lesson 3, Version 1 ME, IIT
Kharagpur 1 » »
“A Textbook of Thermal Engineering”, By R.S.KHURMI & J.K.GUPTA Arora, C.P, “Refrigeration & Air Conditioning”, Tata Mc-Graw Hill Company
Limited, New Delhi.
53
