DESIGN AND CONSTRUCTION OF A PORTABLE REFRIGERATOR
1.1. HISTORY OF REFRIGERATOR
A refrigerator is a popular household appliance that consists of a thermally insulated compartment and a heat pump (mechanical, electronic, or chemical) that transfer heat from the inside of the fridge to its environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room.
Refrigeration is an essential food storage technique in developed countries, of which the lower temperature lowers the reproduction rate of bacteria. So, therefore, the refrigerator reduces the rate of spoilage.
The refrigerator maintains a temperature of few degrees above the freezing point of water, and also the optimum temperature range for perishable food storage is 3 to 5ºC (37 to 47ºF). Another common device that maintains a temperature below the freezing point of water is known as the FREEZER.
The refrigerator replaces the ICEBOX which had been a common household appliance for a century and a half, for these reasons the refrigerator in American usage is sometimes referred to as the ICEBOX.
The first artificial refrigeration system began in the mid-1750s and developed in the early 1800s. In 1834, the first working vapor-compression refrigeration system was built. And also, the first commercial ice-making machine was invented in 1854, and in 1913 the refrigerator for home use was invented. In 1923, Frigidaire introduced the first self-contained unit, and the introduction of Freon in the 1920s expanded the refrigerator market.
Newer refrigerators may include automatic defrosting chilled water and ice from a dispenser in the door. Domestic refrigerators and freezers for food storage are made in a range of sizes, among the sizes; the smallest is a 4l Peltier refrigerator which can hold about 6 cans of beer while the largest size is as tall as a person and about 1m wide with a capacity of 600l.
1.2. HISTORY OF REFRIGERATION TECHNOLOGY
The history of artificial refrigeration began when Scottish professor William Cullen designed a small refrigerating machine in 1755. Cullen used a pump to create a partial vacuum over a container of diethyl ether, which then boiled absorbing heat from the surrounding air. This experiment by Cullen created even a small amount of ice but had no practical application at that time.
In 1805, American inventor Oliver Evans described a closed vapor-compression refrigerator cycle for the production of ice by ether under vacuum. In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low temperatures.
Also, in 1834 an American expatriate to Great Britain Jacob Perkins built the first working vapor-compression refrigeration system and it was a closed-cycle device that could operate continuously. In 1842, a similar attempt was made by American physicist john Gorrie who built a working prototype but it was a commercial disaster.
The first practical vapor-compression refrigeration system was built by James Harrison, a British journal who had immigrated to Australia. His 1856 patent was for a vapor-compression system using ether, alcohol, or ammonia. He built a mechanical ice-making machine in 1851 on the banks of the Barwon River at a rocky point in Geelong, Victoria and his first commercial ice-making machine followed in 1854.
Harrison also introduced a commercial refrigeration system using vapor compression to breweries and meatpacking houses and by 1861 a dozen of his system was in operation.
The first gas absorption refrigeration system using gaseous ammonia dissolved in water (referred to as “aqua ammonia”) was developed by Ferdinand carrě of France in 1859 and patented in 1860. Carl von Linde, an engineering professor at the technology university Munich in Germany, patented an improved method of liquefying gases in 1876. His new process made possible the use of gases such as ammonia sulfur dioxide (SO2) and methyl chloride (CH3Cl) as refrigerants and they were used for that purpose until the late 1920s.
1.2.1. DOMESTIC REFRIGERATION SYSTEM
In 1913, refrigerators for home and domestic use were invented by Fred w. wolf of Fort Wayne, Indiana with models consisting of a unit that was mounted on top of an icebox.
In 1914, engineer Nathaniel B. Wales of Detroit, Michigan, introduced an idea for a practical electrical refrigeration unit which later became the basis for the Kelvinator.
The self-contained refrigerator with a compressor on the bottom of the cabinet was invented by Alfred Mellowes in 1916. Mellowes produced this refrigerator commercially but was brought out by William C, Durrant in 1918, Durrant started the Frigidaire Company to mass-produce the refrigerator. Also in that same year, 1918 Kelvinator Company introduced the first refrigerator with any type of automatic control.
The absorption refrigerator was invented by Baltzar von Platen and Carl Munters from Sweden in 1922, while they were still students at the Royal Institute of Technology in Stockholm. It became a worldwide success and was commercialized by Electrolux. Other pioneers include Charles Teller, David Boyle, and Raoul Picket.
Carl Von Linde was the first to patent and make a practical and compact refrigerator in the whole world
1.2.2. HISTORY OF REFRIGERANT
Commercial refrigerators and domestic refrigerators use gases such as ammonia (R-717) or sulfur dioxide (R-764), which occasionally leaked, making them unsafe for home use.
In the 1930s, a non-flammable refrigerant such as Freon-12( R-12) was introduced but however the R-12 causes damages to the ozone layer which makes the USA government issue a ban on its use in new refrigerators and air conditioning system in 1994.
In 1990, a less harmful refrigerant R-134a (tetrafluoromethane) was used for perfect replacement to R-12 1990 but still found in many old systems.
Figure: 1.1: p-h diagram of refrigeration cycle for R-134a
1.2.3. HISTORY OF STYLES OF REFRIGERATORS
In the 1950s most refrigerators were white, but from the mid-1950s through the present-day designers and manufacturers put colors into refrigerators. In the late 1950s/early 1960s, pastel colors like turquoise and pink became popular, brushed chrome-plating (similar to stainless finish) was available in some models from different brands. In the late 1960s and throughout the 1970s, earth tone colors were popular including Harvest Gold, Avocado Gold, and Almond. In the 1980s, black became fashionable. In the 1990s, stainless steel came into vogue, and in 2009, one manufacturer introduced a multi-color design.
1.3. GENERAL TECHNICAL EXPLANATION OF REFRIGERATING SYSTEM
A vapor-compression cycle is used in most household refrigerators, refrigerator-freezers, and freezers. In this cycle, a circulating refrigerant such as R-134a enters a compressor as low-pressure vapor at or slightly below the temperature of the refrigerator interior. The vapor is compressed and exits the compressor at a very high-pressure superheated vapor, the superheated vapor travels under pressure through coils or tubes that make up the condenser, the coil or tube are passively cooled by exposure to air in the room. The condenser cools the vapor which liquefies.
As the refrigerant leaves the condenser, it is still under pressure but it is slightly above the room temperature of the system. The liquid refrigerant is forced through a metering or throttling device, also known as the expansion valve (essentially a pin-hole-sized construction in the tubing) to an area of much lower pressure. The sudden decrease in pressure results in explosive-liked flash evaporation of a portion (typically about half) of the liquid. The latent heat absorbed by the flash evaporation is drawn mostly from the adjacent still-fluid refrigerants, a phenomenon known as auto-refrigeration. This cold and partially vaporized refrigerant continues through the coil or tubes of the evaporator unit, a fan blows air from the refrigerator or freezer compartment (box air) across these coils or tubes and the refrigerant completely vaporizes, drawing further heat from the box air.
The cooled air is returned to the refrigerator or freezer compartment, and so keeps the box air cold. But the cooled air in the refrigerator or freezer compartment is still warmer than the refrigerant in the evaporator. The refrigerant leaves the evaporator, now fully vaporized and slightly heated, and returns to the compressor inlet to continue the cycle.
1.4. PURPOSE OF CONSTRUCTION
The aim and purpose of which this project is designed are to achieve the followings:
To construct portable lightweight cooling and freezing equipment. To construct movable cooling or freezing equipment, this can easily be transferred from one corner of the apartment to the other. To construct a mobile refrigerator with good performance and a high percentage of local technology. To construct cooling and freezing equipment that will be mobile, economical, and cost-effective. To construct a cooling or freezing equipment that is efficient and with little or no complication in maintenance.
1.5. IMPORTANCE AND SPECIFICATION OF THE PROJECT
The importance attached to this design accomplishment of a fast cooling and freezing system without adverse effects on the food tissue, flavors, fleshiness, and natural nutrients of the food materials. The design intentions are based on reduced cost, longer life spans, fast freezing, and cooling techniques, compactness, probability, ease of mobility, and more of improving on the existing design taking into consideration the Nigeria factor and possibility of expanding and marketability.
The specifications were obtained considering the items, which are to be cooled or preserved. Also, the dimensions of the framework and the covering sheets were also considered immensely.
The component part for the design of the middle cooling system includes:
The Compressors or the Engine The Condenser The Capillary tube The Evaporator Refrigerant Relay Drier Strainer or Drier Thermostat Lubricating Oil Rubber seal Fibre of lagging material Mild steel-square pipe Metal sheets of mild steel / galvanized – sheet Rollers Filler Metal Coal Materials Plastic guilders Metal screw nails
1.6. SCOPE AND LIMITATION
Refrigeration consists of three main categories which include –
Domestic refrigeration Industrial refrigeration Commercial refrigeration
The design scope of the cooling and freezing systems or mobile refrigerators is mainly for commercial domestic reasons due to the movable nature and freezing capacity.
The limitations are the specification in terms of the size, area, and capacity that determines the limitation of the design of the machine. In an industrial situation or uses or purpose where bigger refrigeration units are needed or required, the specification of this equipment may not be ideal (i.e. it might not be suitable).
1.6.1 LIMITATIONS ENCOUNTERED
Inaccessibility of a 12 volts DC compressor. Inaccessibility of a poly-foam for insulation. Lack of sophisticated workshop tools for machining.
1.7. STATEMENT OF THE PROBLEM
The most common uses of this mechanized refrigeration are the preservation of perishable goods more especially foodstuffs, cooling of drinks, etc. In serving both functions and considering the area and situations of need such as resort centers, student hostels, single-room apartments, etc. Hence the need arises more than ever to design mobile cooling and freezing system of an acceptable standard that will meet certain essential requirements such as cost-effectiveness and portability.