The History Of The Kitchen Refrigerators

The History Of The Kitchen RefrigeratorsToday, iceboxs have become an essential differentiate of all kitchen (Tatum, 2010). Refrigeration is employ to store meat, vegetables among strainer(a) foodstuffs at mild temperatures, gum olibanum inhibiting spoilage due to microbial activity. The mold of essentially, manufacturing or making a icebox was gradual and begain in the 18th century. It culmoitated with Carl von Lindens give out in 1876. (Bellis, 2010 Tatum, 2010) tell suggests that since 500 AD, man has know to produce icing the puck by indwelling goes. Egyptians and Indians made ice on frigidity nights by setting peeing on earthenw ar pots. Later on in the 1700s, England servants in the 1700s collected ice in the winter and put into icehouses, which then provided cool storage in the summer. (Bellis, 2010 Tatum, 2010)In 1748, William Cullen of the University of Glasgow developed an entirely new exploit that consequently assume to an artificial modify system medi um being developed. (Tatum, 2010). His experiment produced ice. However he was unable to excuse what it meant. Around 1805, the Oliver Evans was involved in excogitation a infrigidation apparatus, alone unfortunately, he didnt build wholeness until Robert Perkins meliorate on his creation in 1834. (Bellis, 2010). Thomas Moore coined the word refrigerator for these machines. However, as at present Perkins and Evans machines ar called iceboxes. In 1844, Dr. John Gorrie, a physician, was able to construct a working unit that was based on both Evans and Perkins model. constructed. It was because of a eruption of yellow fever that led to Gorrie creating the unit, which was use to cooling the air. (Bellis, 2010 Tatum, 2010)Gorrie is credited as being the unitary who invented the refrigerator by numerous. (Bellis, 2010) However the situation began to transport, when Carl von Linde (1842-1934), a German mechanical engineer published an essay on improved refrigeration techniques, in 1871. He proposed a continuous process of liquefying splashes in large quantities. In 1873, he invented the commencement exercise practical and portable compressor refrigeration machine. (Tatum, 2010) He obtained a patent for his refrigerator in 1877 from the German over-embellished Patent Office. He made use of attackes namely ammonia, sulphur dioxide and methyl radical chloride. (Bellis, 2010 Tatum, 2010)In the 1900s, various refrigeration models were seen. Noteworthy refrigerator models included Servel, Frigidaire, Electroflux among others. (Bellis, 2010) These models of the 1900s had some(a)(prenominal) advancements since designs of pioneers much(prenominal) as Gorrie. By 1918, machine rifle controls were part of some models already. (Tatum, 2010) The gases apply namely ammonia, sulphur and methyl chloride were replaced by Freon in the 1920s in order to comply with safety standards. When one looks at the history, it shows that in 1918, automatic parts were already installed. This included automatic dials that aid in the operation. It was or else unfortunate that the units were non self contained as different parts were by the piece placed from each other. It wasnt until 1923 that self contained refrigerators began appearing. (Bellis, 2010) Ice cube trays were also introduced. (Tatum, 2010) Although umteen advancements were made, the modern refrigerator was put in mass production until 1946 i.e., afterwards the World War II. (Bellis, 2010 Tatum, 2010)People, in the the 1950s and 1960s were the ones that witnessed a flesh of technological innovations by engineers and scientists of the day. Among them were (i) automated defrosting and (ii) making of ice. Today, there are m some(prenominal) features that are intertwined with the features of the olden days and includes power failure alerts, ice cabinets among others. (Bellis, 2010 Tatum, 2010)To present, domestic refrigerators are present in almost e genuinely home worldwide. overdue to the models bring into beingd by Gorrie, Cullen, Carl von Linche among others, the refrigerator has thus become one of the machines or appli shtupces that is inherent to us every day. (Bellis, 2010 Tatum, 2010)TYPES OF REFRIGERATORSRefrigerators are classified into three types (Suyambazhahn, 2009) atmospheric state refrigerator evaporation coalescency refrigeratorVapour absorption refrigerator vaporization COMPRESSION infrigidation SYSTEMThe drying up compression refrigeration trunk is most ordinarily use in refrigerators. A cold is a gas with characteristics that make is suitable for refrigeration and air conditioning. R-22 is a commonly utilise refrigerant. This cycle works in four variants, which are exposit later on because it is similar to the refrigeration cycle.Figure 1 Vapour compression refrigerator (Suyambazhahn, 2009)This type has various uses much(prenominal) as (Suyambazhahn, 2009)Air conditioned cinema t inflameers, restaurants, hospitals, residential buil dings for comfort.Advanced medicines which are manufactured and preserve only in special atmospheric conditions.Preservation of food products. desiccation ABSORPTION REFRIGERATION SYSTEMThe principle of vaporization absorption was first discovered by well known scientist Michael Faraday in 1825. But this purpose is applied to refrigeration during 1860s by French Scientist Ferdinand Carve. The commonly used refrigerant for vapour absorption carcass is ammonia, NH3. In order to channel the conditions and phase of refrigerants, enkindle verve is utilized in vapour absorption carcass where as mechanical pushing is utilized in vapour compression systems.In a vapour absorption system, compressor is replaced by an absorber, a spunk and a generator. The vapour at the low instancy that leaves the evaporator is then move to the absorber. The absorber contains short ammonia solution. The vapour leaving from the evaporator is dissolved in the weak ammonia solution to form a square solution. Cooling irrigate is used to cool he absorber. The strong solution from the absorber is inwardnessed to the generator. The strong solutions squeeze is increase by the pump (10 bar) and is circulated through the system by pump.Figure 2 Vapour absorption refrigerator schematic (Rajadurai, 2009) unremarkably USED REFRIGERANTSEven though there are m both types of refrigerants which are used in various applications, the following types are important from the theme catamenia of view.AMMONIAIt is the most widely used refrigerant. It is mainly used as the refrigerant in ice-cold storage plants and also in ice making plants. Its boilined exhibit at atmospheric pressure is -33 oC and it has a uplifted latent kindle and broad(prenominal) critical temperature which are delectable properties of ammonia as a refrigerant. Also it is less(prenominal) expensive. But its rule becomes molybdenumary due to the following characteristics (Rajadurai, 2003)It is toxicIt is combust ibleIt has an irritating olfactionIt attacks metals like copper and brass in the presence of moisture vitamin C DIOXIDEThe demerits involved in the usage of ammonia clear be eliminated by using carbon dioxide. It is non toxic and scentless. It has a boiling point of -77.6 oC at atmospheric pressure. But it is non so often used because of its high operating pressure that is the operating pressure of CO2 is very high as 70 bar. (Rajadurai, 2003)SULPHUR DIOXIDEIt has a boiling point of -10 oC at atmospheric pressure. IT has a very low working pressure and a large latent love up with a high critical temperature. It is non flammable and on explosive. Even though there are many convinced(p) characters mentioned, the SO2 refrigerant is very toxic and it has an irritating pungent odour. Also it is very corrosive in contact with moisture. (Rajadurai, 2003)FREON 12 (or DICHLOR DI FLUOROMETHANE)It has a boiling point of -30 oC at atmospheric pressure. It is non toxic, non explosive and on flammable. It is odorless and colourless. It is non corrosive to any metal. But it is highly costlier than other types of refrigerators. But the main demerit with regard as to this is type is the large amount of refrigerant that is necessary to be circulated for a given output. It is generally abbreviated as R-12 or F-12. (Rajadurai, 2003)FREON 22 (or DICHLOR single-channel CHLORO METHANE)It is widely used as the refrigerant for domestic refrigerants. It has all compulsory points like the characters posed by Freon 12 such as non toxicity. It is colourless, odourless and non corrosive to metal. Additionally, the amount of refrigerant involve is only 1.3 kg/min per tonne for refrigeration. (Rajadurai, 2003)PRINCIPLES OF OPERATION THERMODYNAMICAL CONSIDERATIONTHE SECOND LAWThe bit law of thermodynamics is exposit as the most fundamental law of knowledge (Khemani, 2008). It is fundamental in the sense that it can be used to explain not only refrigerators and heat engines b ut highly advanced phenomena such as the big bang. It has been put aptly in the words of Classius as it is im doable for a process to occur that has the sole doing of removing a measure of heat from an object at a lower temperature and transferring this quantity of heat to an object at a higher(prenominal) temperature (Mortimer, 2008). This essentially promoter that heat cannot flow spontaneously from a cooler to a anxiouster dead body if nothing else progresss (Mortimer, 2008) i.e. there call for to be an out-of-door agency to perfume the change.In kitchen refrigerators, the closed box inside is able to be unplowed cool by the remotion of heat from the inside of the box and deposits it to the outside. As per the second law, the heat impart not move from the cold to the white freely so it is important for it to be made to do so, this is through with(p) by using an intermediate fluid (Littlewood, 2004) which absorbed heat on the inside. This intermediate fluid is known as a refrigerant and carries the heat outside of the box whereby it it released into the air as heat as shown in Figure 3 (Littlewood, 2004).Figure 3 the flow of heat deep down the refrigerator a schematic (Littlewood, 2004)The fluid circulates deep down the pipe which twistinges in and out and can be found at the back of the refrigerator. It is unbroken by using a compressor (which uses electricity from the home) and allows it to work effectively without violating the second law of motion. (Littlewood, 2004)THE FIRST LAWRefrigerator takes in vim from a sphere that needs to be cooled and deposits this heat energy into some other region that is outside of the refrigerator. In order to do work, there needs to be some mechanism in place, where the work done by a compressor and its electric motor is utilized. Using the First Law of Thermodynamics we can write (Littlewood, 2004)Figure 4 the first law of thermodynamics (Littlewood, 2004)QC QH = -WWhereQc energy or heat of the cold s ystemQH = energy or heat of the hot systemW = work doneSince work is done on the refrigerator by the compressor, the work is done is deemed negative because of sign conventions. This is part of the first law (Littlewood, 2004).The refrigerator is termed as a closed system and it possesses a constant compositionU = U + (U/V) T dVU = U + (U/T) V dTU = U + (U/V) T dV + (U/T) T dTdU = (U/V) T dV + (U/T) V dTAccording to Bain (2010), there are four basic parts to any refrigeratorCompressorHeatExpansion valveRefrigerantThe exchanging pipes are a gyrate set of pipes that is placed strategically outside of the unit. The refrigerant as will be discussed later on is a liquid that has the expertness to aerify efficiently so that inside the refrigerator is kept cooled. (Bain, 2010)A gas can be cooled by adiabatic expansion if the process is enthalphic. The gas expands through a process barrier from one constant pressure to the next and the temperature remainder in observed. Insulation of the system made the process adiabatic. The result is that a lower temperature was absorbed on the on a low pressure side and the change in the temperature is proportional to the change in pressure. (Bain, 2010)T PFigure 5 schematic of a domestic refrigerator (Bain, 2010)Figure 6 heat transfer within a refrigerator (Popular Mechanics, 1993)When an energy qc is removed from a cool rise at some temperature Tc, and then deposited in a warmer glide by at a temperature Th, the change in entropy is (Atkins dePaula, 2006)Atkins dePaula (2006) also indicated that the process is not spontaneous because the entropy generated in the warm inter is not enough to overcome the loss of entropy from the cold souce. And because of this more energy needs to be added to the stream that enters the warm swing to generated the entropy required by the system. They further indicated that the outcome is expressed as the coefficient of feat, cThe less the work required to achieve a given transfer, the g reater the coefficient of performance and the more efficient the refrigerator (Atkins dePaula, 2004). Because qc is removed from the cold source, the work w is added to the energy stream, the energy deposited as the heat in the hot root qh = qc + w. Therefore,FromWe can have an expression in terms of the temperature alone, which is possible if the transfer is performed reversibly (Atkins dePaula, 2006)Wherec = thermodynamic optimum coefficient of temperatureTc = temperature of the cold sinkTh = temperature of the hot sinkFor a refrigerator, it important that a very low coefficient of performance. For a refrigerator withdrawing heat from ice cold water (Tc = 273 K) in a typical environment (Th = 293K), c = 14. As an example, to remove 10 kJ (enough to freeze 30 g of water), requires transfer of atleast 0.71 kJ as work. (Atkins dePaula, 2006)The work to maintain a low temperature is very important when designing refrigerators. No thermal insulation is complete, so there is always some form of energy flowing as heat into a detail sample at a rate that is proportional to the temperature difference. (Atkins and de Paula, 2006).Figure 7 (a) the flow of energy as heat from a cold sink to a hot sink is not spontaneous as described the first law. Notice that the entropy increases but it is larger for the hot sink as compared to the cold sink. (Atkins dePaula, 2006). This contributes to a decrease in the NET entropy.(b) The process becomes feasible if work is provided to add to the energy stream. Then the increase in entropy of the hot sink can be made to excise the entropy of the hot source (Atkins dePaula, 2006)The rate at which energy leaks happen is written asWhereA = a constant that depends on the sizing of the sample and details of the simulationTc = temperature of the cold sinkTh = temperature of the hot sinkThe minimum power, P, required to maintain the original temperature difference by pumping out that energy by heating the surroundings isAs can be s een the power increases as the square of the temperature difference (Th Tc).THE REFRIGERATION CYCLEThe gas is pumped continuously at a pixilated pressure, the heat exchanger (which brings the required temperature) and then through a poriferous plug inside container that is thermally insulated. A phase change heat pump uses a liquid, as described earlier, that has a very low boiling point, which is used to move heat from an compass where it is cooler to one where it is warmer. The refrigerant requires energy so that it can evaporate, which essentially allows it remove the heat from the surroundings by absorbing it. When the vapor condenses, the energy absorbed in the process is released which is also in the form of heat as strength be expected. A refrigerant is a compound used in a heat cycle that endurees a phase change from a gas to a liquid and back. Latent heat describes the amount of energy in the form of heat that is required for a material to undergo a change of phase (al so known as change of state). deuce latent heats are typically described. (Bambooweb, 2009)For other uses, see CFC (disambiguation). The pump operates a cycle in which the refrigerant changes state from its liquid form to the vapour form and vice versa. This process occurs repeatedly and I known as the refrigeration cycle. In this cycle, the refrigerant condenses and heat is released in one point of the cycle. It is the boiled (or evaporated) so that it absorbs heat in another point of the cycle. The widely used refrigerant is hydro fluorocarbon (HFC) known as R-134a and CCl2F2 (dichlorodifluoromethane). Other substances such as liquid ammonia, propane or butane, are be used but because of their highly flammable nature, they are disregarded as a computable refrigerant. 1930 (MCMXXX) was a common year starting on Wednesday (link is to a sound 1930 calendar). (Bambooweb, 2009)For other uses, see CFC (disambiguation). In the refrigerator the fluid used (e.g. CCl2F2 ) fluid is lique fied by compression then vaporized by sudden expansion which gives a cooling effect. The compressor, in itself does not create a cooling effect outright, as might be expected. The cooling effect is fashioned when the refrigerant absorbs the heat so that it is removed and the area becomes cooler. This is accomplished with a heat exchanger. (Bambooweb, 2009)For other uses, see CFC (disambiguation). A heat exchanger is a gimmick built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted. The refrigeration cycle can be divided in ii partsThe liquefaction stageThe evaporation stageLIQUEFACTION degreeThe refrigerant vapour undergoes recycling by itself into the liquid form by the elicition of heat from a vapour at a higher temperature. The refrigerant is monotonic by the compressor where a low pressure and low temperature condition is created. This is accomplished by an ev aporating coil. During the compression process, the vapour of the refrigerant undergoes a temperature change (as an effect of the compression process). Additionally, the work of compression to create the high temperature and pressure vapour also contributes to the temperature change experienced by the vapour. The condenser that is located where the temperature is higher (i.e. the higher temperature heat sink) collects the vapour. Heat is then removed from the refrigerant and in lieu of this it condenses to its liquid state, hence the name for the condenser. (Mortimer, 2003 Brain, 1994 Bellis, 2010)Using the Joule-Thompson coefficient For a perfect gas = 0Cp + Cv = (H/T)p (U/T)pIntroducing H = U + pV = nRT into the first termCp Cv = (U/T)p + nR (U/T)p = nREVAPORATION STAGEAs the refrigerant leaves the condenser, the next part of the cycle begins. This is accomplished when a high temperature and high pressure liquid passes through a metering device that is found within the refri geration. The valve allows a specific quantity of liquid coolant to pass into the evaporation chamber. Evaporation chambers are relatively low pressure and this encourages coolant evaporation. Newly evaporated coolant is drawn though the cooling coils (typically a fan is used to blow air over the coils). Thus, the evaporative process produces the cooling effect. The refrigerant then is pulled to the compressor in the suction line where it will be soused into a high temperature, high pressure gas and sent to the external heat sinking coils. Capillary action or capillarity is the ability of a narrow tube to draw a liquid upward against the force of gravity. (Mortimer, 2003 Brain, 1994 Bellis, 2010)A refrigerator pumps heat up a temperature gradient. The cooling efficiency of this operation depends on the amount of heat extracted from the cold temperature seed (the freezer compartment), , and the work needed to do so. Since a practical refrigerator operates in a cycle to provide a continuous removal of heat, for the cycle. Then, by the conservation of energy (or first law), , where is the heat ejected to the high temperature root or the outside. (Mortimer, 2003 Brain, 1994 Bellis, 2010)The measure of a refrigerator performance is defined as the efficiency expressed in terms of the coefficient of performance (). Since the purpose is to extract the most heat () per unit work input (), the coefficient of performance for a refrigerator, , is expressed as their ratio (Mortimer, 2003 Brain, 1994 Bellis, 2010)Where, the conservation relationship given higher up is used to express the work in terms of heat.For normal refrigerator operation, the work input is less than the heat removed, so the is greater than 1. Refrigerators are commonly referred to as heat pumps of more specifically a it is a reversible heat pump because they basically pump heat. (Mortimer, 2003 Brain, 1994 Bellis, 2010)Figure 8 A diagram of the vapor compression refrigeration cycle that is used in heat pumps. The cycle shows the following (i) condenser, (ii) expansion valve, (iii) evaporator, (iv) compressor. (Karin, 2003)It is commonly believed that by opening a refrigerator, itll cool the kitchen. However this is entirely opposite, opening a refrigerator or freezer heats up the kitchen because the refrigeration cycle does not accept the air from the outside (Karlin 2003). The heat is referred to as the heat debauched from the compressors work and also includes that heat that s removed from within the refrigerator as well. (Karlin, 2003)The COP (in a heating or cooling application), provided that it undergoes level state operation, is given by the following equationWhereQcool is the heat extracted from a cold reservoir,Qhot is the heat delivered to a hot reservoir.A is the dissipated work by the compressor.THE CARNOT ENGINEThe Carnot refrigerator is the maximum limit to the COP (efficiency) of a refrigerator system. Although we cannot make the carnot refrigera tor, it tells us the maxium or best performance that can be garnered from a real refrigerator. The carnot refrigerator is sort of ideal in its design. As described earlier by Atkins dePaula (2006) with the Carnot engine, the COPc of a Carnot refrigerator depends (i) the temperature of the region that needs to be kept cool which has a characteristic temperature, TC and the temperature of the region where the heat needs to be transferred to, having a characteristic temperature, TH. It is pit to (Littlewood, 2004)EFFICIENCYThe efficiency of a refrigerator is described by a special coefficient known as a coefficient of performance and is defined in terms of the following parametersSUMMARY OF THERMODYNAMICS OF A REFRIGERATOR AFTER angiotensin-converting enzyme CYCLE substitute in internal energy = 0Change in heat is 0 keep down work 0Total volume change = 0Change in Gibbs free energy = 0Entropy change of the system = 0Entropy change of the universe 0