Sakshi Education
Nagendra M<br/>
CBM Engineer, Hindusthan Zink .Ltd
Refrigeration 1.1. Introduction
Refrigeration manages cooling of bodies or liquids to temperatures lower than those of surroundings. This includes retention of heat at a lower temperature and dismissal to higher temperature of the surroundings. In long time past days, the fundamental motivation behind refrigeration was to deliver ice, which was utilized for cooling refreshments, nourishment reservation and refrigerated transport and so on. Presently refrigeration and air conditioning cooling discover such a large number of uses that they have ended up exceptionally vital for humanity, and without refrigeration and ventilating the essential fabric of the general public will be unfavorably influenced.
Refrigeration and ventilation are by and large treated in a solitary subject because of the way that a standout among the most critical uses of refrigeration is in cooling and dehumidification as needed for summer ventilating. Obviously, refrigeration is needed for some applications other than cooling, and ventilating additionally includes forms other than cooling and dehumidification.
The temperature scope of enthusiasm for refrigeration reaches out down to about –1000C. At lower temperatures cryogenic frameworks are more prudent. Now a-days refrigeration has turned into a key part of natural way of life from post harvest heat evacuation to handling, appropriation and capacity. Refrigeration has ended up fundamental for some substance and preparing businesses to enhance the standard, quality, accuracy and effectiveness of numerous assembling techniques. Ever-new utilizations of refrigeration emerge constant.
Some extraordinary applications oblige little limits yet are actually captivating and testing. As said some time recently, cooling is one of the significant utilization of refrigeration. Ventilating has made the living conditions more agreeable, hygienic and sound in work places, working environments and homes. Air Conditioning includes control of temperature, mugginess, cleanliness of air and its appropriation to meet the solace prerequisites of people and/or some mechanical necessities. Air Conditioning includes cooling and dehumidification in summer months; this is basically done by refrigeration. It additionally includes heating and humidification in cool atmospheres, which is routinely done by an evaporator unless a heat pump is utilized.
The significant applications of refrigeration can be gathered into taking after four noteworthy similarly essential ranges.
Table 1.1. Effect of storage temperature on useful storage life of food products
If there should be an occurrence of foods grown from the ground, the utilization of refrigeration begins directly in the wake of gathering to evacuate the post-harvest heat, transport in refrigerated transport to the frosty stockpiling or the transforming plant. A piece of it might be put away in chilly stockpiling to keep up its tangible qualities and a part may be disseminated to retail shops, where again refrigeration is utilized for brief time stockpiling. Contingent on the size, the obliged limit of refrigeration plants for frosty stockpiles can be high. Alkali is one of the basic refrigerants utilized as a part of chilly stockpiles. Figure 3.2 demonstrates the photo of smelling salts based refrigerant plant for a frosty stockpiling. Figure 3.3 demonstrates the photo of a commonplace icy stockpiling. Family cooler is the client end of cool chain for brief time stockpiling.
Fig.1.2. Ammonia based refrigeration plant for a large cold storage
Fig.1.3. Photograph of a typical cold storage
The frosty tie has turned out to be exceptionally powerful in decreasing waste of nourishment and in sustenance protection. It is evaluated that in India, the post-harvest misfortune because of deficient icy storage spaces is high as 30 percent of the aggregate yield. The nature of remaining 70 percent is likewise influenced by lacking frosty chain offices. This demonstrates the significance of legitimate refrigeration offices in perspective of the developing nourishment needs of the perpetually developing populace. Refrigeration helps in holding the tangible, nutritious and consuming characteristics of the sustenance.
The over abundance product of foods grown from the ground can be put away for utilization amid crest requests and off-season; and transported to remote areas by refrigerated transport. In India, stockpiling of potatoes and pieces of fruit in substantial scale and some different foods grown from the ground in little scale and solidified stockpiling of peas, beans, cabbage, carrots and so on has enhanced the expectation for everyday comforts. When all is said in did the time span of usability of the vast majority of the leafy foods increments by capacity at temperatures between 0 to 10oC. Table 1.2 demonstrates the regular stockpiling conditions for a few foods grown from the ground as prescribed by ASHRAE. Nuts, dried foods grown from the ground that are inclined to bacterial weakening can likewise be put away for long periods by this strategy.
The before mentioned soil grown foods, vegetables and so on, can be put away in crude state. Some very perishable things oblige beginning handling before capacity. The quick and occupied advanced life requests prepared to-consume solidified or refrigerated nourishment bundles to dispense with the readiness and cooking time. These things are getting to be extremely famous and these oblige refrigeration plants. Freezing of fish aboard the ship right after catch results in better quality than freezing it after the ship docks. In some ships, it is frozen along with seawater since it takes months before the ships return to dock. Long-term preservation of fish requires cleaning, processing and freezing.
1.2.3. Meat and poultry: These things like wise oblige refrigeration directly after butcher amid preparing, bundling. Transient stockpiling is carried out at 0oC. Long haul stockpiling requires solidifying and stockpiling at -25oC.
1.2.4. Dairy Products: The imperative dairy items are milk, spread, buttermilk and ice cream. To keep up great quality, the milk is cooled in mass milk coolers promptly in the wake of being taken from cow. Mass milk cooler is a vast refrigerated tank that cools it between 10 to 15oC. At that point it is transported to dairy ranches, where it is sanitized. Sanitization includes heating it to 73oC and holding it at this temperature for 20 seconds. From that point, it is cooled to 3 to 4oC. The dairies need to have an extensive cooling limit, since a substantial amount of milk must be promptly cooled after landing. Amid the lean period, the refrigeration plants of dairies are utilized to create ice that is utilized amid top periods to give cooling by softening.
This diminishes the obliged top limit of the refrigeration plant. Frozen yogurt assembling obliges sanitization, careful blending, and emulsification also adjustment and thus cooling to 4 to 5oC. At that point it is cooled to temperature of about – 5oC in a cooler where it solidifies yet at the same time stays in fluid state. It is bundled furthermore solidified at –30 to –25oC until it gets to be robust; and afterward it is put away at same temperature. Buttermilk, curd and curds are put away at 4 to 10oC for increment of rack life. Utilization of refrigeration amid assembling of these things likewise expands their time span of usability. There are numerous mixed bags of cheddar accessible nowadays. Including cheddar starter like lactic corrosive and a few substances to the milk makes these. The whey is differentiated and robust part is cured for quite a while at around 10OC to make great quality cheese.
1.2.5. Refreshments: Production of brewskie, wine and concentrated products of the soil juices require refrigeration. The taste of numerous beverages can be enhanced by serving them icy or by adding ice to them. This has been one of the most loved past time of privileged in all the nations. Common or man-made ice for this reason has been made accessible since an extremely long time. Foods grown from the ground juice condensed have been extremely well known in view of minimal effort, great taste and nourishing qualities.
Juices can be safeguarded for a more drawn out time of time than the tree grown foods. Additionally, foods grown from the ground juice condensed when solidified can be all the more effectively dispatched and transported by street. Orange and different citrus juices, squeezed apple, grape juice and pineapple juice are exceptionally mainstream. To safeguard the taste and kind of juice, the water is determined out of it by bubbling it at low temperature under diminished weight. The concentrate is solidified and transported at –20oC. Fermenting and wine making obliges aging response at controlled temperature, for instance lager-sort of brewskie obliges 8 to12oC while wine obliges 27- 30oC. Maturation is an exothermic methodology; subsequently heat must be dismisses at controlled Temperature.
1.2.6. Candy: Utilization of chocolate in confection or its covering with chocolate obliges setting at 5-10oC else it gets to be sticky. Further, it is suggested that it be put away at low temperature for best taste.
1.2.7. Processing and distribution of frozen food: Numerous vegetables, meat, fish and poultry are solidified to manage the taste, which about copies that of the crisp item. Solidifying holds the tactile characteristics of shading, surface and taste separated from nourishing qualities. The refrigeration frameworks for solidified nourishment applications are generously composed, following the sustenance things are solidified in briefest time of time. The sharp solidifying with temperature regularly beneath –30oC, is carried out so the ice gems structured amid solidifying don't get sufficient time to develop and stay little and don't penetrate the cell limits and harm them. Prepared to-consume solidified sustenance’s, stuffed meals and bread shop things are likewise solidified by this technique and put away at temperatures of –25 to -20 oC for dissemination to retail locations amid crest requests or off-season revue.
Vegetables in this rundown are beans, corn, peas, carrots, cauliflower and numerous others. The vast majority of these are whitened before solidifying. There are different techniques of solidifying. Impact coolers give an impact of high speed air at – 30oC on the nourishment holder. In contact solidifying, the nourishment is put between metal plates and metal surfaces that are cooled to -30oC or lower. Drenching solidifying includes submersion of nourishment in low temperature brackish water. Individual speedy solidifying (IQF) is carried out by chilled air at high speeds like 5- 10 m/s that keeps the little vegetable particles or shrimp pieces gliding in air without amassing, so that greatest region is accessible for hotness exchange to individual particles. The solidified particles can be effectively bundled and transported. The refrigeration limits in all the coolers are substantial since solidifying of huge amounts is carried out in a brief time. Fluid nitrogen and carbon dioxide are additionally utilized for solidifying.
Generally market refrigeration is picking up prevalence everywhere throughout the world. At present this constitutes the biggest segment of refrigeration in created nations. In a run of the mill market a huge assortment of items are put away and showed available to be purchased. Since a wide assortment of items are put away, the obliged capacity conditions change broadly. Refrigeration at temperatures more noteworthy than 0oC and under 0oC is needed, as both solidified and new sustenance items are regularly put away in the same grocery store. Figure 1.4 demonstrates the photo of a segment of an ordinary general store. Refrigeration frameworks utilized for markets must be very solid because of the extensive estimation of the exceedingly perishable items. To guarantee legitimate refrigeration of all the put away items, an extensive of refrigerant tubing is utilized, prompting huge refrigerants.
Fig.1.4. Section of a supermarket with refrigerated display cases
1.3. Applications of refrigeration in chemical and process Industries
The industries like petroleum refineries, petrochemical plants and paper mash industries and so on require substantial cooling limits. The prerequisite of every industry process savvy and supplies shrewd is diverse henceforth refrigeration framework must be altered and enhanced for individual application. The fundamental uses of refrigeration in concoction and methodology industries include the accompanying classes.
1.3.1. Separation of gases: In petrochemical plant, temperatures as low as –150oC with refrigeration limits as high as 10,000 Tons of Refrigeration (TR) are utilized for partition of gasses by fragmentary refining. A few gasses gather promptly at lower temperatures from the mixtures of hydrocarbon. Propane is utilized as refrigerant as a part of large portions of these plant.
1.3.2. Condensation of Gases: A few gases that are created artificially are dense to fluid state by cooling, so these can be effortlessly put away and transported in fluid state. Case in point, in engineered smelling salts plant, alkali is dense at –10 to 10oC preceding filling in the barrels, stockpiling and shipment. This low temperature obliges refrigeration.
1.3.3. Dehumidification of Air: Low humidity air is needed in numerous pharmaceutical industries. It is likewise needed for air liquefaction plants. This is likewise needed to counteract friction based electricity and avoids short circuits in spots where high voltages are utilized. The air is cooled underneath its dew point temperature, with the goal that some water vapour consolidates out and the air gets dehumidified.
1.3.4. Solidification of Solute: One of the procedures of detachment of a substance or toxin or contamination from fluid mixture is by its cementing at low temperature. Greasing up oil is De-waxed in petroleum industry by cooling it beneath –25oC. Wax cements at about 25oC.
1.3.5. Storage as liquid at low pressure: Fluid involves less space than gases. A large portion of the refrigerants are put away at high weight. This weight is generally their immersion weight at atmospheric temperature. For a few gases, immersion weight at room temperature is high subsequently these are put away at moderately low weight and low temperature. For instance characteristic gas is put away at 0.7 bar gage weight and –130oC. Hotness pick up by the chamber dividers prompts bubbling of a few gases, which is packed, cooled and extended again to 0.7 bar gauge.
1.3.6. Removal of Heat of Reaction: In many chemical reactions, efficiency is better if the reaction occurs below room temperature. This requires refrigeration. If these reactions are exothermic in nature, then more refrigeration capacities are required. Production of viscose rayon, cellular acetate and synthetic rubber are some of the examples. Fermentation is also one of the examples of this.
1.3.7. Cooling for preservation: Many compounds decompose at room temperature or these evaporate at a very fast rate. Certain drugs, explosives and natural rubber can be stored for long periods at lower temperatures.
1.3.8. Recovery of Solvents: In many chemical processes solvents are used, which usually Evaporate after reaction. These can be recovered by condensation at low temperature by Refrigeration system. Some of the examples are acetone in film manufacture and carbon Tetrachloride in textile production.
1.4. Special applications of refrigeration
In this category we consider applications other than chemical uses. These are in manufacturing processes, applications in medicine, construction units etc.
1.4.1. Cold Treatment of Metals: The dimensions of precision parts and gauge blocks can be stabilized by soaking the product at temperature around – 90oC. The hardness and Wear resistance of carburized steel can be increased by this process. Keeping the cutting tool at –100oC for 15 minutes can also increase the life of cutting tool. In deep drawing process the ductility of metal increases at low temperature. Mercury patterns frozen by refrigeration can be used for precision casting.
1.4.2. Medical: Blood plasma and antibiotics are manufactured by freeze-drying process where water is made to sublime at low pressure and low temperature. This does not affect the tissues of blood. Centrifuges refrigerated at –10oC, are used in the manufacture of drugs. Localized refrigeration by liquid nitrogen can be used as anaesthesia also.
1.4.3. Ice Skating Rinks: Due to the advent of artificial refrigeration, sports like ice hockey and skating do not have to depend upon freezing weather. These can be played in indoor stadium where water is frozen into ice on the floor. Refrigerant or brine carrying pipes are embedded below the floor, which cools and freezes the water to ice over the floor.
1.4.4. Construction: Setting of concrete is an exothermic process. If the heat of setting is not removed the concrete will expand and produce cracks in the structure. Concrete may be cooled by cooling sand, gravel and water before mixing them or by passing chilled water through the pipes embedded in the concrete. Another application is to freeze the wet soil by refrigeration to facilitate its excavation.
1.4.5. Desalination of Water: In some countries fresh water is scarce and seawater is desalinated to obtain fresh water. Solar energy is used in some cases for desalination. An alternative is to freeze the seawater. The ice thus formed will be relatively free of salt. The ice can be separated and thawed to obtain fresh water.
1.4.6. Ice Manufacture: This was the classical application of refrigeration. Ice was manufactured in plants by dipping water containers in chilled brine and it used to take about 36 hours to freeze all the water in cans into ice. The ice thus formed was stored in ice warehouses. Now that small freezers and ice makers are available. Hotels and restaurants make their own ice, in a hygienic manner. Household refrigerators also have the facility to make ice in small quantities. The use of ice warehouses is dwindling because of this reason. Coastal areas still have ice plants where it is used for transport of iced fish. Refrigeration systems are also required in remote and rural areas for a wide variety of applications such as storage of milk, vegetables, fruits, food grains etc., and also for storage of vaccines etc. in health centers.
One typical problem with many of the rural and remote areas is the continuous availability of electricity. Since space is not constraint, and most of these areas in tropical countries are blessed with alternate energy sources such as solar energy, biomass etc., it is preferable to use these clean and renewable energy sources in these areas. Thermal energy driven absorption systems have been used in some instances. Vapour compression systems that run on photovoltaic (PV) cells have also been developed for small applications. Figure 1.5 shows the schematic of solar PV cell driven vapour compression refrigeration system for vaccine storage.
Fig.1.5. Solar energy driven refrigeration system for vaccine storage
1.5 Application of air conditioning:
Air-conditioning is required for improving processes and materials apart formed for comfort of Air-Conditioning required for comfort of persons. The life and efficiency of electronic devices increases at lower temperatures. Computer and microprocessor-based t also require air-conditioning for their efficient operation. Modern electronic equipment with Very Large Scale Integrated (VLSI) chips dissipates relatively large quantities of energy in a small volume. As a result, unless suitable cooling is provided, the chip temperature can become extremely high. As the computing power of computers ore cooling will be required in a small volume. Some super computers required liquid nitrogen for cooling. Air-conditioning applications can be divided into two categories, namely, industrial and comfort air-conditioning.
1.5.1. Industrial Air-conditioning:
The main purpose of industrial air conditioning system is to be provided conducive conditions so that the required processes can be carried out required products can be produced. Of course, the industrial air conditioning systems must also provide at least a partial measure of comfort to the people working in the industries. The applications are very diverse, involving cooling of laboratories down to –40oC for engine testing to applications to name a few.
Laboratories: This may involve precision measurement to performance testing of equipment and processes at controlled temperature and relative humidity. Laboratories carrying out research in electronics and biotechnology areas require very clean atmosphere. Many laboratories using high voltage like in LASERS require very low humidity to avoid the sparking.
Printing: Some colour printing presses have one press for each colour. The paper passes from one press to another press. The ink of one colour must get dried before it reaches the second press, so that the colours do not smudge. And the paper should not shrink, so that the picture does not get distorted. This requires control over temperature as well humidity. Improper humidity may cause static electricity, curling and buckling of paper.
Manufacture of Precision Parts: On the off chance that the metal parts are kept up at uniform temperature amid assembling process, these will not extend or psychologist, keeping up close resilience’s. A lower relative moistness will avert rust development too. A bit of dust in a switch or hand-off can result in aggregate or fractional glitch in space apparatus. The assembling of VLSI chips, microchips, PCs, air ship parts, Micro-Electro Mechanical Systems (MEMS), nano material creation and numerous territories of current advancement oblige a clean air and legitimate control over stickiness. Any pollution in the climate will ruin the VLSI chips. The idea of Clean rooms has been presented for such commercial enterprises. Indeed, all exactness businesses that utilization chip oblige these clean rooms.
Textile Industry: The yarn in the material business high speeds in present day machines. It is extremely touchy to stickiness. The non specific friction based electricity ought to be dodged. Its adaptability and quality ought not change. On the off chance that it breaks amid the procedure, the plant will must be ceased and yarn repaired before restarting the plant.
Pharmaceutical Industries: In these industries to obtain sterile atmosphere, the airborne bacteria and dust must be removed in the air-conditioning system by filters. These industries require clean rooms. If capsules are made or used in the plant, then air has to be dry otherwise the gelatine of capsules will become sticky.
Photographic Material: The raw material used for filmmaking has to be maintained at low temperature, since it deteriorates at high temperature and humidity. The film also has to be stored at low temperature. The room where film is developed requires 100% replacement by fresh air of the air polluted by chemicals.
Farm Animals: The yield of Jersey cows decreases drastically during summer months. Low temperature results in more efficient digestion of food and increase in weight of cow and the milk yield. Animal barns have to be ventilated in any case since their number density is usually very large. In many countries evaporative cooling is used for creating comfort conditions in animal houses.
Computer Rooms: These require control of temperature, humidity and cleanliness. The temperature of around 250 C and relative humidity of 50% is maintained in these rooms. The dust spoils the CD drives and printers etc.; hence the rooms have to be kept clean also by using micro filters in the air-conditioning system.
Power Plants: Most of the modern power plants are microprocessor controlled. In the earlier designs, the control rooms were very large and were provided with natural ventilation. These days the control rooms are very compact, hence these require air conditioning for persons and the microprocessors.
Vehicular Air-conditioning: Bus, tram, truck, car, recreational vehicle, crane cabin, aircraft and ships all require air-conditioning. In bus, tram, aircraft and ship, the occupancy density is very high and the metabolic heat and water vapor generated by persons has to be rejected. The cooling load in these is very high and rapidly changes that provides a challenge for their design.
1.5.2. Comfort Air-Conditioning
Vitality of sustenance is changed over into substance vitality for working of cerebrum, lungs, heart and different organs and this vitality is at last rejected to the surroundings. Likewise the inner organs oblige a temperature near to 350 C for their productive operation, and administrative components of human body keep up this temperature by dismissing suitable measure of hotness. People don't feel good if some additional exertion is needed by the body to reject this vitality. The air temperature, moistness and speed at which human body does not need to make any additional move, is called solace condition. Solace condition is likewise infrequently called as unbiased condition.
The residences, offices, shopping centers, stores, large buildings, theaters, auditorium etc. all have slightly different requirements and require different design. The required cooling capacities also vary widely depending upon the application. The factory assembled room air conditioners are very widely used for small residences, offices etc. These units are available as window type or split type. The capacity of these systems varies from a fraction of a ton (TR) to about 2 TR. These systems use a vapour compression refrigeration system with a sealed compressor and forced convection type evaporators and condensers. Figure 3.6 shows the schematic of a widow type room air conditioner. In this type all the components are housed in a single outer casing. In a split type air Conditioner, the compressor and condenser with fan (commonly known as condensing Hospitals require sterile atmosphere so that bacteria emitted by one patient does given unit) are housed in a separate casing and is kept away from the indoor unit consisting of the evaporator, blower, filter etc. The outdoor and indoor units are connected by refrigerant piping. For medium sized buildings factory assembled package units are available, while for very large buildings a central air conditioning system is used.
Fig.1.6. Schematic of window type room air conditioner
Hospitals require sterile atmosphere so that bacteria emitted by one patient does not affect the other persons. This is specially so for the operation theaters and intensive care units. In these places no part of the room air is re-circulated after conditioning by A/C system. In other places up to 90% of the cold room air is re-circulated and 10% outdoor fresh air is taken to meet the ventilation requirement of persons. In hospitals all the room air is thrown out and 100% fresh air is taken into the A/C system. Since, outdoor air may be at 45oC compared to 25oC of the room air, the air-conditioning load becomes very large. The humidity load also increases on this account. Operation theaters require special attention in prevention of spores, viruses, bacteria and contaminants given off by various devices and materials. Special quality construction and filters are used for this purpose.
Air conditioning in stores and super markets at tracks more customers, induces longer period of stay and thereby increases the sales. Supermarkets have frozen food section, refrigerated food section, dairy and brewage section, all of them requiring different temperatures. The refrigeration system has to cater to different temperatures, apart from air-conditioning. These places also have a wide variation in daily loads depending upon busy and lean hours, and holidays.
Large commercial buildings are a world of their own; they have their own shopping centre, recreation centre, gymnasium swimming pool etc. Offices have very high density of persons during office hours and no occupancy during off time. These buildings require integrated concept with optimum utilization of resources and services. These have security aspects, fire protection, emergency services, optimum utilization of energy all built-in. Modern buildings of this type are called intelligent buildings where air-conditioning requires large amount of energy and hence is the major focus.
Since persons need to spend a real piece of their time inside the building, without much presentation to outside, the idea of Indoor Air Quality (IAQ) has gotten to be imperative. There are countless that are transmitted by the materials utilized as a part of the development of structures and brought into the structures. IAQ locations to these issues and gives proposal for their diminished as far as possible. Debilitated building disorder is exceptionally basic in inadequately planned ventilated structures because of lacking ventilation and disgraceful materials. The wiped out building disorder is described by the inclination of queasiness, migraine, eye and throat aggravation and the general feeling of being uncomfortable with the indoor environment. In created nations this is prompting prosecution too.
In the earlier systems little attention was paid to energy conservation, since fuels were abundant and inexpensive. The energy crisis in early seventies, lead to a review of basic principles and increased interest in energy optimization. The concept of low initial cost with no regard to operating cost has become obsolete now. Approaches, concepts and thermodynamic cycles, which were considered impractical at one time, are receiving serious considerations now. Earlier, the index of performance used to be first law efficiency, now in addition to that; the second law efficiency is considered so that the available energy utilized and wasted can be clearly seen.
Concepts of hybrid cycles, heat recovery systems, alternate refrigerants and mixtures of refrigerants are being proposed to optimize energy use. Large-scale applications of air-conditioning in vast office and industrial complexes and increased awareness of comfort and indoor air quality have lead to challenges in system design and simulations. Developments in electronics, controls and computers have made refrigeration and air-conditioning a high-technology industry.
Refrigeration manages cooling of bodies or liquids to temperatures lower than those of surroundings. This includes retention of heat at a lower temperature and dismissal to higher temperature of the surroundings. In long time past days, the fundamental motivation behind refrigeration was to deliver ice, which was utilized for cooling refreshments, nourishment reservation and refrigerated transport and so on. Presently refrigeration and air conditioning cooling discover such a large number of uses that they have ended up exceptionally vital for humanity, and without refrigeration and ventilating the essential fabric of the general public will be unfavorably influenced.
Refrigeration and ventilation are by and large treated in a solitary subject because of the way that a standout among the most critical uses of refrigeration is in cooling and dehumidification as needed for summer ventilating. Obviously, refrigeration is needed for some applications other than cooling, and ventilating additionally includes forms other than cooling and dehumidification.
The temperature scope of enthusiasm for refrigeration reaches out down to about –1000C. At lower temperatures cryogenic frameworks are more prudent. Now a-days refrigeration has turned into a key part of natural way of life from post harvest heat evacuation to handling, appropriation and capacity. Refrigeration has ended up fundamental for some substance and preparing businesses to enhance the standard, quality, accuracy and effectiveness of numerous assembling techniques. Ever-new utilizations of refrigeration emerge constant.
Some extraordinary applications oblige little limits yet are actually captivating and testing. As said some time recently, cooling is one of the significant utilization of refrigeration. Ventilating has made the living conditions more agreeable, hygienic and sound in work places, working environments and homes. Air Conditioning includes control of temperature, mugginess, cleanliness of air and its appropriation to meet the solace prerequisites of people and/or some mechanical necessities. Air Conditioning includes cooling and dehumidification in summer months; this is basically done by refrigeration. It additionally includes heating and humidification in cool atmospheres, which is routinely done by an evaporator unless a heat pump is utilized.
The significant applications of refrigeration can be gathered into taking after four noteworthy similarly essential ranges.
- Food processing, preservation and distribution
- Chemical and process industries
- Special Applications
- Comfort air-conditioning
1.2. Application of refrigeration in Food processing, preservation and distribution
1.2.1. Storage of Raw Fruits and Vegetables:
It is remarkable that some microscopic organisms are in charge of corruption of sustenance, and enzymatic preparing reason maturing of the leafy foods. The development of microbes and the rate of enzymatic techniques are diminished at low temperature. These aides in decreasing the waste and enhancing the time span of usability of the nourishment. Table 3.1 shows helpful capacity life of some plant and creature tissues at different temperatures. It can be seen that the stockpiling temperature influences the valuable stockpiling life fundamentally. When all is said in done the stockpiling existence of the vast majority of the sustenance items relies on water action, which basically relies on the vicinity of water in fluid structure in the nourishment item and its temperature. Subsequently, it is conceivable to protect different sustenance items for any longer periods under solidified conditions.
| Average useful storage life (days) | ||
| Food Product | 0oC | 38oC |
| Meat | 6-10 | < 1 |
| Fish | 2-7 | < 1 |
| Poultry | 5-18 | < 1 |
| Dry meats and fish | > 1000 | > 100 & < 350 |
| Fruits | 2 – 180 | 1 – 7 |
| Dry fruits | > 1000 | > 100 & < 350 |
| Leafy vegetables | 3 – 20 | 1 – 3 |
| Root crops | 90 - 300 | 2 – 20 |
| Dry seeds | > 1000 | > 100 & < 350 |
Table 1.1. Effect of storage temperature on useful storage life of food products
If there should be an occurrence of foods grown from the ground, the utilization of refrigeration begins directly in the wake of gathering to evacuate the post-harvest heat, transport in refrigerated transport to the frosty stockpiling or the transforming plant. A piece of it might be put away in chilly stockpiling to keep up its tangible qualities and a part may be disseminated to retail shops, where again refrigeration is utilized for brief time stockpiling. Contingent on the size, the obliged limit of refrigeration plants for frosty stockpiles can be high. Alkali is one of the basic refrigerants utilized as a part of chilly stockpiles. Figure 3.2 demonstrates the photo of smelling salts based refrigerant plant for a frosty stockpiling. Figure 3.3 demonstrates the photo of a commonplace icy stockpiling. Family cooler is the client end of cool chain for brief time stockpiling.
Fig.1.2. Ammonia based refrigeration plant for a large cold storage
Fig.1.3. Photograph of a typical cold storage
The frosty tie has turned out to be exceptionally powerful in decreasing waste of nourishment and in sustenance protection. It is evaluated that in India, the post-harvest misfortune because of deficient icy storage spaces is high as 30 percent of the aggregate yield. The nature of remaining 70 percent is likewise influenced by lacking frosty chain offices. This demonstrates the significance of legitimate refrigeration offices in perspective of the developing nourishment needs of the perpetually developing populace. Refrigeration helps in holding the tangible, nutritious and consuming characteristics of the sustenance.
The over abundance product of foods grown from the ground can be put away for utilization amid crest requests and off-season; and transported to remote areas by refrigerated transport. In India, stockpiling of potatoes and pieces of fruit in substantial scale and some different foods grown from the ground in little scale and solidified stockpiling of peas, beans, cabbage, carrots and so on has enhanced the expectation for everyday comforts. When all is said in did the time span of usability of the vast majority of the leafy foods increments by capacity at temperatures between 0 to 10oC. Table 1.2 demonstrates the regular stockpiling conditions for a few foods grown from the ground as prescribed by ASHRAE. Nuts, dried foods grown from the ground that are inclined to bacterial weakening can likewise be put away for long periods by this strategy.
The before mentioned soil grown foods, vegetables and so on, can be put away in crude state. Some very perishable things oblige beginning handling before capacity. The quick and occupied advanced life requests prepared to-consume solidified or refrigerated nourishment bundles to dispense with the readiness and cooking time. These things are getting to be extremely famous and these oblige refrigeration plants. Freezing of fish aboard the ship right after catch results in better quality than freezing it after the ship docks. In some ships, it is frozen along with seawater since it takes months before the ships return to dock. Long-term preservation of fish requires cleaning, processing and freezing.
1.2.3. Meat and poultry: These things like wise oblige refrigeration directly after butcher amid preparing, bundling. Transient stockpiling is carried out at 0oC. Long haul stockpiling requires solidifying and stockpiling at -25oC.
1.2.4. Dairy Products: The imperative dairy items are milk, spread, buttermilk and ice cream. To keep up great quality, the milk is cooled in mass milk coolers promptly in the wake of being taken from cow. Mass milk cooler is a vast refrigerated tank that cools it between 10 to 15oC. At that point it is transported to dairy ranches, where it is sanitized. Sanitization includes heating it to 73oC and holding it at this temperature for 20 seconds. From that point, it is cooled to 3 to 4oC. The dairies need to have an extensive cooling limit, since a substantial amount of milk must be promptly cooled after landing. Amid the lean period, the refrigeration plants of dairies are utilized to create ice that is utilized amid top periods to give cooling by softening.
This diminishes the obliged top limit of the refrigeration plant. Frozen yogurt assembling obliges sanitization, careful blending, and emulsification also adjustment and thus cooling to 4 to 5oC. At that point it is cooled to temperature of about – 5oC in a cooler where it solidifies yet at the same time stays in fluid state. It is bundled furthermore solidified at –30 to –25oC until it gets to be robust; and afterward it is put away at same temperature. Buttermilk, curd and curds are put away at 4 to 10oC for increment of rack life. Utilization of refrigeration amid assembling of these things likewise expands their time span of usability. There are numerous mixed bags of cheddar accessible nowadays. Including cheddar starter like lactic corrosive and a few substances to the milk makes these. The whey is differentiated and robust part is cured for quite a while at around 10OC to make great quality cheese.
1.2.5. Refreshments: Production of brewskie, wine and concentrated products of the soil juices require refrigeration. The taste of numerous beverages can be enhanced by serving them icy or by adding ice to them. This has been one of the most loved past time of privileged in all the nations. Common or man-made ice for this reason has been made accessible since an extremely long time. Foods grown from the ground juice condensed have been extremely well known in view of minimal effort, great taste and nourishing qualities.
Juices can be safeguarded for a more drawn out time of time than the tree grown foods. Additionally, foods grown from the ground juice condensed when solidified can be all the more effectively dispatched and transported by street. Orange and different citrus juices, squeezed apple, grape juice and pineapple juice are exceptionally mainstream. To safeguard the taste and kind of juice, the water is determined out of it by bubbling it at low temperature under diminished weight. The concentrate is solidified and transported at –20oC. Fermenting and wine making obliges aging response at controlled temperature, for instance lager-sort of brewskie obliges 8 to12oC while wine obliges 27- 30oC. Maturation is an exothermic methodology; subsequently heat must be dismisses at controlled Temperature.
1.2.6. Candy: Utilization of chocolate in confection or its covering with chocolate obliges setting at 5-10oC else it gets to be sticky. Further, it is suggested that it be put away at low temperature for best taste.
1.2.7. Processing and distribution of frozen food: Numerous vegetables, meat, fish and poultry are solidified to manage the taste, which about copies that of the crisp item. Solidifying holds the tactile characteristics of shading, surface and taste separated from nourishing qualities. The refrigeration frameworks for solidified nourishment applications are generously composed, following the sustenance things are solidified in briefest time of time. The sharp solidifying with temperature regularly beneath –30oC, is carried out so the ice gems structured amid solidifying don't get sufficient time to develop and stay little and don't penetrate the cell limits and harm them. Prepared to-consume solidified sustenance’s, stuffed meals and bread shop things are likewise solidified by this technique and put away at temperatures of –25 to -20 oC for dissemination to retail locations amid crest requests or off-season revue.
Vegetables in this rundown are beans, corn, peas, carrots, cauliflower and numerous others. The vast majority of these are whitened before solidifying. There are different techniques of solidifying. Impact coolers give an impact of high speed air at – 30oC on the nourishment holder. In contact solidifying, the nourishment is put between metal plates and metal surfaces that are cooled to -30oC or lower. Drenching solidifying includes submersion of nourishment in low temperature brackish water. Individual speedy solidifying (IQF) is carried out by chilled air at high speeds like 5- 10 m/s that keeps the little vegetable particles or shrimp pieces gliding in air without amassing, so that greatest region is accessible for hotness exchange to individual particles. The solidified particles can be effectively bundled and transported. The refrigeration limits in all the coolers are substantial since solidifying of huge amounts is carried out in a brief time. Fluid nitrogen and carbon dioxide are additionally utilized for solidifying.
Generally market refrigeration is picking up prevalence everywhere throughout the world. At present this constitutes the biggest segment of refrigeration in created nations. In a run of the mill market a huge assortment of items are put away and showed available to be purchased. Since a wide assortment of items are put away, the obliged capacity conditions change broadly. Refrigeration at temperatures more noteworthy than 0oC and under 0oC is needed, as both solidified and new sustenance items are regularly put away in the same grocery store. Figure 1.4 demonstrates the photo of a segment of an ordinary general store. Refrigeration frameworks utilized for markets must be very solid because of the extensive estimation of the exceedingly perishable items. To guarantee legitimate refrigeration of all the put away items, an extensive of refrigerant tubing is utilized, prompting huge refrigerants.
Fig.1.4. Section of a supermarket with refrigerated display cases
1.3. Applications of refrigeration in chemical and process Industries
The industries like petroleum refineries, petrochemical plants and paper mash industries and so on require substantial cooling limits. The prerequisite of every industry process savvy and supplies shrewd is diverse henceforth refrigeration framework must be altered and enhanced for individual application. The fundamental uses of refrigeration in concoction and methodology industries include the accompanying classes.
1.3.1. Separation of gases: In petrochemical plant, temperatures as low as –150oC with refrigeration limits as high as 10,000 Tons of Refrigeration (TR) are utilized for partition of gasses by fragmentary refining. A few gasses gather promptly at lower temperatures from the mixtures of hydrocarbon. Propane is utilized as refrigerant as a part of large portions of these plant.
1.3.2. Condensation of Gases: A few gases that are created artificially are dense to fluid state by cooling, so these can be effortlessly put away and transported in fluid state. Case in point, in engineered smelling salts plant, alkali is dense at –10 to 10oC preceding filling in the barrels, stockpiling and shipment. This low temperature obliges refrigeration.
1.3.3. Dehumidification of Air: Low humidity air is needed in numerous pharmaceutical industries. It is likewise needed for air liquefaction plants. This is likewise needed to counteract friction based electricity and avoids short circuits in spots where high voltages are utilized. The air is cooled underneath its dew point temperature, with the goal that some water vapour consolidates out and the air gets dehumidified.
1.3.4. Solidification of Solute: One of the procedures of detachment of a substance or toxin or contamination from fluid mixture is by its cementing at low temperature. Greasing up oil is De-waxed in petroleum industry by cooling it beneath –25oC. Wax cements at about 25oC.
1.3.5. Storage as liquid at low pressure: Fluid involves less space than gases. A large portion of the refrigerants are put away at high weight. This weight is generally their immersion weight at atmospheric temperature. For a few gases, immersion weight at room temperature is high subsequently these are put away at moderately low weight and low temperature. For instance characteristic gas is put away at 0.7 bar gage weight and –130oC. Hotness pick up by the chamber dividers prompts bubbling of a few gases, which is packed, cooled and extended again to 0.7 bar gauge.
1.3.6. Removal of Heat of Reaction: In many chemical reactions, efficiency is better if the reaction occurs below room temperature. This requires refrigeration. If these reactions are exothermic in nature, then more refrigeration capacities are required. Production of viscose rayon, cellular acetate and synthetic rubber are some of the examples. Fermentation is also one of the examples of this.
1.3.7. Cooling for preservation: Many compounds decompose at room temperature or these evaporate at a very fast rate. Certain drugs, explosives and natural rubber can be stored for long periods at lower temperatures.
1.3.8. Recovery of Solvents: In many chemical processes solvents are used, which usually Evaporate after reaction. These can be recovered by condensation at low temperature by Refrigeration system. Some of the examples are acetone in film manufacture and carbon Tetrachloride in textile production.
1.4. Special applications of refrigeration
In this category we consider applications other than chemical uses. These are in manufacturing processes, applications in medicine, construction units etc.
1.4.1. Cold Treatment of Metals: The dimensions of precision parts and gauge blocks can be stabilized by soaking the product at temperature around – 90oC. The hardness and Wear resistance of carburized steel can be increased by this process. Keeping the cutting tool at –100oC for 15 minutes can also increase the life of cutting tool. In deep drawing process the ductility of metal increases at low temperature. Mercury patterns frozen by refrigeration can be used for precision casting.
1.4.2. Medical: Blood plasma and antibiotics are manufactured by freeze-drying process where water is made to sublime at low pressure and low temperature. This does not affect the tissues of blood. Centrifuges refrigerated at –10oC, are used in the manufacture of drugs. Localized refrigeration by liquid nitrogen can be used as anaesthesia also.
1.4.3. Ice Skating Rinks: Due to the advent of artificial refrigeration, sports like ice hockey and skating do not have to depend upon freezing weather. These can be played in indoor stadium where water is frozen into ice on the floor. Refrigerant or brine carrying pipes are embedded below the floor, which cools and freezes the water to ice over the floor.
1.4.4. Construction: Setting of concrete is an exothermic process. If the heat of setting is not removed the concrete will expand and produce cracks in the structure. Concrete may be cooled by cooling sand, gravel and water before mixing them or by passing chilled water through the pipes embedded in the concrete. Another application is to freeze the wet soil by refrigeration to facilitate its excavation.
1.4.5. Desalination of Water: In some countries fresh water is scarce and seawater is desalinated to obtain fresh water. Solar energy is used in some cases for desalination. An alternative is to freeze the seawater. The ice thus formed will be relatively free of salt. The ice can be separated and thawed to obtain fresh water.
1.4.6. Ice Manufacture: This was the classical application of refrigeration. Ice was manufactured in plants by dipping water containers in chilled brine and it used to take about 36 hours to freeze all the water in cans into ice. The ice thus formed was stored in ice warehouses. Now that small freezers and ice makers are available. Hotels and restaurants make their own ice, in a hygienic manner. Household refrigerators also have the facility to make ice in small quantities. The use of ice warehouses is dwindling because of this reason. Coastal areas still have ice plants where it is used for transport of iced fish. Refrigeration systems are also required in remote and rural areas for a wide variety of applications such as storage of milk, vegetables, fruits, food grains etc., and also for storage of vaccines etc. in health centers.
One typical problem with many of the rural and remote areas is the continuous availability of electricity. Since space is not constraint, and most of these areas in tropical countries are blessed with alternate energy sources such as solar energy, biomass etc., it is preferable to use these clean and renewable energy sources in these areas. Thermal energy driven absorption systems have been used in some instances. Vapour compression systems that run on photovoltaic (PV) cells have also been developed for small applications. Figure 1.5 shows the schematic of solar PV cell driven vapour compression refrigeration system for vaccine storage.
Fig.1.5. Solar energy driven refrigeration system for vaccine storage
1.5 Application of air conditioning:
Air-conditioning is required for improving processes and materials apart formed for comfort of Air-Conditioning required for comfort of persons. The life and efficiency of electronic devices increases at lower temperatures. Computer and microprocessor-based t also require air-conditioning for their efficient operation. Modern electronic equipment with Very Large Scale Integrated (VLSI) chips dissipates relatively large quantities of energy in a small volume. As a result, unless suitable cooling is provided, the chip temperature can become extremely high. As the computing power of computers ore cooling will be required in a small volume. Some super computers required liquid nitrogen for cooling. Air-conditioning applications can be divided into two categories, namely, industrial and comfort air-conditioning.
1.5.1. Industrial Air-conditioning:
The main purpose of industrial air conditioning system is to be provided conducive conditions so that the required processes can be carried out required products can be produced. Of course, the industrial air conditioning systems must also provide at least a partial measure of comfort to the people working in the industries. The applications are very diverse, involving cooling of laboratories down to –40oC for engine testing to applications to name a few.
Laboratories: This may involve precision measurement to performance testing of equipment and processes at controlled temperature and relative humidity. Laboratories carrying out research in electronics and biotechnology areas require very clean atmosphere. Many laboratories using high voltage like in LASERS require very low humidity to avoid the sparking.
Printing: Some colour printing presses have one press for each colour. The paper passes from one press to another press. The ink of one colour must get dried before it reaches the second press, so that the colours do not smudge. And the paper should not shrink, so that the picture does not get distorted. This requires control over temperature as well humidity. Improper humidity may cause static electricity, curling and buckling of paper.
Manufacture of Precision Parts: On the off chance that the metal parts are kept up at uniform temperature amid assembling process, these will not extend or psychologist, keeping up close resilience’s. A lower relative moistness will avert rust development too. A bit of dust in a switch or hand-off can result in aggregate or fractional glitch in space apparatus. The assembling of VLSI chips, microchips, PCs, air ship parts, Micro-Electro Mechanical Systems (MEMS), nano material creation and numerous territories of current advancement oblige a clean air and legitimate control over stickiness. Any pollution in the climate will ruin the VLSI chips. The idea of Clean rooms has been presented for such commercial enterprises. Indeed, all exactness businesses that utilization chip oblige these clean rooms.
Textile Industry: The yarn in the material business high speeds in present day machines. It is extremely touchy to stickiness. The non specific friction based electricity ought to be dodged. Its adaptability and quality ought not change. On the off chance that it breaks amid the procedure, the plant will must be ceased and yarn repaired before restarting the plant.
Pharmaceutical Industries: In these industries to obtain sterile atmosphere, the airborne bacteria and dust must be removed in the air-conditioning system by filters. These industries require clean rooms. If capsules are made or used in the plant, then air has to be dry otherwise the gelatine of capsules will become sticky.
Photographic Material: The raw material used for filmmaking has to be maintained at low temperature, since it deteriorates at high temperature and humidity. The film also has to be stored at low temperature. The room where film is developed requires 100% replacement by fresh air of the air polluted by chemicals.
Farm Animals: The yield of Jersey cows decreases drastically during summer months. Low temperature results in more efficient digestion of food and increase in weight of cow and the milk yield. Animal barns have to be ventilated in any case since their number density is usually very large. In many countries evaporative cooling is used for creating comfort conditions in animal houses.
Computer Rooms: These require control of temperature, humidity and cleanliness. The temperature of around 250 C and relative humidity of 50% is maintained in these rooms. The dust spoils the CD drives and printers etc.; hence the rooms have to be kept clean also by using micro filters in the air-conditioning system.
Power Plants: Most of the modern power plants are microprocessor controlled. In the earlier designs, the control rooms were very large and were provided with natural ventilation. These days the control rooms are very compact, hence these require air conditioning for persons and the microprocessors.
Vehicular Air-conditioning: Bus, tram, truck, car, recreational vehicle, crane cabin, aircraft and ships all require air-conditioning. In bus, tram, aircraft and ship, the occupancy density is very high and the metabolic heat and water vapor generated by persons has to be rejected. The cooling load in these is very high and rapidly changes that provides a challenge for their design.
1.5.2. Comfort Air-Conditioning
Vitality of sustenance is changed over into substance vitality for working of cerebrum, lungs, heart and different organs and this vitality is at last rejected to the surroundings. Likewise the inner organs oblige a temperature near to 350 C for their productive operation, and administrative components of human body keep up this temperature by dismissing suitable measure of hotness. People don't feel good if some additional exertion is needed by the body to reject this vitality. The air temperature, moistness and speed at which human body does not need to make any additional move, is called solace condition. Solace condition is likewise infrequently called as unbiased condition.
The residences, offices, shopping centers, stores, large buildings, theaters, auditorium etc. all have slightly different requirements and require different design. The required cooling capacities also vary widely depending upon the application. The factory assembled room air conditioners are very widely used for small residences, offices etc. These units are available as window type or split type. The capacity of these systems varies from a fraction of a ton (TR) to about 2 TR. These systems use a vapour compression refrigeration system with a sealed compressor and forced convection type evaporators and condensers. Figure 3.6 shows the schematic of a widow type room air conditioner. In this type all the components are housed in a single outer casing. In a split type air Conditioner, the compressor and condenser with fan (commonly known as condensing Hospitals require sterile atmosphere so that bacteria emitted by one patient does given unit) are housed in a separate casing and is kept away from the indoor unit consisting of the evaporator, blower, filter etc. The outdoor and indoor units are connected by refrigerant piping. For medium sized buildings factory assembled package units are available, while for very large buildings a central air conditioning system is used.
Fig.1.6. Schematic of window type room air conditioner
Hospitals require sterile atmosphere so that bacteria emitted by one patient does not affect the other persons. This is specially so for the operation theaters and intensive care units. In these places no part of the room air is re-circulated after conditioning by A/C system. In other places up to 90% of the cold room air is re-circulated and 10% outdoor fresh air is taken to meet the ventilation requirement of persons. In hospitals all the room air is thrown out and 100% fresh air is taken into the A/C system. Since, outdoor air may be at 45oC compared to 25oC of the room air, the air-conditioning load becomes very large. The humidity load also increases on this account. Operation theaters require special attention in prevention of spores, viruses, bacteria and contaminants given off by various devices and materials. Special quality construction and filters are used for this purpose.
Air conditioning in stores and super markets at tracks more customers, induces longer period of stay and thereby increases the sales. Supermarkets have frozen food section, refrigerated food section, dairy and brewage section, all of them requiring different temperatures. The refrigeration system has to cater to different temperatures, apart from air-conditioning. These places also have a wide variation in daily loads depending upon busy and lean hours, and holidays.
Large commercial buildings are a world of their own; they have their own shopping centre, recreation centre, gymnasium swimming pool etc. Offices have very high density of persons during office hours and no occupancy during off time. These buildings require integrated concept with optimum utilization of resources and services. These have security aspects, fire protection, emergency services, optimum utilization of energy all built-in. Modern buildings of this type are called intelligent buildings where air-conditioning requires large amount of energy and hence is the major focus.
Since persons need to spend a real piece of their time inside the building, without much presentation to outside, the idea of Indoor Air Quality (IAQ) has gotten to be imperative. There are countless that are transmitted by the materials utilized as a part of the development of structures and brought into the structures. IAQ locations to these issues and gives proposal for their diminished as far as possible. Debilitated building disorder is exceptionally basic in inadequately planned ventilated structures because of lacking ventilation and disgraceful materials. The wiped out building disorder is described by the inclination of queasiness, migraine, eye and throat aggravation and the general feeling of being uncomfortable with the indoor environment. In created nations this is prompting prosecution too.
In the earlier systems little attention was paid to energy conservation, since fuels were abundant and inexpensive. The energy crisis in early seventies, lead to a review of basic principles and increased interest in energy optimization. The concept of low initial cost with no regard to operating cost has become obsolete now. Approaches, concepts and thermodynamic cycles, which were considered impractical at one time, are receiving serious considerations now. Earlier, the index of performance used to be first law efficiency, now in addition to that; the second law efficiency is considered so that the available energy utilized and wasted can be clearly seen.
Concepts of hybrid cycles, heat recovery systems, alternate refrigerants and mixtures of refrigerants are being proposed to optimize energy use. Large-scale applications of air-conditioning in vast office and industrial complexes and increased awareness of comfort and indoor air quality have lead to challenges in system design and simulations. Developments in electronics, controls and computers have made refrigeration and air-conditioning a high-technology industry.
Published date : 03 Mar 2015 03:51PM
