Lecture - 2 - Introduction to Refrigeration & Air conditioning.pptx

Rac lecture

1. REFRIGERATION & AIR CONDITIONING

2. REFRIGERATION Introduction & Applications

3. REFRIGERATION Generally refrigeration is defined as “any process of heat removal” More specially, refrigeration is “that branch of science which deals with the process of reducing and maintaining the temperature of a space or material below the temperature of the surroundings” To accomplish this, heat must be removed from the body being refrigerated and transferred to another body whose temperature is below that of the refrigerated body. To limit the flow of heat into the refrigerated region from the warmer surroundings, there is a need for the thermal insulation It is evident that refrigerating and heating are actually opposite ends of the same process. Often only desired result distinguishes one from the other

4. APPLICATIONS OF REFRIGERATION Drinking foundries Dehumidifiers Ice makers Ice-skating rinks Desalting of seawater Freezing soil Cooling huge masses like concrete Food storage and distribution Food processing Chemical and process industries

5. APPLICATIONS OF REFRIGERATION Drinking foundries Small refrigeration units chill drinking water for storage and use as needed Dehumidifiers An appliance to dehumidify air in homes and buildings uses a refrigeration unit by first passing the air to be dehumidified through the cold evaporator coil of the system, where the air is both cooled and dehumidified. Then this cool air flows over the condenser and is discharged to the room Ice makers The production of ice may take place in domestic refrigerators, ice makers serving restaurants and hotels, and large industrial ice makers serving food-processing and chemical plants

6. Refrigeration in Drinking Foundries Dehumidifiers Ice makers

7. APPLICATIONS OF REFRIGERATION Ice-skating rinks Skaters, hockey players, and curlers cannot rely upon the weather to provide the cold temperatures necessary to freeze the water in their ice rinks. Pipes carrying cold refrigerant or brine are therefore embedded in a fill of sand or sawdust, over which water is poured and frozen Desalting of seawater One of the methods available for desalination of seawater is to freeze relatively salt-free ice from the seawater, separate the ice, and re-melt it to redeem fresh water

8. Ice-skating rinks

9. Desalting of seawater

10. APPLICATIONS OF REFRIGERATION Freezing Soil Refrigeration is sometimes used to freeze soil to facilitate d Cooling Huge masses like concrete Refrigeration is used in cooling huge masses of concrete (the chemical reaction which occurs during hardening gives off heat, which must be removed so that it cannot cause expansion and stress the concrete). Concrete may be cooled by chilling the sand, gravel, water, and cement before mixing, by embedding chilled-water pipes in the concrete

11. Freezing Soil

12. APPLICATIONS OF REFRIGERATION FOOD STORAGE AND DISTRIBUTION To prolong the life of the fruits & vegetables Many meats, fish, fruits, and vegetables are perishable, and their storage life can be extended by refrigeration. Fruits, many vegetables, and processed meat, such as sausage, are stored at temperatures just above freezing to prolong their life. Other meats, fish, vegetables, and fruits are frozen and stored many months at low temperatures until they are defrosted and cooked by the consumer. The frozen-food chain typically consists of the following links: Freezing Storage in refrigerated warehouses Display in a refrigerated case at food markets and finally storage in the home freezer or frozen-food compartment of a domestic refrigerator.

13. APPLICATIONS OF REFRIGERATION Freezing Early attempts to freeze food resulted in a product laced with ice crystals until it was discovered that the temperature must be plunged rapidly through the freezing zone. Approaches to freezing the food include air-blast freezing, where air at approximately -30 o C is blown with high velocity over packages of food stacked on fork-lift pallets; contact freezing, where the food is placed in a low-temperature brine; fluidized-bed freezing, where the individual particles are carried along a conveyor belt and kept in suspension by an upward-directed stream of cold air and freezing with a cryogenic substance such as nitrogen or carbon dioxide.

14. APPLICATIONS OF REFRIGERATION Storage Fruits and vegetables should be frozen quickly after harvesting and meats frozen quickly after slaughter to maintain high quality. Truckload and railcar-load lots are then moved to refrigerated warehouse, where they are stored at -20 to -23 o C, perhaps for many months. To maintain a high quality in fish, the storage temperature is even lower Distribution Food moves from the refrigerated warehouse to food markets as needed to replenish the stock there. In the market the food is kept refrigerated in display cases held at 3 to 5 o C for dairy products and unfrozen fruits and vegetables at approximately -20 o C for frozen foods and ice cream. The consumer finally stores the food in a domestic refrigerated or freezer until used

15. APPLICATIONS OF REFRIGERATION FOOD PROCESSING Some foods need operations in addition to freezing and refrigerated storage, and these processes entail refrigeration as well. Dairy products The chief dairy products are milk, ice cream, and cheese. To pasteurize milk the temperature is elevated to approximately 73 o C and held for about 20s. From that process the milk is cooled and ultimately refrigerated to 3 or 4 o C for storage. In manufacturing ice cream the ingredients are first pasteurized and thoroughly mixed. Then, refrigeration equipment cools the mix to about 6 o C, whereupon it enters a freezer. The freezer drops the temperature to -5 o C, at which temperature the mix stiffens but remains fluid enough to flow into a container. From this point on the ice cream is stored below freezing temperatures.

16. APPLICATIONS OF REFRIGERATION There are hundreds of varieties of cheese, each prepared by a different process, but typical steps include bringing the temperature of milk to about 30 o C and then adding several substances, including a cheese starter and sometimes rennet. Part of the mixture solidifies into the curds, from which the liquid whey is drained. A curing period in refrigerated rooms follows for most cheeses at temperature of the order of 10 o C.

17. APPLICATIONS OF REFRIGERATION Beverages Refrigeration is essential in the production of such beverages as concentrated fruit, beer, and wine. The taste of many drinks can be improved by serving them cold. Juice concentrates are popular because of their high quality and reasonable cost, It is less expensive to concentrate the juice close to the orchards and ship it in its frozen state than to ship the raw fruit. To preserve the taste of juice, its water must be boiled off at a low temperature, requiring much below a atmospheric.

18. APPLICATIONS OF REFRIGERATION In the brewing industry refrigeration controls the fermentation reaction and preserves some of the intermediate and final products. A key process in the production of alcohol is fermentation, an exothermic reaction. For production a larger-type beer, fermentation should proceed at a temperature between 8 and 12 o C, which is maintained by refrigeration. From this point on in the process the beer is stored in bulk and ultimately bottled or kegged (Fig. 1-7) in refrigerated spaces.

19. APPLICATIONS OF REFRIGERATION The major reason for refrigerating bakery products is to provide a better match between production and demand and thus prevent waste. Many breads and pastries are frozen following baking to provide a longer shelf life before being sold to the consumer. A practice that provides freshly baked products (and the enticing aroma as well) in individual supermarkets but achieve some of the advantages of high production is to prepare the dough in a central location, freeze it, and then transport it to the super market, where it is baked as needed.

20. APPLICATIONS OF REFRIGERATION Some biological and food products are preserved by freeze drying, in which the product is frozen and then the water is removed by sublimation (direct transition from ice to water vapor). The process takes place in a vaccum while heat is carefully applied to the product to provide the heat of sublimation. Some manufacturers of instant coffee use the freeze-drying process.

21. APPLICATIONS OF REFRIGERATION CHEMICAL AND PROCESS INDUSTRIES The chemical and process industries include the manufacturers of chemicals, petroleum refiners, petrochemical plants, paper and pulp industries, etc. these industries require good engineering for their refrigeration since almost every installation is different and the cost of each installation is so high. Some important functions served by refrigeration in the chemical and process industries are separation of gases condensation of gases solidification of one substance in a mixture separate it from others maintenance of a low temperature of stored liquid so that the pressure will not be excessive Removal of heat of reaction.

22. APPLICATIONS OF REFRIGERATION A mixture of hydrocarbon gases can be separated into its constituents by cooling the mixture so that the substance with the high-temperature boiling point condenses and can be physically removed from the remaining gas. Sometimes in petrochemical plants hydrocarbons, such as propane, are used as the refrigerant. Propane is relatively low in cost compared with other refrigerants, and the plant is completely equipped to handle flammable substances. In other applications separating refrigeration units, such as the large packaged unit, provide refrigeration for the process.

23. AIR CONDITIONING Introduction & Applications

24. AIR CONDITIONING In a similar manner, air conditioning embraces more than cooling Air conditioning is “the process of treating air to control simultaneously its temperature, humidity, cleanliness, and distribution in an internal environment to establish and maintain required standards to meet the comfort requirements of the occupants of the conditioned space” Air conditioning therefore includes the entire heating operation (which does not involve refrigeration except for heat pumps) as well as the regulation of velocity, thermal radiation, and the quality of air, including removal of foreign particles and vapors.

25. AIR CONDITIONING OF MEDIUM-SIZED AND LARGE BUILDINGS Most of the air-conditioning units in service provide comfort air conditioning, the purpose of which is to supply comfortable space for people. Summer cooling systems have become a standard utility in large buildings throughout the world. Large build ings may have to be cooled in order to remove the heat generated internally by people, lights and other electrical equipment. In hot climates, some form of central system usually serves large buildings. It may consists of one or more water-chilling plants and a water heater (traditionally) referred to as a boiler located in a machine room. The conditioned spaces are served by one or more air-supply and return systems, or the hot or chilled water may be piped to heat exchangers in the conditioned space.

26. AIR CONDITIONING OF MEDIUM-SIZED AND LARGE BUILDINGS Single-story commercial buildings such as stores and factories are often served by rooftop units mounted on the roof and providing conditioned air to the space below. The unit in is a heat pump, which is capable of providing either heated or cooled air to the conditioned space. Another important class of air-conditioned installation is for hospitals and other medical buildings. Many of the same requirements that prevail in office-building air conditioning apply to hospitals, but there are a number of additional concerns as well. Ventilation requirements often specify the use of 100 percent outdoor air, and humidity limits may be more sever in operating rooms to avoid static electricity. The design of an energy-efficient system for a hospital that also meets the special requirements poses an engineering challenge.

27. INDUSTRIAL AIR CONDITIONING The term industrial air conditioning will refer here to provide at least a partial measure of comfort for workers in hostile environments but also to controlling air conditions so that they are favorable to processing some object or material. Spot heating During cold weather it may be more practical to warm a confined zone where a worker is located. One such approach is through the use of an infrared heater. When its surfaces are heated to a high temperature by means of a burner or by electricity, they radiate heat to the affected area. Spot cooling It may be impractical to cool an entire steel mill, but conditions may be kept tolerable for worker by directing a stream of cool air onto occupied.

28. INDUSTRIAL AIR CONDITIONING Environmental laboratories The role of air conditioning varies from one environmental laboratory to another. In one a temperature of -40 o C must be maintained to test engines at low temperatures, and in another a high temperature and humidity may be maintained to study the behavior of animals in tropical climates. Printing Control of humidity is one of the primary reasons for air conditioning printing plants. In some printing processes the paper is run through several different presses, and the air conditioning must be maintained to provide proper registration. Other trouble caused by improper humidity are static electricity , curling or buckling of the paper, or failure of the ink to dry.

29. INDUSTRIAL AIR CONDITIONING Textiles Like paper, textiles are sensitive to changes in humidity and to a lesser extent changes in temperature. The yarn in modern textile plants moves at tremendous speeds, and changes in the flexibility and strength of the textile or generation of static electricity must be prevented. Precision parts and clean rooms For manufacturing of precision metal parts air conditioning performs three services: keeping the temperatures uniform so that the metal will not expand and contract, maintaining a humidity so that rust is prevented, and filtering the air to minimize dust. A technology for clean rooms has developed for the design and construction of such enclosures to manufacture electronic components and other materials.

30. INDUSTRIAL AIR CONDITIONING Photographic Products: The photographic products industry is a large user of air conditioning and refrigeration. Raw photographic material deteriorates rapidly in high temperatures and humidities, and other materials used in coating film require careful control of temperature. Computer Rooms The air-conditioning system for computer rooms should control the temperature, humidity, and cleanness of the air. Some electronic components operate in a faulty manner if they become too hot, and one means of preventing such localized high temperature is to maintain the air temperature in the computer room in the range of 20 o C to 23 o C.

31. INDUSTRIAL AIR CONDITIONING The electronic components in the computer function favorably at even lower temperatures, but this temperature is a compromise with the lowest comfortable temperature for occupants. A relative humidity between 30 and 45 percent is desirable for handling cards, since too high a relative humidity can result in improper feeding of cards and too low a relative humidity could cause static electricity in card decks. For long-term storage of magnetic tape the uniformity of temperature is an important requirement. Well-filtered air is necessary to facilitate low maintenance operation of printers, tap drives, and card readers . Power Plants Traditionally steam power plants were kept tolerable for workers by ventilating with outdoor air. The compactness and the increase in heat-flow intensities now no longer leave adequate space for air ducts. To provide cooling for many confined spaces in modern power plants air-cooling coils are supplied with refrigerated water that is conveyed through pipes much smaller than the conventional air ducts.

32. RESIDENTIAL AIR CONDITIONING In residential air conditioner, the central or unitary system, a condensing unit consisting of the compressor and condenser is located out of doors and evaporator coil in the interior air duct. Another system that is growing in importance for the combined heating and cooling of residences is the heat pump. It first appeared on the market in the 1950s.

33. AIR CONDITIONING OF VEHICLES The most air-conditioning vehicle is the automobile for which between 5 and 10 million systems are sold annually. But many other conveyances are air-conditioned as well, including buses, trains, trucks, recreational vehicles, tractors, crane cabs, aircraft, and ships. The major contributor to the cooling load in many of these vehicles is heat from solar radiation, and, in the case of public transportation, heat from people. The loads are also characterized by rapid changes and a high intensity per unit volume in comparison to building air conditioning.

34. RELATIONSHIP OF THE REFRIGERATION & AIR CONDITIONING FIELDS The field of refrigeration and air conditioning are interconnected, but each also has its own province. The largest application of refrigeration, which is the process of cooling, is for air conditioning. In addition, refrigeration embraces industrial refrigeration, including the processing and preservation of food; removing heat from substances in chemical, petroleum, and petrochemical plants; and numerous special applications such as those in the manufacturing and construction industries.

35. RELATIONSHIP OF THE REFRIGERATION & AIR CONDITIONING FIELDS REFRIGERATION Industrial refrigeration, Including food preservation Chemical and process industries AIR CONDITIONING Heating Humidifying, and control of air quality COMMON PROVINCE Cooling and dehumidifying operations in air conditioning

36. CONCLUSION The refrigeration and air conditioning industry is characterized by steady growth. It is a stable industry in which replacement markets join with new applications to contribute to its health. The high cost of energy since the 1970s has been significant factor in stimulating technical challenges for the individual engineer. Innovative approaches to improving efficiency which once were considered impractical now receive serious consideration and often prove to be economically justified. An example is the recovery of low-temperature heat by elevating the temperature level of this energy with a heat pump (which is a refrigeration system). The days of designing the system of lowest first cost with little or no consideration of the operating cost now seem to be past.

37. REFERENCES Refrigeration and air conditioning by Wilbert F . Stocker/ J erold W. Jones – chapter # 01