REFRIGERATION AND AIR CONDITIONING

1. REFRIGERATION AND AIR CONDITIONING

2. Refrigeration • It is defined as the process of providing and maintaining a temperature well below that of surroundingatmosphere. • In other words refrigeration is the process of coolingsubstance.

3. Refrigerators and heatpumps • If the main purpose of the machine is to cool some object, the machine is named as refrigerator. • If the main purpose of machine is to heat a medium warmer than the surroundings, the machine is termed as heatpump.

4. Refrigerator and Heatpump WarmSpace QR WorkInput Heat Pump QR Refrig erator WorkInput ColdSpace

5. Terminologies ofRefrigeration Refrigerating Effect (N): It is defined as the quantity of heat extracted from a cold bodyor space to be cooled in a giventime. N= Heat extracted from the coldspace Timetaken Specific Heat of water and ice :It is the quantityof heat required to raise or lower the temperature of one kg of water (or ice), through one kelvin or(10 c) in onesecond. Specific heatofwater, Cpw = 4.19 kJ/kgK Specific heatofice, Cpice = 2.1 kJ/kgK.

6. Terminologies ofRefrigeration • Capacity of a Refrigeration Unit: • Capacity of a refrigerating machines are expressed by their coolingcapacity. • The standard unit used for expressing the capacityof • refrigerating machine is ton ofrefrigeration. • One ton of refrigeration is defined as, “the quantity of heat abstracted (refrigerating effect) to freeze one ton of water into one ton ofice in a duration of 24 hours at 0oc”. • Heat extracted fromat0o c = latent heat ofice • Latent heatofice = 336kJ/kg • i.e., 336 kJ of heat should be extracted from one kg of water at 0o C to convert it intoice.

7. Terminologies ofRefrigeration =336x1000 kJ/24hrs. = 336x1000kJ/min 24x60 = 233.333kJ/min = 3.8889kJ/sec One ton ofrefrigeration One ton ofrefrigeration

8. Terminologies ofRefrigeration Co efficient of Performance:It is defined as theratio of heat extracted in a given time (refrigerating effect) to the workinput. Co efficient ofperformance= Heat extracted inevaporator Work Input RefrigeratingEffect Co efficient of performance= WorkInput N W Co efficient of performance= The COP is always greater than1 and known astheoretical coefficient ofperformance.

9. Refrigerants • Refrigerant:Any substance that absorbs heat through expansion and vaporisation process and loses heat due to condensation is a refrigeration process is called refrigerant. • Some examples of refrigerantsare, • Air • Ammonia(NH3) • Carbon dioxide(CO2) • Sulphur dioxide(SO2) • Freon –12 • MethylChloride • Methylenechloride.

10. Classification ofRefrigerants Refrigerants are classifiedas, (a) Primary Refrigerants:It is a working medium which is used for cooling the substance by absorption of latentheat. E.G Ammonia (NH3), Carbon dioxide (CO2), Sulphur dioxide (SO2), Freon 12,etc., (b) Secondary Refrigerants:Secondary refrigerant is a substance already cooled by primary refrigerant and then employed for coolingpurposes. E.g Ice, solid carbondioxide. These refrigerants cool the substance by absorption of their sensibleheat.

11. Types ofRefrigerators • Ice Refrigerators :Ice is kept in the cabinet of refrigerators and this acts as the refrigeratingmeans. • Air Refrigerators :Air is used as working agent in thesetypesof refrigerators. • E.g., Bell ColemanCycle. • Vapour Refrigerators:The workingagents employed in this type of refrigerators are ammonia, CO2, SO2, freonsetc.,

12. Applications ofRefrigeration • In chemical industries, for separating andliquefying • thegases. • In manufacturing and storingice. • For the preservation of perishable food items in cold storages. • For coolingwater. • For controlling humidity of air manufacture and heat treatment ofsteels. • For chilling the oil to remove wax in oilrefineries. • For the preservation of tablets and medicines in pharmaceutical industries. • For the preservation of blood tissuesetc., • For comfort air conditioning the hospitals, theatres, etc.,

13. Properties ofRefrigeration • A good refrigerant should have high latent heatof • vapourisation. • It should have low boiling and low freezingpoint. • It should be non toxic and should non corrosiveness • It should be non flammable and nonexplosive. • It should have high thermalconductivity • It should be easy to handle • It should have low specific volume ofvapour. • It should have high co efficient ofperformance

14. VapourCompressionRefrigerationSystem

16. S – entropy means transformation, increases with increase intemperature and decreases with decrease intemperature ᵹ Q = Tds

17. Vapour Compression Refrigeration System -Construction • This system consists of a compressor, condenser, a receiver tank, an expansion valve and anevaporator. • Compressor :Reciprocating compressors generally used. For very big plantscentrifugal • compressors directly coupled with high speed rotating engines (gas turbine) areused.

18. Vapour Compression Refrigeration System -Construction Compressor: For very big plants Centrifugal compressors directly coupled with high speed rotatingengines (gas turbine) areused

19. Vapour Compression Refrigeration System -Construction • Condenser :It is a coil of tubes made of copper. • Receiver tank:It is the reservoir of liquid refrigerant. • Expansion Valve:This is a throttle valve. High pressure refrigerant is made to flow at a controlled rate through thisvalve. • Evaporator :It is the actual cooler and kept in the space to be cooled. The evaporator is a coil of tubes made ofcopper

20. Working Vapour Compression Refrigeration System- Working: The low pressure refrigerant vapour coming out ofthe evaporator flows into thecompressor. The compressor is driven by a primemover. In the compressor the refrigerant vapour iscompressed. The high pressure refrigerant vapour from the compressor is then passed through thecondenser. The refrigerant gives out the heat it had taken in the evaporator(N)

21. Vapour Compression RefrigerationSystem -Working

22. -Working Vapour Compression RefrigerationSystem Working: Most of the refrigerant is vapourised only inthe evaporator, at a lowpressure. In the evaporator the liquid refrigerant absorbs its latent heat of vapourisation from thematerial which is to becooled. Thus the refrigerating effect (N) isobtained. Then the low pressure refrigerant entersthe compressor and the cycle isrepeated.

23. Vapour Absorption Refrigerationsystem In this system compression process of vapour compression cycle is eliminated. Instead ofthat the following three processes are carriedout. Absorbing ammonia vapour intowater. Pumping this solution to a high pressurecycle Producing ammonia vapours from ammoniasolution byheating.

24. Vapour Absorption Refrigerationsystem

25. Vapour Absorption Refrigeration system - Construction • Construction: • The vapour absorption system consists ofa condenser, an expansion valve and an evaporator. • They perform the same as they do invapour compressionmethod. • In addition to these, this system has anabsorber, a heat exchanger, an analyser and arectifier.

26. Vapour Absorption Refrigeration system – Working Working: Dry ammonia vapor at low pressure passes in to the absorber from theevaporator. In the absorber the dry ammonia vapor is dissolvedin cold water and strong solution of ammonia isformed. Heat evolved during the absorption of ammonia is removed by circulating cold water through the coils kept in theabsorber. The highly concentrated ammonia (known as Aqua Ammonia) is then pumped by a pump to generator through a heatexchanger.

27. Vapour Absorption Refrigeration system - Construction Working: In the heat exchanger the strong ammonia solution is heated by the hot weak solution returning from the generator to theabsorber. In the generator the warm solution is further heated by steam coils, gas or electricity andthe ammonia vapour is driven out ofsolution. The boiling point of ammonia is less than thatof water. Hence the vapours leaving the generatorare mainly ofammonia.

28. Vapour Absorption Refrigeration system- Construction Working: The weak ammonia solution is left inthe generator is called weakaqua. This weak solution is returned to theabsorber through the heatexchanger. Ammonia vapours leaving the generatormay contain some watervapour. If this water vapour is allowed to thecondenser and expansion valve, it may freeze resulting in chockedflow. Analyser and rectifiers are incorporated inthe system beforecondenser.

29. Vapour Absorption Refrigeration system- Construction Working: The ammonia vapour from the generator passes through a series of trays in the analyser and ammonia is separated from watervapour. The separated water vapour returned togenerator. Then the ammonia vapour passes through arectifier. The rectifier resembles a condenser and water vapour still present in ammonia vapour condenses and the condensate is returned toanalyser. The virtually pure ammonia vapour then passes through thecondenser.

30. Vapour Absorption Refrigeration system- Construction Working: The latent heat of ammonia vapour is rejectedto the cooling water circulated through the condenser and the ammonia vapour is condensed to liquidammonia. The high pressure liquid ammonia isthrottled by an expansion valve or throttlevalve. This reduces the high temperature of theliquid ammoniato a low value and liquid ammonia partlyevaporates. Then this is led to theevaporator. Inthe evaporator the liquid fullyvaporizes.

31. Vapour Absorption Refrigeration system- Construction Working: The latent heat of evaporation is obtainedfrom the brine or other body which is beingcooled. The low pressure ammonia vapour leavingthe evaporator again enters the absorber and the cycle iscompleted. This cycle is repeated again to providethe refrigeratingeffect.

32. Applications of refrigerationsystem • Preservation of food items like vegetables, milk andeggs. • Preservation ofmedicines. • Preservation of blood, tissues,etc., • Preservation and cooling of cooldrinks. • Preservation of chemicals (Chemical industries) • Cooling ofwater. • Industrial and comfortairconditioning. • Processing of dairyproducts.

34. Comparison between Vapour compression & Vapour Absorption refrigeration systems

35. Layout of DomesticRefrigerator

36. Layout of Domesticrefrigerator

37. Domesticrefrigerator…… • House hold refrigerators use vapor compression cycle • Less energy: (90 W to 600W) • Due to small and high efficiency motors andcompressors, • better insulationmaterials, • large coil surfacearea, • better doorseals • Designed tomaintain: • Freezer section -18°C • Refrigeration section at3°C

38. Domesticrefrigerator…… • Insulationmaterials: • Fiber glass, k= 0.032 W/m°C • Urethane foam, k= 0.019 W/m°C • Wall thickness forfoam • For freezer section reduced from 90 to 48mm • For refrigeration section reduced from 70 to 40mm • Works better up to the environment of43°C • Ice maker (2 to 3kg/day) • Vapor absorption is more expensive and less efficient

39. Domesticrefrigerator…… • Energy consumption can be minimized for practicing goodmeasures • Open the refrigeration doors fewest timespossible • Cool the hot foods to roomtemperature • Clean the condenser coil behind therefrigerator • Check the door gaskets for airleaks • Avoid unnecessary low temperaturesettings • Avoid excessive ice buildup • Use the power saverswitch • Do not block the air flow passages to and fromthe • condensercoil.

40. AIRCONDITIONING AIRCONDITIONING: Air Conditioning is the process of conditioning the air according to the human comfort, irrespective of external conditions.

41. AIRCONDITIONING • Applications of AirConditioning • Used in offices, hotels, buses,cars.,etc • Used in industries having tool room machines. • Used in textile industries to control moisture. • Used in printingpress. • Used in Food industries, Chemicalplants.

42. Air conditioning systems are classifiedas CLASSIFICATIONOFAIRCONDITIONING • According to thepurpose • Comfort Airconditioning. • Industrial Airconditioning. • According to Season of theyear • Summer Airconditioning. • Winter Airconditioning. • Year round Airconditioning.

43. AIRCONDITIONING Types of Airconditioners Room Airconditioners Winter Airconditioners Central Air conditioners Functions of Airconditioners Cleaningair. Controlling the temp ofair. Controlling the moisturecontent. Circulating theair.

44. TERMINOLOGIES Dryair: The atmospheric air which no water vapour is called dryair. Psychrometry: Psychrometry is the study of the properties of atmosphericair. Temperature: The degree of hotness (or) Coldness is called thetemperature. Moisture: Moisture is the water vapour present in the air.

45. TERMINOLOGIES Humidity: mass of water vapor present in1kg of dryair Absolute humidity: mass of watervapor present in 1cu.m of dryair Relative humidity: Relative humidity is the ratio of actual mass of water vapour in agiven volume to the mass of water vapour actually can withhold by the samevolume. Dry bulb temperature: The temperature ofair measured by the ordinary thermometer is called dry bulbtemperature:

46. TERMINOLOGIES Wet bulb Temperature: The temperature of air measured by the thermometer when it is covered by the wet cloth is known as wetbulb Temperature. Dew point Temperature:The temperature at which the water vapour starts condensing is called dew pointTemperature Wet bulb depression: (DBT- WBT)indicates relativehumidity Dew point depression: (DBT- DPT)

47. Window Type AirConditioner

48. Window Type AirConditioner

49. Window Type AirConditioner

50. WindowTypeAirConditioner-Working • The low pressure vapour refigerant from the evaporator is sucked by compressor through the open inletvalve. • The compressor compresses thevapour • refrigerant. • The high pressure and high temperature vapour refrigerant then flows to the condenser through the open outletvalve. • In the condenser, the outside atmospheric temperature in summer being around 42o C, air is circulated byfan. • After condensation, the high pressure liquid refrigerant formed passes through an expansion valve which reduces itspressure