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  • Madhup T

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Refrigerator and Air Conditioning

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    REFRIGERANTS A refrigerant is the working substance in a refrigeration system and is generally a volatile substance which can remain in liquid phase at the evaporator pressure, although gaseous refrigerants may find application if the conditions favour. Refrigerants can be classified as : (i) primary (ii) secondary #PrimamrefrigeraMts include organic substances such as hydrocarbons WCs), ChloroFluoroCarbons (CFCs), UydroChloroFluoroCarbons(UCFCs), UydroFluoroCarbons (UFCs), brominated compounds, various isomers, azeotropes, zeotropes and unsaturated compounds (like ethylene), and inorganic substances like ammonia, water, carbon-dioxide, sulphur dioxide, etc. CFCs, UCFCs, uFCs and some brominated compounds are derived mainly from the saturated hydrocarbons methane (Ck4) and ethane (CZU6) by substituting chlorine/bromine or fluorine in place of hydrogen atoms. #gecondamrefrigerants include brines (calcium chloride, sodiUM chloride), glycol solutions (ethylene glycol and propylene glycol), water, air and other substances. SATURATED HYDROCARBONS and derived from saturated hydrocarbons with the chemical formula: CMUnFpClq n+p+q=2M+2 Designation: R(M-I) (n+l) (p).
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    EXAMPLE: methane (CU4) is ROSO or RSO, ethane CZu6) is R170, propane (C3Ug) is R2qo, monochlorodifluoromethane or CUCIFZ is RZZ, dichlorodifluoromethane or CCIZFZ is RTZ, trichloromonofluoromethane or CC13F is Rll, dichlorotrifluoroethane or CUClZCF3 is or UCFClZ3, tetrafluoroethane or CUZFCF3 is R134a or UFC134a, etc. Uydrocarbons with the number of hydrogen atoms exceeding g result in double digits as in, for example, R(3) (Il) (O) for butane C4UlO. To avoid this problem, such hydrocarbons are given arbitrary numbers. For example R600 is normal or n-butane and R600a is isobutane. #Brominated compounds are designated by adding the number of bromine atoms displacing the chlorine atoms to the designation of the original refrigerant CF3Br is R13Bl, since CF3Cl is RE. #lsomers, i.e., compounds with the same chemical formula but with differing molecular structure, are designated by adding the alphabets a, b, c, etc. #Azeotropes (refrigerant Mixtures which behaves like a pure refrigerants, evaporating and condensing at constant pressure/ temperature) are designated by 500 series numbers, e.g., RSOO, RSOZ, RS03, RS07A, etc. #Zeotropes (also called Non-azeotropic refrigerant Mixtures NARMs or blends NARBs) are refrigerant Mixtures which do not behave like a pure refrigerant. When they boil, the more volatile component is released first and when they condense, the higher boiling point component condenses first. Zeotropes are designated by 400 series numbers,
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    e.g., R401A, R413A, R401B, R410A, R407A, R407B, R407C, R417A, R40ZA, #Unsaturated compounds, i.e., compounds with the chemical formula CMUnFpClq where n+p+q=ZM, the designation is prefixed to the usual designation ROM-I) 01+1) Thus ethylene (CZU4) is Ri150. #lnorganic substances are designated by writing the molar mass after 7, as in, for example, R717 for ammonia (NU3), R7tg for water (1-120), R744 for carbon dioxide (COZ), R764 for sulphur dioxide (C02), etc. IMPORTANT REFRIGERENT AND ITS APPLICATION: #CFCII (CC13F; NBP = 23.goC): Air-conditioning of large buildings requiring hundreds of kW of refrigerating capacity, industrial process water and brine cooling, with single or multi-stage centrifugal compressors, as a brine in indirect low-temperature systems (down to -IOOoC ). #CFC114 (CCIFZCCIFZ, NBP=3.goC): Small fridges and drinking water coolers with rotary compressors; air conditioning of buildings, industrial process water and brine cooling with multistage centrifugal compressors. #CFCIZ (CCIZFZ, NBP= -zq.goc): Automotive AC, household refrigerators, water coolers, ice cream and frozen food cabinets, food locker plants, industrial process water and brine cooling, with reciprocating, rotary and centrifugal compressors.
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    #R500: R500 is an azeotropic Mixture consisting of 73.8% CFCIZ and 26.2% UFC152a and is used in medium temperature systems. These systems, if charged with UCFCZZ, give about 35% higher refrigerating capacity. #UCFCZZ (CUCIFZ, NBP = - 40.800: ROOM and central AC, heat pumps, industrial and commercial low temperature systems, with reciprocating and rotary compressors. #R50Z: RSOZ is an azeotropic Mixture. Results in good capacity and lower compressor discharge temperature in commercial and low temperature applications with single- and two-stage reciprocating compressors; home freezers, display cases, frozen food and ice cream cabinets, environmental test chambers and heat pumps. #CFC13 (CClF3, NBP= -7.400 and RS03: RS03 is an azeotropic Mixture .Applications of CFC13 and R503 are industrial very low- temperature cascade systems, with reciprocating or rotary compressors.
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    NEW & PREVIOUS YEARS PROBLEMS: (#NEW also from these above notes only if you follow properly) 1. Environment friendly refrigerant R134a is used in the new generation domestic refrigerators. Its chemical formula is: a) CH clF2 (b) c13 F3 (c) c12 F4 2.Match List-I (Refrigerant) with List-Il (Principal application) and select the correct answer using the codes given below the lists: List-I A.Air B.Ammonia C.Carbon dioxide D.Refrigerant-11 Codes: ABCD (a) 3412 (c) 2435 List-Il I.Direct contact freezing of food 2.CentrifugaI compressor system 3.Large industrial temperature installation 4.Automotive air-conditioners 5.Aircraft refrigeratin ABCD (b) 5312 (d) 5321 3. In conventional refrigerants what is the element responsible for ozone depletion? (a) Chlorine (b) Fluorine (c) Carbon (d) Hydrogen 4. Match List-I (Refrigerant) with List-Il (Chemical constituent) and select the correct answer using the codes given below the lists: List-I A.R-12 B.R-22 C.R-717 D.R-113 Codes: ABCD (a) 3241 (c) 3142 List-Il 1. Trichlorotrifluroethane (CC12FCClF2) 2.Difluoro monochloro methane (CHF2Cl) 3.Ammonia (NH3) 4.Difluoro dichloro methane (CC12F2) ABCD (b) 4231 (d) 4132


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