Vapour absorption cycle

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  • 1. module2 Vapour compression refrigeration – working principle and essential components- simple vapour compression refrigeration cycle – representation of cycle on T-S and p-h charts – thermodynamic analysis - effect of operating parameters on the performance – liquid vapour regenerative heat exchanger - actual cycle - numerical Problems. Multi pressure systems – multi compression and multi evaporator systems – inter cooling – flash inter cooling and flash gas removal. Vapour Absorption System – working principle - calculation of max COP – description and working of NH3 – water and Li Br –water systems - comparison with vapour compression system. Three fluid absorption system. Refrigerants and their properties – nomenclature of refrigerants - selection of refrigerants – environmental Manoj.P.J Assistant Prof(Mech)
  • 2. Vapour absorption refrigeration system Heat operated refrigeration cycle Aqua ammonia refrigeration systemby Manoj.P.J Assistant Prof(Mech)
  • 3. by Manoj.P.J Assistant Prof(Mech)
  • 4.  Compressor work can be reduced if vapour is dissolved in a suitable liquid before compression. At the exit of evaporator (state1) the vapour is dissolved in a weak ammonia solution in the absorberby Manoj.P.J Assistant Prof(Mech)
  • 5.  During this state heat must be removed to increase the absorption rate. The strong solution is pumped to generator pressure. Before reaching the generator the solution is first heated in the heat exchanger. Further heated in the Manoj.P.J Assistant Prof(Mech)
  • 6.  Since the saturation temperature of ammonia is less than water, ammonia vapour leaves the generator first and the left out weak solution goes back the absorber via heat exchanger and expansion valve. The heating source in the generator may be waste heat or by seam coil.by Manoj.P.J Assistant Prof(Mech)
  • 7.  Energy balance= Qg +QL +Wp = Qh +Qaby Manoj.P.J Assistant Prof(Mech)
  • 8. by Manoj.P.J Assistant Prof(Mech)
  • 9. Practical ammonia absorption systemby Manoj.P.J Assistant Prof(Mech)
  • 10. by Manoj.P.J Assistant Prof(Mech)
  • 11.  Analyzer and rectifier remove water vapour completely Other wise it may freeze at expansion valve. sub-cooler using evapourator out let improve refrigeration effectby Manoj.P.J Assistant Prof(Mech)
  • 12. Comparison of absorption with compression system. Absorption system -bulky -High capital cost -Use waste heat - can go well above 1000 TONS (vapour compression generally below 100 TON -inertia) COP is low(but using waste heat)by Manoj.P.J Assistant Prof(Mech)
  • 13. by Manoj.P.J Assistant Prof(Mech)
  • 14. Lithium Bromide absorption refrigeration systemby Manoj.P.J Assistant Prof(Mech)
  • 15. by Manoj.P.J Assistant Prof(Mech)
  • 16.  Water itself work as refrigerant. Lithium Bromide act as absorbent. The vapour pressure of an aqua solution of Lithium bromide is very low There fore it has high affinity towards water vapour. So if water and Lithium Bromide solution are placed adjacent to each other, in a closed evacuated system the water will evaporate.by Manoj.P.J Assistant Prof(Mech)
  • 17.  The weak LB solution is pumped to generator. The heating is done at generator and steam get separated and goes to condenser. The strong LB solution goes to absorber and mix with stem from evapourator. The steam entered in condenser get condensed by liberating heat out side and converted to water This water throttle to evapourator pressure. There again evaporation of water at low pressure takes place cooling Manoj.P.J Assistant Prof(Mech)
  • 18. comparison L B solution absorber  Ammonia absorber 1. pure water vapour  1. ammonia vapour may leaves the generator contain water vapour since Lithium Bromide and there fore analyser & salt does not evaporate. rectifier are needed. No need of analyser and rectifierby Manoj.P.J Assistant Prof(Mech)
  • 19.  2. working pressure are  2. pressure limits are below atmosphere. No higher. fear of bursting, toxicity. Pressure limit between evapourator and generator are lowby Manoj.P.J Assistant Prof(Mech)
  • 20.  3. pump work is less due  3. pump work is higher. to lower pressure limits. Some times pump can be eliminated with the proper placing of components. less vibrationby Manoj.P.J Assistant Prof(Mech)
  • 21.  4. temperature below 2  4. temperature can be degree C not possible. much less than 2 degree Larger volume flow rate. Manoj.P.J Assistant Prof(Mech)
  • 22. Three fluid absorption system (Electrolux refrigerator) Ammonia , hydrogen and waterby Manoj.P.J Assistant Prof(Mech)
  • 23. by Manoj.P.J Assistant Prof(Mech)
  • 24.  Ammonia evaporate in the presents of lighter gas In the generator the ammonia is separated due to heating . Passed through separator, rectifier and analyser to remove water content. Passed through condenser become liquid ammonia. Liquid ammonia is mixed with hydrogen and passed through Manoj.P.J Assistant Prof(Mech)
  • 25.  Ammonia liquid get evaporated in the presence of lighter hydrogen gas produce refrigeration effect. The mixture (ammonia and hydrogen) is passed to through the absorber through a heat exchanger. The hot hydrogen coming from absorber is cooled by the cold mixture coming from evaporator. The mixture is comes contact with the weak ammonia liquid comes from generator. the weak liquid ammonia liquid absorb ammonia vapour liberating Manoj.P.J Assistant Prof(Mech)
  • 26.  During absorption, the heat is liberated and hydrogen absorb this heat and become hot. This hot hydrogen is cooled in the heat exchanger. The strong solution from the absorber is passed to the generator through liquid heat exchanger where the strong solution is heated and weak solution is cooled. No need of pump and expansion valve. Uniform pressure though out the Manoj.P.J Assistant Prof(Mech)
  • 27.  Permitting the refrigerant to evaporate at the low temperature corresponding to it’s partial pressure of ammonia (because it is a mixture of ammonia and hydrogen). In the condenser side , there exists only the refrigerant (ammonia) , which is subjected to the total pressure of the system so that it is condensed by normal cooling water. the solution is circulated by thermal action Manoj.P.J Assistant Prof(Mech)