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Lecture Objectives:

This lecture introduces the absorption cooling cycle, focusing on sorption cooling and the absorption cycle. It explores system improvements such as vapor enrichment, preheating, and precooling. Topics include the use of h-x diagrams, mixing processes, heat rejections, and energy balances. Real-life examples and applications are discussed.

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Lecture Objectives:

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  1. Lecture Objectives: • Start energy production systems - Sorption cooling

  2. Absorption Cycle Replace compressor Same as vapor compression but NO COMPRESSOR

  3. Absorption cooling cycle Rich solution of Heat H2O + NH3 H2O H2O Rich solution of H2O + NH3

  4. Mixtures(T-x diagram) Dew point curve Saturated vapor Mixture of liquid and vapor Saturated liquid Bubble point curve For P= 4 bar

  5. h-x diagram hfg for H2O hfg for NH3 Isotherms are shown only in liquid region

  6. Composition of h-x diagram Saturated vapor line at p1 Equilibrium construction line at p1 1e Used to determine isotherm line in mixing region! Start from x1; move up to equilibrium construction line; move right to saturated vapor line; determine 1’; connect 1 and 1’. Isotherm at P1 and T1 Adding energy B A x1 X1’ mass fraction of ammonia in saturated vapor

  7. h-x diagramat the end of your textbook you will find these diagramsfor 1) NH3-H2O2) H2O-LiBr LiBr is one of the major liquid descants in air-conditioning systems

  8. Adiabatic mixing in h-x diagram(Water – Ammonia) From the textbook (Thermal Environmental Eng.; Kuehen et al)

  9. Absorption cooling cycle Rich solution of Heat H2O + NH3 H2O H2O Rich solution of H2O + NH3

  10. Mixing of two streams with heat rejection (Absorber) mixture of H2O and NH3 m3 m2 =pure NH3 (x2=1) m1 m3 m2 Not the isotherm ! 2 m1 Q cooling 3’ Mixture of 1 and 2 Heat rejection Mass and energy balance: (1) 1 3 (2) (3) x3 x From mixture equation: Substitute into (2) Substitute into (3) From adiabatic mixing (from previous slide)

  11. Change of pressure(pump) Sub cooled liquid at p2 2 Saturated liquid at p1 1 p1 ≠p2 Very small ∆h1-2 (insignificant) m1 =m2 p2 Saturated liquid at x1 =x2 2 p1 Saturated liquid at 1 x1=x2

  12. Heat transfer with separation into liquid and vapor (Generator) Saturated vapor Heat =2V Sub cooled liquid Saturated liquid Isotherm We can “break” this generator into 2 units heating m4 Q12 /m1 2L= m1 =m2 Separator mixture sub cooled liquid x1 m3 Q12 Apply mass and energy balance In the separator : Apply mass and energy balance In the heat exchanger defines point 2 in graph Defines points 3 and 4 in graph

  13. Heat rejection with separation into liquid and vapor (Condenser) Saturated vapor at p1 m1 Saturated vapor 1 heat rejection m2 Q1-2/m1 m1 =m2 Saturated liquid at p1 x1 =x2 2 p1 =p2 x1=x2

  14. Throttling process (Expansion valve) Saturated vapor 1 2V Isotherm 1 2 T1 h1 =h2 2 p1 Saturated liquid at p1 ≠p2 T2 2L Saturated liquid p2 m1 =m2 p1 ≠p2 Saturated liquid at x1 =x2 x1 =x2

  15. Simple absorption system 3V 3L 3LLP

  16. Simple absorption system Saturated vapor at p2=p3=p4 3V 6 3 5V mixing 1’ Needed thermal energy Useful cooling energy 4 3L 5 3LLP 2 Saturated liquid at p2=p3=p4 Saturated liquid at p1=p5=p6=p3_LLP 1 5L

  17. Heat transfer with separation into liquid and vapor (Generator) How to move point 4 to right ? =2V =2V heating m4 Q12 /m1 2L= 2L= =m2 m1 =m2 mixture Separator mixture sub cooled liquid x1 x1 m3 Q12 m3 Q12

  18. Heat rejection with separation into liquid and vapor (Enrichment NH3 in the vapor mixture) This is our point cooling 1 4=2V Separator 6=5V Q12 /m1 cooling Q45 /m4 x8 m8 8 7 5 m1 =m2 2 mixture isotherm sub cooled liquid m3 2L Q12 x8 x1

  19. Heat rejection with separation into liquid and vapor (Enrichment NH3 in the vapor mixture) This is our point cooling 1 4=2V Separator 6=5V Q12 /m1 cooling Q45 /m4 x8 m8 8 7 5 m1 =m2 2 mixture isotherm sub cooled liquid m3 2L Q12 x8 x1

  20. Ammonia Vapor Enrichment Process(Rectification)

  21. Absorption cooling with preheaterSystem improvement #1 Rich ammonia vapor 4 5 Refrigeration and air conditioning (Ramesh et al)

  22. Absorption cooling with preheater Saturated vapor at p1’ 1’’’V=3 Major heat source 6 1’’’ mixing isotherm 6h 1’’ Useful cooling energy 1’’’L =2 4 5 1’ Saturated liquid at p1’ 2’ , 2’’ Saturated liquid at p1 1 Cooling tower Pumping energy COP= Q cooling / Q heating (Pump ???)

  23. For Real energy analysis you need real h-x diagram! hfg for H2O hfg for NH3

  24. Use of precooling(system improvement #2)

  25. Absorption cooling with precooling Saturated vapor at p1’ 1’’’V=3 Major heat source 6’ 6 1’’’ 6h mixing Saturated liquid at p1’ isotherm 1’’ Useful cooling energy (larger!) 1’’’L =2 4 1’ Saturated liquid at p1 4’ 2’ , 2’’ 5 1 Cooling tower (needs to cool more!) Pumping energy

  26. System improvement #3(described as Rectification) Generator with Enrichment of NH3 Different 8V 9 8L 10 8LLP 11

  27. Heat rejection with separation into liquid and vapor (Enrichment NH3 in the vapor mixture) This is our point cooling 1 4=2V Separator 6=5V Q12 /m1 cooling Q45 /m4 x8 m8 8 7 5 m1 =m2 2 mixture isotherm sub cooled liquid m3 2L Q12 x8 x1

  28. Absorption system with Enrichment (no preheater nor precooler) Saturated vapor at p2 3V 8V mixing 3 11 8L 1’ Useful cooling energy 8LLP 10 2 3L 9 Saturated liquid at p2 Saturated liquid at p1 1

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