Lecture Objectives: Start energy production systems - Sorption cooling

Absorption Cycle Same as vapor compression but NO COMPRESSOR Replace compressor

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

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

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

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

h-x diagram at the end of your textbook you will find these diagrams for 1) NH3-H2O 2) H2O-LiBr LiBr is one of the major liquid descants in air-conditioning systems

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

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

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

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

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 sub cooled liquid mixture x1 Q12 m3 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

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

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

Simple absorption system 3V 3L 3LLP

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

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 sub cooled liquid mixture x1 x1 Q12 m3 Q12 m3

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 m1 =m2 5 2 sub cooled liquid mixture isotherm m3 2L Q12 x1 x8

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 m1 =m2 5 2 sub cooled liquid mixture isotherm m3 2L Q12 x1 x8

Ammonia Vapor Enrichment Process (Rectification)

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

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’’ 1 Saturated liquid at p1 Cooling tower Pumping energy COP= Q cooling / Q heating (Pump ???)

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

Use of precooling (system improvement #2)

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

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

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 m1 =m2 5 2 sub cooled liquid mixture isotherm m3 2L Q12 x1 x8

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