Lecture Objectives Start energy production systems Sorption cooling

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 H 2 O Rich solution of H 2 O + NH 3

Mixtures (T-x diagram) Satu rate d va por Mixture of liquid and vapor Sa tura ted liqu id Bubble point curve For P= 4 bar Dew point curve

h-x diagram hfg for H 2 O hfg for NH 3 Isotherms are shown only in liquid region

Composition of h-x diagram Saturated vapor line at p 1 Equilibrium construction line at p 1 1 e Used to determine isotherm line in mixing region! Start from x 1; move up to equilibrium construction line; move right to saturated vapor line; determine 1’; connect 1 and 1’. 1 d. T rm at P 1 an e oth Adding energy Is B A x 1 X 1’ mass fraction of ammonia in saturated vapor

h-x diagram at the end of your textbook you will find these diagrams for 1) NH 3 -H 2 O 2) H 2 O-Li. Br 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 H 2 O Rich solution of H 2 O + NH 3

Mixing of two streams with heat rejection (Absorber) mixture of H 2 O and NH 3 m 1 m 2 =pure NH 3 (x 2=1) m 3 m 2 Not the isotherm ! 2 m 1 Q Heat rejection Mixture of 1 and 2 3’ cooling Mass and energy balance: (1) 1 (2) (3) 3 x 3 From mixture equation: Substitute into (2) Substitute into (3) From adiabatic mixing (from previous slide) x

Change of pressure (pump) Sub cooled liquid at p 2 2 Saturated liquid at p 1 1 p 1 ≠p 2 Very small ∆h 1 -2 (insignificant) m 1=m 2 Saturated liquid at x 1 =x 2 2 Saturated liquid at p 1 1 x 1=x 2 p 2

Heat transfer with separation into liquid and vapor (Generator) Saturated vapor Heat =2 V Sub cooled liquid We can “break” this generator into 2 units heating m 4 m 1=m 2 sub cooled liquid Is ot he rm Saturated liquid 2 L= Separator mixture Q 12 /m 1 m 3 Apply mass and energy balance In the separator : x 1 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) m 1 m 2 m 1=m 2 x 1 =x 2 p 1 =p 2 Saturated vapor at p 1 Saturated vapor 1 heat rejection Q 1 -2/m 1 Saturated liquid at p 1 2 x 1=x 2

Throttling process (Expansion valve) Saturated vapor 1 2 V r he m ot Is 2 h 1 =h 2 T 1 1 2 Saturated liquid at p 1 ≠p 2 p 1 T 2 2 L m 1=m 2 x 1 =x 2 p 1 ≠p 2 Saturated liquid x 1 =x 2 Saturated liquid at p 2

Simple absorption system 3 V 3 L 3 LLP

Simple absorption system Saturated vapor at p 2=p 3=p 4 3 V 3 Needed thermal energy 6 g xin i m 5 V 1’ 4 3 L 3 LLP 2 1 5 Saturated liquid at p 2=p 3=p 4 5 LSaturated liquid at p 1=p 5=p 6=p 3_LLP Useful cooling energy

Heat transfer with separation into liquid and vapor (Generator) How to move point 4 to right ? =2 V heating m 4 =m 2 m 1=m 2 sub cooled liquid Q 12 mixture Q 12 /m 1 2 L= Separator m 3 x 1

Heat rejection with separation into liquid and vapor (Enrichment NH 3 in the vapor mixture) This is our point cooling Separator x 8 1 4=2 V 6=5 V Q 12 /m 1 m 8 5 rm m 1=m 2 2 is o th e mixture sub cooled liquid 7 8 Q 12 m 3 2 L x 1 x 8 cooling Q 45 /m 4

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 p 1’ 1’’’V=3 Major heat source 6 iso th er m 1’’’ 6 h 1’’’L =2 1’ 2’ , 2’’ Cooling tower 1 m g in ix 1’’ 4 5 Useful cooling energy Saturated liquid at p 1’ Saturated liquid at p 1 Pumping energy COP= Q cooling / Q heating (Pump ? ? ? )

hfg for H 2 O For Real energy analysis you need real h-x diagram! hfg for NH 3

Use of precooling (system improvement #2)

Absorption cooling with precooling Saturated vapor at p 1’ 1’’’V=3 Major heat source 6’ ix in 6 er m m 6 h g 1’’’ iso th Saturated liquid at p 1’ 1’’’L =2 Saturated liquid at p 1 Cooling tower 1’’ 1’ 4 4’ 2’ , 2’’ Useful cooling energy (larger!) 5 1 (needs to cool more!) Pumping energy

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

Heat rejection with separation into liquid and vapor (Enrichment NH 3 in the vapor mixture) This is our point cooling Separator x 8 1 4=2 V 6=5 V Q 12 /m 1 m 8 5 rm m 1=m 2 2 is o th e mixture sub cooled liquid 7 8 Q 12 m 3 2 L x 1 x 8 cooling Q 45 /m 4

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