Lecture Objectives:

• Analyze absorption cooling

Mixtures(T-x diagram)

For P= 4 bar

Dew point curve

Bubble point curve

Saturated vapor

Saturated liquid

Mixture of liquid and vapor

h-x diagram

Isotherms are showmen only in liquid region

hfg for H2O

hfg for NH3

Composition of h-x diagramSaturated vapor line at p1

Equilibrium construction line at p1

x1

A

Adding energy

B

Isotherm

at P 1 and T 1

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’.

X1’mass fraction of ammonia in saturated vapor

1e

h-x diagramat the end of your textbook you will find these diagrams

for 1) NH3-H2O

2) H2O-LiBr

LiBr is one of the major liquid descantsin air-conditioning systems

Adiabatic mixing in h-x diagram(Water – Ammonia)

From the textbook (Thermal Environmental Eng.; Kuehen et al)

Absorption cooling cycle

HeatRich solution of

Rich solution of

H2O

H2O H2O + NH3

H2O + NH3

Mixing of two streams with heat rejection (Absorber)

QHeat rejection

m1

m2

m3

xx3

1

2

3’

3

Mass and energy balance:

From mixture equation:

(1)

(2)

(3)

Substitute into (2)

Substitute into (3)

From adiabatic mixing (from previous slide)

m1

m2

m3

=pure NH3 (x2=1)

Mixture of 1 and 2cooling

mixture of H2O and NH3

Change of pressure(pump)

1

2

p1 ≠p2

p2

p1Saturated liquid at

Saturated liquid at

m1=m2

x1 =x2

x1=x2

1

2

Saturated liquid at p1

Sub cooled liquid at p2

Heat transfer with separation into liquid and vapor (Generator)

Apply mass and energy balance In the separator :

Defines points 3 and 4 in graph

Heat

Sub cooled liquid Saturated

liquid

Saturated vapor

We can “break” this generator into 2 units

Q12

m1=m2

m4

m3

Separator

Apply mass and energy balance In the heat exchanger

defines point 2in graph

Q12 /m1

x1

sub cooled liquid

mixture

=2V

2L=

heating

Heat rejection with separation into liquid and vapor (Condenser)

m1=m2

Saturated vapor

m1

m2

1

Saturated vapor at

p1

Saturated liquid at

p1

x1=x2

2x1 =x2

p1 =p2

Q1-2/m1

heat rejection

Throttling process (Expansion valve)

m1=m2

x1 =x2

p1 ≠p2

1

2

x1 =x2

p1 ≠p2

p1

p2

h1 =h21

2

Saturated liquid at

Saturated liquid at

T2

T1

2V

2L

Saturated vapor

Saturated liquid

Simple absorption system

3L

3V

3LLP

Saturated vapor at p2=p3=p4

Saturated liquid at p2=p3=p4

Saturated liquid at p1=p5=p6=p3_LLP

Simple absorption system

1

2

3

3V

3L 4 5

1’

5L

65V

3LLP

mixing

Useful cooling energy

Needed thermal energy

More detailed absorption cooling

Refrigeration and air conditioning (Ramesh et al)