Lecture Objectives:

1
Lecture Objectives

• Analyze absorption cooling

2
Mixtures(T-x diagram)
Dew point curve
Saturated vapor
Mixture of liquid and vapor
Saturated liquid
Bubble point curve
For P 4 bar
3
h-x diagram
hfg for H2O
hfg for NH3
Isotherms are showmen only in liquid region
4
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
5
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
6
Adiabatic mixing in h-x diagram(Water Ammonia)
From the textbook (Thermal Environmental Eng.
Kuehen et al)
7
Absorption cooling cycle
Rich solution of
Heat
H2O NH3
H2O
H2O
Rich solution of
H2O NH3
8
Mixing of two streams with heat rejection
(Absorber)
mixture of H2O and NH3
m3
m2
pure NH3 (x21)
m1
m3
m2
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)
9
Change of pressure(pump)
Sub cooled liquid at p2
2
Saturated liquid at p1
1
p1
?p2
m1
m2
p2
Saturated liquid at
x1
x2
2
p1
Saturated liquid at
1
x1x2
10
Heat transfer with separation into liquid and
vapor (Generator)
Saturated vapor
Heat
2V
Sub cooled liquid
Saturated liquid
We can break this generator into 2 units
heating
m4
Q12 /m1
2L
m1
m2
Separator
mixture
sub cooled liquid
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
11
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
x1x2
12
Throttling process (Expansion valve)
Saturated vapor
1
2V
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
13
Simple absorption system
3V
3L
3LLP
14
Simple absorption system
Saturated vapor at p2p3p4
3V
6
3
5V
mixing
1
Needed thermal energy
Useful cooling energy
4
3L
5
3LLP
2
Saturated liquid at p2p3p4
Saturated liquid at p1p5p6p3_LLP
1
5L
15
More detailed absorption cooling
Refrigeration and air conditioning (Ramesh et al)