Heat Pump Laboratory, IITB 1 of 32
PSYCHROMETRY
AND AIR-CONDITIONING PROCESSES
• Moist Air as Mixture of Ideal Gases
Dalton’s law of additive pressures
Amagat’s law of additive volumes
• Psychometric Chart
Properties of Moist Air
DBT, WBT, DPT, RH
Humidity Ratio w kg H2O/kg DA
Specific Enthalpy of moist air h kJ/kg DA
Specific Volume of moist air v m3/kg DA
• Air-Conditioning Processes
Sensible heating and cooling
Cooling and dehumidifying
Heating and humidifying
Mixing of two air streams
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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T-v DIAGRAM FOR WATER VAPOURMoran & Shapiro (2006) Figure 12.4
in an Air-Water Mixture
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 2
DALTON’S LAW OF ADDITIVE PRESSURES
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 3
AMAGAT’S LAW OF ADDITIVE VOLUMES
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 4
RELATING p, V & T
for Ideal Gas Mixtures
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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p nR T
V
n number of moles of mixture
R Universal Gas Constant, 8.314 kJ/kmol.K
Dalton Model
pi niR T
V
pi yi p
p
1
j
i
pi
Amagat Model
Vi niR T
p
Vi yi V
V
1
j
i
Vi
Heat Pump Laboratory, IITB 5
RELATING p, V & T
Moist Air & Partial Pressures of Dry Air and Water Vapour
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Moist Air
pn R T
V
m R M1
T
V
n number of moles of mixturem mass of mixture, kgM molecular weight of mixture, kg/kmol
each mixture component is considered as if it existed alone in the volume V at themixture temperature T while exerting part of the pressure
Partial Pressures of Dry Air and Water Vapour
pa
na R T
V
ma R Ma1
T
V
pv
nv R T
V
mv R Mv1
T
V
Heat Pump Laboratory, IITB 6
RELATING p, V & T
Humidity Ratio and Relative Humidity
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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mv
ma
mv
ma
Mv pv V R T( )1
Ma pa V R T( )1
Mv pv
Ma pa
0.622pv
p pv
where pg is the saturation pressure of
water at mixture temperature T
yv
yv.sat
pv
pg
Heat Pump Laboratory, IITB 7
RELATING p, V & T
Enthalpy of Moist Air, Water vapour and Dry Air
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Enthalpy of Moist Air
H Ha Hv ma ha mv hv kJ
H
ma
ha
mv
ma
hv ha hvkJ
kgdry.air
Enthalpy of Water Vapour in the Moist Air
Reference to steam table data or Mollier diagram for water shows that the enthalpy
of superheated water vapour at low vapour pressures is very closely given by thesaturated vapour value corresponding to the given temperature.
hv hg T( ) an approximationkJ
kgwater
Enthalpy of Dry Air
ha
273.15 K
T
Tcp.a
dkJ
kgdry.air
Heat Pump Laboratory, IITB 8
MOIST AIR COOLED AT CONSTANT PRESSUREMoran & Shapiro (2006) Figure 12.6
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 9
DEW POINT TEMPERATUREMoran & Shapiro (2006) Figure 12.6
State of Water for Moist Air Cooled at Constant Mixture Pressure
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 10
ADIABATIC SATURATORMoran & Shapiro (2006)
(a) Schematic and (b) Process Representation
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 11
WBT MEASURING DEVICESMoran & Shapiro (2006) Figure 12.8
(a) Sling Psychrometer and (b) Aspirating Psychrometer
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 12
PSYCHROMETRIC CHARTMoran & Shapiro (2006) Figure 12.10
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Heat Pump Laboratory, IITB 13
ME 335 Introduction to Thermal Machines Lecture Presented by Prof M V Rane at IIT Bombay
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PSYCHROMETRIC CHARTMoran & Shapiro (2000)
LINES OF CONSTANT PROPERTY VALUE
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Heat Pump Laboratory, IITB 15
WBT & ENTHALPY LINES
Why are they not Exactly Parallel?
• Adiabatic Saturation Process
Adiabatic saturation temperature, tas
Energy balance
• Wet Bulb Temperature
Adiabatic saturation temperature, twb
Energy balance
• What Contributes to the Deviation?
Contribution of the energy entering the adiabatic saturator with the makeup water is
normally much smaller than that of moist air
Enthalpy of entering moist air is very nearly equal to the enthalpy of the saturated
mixture exiting
This slight effect is ignored in some psychometric chart
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 16
DIRECTION OF INCREASING PROPERTY VALUES
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 17
ASHRAE SUMMER AND WINTER COMFORT CONDITIONASHRAE Fundamentals 1997, Fig 4, pp 8.21
• Air Temperature
22 to 27 C
• Mean Radiant Temperature
Air temperature +10 C
• Humidity
4.5 to 11 g moisture/kg DA
• Air velocity
0.1 to 0.25 m/s
• Summer Design Comfort Conditions are Higher than that in the Winter
This reduces Air Conditioning Load and Save Energy
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 18
DEHUMIDIFICATIONMoran & Shapiro (2006) Figure 12.11
(a) Equipment Schematic and (b) Representation on Psychrometric Chart
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 19
HUMIDIFICATIONMoran & Shapiro (2006) Figure 12.12
Steam Injection and Water Injection
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 20
EVAPORATIVE COOLINGMoran & Shapiro (2006) Figure 12.13
(a) Equipment Schematic and (b) Representation on Psychrometric Chart
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 21
ADIABATIC MIXING OF TWO MOIST AIR STREAMS Moran & Shapiro (2006) Figure 12.14
Equipment Schematic
Mass Balance of Dry Air
ma3 = ma1 + ma2
Mass Balance of Water Vapour
ma3 w3 = ma1 w1 + ma2 w2
Energy Balance
ma3 (ha3 -w3 hg3) = ma1 (ha1 -w1 hg1) + ma2 (ha2 -w3 hg2)
ME 306 Applied Thermodynamics Lecture Presented by Prof M V Rane at IIT Bombay
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Heat Pump Laboratory, IITB 22
ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12.34 1 of 2
Exploring Psychrometric Principles
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ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12.34 1 of 2
Exploring Psychrometric Principles
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ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12..48
Exploring Psychrometric Principles
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ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12.50 1of 2
Exploring Psychrometric Principles
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ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12.50 2 of 2
Exploring Psychrometric Principles
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ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12.51 1of 1
Exploring Psychrometric Principles
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ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12.52 1of 2
Exploring Psychrometric Principles
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ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12.52 2of 2
Exploring Psychrometric Principles
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ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12.56 1of 1
Exploring Psychrometric Principles
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ASSIGNMENT PROBLEMMoran & Shapiro (2006) P 12.58 1of 1
Exploring Psychrometric Principles
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