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 H 2 O/kg DA Specific Enthalpy of moist air h kJ/kg DA Specific Volume of moist air v m 3 /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 Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs
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
Saved as E:/Lectures/ME 306\2012\Psychrometry was last updated on 9/01/2012 at 2330 hrs