2 Gas Mixtures
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Transcript of 2 Gas Mixtures
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8/6/2019 2 Gas Mixtures
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Gas Mixtures 1 Adv. Thermo-fluids
Composition of gas mixtures
P-v-T behaviour of gas mixtures
Properties of gas mixtures
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Gas Mixtures 2 Adv. Thermo-fluidsIntroduction
composition of gas mixture
properties of components
Many important engineering applications involve gas mixtures
In this study, gas mixtures are considered non-reacting
Non-reacting gas mixture can be treated as pure
substance because its composition is homogeneous
Each gas in gas mixture => called component orconstituent
Properties of gas
mixture depends on:
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Gas Mixtures 3 Adv. Thermo-fluidsGas Mixture Composition
molar analysis Mole numberof each component
gravimetric analysis Mass of each component
=
=k
iim mm
1
=
=k
i
im NN1
Composition of gas mixture can be described by:
Mass of mixture = sum ofmasses of
components
Mole number of mixture = sum of
mole numbers of components
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Gas Mixtures 4 Adv. Thermo-fluidsGas Mixture Composition
Mass fraction = mass ratio
of component to mixturem
iim
mmf =
Mole fraction = mole ratio ofcomponent to mixturem
ii
NNy =
Sum of mass fractions or
mole fractions equal to 1 ==
==k
ii
k
ii ymf
11
1
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Gas Mixtures 5 Adv. Thermo-fluidsGas Mixture Composition
Relation between mass m
and mole number N: NMm =
Apparent or average molar
mass Mm of mixture: ==
k
iiim MyM 1
Apparent or average gasconstant of mixture Rmm
um
MRR =
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Gas Mixtures 6 Adv. Thermo-fluidsP-v-T Behaviour
For ideal gases:
RTPv=
For real gases: ZRTPv =
For gas mixtures,
P-v-T behaviour can
be predicted using:
Daltons law of additive pressures
Amagats law of additive volumes
Kays Rule
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Gas Mixtures 7 Adv. Thermo-fluids
Daltons law of additive pressure
P-v-T Behaviour
Pressure of gas mixture equal to sum of
pressures each gas would exertif it existed
alone at the mixture temperature and volume
=
=k
i
mmim VTPP
1
),(Exact for ideal gases,
Approximate for real gases
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Gas Mixtures 8 Adv. Thermo-fluids
Amagats law of additive volume
P-v-T Behaviour
Volume of gas mixture equal to sum of volumes
each gas would occupy if it existed alone at the
mixture temperature and pressure
=
=k
i
mmim PTVV
1
),(Exact for ideal gases,
Approximate for real gases
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Gas Mixtures 9 Adv. Thermo-fluidsP-v-T Behaviour
=
==
k
i
iimmummmm ZyZTRNZVP1
,
For ideal gas, pressure fraction andvolume fraction equal to mole fraction i
m
i
m
i
m
i yNN
VV
PP ===
For real gases, deviation from ideal gas behaviour can beapproximated by including compressibility factor
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Gas Mixtures 10 Adv. Thermo-fluidsP-v-T Behaviour
=
=k
i
icrimcr PyP1
,,
=
=k
i
icrimcr TyT1
,,
cr
mR
T
TT
=
cr
mR
P
PP
=
Kays Rule:Use of pseudocritical pressure Pcrand pseudocritical temperature Tcr
mZ
mmmmm TRZVP =
Compressibility
Chart
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Gas Mixtures 12 Adv. Thermo-fluidsP-v-T Behaviour
==
==k
i
iim
k
i
iim uyuumfu11
,
==
==
k
i
iim
k
i
iim hyhhmfh11
,
==
==
k
i
iim
k
i
iim syssmfs11
,
== ==k
i
ipimp
k
i
ivimv CmfCCmfC1
,,
1
,, ,
Intensive property of gas mixture equal to sum of
intensive property of components multiplied by
mass fraction or mole fraction
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Gas Mixtures 13 Adv. Thermo-fluids