chapter 2 Properties of Pure Substances
2-1 Pure Substance2-1-1 Definition of Pure Substance
A homogeneous substance is pure substance
2-1-2 Phases of Pure Substance
Solid
Liquid
Gas
Plasma
2-2 Phase Change Process of Pure Substance2-2-1 Constant Pressure Process of Water
p
v
1 2 3 4 5
5’1’ 2’ 3’ 4’
5”1” 2” 3” 4”
c
T
v
1
2 3 4
5
1’
2’ 3’ 4’
5’
1”
2”
3” 4”
5”
c
T=constant
vapor
Liquid +Vapor
Critical point
Liq
uid
Liq
uid
+so
l id
Solid+Vapor
soli
d
p
T
Triple line
2-2-1 Properties of Water
1.One point : Critical point C
2.Two lines : Saturated water line, Saturated vapor line
3.Three Regions: Compressed water region, Saturated mixture region, superheated vapor region
4.Five states: Compressed water, Saturated water, Saturated mixture, Saturated vapor, superheat vapor
2-3-1 p-v-T Surface
2-3 P-v-T surface and P-T diagram
2-3-2 p-T diagram
P
T
SolidVapor
liquid
Melting line
Vaporization
Sublimation
Expand on freezing
Extract on freezing Critical
point
2-4 Property Tables
2-4-1 Saturated Liquid and Vapor
One property is enough to Calculate other properties.
t ℃ P, MPa v’ v” h’ h” s’ s”
100 0.1013 0.00104
1.6738 419.06 2676.3 1.3069 7.3564
200 1.5551 0.00116 0.12714 352.4 2791.4 2.3307 6.4289
Enthalpy ---- the combination property:
H=U+PV
Or, per unit mass h=u+Pv
2-4-2 Saturated Mixture
One property to calculate saturated properties, but how to determine the properties of saturated mixture?
One special property to calculate the fraction of liquid and vapor, the quality
total
vapor
m
mx
')1(" vxxvvmix
')1(" hxxhhmix ')1(" sxxssmix
2-4-3 Superheated Vapor
Two independent properties are used to Calculate other properties
T ℃ P=0.1 MPav, m3/kg h, kJ/kg s, kJ/kg.K
100 1.6958 2676.2 7.3628150 1.9364 2776.4 7.5438
2-4-4 Reference state and reference value
Water: Saturated liquid at 0.01 is taken as the referenc℃e state, where u=0 s=0
R-12: Saturated liquid at -40 is taken as the reference s℃tate, where u=0 s=0
Notice: The reference state differ with different tables
2-5-1 The Ideal-Gas
The molecules of ideal-gas have no volume
There are no attraction among molecules of ideal-gas
2-5-2 The Ideal-Gas Equation of State
2-5 The Ideal-Gas Equation of State
(1). pV = mRT pv=RT
R------The gas constant(2) pVm = μRμT pvm=RμT
Rμ-----The universal gas constant
= 8.314kJ/kmol.K
2-6 Real Gases2-6-1 Compressibility Factor
Pv=RT can only be employed for the gas under high temperature or low pressure
For real gas, from pv=RT :
RT
pvz z------- Compressibility Factor:
a measure of deviation from ideal-gas behavior
z=1: Ideal-Gas
z>1 or z<1: Real-Gas
2-6-2 Van der Waals Equation of State
(1)consider the volume occupied by the molecules themselves
from pv=RT :
v
RTp
Since the smaller space for the molecules flying will lead to more chance of hit on its container ,the pressure of the gas will increase then .
Correct this by replacing v as v-b
bv
RTp
(2) consider contraction among the molecules
The contraction will lead to a decrease on pressure, so correct the equation as following:
2v
a
bv
RTp
The contraction should be in proportion to ρ2 which can be write as 1/v2.
‘a’ is proportional coefficient decided by experiment
2-6-3 Other Equations of State
(1) Beattie-Bridgeman Equation
(2) Martin-Hou Equation
(3) Virial Equation
The end of This Chapter
Thank you
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