chapter 3 properties of pure substances 純質的性質. 3.1 pure substance 純質 a substance that...
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CHAPTER
3
Properties of Pure Substances純質的性質
3.1 Pure Substance純質
3.1 Pure Substance純質
A substance that has a fixed chemical composition throughout is called a Pure Substance.
Pure Substance: - N2, O2, gaseous Air -A mixture of liquid and gaseous
water is a pure substance, but a mixture of liquid and gaseous Air is not.
A substance that has a fixed chemical composition throughout is called a Pure Substance.
Pure Substance: - N2, O2, gaseous Air -A mixture of liquid and gaseous
water is a pure substance, but a mixture of liquid and gaseous Air is not.
3.2 Phases of a Pure Substance純質的相
3.2 Phases of a Pure Substance純質的相
Solid 固體 : -The molecules in a solid are kept at their
positions by the large springlike intermolecular forces.
-The attractive and repulsive forces between the molecules tend to maintain them at relatively constant distances from each other.
Liquid 液體 : Groups of molecules move about each other.
Gas 氣體 : Molecules move about at random.
Solid 固體 : -The molecules in a solid are kept at their
positions by the large springlike intermolecular forces.
-The attractive and repulsive forces between the molecules tend to maintain them at relatively constant distances from each other.
Liquid 液體 : Groups of molecules move about each other.
Gas 氣體 : Molecules move about at random.
3.3 Phase-Change Processes of Pure Substance 純質的相變化過程
3.3 Phase-Change Processes of Pure Substance 純質的相變化過程
Compressed liquid 壓縮液體 or a subcooled liquid 過冷液體 : A liquid that is not about to vaporize. 汽化
Saturated liquid 飽和液體 : A liquid that is about to vaporize.
Saturated vapor 飽和蒸汽 : A vapor that is about to condense.
Saturated liquid-vapor mixture 飽和液汽混合物 : the liquid and vapor phases coexist in equilibrium.
Superheated vapor 過熱汽體 : A vapor that is not about to condense
Compressed liquid 壓縮液體 or a subcooled liquid 過冷液體 : A liquid that is not about to vaporize. 汽化
Saturated liquid 飽和液體 : A liquid that is about to vaporize.
Saturated vapor 飽和蒸汽 : A vapor that is about to condense.
Saturated liquid-vapor mixture 飽和液汽混合物 : the liquid and vapor phases coexist in equilibrium.
Superheated vapor 過熱汽體 : A vapor that is not about to condense
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2-1
FIGURE 3-11T-v diagram for the heating process of water at constant pressure.
3.3 Phase-Change Processes of Pure Substance
3.3 Phase-Change Processes of Pure Substance
Saturated temperature 飽和溫度 , Tsat: At a given pressure, the temperature at which a pure substance changes phase.
Saturated pressure 飽和壓力 , Psat: At a given temperature, the pressure at which a pure substance changes phase.
Latent heat 潛熱 : the amount of energy absorbed or released during a phase-change process.
Latent heat of fusion 熔解潛熱 : the amount of energy absorbed during melting.
Latent heat of vaporization 蒸發潛熱 : the amount of energy absorbed during vaporization.
Saturated temperature 飽和溫度 , Tsat: At a given pressure, the temperature at which a pure substance changes phase.
Saturated pressure 飽和壓力 , Psat: At a given temperature, the pressure at which a pure substance changes phase.
Latent heat 潛熱 : the amount of energy absorbed or released during a phase-change process.
Latent heat of fusion 熔解潛熱 : the amount of energy absorbed during melting.
Latent heat of vaporization 蒸發潛熱 : the amount of energy absorbed during vaporization.
3.4 Property Diagrams for Phase-Change Processes
3.4 Property Diagrams for Phase-Change Processes
The T-v diagram:
-Critical point: the point at which the saturated liquid and saturated vapor states are identical.
-Saturated liquid line:
-Saturated vapor line:
-Compressed liquid region:
-Superheated vapor region:
-Saturated liquid-vapor mixture region:
The T-v diagram:
-Critical point: the point at which the saturated liquid and saturated vapor states are identical.
-Saturated liquid line:
-Saturated vapor line:
-Compressed liquid region:
-Superheated vapor region:
-Saturated liquid-vapor mixture region:
3.4 Property Diagrams for Phase-Change Processes
3.4 Property Diagrams for Phase-Change Processes
The critical-point properties of water: - Pcr= 22.09MPa - Tcr= 374.14C - vcr= 0.003155 m3 /kg
The critical-point properties of helium: - Pcr= 0.23MPa - Tcr= -267.85C - vcr= 0.01444 m3/kg
The critical-point properties of water: - Pcr= 22.09MPa - Tcr= 374.14C - vcr= 0.003155 m3 /kg
The critical-point properties of helium: - Pcr= 0.23MPa - Tcr= -267.85C - vcr= 0.01444 m3/kg
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2-2
FIGURE 3-16T-v diagram of constant-pressurephase-change processes of a puresubstance at various pressures(numerical values are for water).
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2-3
FIGURE 3-18T-v diagram of a pure substance.
3.4 Property Diagrams for Phase-Change Processes
3.4 Property Diagrams for Phase-Change Processes
The P-v diagram: - The triple line 三相線 : three phases of a
pure substance coexist in equilibrium, these triple-phase states forms a line.
- The triple point 三相點 : the triple line appears as a point on the P-T diagrams.
For water, 0.01C & 0.06113 kPa -Sublimation 昇華 : Passing from the solid
phase directly into the vapor phase. The P-T diagram(phase diagram 相圖 ): The P-v-T surface:
The P-v diagram: - The triple line 三相線 : three phases of a
pure substance coexist in equilibrium, these triple-phase states forms a line.
- The triple point 三相點 : the triple line appears as a point on the P-T diagrams.
For water, 0.01C & 0.06113 kPa -Sublimation 昇華 : Passing from the solid
phase directly into the vapor phase. The P-T diagram(phase diagram 相圖 ): The P-v-T surface:
FIGURE 3-19P-v diagram of a pure substance.
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2-4
臨界點
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2-5
FIGURE 3-21P-v diagram of a substance thatcontracts on freezing.
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2-6
FIGURE 3-22P-v diagram of a substance that expands on freezing (such as water).
EVALUATING THERMODYNAMIC PROPERTIES
The P-V-T Surface for Water
Description of thermodynamic state
f(f(PP11,P,P22,P,P3 3 ) = 0) = 0
P1
P2
P3
Experimental basis
One independent propertyOne independent property for each for each way that the energy of the system way that the energy of the system can be varied independently.can be varied independently.
Experimental basis
The number of independent The number of independent properties that uniquely describes properties that uniquely describes the state of the system is the the state of the system is the numbernumberof relevant work interactions plusof relevant work interactions plus one.one.
Simple, compressible systems
In simple chemical systems, there is only In simple chemical systems, there is only oneone way to alter E, or U, by way to alter E, or U, by workwork via a via a quasistatic process.quasistatic process.
p, Vp, V
Simple chemical systems
Work interactionWork interaction
Heat interactionHeat interaction SurroundingsSurroundings
SystemSystem
externalF
Q
Interactions = 2Interactions = 2Properties Needed = 3Properties Needed = 3
Simple compressible systems
f(p,V,T) = 0f(p,V,T) = 0
p = p(V,T)p = p(V,T)
V = V(p,T)V = V(p,T)
State and Equilibrium State and Equilibrium
A simple compressible system: The state of a simple compressible system
is completely specified by two independent, intensive properties.
-two properties specified be independent to fix the state.
-Once the two properties are fixed, all the other properties become dependent properties.
A simple compressible system: The state of a simple compressible system
is completely specified by two independent, intensive properties.
-two properties specified be independent to fix the state.
-Once the two properties are fixed, all the other properties become dependent properties.
State Equations
f(p,V,T) = 0
p(V,T) = p
v(p,T) = V
T(p,V) = T
f(U,V,T) = 0f(U,V,T) = 0
U = U(V,T)U = U(V,T)
V = V (U, T)V = V (U, T)
T = T(U,V)T = T(U,V)
The p-V-T surface for water...
The P-v-T surface for water
Ice cube Ice cube andandpure water vaporpure water vapor
Solid-vapor equilibrium.Solid-vapor equilibrium.
At a total constant pressure....At a total constant pressure....p
Water vaporWater vaporWater vaporWater vaporand and
liquid waterliquid water
Ice cube Ice cube andand
water vaporwater vapor
p
p
Add heatAdd heat
The p-V-T surface for water
• Solid in equilibrium with vapor (0 oC)• Solid in equilibrium with vapor and
liquid (0 oC)• Liquid and vapor in equilibrium
( 0 < T < 100 oC)• Saturated Vapor (T = 100 oC)• Superheated Vapor (T > 100 oC)
The P-v-T Surface for Water
Vapor
T
P
V
Liquid
Solid
Critical Point
The p-T plane for water, Phase diagram
Liquid
Vapor- LiquidVapor- Liquid
Critical PointCritical Point
Vapor
Triple Point
p p
T T
Solid
Water
Liquid-vapor Liquid-vapor dome (two-phase)dome (two-phase)
vTriple line (solid-Triple line (solid-liquid-vapor line)liquid-vapor line)
p
Critical pointCritical point
Triple pointTriple point
Tc
Water
v
p Tc
T = TT = Tsatsat
p = pp = psatsat
pp
ppcc
Vapor-liquidVapor-liquidequilibrium atequilibrium atp and Tp and T..
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2-7
FIGURE 3-25P-T diagram of pure substances.
FIGURE 3-26P-v-T surface of a substance that contracts on freezing.
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2-8
FIGURE 3-27P-v-T surface of a substance that expands on freezing (like water).
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2-9
3.5 Property Tables3.5 Property Tables
Table A-4: Saturated water-Temperature table Table A-5: Saturated water-Pressure table Table A-6: Superheated water
Enthalpy, H H= U + PV (kj) h= u + Pv (kj/kg) Entropy, S
Table A-4: Saturated water-Temperature table Table A-5: Saturated water-Pressure table Table A-6: Superheated water
Enthalpy, H H= U + PV (kj) h= u + Pv (kj/kg) Entropy, S
FIGURE 3-30A partial list of Table A–4.
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2-10
FIGURE 3-40A partial listing of Table A–6.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2-11
Quality... 質
Liquid-vapor equilibrium
Liquid at P,TLiquid at P,T Surroundings
Vapor at P,TVapor at P,TVapor at P,T
Quality
vaporliquid
vapor
mm
mx
The two-phase region for water
pp
Saturated LiquidSaturated Liquid V
Saturated VaporSaturated Vapor
Critical PointCritical Pointgl VVV
gl vvv
lgfg vvv
Quality defined
Quality, x, allows location of states inside Quality, x, allows location of states inside the vapor-liquid region.the vapor-liquid region.
gl vvv
gf vvv
pp
Vgvfv v
Water
v
p Tc
T = TT = Tsatsat
p = pp = psatsat
pp
ppcc
Vapor-liquidVapor-liquidequilibrium atequilibrium atp and Tp and T..
lv gvSpecific volume ofSpecific volume ofthe liquid at p and Tthe liquid at p and T
Specific volume ofSpecific volume ofthe gas at p and Tthe gas at p and T
Quality
vaporliquid
vapor
mm
mx
fgg
fgf
vxxvv
xvvv
1
Internal energy 內能 in the vapor-liquid region
fgg
fgf
uxxuu
xuuu
)1(
Key concepts and terms
Critical point
P - v - T surface
Quality
Saturation pressure
Saturation temperature
State equation
State surface
The State Principle
Triple point
ADDITIONAL ASPECTS OF THE P-V-T SURFACE FOR WATER
The P-v-T surface for water
Liquid
Vapor- Liquid
Critical Point
Vapor
T
P
V
Liquid
Solid
Critical Point
Vapor
Triple Point
P
T
Solid
Water
Temp
(deg C)
Pressure, P
(bars)
Sat Liq, vf x 1000
(m3/kg)
Sat Vapor vg
(m3/kg)
Interanl Engery, uf
(kJ/kg)
Internal Energy, ug
(kJ/kg)
15
0.017
1.001
77.93
62.99
2396.1
20 0.023 1.002 57.79 83.95 2402.9
50 100
0.124 1.014
1.012 1.043
12.03 1.673
209.3 418.9
2443.5 2506.5
At the critical point for water
CT
barp
kgkJuu
oc
c
gf
14.374
9.220
/6.2029
Compressed liquids
v v f
u u f
3.6 The Ideal-Gas Equation of State理想氣體方程式
3.6 The Ideal-Gas Equation of State理想氣體方程式
Equation of state 狀態方程式 :
Any equation that relates the pressure, temperature, and specific volume of a substance.
Gas: The vapor phase of a substance Vapor: A gas that is not far from a
state of condensation
Equation of state 狀態方程式 :
Any equation that relates the pressure, temperature, and specific volume of a substance.
Gas: The vapor phase of a substance Vapor: A gas that is not far from a
state of condensation
Definition of gas...
Fluids 流體 and gases 氣體
A liquid will take the shape of its containerbut exhibits a free surface.
A liquid will take the shape of its containerbut exhibits a free surface.
A gas will fill its containercompletely and does notexhibit a free surface.
A gas will fill its containercompletely and does notexhibit a free surface.
What is gas?
gasgas
containergas
PT
VV
,
The ideal gas...
P-V-T relation for ideal gases
TT11
TT22
TT33
pp
T
vp
RT
vp
p
lim0
The ideal gas equation of state
TRvp This implies: (1) very little molecular interaction (p = 0),(2) molecules are point masses, i.e., zero volume.
The universal gas constant 萬有氣體常數
Rlbmollbfft
KkmolkJ
RMR
/1545
/314.8
M = Molecular weightM = Molecular weight 分子量分子量 , , kg/kmol or lbm/lbmol.kg/kmol or lbm/lbmol.
The ideal gas state surface
Ideal Gas State Surfacepp
VTT
The perfect gas
1
.
RT
Pv
Rvcpc
constvc
3.7 Compressibility Factor 壓縮因子 - A Measure of Derivation from Ideal-Gas
Behavior
3.7 Compressibility Factor 壓縮因子 - A Measure of Derivation from Ideal-Gas
Behavior Compressibility Factor, Z Z = Pv/RT Z = vactual/videal
Ideal gas: Z = 1 Real gases: Z > 1 Z = 1 Z < 1
Compressibility Factor, Z Z = Pv/RT Z = vactual/videal
Ideal gas: Z = 1 Real gases: Z > 1 Z = 1 Z < 1
Real gases...
Real Gases
P
1
Z
T1
T2
T3
T1 < T2 < T3Ideal Gas
TR
vp
The virial form for compressibility
....3
)(2
)()(1
v
TD
v
TC
v
TBZ
TRZvp
3.8 Other Equations of State3.8 Other Equations of State
Van der Waals Equation of state: Beattie-Bridgeman Equation of state: Benedict-Webb-Rubin Equation of
state: Virial Equation of state:
Van der Waals Equation of state: Beattie-Bridgeman Equation of state: Benedict-Webb-Rubin Equation of
state: Virial Equation of state:
Key concepts and terms
FluidFluid
GasGas
Ideal gasIdeal gas
Perfect gasPerfect gas
Compressibility factorCompressibility factor
Compressibility chartCompressibility chart
Local equilibriumLocal equilibrium
Reduced pressureReduced pressure
Reduced temperatureReduced temperature
Thermodynamic pressureThermodynamic pressure
Virial equation of stateVirial equation of state
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