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進二冷三
冷凍空調熱力熱傳學(一）
授課教師：施陽正
2009年9月
博士
1
CHAPTER
Introduction
and Overview
I. Introduction and Overview
1. Introduction to Thermal-Fluid Sciences
2. Thermodynamics
3. Heat Transfer
4. Fluid Mechanics
5. A Note on Dimensions and Units
6. Closed and Open System
7. Properties of a System
8. Solving Engineering Problems
9. Problem Solving Technique
10. Conservation of Mass Principle
1. Introduction to Thermal-Fluid Sciences
 The physical sciences that deal with energy and
the transfer, transport, and conversion of energy
are usually referred to as thermal-fluid sciences or
thermal sciences.
 Thermal-fluid sciences:

Thermodynamics

Fluid mechanics

Heat transfer
1. Introduction to Thermal-Fluid Sciences
 Application Areas of Thermal-Fluid Sciences
1. Introduction to Thermal-Fluid Sciences
1. Introduction to Thermal-Fluid Sciences
2. Thermodynamics
 Thermodynamics can be defined as the science of
energy.
 First law of thermodynamics
 Second law of thermodynamics
2. Thermodynamics
2. Thermodynamics
2. Thermodynamics
3. Heat Transfer
 Energy exists in various forms. Heat is the form of
energy that can be transferred from on system to
another as a result of temperature difference.
 The science that deals with the determination of the
rates of such energy transfer is heat transfer.

Heat is transferred by three mechanisms:

Conduction

Convection

Radiation
3. Heat Transfer
3. Heat Transfer
3. Heat Transfer
3. Heat Transfer
4. Fluid Mechanics
 Fluid mechanics is defined as the science that deals
with the behavior of fluids at rest (fluid statics) or in
motion (fluid dynamics).
4. Fluid Mechanics
4. Fluid Mechanics
4. Fluid Mechanics
4. Fluid Mechanics
5. A Note on Dimensions and Units
5. A Note on Dimensions and Units
5. A Note on Dimensions and Units
5. A Note on Dimensions and Units
Force  ( Mass )( Acceleration)
F  ma
or
(1  1)
5. A Note on Dimensions and Units
5. A Note on Dimensions and Units
5. A Note on Dimensions and Units
W  mg
(N )
(1  2)
5. A Note on Dimensions and Units
5. A Note on Dimensions and Units
5. A Note on Dimensions and Units
 Dimensional Homogeneity
5. A Note on Dimensions and Units
5. A Note on Dimensions and Units
6. Closed and Open System
6. Closed and Open System
6. Closed and Open System
6. Closed and Open System
6. Closed and Open System
6. Closed and Open System
7. Properties of a System
m

V
s 
3
(kg / m )

H
2O
(1  3)
(1  4)
7. Properties of a System
7. Properties of a System
V
1
 
m 
3
(m / kg)
(1  5)
7. Properties of a System
8. Solving Engineering Problems
9. Problem Solving Technique
 Step1: Problem Statement
Step2: Schematic
Step3: Assumptions
Step4: Physical Laws
Step5: Properties
Step6: Calculations
Step7: Reasoning,Verification,and Discussion
9. Problem Solving Technique
9. Problem Solving Technique
9. Problem Solving Technique
 A Remark on Significant Digits
10. Conservation of Mass Principle
10. Conservation of Mass Principle
10. Conservation of Mass Principle
 Mass and Volume Flow Rates

d m  n dA

m   n dA (kg / s)
A
(1  7)
(1  8)
10. Conservation of Mass Principle
10. Conservation of Mass Principle

m  m A
(kg / s)

V    n dA   m A
(1  9)
(1  10)
A


m  V 

V

(1  11)
10. Conservation of Mass Principle
 Conservation of Mass Principle
Total mass
Total mass

 
  Net chang in mass 

 
 

 Entering the system   leaving the system   within the system 

 
 

10. Conservation of Mass Principle
min  mout  msystem


min  mout  dmsystem / dt
(1  12)
(kg / s) (1  13)
 mi   me  (m2  m1 ) system
(1  14)
10. Conservation of Mass Principle
10. Conservation of Mass Principle
10. Conservation of Mass Principle
 Mass Balance for Steady-Flow Processes
 T otal mass entering  T otal mass leaving

  

 CV per unit time   CV per unit time
10. Conservation of Mass Principle
10. Conservation of Mass Principle
Steady Flow :  mi   me (kg/s)

(1 -17)

Steady Flow (single stream): m1  m2  1 1A1   2 2 A 2
(1- 18)
10. Conservation of Mass Principle
 Special Case:Incompressible Flow (

 =constant)

Steady Incompressible Flow : V i  V e (m3/s)
(1- 19)
Steady Incompressibe Flow
(single stream):


V 1  V 2  1A1   2 A 2
(1- 20)
10. Conservation of Mass Principle
CHAPTER
2
Basic Concepts of
Thermodynamics
I. Basic Concepts of Thermodynamics
1. Introduction 前言.
2. Dimensions and Units 單位與因次
3. Closed and Open Systems 密閉系統或開放系統
4. Forms of Energy 能量的形式
5. Properties of a system 性質
6. State and Equilibrium 狀態與平衡
7. Processes and Cycles 過程與循環
8. State Postulate 狀態假說
9. Pressure and Temperature 壓力與溫度
1. Introduction
 Thermodynamics is the science of energy and
entropy.
 The first law of thermodynamics is simply an
expression of the conservation of energy principle,
and it asserts that energy is a thermodynamic
property.
 The second law of thermodynamics asserts that
energy has quality as well as quantity, and actual
processes occur in the direction of decreasing quality
of energy.
2. Dimensions and Units
Dimension
Primary dimensions --mass m, length L, time t, temperature T.
Secondary dimensions -- energy E, volume V
Units
English system
International system (SI)
2. Dimensions and Units
Dimension
SI Unit
IP Unit
Length, L
Time, t
Mass, m
Energy, E
m
sec
kg
Joule
ft
sec
lbm
Btu
Power, W
Waltt
Btu/hr
Dimension
density, 
SI Unit
IP Unit
kg/m3
m/sec
lbm/ft3
ft/sec
velocity, v
2. Dimensions and Units
Multiple
Prefix
1012
109
106
103
tera, T
giga, G
mega, M
kilo, k
10-2
10-3
10-6
centi, c
milli, m
micro, m
10-9
10-12
nano, n
pico, p
3. Closed and Open Systems
 A thermodynamic system, or
simply a system, is defined as a
quantity of matter or a region in
space chosen for study.
 The mass or region outside the
system is called the surroundings.
 The real or imaginary surface that
separates the system from its
surrounding is called the boundary.
3. Closed and Open Systems
 A system of fixed mass is called a closed system, or
control mass. -- Energy, not mass, crosses closed-system
boundaries.
3. Closed and Open Systems
 A system that involves mass transfer across its
boundaries is called an open system, or control
volume.– Mass and energy cross control volume boundaries.
3. Closed and Open Systems
 An isolated system is a general system of fixed
mass where no heat or work may cross the
boundaries.
 The thermodynamic relations that are applicable
to closed and open systems are different.
Therefore, it is extremely important that we
recognize the type of system we have before we
start analyzing it.
4. Forms of Energy
 Energy – Stored energy and Transient energy
 Stored energy (儲能)

Internal energy (內能)

Potential energy (位能)

Kinetic energy (動能)

Chemical energy (化學能)

Nuclear (atomic) energy (核能或原子能)
 Transient energy (轉移能或暫態能)

Heat (熱)

Work (功)
5. Properties of a System
 Any macroscopic characteristic of a system is called
a property.

Pressure, P

Temperature, T

Volume, V

Mass, m

Density, 

Energy, E; Enthalpy, H; Entropy, S
5. Properties of a System
 The mass-dependent properties of a system are
called extensive properties (uppercase letters) and the
others, intensive properties (lowercase letters) .
5. Properties of a System
 Extensive properties per unit mass are called
specific properties.

Specific volume, v=V/m

Specific total energy, e=E/m

Specific internal energy, u=U/m

Specific enthalpy, h=H/m

Specific entropy, s=S/m
6. State and Equilibrium
6. State and Equilibrium
 A system is said to be in thermodynamic equilibrium
if it maintains thermal, mechanical, phase and chemical
equilibrium.

Thermal equilibrium – the temperature is the same throughout
the entire system.

Mechanical equilibrium – there is no change in pressure at any
point of the system with time.

Phase equilibrium – the mass of each phase reaches an
equilibrium level and stays there.

Chemical equilibrium – the chemical composition does not
change with time.
6. State and Equilibrium
State Postulate
 The state of a simple compressible system is
completely specified by two independent, intensive
properties.
7. Processes and Cycles
 Any change that a system undergoes from one
equilibrium state to another is called a process.
(Fig.1-26)
 When a process proceeds in such a manner that the
system remains infinitesimally close to an equilibrium
state at all times, it is called a quasi-static, or quasiequilibrium, process. (Fig. 1-29)
Quasi-equilibrium
7. Processes and Cycles
7. Processes and Cycles
Process
Property held constant
isobaric
pressure
isothermal
temperature
isochoric
volume
isentropic
entropy (see Chapter 6)
System
Boundary
F
Water
Constant Pressure Process
7. Processes and Cycles
 A process with identical end states is called a cycle.
(Fig.1-30)
P
2
Process
B
Process
A
1
V
9. Pressure and Temperature
Pgage  Pabs  Patm
Pvac  Patm  Pabs
Pabs  Patm  Pgage
9. Pressure and Temperature
P   g h
( kPa )
9. Pressure and Temperature
T K = T C + 273.15
T R = T  F + 459.69
9. Pressure and Temperature
 Two bodies are in thermal equilibrium when they have
reached the same temperature.
 Zeroth law of thermodynamics (熱力學第零定律)
If two bodies are in thermal equilibrium with a third body,
they are also in thermal equilibrium with each other.
CHAPTER
3
Properties of Pure
Substances
II. Properties of Pure Substances
1. Pure substance 純物質
2. Phase of a pure substance 純物質之相
3. Phase change processes of pure substances 純物質之
相變化
4. Property diagrams for phase change processes 相變過
程之性質圖
5. Vapor Pressure and Phase Equilibrium 蒸氣壓與相平衡
6. Property Tables 熱力性質表
II. Properties of Pure Substances
7. The ideal-gas equation of state 理想氣體狀態方程式
8. Compressibility factor – a measure of deviation from
ideal-gas behavior 壓縮因子
9. Other Equations of State 其他氣體狀態方程式
10. Internal Energy, Enthalpy, and Specific Heats of Ideal Gases
內能、焓與比熱
1. Pure Substance
 A pure substance has a homogeneous and
invariable chemical composition and may exist in
more than one phase. -- Water, nitrogen, helium, and
carbon dioxide.
 A pure substance does not have to be of a single
chemical element or compound. A mixture of various
chemical elements or compounds also qualifies as a
pure substance as long as the mixture is
homogeneous. -- Air
 A mixture of two or more phases of a pure substance
is still a pure substance. – a mixture of ice and liquid water.
2. Phase of a Pure Substance
 Pure substance have three principal phases – solid,
liquid, and gas.
3. Phase Change Processes of
Pure Substances
 Compressed liquid and saturated liquid.
 Saturated vapor and superheated vapor.
 Saturation temperature and saturation pressure.
3. Phase Change Processes of
Pure Substances
4. Property Diagrams for Phase
Change Processes
 The T-v diagram
4. Property Diagrams for Phase
Change Processes
 The T-v diagram
4. Property Diagrams for Phase
Change Processes
 The P-v diagram
4. Property Diagrams for Phase
Change Processes
 The P-T diagram
 P-v-T Surface of a substance that contracts on freezing
 P-v-T Surface of a substance that expands on freezing
5. Vapor Pressure and Phase
Equilibrium
Patm  Pa  Pv
Pv  Psat @T
5. Vapor Pressure and Phase
Equilibrium
6. Property Tables
 Enthalpy – a combination property
H  U  PV
h  u  Pv
6. Property Tables
1a. Saturated Liquid and Saturated Vapor States
vf = specific volume of saturated liquid
vg = specific volume of saturated vapor
vfg = difference between vg and vf,
vfg = vg - vf
6. Property Tables
Example 2-1
A rigid tank contains 50 kg of saturated liquid water at
90℃. Determine the pressure in the tank and the volume
of the tank.
Example 2-2
A mass of 200 g of saturated liquid water is completely
vaporized at a constant pressure of 100kPa. Determine
(a) the volume change and (b) the amount of energy
added to the water.
6. Property Tables
1b. Saturated Liquid-Vapor Mixture
 Quality x is defined as
x
masssaturated vapor
masstotal

mg
m f  mg
6. Property Tables
1b. Saturated Liquid-Vapor Mixture
y  y f  x( yg  y f )
 y f  x y fg
y may be replaced by
any of the variables v,
u, h, or s.
x
y  yf
y fg
v  v f  x (v g  v f )
6. Property Tables
2. Superheated Vapor
6. Property Tables
3. Compressed Liquid
y  y f @T
y may be replaced by
any of the variables v,
u, h, or s.
7. Ideal-Gas Equation of State
Specific volume
[m3/kg]
Pv  RT
Pressure
[kPa]
Temperature
[℃, K]
Gas constant
[kJ/(kg K)]
or kPa.m3/(kg K)
7. Ideal-Gas Equation of State
Universal gas constant
[℃, K]
Ru
R
M
Molar mass
[g/(gmol)]
or [kg/(kmol)]
7. Ideal-Gas Equation of State
Pv  RT
V
P  RT
m
PV  mRT
7. Ideal-Gas Equation of State
Example 2-3
Determine the mass of the air in a room whose
dimensions are 4mx5mx6m at 100kPa and 25 C.
Is Water Vapor an Ideal Gas ?
err %

vtable  videal
vtable
100%
 Z is called compressibility factor (壓縮性因子)
Pv
Z
RT
Pv  ZRT
vactual
v
Z

RT / P videal
 For ideal gas: Z = 1
8. Other Equations of State
 Van der Waals Equation of State
 Beattie-Bridgeman Equation of State
 Benedict-Webb-Rubin Equation of State
9. Specific Heats
 The specific heat is
defined as the energy
required to raise the
temperature of a unit
mass of a substance by
one degree.
 Specific heat at
constant volume: Cv
 Specific heat at
constant pressure: Cp
10. Internal Energy, Enthalpy, and
Specific Heats of Ideal Gases
 For an ideal gas
u  u (T )
h  h(T )
 u 
Cv     du  Cv (T )dT
 T  v
 h 
C p     dh  C p (T )dT
 T  p
10. Internal Energy, Enthalpy, and
Specific Heats of Ideal Gases
 Fig. 3-56
Ideal-gas Cp for
some gases.
 Table A-2 (p.845)
10. Internal Energy, Enthalpy, and
Specific Heats of Ideal Gases
 For small temperature intervals, specific heat may be
assumed to vary linearly with temperature.
10. Internal Energy, Enthalpy, and
Specific Heats of Ideal Gases
 Specific-heat relations of ideal gases.



specific heat ratio,
kR
CP 
k 1
and
R
CV 
k 1
10. Internal Energy, Enthalpy, and
Specific Heats of Ideal Gases
 Example 3-16
A piston-cylinder device initially contains air at 150kPa and 27C. At
this state, the piston is resting on a pair of stops, and the enclosed
volume is 400L. The mass of the piston is such that a 350 kPa
pressure is required to move it. The air is now heated until its
volume has doubled. Determine (a)the final temperature, (b)the
work done by the air, and (c)the total heat added.
10. Internal Energy, Enthalpy, and
Specific Heats of Solids and Liquids
 For incompressible substances (liquids and solids),
both the constant-pressure and constant-volume
specific heats are identical and denoted by C:
du  C (T )dT
10. Internal Energy, Enthalpy, and
Specific Heats of Solids and Liquids
du  C (T )dT
CHAPTER
4
Energy Transfer
by Heat, Work,
and Mass
IV.
Energy Transfer by Heat, Work,
and Mass
1. Heat Transfer
2. Energy Transfer by Work
3. Mechanical Forms of Work
4. Nonmechanical Forms of Work
5. Flow Work and the Energy of a Flowing Fluid
1. Heat Transfer
 Energy can cross the boundary of a closed system in
two distinct forms: heat and work.
 Heat is defined as the form of energy that is transferred
between two systems (or a system and its surroundings) by
virtue of a temperature difference.
 Several phrases which are in common use today such
as: heat flow, heat addition, heat rejection, heat removal
, heat gain, heat loss, heat storage, heat generation,
electrical heating, resistance heating, heat of reaction,
specific heat, sensible heat, latent heat, waste heat,
body heat, are not consistent with the strict
thermodynamic meaning of the term heat, which limits
its use to the transfer of thermal energy during a
process.
 In thermodynamics the term heat simply means heat
transfer.
 A process during which there is no heat transfer is
called an adiabatic process.
 Heat has energy units, kJ or Btu.
 The amount of heat transferred during the process
between two states is denoted by Q12 or just Q.
 Heat transfer per unit mass of a system is denoted q
and is determined from
Q
q
[kJ/kg]
m
 The heat transfer rate (the amount of heat transferred
per unit time) is denoted
Q [kJ/s] or [kW]
 The amount of heat transfer during a process is
determined by
t2
Q   Q dt
t1
[kJ]
 When heat transfer rate remains constant during a
process, then.
Q  Q t
[kJ]
 The sign for heat is as follows: heat transfer to a system
is positive, and heat transfer from a system is negative.
 Modes of heat transfer
Heat can be transferred in three different ways:
conduction (傳導), convection (對流), and radiation (
輻射).
2. Energy Transfer by Work
 Work, like heat, is an energy interaction between a
system and its surroundings.
 If the energy crossing the boundary of a closed system
is not heat, it must be work.
 Work is the energy transfer associated with a force
acting through a distance.
 Work is also a form of energy and has energy units
such as kJ.
 The work done during a process between states 1 and
2 is denoted W12, or simply W.
 The work done per unit mass of a system is defined as
W
w
m
[kJ/kg]
 The work done per unit time is called power
W [kJ/s] or [kW]
(+)
(–)
(–)
(+)
 Work and heat are interactions between a system and
its surroundings, and there are many similarities
between the two:
i.
Both are recognized at the boundaries of the system as they
cross them. – Both heat and work are boundary phenomena.
ii.
Systems possess energy, but not heat transfer or work. – Heat
and work are transient phenomena.
iii.
Both are associated with a process, not a state. Unlike
properties, heat or work has no meaning at a state.
iv. Both are path functions (I.e., their magnitudes depend on the
path followed during a process as well as the end states.)
 path functions – inexact differentials (d)
 point functions – exact differentials (d)
2
 dV  V
 V1  V
2
1
2
 dW  W
12
1
(not W )
Example 4-1
Burning of a Candle in an Insulated Room
A candle is burning in a well-insulated room. Taking the room (the air
plus the candle) as the system, determine (a) if there is any heat
transfer during this burning process and (b) if there is any change in
the internal energy of the system.
Example 4-2
Heating of a Potato in an Oven
A potato that is initially at room temperature (25C) is being baked in
an oven which is maintained at 200C. Is there any heat transfer
during this baking process?
Example 4-3
Heating of an Oven by Work Transfer
A well-insulated electric oven is being heated through its heating
element. If the entire oven, including the heating element, is taken to
be the system, determine whether this is a heat or work interaction?
Example 4-4
Heating of an Oven by Heat Transfer
Answer the question in Example 3-4 if the system is taken as only
the air in the oven without the heating element?
3. Mechanical Forms of Work
Moving boundary work:
(kJ)
› Shaft work:
(kJ)
› Spring work:
(kJ)
 Moving Boundary Work
dW  Fds
 PAds  PdV
2
Wb   PdV
(kJ)
1
2
2
1
1
Area  A   dA   PdV
 Moving Boundary Work
2
2
1
1
Area  A   dA   PdV
Example 3-7
Boundary Work during a Constant-Volume Process
A rigid tank contains air at 500 kPa and 150C. As a result of
heat transfer to the surroundings, the temperature and
pressure inside the tank drop to 65C and 400 kPa, respectively.
Determine the boundary work done during this process.
Example 4-7

Boundary Work during an Isothermal Process
A piston-cylinder device initially contains 0.4 m3 of air at 100kPa
and 80C. The air is now compressed to 0.1 m3 in such a way
that the temperature inside the cylinder remains constant.
Determine the work done during this process.

Polytropic process (多變過程) (Pvn = constant)
PV
2 2  PV
1 1
Wb 
1 n
(n  1)
( kJ )
 Spring Work
4. Nonmechanical Forms of Work
› Electrical work:
(kJ)
5. Flow Work and the Energy of a
Flowing Fluid
 Flow work
F  PA
W flow  FL  PAL  PV
(kJ)
w flow  Pv (kJ/kg)
 Total Energy of a Flowing Fluid
V2
e  u  ke  pe  u 
 gz
2
  Pv  e  Pv  (u  ke  pe)
2
V
  h  ke  pe  h 
 gz
2
 Energy Transport by Mass
2
V
Emass  m  m(h 
 gz ) (kJ)
2
2
V
E mass  m   m (h 
 gz ) (kW)
2
CHAPTER
5
The First Law of
Thermodynamics
V.
The First Law of Thermodynamics
1. The First Law of Thermodynamics
2. Energy Balance for Closed Systems
3. Energy Balance for Steady-Flow Systems
4. Some Steady-Flow Engineering Devices
5. Energy Balance for Unsteady-Flow Processes
1. The First Law of Thermodynamics
 Energy can be neither created nor destroyed.
 First law of thermodynamics, or the conservation of
energy principle, is based on experimental
observations.
 During an interaction between a system and its
surroundings, the amount of energy gained by the
system must be exactly equal to the amount of energy
lost by the surroundings.
Energy Balance
Energy Balance
Energy Balance
2. Energy Balance for Closed Systems
 The first law of thermodynamics, or the conservation of
energy principle for a closed system or a fixed mass,
may be expressed as follows:
Qnet ,in  Wnet ,out  Esystem
or
Q  W  E
(kJ)
(kJ)
Net work done in all form
 Wout  Win
Q  W  E
(kJ)
Net heat transfer
across system
boundaries
Net change in total
energy of system
  Qin   Qout
 U  KE  PE
 E2  E1
 For a stationary closed systems
Q  W  U  KE  PE
 For a cyclic process
Q W  0
 Various forms of the first-law relation for closed systems.
Examples
 Example 5-1: Cooling of a Hot Fluid in a Tank
 Example 5-2: Electric Heating of a Gas at Constant
Pressure
 Example 5-3: Unrestrained Expansion of Water into
an Evacuated Tank
 Example 5-4: Heating of a Gas in a Tank by Stirring
 Example 5-5: Heating of a Gas by a Resistance
Heater
 Example 5-6: Heating of a Gas at Constant Pressure
 Example 5-7: Cooling of an Iron Block by Water
3. Energy Balance for
Steady-Flow Systems
 Mass balance for steady-flow systems:
dmCV
i m i  e m e  dt
 m   m
i
i
e
e
 Energy balance for steady-flow systems:
dECV


Ein  Eout 
dt
E in  E out
2
2
V
V
Q in  Win   m i (hi  i  gzi )  Q out  Wout   m e (he  e  gze )
2
2
i
e
2
2
V
V
Q  W   m e (he  e  gze )   m i (hi  i  gzi )
2
2
e
i
4. Some Steady-Flow Engineering
Devices
 Nozzles and Diffusers
 Turbines and Compressors
 Throttling Valves
 Mixture Chambers
 Heat Exchangers
 Pipe and Duct Flow
(Fig. 4-25)
Nozzle and Diffuser
Q  0
W  0
ke  0
pe  0
Example 5-11
Deceleration of Air in a Diffuser
Air at 10C and 80kPa enters the diffuser of a jet engine
steadily with a velocity of 200m/s. The inlet area of the
diffuser is 0.4 m2. The air leaves the diffuser with a velocity
that is very small compared with the inlet velocity. Determine
(a) the mass flow rate of the air and (b) the temperature of
the air leaving the diffuser.
Turbines and Compressors

Q0
W  0
ke  0
pe  0
Example 5-13
Compressing Air by a Compressor
Air at 100kPa and 280K is compressed steadily to 600kPa
and 400K. The mass-flow rate of the air is 0.02 kg/s, and a
heat loss of 16kJ/kg occurs during the process. Assuming
the changes in kinetic and potential energies are negligible,
determine the necessary power input to the compressor.
Example 5-14
Power Generation by a Steam Turbine
The power output of an adiabatic gas turbine is 5MW, and
the inlet and the exit conditions of the hot gases are as
indicated in Fig.4-30. The gases can be treated as air.
(a) Compare the magnitudes of h, ke, and pe.
(b) Determine the work done per unit mass of hot gases.
(c) Calculate the mass flow rate of the steam.
Throttling Valves
Q  0
W  0
ke  0
pe  0
h1  h2
u1  p1v1  u2  p2 v2
internal energy  flow energy  constant
The temperature of an ideal gas does not change during
a throttling(h =constant) process since h = h (T)
Example 5-15
Expansion of R-134a in a Refrigerator
R-134a enters the capillary tube of a refrigerator as
saturated liquid at 0.8MPa and is throttled to a pressure
of 0.12MPa. Part of the refrigerant evaporates during
this process and the refrigerant exists as a saturated
liquid-vapor mixture at the final state. Determine the
temperature drop of the refrigerant during this process.
Mixing Chamber
Q  0
W  0
ke  0
pe  0
Heat Exchanger
The heat transfer associated with a heat exchanger may be
zero or nonzero depending on how the system is selected
Pipe and Duct Flow
.