translated热能与动力工程专业英语

2021年1月20日发(作者：health)
热能与动力工程专业英语

Chapter 1 Introduction to Thermal
Science
第一章

热科学基础

Acoustic flow meter
声波流量计

Adiabatic
[
]
绝热的

Aerodynamics
空气动力学

Affiliation
联系

Airfoil
机翼
,
螺旋桨

Alternative
替代燃料

Anemometer
风速计

Angular speed
角速度

Area density
表面密度

Baffle
挡板

Bifurcation
分形

Blackbody
黑体

Blade
浆叶
,
叶片

Boiler
锅炉

Boundary layer
边界层

Carnot Cycle
卡诺循环

Cartesian
coordinates
笛卡尔坐标系
Celsius Degree
摄氏度

Compact heat exchanger
紧凑式换热
器

Composition
成分
,
合成物

Compressed liquid
压缩液体

Compressibility
可压缩性
,
压缩率

Condensation
凝结

Condenser
冷凝器

Conduction
导热

Control volume
控制体

Corrugated fin
波状散热片

Cross product
矢量积

Denominator
分母

Developed flow
充分
发展流

Diffusion
扩散

Doppler effect
多普勒效应

Double-pipe heat exchanger
套管式
换热器

Dry saturated vapor
干饱与蒸汽

Electrode
电极

Electrolyte
电解
,
电解液

Electrostatic
静电的

Emissivity
发射率

Equilibrium
平衡

Fluid mechanics
流体力学

Forced convection
强制对流

Free convection
自然对流

Friction loss
摩擦损失

Glass ceramic
微晶玻璃
,
玻璃陶瓷

Heat engine
热机

Heat pump
热泵

Hydrofoil
水翼

Hypersonic speed
高超音速

Infinitesimal
无穷小的

Inflating/deflating
充气
/
压缩

Internal combustion engine
内燃机

Isentropic
等熵的


热能与动力工程专业英语

Convection
对流

Coriolis-accelaration
flowmeter
科
氏加速流量计

Isometric
等容的

Isothermal
等温的

Kinematic viscosity
运动黏度

Laminar
层流

Manuscript
手稿
,
原稿

Moisture
湿度
,
水分

Molecule (
化学
)
分子

Molten polymer
熔融聚合物

Muti-disciplinary
多学科的

Newtonian Fluid
牛顿流体

Nominal temperature gradient
法向
温度梯度

Numerator (
数学
)
分子

Parallel flow
平行流动
,
并流

Pathline
迹线

Phase change
相变

Plane flow
平面流
,
二元流

Plate and flame heat exchanger
板式换热器

Polymer solution
胶浆

Proof
校样

Propeller
螺旋桨
,
推进器

Pump
泵

Qulity
干度

Qusi- equilibrium
准平衡、准静态

Radiation
辐射

Rankin Cycle
朗肯循环

Regenerative heat exchanger
蓄热
/
再生式换热器

Isobaric
等压的

Isolated system
孤立体系的

Rough-wall tube
粗糙管

Saturation
饱与

Shear stress
剪切力、切应力

Shell-and- tube heat exchanger
管壳
式换热器

Specific volume
比容

Steady
稳态的
,
定常的

Stifling engine
斯特林机

Strain rate
变形速度
,
应变率

Streamline
流线

Strut
支撑
,
支柱

Subcooled liquid
过冷液体

Superheated vapor
过热蒸汽

Surrounding
环境
,
外界

Thermal conductivity
热传导率

Thermal efficiency
热效率

Thermodynamics
热力学

Torsional
扭力的
,
扭转的

Trailing edge
机翼后缘、尾缘

Transmitter
传送装置、发送器

Turbine meter
涡轮流量计

Turbulent
湍流的

Ultrosonic
超声波的

Uniform flow
均匀刘

Vacuum
真空

View factor
角系数

Viscous
黏性的

热能与动力工程专业英语

Reservoir
水库
,
蓄水池

Reversible
可逆的

Rotameter
转子流量计

Bi Biot number
比澳数

CFD
计算流体力学

CHF
临界热流量

COP
制冷系数

Eu
欧拉数

Fo
富立叶数

Fr
弗劳德数

Gr
格拉晓夫数

KE
动能

LMTD
对数平均温差

Cortex shedding
漩涡脱落

Water faucet
水龙头
,
水嘴



NPSH
汽蚀余量

NTU
传热单元数

Nu
努谢尔特数

PE
势能

Pr
普朗特数

Ra
瑞利数

Re
雷诺数

Sc
施密特数

St
斯坦顿数
,
斯特劳哈数

We
韦伯数

1.1

Fundamental of Engineering Thermodynamics
1.1

工程热力学基础


Thermodynamics
is
a
science
in
which
the
storage,
transformation
and
transfer of energy are studied
、
Energy is stored as internal energy
(associated with temperature), kinetic energy (du to motion), potential
energy
(due
to
elevation)
and
chemical
energy
(due
to
chemical
composition); it is transformed from one of these forms to another; and
it is transferred across a boundary as either heat or work
、

热力学就是一门研究能量储存、
转换及传递的科学。
能 量以内能
(
与温度有关
)
、
动能
(
由
物体 运动引起
)
、势能
(
由高度引起
)
与化学能
(与化学组成相关
)
的形式储存。不同形式的能
量可以相互转化
,
而且能量在边界上可以以热与功的形式进行传递。


In
thermodynamics,
we
will
derive
equations
that
relate
the
transformations
and
transfers
of
energy
to
properties
such
as
temperature, pressure and density
、
Substances and their properties,
thus,
become
very
important
in
thermodynamics
、
Many
of
our
equations
will
be based on experimental observations
that have been organized into
mathematical
statements
or
laws,
the
first
and
second
laws
of
热能与动力工程专业英语

thermodynamics are most widely used
、
< br>在热力学中
,
我们将推导有关能量转化与传递与物性参数
,
如温度、< br>压强及密
度等关系间的方程。
因此
,
在热力学中
,
物 质及其性质变得非常重要。
许多热力学
方程都就是建立在实验观察的基础之上
,
而且这些实验观察的结果已被整理成数
学表达式或定律的形式。其中
,
热力学第一定 律与第二定律应用最为广泛。


1.1.1

Thermodynamic system and control volume
1.1.1


热力系统与控制体

A
thermodynamic
system
is
a
fixed
quantity
of
matter
contained
within
some
enclosure
、

The
surface
is
usually
an
obvious
one
(like
that
surrounding the gas in the cylinder)
、
However, it may be an imagined
boundary (like the deforming boundary of a certain amount of mass as it
flows through a pump)
、

热力系统就是一包围在某一封闭边界内的具有固定质量的物质。系统边 界通常就是比
较明显的
(
如气缸内气体的固定边界
)
。
然而
,
系统边界也可以就是假想的
(
如一定质量的流体
流经泵时不断变形 的边界
)
。


All
matter
and
space
external
to
a
system is
collectively
called
its
surroundings
、
Thermodynamics is concerned with the interaction of a
system and its surroundings, or one system interacting with another
、
A
system
interacts
with
its
surroundings
by
transferring
energy
across
its
boundary
、
No material crosses the boundary of a system
、
If the system
does
not
exchange
energy
with
the
surroundings,
it
is
an
isolated
system
、

系统之外的所有物质与空间统 称外界或环境。热力学主要研究系统与外界或系统与系
统之间的相互作用。
系统通过在边界上进 行能量传递
,
从而与外界进行相互作用
,
但在边界上
没有质量交换。 当系统与外界间没有能量交换时
,
这样的系统称为孤立系统。


In many cases, an analysis is simplified if attention is focused on
a
particular
volume
in
space
into
which,
or
from
which,
a
substance
flows
、

Such a volume is a control volume
、
A pump, a turbine, and an inflating
or deflating balloon are examples of control volume
、
The surface that
completely surrounds the control volume is called a control surface
、

在许多情况下
,< br>当我们只关心空间中有物质流进或流出的某个特定体积时
,
分析可以得
到简化。 这样的特定体积称为控制体。例如泵、透平、充气或放气的气球都就是控制体的例
热能与动力工程专业英 语

子。包含控制体的表面称为控制表面。


Thus, we must choose, in a particular problem, whether a system is to
be considered or whether a control volume is more useful
、
If there is
mass
flux
across
a
boundary,
then
a
control
volume
is
required;
otherwise,
a system is identified
、

因此
,
对于具体的问题
,
我们必须确定就是选取系统作为研究对象有利还就是选取控制
体作为研究对象有利。如果边界上有质量 交换
,
则选取控制体有利
;
反之
,
则应选取系统作为
研究对象。


1.1.2

Equilibrium, process and cycle
平衡、过程与循环

When the temperature of a system is referred to, it is assumed that
all
points
of
the
system
have
the
same,
or
essentially
the
same
temperature
、
When the properties are constant from point to point and
when
there
is
no
tendency
for
change
with
time,
a
condition
of
thermodynamic
equilibrium
exists
、
If
the
temperature,
say,
is
suddenly
increased
at
some
part
of
the
system
boundary,
spontaneous
redistribution
is assumed to occur until all parts of the
教材
1
页

system are at the same temperature
、

对于某一参考系统
,
假设系统内各点温 度完全相同。
当物质内部各点的特性参数均相同
且不随时间变化时
,
则称系统 处于热力学平衡状态。当系统边界某部分的温度突然上升时
,
则系统内的温度将自发地重新分布
,
直至处处相同。


When
a
system
changes
from
one
equilibrium
state
to
another,
the
path
of successive sates through which the system passes is called process
、

If, in the passing
one state
to
the next, the deviation
from equilibrium
is infinitesimal, a quasi-equilibrium process occurs, and each state in
the
process
may
be
idealized
as
an
equilibrium
state
、
Quasi- equilibrium
processes can approximate many processes, such as the compression and
expansion
of
gases
in
an
internal
combustion
engine,
with
no
significant
loss
of
accuracy
、
If
the
system
goes
from
one
equilibrium
state
to
another
热能与动力工程专业英语

through
a
series
of
non- equilibrium
states
(as
in
combustion),
a
non-equilibrium process occurs
、

当系统从一个平衡状态转变为另一个平衡状态时
,
系统所经历的一系列由中间状态组
成的变化历程称为过程。
若从一个状态到达另一个状态的过程 中
,
始终无限小地偏离平衡态
,
则称该过程为准静态过程
,
可以把其中任一个中间状态瞧作为平衡状态。准静态过程可近似
视为许多过程的叠加结果
,而不会显著减小其精确性
,
例如气体在内燃机内的压缩与膨胀过
程。
如果 系统经历一系列不平衡状态
(
如燃烧
),
从一个平衡状态转变为另一个平衡状 态
,
则其
过程为非平衡过程。


When
a
system
in
a
given
initial
state
experiences
a
series
of
process
and returns to the initial state, the system goes a cycle
、
At the end
of the cycle, the properties of the system have the same values they had
at the beginning
、

当系统从一个给定的初始状态出发
,
经历一系列中间过程又回到其初始状态
,
则称系统
经历了一个循环。循环结束时
,
系统中的各参数又与初始参数相同。


The prefix iso- is attached to the names of any property that remain
unchanged in a process
、

An isothermal process is one in
which the
temperature is held constant; in an iso-baric process, the pressure
remains constant; an isometric process is a constant-volume process
、

在任一特性参数名称前加上前缀
iso-,
表示 该参数在整个过程保持不变。等
温
(isothermal)
过程中温度保持不变;
等压
(isobaric)
过程中压强恒定
;
等容
( isometric)
过程
中体积保持不变。


1.1.3

Vapor-liquid phase equilibrium in pure substance
纯物质的气
-
液相平衡

Consider as a system 1 kg of water contained in the piston or
cylinder
arrangement
shown
in
Fig
、
1-1(a)
、
Suppose
the
piston
and
weight
maintain a pressure of 0
、
1MPa in the cylinder and that the initial
temperature
is
20
℃、
As
heat
is
transferred
to
the
water,
the
temperature
increase appreciably, the specific volume increase slightly, and the
pressure
remains
constant
、

When
the
temperature
reaches
99
、
6
℃
,
additional heat transfer results in a change of phase, as indicated in
Fig
、
1-1
(b)
、
That
is,
some
of
the
liquid
becomes
vapor,
and
during
this
热能与动力工程专业英语

process
both
the
temperature
and
pressure
remain
constant,
but
the
specific
volume
increases
considerably
、
When
the
last
drop
of
liquid
has
vaporized,
further
transfer
of
heat
results
in
an
increase
in
both
temperature and specific volume of the vapor, as shown in Fig
、
1-1(c)
、

如图
1-1(a)
所示
,
由活塞与气缸组成的装置中装有
1kg
水。
假定活塞与其上的重物 使气
缸内压强维持在
0
、
1Mpa,
初始温度
20
℃。当有热量开始传递给水时
,
缸内水温迅速上升
,
而
比容略有增加
,
气缸内压强保持恒定不变。当水温达到
99
、
6
℃时,
如若再增加传热量
,
水将
发生相变
,
如图
1 -1(b)
所示。也就就是说
,
一部分水开始气化变为蒸汽
,
在此相 变过程中
,
温
度与压强始终保持不变
,
但比容却有大幅度的增加。< br>当最后一滴液体被气化时
,
进一步的加热
将使蒸汽温度与比容均有所增加
,
如同
1-1(c)
所示。


图
1-1
液体在常压下的蒸发过程

The term saturation temperature designates the temperature at which
vaporization takes place at a given pressure
、
This pressure is called
the saturation pressure for the given temperature
、
Thus, for water at
99
、
6
℃
,
the
saturation
pressure
is
0
、
1MPa,
and
for
water
at
0
、
1MPa
the
saturation temperature is 99
、
6
℃、

在给定压强下发生气化的温度称为饱与温度
,
压强称为给定温度下的饱与压强。因
此
,99
、
6
℃水的 饱与压强就是
0
、
1MPa,0
、
1MPa
水的饱与温度为
99
、
6
℃。


If
a
substance
exists
as
liquid
at
the
saturation
temperature,
it
is
called
saturated
liquid
、
If
the
temperature
of
the
liquid
is
lower
than
the
saturation
temperature
for
the
existing
pressure,
it
is
called
either
a subcooled liquid (implying that the temperature is lower
教材
2
页

than
the
saturation
temperature
for
the
given
pressure)
or
a
compressed
liquid
(implying
that
the
pressure
is
greater
than
the
saturation pressure for the given temperature)
、

如果某一工质为液态并处于其饱与温度与饱与压强下< br>,
则称该液体为饱与液体。
如果液
体温度低于当前压强下的饱与温度
,
则称该液体为过冷液体
(
表明液体的当前温度低于给定
压强下的饱与温度)
或压缩液体
(
表明液体的当前压强大于给定温度下的饱与压强
)
。


When
a
substance
exists
as
part
liquid
and
part
vapor
at
the
saturation
temperature, its quality is defined as the ratio of the mass of vapor to
热能与动力工程专业英语

the total mass
、
Thus, in Fig
、
1-1(b), if the mass of vapor is 0
、
2 kg
and the mass of liquid is 0
、
8 kg, the quality is 0
、
2 or 20%
、
Quality
has meaning only when the substance is in a saturated state
、

若某一 工质在饱与温度下以液、气共存的形式存在
,
则称蒸汽质量与总质量之比为干
度。因此
,
如图
1-1(b)
所示
,
若蒸汽质量为
0
、
2kg,
液体质量为
0
、
8kg,
则其干度为
0
、
2
或
20%
。干度只有在饱与状态下才有意义。


If a substance exists as vapor at the saturation temperature, it is
called
saturation
vapor
(Some
times
the
term
dry
saturation
vapor
is
used
to
emphasize
that
the
quality
is
100%)
、
When
the
vapor
is
at
a
temperature
greater
than
the
saturation
temperature,
it
is
said
to
exist
as
superheated
vapor
、
The
pressure
and
temperature
of
superheated
vapor
are
independent properties, since the temperature may increase while the
pressure remains constant
、

若某一工质处于饱与温度下并以蒸汽形态存 在
,
则称该蒸汽为饱与蒸汽
(
有时称为干饱
与蒸汽
,
意在强调其干度为
100%)
。当蒸汽温度高于其饱与温度时
,
则称之为过 热蒸汽。过热
蒸汽的压强与温度就是彼此独立的
,
因为温度上升时
,
压强可能保持不变。


Let
us
plot
on
the
temperature-value
diagram
of
Fig
、
1-2
the
constant-pressure
line
that
represents
the
states
through
which
the
water
passes as it is heated from the initial state of 0
、
1 MPa and 20
℃、
Let
state A represent the initial state, B the saturated- liquid state(99
、
6
℃
),
and
line
AB
the
process
in
which
the
liquid
is
heated
from
the
initial
temperature
to
the
saturation
temperature
、
Point
C
is
the
saturated-vapor
state,
and
line
BC
is
the
constant- temperature
process
in
which
the
change
of phase from liquid to vapor occurs
、
Line CD represents
[
]

the process in which the steam is superheated at constant pressure
、

Temperature and volume both increase during this process
、

在图
1-2
所示的温度
-
比容图上作等压线
,
表示 水由初压
0
、
1MPa
、初温
20
℃被加热的
过程 。
点
A
代表初始状态
,
点
B
为饱与液态
( 99
、
6
℃
),
线
AB
表示液体由初始温度被加热 至饱
与温度所经历的过程。点
C
表示饱与蒸汽状态
,
线
BC
表示等温过程
,
即液体气化转变为蒸汽
的过程。
线
CD表示在等压条件下蒸汽被加热至过热的过程
,
在此过程中
,
温度与比容均 增大。


图
1-2
温度
-
比容曲线

热能与动力工程专业英语

表
1-1
一些物质的临界参数

In a similar name, a constant pressure of 10 MPa is represented by
line
IJKL,
for
which
the
saturation
temperature
is
311
、
1
℃、
At
a
pressure
of 22
、
09MPa, represented by line MNO, we find, however, that there is
no
constant-temperature
vaporization
process
、
Instead,
point
N
is
a
point
of
inflection
with
a
zero
slope
、
This
point
is
called
the
critical
point
、

At
the
critical
point
the
saturated-liquid
and
saturated-vapor
states
are
identical
、
The temperature, pressure and specific volume at critical
point
are
called
the
critical
temperature,
critical
pressure
and
critical
volume
、
The critical-point data for some substances are given in Table
1-1
、

类似地
,
线
IJKL
表示压强 为
10MPa
下的等压线
,
相应的饱与温度为
311
、1
℃。但就是
,
在压强为
22
、
09MPa
条 件下
(
线
MNO),
不存在等温蒸发过程。相反
,
点
N
就是个转折点
,
在该
点上
,
切线斜率为零
,< br>通常把
N
点称为临界点。在临界点处
,
饱与液体与饱与气体的状态都就
是相同的。
临界点下的温度、压强与比容分别称为临界温度、
临界压强与临界比容。一 些工
质的临界点数据如表
1-1
所示。


1
、
1
、
4 The first law of thermodynamics
The first law of the thermodynamics is commonly called the law of
conservation of energy
、

教材
3
页

In elementary physics courses, the study of conservation of energy
emphasizes
changes
in
kinetic
and
potential
energy
and
their
relationship
to work
、
A more general form of conservation of energy includes the
effects of heat transfer and internal energy changes
、
Other forms of
energy could also be included, such as electrostatic, magnetic, strain
and surface energy
、

1
、
1
、
4
热力学第一定律

通常把热 力学第一定律称为能量守恒定律。在基础物理课程中
,
能量守恒定律侧重动
能、
势能的变化以及与功之间的相互关系。
更为常见的能量守恒形式还包括传热效应与内能
的变化 。当然
,
也包括其它形式的能
,
如静电能、磁场能、应变能与表面能。


Historically,

[
]

the first law of thermodynamics was
热能与动力工程专业英语

stated for a cycle: the net heat transfer is equal to the net work done
for a system undergoing a cycle
、

历 史上
,
用热力学第一定律来描述循环过程
:
净传热量等于循环过程中对系统所 做的净
功。


1
、
1
、
5 The second law of thermodynamics
The second law of thermodynamics can be stated in a variety of ways
、

Here
we
present
two:
the
Clausius
statement
and
the
Kelvin-Planck
statement
、

1
、
1
、
5
热力学第二定律

热力学第 二定律有多种表述形式。
在此列举两种
:
克劳修斯表述与凯尔文
-
普 朗克表述。


Clausius statement
It is impossible to construct a device that operates in a cycle and
whose
sole
effect
is
transfer
of
heat
from
a
cooler
body
to
a
hotter
body
、

克劳修斯表述
:
制造一台唯一功能就是把热量 从低温物体传给高温物体的循环设备就是
不可能的。

图
1-3
第二定律的违背

This
statement
relates
to
a
refrigerator
(or
a
heat
pump)
、
It
states
that it is impossible to construct a refrigerator that transfers energy
from a cooler body to a hotter body without the input of work; this
violation is shown in Fig
、
1-3(a)
、

以冰箱
(
或热泵
)
为例
,
不可能制造一台不用输入功就能把热量从低温物体传给高温物体
的 冰箱
,
如图
1-3(a)
所示。


It is impossible to construct a device that operates in a cycle and
produces no other effect
than the production
of work and
the transfer of
heat from a single body
、

凯尔文
-< br>普朗克表述
:
制造一台从单一热源吸热与做功的循环设备就是不可能的。


In other words, it is impossible to construct a heat engine that
extracts
energy
from reservoir,
does
work,
and
does
not
transfer
heat
to
a
low-temperature
reservoir
、
This
rules
out
any
heat
engine
that
is
100
percent efficient, like the one shown in Fig
、
1-3(b)
、

热能与动力工程专业英语

换句话说
,
制造这样一台从某一热源吸热并对外做功
,
而没有与低温 热源进行换热的热机
就是不可能的。因此
,
该表述说明了不存在工作效率为
1 00%
的热机
,
如图
1-3(b)
所示。

1
、
1
、
6 The Carnot Cycle
The
heat
engine
that
operates
most
efficiently
between
a
high-temperature
reservoir
and
a
low-temperature
reservoir
is
the
Carnot
engine
、
This
is
an
ideal
engine
that
uses
reversible
process
to
form
its
cycle of operation; such a cycle is Carnot cycle
、
The Carnot engine is
very
useful,
since
its
efficiency
establishes
the
maximum
possible
efficiency
of
any
real
engine
、

If
the
efficiency
of
a
real
is
significantly
lower
than
the
efficiency
of
Carnot
engine
between
the
same
temperature limits, then additional improvements may be possible
、

1
、
1
、
6
卡诺循环

卡诺机就是低温 热源与高温热源间运行效率最高的热机。
卡诺机就是一个理想热机
,
利
用多个 可逆过程组成一循环过程
,
该循环称为卡诺循环。
卡诺机非常有用
,
因为它的运行效率
为任何实际热机最大可能的效率。因此
,
如果一台实际热机的效率要 远低于同样条件下的卡
诺机效率
,
则有可能对该热机进行一些改进以提高其效率。
图
1-4
卡诺循环

The ideal Carnot cycle in Fig
、
1-4 is composed of four reversible
processes:
1
?
2:
Isothermal
expansion:
2
?
3;Adiabatic
reversible
expansion:3
?
4;Isothermal
compression:4
?
1;Adiabatic
教材
4
页

reversible
compression
、
The efficiency of a Carnot cycle is
?
?
1
?
T
L

T
H
Note that the efficiency is increased by raising the temperature T
H

at which heat is added or by
decreasing
the temperature T
L
at which heat
is rejected
、

理想的卡诺循环包括四 个可逆过程
,
如图
1-4
所示
:1
→
2
等 温膨胀
;2
→
3
绝热可逆膨
胀
;3
→
4< br>等温压缩
;4
→
1
可逆绝热压缩。卡诺循环的效率为

?
?
1
?
T
L
(1-1)
T
H
注意
,
提高
T
H
(提高吸热温度
)
或降低
T
L
(
降低放热温度
)
均可使循环效率提高。


热能与动力工程专业英语

1
、
1
、
7 The Rankine cycle
The
first
class
of
power
cycles
that
we
consider
are
those
utilized
by the electric power generating industry, namely, power cycles that
operates
in
such
a
way
that
the
working
fluid
changes
phases
from
a
liquid
to vapor
、
The simplest vapor-power cycle is called the Rankine cycle,
shown
schematically
in
Fig
、
1-5(a)
、
A
major
feature
of
such
cycle
is
that
the
pump
requires
very
little
work
to
deliver
high- pressure
water
to
the
boiler
、
A possible disadvantage is that the expansion process in the
turbine
usually
enters
the
quality
region,
resulting
in
the
formation
of
liquid droplets that may damage the turbine blades
、

1
、
1
、
7
朗肯循环

我们所关心的第 一类动力循环为电力生产工业所采用的
,
也就就是说
,
动力循环按这样
的方式运行
:
工质发生相变
,
由液态变为气态。最简单的蒸汽
-< br>动力循环就是朗肯循环
,
如图
1-5(a)
所示。
朗肯循环的 一个主要特征就是泵耗费很少的功就能把高压水送入锅炉。
其可能
的缺点为工质在汽机内膨胀做 功后
,
通常进入湿蒸汽区
,
形成可能损害汽轮机叶片的液滴。

图
1-5
朗肯循环

The Rankine cycle is an idealized cycle in which friction losses in
each
of
the
four
components
are
neglected
、
The
losses
usually
are
quite
small
and
will
be
neglected
completely
in
initial
analysis
、
The
Rankine
cycle is composed of the four ideal processes shown on the T-s diagram
in
Fig
、
1-5(b):1
?
2:
Isentropic
compression
in
a
pump;2
?
3:
Constant-pressure heat addition in a boiler; 3
?
4: Isentropic expansion
in a turbine; 4
?
1: Constant pressure heat rejection in a condenser
、

朗肯循环就是一个理想循环
,
其忽略了四个过程中的摩擦损失。
这些损失通常很小
,
在初
始分析时可完全忽略。朗肯循环由四个理想过程组成
,
其
T
-
s< br>图如图
1-5(b)
所示
:1
→
2
为泵
内等 熵压缩过程
;2
→
3
为炉内定压吸热过程
;3
→
4
为汽轮机内等熵膨胀做功过程
;4
→
1
为凝
汽器内定压放热 过程。


The pump is used to increase the pressure of the saturated liquid
、

Actually,
states
1
and
2
are
essentially
the
same,
since
the
high-pressure
lines
are
extremely
close
to
the
saturation
curve;
they
are
shown
separated
for
illustration
only
、

The
boiler
(also
called
a
steam
generator)
and
the
condenser
are
heat
exchangers
that
neither
require
nor
热能与动力工程专业英语

produce any work
、

泵用于提高饱与液体的压强。事实上
,
状态
1
与状态
2
几乎完全一样
,
因为由
2
点开始
的较高压强下的吸热过程线非常接近饱与曲线
,
图中仅为了解释说明的需要分别标出。锅炉(
也称蒸汽发生器
)
与凝汽器均为换热器
,
它们既不需要功也不 产生功。


If we neglect kinetic energy and potential energy changes, the net
work
output
is
the
area
under
the
T-s

diagram,
represented
by
area
1-2-3-4-1
of
Fig
、
1-5(b);
this
is
true
since
the
first
law
requires
that
W
out
=
Q
net
、
The
heat
transfer
to
the
working
substance
is
represented
by
area
a-2-3-b-a
、
Thus, the thermal efficiency
η
of the Rankine cycle is
?
?
area

1
?
2
?
3
?
4
?
1

area

a
?
2
?
3
?
b?
a
That
is,
the
desired
output
divided
by
the
energy
input
(the
purchased
energy)
、
Obviously,
教材
5
页

the
thermal
efficiency
can
be
improved
by
increasing
the
numerator
or
by
decreasing
the
nominator
、
This
can
be
done
by
increasing
the
pump
outlet
pressure p
2
, increasing the boiler outlet temperature T
3
, or decreasing
the turbine outlet pressure p
4
、

如果忽略动能 与势能的变化
,
输出的净功等于
T
-
s
图曲线下面的面积< br>,
即图
1-5(b)
中
1-2-3-4-1
所包围的面积,
由用热力学第一定律可证明
W
net
?
Q
net。循环过程中工质的吸热量
对应面积
a-2-3-b-a
。因此
,
朗肯循环的热效率可表示为


?
?
面积
1
?
2
?
3
?
4
?
1
(1-2)
面积
a
?
2
?
3
?
b?
a
即
,
热效率
?
等于输出能量除以输入能量
(
所购能量
)
。显然
,
通过增大分子或减小分母均可以
提高 热效率。这可以通过增大泵出口压强
p
2
,
提高锅炉出口温度
T3
,
或降低汽机出口压强
p
4
来实现。


1
、
1
、
8 The Reheat cycle
It
is
apparent
that
when
operating
in
a
Rankine
cycle
with
a
high
boiler
pressure or a low condenser pressure it is difficult to prevent liquid
droplets
from
forming
in
the
low-pressure
portion
of
the
turbine
、
Since
most metal cannot withstand temperatures above about 600
℃
, the reheat
cycle
is
often
used
to
prevent
liquid- droplet
formation:
the
steam
passing
热能与动力工程专业英语

through the turbine is reheat at some intermediate pressure, thereby
raising the temperature to state 5 in the T-s diagram of Fig
、
1-6
、
The
steam then passes through the low-pressure section of the turbine and
enters
the
condenser
at
state
6
、
This
controls
or
completely
eliminates
the
moisture
problem
in
the
turbine
、

The
reheat
cycle
dose
not
significantly
influences
the
thermal
efficiency
of
the
cycle,
but
it
does
result
in
a
significant
additional
work
output,
represented
in
the
figure
by
area
4-5-6-4
’
-4
of
Fig
、
1-6
、
The
reheat
cycle
demands
a
significant
investment in additional equipment, and the use of such equipment must
be
economically
justified
by
the
increased
work
output
、
If
reheat
is
not
used to avoid droplet formation, the condenser pressure must be quite
high, resulting relatively low cycle efficiency
、
In that sense, reheat
significantly increase cycle efficiency when compared to cycle with no
reheat but with the higher condenser pressure
、

1
、
1
、
8
再热循环

对于一个处于高锅炉压强与低凝汽器压强条件下的朗肯循环
,显然
,
很难阻止液滴在汽
轮机低压部分的形成。
由于大多数金属不能承受
600
℃以上的高温
,
因此
,
通常采用再热循环
来 防止液滴的形成。
再热过程如下
:
经过汽轮机的部分蒸汽在某中间压强下被再热
,
从而提高
蒸汽温度
,
直至达到状态
5,
如图
1 -6
所示。然后这部分蒸汽进入汽轮机低压缸
,
而后进入凝
汽器
(< br>状态
6)
。
再热循环方式可以控制或者完全消除汽轮机中的湿蒸汽问题
,
因此
,
通常汽轮
机分成高压缸与低压缸两部分。虽然再热循环不会显著影响 循环热效率
,
但带来了显著的额
外的输出功
,
如图
1-6< br>中的面积
4-5-6-4
?
-4
所示。当然
,
再热循 环需要一笔可观的投资来购
置额外的设备
,
这些设备的使用效果必须通过与多增加的输 出功进行经济性分析来判定。如
果不采用再热循环来避免液滴的形成
,
则凝汽器出口压 强必须相当地高
,
因而导致循环热效
率较低。
在这种意义上
,
与无再热循环且高凝汽器出口压强的循环相比
,
再热可以显著提高循
环效率。

图
1-6
再热循环

1
、
2 Fundamental of Fluid Mechanics
Fluid motions manifest themselves in many different ways
、
Some can
be described very easily, while others require a thorough understanding
of
physical
laws
、

In
engineering
applications,
it
is
important
to
describe the fluid motions as simply as can be justified
、
This usually
depends
on
the
required
accuracy
、

Often,
accuracies
of
±
10%
are
acceptable, although in some applications higher accuracies have to be
热能与动力工程专业英语

achieved
、
The general equations of motion are very difficult to solve;
consequently,
it
is
the
engineer
’
s
responsibility
to
know
which
simplifying
assumptions
can
be
made
、
This,
of
course,
requires
experience
and, more important,
教材
6
页

a understanding of the physics involved
、

1
、
2
流体力学基础

流体运动表现出多种不同的运动形 式。
有些可以简单描述
,
而其它的则需要完全理解其
内在的物理规律。在工程 应用中
,
尽量简单地描述流体运动就是非常重要的。简化程度通常
取决于对精确度的要 求
,
通常可以接受±
10%
左右的误差
,
而有些工程应用则 要求较高的精
度。描述运动的一般性方程通常很难求解
,
因此
,
工程 师有责任了解可以进行哪些简化的假
设。当然
,
这需要丰富的经验
,
更重要的就是要深刻理解流动所涉及的物理内涵。


Some
common
assumptions
used
to
simplify
a
flow
situation
are
related
to
fluid
properties
、
For
example,
under
certain
conditions,
the
viscosity
can affect the flow significantly; in others, viscous effects can be
neglected
greatly
simplifying
the
equations
without
significantly
altering the predictions
、
It is well known that the compressibility
effects do not have to be taken into account to predict wind forces on
buildings
or
to
predict
any
other
physical
quantity
that
is
a
direct
effect
of wind
、
After our study of fluid motions, the appropriate assumptions
used
should
become
more
obvious
、
Here
we
introduce
some
important
general
approaches used to analyze fluid mechanics and give a brief overview of
different types of flow
、

一些常见的用来简化 流动状态的假设就是与流体性质有关系的。
例如
,
黏性在某些条件
下对流体有 显著的影响
;
而在其它条件下
,
忽略黏性效应的影响可以大大地简化方程,
但并不
会显著改变计算结果。
众所周知
,
气体速度很高时必须 考虑其压缩性
,
但在预测风力对建筑物
的影响程度
,
或者预测受风力 直接影响的其它物理量时
,
可以不计空气的压缩性。
学完流体运
动学之后,
可以更明显地瞧出采用了哪些恰当的假设。
这里
,
将介绍一些重要的用 来分析流体
力学问题的一般性方法
,
并简要介绍不同类型的流动。


1
、
2
、
1 Lagrangian and Eulerian Descriptions of Motion
In the description of a flow field, it is convenient to think of
热能与动力工程专业英语

individual particles of which
is considered to
be a small
mass of fluid,
consisting of a large number of molecules that occupies a small volume
that
moves
with
the
flow
、
If
the
fluid
is
incompressible,
the
volume
does
not change in magnitude but may deform
、
If the fluid is compressible,
as
the
volume
deforms,
it
also
changes
its
magnitude
、
In
both cases
the
particles are considered to move through a flow field as an entity
、

1
、
2
、
1
拉格朗日运动描述与欧拉运动描述

描述流场时
,
将着眼点放在流体质点上就是非常方便的。
每个质点都包含了微 小质量的
流体
,
它由大量分子组成。质点占据很小的体积
,
并随流体 流动而移动。对不可压缩流体
,
其
体积大小不变
,
但可能发生形变。 对可压缩流体
,
不但体积发生形变
,
而且大小也将改变。在
上述两种 情况下
,
均将所有质点瞧作一个整体在流场中运动。


In the study of particle mechanics, where attention is focused on
individual particles, motion is observed as a function of time
、
The
position,
velocity
and
acceleration
of
each
particle
are
listed
as
s
(x
0
,y
0
,z
0
,t),
V
(x
0
,y
0
,z
0
,t)
and

a
(x
0
,y
0
,z
0
,t)
and
quantities
of
interest
can
be
calculated
、
The
point

(x
0
,y
0
,z
0
)
locates
the
starting
point
the
name-of
each particle
、
This is the Lagrangian description, named after Joseph
L
、
Lagrange, of motion that is used in a course on dynamics
、
In the
Lagrangian
description
many
particles
can
be
followed
and
their
influence
on one another noted
、
This becomes, however, a difficult task as the
number of particles becomes extremely large, as in a fluid flow
、

质点力学主要研究单个质点
,< br>质点运动就是时间的函数。
任一质点的位移、
速度与加速
度可表示为
s
(
x
0
,
y
0
,
z
0
,
t
),
V
(
x
0
,
y
0
,
z
0
,
t
),
a
(
x
0
,
y
0
,
z
0
,
t
),
其它相 关参量也可计算。
坐标
(
x
0
,
y
0
,
z
0
)
表示质点的起始位置
,
也就是每个质点的名字。这就就是拉格朗日运动描述
,
以约瑟夫
?
Ｌ
?
拉格朗日 的名字命名
,
该描述方法通常用于质点动力学分析。
拉格朗日法跟踪多
个质点 的运动过程并考虑质点间的相互作用。
然而
,
由于实际流体包含质点数目巨大
,
因而采
用拉格朗日法研究流体流动则非常困难。


An alternative to following each fluid particle separately is to
identify points in space and then observe the velocity of particles
passing each point; we can observe the rate of change of velocity as the
particles pass each point, that is,
?
V
/
?
x,
?
V
/
?
y,
?
V
/
?
z
and
we can observe
if the velocity is
changing with
time
at each particular point,
that is,
热能与动力工程专业英语

?
V
/
?
t
、
In this Eulerian description, named after Leonhard Euler, of
motion,
the
flow
properties,
such
as
velocity,
are
functions
of
both
space
and
time
、
In
rectangular,
Cartesian
coordinates
the
velocities
expressed
as
V
=
V
(x, y, z, t)
、
The region of flow that is considered is called a
flow field
、

与分别跟踪每个流体质点不同的另一种方法就是将 着眼点放在空间点上
,
然后观察质
点经过每个空间点时的质点速度
,
由此可以得到质点流经各空间点时的速度变化率
,
即
?
V
/
?
x
,
?
V
/
?
y
,
?
V
/
?
z
;
还可以判断某一点上的速度就是否随时间变化
,
即计算
?
V
/
?
t
。
这种描述
方 法称为欧拉运动描述
,
以莱昂哈德
?
欧拉的名字命名。在欧拉法中
,
速度等流动参数就是空
间与时间的函数。在直角笛卡儿坐标系中
,
速度表示为
V
=
V
(
x
,
y
,
z
,
t
)
。我们所研究的流
动区域称为流场。


1
、
2
、
2 Pathlines and streamlines
Two different lines help us in describing a flow field
、
A pathline
is the focus of points traversed by a given particle as it travels in a
field
of
flow;
the
pathline
provides
us
with
a
“
history
”
of
the
particle
’
s locations
、
A photograph of a pathline would required a time exposure
of an illuminated particle
、

教材
7
页

1
、
2
、
2
迹线与流线

可采用两种不同的流动线来帮助我们描述流场。迹线就是某一给定质点在 流场中运动
时所经过的不同空间点形成的轨迹
,
它记录了质点的“历史”位置。一定曝 光时间下可以拍
得发亮粒子的运动迹线。


A
streamline
is
a
line
in
the
flow
possessing
the
following
property:
the
velocity
vector
of
each
particle
occupying
a
point
on
the
streamline
is tangent to the streamline, that is,
V
×
d
r
=0
、
Since
V
and d
r
are in
the same direction; recall that the cross product of two vectors in the
same direction is zero
、
A photograph of a streamlines cannot be made
directly
、
For a general unsteady flow the streamlines can be inferred
from photographs of short pathlines of a large number of particles
、

流线就是流场中具有这样特性的线
:
任一质点在流线上某点处的速度矢量与该流线相
切
,
即
V
?
d
r
=0
。
这就是因为
V
与
d
r
具有相同的方向
,
而具有相同方向的两个矢量的叉乘积等
于零。
同迹线相比< br>,
流线不能直接由相机拍摄获得。
对于一般的非定常流动
,
根据大量质 点的
热能与动力工程专业英语

短迹线相片可以推断出流线的形状。


1
、
2
、
3 One-, two-, and three-dimensional flows
In
the
Eulerian
description
of
motion
the
velocity
vector,
in
general,
depends on three space variables and time, that is, V=V(z,y,z,t)
、
Such
a
flow
is
a
three-
dimensional
flow,
because
the
velocity
vector
depends
on
three
space
coordinates
、
The
solutions
to
problems
in
such
a
flow
are
very
difficult
and
are
beyond
the
space
of
an
introductory
course
、
Even
if the flow could be assured to be steady [i
、
e, V=V(x,y,z)], it would
remain a three-dimensional flow
、

1
、
2
、
3
一维、二维与三维流动

一 般来说
,
欧拉运动描述中的速度矢量取决于三个空间变量与时间变量
,
即V
=
V
(
x
,
y
,
z
,
t
)
。这样的流动称为三维流动
,
因为速度矢量依赖于三个空间坐标 。三维流动的求解非常
困难
,
并且也超出了序言的范围。即使假设流动为定常的
(
如
,
V
=
V
(
x
,
y
,
z
)),
该流动仍为三
维流动。


Often
a
three
dimensional
flow
can
be
approximated
as
a
two-dimensional
flow
、

For
example,
the
flow
over
a
wide
dam
is
three-dimensional because of the end conditions, but the flow in the
central portion away from the ends can be treated as two-dimensional
、

In
general,
a
two-dimensional
flow
is
a
flow
in
which
the
velocity
vector
depends
on
only
two
space
variables
、
An
example
is
a
plane
flow,
in
which
the velocity vector depends
on two spatial
coordinates, x and
y, but not
z [i
、
e
、
V=V(x,y)]
、

三维流动常常可以近似成二维流动。例如
,
对于一个很宽的大坝
,
受坝两端条件的影
响
,
水流经大坝时的流动为 三维流动
;
但远离坝端的中间部分的流动可瞧作就是二维的。
一般
来说
,
二维流动就是指其速度矢量只取决于两个空间坐标的流动。
平面流动即就是如此
,
速度
矢量只依赖于
x
,
y
两个空间坐标
,
而与
z
坐标无关
(
如
,
V
=
V
(
x
,
y
))
。


A
one-dimensional
flow
is
a
flow
in
which
the
velocity
vector
depends
on
only
one
space
variable
、
Such
flows
occur
in
long,
straight
pipes
or
between
parallel
plates
、
The
velocity
in
the
pipe
varies
only
with
r
i
、
e
、
, u=r(r)
、
The velocity between parallel plates varies only with the
coordinate
y
i
、
e
、
,
u=u(y)
、
Even
if
the
flow
is
unsteady
so
that
u=u(y,t),