AN INTRODUCTION TO
介绍
Transport Phenomena in Materials Engineering
材料工程中的传输现象
S E C O N D E D I T I O N
第二版
DAVID R. GASKELL
大卫·R·加斯凯尔
An Introduction to TRANSPORT PHENOMENA
运输现象导论
in
在
MATERIALS ENGINEERING,
材料工程，
2nd Edition
第二版
An Introduction to TRANSPORT PHENOMENA
运输现象导论
in
在
MATERIALS ENGINEERING,
材料工程，
2nd Edition
第二版
DAVID R. GASKELL
大卫·R·加斯凯尔
MOMENTUM PRESS, LLC, NEW JERSEY
动量出版社，有限责任公司，新泽西
An Introduction to Transport Phenomena in Materials Engineering, 2nd Edition
材料工程中的传输现象导论（第二版）
Copyright © Momentum Press®, LLC, 2013
版权 © Momentum Press®, LLC, 2013
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means—electronic, mechanical, photocopy, recording or any other—except for brief quotations, not to exceed 400 words, without the prior permission of the publisher.
版权所有。未经出版商事先许可，任何部分不得以任何形式或通过任何手段（电子、机械、复印、录音或其他）复制、存储在检索系统中或传输——除非是简短引用，不超过 400 字。
First edition published by Macmillan Publishing Company, New York;
第一版由麦克米伦出版公司出版，纽约；
Maxwell Macmillan Canada, Toronto; Maxwell Macmillan International in 1991
麦克斯韦·麦克米兰加拿大，多伦多；1991 年麦克斯韦·麦克米兰国际
Second edition published in 2012 by Momentum Press®, LLC
2012 年由 Momentum Press®，LLC 出版的第二版
222 East 46th Street New York, NY 10017
纽约，东 46 街 222 号，邮政编码 10017
ISBN-13: 978-1-60650-355-3 (hard cover, case bound) ISBN-10: 1-60650-355-3 (hard cover, case bound) ISBN-13: 978-1-60650-357-7 (e-book)
ISBN-13: 978-1-60650-355-3（精装，盒装） ISBN-10: 1-60650-355-3（精装，盒装） ISBN-13: 978-1-60650-357-7（电子书）
ISBN-10: 1-60650-357-X (e-book) DOI: 10.5643/9781606503577
ISBN-10: 1-60650-357-X (电子书) DOI: 10.5643/9781606503577
Cover design by Jonathan Pennell 10 9 8 7 6 5 4 3 2 1
封面设计：Jonathan Pennel 10 9 8 7 6 5 4 3 2 1
Printed in the United States of America
在美国印刷
For Ivy Jean
给艾薇·简
Preface to the Second Edition
第二版前言
The first edition of this textbook contained a large number of typographical errors. In this, the second edition, a serious attempt has been made to correct these errors. The major difference, however, between the first and this edition is that this edition contains an additional chapter, Chapter 12, titled “Boiling and Condensation.” The material presented in this chapter is particularly important in view of the current interest in Renewal Energy Resources involving such devices as windmills and solar panels. Developments in this field require a thorough familiarity with the phenomena and mechanisms of boiling and condensation.
本教材的第一版包含大量排版错误。在这一版，即第二版中，已认真尝试纠正这些错误。然而，第一版与这一版之间的主要区别在于这一版包含了一个附加章节，第 12 章，标题为“蒸发与冷凝”。考虑到当前对可再生能源资源的兴趣，涉及风车和太阳能电池板等设备，本章所呈现的材料尤为重要。该领域的发展需要对蒸发和冷凝的现象和机制有透彻的了解。
vii
ix
x Preface
x 前言
List of Symbols xvii
符号列表 xvii
Engineering Units and Pressure in Static Fluids 1
静态流体中的工程单位和压力 1
Origins of Engineering Units 1
工程单位的起源 1
Concept of Pressure 5
压力的概念 5
Measurement of Pressure 11
压力测量 11
Pressure in Incompressible Fluids 15
不可压缩流体中的压力 15
Buoyancy 21
浮力 21
Summary 26
摘要 26
Problems 27
问题 27
Momentum Transport and Laminar Flow of Newtonian Fluids 30
牛顿流体的动量传输和层流
Introduction 30
介绍 30
Newton’s Lax of Viscosity 32
牛顿的粘度定律 32
Conservation of Momentum in Steady-State Flow 36
稳态流动中的动量守恒 36
Fluid Flow Between Two Flat Parallel Plates 40
两个平行平板之间的流体流动 40
Fluid Flow down in Inclined Plane 48
倾斜平面上的流体流动 48
Fluid Flow in a Vertical Cylindrical Tube 53
垂直圆柱管中的流体流动 53
Capillary Flowmeter 65
毛细管流量计 65
xi
xii Contents
内容
Fluid Flow in an Annulus 69
环形间隙中的流体流动 69
Mean Residence Time 76
平均停留时间 76
Calculation of Viscosity from the Kinetic Theory of Gases 78
气体动理论中的粘度计算 78
Viscosities of Liquid Metals 90
液态金属的粘度 90
方程式 of
的 Continuity
连续性 and
和 Conservatio
保护n of Momentum and Fluid Flow Pas
动量和流体流动的 Past Submerged Objects
沉没物体 102
Equation of Continuity 102
连续性方程 102
Conservation of Momentum 104
动量守恒 104
Navier-Stokes Equation for Fluids of Constant Density and Viscosity 108
常密度和粘度流体的纳维-斯托克斯方程 108
Fluid Flow over a Horizontal Flat Plane 115
水平平面上的流体流动 115
Approximate Integral Method in Obtaining Boundary Layer Thickness 117
在获得边界层厚度中的近似积分法 117
Creeping Flow past a Sphere 125
球体周围的爬行流动 125
Graphical Representation of Fluid Flow 139
流体流动的图形表示 139
Friction Factor and Turbulent Flow in Cylindrical Pipes 141
圆管中的摩擦因子和湍流 141
Flow Over a Flat Plate 153
平板上的流动 153
Flow Past a Submerged Sphere 160
沉浸球体周围的流动 160
Flow Past a Submerged Cylinder 163
沉浸圆柱体周围的流动 163
Flow Through Packed Beds 167
流经填充床 167
Mechanical Energy Balance and Its Application to Fluid Flow 185
机械能平衡及其在流体流动中的应用 185
内容 xiii
Friction Loss, Ef 188
摩擦损失，Ef 188
Influence of Bends, Fittings, and Changes in the
弯头、配件和变化的影响
Fluid Flow in an Open Channel 205
开放渠道中的流体流动 205
Drainage from a Vessel 207
从容器排水 207
Emptying a Vessel by Discharge Through an Orifice 209
通过孔口排放排空容器 209
Drainage of a Vessel Using a Drainage Tube 213
使用排水管排放容器的排水 213
Emptying a Vessel by Drainage Through a Drainage Tube 215
通过排水管排空容器 215
Bernoulli Equation for Flow of Compressible Fluids 219
可压缩流体流动的伯努利方程 219
Transport of Heat by Conduction 235
通过导热传输热量 235
Fourier’s Law and Newton’s Law 236
傅里叶定律和牛顿定律 236
Conduction in Heat Sources 256
热源中的传导 256
Thermal Conductivity and the Kinetic Theory of Gases 267
热导率与气体动理论 267
General Heat Conduction Equation 274
一般热传导方程 274
Conduction of Heat at Steady State in Two Dimensions 278
二维稳态热传导 278
Transport of Heat by Convection 295
对流传热 295
Heat Transfer by Forced Convection from a Horizontal Flat Plate at a Uniform Constant Temperature 295
水平平板在均匀恒定温度 295 下的强制对流热传递
Heat Transfer from a Horizontal Flat Plate with Uniform Heat Flux Along the Plate 315
沿板的均匀热流从水平平板的热传递 315
Heat Transfer During Fluid Flow in Cylindrical Pipes 317
圆管内流体流动中的热传递 317
Energy Balance in Heat Transfer by Convection Between a Cylindrical Pipe and a Flowing Fluid 322
圆柱管与流动流体之间的对流热传递中的能量平衡 322
Heat Transfer by Forced Convection from Horizontal Cylinders 331
水平圆柱体的强制对流热传递 331
Heat Transfer by Forced Convection from a Sphere 334
球体的强制对流热传递 334
General Energy Equation 335
一般能量方程 335
Heat Transfer from a Vertical Plate by Natural Convection 346
通过自然对流从垂直板的热传递 346
xiv Contents
内容
Heat Transfer from Cylinders by Natural Convection 358
通过自然对流从圆柱体的热传递 358
Transient Heat Flow 365
瞬态热流 365
Lumped Capacitance Method; Newtonian Cooling 365
集中电容法；牛顿冷却 365
Non-Newtonian Cooling in Semi-infinite Systems 373
半无限系统中的非牛顿冷却 373
Non-Newtonian Cooling in a One-Dimensional Finite Systems 382
一维有限系统中的非牛顿冷却 382
Non-Newtonian Cooling in a Two-Dimensional Finite Systems 394
二维有限系统中的非牛顿冷却 394
Solidification of Metal Castings 401
金属铸件的固化 401
Heat Transport by Thermal Radiation 421
热辐射传输 421
Intensity and Emissive Power 423
强度和发射功率 423
Blackbody Radiation 427
黑体辐射 427
Absorptivity, Reflectivity, and Transmissivity 436
吸收率、反射率和透射率 436
Kirchho$’s Law and the Hohlraum 437
基尔霍夫定律与霍尔 raum 437
Radiation Exchange Between Surfaces 439
表面之间的辐射交换 439
Radiation Exchange Between Blackbodies 450
黑体之间的辐射交换 450
Radiation Exchange Between Di$use-Gray Surfaces 453
扩散灰表面之间的辐射交换 453
Reradiating Surface 463
重新辐射表面 463
Heat Transfer from a Surface by Convection and Radiation 466
通过对流和辐射从表面传递的热量 466
Mass Transport by Di$usion in the Solid State 476
固态中的扩散质量传输 476
Atomic Di$usion as a Random-Walk Process 476
原子扩散作为随机游走过程 476
Contents
内容 xv
One-Dimensional Non-Steady-State Di$usion in a Solid; Fick ’s Second Law of Di$usion 483
一维非稳态扩散在固体中；菲克第二扩散定律 483
Infinite Di$usion Couple 489
无限扩散耦合 489
One-Dimensional Di$usion in a Semi-infinite System Involving a Change of Phase 491
半无限系统中涉及相变的一维扩散 491
Steady-State Di$usion Through a Composite Wall 498
复合墙的稳态扩散 498
Di$usion in Substitutional Solid Solutions 502
替代固溶体中的扩散 502
Darken’s Analysis 502
Darken 的分析 502
Self-Di$usion Coefficient 506
自扩散系数 506
Measurement of the Interdifussion Coefficient: Boltzmann–Matano Analysis 510
扩散系数的测量：Boltzmann–Matano 分析 510
Influence of Temperature on the Di$usion Coefficient 514
温度对扩散系数的影响 514
Mass Transport in Fluids 522
流体中的质量传输 522
Mass and Molar Fluxes in a Fluid 522
流体中的质量和摩尔通量 522
Equations of Di$usion with Convection in a Binary Mixture A–B 524
二元混合物 A–B 中的扩散与对流方程 524
One-Dimensional Transport in a Binary Mixture of Ideal Gases 527
理想气体二元混合物中的一维传输 527
Equimolar Counterdi$usion 528
等摩尔反向扩散 528
One-Dimensional Steady-State Di$usion of Gas A Through Stationary Gas B 529
气体 A 在静止气体 B 中的一维稳态扩散 529
Sublimation of a Sphere into a Stationary Gas 536
球体在静止气体中的升华 536
Catalytic Surface Reactions 539
催化表面反应 539
Di$usion and Chemical Reaction in Stagnant Film 542
静止薄膜中的扩散和化学反应 542
Mass Transfer at Large Fluxes and Large Concentrations 547
大流量和高浓度下的质量传递 547
Influence of Mass Transport on Heat Transfer in Stagnant Film 550
静止薄膜中质量传输对热传递的影响 550
Di$usion into a Falling Film of Liquid 553
液体下落薄膜中的扩散 553
Di$usion and the Kinetic Theory of Gases 560
扩散与气体的动理论 560
Mass Transfer Coefficient and Concentration Boundary Layer on a Flat Plate 569
平板上的质量传递系数和浓度边界层 569
Approximate Integral Method 573
近似积分法 573
Mass Transfer by Free Convection 583
自由对流的质量传递 583
Simultaneous Heat and Mass Transfer: Evaporate Cooling 586
同时的热量和质量传递：蒸发冷却 586
Chemical Reaction and Mass Transfer: Mixed Control 589
化学反应与质量传递：混合控制 589
Dissolution of Pure Metal A in Liquid B: Mixed Control 593
纯金属 A 在液体 B 中的溶解：混合控制 593
xvi Contents
xvi 目录
Condensation and Boiling 601
凝结与沸腾 601
Dimensionless Parameters in Boiling and Condensation 602
无量纲参数在沸腾和冷凝中的应用 602
Pool Boiling Correlations 606
池沸腾相关性 606
Appendix A Elementary and Derived SI Units
附录 A 基本和衍生 SI 单位
Appendix B Prefixes and Symbols for Multiples and Submultiples of SI Units 617
附录 B SI 单位的倍数和分数的前缀和符号 617
Appendix C Conversion from British and U.S. Units to SI Units 618
附录 C 从英制和美制单位转换为国际单位制 618
Appendix D Properties of Solid Metals 620
附录 D 固体金属的性质 620
Appendix E Properties of Nonmetallic Solids 623
附录 E 非金属固体的性质 623
Appendix F Properties of Gases at 1 Atm Pressure 627
附录 F 1 个大气压下气体的性质 627
Appendix G Properties of Saturated Liquids 635
附录 G 饱和液体的性质 635
Appendix H Properties of Liquid Metals 639
附录 H 液态金属的性质 639
Recommended Readings 642
推荐阅读 642
xvii
十七
xviii List of Symbols
xviii 符号列表
List of Symbols xix
符号列表 xix
xx List of Symbols
xx 符号列表
Condensation and Boiling
凝结与沸腾
Introduction
介绍
Evaporation is a process that occurs when a liquid, maintained at a constant temperature, exerts a partial vapor pressure in the gas phase, in contact with the liquid, which is less than the saturated vapor pressure of the liquid at the same temperature. At any finite temperature, the atoms or molecules in the liquid are in constant motion, vibrating in a cage of adjacent atoms or molecules as a result of the attractive and repulsive forces on the central atom by its neighbors. The magnitude of this agitation, which is determined by the temperature of the liquid, increases with increasing temperature. Thus, the atoms in the layer of liquid in contact with the gas phase can attain increases in energy which are greater than the activation energy required for evaporation, in which case the atom is transferred from the liquid phase to the gas phase. This process, which is called evaporation, continues until, thereby, the partial pressure of the component in the gas phase reaches its saturated vapor pressure at the temperature of interest.
蒸发是一个过程，当液体在恒定温度下，施加于与液体接触的气相中的部分蒸气压小于该温度下液体的饱和蒸气压时，就会发生蒸发。在任何有限温度下，液体中的原子或分子都在不断运动，由于邻近原子或分子对中心原子的吸引和排斥力，导致它们在一个相邻原子或分子的笼子中振动。这种激动的大小由液体的温度决定，随着温度的升高而增加。因此，接触气相的液体层中的原子可以获得超过蒸发所需的活化能的能量，在这种情况下，原子从液相转移到气相。这个被称为蒸发的过程持续进行，直到气相中该组分的部分压力达到其在所关注温度下的饱和蒸气压。
When a liquid is contained in a vessel, its surface tension prevents it from completely filling the invariable imperfections that occur on the inner surface of the vessel. Thus, small pockets of air or nitrogen are trapped in these imperfections, and atoms on the liquid side of the interface, when acquiring an increase in energy greater than the activation energy for evaporation transfer into the trapped bubble. This process continues until the partial pressure of the component in the bubble reaches the saturation pressure. This partial pressure increases with increasing temperature until it reaches the total pressure of the gas in contact with the liquid, which is, by definition, the boiling temperature of the liquid. During the period during which the liquid is being heated, the partial pressure of the component in the trapped bubble increases, as a consequence of which, the volume of the bubble increases. At the boiling
当液体被容器包围时，其表面张力阻止液体完全填充容器内表面上出现的不变缺陷。因此，空气或氮气的小口袋被困在这些缺陷中，当界面液体侧的原子获得的能量增加超过蒸发转移的活化能时，就会转移到被困的气泡中。这个过程持续进行，直到气泡中成分的分压达到饱和压力。随着温度的升高，这个分压增加，直到达到与液体接触的气体的总压力，这在定义上是液体的沸点。在液体加热的过程中，被困气泡中成分的分压增加，因此气泡的体积也增加。 在沸腾时
602 凝结与沸腾
temperature of the liquid, the geometry of the bubble makes it unstable and it detaches from the imperfection and, due the difference between densities of the liquid and vapor phases, rises to the free surface of the liquid where it is ejected into the gas. The decreasing hydrostatic pressure on the rising bubble causes it to increase in volume. When the bubble detaches from the imperfection, the volume of gas in the imperfection decreases, and the growth process begins again. This process is the same as that when a bottle of soft drink, carbonated with CO2 at high pressure, is opened and poured into a drinking glass. The rapid nucleation, growth, and release of the bubbles at the surface imperfections can be seen through the glass. When the liquid is a single component, boiling occurs at a fixed temperature, and the rate of boiling increases with increasing rate of transfer of heat to the liquid.
液体的温度，气泡的几何形状使其不稳定，并且它从缺陷上脱离，由于液相和气相之间的密度差，气泡上升到液体的自由表面，在那里被喷射到气体中。上升气泡上减少的静水压力导致其体积增加。当气泡从缺陷上脱离时，缺陷中的气体体积减少，生长过程再次开始。这个过程与打开高压二氧化碳（CO 2 ）碳酸饮料瓶并倒入饮用杯时的过程相同。通过玻璃可以看到表面缺陷处气泡的快速成核、增长和释放。当液体是单一组分时，沸腾发生在固定温度下，沸腾速率随着传递给液体的热量增加而增加。
Condensation occurs when an atom or molecule in the gas phase strikes the free surface of the liquid and is captured. The individual atoms or molecules in the gas phase have velocities within a spectrum of velocities, the extremes of which are determined by the temperature of the gas and the atomic or molecular weights of particles in the gas. Particles with a high enough velocity, and hence high enough kinetic energy, are captured by the liquid and this process is called condensation. Particles with less than this velocity undergo elastic collisions with the free surface and bounce back into the gas phase. When the partial pressure of the component in the gas phase equals its saturated vapor pressure, the rates of evaporation and condensation are equal and phase equilibrium occurs.
当气相中的原子或分子撞击液体的自由表面并被捕获时，就会发生凝结。气相中的单个原子或分子具有一系列速度，这些速度的极值由气体的温度和气体中粒子的原子或分子量决定。具有足够高速度（因此具有足够高动能）的粒子被液体捕获，这个过程称为凝结。速度低于这个值的粒子与自由表面发生弹性碰撞，并反弹回气相。当气相中组分的分压等于其饱和蒸气压时，蒸发和凝结的速率相等，发生相平衡。
A knowledge of the mechanisms of the transport of heat between a solid surface and the fluid with which it is contact is important in the heat treatment of ferrous alloys. Time-Temperature-Transformation (T-T-T) Diagrams for ferrous alloys show the influence of cooling rates (quenching rates) on the microstructure obtained at room temperature. In the case of plain carbon steels of the eutectoid composition, increasing the cooling rate causes microstructures to vary in the range of coarse pearlite, fine pearlite, upper bainite, lower bainite. If the cooling rate is rapid enough that the variation of temperature with time misses the nose of the T-T-T curve, austenite is retained until the Ms (martensite start) temperature is reached. At this point, with further cooling, the face-centered cubic γ phase transforms, by diffusionless shear, to the body-centered tetragonal martensite phase. This transformation continues until the temperature reaches the Mf (martensite finish) temperature. The change in molar volume accompanying this phase change gives rise to high shear stresses at the phase boundaries, which causes the martensite phase to be brittle. This brittleness is removed by tempering the alloy at a temperature high enough to allow some nucleation and precipitation of cementite from the martensite.
固体表面与其接触的流体之间热量传输机制的知识在铁合金的热处理过程中非常重要。铁合金的时间-温度-转变（T-T-T）图显示了冷却速率（淬火速率）对室温下获得的微观结构的影响。在共析成分的普通碳钢中，增加冷却速率会导致微观结构在粗珠光体、细珠光体、上贝氏体和下贝氏体的范围内变化。如果冷却速率足够快，以至于温度随时间的变化错过了 T-T-T 曲线的鼻部，奥氏体会保持直到达到 Ms（马氏体开始）温度。在这一点上，随着进一步冷却，面心立方γ相通过无扩散剪切转变为体心四方马氏体相。这一转变持续到温度达到 M f （马氏体结束）温度。伴随这一相变的摩尔体积变化在相界面产生高剪切应力，导致马氏体相变得脆弱。 这种脆性通过在足够高的温度下对合金进行回火来消除，以允许一些水泥石的成核和从马氏体中沉淀。
Dimensionless Parameters in Boiling and Condensation
无量纲参数在沸腾和冷凝中
For both the boiling and the condensation processes, the convection coefficient could depend on the difference between the surface and saturation temperatures,
对于沸腾和冷凝过程，传热系数可能依赖于表面温度和饱和温度之间的差异，
Te = Ts Tsat, the body force caused by the difference between the densities of the
T e = T s T sat ，由密度差引起的体力
liquid and vapor phases, g ( ρ1 ρv), the latent heat of evaporation Hevap, the surface
液体和蒸气相，g ( ρ 1 ρ v ), 蒸发潜热 H evap , 表面
Modes of Boiling 603
沸腾的模式 603
tension σ, a characteristic length L and the thermophysical properties of the liquid or vapor, density , molar heat capacity cp, thermal conductivity k and viscosity η; that is,
张力 σ、特征长度 L 和液体或蒸气的热物理性质，密度 、摩尔热容 c p 、热导率 k 和粘度 η；也就是说，
h = h[T, g (ρl – ρv), Hevap , σ, L, ρ, cp, k, η]
Straightforward dimensionless gives the relationship
简单的无量纲给出了关系
(12.1)
hL f ρ g( ρl ρv ) L 3 ,
hL = f [ρ g(ρ - ρ v ) L 3 ,
cp T , ηcp
, g ( ρl
ρv) 2L
(12.2)
k η2
Hevap k
σ
or, defining the dimensionless groups,
或者，定义无量纲组，
Nu
f ρg( ρl ρv ) L3
Ja , Pr, Bo (12.3)
L η 2
The Prandtl number, Pr hcp /k, was defined on p. 298 and the Nusselt number, Nu hL/k, was defined on P. 299. The Jacob number, Ja, which is the ratio of the maximum sensible energy absorbed by the liquid (or vapor) to the latent heat absorbed by the liquid (or vapor) during condensation (or boiling) is given by
普朗特数，Pr hc p /k，在第 298 页定义，努塞尔数，Nu hL/k，在第 299 页定义。雅各布数，Ja，是液体（或蒸气）在凝结（或蒸发）过程中吸收的最大显热与液体（或蒸气）吸收的潜热之比。
Ja
cp (Ts Tsat )
Hevap
(12.4)
and the Bond number, Bo, which is the ratio of the gravitational body force to the surface tension force, is given by
和邦德数 Bo，它是重力体力与表面张力力的比率，表示为
Bo
g ( ρf
ρv )L 2
σ
(12.5)
Modes of Boiling
沸腾的模式
The term boiling is used to describe the process of evaporation at the free surface of a liquid. The modes of boiling are shown graphically on a log-log plot of the variation of the heat flux from the solid surface to the liquid, q"s , with the excess temperature,
“沸腾”一词用于描述液体自由表面上的蒸发过程。沸腾的模式在固体表面到液体的热流量 q" s 与过剩温度的对数-对数图上以图形方式显示。
Te = Ts Tsat, where Ts is the temperature of the surface and Tsat is the temperature
T e = T s T sat ，其中 T s 是表面的温度，T sat 是温度
at which the partial pressure of the component in the gas phase is equal to the saturated vapor pressure. Heat is transferred from solid surface to the liquid according to Newton’s Law as
在气相中该组分的分压等于饱和蒸气压时。根据牛顿定律，热量从固体表面传递到液体。
qs h (Ts
Tsat ) hTe
(12.6)
The process is characterized by the formation of bubbles of vapor, which grow and, subsequently, detach from the surface.
该过程的特点是形成蒸汽气泡，这些气泡不断增大，随后从表面脱离。
The various regimes of boiling are identified in the boiling curve, shown as Fig. 12.1, which is drawn for water at one atmosphere pressure. Eq. (12.6) shows that
沸腾的各种状态在沸腾曲线中被识别，如图 12.1 所示，该图是为在一个大气压下的水绘制的。方程（12.6）显示出
604 Condensation and Boiling
604 凝结与沸腾
Free
免费
Boiling Regimes Nucleate
沸腾状态成核
Transition
过渡
Film
电影
107
convection isolated
对流隔离
jets and columns
喷气机和柱子
106
9”max
P
105
point, 9” min
点，9” 最小
104
∆Te,A ∆Te,B
∆Te,C
∆Te,
103
1
5 10
30
∆Te = Ts – Tsat
120
Centigrade Degrees
摄氏度
1000
FIGURE 12.1 The boiling curve for water at 1 atm.
图 12.1 1 个大气压下水的沸腾曲线。
q"s depends on both the convection coefficient, h, and the excess temperature, Te.
q" s 依赖于对流系数 h 和过剩温度 T e 。
The various boiling regimes are delineated by their values of Te.
各种沸腾状态由它们的 T e 值划分。
Free Convection Boiling
自由对流沸腾
Free convection boiling occurs when Te Te, A ≈ 5 centigrade degrees. In this regime, the amount of vapor in contact with the liquid phase is not enough to cause boiling at the temperature at which the liquid exerts its saturated vapor pressure. As the excess temperature is increased, the formation of bubbles eventually begins, but
自由对流沸腾发生在 T e T e A ≈ 5 摄氏度。在这个状态下，与液相接触的蒸汽量不足以在液体施加其饱和蒸汽压力的温度下引起沸腾。随着过剩温度的增加，气泡的形成最终开始，但
模式 of
的 Boiling
煮沸 605
at temperatures lower than the point A, termed the onset of nucleate boiling, ONB, fluid motion is determined mainly by free convection. According to whether the flow is laminar or turbulent, h varies with Te to the 1/4 or 1/3 power, respectively, in which
在低于点 A 的温度下，称为成核沸腾的开始（ONB），流体运动主要由自然对流决定。根据流动是层流还是湍流，h 分别与ΔT 的 0 次方、1/4 次方或 1/3 次方变化。
case q"s varies with Te to the 5/4 or 4/3 power.
情况 q" s 随着 T e 变化至 5/4 或 4/3 次方。
Nucleate Boiling
成核沸腾
Nucleate boiling occurs in the range Te, A δ Te δ Te, C, where Te, C ≈ 30 centigrade degrees. Two flow regimes exist in this range. At lower temperatures in the region AB, isolated bubbles form at nucleation sites and separate from the surface, which, by causing significant mixing in the fluid adjacent to the surface, substantially increases both h and q"s . Most of the heat exchange is by direct transfer from the surface to the liquid in motion at the surface. As Τe is increased beyond Τe, B, more nucleation sites become active and the consequent increased formation of bubbles causes interference between, and coalescence of, the bubbles. In the region B — C the vapor escapes in columns, which eventually merge into slugs of vapor. Motion of the liquid near the surface is inhibited by interference between the densely populated bubbles. Point P in Fig. 12.1 is a point of inflection on the boiling curve at which h has a maximum value. At this point h begins to decrease with increasing Τe, although q"s , which is the product of h and Τe continues to increase. This situation arises because, for Τe Τe, P the relative increase in Τe exceeds the relative decrease in h. At the point C, however, the further increase in Τe is balanced by the decrease in h. The maximum heat flux, qs, C" = qmax", the critical heat flux, in water at atmospheric pressure exceeds 1 MW/m2. At this point, the amount of vapor formed makes it difficult for the liquid to continuously wet the surface.
核化沸腾发生在范围 T e A δ T e δ T e C ，其中 T e C ≈ 30 摄氏度。这个范围内存在两种流动状态。在 A−B 区域的较低温度下，孤立气泡在成核点形成并从表面分离，这通过在靠近表面的流体中造成显著混合，显著增加了 h 和 q" s 。大部分热交换是通过表面与表面上运动的液体之间的直接传递进行的。当 Τ e 超过 Τ e B 时，更多的成核点变得活跃，随之而来的气泡形成增加导致气泡之间的干扰和合并。在 B — C 区域，蒸汽以柱状形式逃逸，最终合并成蒸汽块。靠近表面的液体运动受到密集气泡之间干扰的抑制。图 12.1 中的点 P 是沸腾曲线上的一个拐点，在该点 h 达到最大值。在这一点上，h 开始随着 Τ e 的增加而减少，尽管 q" s ，即 h 和 Τ e 的乘积继续增加。 这种情况出现是因为，对于 Τ e Τ e P ，Τ e 的相对增加超过了 h 的相对减少。然而，在点 C，Τ e 的进一步增加被 h 的减少所平衡。在大气压力下，水的最大热流量 q s C " = q max "，临界热流量超过 1 MW/m2。在这一点上，形成的蒸汽量使得液体难以持续润湿表面。
Transition boiling
过渡沸腾
The region Τe,C Τe Τe, D, where Τe, D is called, transition boiling, film boiling or partial film boiling. The rate of formation of bubbles is now so rapid that a film of vapor begins to form on the surface. At any point on the surface, conditions may change from film to nucleate boiling, but the fraction of the total surface covered by the film increases with increasing Τe. Because the thermal conductivity of the vapor is much less than that of the liquid, h, and q"s , decrease with increasing Τe .
该区域 Τ e C Τ e Τ e D 被称为过渡沸腾、膜沸腾或部分膜沸腾。气泡的形成速率现在如此迅速，以至于在表面开始形成一层蒸汽膜。在表面的任何一点，条件可能会从膜沸腾变化为成核沸腾，但被膜覆盖的总表面比例随着 Τ e 的增加而增加。由于蒸汽的热导率远低于液体的热导率，h 和 q" s 随着 Τ e 的增加而降低。
Film Boiling
电影沸腾
Film boiling occurs in the range Τe Τe, D. At the point D on the boiling curve, referred to as the Leidenfrost point, the heat flux is a minimum, q"s , = q"min and the surface is completely covered with a film of vapor. Heat transfer from the surface to the liquid occurs by conduction through the vapor.