化工专业英语

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2024年1月22日发(作者：)

Unit1

(1) Chemical Engineering化学工程

Chemical engineering is defined as “…the application of the principles of the physical sciences, together with the principles of

economics and human relations, to fields that pertain directly to processes and process equipment in which matter is treated

to effect a change in state, energy content, or composition „”. 化学工程的定义是：将自然科学原理与经济规律和人际关系一起应用到与工艺或工艺设备直接相关的领域，在这些领域中物料的状态、能量或组成发生变化。

This very vague[veig] definition is intentionally broad and indefinite as to the extent of the field. It is probably as satisfactory a

definition as any practicing chemical engineer would give. It should be noted that considerable emphasis is placed on the

process and process equipment. The work of many chemical engineers would better be called process engineering. 这种极不明确的定义故意夸大或模糊了此领域的范围。可能任何一个有经验的化学工程师都能给出一个令人满意的定义。需要指出的是，强调的重点应放在工艺或工艺设备上。因此，许多化学工程师的工作最好称为过程工程。

The process may be any collection of steps involving changes in chemical composition or involving certain physical changes in

material being prepared, processed, separated, or purified. （这种过程可能是任何步骤的组合， 这些步骤包括要制备的、分离的或提纯的物料的化学组成变化或一定的物理变化。）

The work of many chemical engineers involves choosing the appropriate steps in the appropriate order to formulate a process

for accomplishing a chemical manufacturing operation, a separation, or a purification.（许多化学工程师的工作包括选择合适的步骤，这些步骤按适当的顺序描述完成一个化学生产操作、分离或提纯的过程。）

Since each of the steps constituting a process is subject to variations, the process engineer must also specify the exact

conditions under which each step is to be carried out.（由于组成一个过程的每一步骤都含有变化影响，因此，工艺工程师还必需确定完成每一个步骤的准确条件。）

As the process evolves and equipment must be designed, the work of the chemical engineer merges with that of the

mechanical and civil engineer.由于需要改进工艺并设计设备，化学工程师的工作就与机械工程师和土木工程师的工作紧密结合在一起。

The transfer of primary responsibility from the process engineer to the mechanical[mik] engineer can take place satisfactorily

at various stages of the design, so it is impossible to define a fixed extent to which the responsibility should be called that of a

chemical engineer or a stage at which the mechanical engineer should take over responsibility for equipment.由工艺工程师到机械工程师主要职能的转变，可以在设计的任何阶段很自然地发生，所以很难找出一个特定领域说它是化学工程师的职责，或者找出一个阶段完全由机械工程师负责设备。

At the time the definition quoted above was presented, the physical sciences referred to were primarily chemistry and some

classical[klesikEl] physics. As the understanding of mathematical models of chemical processes advances, the treatment of the

chemistry and physics of the process is expressed in considerably more mathematical form. 上面引用的定义提出时，所说的自然科学主要是指化学和经典物理学。随着人们对数学模型和化学过程理解的不断深入，化学和物理过程的处理则多倾向于数学形式。

Increasing use of thermodynamics, fluid dynamics, and mathematical techniques such as probability and statistics, matrix

manipulation, and complex variables is characteristic of modern chemical engineering practice. 热力学、流体力学和概率与统计、矩阵变换、复变函数等数学技术的日益广泛应用，是现代化学工程实践的特点。

In most processes being carried out on a large scale, however, the chemistry has been previously worked out, and the physical

changes incident to separation and purification of the reaction mixtures demand considerably more study than does the

chemical reaction. 在大规模进行的许多生产过程中，虽然化学过程早已完成，但与反应混合物处理和提纯有关的物理变化需要比化学反应进行更深入的研究。

Frequent application of the principles of physics and of physical chemistry is required in the processing steps that produce

physical changes, such as vaporization, condensation, or crystallization. 在蒸发、冷凝、结晶这些能引起物理变化的过程中，常用到物理和物理化学原理。

As a process evolves into a plant and the work merges with that of mechanical designers, the science of mechanics becomes

increasingly important. 随着某一工艺的工业化和工作与机械设计人员的日益结合，机械科学变得非常重要。

The chemical engineer who specialize in equipment must have thorough and extensive grounding in mechanics of materials.

设备专业的化学工程师必须在物料的机械性能上受过透彻、广泛的训练。

All of an engineer’s work must be quantitative, and mathematics is therefore a fundamental tool of the engineer. 所有工程师的工作必须是定量的，因此，数学是他们的基本工具。

Unfortunately, our understanding of mathematics is largely restricted to the domain of linear mathematics, and, equally

unfortunately, chemical molecules seldom behaved in accordance with linear mathematical rules.但遗憾的是，人们对数学的理解在很大程度上局限于线性代数的领域，然而，化学分子的行为很少符合线性代数的规律。

Energy and material balance calculations, which are fundamental to any process study, can usually be expressed with

confidence and precision in terms of linear mathematics, as long as we omit atomic and nuclear processes from our

considerations.能量和物料衡算，是研究任何过程的基础。当忽略原子和原子核之间的作用时，它们可以根据线性代数用置信度和精确度来表示。

In the economic study to determine the most profitable operating conditions-and in accounting for the sales receipts and

distribution of income to profits and costs, including replacement of the plant-mathematical calculations are universal. 在确定最适宜操作条件的经济评价中，在解释销售收入和收入在效益和支出的分配（包括更换新设备）中，数学计算的应用十分普遍。

The existence or contemplation of a process implies that a material is to be produced for which customers will pay. It must be

delivered in a quantity, of a quality, and at a price which are acceptable to the customer . 一个工艺过程的存在和规划都意味着必须生产某种顾客可以接受的产品，该产品在交货时必须符合一定的数量的质量，且价格也可以被顾客所接受。

Simultaneously, it must pay for materials, labor, and equipment used in the manufacture and return a profit over and above all

cost. 同时，还必须付出原料、劳动力和设备制造的费用，并且在除去所有费用后还要获得利润。

Many materials produced by the chemical industry are planned and plants built before the real market potential has been

developed.化学工业生产的许多产品都是有计划的，工厂在真正的市场潜力形成以前已经建成。

For a completely new product, some estimate of the size of the market must be made, and the plant should be scaled in

proportion. 对一个全新产品而言，必须对市场前景做充分估计，工厂的规模要适当。

The human-relations aspect of engineering practice is not usually emphasized in undergraduate training because of the great

quantity of techniques the student must learn. 因为学生们需要学习大量技术信息和技术，因此，大学期间很少强调工程实践中的人际关系问题。

That this may be a fallacious course is implied by the fact that failures of young engineers because of personnel problems are

at least five times as frequent as failures because of inadequate technical training. 许多年轻的工程师，由于自身原因，缺乏足够的技术训练，在工作中就会频繁出错。这上事实说明，这种课程安排是不合理的。

All engineers must realize that the industry in which they are working requires team effort of all personnel. 所有工程师都应该意识到他们所从事的工作需要所有人共同努力。

Valuable information can be obtained form operators of limited educational background who have observed similar processes.

从文化程度很低但看到过相似工艺的操作工那里，可以得到很有价值的信息。

The person who has “lived” with an operation has probably observed actions and effects and has learned methods of

detailed control that cannot be approached by formal theory alone. （一个在某工段生活多年的人可能观察到了调节动作及其作用，他可能找到了仅仅用理论方法不能达到的精密控制。）

The best engineering job can be done only with proper regard for all available facts regardless of their source .A new process

or the technical improvement of an existing one designed without due regard for the operators is usually destined to failure.

只有正确看待得到的所有事实而不管其来源，才能把技术工作做得更好。一个新工艺或对现有工艺的改进，如果没有充分考虑操作工，通常最终会导致失败。

The star-up of a new plant or the installation of a technical change is likely to be much smoother and the cost of it much less if

the operating personnel understand the objectives and are convinced of their soundness. 如果操作工了解操作对象并得到充分的信任，新工厂的开车或技改时的安装会更加顺利，并且花费更少。

(2) Unit Operations单元操作

Chemical processes may consist of widely varying sequences of steps ,the principles of which are independent of the material

being operated upon and of other characterstics of the particular system. （化工过程包括的各种步骤的顺序变化很大，这些步骤的原理与处理的物料及待定体系的其它性质无关。）

In the design of a process, each step to be used can be studied individually if the step are recognized. Some of the steps are

chemical reactions, whereas others are physical changes. （在工艺设计过程中，每一个考虑到的步骤都将被逐一地研究。这些步骤当中一些是化学反应，另外一些是物理变化。）

The versatility of chemical engineering originates in training to the practice of breaking up a complex process into individual

physical steps, called unit operations, and into the chemical reactions. （化学工程的通用性使人们在实际工作中可把复杂的过程分为单个的物理步骤（称单元操作）和化学反应。）

The unit-operations concept in chemical engineering is based on the philosophy that the widely varying sequences of steps

can be reduced to simple operations or reactions, hich are indentical in fundamentals regardless of the material being

processed. This principle, which became obvious to the pioneers during the development of chemical industry, was first clearly

presented by in 1995:化学工程的的单元操作概念是基于以下观点提出的：这些变化很大的步骤可以简化为简单的操作或反应，如果不考虑被处理的物料，它们在基本原理上也是相同的。这些在化学工业发展中被先驱们所承认的原理，是由A.D. Little在1915年首先提出的。

“Any chemical process, on whatever scale conducted, may be resolved into a coordinated series of what may be termed’unit

actions’, as pulverizing,mixing,heating,roasting,absorbing,condesing,lixiviating, precipitating, crystallizing, filtering, dissolving,

electrolyzing and so on .The number of these basic unit operations is not very large and relatively few of them are involved in

any particular process.任何化学过程，无论其规模如何，都可以归结为一系列称为单元效应的相互配合的步骤，例如：粉碎、混合、加热、焙烧、吸收、冷凝、浸出、沉淀、结晶、过滤、溶解和电解等。这些基本单元操作的数量并不是很大，并且在一个特定过程中所涉及到的单元操作也不多。

The complexity of chemical engineering result from the variety of conditions as to temperature, pressure, etc., under which

the unit actions must be carried out in different processes and from the limitations as materials of construction and chemical

character of the reacting substance.（化学工程的复杂性起因于下列两点：１）温度压力等条件的多样性，而不同过程中的单元操作必然是在这种差异很大的条件下实现的；２）受到设备设计和建造材料的限制，而选用设备和材料又受制于反应物质的物理和化学性质。）

The original listing of the unit operations quoted above names twelve actions, not all of which are considered unit operations.

Additional ones have been designated since then, at a modest rate over the years but recently at an accelerating rate .Fluid

flow, heat transfer, distillation, humidification, gas absorption, sedimentation, classification, agitation, and centrifugation have

long been recognized.上面引用的最初列出的“单元操作”只能称为十二种操作，但并不是所有都称为单元操作。从那以后，人们又陆续提出了一些新的单元操作，而近几年提出的速度又有所增加。流体的流动、热传递、精馏、增湿、气体吸收、沉积、分级、搅拌和离心分离等都已被承认。

In recent years increasing understanding of new techniques- and adaptation of old but seldom used separative techniques-has

led to a continually increasing number of separations, processing operations, or steps in a manufacture that could be used

without significant alteration in a variety of processes. 最近几年，随着对新技术认识的增加和对很少用的过时的分离技术的重新归类，导致了分离、加工操作和生产中不能用其它有效操作代替的步骤增加。

This is the basis of a terminology of ‘unit operations’, which now offers us a list of techniques, all of which cannot be covered

in a reasonable text.这是术语“单元操作”提出的基础，它所包括的一系列技术即使在较好的教科书中也不能全部包含。

Very frequently chemical changes occur in a material being distilled or heated .In such cases the physical operation is the

primary concern, and if a chemical change occurs simultaneously, it is commonly handled by a modification of the physical of

the material. When chemical rate and equilibria are known, these may be mathematically modeled into the unit operation

calculations.物料被蒸馏或加热时，常发生化学变化。此时首先应关心的是物理操作，如果化学变化同时发生，通常通过修正物料的物理性质进行处理。如果化学反应速度和化学平衡已知，就可以用数学模型对单元操作进行计算。

The typical chemical manufacturing operation involves a few chemical steps that are probably straightforward and well

understood .Extensive equipment and operations are usually needed for refining or further preparing the often complex

mixture for use as an end product. The result is that the work of the typical process engineer is much more concerned with

physical changes than with chemical reactions .典型的化工生产操作包含一些简单并且容易理解的化学步骤。对复杂混合物的提纯或进一步制备成终产品的过程，通常需要大量设备和操作。结果导致典型的过程工程师的工作设计的物理变化比化学反应还要多。

The importance of the chemical reactions must not be overlooked because of the economic importance of small

improvements in percentage yield from chemical reactions .但是，由于化学反应过程中即使百分收率增加很小，也会对经济效益产生很大的影响，因此它的重要性并不能被忽视。

In many cases a relatively small percentage improvement in yield may economically justify considerably more extensive

processing operations and equipment.（许多情况下，一个很小的百分产率的提高可能会引起在经济上对更大范围的过程操作和设备进行调整。）

All unit operations are based upon principles of science that are translated into industrial applications in various fields of

engineering. The flow of fluids, for instance, has been studied extensively in theory under the name of hydrodynamics or fluid

mechanics. It has been important part of the work of civil engineers under the name of hydraulics and is of major importance

in sanitary engineering .problems of water supply and control have been met by every civilization.所有单元操作依据的是在工程的各个领域可能转化为工业应用的科学原理。例如，流体的流动，已经在流体动力学和流体力学两个方面进行了广泛的理论研究。水力学一直是土木工程师很重要的一部分工作，并且在排水工程中也非常重要。每个社会都会在给排水中遇到问题。

Heat transfer has been the subject of many theoretical investigations by physicists and mathematicians; it has played a major

part in the generation of power from fuels, as developed by mechanical engineers. Dissipation of heat in electrical equipment

is a major limitation on the power output of such machinery. Pyrometallurgy and the heat treatment of materials of

construction and tools represent additional major applications.传热是物理学家和数学家进行广泛理论研究的课题，随着机

械工程师的更深入开发，使得它在火力发电厂中起到了主导的作用，电厂的输出功率主要取决于发电设备中的热消耗。高温冶金和结构与工具材料的热处理是另一具有代表性的应用。

Throughout industry, one finds examples of most of the unit operations on applications that are in the province of other

engineering fields.（纵观整个工业，人们可以找到这样的例子；大部分应用中的单元操作也应用于其它工程领域。）

The chemical engineer must carry out many unit operations on materials of widely varying physical and chemical properties

under extremes of conditions such as temperature and pressure.化学工程师必须在温度和压力差异很大的条件下，对物理和化学性质变化很大的物料进行许多单元操作。

The unit operations used to separate mixtures into more or less pure substances are unique to chemical engineering. 将混合物分成更多或更少纯净物质的单元操作只有化学工程师才会遇到。

The materials being processed may be naturally occurring mixture or they may be the products of chemical reactions, which

virtually never yield a pure substance.（处理的物料可能是天然的混合物，或是化学反应的产物，化学反应实际上根本不能得到纯的物质。）

Unit 2 (1)Flow of Fluids

The chemical engineer is interested in many aspects of the problems involved in the flow of fluids. In the first place, in

common with many other engineers, he is concerned with the transport of fluids from one location to another through pipes

or open ducts；This requires determination of the pressure drops in the system, and hence of the power required for pumping,

selection of the most suitable type of pump, and measurement of the flow rates.化学工程师对涉及流体流动问题的许多方面很感兴趣。首先，与其他工程师一样，会遇到利用管道或明渠将流体从一个地方输送到另一个地方的问题。这就需要确定系统的压降和输送所需的功率、选择泵的适宜型号并确定流速。

In many cases, the fluid contains solid particles in suspension and it is necessary to determine the effect of these particles on

the flow characteristics of the fluid or, alternatively（做为选择, 二者择一地）, the drag force exerted（外露的） by the fluid

on the particles. 在大多数情况下，流体中含有悬浮的固体颗粒，这就必须确定这些颗粒对流体流动特性的影响或流体对这些颗粒所产生的阻力。

In some cases, such as filtration（过滤筛选）, the particles are in the form of a fairly stable bed（河床、基层） and the fluid

has to pass through the tortuous（曲折的） channels formed by the pore spaces（孔隙）,有时，例如过滤，颗粒呈固定床的状态，流体必须通过由孔隙组成的曲折迂回的通道。

In other cases the shape of the boundary surfaces must be so arranged that a particular flow pattern is obtained: for example,

when solids are maintained in suspension in a liquid by means of agitation, the desired effect can be obtained with the

minimum expenditure（支出, 花费） of energy if the most suitable flow pattern is produced in the fluid. （在另外一些情况下 ，必须调整边界表面的形状而得到特定的流动形式，例如，当通过搅拌使固体悬浮在液体中时，如果流体中产生了最合适的流动形式，就可以用最小的能量消耗而得到所需的结果。）

Further, in those processes where heat transfer or mass transfer to a flowing fluid occurs, the nature of the flow may have a

profound（深刻的） effect on the transfer coefficient for the process.另外，在对某一流体进行热量或质量传递的过程中，流体的性质对整个过程的传递系数会产生很大的影响。

When a fluid flow through a duct or over a surface, the velocity over a plane（剖面） at right angels （直角）to the stream is

not normally uniform（统一，一致） ,the variation of velocity can be shown by the use of streamlines which are lines so drawn

that the velocity vector is always tangential to them . 当流体流过管道或某一表面时，垂直于流向方向的某一平面处的流速通常是不同的，速度的变化可以用流线表示，流线是速度矢量与其相切的直线。

The flow rate between any two streamlines is always the same. Constant velocity over a cross-section(横断面) is shown by

equidistant streamlines and an increase in velocity by closer spacing of the streamlines.任意两条流线间的流速总是相同的的。某一横截面上的相同流速可以用等距流线来表示，流速增加靠减小流线间的距离来表示。

There are two principal types of flow which will be discussed in detail later, namely（即，也就是） streamlines（流线型的）

and turbulent（狂暴的, 吵闹的） flow . 下面我们将详细讨论两种流型，即层流和湍流。

In streamlines flow, movement across streamlines occurs solely as the result of diffusion （扩散）on a molecular scale and the

flow rate is steady, In turbulent flow ，the presence（存在） of circulating （循环）currents results in transference of fluid on

a large scale, and cyclic fluctuations （波动）occur in the flow rate , though the time-average rate remains constant.在层流中，只是分子规模的扩散才会产生穿过流线的运动，流速是稳定的。而对于湍流，环流的存在导致了流体大规模地传递尽管平均流速不变，但流速出现周期性波动。

When a fluid flows from one location to another, energy will, in general, be converted from one form to another . 当流体从一个位置留到另一个位置，能量也会从 一形式变到另一种形式。

The energy which is attributable to（可归于„的） the physical state of the fluid is known as internal energy ; it is arbitrarily（任意的） taken as zero at some reference state, such as the absolute zero of temperature or the melting point of ice at

atmospheric pressure. 当流体由一处流向另一处时，一般而言，能量要从一种形式转变成另一种形式。由流体的物理状态所决定的能量称为内能，它可以任取某一参考态作为零点，例如温度的绝对零度或冰在常压下的熔点。

A change in the physical state of a fluid will, in general cause an alteration in the internal energy.通常说来，流体物理状态的变化将导致内能的改变。

An elementary reversible change results from an infinitesimal change in one of the intensive factors acting on the system; the

change proceeds at an infinitesimal rate and a small change in the intensive factor in the opposite direction would have caused

the process to take place in the reverse direction .（一个强度因素对体系作用的微小变化可引起一个微小的可逆变化，这个变化以微小的速度进行，强度因素在反方向的微小变化就会使这个过程犯方向进行。）

truly reversible changes never occur in practice but they provide a useful standard with which actual processes can be

compared.（当然，实际上不可能发生真正的可逆变化，但这提供了一个实际过程可与之相比较的游泳标准。）

In an irreversible（不可取消的） process, changes are caused by a finite difference in the intensive factor（主要因素） and

take place at a finite rate,对不可逆过程，变化是由强度性质的有限差引起的，并且以有限的速度进行。

In general the process will be accompanied by the conversion of electrical or mechanical energy into heat, or the reduction of

the temperature difference between different parts of the system.一般而言，这些过程中常伴有电能到机械能或热能的转化，或系统中不同部分间温差的减小。

In the process industries（流程工业：化工，石油，冶金等工业）

it is often necessary to pump fluids over long distances from storage to reactor units, and there may be a substantial （物质的，丰富的，大量的）drop in pressure in both the pipeline and in the individual units themselves. 在加工工业中，经常需要从贮槽到反应器单元长距离输送流体，无论是在管线还是每个单元中，都会产物显著的压降。

Many intermediate（中间） products are pumped from one factory site to another,and raw materials such as natural gas and

petroleum（石油） products may be pumped very long distances to domestic（国内的，驯服的） or industrial consumers.许多中间产物需要从工厂的一处输送到另一处，天然气和石油产品等这些原材料，需要经过很长距离输送到用户家中或工厂中。

It is necessary , therefore , to consider the problems concerned with calculating the power requirements for pumping , with

designing the most suitable flow system , with estimating the most economical sizes of pipes , with measuring the rate of flow ,

and frequently with controlling this flow at a steady rate .因此，必须考虑所涉及的以下问题：计算泵所需的功率，设计最

适宜的流动系统，估计管道最经济的尺寸，测量流速并控制其稳定。

The flow may take place at high pressure, for instance when nitrogen（氮） and hydrogen（氢） flow to an ammonia ynthesis

plant（合成氨）, or at low pressures when, for example, vapor （水蒸气）leaves the top of a vacuum distillation plant（真空蒸馏塔）. 流动可能在高压下进行，例如氮和氢流入氨合成塔中，也可能在低压下进行，如蒸汽离开真空精馏塔的顶部。

The fluid may consist of one or more phases, it may contain suspended solids, it may be near its boiling point, and it may have

non-Newtonian properties, all of which complicate the analysis.流体可能含有一相或几相，可能含有悬浮固体，可能接近沸点，也可能具有非牛顿性质，所有这些将使分析复杂化。

The design and layout of pipe systems is an important factor in the planning of modern plants and may represent a significant

part of the total cost.现代工厂中管道系统的设计和布置是一个很重要的因素，它在总费用中占很大的比重。

Chemical engineering design frequently concerns equipment for the transfer of material or heat from one phase to another,

and, in order to understand the mechanism of the transport process, the flow pattern of the fluid, and particularly the

distribution of velocity near a surface, must be studied. （化工设计通常考虑的是从一个相到另一个相的传质或传热设备；为了理解传递过程的机理，必需研究流体的流动形式，特别是靠近表面的速度分布。）

It must be realized that when a fluid is flowing over a surface or through a pipe , the velocity at various points in a right

angles（直角） to the stream is rarely uniform , And the rate of change of velocity with distance from the surface will exert（施加） a influence on the resistance to flow and on the rate of mass or heat transfer. 必须注意的是，当流体流过某一表面或管道时，与流体流向垂直方向上各点的速度通常是不同的，流速随距表面距离变化的速率将对流动阻力产生很大影响，并将影响传质和传热的速度。

Unit2-2

(2)Pumping of Fluids

For the pumping（动词 抽取，汲取） of liquids or gases from one vessel to another or through long pipes, some form of

mechanical pump is usually employed（雇佣，采用） .对于从一个容器到另一个容器或通过长的管道输送液体或气体，通常需要采用某种形式的机械泵。

The energy required by the pump will depend on the height through which the fluid is raised, the pressure required on

delivery, the length and diameter of the pipe, the rate of flow ,together with the physical properties of the fluid, particularly its

viscosity and density .泵所需的能量取决于流体被提升的高度、需要输出的压力、管道的长度与直径以及流速和流体的物理性质，尤其是它的粘度和密度。

The pumping（动名词） of liquids such as sulphuric acid or petroleum products like benzene or naphtha from bulk store to

process buildings, or the pumping of fluids round reaction units and through heat exchangers, are typical illustrations of the

use of pumps.例如从原料库向生产装置中输送硫酸或苯和石脑油等这些石油产品，或使流体在反应单元或热交换器之间流动，这些都是使用泵的典型例子。

The pumping of crude oil or natural gas over long distances, or of fluids from one section of a works to another, are further

example .远距离输送石油或天然气，或从工厂的一个工段向另一个工段输送流体，是另外的例子。

On the one hand , it may be necessary to inject（注入，用的好表示精确） reactants or catalyst into a reactor at a low but

accurately controlled rate and on the other to pump cooling water to power station or refinery at a very high rate. 一方面，必须以缓慢但准确控制的速度向反应器注入反应物或催化剂，而另一方面要高速向发电厂或炼油厂输送冷却水。

The fluid may be a gas or liquid of low viscosity, or it may be a highly viscous liquid, possibly with non-Newtonian

characteristics. It may be clear or it may contain suspended particles and be very corrosive . All these factors influence the

choice of pump. 流体可能是低粘度的气体或液体，或是高粘度的液体，也可能具有非牛顿性质，可能是清澈的，也可能含有悬浮颗粒，并具有强腐蚀性，所有这些将影响到泵的选择。

Pump design and construction is a specialist field , and manufacturers should always be consulted. 泵的设计和结构是一个非常专业的领域，顾客经常就此请教制造商。

In general pumps used for circulating gases work at higher speeds than those used for liquids, and lighter valves are used .一般说来，使输送气体的泵要比输送液体的泵转速要高，可以用较轻一些的阀门。

Moreover , the clearances（间隙） between moving parts are smaller on gas pumps because of the much lower viscosity of

gases, giving rise to （导致）an increased tendency for leakage to occur.而且因为气体的粘度很小，产生泄漏的可能性增大，因此气泵运动部件间的间隙应更小。

When a pump is used to provide a vacuum, it is even more important to guard against leakage.当泵用来产生真空时，预防泄漏就更加重要。

The work done by the pump is found by setting up an energy balance equation. If Ws is the shaft work done by unit mass of

fluid on the surroundings, then-Ws is the shaft work done on the fluid by the pump. 通过建立能量平衡方程方程就可以得到泵所做的功。如果Ws是单位质量流体对环境所做的轴功，那么－Ws就是泵对流体所做的轴功。

In any practical system,the pump will not be 100 percent efficient, and more energy must be supplied by the motor driving the

pump than is given by-Ws. 在任何实际系统中，泵的效率都不可能达到100%，驱动泵的电机必须提供比－Ws更多的能量。

If liquids are considered to be incompressible, there is no change in specific volume from the inlet to the delivery side of the

pump. 如果液体可以看作是不可压缩的，从泵的入口到出口，它的比容就没有变化。

The physical properties of gases are, however, considerably influenced by the pressure, and the work done in raising the

pressure of a gas is influenced by rate heat flow between the gas and the surroundings.便是，气体的物理性质受压力的影响很大，提高气体压力所做的功，受气体与环境间热传递的速率影响。

Thus if the process is carried out adiabatically（绝热） all the energy added to the system appears in the gas and its

temperature rises. 因此，如果整个过程在绝热的条件下进行，那么加到系统中的能量会以热能的形式存在于系统中，气体的温度会上升。

If an ideal gas is compressed and then cooled to its initial temperature, its enthalpy(焓) will be unchanged and the whole of

the energy supplied by the compressor is dissipated to the surroundings.如果压缩理想气体，然后冷却到它的初始温度，它的焓不变，压缩机提供的全部能量将分散到环境中。

However, if the compressed gas is allowed to expand it will absorb heat and is therefore capable of doing work at the expense（以..为代价） of heat energy from the surroundings.但是，如果让压缩后的气体膨胀，它将从周围环境吸收的热量，并且能够利用这些能量做功。

As already indicated, the liquids used in the chemical industries differ considerably in physical and chemical properties, and it

has been necessary to develop a wide variety of pumping equipment.正如已经提到的，化学工业中所用的液体在物理和化学性质上存在很大的差别，因此需要开发大量输送设备。

The two main forms are the positive displacement type and the centrifugal pumps. 其中的两种主要类型是正位移泵和离心泵。

In the former,（前者） the volume of liquid delivered is directly related to the displacement of the piston element and

therefore increases directly with speed and is not appreciably influenced by the pressure. 对于前者，输出液体的体积与活塞的位移直接相关，因此随活塞速度的增加而增加，且几乎不受压力的影响。

In this group are the reciprocating piston pump and the rotary-gear pump, both of which are commonly used for delivery rates

are required.这一类型主要有往复活塞泵和旋转齿轮泵，它们通常用在高压并要求流量相对稳定的情况下。

The centrifugal type depends on giving the liquid a high kinetic energy which is then converted as efficiently as possible into

pressure energy. 离心式泵是靠给液体一个高的动能，然后使它尽可能转化为压力能。

For some applications such as the handling of liquids which are particularly corrosive or contain abrasive solids in suspension,

compressed air is used as the motive force instead of a mechanical pump. 在输送强腐蚀性液体或含有悬浮的具有磨损性固体的液体时，常用压缩空气代替机械泵作为动力。

An illustration of the use of this form of equipment is the blowing of the contents of a reaction mixture from one vessel to

another.应用这种设备的一个例子是把反应混合物从一个容器压到另一个容器。

The following factors influence the choice of pump for a particular operation.对一个特定的操作，下列因素将影响泵的选择：

The quantity of liquid to be handled. This primarily affects the size of the pump and determines whether it is desirable to use a

number of pumps in parallel.要输送的流体质量。这主要影响泵的尺寸，并决定是否需要一系列泵并联使用。

The head against which the liquid is to be pumped. This will be determined by the difference iv pressure and vertical height of

the downstream and upstream reservoirs and by the frictional losses which occur iv the delivery line. The suitability of a

centrifugal pump and the number of stages required will largely be determined by this factor.输送流体所需抵抗的压头。这将取决于上游和下游容器的压差和垂直高度，也取决于输送管线的摩擦损失。能否采用离心泵以及所需要的级数主要由此因素决定。

The nature of the liquid to be pumped. For a given throughput the viscosity largely determines the friction losses and hence

the power required. The corrosive nature will determine the material of construction both for the pump and the packing. With

suspensions. The clearances in the pump must be large compared with the size of the particles.被输送液体的性质。对某一给定流量，粘度在很大程度上决定了摩擦损失的大小，从而影响到所需的功率。而泵和密封件的结构材料取决于液体的腐蚀性，对于悬浮液，泵的间隙应该大于 颗粒尺寸。

The nature of the power supply. If the pump is driven by an electric motor or internal combustion engine, a high-speed

centrifugal or rotary pump will be preferred as it can be coupled directly to the motor. Simple reciprocating pumps can be

connected to steam or gas engines.能量提供的方式。如果泵靠电动机或内燃机驱动，最好选用高速离心或旋转泵，因为它们可以直接和发动机相配合。简单的往复泵可以和蒸汽或气体发动机相连。

If the pump is used only intermittently corrosion troubles are more likely than with continuous working.如果泵只是间歇的使用那么可能会产生比连续使用更多的麻烦。

The cost and mechanical efficiency of the pump must always be considered, and it may be advantageous to select a cheap

pump and pay higher replacement or maintenance costs rather than （而不是）to install a very expensive pump of high

efficiency.泵的投资和机械效率通常也是需要考虑的。选择较便宜的泵而花较高的维修保养费用比选用价格昂贵、效率高的泵要划算。

Essentially the same basic types of mechanical equipment are used for handling gases and liquids though the construction

may be very different in the two cases. 尽管这两种形式的机械泵在结构上存在很大差别，便输送气体或液体时基本上都是选用这两种类型。

Under the normal range of operating pressures， The density of a gas is considerably less than that of a liquid so that higher

speeds of operation can be employed and lighter valves fitted to the delivery and suction lines. 在一般操作压力下，气体的密度比液体小的多，因此，操作速度可能高些，输入输出管线上可以采用较轻一些的阀门。

Because of the lower viscosity of a gas there is a greater tendency for leakage to occur， and therefore gas compressors are

designed with smaller clearance between the moving parts，Further difference in construction are necessitated by the

decrease in volume of gas as it is compressed， and this must be allowed for in the design.由于气体的粘度较低，产生泄露的机会就会加大，因此设计气体压缩机时要减小转动部件间的间隙。结构上的不同也是由于气体压缩时体积减小所决定的，这在设计时就应该考虑到。

Since a large proportion of the energy of compression appears as heat in the gas , there will normally be a considerable

increase in temperature which may limit the operation of the compressor unless suitable cooling can be effected.由于有很大一部分压缩的能量被转换成气体的热能，因此必须采用合适的冷却手段否则气体温度的上升降会限制压缩机的操作条件。

For this reason gas compression is often carried out in a number of stages and gas is cooled between each stage.如果没有合适的冷却装置，将会影响压缩机的操作。正是由于这个原因，气体的压缩常常分几段进行，在每一段间气体会被冷却。

Any gas which is not expelled from the cylinder at the end of compression (the clearance volume)must be expanded again to

the inlet pressure before a fresh charge（装料） can be admitted （接受）.压缩结束后，没有从气缸排出的气体（空隙体积）在新鲜气体进入前必须肿胀到进口压力。

This continual compression and expansion of the residual gas results in loss of efficiency because neither the compression nor

the expansion can be carried out completely reversibility . 由于压缩和膨胀都不可能是完全可逆的，因此这种剩余气体的连续膨胀和压缩会导致效率的降低。

With liquids this factor has no effect on the efficiency because the residual fluid is not compressed.对于液体，因为剩余液体不再被压缩，这种因素对效率几乎没有影响。

Unit 3 (1) the boundary layer边界层

When a fluid flows over a solid surface a velocity gradient is set up at right angles to the direction of flow because of the

viscous forces acting within the fluid. The fluid in contact with the surface must necessarily be brought to rest since, otherwise,

the velocity gradient and the shear stress at the surface would be infinite.流体流过固体表面时，由于流体内部存在粘滞力，在垂直于流动方向上将会形成速度梯度。与表面接触的流体会趋于静止，也就是说，表面处的速度梯度和剪应力趋于无穷大。

The drag force resulting from the retardation of the fluid at the surface is transmitted throughout the whole of the fluid and

therefore the velocity gradient also extends through the whole of the fluid.由表面液体的阻滞作用产生的阻力的传递贯穿全部液体，因此速度梯度也贯穿液体的全部。

At progressively greater distances from the surface, however, the effect of the drag becomes smaller and, for all practical

purposes, can be regarded as being confined to a region close to the surface and known as the boundary layer. 然而随着与固体表面距离的增大,阻力的影响变得更小, 实际上,靠近表面有限的一个区域称为边界层。

The whole of the velocity gradient is thus assumed to lie within the boundary layer and, outside it, the velocity is assumed to

remain constant. 整个速度梯度假设位于在边界层以内,在它外面，速度假设保持不变。

The thickness of the boundary layer will be a function of the distance from the leading edge of the surface. 边界层的厚度是距表面前缘距离的函数。

Since the viscous drag of the fluid can be transmitted only at a finite rate, the boundary layer thickness will be zero at the

leading edge and gradually increase as the distance from the leading edge increase.由于液体的粘滞阻力仅能以有限速率传递,在前缘边界层的厚度是零并且随着与前缘距离的增大逐渐地增大。

In any plane at right angles to the direction of flow, however, the velocity within the boundary layer will vary from zero at the

surface to us, the velocity of the undisturbed stream, at its outer edge. Where the boundary layer thickness is small, the flow

is streamline and the velocity at any distance from the surface is a simple function of that distance. 然而在垂直于流动方向的任何平面上，边界层内的速度会从零（表面处）变到us（外缘未扰动的流体速度）。当边界层厚度较小时，流动呈层流状态，某一点处的速度是与表面间距离的简单函数。

At a certain critical thickness, however, the flowchanges from streamline to turbulent, except within a very thin layer near the

surface, where it remains streamline: this thin layer is known as the laminar sub-layer. 在某个批评的厚，然而,flowchanges从流线型到狂暴,除了在在表面附近的很薄的层以内，它在哪儿留下流线型:作为层的附属层这薄层被知道。

Between the laminar sub-layer and the turbulent portion of the boundary layer is a region in which the flow is neither

streamline nor fully turbulent; this is known as the buffer layer. 在边界的层的附属层和狂暴的部分之间层是流动在其的一个区域既不流线型也不充分狂暴;作为缓冲区层这被知道。

The change from streamline to turbulent conditions the boundary layer occurs at a certain critical distance from the leading

edge. 变化从流线型在某个批评的距离从前缘层发生的边界到狂暴的条件。

This distance depends on the shape of the leading edge and the roughness of the surface, and also on the velocity and

properties of the fluid: thus with a rough surface or a blunt edge it is comparatively short. 这距离表面上依靠前缘和粗糙的形状,和在液体的速率和属上:与粗糙的表面或一个钝边它这样是相当地短的。

For a given surface the transition takes place at some critical value of the Reynolds group with respect to distance x from the

leading edge. 在雷纳兹团体的一些批评的价值关于距离x从前缘为给定的表面转换发生。

This Reynolds group will be denoted by the symbol Rex and its critical value at a distance xc from the leading edge by the

symbol Rexc; Rexc is of the order of 105. 这个雷纳兹团体将被标志雷克斯和它的批评的价值隔开一段距离指示从由标志Rexc的前缘的xc;Rexc数量级为105。

unit3-2 (2)Humidification and Water Cooling增湿和水冷

In the processing of materials it is often necessary either to increase the amount of vapour present in a gas stream an

operation know as humidification, or to reduce the vapour present, a process referred to as dehumidification. 在材料加工过程中，有时需要增加气流中的水汽含量，这就是所谓的增湿操作，而有时需要减小水汽含量，这类操作称为除湿。

In humidification, the vapour content can be increased by passing the gas over a liquid which then evaporates into the gas

stream. 在增湿操作中，可以使气体流过液体表面，液体蒸发至汽体中使蒸汽含量增加。

This transfer into main stream takes place by diffusion, and at the interface simultaneous transfer of heat and mass takes place

according to the relations developed in previous units. （这种朝汽流主体的传质是通过扩散进行的，而在气液界面处，按前面单元中建立的关系，同时进行热量和质量的传递。）

In the reverse operation, that is dehumidification, partial condensation must be effected and the condensed vapour removed.（在与之相反的操作中，也就是除湿过程中，必须进行部分冷凝，而且要除去冷凝的蒸汽。）

The most widespread application of humidification and dehumidification operations involves the air-water system, and a

discussion of this forms the greater part of the present unit.增湿和除温最广泛的应用在于空气－水系统，关于此问题的讨论占了本单元的一大部分。

although the drying of wet solids is an example of a humidification operation, the reduction of the moisture content of the

solids is the main aim and the humidification of the air stream is a secondary effect.尽管潮湿固体的烘干是增湿操作的一个例子，固体湿气含量的减少是主要目的，而气流的增湿是次要作用。）

Much of the present unit is, however, of vital significance in any drying operation. Air conditioning and gas drying involve

humidification and dehumidification operations. 同时，本单元的大部分问题在干燥操作中也是非常重要的。空气调节和气体干燥操作中也包含增湿和除湿操作。For example, moisture must be removed from wet chlorine so that the gas can be

handled in steel equipment which would otherwise be severely corroded. 例如，湿分必须从湿氯气中除掉，这样才可以将它贮存在钢制容器中，否则会发生严重的腐蚀。

Similarly, the gases used in the manufacture of sulphuric acid must be dried or dehumidified before they enter the converters,

and this is achieved by passing the gas through a dehydrating agent such as sulphuric acid, in essence an absorption operation,

or by an alternative dehumidification process.（同样，硫酸生产中的气体在进入转化炉前必需干燥或除湿，这可以使气体通过象硫酸这样的脱水剂来实现（其实是吸收操作），或采用其它的减湿操作。）

In order that hot condenser water may be returned to the plant, it is normally cooled in contact with an air stream. 为使冷凝水返回装置中，通常采用空气流进行冷却。

The equipment usually takes the form of a tower in which the hot water is run in at the top and allowed to flow downwards

over a packing against a counter-current flow of air which enters at the bottom of the cooling tower. （这种设备通常采用塔式，热水从塔顶进入，向下经过填料，在塔内与从冷却塔底加入的逆向流动的空气接触。）

The design of such towers forms an important part of the present unit, though at the outset it is necessary to consider basic

definitions of the various quantities involved in humidification, in particular wet-bulb and adiabatic saturation temperatures,

and the way in which humidity data can be presented on charts and graphs. 这种冷却塔的设计是本单元的重要部分。但在开始时必须考虑增温过程中的各种量的基础数据，尤其是湿球温度和绝热饱和温度以及湿度以图表表示的方式。

While the present discussion is devoted to the very important air-water system, which is in some ways unique, the same

principles can be applied to other liquids and gases. 而目前我们的讨论将集中在非常重要的空气－水系统，尽管在某些方面它具有特殊性，但其相似的原理可以应用到其它气－液系统中。

Dehumidification of air can be effected by bringing it into contact with a cold surface, either liquid or solid. If the temperature

of the surface is lower than the dew point of the gas, condensation takes place and the temperature of the gas falls. 空气的除湿可以通过让它与冷的液体或固体表面而实现。如果此表面的温度低于气体的露点，就会发生冷凝现象且气体的温度会降低。

The temperature of the surface tends to rise because of the transfer of latent and sensible heat from the air.（由于空气中潜热和显热的传递界面温度会升高。）

It would be expected that the air would cool at constant humidity until the dew point was reached, and that subsequent

cooling would be accompanied by condensation. （可以预计， 空气在恒定的湿度下冷却直至到达露点，进一步冷却将会产生冷凝。）

It is found, in practice, that this occurs only when the air is well mixed. 在实际应用中发现，这种情况只有在空气混合良好的情况下才会出现。

Normally the temperature and humidity are reduced simultaneously throughout the whole of the process.通常情况下，温度和湿度在整个过程中会同时降低。

The air in contact with the surface is cooled below its dew point, and condensation of vapour therefore occurs before the

more distant air has time to cool. （和界面接触的空气冷却到露点以下，因此，在远处空气还没有时间冷却蒸汽就冷凝了。）

Where the gas stream is cooled by cold water, countercurrent flow should be employed because the temperature of the water

and air are changing in opposite directions.当用水冷却空气流时，由于水和空气温度的变化方向相反，因此最好采用逆流操作。

The humidity can be reduced by compressing air, allowing it to cool again to its original temperature, and draining off the

water which has condensed. 空气的除湿也可以靠压缩实现，压缩后再将其冷却到初始温度，并排出冷凝水。

During compression, the partial pressure of the vapour is increased and condensation takes place as soon as it reaches the

saturation value. （在压缩过程中水蒸汽的分压增加，当达到饱和蒸汽压时就发生冷凝。）

Thus, if air is compressed to a high pressure, it becomes saturated with vapour, but the partial pressure is a small proportion of

the total pressure. 因此，如果将空气压缩至较高的温度，其中的蒸汽将达到饱和状态，但其分压只占总压的很小一部分。

Compressed air from a cylinder therefore has a low humidity. Town gas is frequently compressed before it is circulated so as to

prevent condensation in the mains.从气缸中排出的压缩空气具有很小的湿度。为防止民用燃气在管道内冷凝，在输送前通常需要压缩。

Many large air-conditioning plants incorporate automatic control of the humidity and temperature of the issuing air. 许多大型空气调节装置中含有排出空气湿度和温度自控系统。

Temperature control is effected with the aid of a thermocouple or resistance thermocouple recording the difference between

the wet-and-dry bulb temperatures.（温度的控制是借助于热电偶或电阻温度计的作用，温度的控制则通过热电偶记录干湿泡温度差来实现）

Unit 5 Lesson 1

If a fluid passed downwards through a bed of solids, no relative movement between the particles takes place, unless the initial

orientation is unstable.（如果流体向下流经固体颗粒床层，粒子间不会产生相对运动，除非最初的定位不牢固。）

If the flow is streamline, the pressure drop across the bed will be directly proportional to the rate of flow but at higher rates it

will rise more rapidly.如果流动是层流，通过床层的压降与流速成正比，但速度更高时，压降将迅速增大。

If the fluid passes upwards through the bed, the pressure drop will be the same as for downward flow at low rates, but when

the frictional drag on the particles becomes equal to their apparent weight ( actual weight less buoyancy), the particles

become rearranged so that they offer less resistance to the flow of fluid and the bed starts to expand .（如果流体向上流经床层，在流速较低时，向上流动的压降与向下流动的相同，但是当颗粒的摩擦力等于表观重量（实际重量减去浮力）时，颗粒重新排列，对流体的流动阻力减小，床层开始膨胀。）

This process continues as the velocity is increased, with the total frictional force remaining equal to the weight of the particles,

until the bed has assumed the loosest stable form of packing. 当总的摩擦力与粒子重量保持相等时，随着流速的增加，床层继续膨胀，直到床层呈现最松散的稳定形式。

If the velocity is then increased still further, the individual particles separate from one another and become freely supported in

the fluid and the bed is said to be fluidized流态化.如果流速继续增大，颗粒彼此分离开来，（被流体自由托起）自由悬浮在流体中，我们就说床层流态化了。Further increase in the velocity caused the particles to separate still further from one

another, and the pressure difference remains approximately equal to the weight per unit area of the bed.继续增大流速会导致粒子间彼此进一步分离，床层的压降仍近似等于单位面积床层的重量。

Up to this stage the system behaves in a similar way whether the fluid is a liquid or gas, but at high fluid velocities when the

expansion of the bed is large there is a fairly sharp distinction between the behaviour in the two cases.到这个阶段为止，无论流体是液体还是气体，体系的行为表现相似，但是，若流体流速很高，床层膨胀度很大时，这两种情况间的行为就会有很明显的区别。

With a liquid, the bed continues to expand as the velocity is increased and it maintains its uniform character, with the amount

of agitation of the particles increasing progressively，this type of fluidization is known as particulate fluidization.对于液体，当速度增加时床层继续膨胀，随着粒子的搅动强度逐渐增加，体系仍保持均匀的特性，这种流态化的形式就是所说的散式流态化。

With the gas, however, uniform fluidization is obtained only at relatively low velocities. 然而，对于气体，只有在流速相对低的情况下才能产生均匀流化。

At high velocities two separate phases are formed; the continuous phase which is often referred to as the dense or emulsion

phase, and the discontinuous phase known as the lean or bubble phase. The fluidization is then said to be aggregative.在速度较高时，床层内分为两相，连续相称为密相或乳化相，不连续相称为疏相或气泡相。 这种情况下认为流态化产生了聚合。

Gas bubbles pass through a high-density fluidized bed with the result that the system closely resembles a boiling liquid, with

the lean phase corresponding to the vapor and the dense or continuous phase to the liquid.气泡通过高密度流化床时，使得体系象沸腾的液体，疏相好像是蒸汽，密相或乳化相好像是液体。

The bed is then often referred to as a boiling bed, as opposed to a quiescent bed at low flow rates.为了和低流速下的固定床相区别，这类床层常称为沸腾床。

Thus as the flow of the gas is increased, its velocity relative to the particles in the dense phase may not change appreciably,

and it has been shown that the flow relative to the particles can as a result remain streamline even at very high overall rates of

flow.随着气体流速的增加，关于密相中颗粒的速度基本不变，并且结果证明，即使在总体流速很高的情况下，颗粒的流动，仍保持层流。

If the rate of passage of gas is high, and if the bed is deep, coalescence of the bubbles take place, and in a narrow vessel slugs

of gas occupying the whole cross section may be produced.如果气体通过的速率很大，而且床层很厚，气泡就会发生聚集，在较窄的容器内，将会出现气团充满整个横截面的情况。

These slugs of gas alternate with slugs of fluidized solids which are carried upwards and subsequently collapse, causing the

solids to fall back again.这些气团与流化的固体颗粒团相互交替（形成相互间隔的气泡层和颗粒层），颗粒层被推着向上运动，随后破裂，固体颗粒又分散落下。

It has been suggested that the Froude group u2mf/gd gives a criterion from which the type of fluidization can be predicted.有人提出，弗鲁德组数umf2/gd可以作为一个预测发生何种流态化的判据。

Here, umf is the minimum velocity of flow, calculated over the whole cross-section of the bed, at which fluidization takes place,

d is the diameter of the particles, and g is the acceleration due to gravity. 这里， umf是以发生流态化床层的整个横断面计算的最小流速，d是颗粒直径，g是重力加速度。

At values less than unity（联合, 统一,一）, particulate fluidization occurs and, at higher values, aggregative fluidization takes

place. 在数值小于1的情况下，会发生散式流态化，而在较高的值时，将产生聚式流态化。

Much lower values of the Froude number弗劳德数are generally obtained with liquids because the velocity required to

produce fluidization is less. 由于液体中发生流态化所要求的流速比较低，因此计算得到的弗劳德数值也较低。

A theoretical justification for using the Froude group to distinguish between particulate散式流化and aggregative fluidization聚式流化is provided in the work of Jackson.在杰克逊的著作中提出了一个如何利用弗劳德准数判断散式流化和聚式流化的理论依据。

Although the possibility of forming fluidized [flu﹕idaizd] beds had been known for many years, the subject remained of

academic interest until the adoption of fluidized catalysts by the petroleum industry for the cracking of heavy hydrocarbons

and for the synthesis of fuels from natural gas or from carbon monoxide and hydrogen.（尽管人们早就知道形成流化床的可能性，但在石油工业中用流态化催化剂裂解重质碳氢化合物以及用天然气或CO加H2合成燃料之前，这一课题只有其学术意义。）

The fluidized bed in many ways behaves as a fluid of the same density as that of the solids and fluid combined. 在许多方面，流化床表现得像由固体和流体组成的相同密度的流体。

It transmits hydrostatic force流体静力, and solid objects float if their densities are lower than that of the bed. 它传递静压力，如果固体密度小于床层密度，固体就会漂浮在上面。

Intimate mixing takes place and heat transfer within the bed is very rapid, and therefore uniform temperatures are quickly

attained throughout the system.床层内部的完全混合和热传递发生很快，因此，整个系统温度会很快达到一致。

The easy control of fluidized temperature is the feature which has led to the use of fluidized solids for strongly exothermic

processes, and where close control of temperature is important. （容易控制温度是其特点，因此，对于精确温度控制很重

要的强防热过程用流化态固体。）

In order to understand the properties of a fluidized system it is necessary to study the flow patterns of the solids and the fluid为了了解流化体系的性质，研究固体和流体的流动方式是很有必要的。

In this connection the mode of formation and behaviour of fluid bubbles is of particular importance because they can account

for the flow of a large proportion of the fluid in a gas-solid system.其中，由于在气固系统中，气泡可以引起大量气体的流动，因此它们的形成和行为方式非常重要。

In any study of the properties of a fluidized system, it is necessary to select conditions which are reproducible, and the lack of

agreement between the results of many workers, particularly those relating to heat transfer, is largely attributable to the

existence of widely different conditions within the bed.在对流态化体系性质的任何研究中，选择可重复的条件是很有必要的，在许多工作者研究结果特别是有关于热传递的结果之间缺乏一致性，主要原因在于床层的条件存在很大的不同。

One of the prime requirements is that the fluidization shall be of a good quality; that is to say, that the bed shall be free from

irregularities and channeling.一个基本要求就是流态化必须进行得很好，也就是说，床层必须是均匀的且没有沟流现象。

It must be accepted that many solids will never give good fluidization, particularly those whose shape is appreciably

non-isometric, and those which form soft particles which readily form agglomerates.必须承认许多固体永远不会形成好的流态化，特别是那些形状是非立方的，还有那些形成软颗粒容易形成凝聚物的粒子。

Furthermore, when the solid is capable of giving good quality fluidization, the fluid must be evenly distributed at the bottom

of the bed and this necessitates the provision of a distributor given rise to引起pressure drop at least equal to that across the

bed. 而且，当固体有可能被很好的流态化时，流体在 床层底部必须均匀分布，这需通过分布板来完成，其引起压降至少与气体通过床层的压降相等。

This condition is much more readily satisfied in a small laboratory apparatus than in large-scale industrial equipment.这个条件在实验室仪器中比在大规模工业装置中更容易得到满足。

As already mentioned, systems fluidized with a liquid do not tend to give rise to bubbles, whereas those fluidized with a gas

tend to produce bubbles when the flow rate appreciably exceeds the minimum for fluidization.正好前面已经提到的，由液体形成流态化体系时，不会形成气泡；然而对于气体系统的流态化，当流速远大于可产生流态化的最小气速时，会产生气泡。

In an attempt to improve the reproducibility of conditions within the bed, much of the earlier research work with gas fluidized

systems was carried out at gas velocities sufficiently low for bubble formation to be absent.为提高床层条件的可重复性，许多早期关于气体系统流态化的的研究工作是在气速足够低的条件下进行的，这样做是为了不产生气泡。

In recent years, however, it has been recognized that bubbles normally tend to form in such system, that they exert an

important influence on the flow pattern of both gas and solids, and that the behaviors of individual bubbles can be predicted

quite accurately.然而，近年来，人们已经认识到在这种体系中通常会产生气泡，并且它们会对气体和固体的流动形式产生影响，目前人们已经可以对单个气泡的行为进行相当准确地预测。

（2）Fluidised Bed Catalytic Cracking

The existence of a large surplus of high boiling material after the distillation of crude oil led to the introduction of a cracking

process to convert these materials into compounds of lower molecular weight and lower boiling point-in particular into

petroleum spirit（原油精馏后剩余大量的高沸点物质，这就引出了一个裂化过程：将这些物质变为低分子量和低沸点的化合物-尤其是汽油。）.

The cracking was carried out using a fixed catalyst, but local variation in temperature in the bed led to a relatively inefficient

process, and the deposition of carbon on the surface of the catalyst particles necessitated taking the catalyst bed out of

service periodically so that the carbon could be burned off烧掉, 蒸发.裂化在固定催化床上进行，但床层内局部温度的变化会导致过程效率较低，因此应该定期停车，以便使沉积在催化剂颗粒表面的碳燃烧掉。

Many of these difficulties are obviated by the use of fluidized catalyst, since it is possible continuously to remove catalyst from

the reaction vessel and to supply regenerated catalyst to the plant.如果使用流态化催化剂，多数困难就可以避免，由于它可以连续从反应器重移走催化剂并项设备中补充再生的催化剂.

The high heat transfer coefficients for fluidized systems account for the very uniform temperatures within the reactors and

make it possible to control conditions very closely精密地， 严密地. 流化系统中较高的传热系数使反应器内的温度非常均匀，使得经精确控制反应条件成为可能。

The fluidized system has one serious drawback: some longitudinal mixing occurs and this gives rise to a number of side

reactions.流化系统 有一个严重的不足，会出现纵向混合而引起一些副反应。

The catalytic cracking process is an example. Hot oil vapour containing the required amount of regenerated catalyst, is

introduced into the reactor which is at a uniform temperature of about 775K. 催化裂化过程就是一个例子，含有所需再生催化剂量的热油蒸汽，进入温度约为775K的均温反应器中。

As the velocity of the vapour falls in the reactor . Because of the greater cross-sectional area for flow, a fluidized bed is formed

and the solid particles are maintained in suspension. 由于在反应器内流动的横截面加大，蒸汽流速降低，这就形成了一个流化床，固体颗粒保持悬浮状态。The vapours escape from the top and the flowrate is such that the vapour remains in the

reactor for about 20s.蒸汽从顶部放出，流速满足蒸汽在反应器内停留时间大约20s。

It is necessary to provide a cyclone separator at the gas outlet to remove除去entrained catalyst particles and droplets of

heavy oil. 必须在气体的出口处采用一套旋风分离器除去所夹带的催化剂颗粒和重油的液滴。

The vapour from the cracked material then passes to the fractionating unit, whilst the catalyst particles and the heavy residue重残渣,重质残渣are returned to the bed. 裂化物料的蒸汽通过精馏单元，而催化剂颗粒和重残渣又返回催化床中。

Some of the catalyst is continuously removed from the bottom of the reactor and, together with any fresh catalyst which is

required, is conveyed in a stream of hot air into the regenerator where the carbon deposit and any adhering粘附film薄膜,

膜层, 影片, 电影of heavy oil is burned off at about 875K: in the regenerator the particles are again suspended as a fluidized

bed.连续从反应器底部取出定量催化剂，和需要补充的新鲜催化剂一起，用热空气输送到再生器中，在这里沉积的碳和重油粘附膜在875K被烧掉。在再生器中，颗粒又象流化床一样处于悬浮状态。

The hot gases leave the regenerator through a cyclone separator, from which the solids return to the bed, and then flow to

waste废物through an electrostatic静电的precipitator除尘器which removes any very fine particles which are still in

suspension.热气体经过一旋风分离器离开再生器 ，固体返回床层中，气体经过静电除尘器除去仍处于悬浮状态的非常精细的颗粒后放空。

The temperature in the regenerator remains constant to within about 3 deg K, even where the fluidized bed is as much as 6m

deep and 15m in diameter.尽管流化床大到深6米，直径15米，但再生器内的温度仍保持恒定，温差只有3K。

Catalyst is continuously returned from the regenerator to the reactor to the reactor by introducing it into the supply of hot

vapour. The complete time cycle for the catalyst material is about 600s.通过把催化剂引入热蒸汽中使它连续从再生器回到反应器中，催化剂完全循环一次的时间大约为600秒。

by this process a product consisting of between about 50 percent and 75 percent of petroleum spirit汽油、石油精、轻质烃混合物of high octane number is obtained. 通过这个过程，就得到了含量在50%-70%的高辛烷值的汽油产品。

The quality of the product can be controlled by the proportion of catalyst which is used and the exact精确的, 准确的temperature in the reactor. 产品的性质由所用催化剂所占的比例和反应器的准确温度控制。

More recent experimental work has shown that much of the cracking takes place in the transfer line in which the regenerated

catalyst is conveyed into the reactor in the stream of oil vapour.较近的实验工作表明，许多裂化是在输送管道中进行的，在输送管内用油汽把在生后的催化剂送到反应器。

The chemical reaction involved is very fast and the performance of the reactor is not sensitive to the hydrodynamic水力的;

水压的, 液力的、流体动力学的 conditions.所涉及的化学反应非常迅速，反应器的性能对流体力学条件并不敏感。

Unit 6 (1) Azeotropic and Extractive Distillation

Many mixtures are difficult to separate by distillation because their relative volatilities are close to 1.0. Some of these mixtures

may be separated by the addition of another component that increase the relative volatilities of the original constituents.•许多混合物的相对挥发度接近于1.0，因此很难用精馏的方法将它们分离。但是，当加入另外一种组分后，就可以增大初始组分的相对挥发度而使它们得到分离。

Fractionation after the addition of a component to increase relative volatilities is referred to as azeotropic distillation or as

extractive distillation, depending upon the nature of the added component.•加入一个组分增加相对挥发度的的精馏称为恒沸蒸馏或萃取精馏（这取决于加入组分的性质）。

In azeotropic distillation the added component is relatively volatile, so that it appears in the distillate. In many cases it forms

low-boiling-point azeotrope with one of the original component.•在恒沸精馏中，加入的组分挥发度较高，因此它出现在馏中物中。在多数情况下，它与一种初始组分形成最低共沸物。

The low-boiling azeotrope goes overhead in the distillate, and the remaining components go out at the bottoms. Of course, it

is then necessary to separate the azeotropic agent from the original component by an appropriate separation process.•低沸点共沸物进入塔顶馏出物中，而剩余组分从塔底流出。当然，随后还必须采用适当的分离方法将恒沸剂与初始组分分离。

Extractive distillation involves the addition of a relatively nonvolatile component. The “solvent” added flows downward from

stage to stage, increasing the relative volatilities. It finally flows out with the bottoms.萃取精馏加入的则是挥发性较差的组分。加入的“溶剂”逐板向下流动，在此过程中增加了相对挥发度，它最终从塔底流出。

Azeotropic or extractive distillation is used to separate both binary and multicomponent mixtures. For simplicity, only binary

mixtures are discussed here, but the principles and calculations are the same for multicomponent mixtures.•恒沸精馏和萃取精馏都可以用来分离二元或多员混合物。为简便起见，这里只讨论二元混合物的情况，但对于多元混合物，其原理和计算方法是相似的。

Azeotropic or extractive distillation is based on the interactions of the components of nonideal solutions. The azeotropic or

extractive agent is chosen because it interacts more strongly with one of the components than it does with the other.•恒沸精馏或萃取精馏均是建立在非理想溶液中各组分的相互作用的基础之上的。恒沸剂或萃取剂的选择依据主要是它能和一种组分发生强烈的相互作用，而与另一种的作用较弱。

An azeotropic agent may be added to a nearly ideal binary mixture of low relative volatility( that is, the two components have

nearly the same boiling point).•恒沸剂可以加入到具有较低相对挥发度的接近理想的二元混合物中（即这两种组分具有相似的沸点）。

If the structures of the original components are sufficiently different, the azeotropic agent may interact with one of them( for

example, by hydrogen bonding, thereby increasing their relative volatility).•如果最初组分的结构差异很大，恒沸剂只和其中一种组分起作用（例如，通过氢键作用来增大它们的相对挥发度）。

The original binary solution may be sufficiently nonideal to contain a binary azeotrope that blocks the production of pure

components by simple distillation. 最初的二元溶液可能具有很强的非理想性，其中含有二元共沸物，采用简单精馏的方法不能得到纯组分。

Addition of an azeotropic agent may “break” the binary azeotrope and allow production of pure components, although it my

require additional separation steps to recover the azeotropic agent.尽管还需要采用另外的分离步骤回收恒沸剂，但它的加入可以打破二元共沸物并得到纯净的组分。

For example, ethyl alcohol and water form a binary azeotrope at 0.89 mole fraction alcohol, so that this is the richest alcohol

solution that can be recovered by simple distillation.例如，乙醇和水可形成含乙醇摩尔分率为0.89的二元共沸物，因此这是用简单精馏得到的最高浓度的乙醇溶液。

Addition of benzene as an azeotropic agent yields a distillate product consisting of a ternary azeotrope. The bottoms is the

desired pure alcohol.•加入苯作为恒沸剂后可以在塔顶馏出物中得到三元共沸物。塔底得到的是想要的纯乙醇。

Sufficient alcohol is lost in the ternary azeotrope to require its recovery. On condensation, the ternary azeotrope in the

distillate splits into two liquid phases.随三元共沸物损失掉大量乙醇，因此必须将其回收。冷凝后，馏出物中的三元共沸物分成两液相。

The benzene-rich phase is returned to the first distillation column, while the water-rich phase is sent to a second column. In

this second column, the distillate is again the ternary azeotrope, which is condensed and sent to the phase splitter( together

with the distillate from the first column).•富含苯的相返回到第一个塔中，而富含水的相进入到第二个塔中。在第二个塔中，塔顶馏出物仍然是三元共沸物，和第一个塔的馏出物一起，进入分相器中。

The bottoms from the second column is an aqueous solution of alcohol. It is sent to a third column that produces the

water-alcohol azeotrope as the distillate and pure water as the bottoms.从第二个塔塔底流出的是乙醇的水溶液。它被送到第三个塔中，塔顶馏出物是乙醇－水的二元共沸物，而塔底则得到纯水。

This distillate is mixed with the feed to the first column. Thus, the net effect of the process is to produce pure alcohol and pure

water from the alcohol-water azeotrope.塔顶馏出物和进料一起混合再进入第一个塔。这样，此过程的净结果就是从乙醇－水的共沸物中得到了纯乙醇和纯水。

Calculations for azeotropic distillation are nearly the same as those for simple multicomponent distillation. The addition of an

azeotropic agent to a binary mixture produces a multicomponent mixture.恒沸精馏的计算类似于简单的多组分精馏。恒沸剂加入到二元混合物中就相当于产生了多组分混合物。

Stage-to-stage calculations can be used to determine the separation possible with a given column or to determine the number

of stages required for a given separation.对于给定的塔高，可以采用逐级计算法确定分离效果，或根据给定的分离要求计算所需的塔板数。

Two differences arise. Equilibrium data more complex because the K for a given component is a function not only of

temperature and pressure, but also of the nature and concentration of other components present. 不同点主要有两个。首先，对于一个给定组分，其K值不仅是温度和压力的函数，也是其它组分性质和浓度的函数。

A second difference arises from the fact that the azeotropic agent may be fed at more than one point in the column.

Calculations must take into account these intermediate streams. In extractive distillation, the nonvolatile solvent is fed as an

intermediate stream near the top of the column.•另外一个不同就是恒沸剂可能不只在在塔的一个位置处加入。计算时必须考虑这些中间流股。在萃取精馏中，非挥发性溶剂在靠近塔的上部作为中间流股加入。

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