过程装备与控制工程专业英语

Reading Material 16

Pressure Vessel Codes

①History of Pressure Vessel Codes in the United States Through the late 1800s and early 1900s, explosions in boilers and pressure vessels were frequent. A firetube boiler explosion on the Mississippi River steamboat Sultana on April 27, 1865, resulted in the boat's sinking within 20 minuted and the death of 1500 soldiers going home after the Civil War. This type of catastrophe continued unabated into the early 1900s. In 1905, a destructive explosion of a firetube boiler in a shoe factory in Brockton, Massachusetts, killed 58 people, injured 117 others, and did $400000 in property damage. In 1906, another explosion in a shoe factory in Lynn, Massachusetts, resulted in death, injury, and extensive property damage. After this accident, the Massachusetts governor directed the formation of a Board of Boiler Rules. The first set of rules for the design and construction of boilers was approved in Massachusetts on August 30, 1907. This code was three pages long.

②In 1911, Colonel E. D. Meier, the president of the American Society of Mechanical Engineers, established a committee to write a set of rules for the design and construction of boilers and pressure vessels. On February 13, 1915, the first ASMEBoiler Code was issued. It was entitled "Boiler Construction Code, 1914 Edition". This was the beginning of the various sections of the ASME Boiler and Pressure Vessel Code, which ultimately became Section 1, Power Boilers.

③The first ASME Code for pressure vessels was issued as "Rules for the Construction of Unfired Pressure V essels", Section Ⅷ, 1925 edition. The rules applied to vessels over 6 in. in

diameter, volume over 1.5 3ft, and pressure over 30 psi. In December 1931, a Joint API-ASME

Committee was formed to develop an unfired pressure vessel code for the petroleum industry. The first edition was issued in 1934. For the nest 17 years, two separated unfired pressure vessel codes existed. In 1951, the last API-ASME Code was issued as a separated document. In 1952, the two codes were consolidated into one code----the ASME Unfired Pressure Vessel Code, Section Ⅷ. This continued until the 1968 edition. At that time, the original code became Section Ⅷ, Division 1, Pressure Vessels, and another new part was issued, which was Section Ⅷ, Division 2, Alternative Rules for Pressure Vessels.

④The ANSI/ASME Boiler and Pressure Vessel Code is issued by the American Society of Mechanical Engineers with approval by the American National Standards Institute (ANSI) as an ANSI/ASME document. One or more sections of the ANSI/ASME Boiler and Pressure Vessel Code have been established as the legal requirements in 47 states in the United Stated and in all provinces of Canada. Also, in many other countries of the world, the ASME Boiler and Pressure Vessel Code is used to construct boilers and pressure vessels.

⑤Organization of the ASME Boiler and Pressure Vessel Code The ASME Boiler and Pressure Vessel Code is divided into many sections, divisions, parts, and subparts. Some of these sections relate to a specific kind of equipment and application; others relate to specific materials and methods for application and control of equipment; and others relate to care and inspection of installed equipment. The following Sections specifically relate to boiler and pressure vessel design and construction.

Section ⅠPower Boilers (1 volume)

Section Ⅲ

Division 1 Nuclear Power Plant Components (7 volumes)

Division 2 Concrete Reactor Vessels and Containment (1 volume)

Code Case Case 1 Components in Elevated Temperature service (in Nuclear Code N-47

Case book)

Section ⅣHeating Boilers (1 volume)

Section Ⅷ

Division 1Pressure Vessels (1 volume)

Division 2 Alternative Rules for Pressure Vessels (1 volume)

Section ⅩFiberglass-Reinforced Plastic Pressure Vessels (1 volume)

⑥A new edition of the ASME Boiler and Pressure Vessel Code is issued on July 1 every three years and new addenda are issued every six months on January 1 and July 1. The new edition of the code becomes mandatory when it appears. The addenda are permissive at the date of issuance and become mandatory six months after that date.

⑦Worldwide Pressure Vessel Codes In addition to the ASME Boiler and Pressure Vessel Code, which is used worldwide, many other pressure vessel codes have been legally adopted in various countries. Difficulty often occurs when vessels are designed in one country, built in another country, and installed in still a different country. With this worldwide construction this is often the case.

⑧The following list is a partial summary of some of the various codes used in different countries:

Australia Australian Code for Boilers and Pressure Vessels, SAA Boiler Code (Series AS 1200):AS 1210, Unfired Pressure Vessels and Class 1 H, Pressure Vessels of Advanced Design and Construction, Standards Association of Australia.

France Construction Code Calculation Rules for Unfired Pressure Vessels, Syndicat National de la Chaudronnerie et de la Tuyauterie Industrielle (SNCT), Paris, France.

United Kingdom British Code BS. 5500, British Standards Institution, London, England.

Japan Japanese Pressure V essel Code, Ministry of Labour, published by Japan Boiler Association, Tokyo, Japan; Japanese Standard, Construction of Pressure Vessels, JIS B 8243, published by the Japan Standards Association, Tokyo, Japan; Japanese High Pressure Gas Control Law, Ministry of International Trade and Industry, published by The Institution for Safety of High Pressure Gas Engineering, Tokyo, Japan.

Italy Italian Pressure Vessel Code, National Association for Combustion Control (ANNCC), Milan, Italy.

Belgium Code for Good Practice for the Construction of Pressure Vessels, Belgian Standard Institute (IBN), Brussels, Belgium.

Sweden Swedish Pressure Vessel Code, Tryckkarls kommissioner, the Swedish Pressure Vessel Commission, Stockholm, Sweden.

压力容器准则

①美国的压力容器规范历史在19世纪和20世纪初期，锅炉和压力容器频繁发生爆炸事件。1865年4月27日，苏丹轮船的火管锅炉在密士西比河爆炸，导致轮船在20分钟内沉没，且参加南北战争的1500准备回家的士兵全部死忙。这类大灾难一直持续到20世纪初期。1905年，马萨诸塞州布拉克顿一鞋厂发生毁灭性的火管锅炉爆炸事件，造成58人死亡，117人受伤，财产损失400000$。1906年，马萨诸塞州林恩一个鞋厂发生爆炸，导致死亡，受伤，且持续性损失。这次意外后，马萨诸塞州州长组织成立锅炉标准委员会。1907年8月30日，第一部锅炉设计及结构规范获得通过，长达3页。

②1911年，德梅尔上校，美国机械工程师学会主席，成立一个委员会来编写锅炉及压力容器的设计和结构规范。1915 2月13日，第一个美国机械工程师学会锅炉规范发布，叫做《锅炉构造规范，1914版本》。这是系列美国机械工程师学会锅炉及压力容器规范的开端，最终变成第一章《电站锅炉》。

③第一部关于压力容器的机械工程师协会标准作为热交换器结构规则发布，共8章，1925版本。规定容器直径为6英尺，体积为1.5英尺，并且压力为每平方英寸30磅。1931年12月，美国石油组织-美国机械工程师学会委员会成立并致力于研究用于石油工业的热交换器规则。1934开始发行第一个版本。接下来的17年，就有两部分离热交换器规则。1951年，美国石油组织与美国机械工程师协会标准作为单独文件发布。1952年，这两部规则合并成一部--美国机械工程师学会热交换器规则，共8章。一直延续到1968年版。那时，原始的规则变成8章，1部是压力容器，另一部分是2章的压力容器替换规则。

④《美国国家标准协会／美国机械工程师学会锅炉及压力容器规则》由美国机械工程师学会发布，由美国国家标准协会批准的作为《美国国家标准协会／美国机械工程师学会》文件。更多的《美国国家标准协会／美国机械工程师学会锅炉及压力容器规则》在美国47州和加拿大所有城市作为法定使用。同时，世界上许多其他国家使用《美国机械工程师学会锅炉及压力容器规则》来制造造锅炉及压力容器。

⑤ASME 锅炉及压力容器规范《美国机械工程师学会锅炉及压力容器规则》分成许多章。有些章节涉及到一些特殊设备及使用；有些涉及到特殊材料和设备的操作和控制方法；其他的涉及到设备的安装及维护等。下面的章节与锅炉及压力容器设计和结构有关。

第一章电站锅炉（1卷）

第3章

节1 核电站元件（７卷）

节2 混凝土电抗器容器及防范（1卷）

规则事例事例1，高温保养元件（核的规则手册的氮-47）

第7章锅炉供暖（1卷）

第8章

节1 压力容器（1卷）

节２压力容器替换规则（1卷）

第9章玻璃钢压力容器（1卷）

⑥每三年发布一次新版《美国机械工程师学会锅炉及压力容器规则》，每六个月发布新的附录，分别是1月1日和7月1日。每当新版规则发布就强制执行，附录的发行允许不执行，但即日起六个月后腰强制执行。

⑦压力容器国际规范除国际使用的《美国机械工程师学会锅炉及压力容器规则》外，许多其他的压力容器规范在多个国家可以使用。在一个国家设计的容器在他国使用时经常发生故障，这种情况常发生在国际性结构。

⑧下面的目录是被用于列国中的各种规则的一部分的一些摘要信息：

澳大利亚锅炉及压力容器的澳大利亚规则，《表面活性剂锅炉规范（1200系列）》:

系列1210，热交换器，先进的压力容器设计和结构，澳大利亚标准协会。

法国热交换器结构规则计算规则，巴黎，法国。

英国反散射能谱法英国规则。5500，英国标准协会，伦敦，英国。

日本日本压力容器规范》，劳工部，由日本锅炉协会出版，东京，日本；日本标准，《压力容器结构》，日本工业标准B，8243，由日本标准协会出版，东京，日本；《日本高压气体管制法》，日本通商产业省，由安全的高压气体工程师协会出版，东京，日本。

意大利《意大利压力容器规范》，燃烧过程控制（anncc）国家协会，米兰，意大利。

比利时《国际惯例压力容器结构规则》，比利时的标准协会，布鲁塞尔，比利时。

瑞典《瑞典压力容器规范》，tryckkarls kommissioner，瑞典压力容器试运行，斯德哥尔摩，瑞典。

Reading Material 17

Stress Categories

①The various possible modes of failure which confront the pressure vessel designer are:

(1) Excessive elastic deformation including elastic instability.

(2) Excessive plastic deformation.

(3) Brittle fracture.

(4) Stress rupture/creep deformation (inelastic).

(5) Plastic instability-incremental collapse.

(6) High strain-low cycle fatigue.

(7) Stress corrosion.

(8) Corrosion fatigue.

②In dealing with these various modes of failure, we assume that the designer has at his disposal a picture of the state of stress within the part in question. This would be obtained either through calculation or measurements of the both mechanical and thermal stresses which could occur throughout the entire vessel during transient and steady state operations. The question one must ask is what do these numbers mean in relation to the adequacy of the design? Will they insure safe and satisfactory performance of a component? It is against these various failure modes that the pressure vessel designer must compare and interpret stress values. For example, elastic deformation and elastic instability (buckling) cannot be controlled by imposing upper limits to the calculated stress alone. One must consider, in addition, the geometry and stiffness of a component as well as properties of the material.

③The plastic deformation mode of failure can, on the other hand, be controlled by imposing limits on calculated stresses, but unlike the fatigue and stress corrosion modes of failure, peak stress does not tell the whole story. Careful consideration must be given to the consequences of yielding, and therefore the type of loading and the distribution of stress resulting therefrom must be carefully studied. The designer must consider, in addition to setting limits for allowable stress, some adequate and proper failure theory in order to define how the various stresses in a component react and contribute to the strength of that part.

④As mentioned previously, different types of stress require different limits, and before establishing these limits it was necessary to choose the stress categories to which limits should be applied. The categories and sub-categories chosen were as follows:

A. Primary Stress.

(a) General primary membrane stress.

(b) Local primary membrane stress.

(c) Primary bending stress.

B. Secondary Stress.

C. Peak Stress.

⑤The major stress categories are primary, sec9ondary, and peak. Their chief characteristics may be described briefly as follows:

(a) Primary stress is a stress developed by the imposed loading which is necessary to satisfy the laws of equilibrium between external and internal forces and moments. The basic characteristic of a primary stress is that it is not self-limiting. If a primary stress exceeds the yield strength of the material through the entire thickness, the prevention of failure is entirely dependent on the strain-hardening properties of the material.

(b) Secondary stress is a stress developed by the self-constraint of a structure. It must satisfy an imposed strain pattern rather than being in equilibrium with an external load. The basic characteristic of a secondary stress is that it is self-limiting. Local yielding and minor distortion can satisfy the discontinuity conditions or thermal expansions which cause the stress to occur.

(c) Peak stress is the highest stress in the region under consideration. The basic characteristic of a peak stress is that it causes no significant distortion and is objectionable mostly as a possible source of fatigue failure.

⑥The need for dividing primary stress into membrane and bending components is that, as will be discussed later, limit design theory shows that the calculated value of a primary bending stress may be allowed to go higher than the calculated value of a primary membrane stress. The placing in the primary category of local membrane stress produced by mechanical loads, however, requires some explanation because this type of stress really has the basic characteristics of a secondary stress. It is self-limiting and when it exceeds yield, the external load will be resisted by other parts of the structure, but this shift may involve intolerable distortion and it was felt that must be limited to a lower value than other secondary stresses, such as discontinuity bending stress and thermal stress.

⑦Secondary stress could be divided into membrane and bending components, just as was done for primary stress, but after the removal of local membrane stress to the primary category, kit appeared that all the remaining secondary stresses could be controlled by the same limit and this division was unnecessary.

⑧Thermal stress are never classed as primary stresses, but they appear in both of the other categories, secondary and peak. Thermal stresses which can produce distortion of the most complete suppression of the differential expansion, and thus cause no significant distortion, are classed as peak stresses.

⑨One of the commonest types of peak stress is that produced by a notch, which might be a small hole or a fillet. The phenomenon of stress concentration is well-known and requires no further explanation here.

⑩Many cases arise in which it is not obvious which category a stress should be placed in, and considerable judgment is required. In order to standardize this procedure and use the judgment of the writers of the Code rather than the judgment of individual designers, a table was prepared covering most of the situations which arise in pressure vessel design and specifying which category each stress must be placed in.

⑴The potential failure modes and various stress categories are related to the Code provisions as follows:

(a) The primary stress limits are intended to prevent plastic deformation and to provide a nominal factor of safety of the ductile burst pressure.

(b) The primary plus secondary stress limits are intended to prevent excessive plastic deformation leading to incremental collapse, and to validate the application of the elastic analysis when performing the fatigue evaluation.

(c) The peak stress limit is intended to prevent fatigue failure as a result of cyclic loading.

(d) Special stress limits are provided for elastic and inelastic instability.

⑵Protection against brittle fracture are provided by material selection, rather than by analysis. Protection against environmental conditions such as corrosion and radiation effects are the responsibility of the designer. The creep and stress rupture temperature range will be considered in later condition.

应力类型

①压力容器设计者遇到的多种可能的失效形式：

（1）过度弹性变形包括弹性失稳。

（2）过度塑性变性。

（3）脆性断裂。

（4）应力断裂/蠕变变形（非弹性的）。

（5）塑性不稳性增加失稳。

（6）高应变低周期疲劳。

（7）应力腐蚀。

（8）疲劳腐蚀。

②在处理这些不同的失效形式上，我们假设设计者在局部问题的处理上，有一副应力状态图。这需要通过对机械和热应力的计算或测量来得到，它们（应力）在短暂稳定的状态操作期间，存在于整个容器中。有人会问，这些数据与设计的合理性有什么关系？它们能确保一个构件的安全和满意的性能吗？它与这些各种各样的失效形式对立，压力容器设计者必须比较和说明应力值。例如，通过单独计算应力来强加上限，是不能控制弹性变形和弹性失稳。此外，还必须考虑构件的几何形状和硬度，以及材料的特性。

③从另一方面来看，塑性变形失效形式可以通过在计算的应力上强加极限来控制，但不象疲劳和应力腐蚀失效形式，峰值应力不做整体描述。必须对屈服结果进行仔细考虑。因此，载荷的类型和由那里引起的应力分布，必须被仔细研究。除了限制许用应力外，设计者还必须考虑一些适当的失效理论，来解释各种应力怎样在构件内起作用和对那些部分的强度所做的贡献。

④正如前面所涉及的，不同类型的应力需要不同的限制，在确定这些限制之前，选择应用于什么限制的应力类型是必要的。供选择的应力类型如下：

A、主应力。

（a）普通的薄膜主应力

（b）内部薄膜主应力

（c）主要弯曲应力

B、副应力

C、最大应力

⑤应力类型是主应力、副应力及最大应力。它们的主要特征简略描述如下：

（a）主应力是由施加载荷产生的应力，载荷在满足外部和内部的作用力和力矩之间的平衡规律是必要。一次应力的基本特征是自身不受限制。在整个厚度上，如

果一次应力超过了材料的屈服强度，防止失效必须完全依赖材料的变形硬化性

质。

（b）副应力是由结构的自身约束二产生的应力。它必须满足一个强加应变的式样，而不是与一个外载荷平衡。副应力的基本特征是自身受限制。局部屈服和较小

变形，能够满足引起应力产生的不连续条件或者热膨胀。

（c）最大应力是所考虑范围内的最高应力。峰值应力的基本特征，是不会引起大的变形和作为疲劳失效一个可能的源头是令人讨厌的。

⑥将主应力分成薄膜和弯曲部分的必要，以后再讨论，极限设计理论表明主弯曲应力的计算值允许高于主薄膜应力的计算值。然而，我们应该解释一下由机械载荷产生的局部薄膜应力的主要种类的位置，因为这种应力确实有副应力的基本特征。它是自身受限制的，而且当它超过屈服极限后，外载荷将受到结构的其他部分抵抗，但这种转变可能会产生严重变形，因此必须将它限制在比其他副应力更小的值，例如不连续弯曲应力和热应力。

⑦正如主应力那样，副应力被分为薄膜和弯曲部分，但是，在将局部薄膜应力归到主应力类型后，就会有所有剩余的副应力被相同的限制控制，这种分划是没有必要的。

⑧热应力从来不被归类为主应力，但它却出现在其他两种类型中，副和最大应力中。能够通过大部分抑制小膨胀而产生变形，以及不会引起严重变形的热应力，被归为最大应力。

⑨最大应力的一个最普通的类型，是由缺口引起的，它可能是一个小洞或一条裂痕。我们都知道应力集中现象，这里不做进一步解释。

⑩许多情况出现在不明显的地方，一种应力该归纳为哪种，需要考虑到判断能力。为了使这个程序规范化，并且使用规范作者的判断法，而不是个别设计者的判断法，准备一份能够包括大多数情况的表格，这些情况出现在压力容器设计和详细说明中，每种应力都必须填入其中。

⑾潜在的失效形式和各种应力类型，与规范条款有如下的联系：

（a）主应力的限制，目的是防止塑性变形，并在韧性爆破压力上提供一个名义安全因素。

(b)主应力和副应力的限制，目的是防止导致失稳增加的过量塑性变形和做疲劳估算时，

确认弹性分析的应用。

(c)最大应力的极限，目的是防止因周期载荷产生的疲劳失效。

(d)特殊应力的限制，提供给弹性和非弹性失稳。

⑿应对脆性断裂的保护，是通过材料的选择，而不是分析提供的。对环境条件比如腐蚀和辐射的保护，是每个设计者的职责。蠕变和应力断裂的温度范围，将在以后的章节中考虑。

Reading Material 18

Packed Towers

①In comparison with tray towers, packed towers are suited to small diameters (24 in. or less), whenever low pressure is desirable, whenever low holdup is necessary, and whenever plastic or ceramic construction is required. Applications unfavorable to packings are large diameter towers, especially those with low liquid and high vapour rates, because of problems with liquid distribution, and whenever high turndown is required. In large towers, random packing may cost

more than twice as much as sieve or valve trays.

②Depth of packing without intermediate supports is limited by its deformability; metal construction is limited to depths of 20 ~ 25 ft, and plastic to 10 ~ 15 ft. Intermediate supports and liquid redistributors usually are needed every 2.5 ~ 3 tower diameters for Raschig rings and every

5 ~ 10 diameters for Pall rings, but at least every 20 ft.

③The various kinds of internals of packed towers are represented in Fig. 4.2 whose individual parts may be described one-by-one.

(a) is an example column showing the inlet and outlet connections and some of the kinds of internals in place.

(b) is a combination packing support and redistributor that can also serve as a sump for withdrawal of the liquid from the tower.

(c) is a trough-type distributor that is suitable for liquid rates in excess of 2 gpm/sqft in towers 2 feet and more in diameter. They can be made in ceramics or plastics.

(d) is an example of a perforated pipe distributor which is available in a variety of shapes, and is the moat efficient type over a wide range of liquid rates; in large towers and where distribution is especially critical, they are fitted with nozzles instead of perforations.

(e) is a redistribution device, the rosette, that provides adequate redistribution in small diameter towers; it diverts the liquid away from the wall towards which it tends to go.

(f) is a hole-down plate to keep low density packings in place and to prevent fragile packings such as those made of carbon, for instance, from disintegrating because of mechanical disturbances at the top of the bed.

④The broad classes of packings for vapour-liquid contacting are either random or structured. The former are small, hollow structures with large surface per unit volume that are loaded at random into the vessel. Structured packings may be layers of large rings or grids, but are most commonly made of expanded metal or woven wire screen that are stacked in layers or as spiral windings.

⑤There are several kinds of packings. The first of the widely used random packings were Raschig tings which are hollow cylinders of ceramics, plastics, or metal. They were an economical replacement for the crushed rock often used then. Because of their simplicity and their early introduction, Raschig rings have been investigated thoroughly and many data of their performance have been obtained which are still useful, for example, in defining the lower limits of mass transfer efficiency that can be realize with improved packings.

⑥Structured packings are employed particularly in vacuum service where pressure drops must be kept low. Because of their open structure and large specific surface, their mass transfer efficiency is high when proper distribution of liquid over the cross section can be maintained.

填料塔

①与板式塔相比，填料塔适用于直径较小的物质（不大于24英寸），并且要是低压、低粘度、塑料或陶瓷结构。大直径塔特别是其内流动低速液体与高速气体的塔不适用于填料，因为液体分布难以控制及不能随时调节。在大的塔设备中，用散装填料的消耗可能是筛板或真空板式填料的2倍多。

②无中间支撑物的填料塔深度会受其可变形能力的限制。金属结构尺寸被限制在20~~25英尺，而塑性是10~~15英尺。中间支撑物和液体重新分配器应用在深床、液体回收

或进料装置点。对拉西环，2.5~~3米塔径需要液体重新分配器。而鲍尔环是每5~~10米塔径，最少要20英尺。

③填料塔内部结构如图4.2所示，下面一一介绍：

(a)是一个柱形填料塔显示入水口与出水口连接部分的实例图及其内部的一些结构

(b)是一个组合填充支撑物与液体重新分配器，其功能是像一个水箱一样将塔中液体回收。

(c)是一个槽式分配装置，它适用于塔径超过2英尺、液体流速超过2m/s的情况

(d)是一个针孔管式分配装置实例，有许多不同的形状，它对很大范围内的液体流速都很有效，在大直径塔中分配装置十分危险，它们适合用喷嘴来代替打孔。

(e)是一个玫瑰形的重新分配装置，在小直径塔中它能提供合理的液体重新分配，它可将塔内的液体转移。

(f)是一个压制向下的板，它用来保持各处的底密度填充物，并阻止像碳制的脆性材料，例如：由塔床顶部的机械干扰造成的分裂。

④用于气液接触的大面积填充物一般分为散装的，或者有规则的，前者很小，每单位体积的大表面积空心结构被装配到容器中。组合填充物可能是大形环状物层或栅格，但很多都是由金属或金属丝织成的屏状制成的，它们被堆成层状或弯曲的螺丝。

⑤有几种不同的填料，使用得最广泛的填充物是拉西环。它是陶瓷制成的、带塑料的、金属的圆筒。它们能很经济地替换过去使用的粉状岩石，由于它们品种单一和早就使用了，拉西环已经被彻底地研究，并且获得了各种有用的、性能不同的材料，例如：在定义较低传质效率上，可以用改善的填料。

规则的填料是由于其在真空下的独特性能而被使用，在真空下压降必须保持很小的数值。由于它打开的结构及特殊的大表面，在横截面的液体合适分布，可保持较高的传质效率。

Reading Material 19

Shell-and-Tube Heat Exchangers

①Shell-and-tube exchangers are made up of a number of tubes in parallel and series through which one fluid travels and enclosed in a shell through which the other fluid is conducted. The shell side is provided with a number of baffles to promote high velocities and largely more efficient cross flow on the outsides of the tubes. The versatility and widespread use of this equipment has given rise to the development of industrywide standards of shich the most widely observed are the TEMA standards. A typical shell-and-tube exchanger is presented on Fig. 4. 3.

②Baffle pitch , or distance between baffles, normally is 0. 2~1. 0 times the inside diameter of the shell. Both the heat transfer coefficient and the pressure drop depend on the baffle pitch, so that is selection is part of the optimization of the heat exchanger. The window of segmental baffles commonly is abort 25%, but it also is a parameter in the thermal-hydraulic design of the equipment.

③In order to simplify external piping, exchangers mostly are built with even number of tube passes. Partitioning reduces the number of the tubes that can be accommodated in a shell of a given size. Square tube pitch in comparison with triangular pitch accommodates fewer tubes but is preferable when the shell side must be cleaned by brushing.

④Two shell passes are obtained with a longitudinal baffle. More than two shell passes normally are not provided in a single shell, brt a 4~8 arrangement is thermally equivalent to two 2~4 shells in series, and higher combinations is obtainable with shell-and –tube exchangers, in

particular:

●Single phase, condensation or boiling can be accommodated in either the tubes or the shell, in vertical or horizontal positions.

●Pressure range and pressure drop are virtually unlimited, and can be adjusted independently for the two fluids.

●Thermal stresses can be accommodated inexpensively.

● A great variety of materials of construction can be used and may be different for the shell

and tubes.

●Extended surfaces for improved heat transfer can be used on either side.

● A great range of thermal capacities is obtainable.

●The equipment is readily dismantled for cleaning or repair.

⑤Several considerations may influence which fluid goes on the tube side or the shell side.The tube side is preferable for the fluid that has the higher pressure, or the higher temperature or is more corrosive. The tube side is less likely to leak expensive or hazardous fluids and is more easily cleaned. Both pressure drop and laminar heat transfer can be predicted more accurately for the tube side. Accordingly, when these factors are critical, the tube side should be selected for that fluid.

⑥Turbulent flow is obtained at lower Reynolds numbers on the shell side, so that the fluid with the lower mass flow preferably goes on that side. High Reynolds numbers are obtained by multipassing the tube side, but at a price.

⑦A substantial number of parameters is involved in the design of a shell-and –tube heat exchanger for specified thermal and hydraulic conditions and desired economics, including: tube diameter, thickness, length, number of passes, pitch, square or triangular; size of shell, number of shell baffles, baffle type, baffle windows, baffle spacing, and so on. For even a modest sized design program, it is estimated that 40 separate logical designs may need to be made which lead to 240=1.0*1012 different paths through the logic. Since such a number is entirely too large for normal computer process, the problem must be simplified with some arbitrary decisions based on as much current practice as possible.

管壳式换热器

①管壳式换热器是有许多平行管，和一个封闭的壳体组成，一种液体走管道，另一种液体走壳道。壳程安装了许多折流挡板以提高液体流速，使液体在管外更有效地流动。由于换热器的广泛使用及其功能的多样性，使它成为最受TEMA标准关注的工业标准的设备，如图4.3所示：典型的管壳式换热器。

②折流板的间距通常是壳体内径的0.2~~1倍，挡板间距决定了传热系数和压降，因此，决定其数值的大小是优化热交换器的一部分。弓形挡板的横截面积通常是壳体截面的25%，这是设备设计的热力学参数。

③为了简化外部管道，换热器通常采用多管程，将管子分层可减少管子的数量。管子被安置在壳内指定位置，管子正方形排列比三角形排列所使用的管子少，但它适用于壳程为洁净流体。

④两管程可通过安装一块纵向挡板获得，在单一壳程换热器中通常没有超过两壳程的，4~~8个单壳程在热交换上与两个2~~4壳程等同，组合越多所需要的壳体就会越多，在管壳式换热器中需要注意设计方法和操作条件，特别是：

·单壳程结构冷凝或蒸发可在管中或壳内进行，换热器可水平或垂直放置。

·热应力较小

·可使用多种材料制造且壳和管的材料可不同

·可在壳程或管程内增大表面积以改善热交换系数

·设备可拆开清洗或维修

⑤一些因素会影响流体走管内还是管外，管程适合走高温、高压或强腐蚀性的流体，管程的制造费用较低且不易发生危险，还易于清洗，管程的压降和层流热交换能更准确地预测。当像雷诺数等因素处于临界状态时，管程因根据流体来选择。

⑥壳程流体在较低的雷诺数时就可获得湍流流动，因此，壳程适合低密度流体。在管程通过多管道可获得很高的雷诺数，但这不经济。

⑦在指定的热量和压力，所需实现的经济要求下，设计一台管壳式换热器包括许多固定的参数，如管径、壁厚、管长、管程数、管间距、排管方式、壳的大小、折流板数、折流板类型、折流板大小等，对一个中等尺寸的换热器设计来说，大概需要40步独立地逻辑设计，这将导致240=1.0*1012个不同路径，这对较老的计算机程序来说数据量太大了，所以，应该在符合实际经验基础上简化问题。

Reading Material 20

Basic Stirred Tank Design

①The dimensions of the liquid content of a vessel and the dimensions and arrangement of impellers, baffles and other internals are factors that influence the amount of the energy required for achieving a needed amount of agitation or quality of mixing. The internal arrangements depend on the objectives of the operation: whether it is to maintain homogeneity of a reacting mixture or to keep a solid suspended or a gas dispersed or to enhance heat or mass transfer. A basic range of design factors, however, can be defined to cover the majority of the cases, for example as in Fig.

4.4 (a).

②The Vessel A dished bottom requires less power than a flat one. When a single impeller is to be used, a liquid level equal to the diameter is optimum, with the impeller located at the center for an all-liquid system. Economic and manufacturing considerations, however, often dictate higher ratios of depth to diameter.

③Baffles Except at very high Reynolds numbers, baffles are needed to prevent vortexing and rotation of the liquid mass as a whole. When solids are present or when a heat transfer jacket is used, the baffles are offset from the wall a distance equal to one-sixth the baffle width which is about one-twelfth the tank diameter. Four radial baffles at equal spacing are standard; six are only slightly more effective, and three appreciably less so. When the mixer shaft is located off center, the resulting flow pattern has less swirl, and baffles may not be needed, particularly at low viscosity.

④Draft Tubes A draft tube is a cylindrical housing around and slightly larger in diameter than the impeller. Its height may be little more than the diameter of the impeller or it may extend the full depth of the liquid, depending on the flow pattern that is required. Usually draft tubes are used with axial impellers to direct suction and discharge streams. An impeller-draft tub e system behaves as an axial flow pump of somewhat low efficiency. Its top to bottom circulation

behaviour is of particular valve in deep tanks for suspension of solids and for dispersion of gases.

⑤Impeller Size With commercially available motors and speed reducers, standard speeds are 37, 45, 56, 68, 84, 100, 125, 155, 190, and 320 rpm. Power requirements usually are not great enough to justify the use of continuously adjustable steam turbine drives. Two-speed drives may be required when starting torques are high, as with a settled slurry.

⑥Impeller Location As a first approximation, the impeller can be placed at 1/6 the liquid level off the bottom. In some cases there is provision for changing the position of the impeller on the shaft. For off-bottom suspension of solids, an impeller location of 1/3 the impeller diameter off the bottom may be satisfactory.

⑦Kinds of Impellers A rotating impeller in a fluid imparts flow and shear to it , the shear resulting from the flow of one portion of the fluid past another. Limiting cases of flow are in the axial or radial directions so that impellers are classified conveniently according to which of these flows is dominant. By reason of reflections from vessel surfaces and obstruction by baffles and other internals, however, flow patterns in most cases are mixed.

⑧Because the performance of a particular shape of impeller usually cannot be predicted quantitatively, impeller design is largely an exercise of judgment so a considerable variety has been put forth by various manufacturers. A few common types are illustrated on Fig. 4.4 (b) ~ (i) and are described as follows;

b. The three-bladed mixing propeller id\s modeled on the marine propeller but has a pitch selected for maximum turbulence. They are used at relatively high speeds ( up to 1800 rpm) with low viscosity fluids, up to about 4000 cP. The stabilizing ring shown in the illustration sometimes is included to minimize shaft flutter and vibration particularly at low liquid level.

c. The turbine with flat vertical blades extending to the shaft is suited to the vast majority of mixing duties up to 100000 cP or so at high pumping capacity.

d. The horizontal plate to which the impeller blades of this turbine are attached has a stabilizing effect. Backward curved blades may be used for the same reason as for type

e.

e. Turbine with blades are inclined 45°(usually). Constructions with two to eight blades are used, six being most common. Combined axial and radial flow are achieved. Especially effective for heat exchange with vessel walls or internal coils.

f. Curved blade turbines effectively disperse fibrous materials without foulin

g. The swept back blades have a lower starting torque than straight ones, which is important when starting up settled slurries.

g. Shrouded turbines consisting of a rotor and a stator ensure a high degree of radial flow and shearing action, and are well adapted to emulsification and dispersion.

h. Anchor paddles fit the contour of the container, prevent sticking of pasty materials, and promote good heat transfer with the wall.

i. Gate paddles are used in wide, shallow tanks and for materials of high viscosity when low shear is adequate. Shaft speeds are low.

搅拌槽设计基础

①容器液体容量的尺寸及叶轮、档板和其它内部结构的安装和面积是影响振动次数和混合质量的因素。内部结构取决于操作目的：是保持反应混合物的相似性或是保持固体悬浮形

式或是使气体分散或提高热交换和质量交换设计因素的基本范围，可以用来代表大多数情况，如图4.4(a)所示。

②容器圆底比平底要求的原动力更小，当使用一个单叶轮时，对一个全液系统来说，与在中心的叶轮一起的液线与直径相等时是最好的。但是，出于对经济和制造因素的考虑，经常选择较大的深度与直径的比例。

③挡板除雷诺数很大时外，都需要用隔板来阻止涡流的产生和液体整体旋转。当有固体出现或使用热交换外壳时，隔板用来抵消隔板间距。它等于挡板宽的1/6、槽径的1/12。四块空间位置对称的辐射状的隔板较常见，6个细小的叶片工作效率更高，三块叶片的效率较低。当搅拌器位于中心附近时，很少会产生漩涡，此时，隔板也可以不用，特别是在低粘度液体时。

④循环管循环管是一个圆筒形框架，其直径比叶轮直径稍大。其高度比叶轮直径稍大，且可增大液体深度，这取决于所要求的流动类型。通常循环管与轴向叶轮一起用来控制吸、排气。叶轮—循环管系统类似于效率稍低的轴向流动抽水机，在深水槽中对固体悬浮物和气体分散来说，该系统从顶部到底部的循环过程是具有特殊价值的。

⑤叶轮尺寸取决于叶轮尺寸和由雷诺数、弗诺德和动力数值所描述的操作条件，这些数值与液体本身的特性有关。对普通的涡轮叶轮来说，叶轮直径与容器下陷距离的比值范围为 d / D t = 0.3~~0.6 , 例如，在气体分散中，高转速的价值不高。

⑥叶轮速度商用发动机和减速器规定叶轮标准速度有37、45、56、68、84、100、125、155、190和320转 / 分钟。动力设备通常无法提供连续调节气轮机的使用动力，当起始转矩很高时就需要两级速度来固定泥浆。

⑦叶轮位置在以前的一个近似值，叶轮被安装在离底部1/6的液线上。在有些时候有改变叶轮位置的装置，对悬浮在溶液中的固体悬浮液来说，叶轮底部的距离是叶轮直径的1/3时较合适。

⑧叶轮种类个旋转叶轮使液体流动，以搅拌液体，不断的搅拌，促使液体分离和融合。流动的极限情况是在垂直或辐射状位置，这使得通过流体流过叶轮方式将叶轮很好的分类。由于容器表面及挡板的阻碍，使得流型在大多数情况下是混合型的。

⑨由于特殊形状的叶轮的性能不能定量的预测，所以叶轮设计在很大程度上依靠经验的判断，通过各种产品来实现各种设计方案。图4.4(b)~~(i)列举了一些普通的类型，现在说明如下：

b. 三刀片混合型螺旋桨是以航海用螺旋桨为原型的，但三刀片混合型的叶片成一定的倾斜度以使流体得到最大限度的湍流。三刀片型用于流速较高、低粘度的流体，产量大约为4000。图中所示稳定圈用来减少轴的振动和低液面时的特殊振动。

c. 平板竖直叶片延伸至轴的涡轮适合大多数混合流体，其产量为100000或在高的泵容量。

d. 装在涡轮叶片上的水平圆盘起固定作用，叶轮上的后弯叶片与e型叶片的功能相同。

e. 叶轮叶片间彼此成450倾角（通常情况），叶轮上的叶片数有从2~~8片，大多数情况下是6片，该叶轮可完成液体轴向和辐射状流动，它对容器内壁和内部圆盘的热交换特别有效。

f. 弯曲叶片在没有污垢时，对纤维物质的搅拌非常有效，弯曲叶片的转动比直的需要更小的启动转矩，这种性质在启动搅拌泥浆时很重要。

g. 隐蔽式叶轮机是由一个转子和定子组成的，它使流体作辐射状流动并截断流体。它还适用于将流体乳化和均匀分散。

h. 锚式叶轮适用于容器的外轮廓，用来防止杂质的混入，还可促进容器内壁的热交换。

i. 大浆型的涡轮适用于宽、浅槽和低剪切的高粘度液体的搅拌，其轴转速较慢。

Reading Material 21

The Centrifugal Pump

①The centrifugal pump is by far the most widely used type in the chemical and petroleum industries．It will pump liquids with very wide ranging properties and suspensions with a high solids content including，for example，cement slurries，and may be constructed from a very wide range of corrosion resistant materials．The whole pump casing may be constructed from plastics such as polypropylene or it may be fitted with a corrosion．resistant lining．Because it operates at high speed，it may be directly coupled to an electric motor and it will give a high flowrate for its size．

②In this type of pump，the fluid is fed to the centre of a rotating impeller and is thrown outward by centrifugal action．As a result of the high speed of rotation the liquid acquires a high kinetic energy and the pressure difference between the suction and delivery sides arises from the conversion of kinetic energy into pressure energy．

③The impeller consists of a series of curved vanes SO shaped that the flow within the pump is as smooth as possible．The greater the number of vanes on the impeller，the greater is the control over the direction of motion of the liquid and hence the smaller are the losses due to turbulence and circulation between the vanes．In the open impeller。the vanes are fixed to a central hub，whereas in the closed type the vanes are held between two supporting plates and leakage across the impeller is reduced．As will be seen later，the angle of the tips of the blades very largely determines the operating characteristics of the pump．

④The liquid enters the casing of the pump，normally in an axial direction，and is picked up by the vanes of the impeller．In the simple type of centrifugal pump，the liquid discharges into a volute，a chamber of gradually increasing cross—section with a tangential outlet．A volute type of pump is shown in Fig．5．1(a)．In the turbine pump[-Fig．5．1(b)]the liquid flows from the moving vanes of the impeller through a series of fixed vanes forming a diffusion ring．This gives a more gradual change in direction to the fluid and more efficient conversion of kinetic energy into pressure energy than is obtained with the volute type．The angle of the leading edge of the fixed vanes should be such that the fluid is received without shock．The liquids flows along the surface of the impeller vane with a certain velocity whilst the tip of the vane is moving relative to the casing of the pump．The direction of motion of the liquid relative to the pump casing--and the required angle of the fixed vanes—is found by compounding these two velocities．In Fig．5．2，uv is the velocity of the liquid relative to the vane and ut is the tangential velocity of the tip of the vane；compounding these two velocities gives the resultant velocity u2 of the liquid．It is apparent，therefore，that the required vane angle in the diffuser is dependent on the throughput，the speed of rotation，and the angle of the impeller blades．The pump will therefore operate at maximum efficiency only over a narrow range of conditions．

⑤Virtual head of a centrifugal pump

The maximum pressure is developed when the whole of the excess kinetic energy of the fluid is converted into pressure energy. As indicated below．the head is proportional to the square of the radius and to the speed，and is of the order of 60m for a single—stage centrifugal pump；tor higher

pressures，multistage pumps must be used．Consider the liquid which is rotating at a distance of between r and r+dr from the centre of the pump(Fig．5.3)．The mass of this element of fluid dM is given by 2πrdrdρ，where ρ is the density of the fluid an d 6 is the width of the element of fluid。

⑥If the fluid is traveling with a velocity u and at an angle θ to the tangential direction．The angular momentum of this mass of fluid

=dM(urcosθ)

⑦The torque acting on the fluid dτ is equal to the rate of change of angular momentum with time，as it goes through the pump

dτ=dMα/αt(urcosθ)=2πrbρdrα/αt(urcosθ)

⑧The volumetric rate of flow of liquid through the pump：

Q=2πrbα/αt

dr=Qρd(urcosθ)

⑨The total torque acting on the liquid in the pump is therefore obtained integrating dτbetween the limits denoted by suffix 1 and suffix 2，where suffix 1 refers to the conditions at the inlet to the pump and suffix 2 refers to the condition at the discharge．

Thus，τ=Qρ(u2r2cosθ2一ulr lcosθ1)

The advantages and disadvantages of the centrifugal pump

⑩The main advantages are：

(1) It is simple in construction and can，therefore，be made in a wide range of materials

(2)There is a complete absence of valves．

(3)It operates at high speed(up to 100 Hz)and，therefore，can be coupled directly to

an electric motor. In general，the higher the speed the smaller the pump and motor for a give n duty．

(4)It gives a steady delivery．

(5)Maintenance costs are lower than for any other type of pump．

(6)No damage is done to the pump if the delivery line becomes blocked，provided it is not run in this condition for a prolonged period．

(7)It is much smaller than other pumps of equal capacity．It can，therefore，be made into a sealed unit with the driving motor and immersed in the suction tank．

(8)Liquids containing high proportions of suspended solids are readily handled．

⑴The main disadvantages are：

(1)The single—stage pump will not develop a high pressure．Multistage pumps will develop greater heads bat they are very much more expensive and cannot readily be made in corrosion—resistant material because of their greater complexity．It is generally better to use very high speeds in order to reduce the number of stages required．

(2)It operates at a high efficiency over only a limited range of conditions; this applies especially to turbine pumps．

(3)It is not usually self-priming.

(4)If a non-return valve is not incorporated in the delivery or suction line, the liquid will run back into the suction tank as soon as the pump stops．

(5)Very viscous liquids cannot he handled efficiently．

离心泵

①离心泵是化工和石油工业中应用最广泛的一种泵。它能输送性能非常广泛的液体和固体含量高的悬浮液，像水泥浆，可以用多种抗腐蚀材料建造。泵的整个外壳可用像聚丙烯这样的塑料来建造，或者用腐蚀衬里加工。由于它的高速运转，可将其直接耦合到电动机上，由电动机的规格大小决定流量高低。

②在这样的泵中，流体被灌入到旋转叶轮的中心，通过离心作用向外流动。由于高速旋转，液体在吸入口和因动能转化为压能的出口侧获得较高的动能和压力差。

③叶轮由一系列弧形叶片组成，因此能使液体的流动尽可能平稳。叶轮中叶片越多，则液体的流动方向越好控制，那么液体循环流动时因波动引起的损失就越少。在开式叶轮中，叶片被固定在中心轮毂上，而在闭式中叶片则是用两块钢板支撑以减少漏液。由此可以看出，在很大程度上，叶片末端的角度决定了泵的工作特性。

④流体通常在轴向上通过叶片的上升进入泵壳。在这种简单类型的离心泵中，液体由切向方向随着横截面逐步流到蜗壳中。图5.1（a ）所示为旋涡型泵。图5.1（b ）中，在涡轮泵中的液体随移动的叶轮在一系列固定叶片中形成扩散环。这种旋涡能逐渐改变流体的流动方向，并有效地将动能转化成压能。固定叶片前缘处的流体应该没有受到冲击。沿着叶轮叶片，液体的流动具有一定速度，同时，叶片末端相对于泵体又移动。液体的运动方向相对于泵壳——和固定叶片所需的角度一样——是两个速度的合成方向。在图5.2中，u v 是液体相对于叶片的速度，u t 是叶片上某点的切向速度；将这两个速度合成即可得到液体的速度u 2。因此，很明显，在扩散环中所需要的叶轮角由叶轮的产量、旋转速度和叶片的角度决定。所以，泵在很严格的条件下才能有最大的运行效能。

⑤离心泵的有效压头

当流体所剩余的动能全部转化为压能时，压力最大。如下文所述，有效压头和半径的平方以及速度成正比，压力更高时，必须使用多级泵。考虑到液体在离泵中心r 到r+dr 的距离内旋转，如图5.3所示。这一部分流体的质量为d M =2πr d r d ρ，其中ρ是流体的密度，b 是这部分流体的宽度。

⑥如果流体在与切向方向成θ角上以速度u 流动，则这部分质量流体的角动量为 =d M (ur cos θ)

⑦流体通过泵所产生的扭转力等于角动量对时间的改变量

d τ=d M

t ??(ur cos θ)=2πrb ρd r t

??( ur cos θ) ⑧液体的体积流速为： Q=2πrb

t ?? d r =Q ρd (ur cos θ)

⑨因此，液体在泵中受到总的扭转力由d τ在小标1和2之间积分而得，下标1引用的是泵入口处的条件，小标2是出口时的条件。

于是有：τ=Q ρ（u 2r 2cos θ2 – u 1r 1cos θ1）

离心泵的优缺点

?主要优点有：

（1）制造简单，可用多种材料加工。

（2）无阀门。

（3）高速运转（高达100赫兹），因此可直接耦合到电动机上。一般地，速度越大，泵和电动机的效率越小。

（4）能平稳传送。

（5）维修费用比其他类型的泵少。

（6）输送堵塞时，只要不是长时间运作，泵就不会被损坏。

（7）与其它泵相比，体积较小。因此，它可以利用电动机做成密封装置沉浸在吸收罐中。

（8）能容易输送含有高比例悬浮固体的液体。

⑴主要缺点有：

（1）单级泵不能提高压力。而多级泵能提高压头，但价格昂贵而且由于它们的复杂性不能用抗腐蚀的材料加工建造。通常用较高的速度来减少所需要的级数。

（2）只有在有限条件下才能以最高效能运作：尤其是涡轮泵。

（3）它不能自动注水。

（4）在输送和吸收管道中，如果没有止回阀，液体就会在泵停止瞬间倒流到吸入槽内。

（5）不能有效处理粘性液体。

Reading Material 22

Reciprocating Compressors and Their Applications

①1．Introduction

The purpose of compressors is to move air and other gases from place to place．Gases，unlike liquids，are compressible and require compression devices，which although similar to pumps ,operate on somewhat different principles．Compressors，blowers，and fans are such compression devices．

②Compressors．Move air or gas in higher differential pressure ranges from 35 psi to as high as 65000 psi in extreme cases．

③Blowers．Move large volumes of air or gas at pressures up to 50 pounds per square inch．

④Fans．Move air or gas at a sufficiem pressure to overcome static forces．Discharge pressures range from a few inches of water to about 1 pound per square inch．

⑤2．What is a Compressor?

Basic Gas Laws

Before discussing the types of compressors and how they work，it will he helpful to consider some of the basic gas laws and the manner in which they affect compressors．

⑥By definition，a gas is a fluid having neither independent shape nor form，which tends to expand indefinitely．

⑦Gases may be composed of only one specific gas maintaining its own identity in the gas mixture．Air，for example，is a mixture of several gases，primarily nitrogen(78％by volume)，oxygen(21％)，argon(about 1％)，and some water vapor．Air may also，due to local conditions，contain varying small percentages of industrial gases not normally a part of

air．

⑧The First Law of Thermodynamics

This law states that energy cannot be created or destroyed during a process，such as

compression and delivery of a gas ．In other words ，whenever a quantity of one kind of energy disappears ．an exactly equivalent total of other kinds of energy must be produced ．

⑨The Second Law of Thermodynamics

This Law is more abstract ，but can be stated in several ways ：

(1)Heat cannot ，of itself ，pass from a colder to a hotter body ．

(2)Heat can be transferred from a body at’a lower temperature to one at a higher

temperature only if external work is performed ．

(3)The available energy of the isolated system decreases in all real processes ．

(4)By itself ，heat or energy(1ike water)，will flow only downhill(i ．e ．，from hot to cold)．

⑩Basically ，then ，these statements say that energy which exists at various levels is available for use only if it can move from a higher to a lower level ．

Ideal or Perfect Gas Laws

⑴An ideal or perfect gas is olle to which the laws of Boyle ，Charles ，and Amonton apply. Such perfect gases do not really exist ，but these three laws of thermodynamics can be used if corrected by compressibility factors based on experimental data ．

⑵Boyle’s Law states that at a constant temperat ure ，the volume of an ideal gas decreases with an increase in pressure ．

⑶For example ．it a given amount of gas is compressed at a constant temperature to half its volume ，its pressure will be doubled ．

11222

112V P V orP P P V V ===constant ⑷Charles ’Law states that at constant pressure ，the volume of an ideal gas will increase s the temperature increases ．

⑸If heat is applied to a gas it will expand ，and the pressure will remain the same ．This law assumes the absence of friction or the presence of an applied force ．

1

1221212T V T V or T T V V == ⑹Amonton’s Law states that at constant volume ，the pressure of an ideal gas will

increase as the temperature increases ．

1

1221212T P T P or T T P P == ⑺Gas and Vapor By definition ，a gas is that fluid form of substance in which the substance

can expand indefinitely and completely fill its container ．A vapor is a gasified liquid or sdid —a substance in gaseous form ．

The terms gas and vapor are generally used interchangeably ．

⑻3．How Compressors Work?

To understand how gases and gas mixtures behave ，it is necessary tO recognize that gases consist of individual molecules of the various gas components ，widely separated compared to their size ．These nolecules are always traveling at high speed ；they strike against the walls of the

enclosing vessel and produce what we know as pressure．Refer to Fig．5．7．

⑼Temperature affects average molecule speed．When heat is added to a fixed volume of gas，the molecules travel faster，and hit the containing walls of the vessel more often and with greater force．See No．5．8．This then produces 8 greater pressure．This is consistent with Amonton’s Low.

⑽If the enclosed vessel is fitted with a piston so that the gas can be squeezed into a smaller space，the molecule travel is now restricted．The molecules flow hit the walls with a greater frequency，increasing the pressure，consistent with Boyle’s Law。See Fig．5．9．（21）However，moving the piston also delivers energy to the molecules，causing them to move with increasing velocity．As with heating．This resuits in a temperature i’ncrease．Furthermore in all the molecules have been forced into a smallter space，which results in an increased number of collisions on a unit area of the wall．This，together with the increased velocity，results in increased pressure．．

（22）The compression of gases tohigher pressures。results in higher temperatures，creating problems in compressor design．All basic compressor elements，regardless of type，have certain design—limiting operating conditions．When any limitation is involved，it becomes necessary to perform the work in more than one step of the．Compression process．This is termed multistaging and uses one basic machine element designed to operate in series with other elements of the machine．

（23）This limitation varies with the type of compressor，but the most。inmportant limitations include；

(1)Discharge pressure ____all types．

(2)Pressure rise or differential______ dynamic units and most displacement types．

(3)Compression ratio______dynamic units．

(4)Effect of clearance_____reciprocating units(this is related tothe compression ratio)．

(5)Desirability of saving power．

（24）Methods of compression

Four methods are used to compress gas．Two are in the intermittent class，and two are

in the continuous flow class．(These are descriptive，not thermodynamic or dutv classifieation terms．)

(1)Trap consecutive quantities of gas in some type of—enclosure．reduce the volume (thus increasing the pressure)，then push the compressed gas out of the enclosure．

(2)Trap consecutive quant~ies 0f gas in some type of enetosure．carry it without

volume change to the discharge opening，compress the gas b§r haekflow from the discharge system，then push the eompressed gas out of the enclosure。

(3)Compress the gas by the mechanical action of rapidly rotating impellers or bladed

rotors that impart velocity and pressure to the flowing gas．(Velocity is further converted

into pressure in stationary diffusers or blades．)

(4)Entrain the gas in a high velocity jet of the same or another gas(usually，but not necessarily，steam)and eonven the high velocity of the mixture into p~essure in a diffuser．

往复式压缩机与应用

? 1.介绍

压缩机工作的目的是把空气和其他气体移动到另一处。气体不像液体，它们是可压

缩的，因此要求使用压缩设备，这些设备类似于泵，但遵循的原则有所不同。这类设备有压缩机，鼓风机和风机。

?压缩机，可从35psi 的风压至65000psi 的极限情况下移动空气或气体。

?鼓风机，可移动压力高达50磅每立方英寸的大体积空气或气体。

?风机，在足够气压下克服静压，从数英寸水柱压解压至一磅每立方英寸下移动气体。

? 2.何为压缩机？

基本气体法则：在讨论压缩机如何工作之前考虑一些基本气体法则和它们作用于压缩机的方式是很有益的。

?通过定义可知，气体可看作可无限扩散的无定形液体。

?气体可能只由一种特定的在混合气体中保持自身性质的气体组成。比如空气，是各种气体的混合物，主要含有氮（体积分数71%），氧（21%），氢（约1%），还有一些水蒸气。空气可能也会随当地气体大气状况而含有少量工业气体。

?第一热力学法则：这些法则表明能量不可能在某一过程中凭空产生或消失。比如压缩或气体传递过程。换句话说一定量的某种能量的消失，必然会有等量的另一种形式的能量产生。

?第二热力学法则：这一定律较抽象，但可有几种表述方式：

（1） 热量不能自发地从低温体传至高温体；

（2） 热量只能在外力作用下由低温物体传至高温物体；

（3） 孤立系统的可用能量在实际过程中减少。

（4） 热或能量，只能自发地向下降。

?根本上说，这些表述表明，各种存在形式的可用能量，只能从高到低地流动。

⑴理想气体法则：理想气体指遵循波尔定律、查斯里定律、阿孟定律的气体，这样的理想气体并不存在，但用基于实验数据的压缩因子修正后可应用这三条热力学定律。 ⑵波尔定律表述为一定温度下，理想气体的体积随压力增加而减少。

⑶例如，当一定量的气体在定温下压缩至一半体积时，它的压力将增加一倍。

11222

112V P V orP P P V V == ⑷查尔斯定律表述为，定压下，理想气体的体积随温度升高而增加。

⑸如果热量施加于膨胀气体，则压力将保持不变。这一法则假定为摩擦力损失或施加力。

1

1221212T V T V or T T V V ==

⑹阿孟定律表述为对于定体积条件下，理想气体的压力将随温度增加而增大。

1

1221212T P T P or T T P P == ⑺气体与蒸汽 通过定义可知，气体是指流体中无限扩张并充满容器的物质。蒸汽是气化了的液体或固体，即物质的气化状态。

气体与蒸汽通常可以互换使用。

⑻ 3.压缩机如何工作

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