制冷专业英语课件.ppt

1、Part 1 Thermodynamics and Heat Transfer,This unit introduces the basic and elementary knowledge of thermodynamics and heat transfer. After learning, you will be able to understand: The basic concepts and terminology in thermodynamics and heat transfer The three ways of thermal transmission The compo

2、sition of thermal systems The thermodynamic cycle principle,Return to contents,Part 1 Thermodynamics and Heat Transfer,Text 1 Thermodynamic System Text 2 General Characteristics of Heat Transfer Text 3 Conduction Text 4 Convection,Return to contents,Text 1 Thermodynamic System,In the thermal enginee

3、ring, the studied objects normally are isolated from one another and then we try to analysis the change and interaction, the studied objects isolated is named thermodynamic system.1 The boundary of a system can be either real or imaginary, and either fixed or movable. If the gas in a cylinder is the

4、 studying object, then it is the thermodynamic system. 2 There may be many objects in an engineering problem. The solution of a system is dependent on which objects are under consideration. In a thermodynamics system, we can do it either by placing an imaginary envelope around the objects under cons

5、ideration or by using an actual envelope if it exists. 3,contents,Unit 1,New words,For example, when dealing with a gas in the cylinder where the boundaries are located on the outside of the cylinder, 4 the system includes both the cylinder and its contained gas. On the other hand, when the boundari

6、es are placed at the inner face of the cylinder, the system consists solely of the gas itself. So it is very important and essential for us to specify the boundaries of the system carefully. 5 The boundaries of a closed system may be either rigid or may expand or contract, 6 but its mass will not ch

7、ange. When the energy crossing the boundaries of a closed system is zero, the system may be treated as an isolated system.,Based on the difference of the characteristic of the systems, the different systems are named. (1) When the boundaries of a system would not exchange with the surroundings, then

8、 can said that it is a closed system. However, it may exchange energy in any form of heat or work with the surroundings.,(2) Conversely, if there are any matter exchange between the system and the surroundings, then it is an open system. The quantity of the matter in an open system may be either var

9、iable or constant. The boundaries of an open system are so placed that their location does not change with time. Thus, the boundaries enclose a fixed volume, commonly known as the control volume. Sometimes a system may be a closed system at one moment and an open one the next. For example, consider

10、we would study a cylinder of an internal combustion engine, when the valves close, the system is a closed system. And when either or both of the valves open, the system will become an open system.,In most cases, a studied object would be a large and very complex system. We can break down it into a l

11、ot of component parts and analyze every component parts. Then the performance of the entire system can be determined by the summation of the performance of the individual component systems. 7 For example, consider the liquid-vapor part of a steam power plant as a total system. This closed system con

12、tains the steam generator, the steam turbine, the steam condenser, the feed-water pumps, and the feed-water heaters. All of these units may be considered separately by throwing a boundary around them. Since a fluid enters and leaves each of these smaller systems, each one is an open system and must

13、be analyzed .,boundaryn.边界, 分界线 considerationn.体谅,考虑,需要考虑的事项,报酬 cylinder n.圆筒, 圆柱体, 汽缸, 柱面 envelopen.信封,封袋,天包层,数包迹,生包膜 imaginarya.假想的,想象的,虚构的 Solely ad.独自地, 单独地 solutionn.解答,解决办法,溶解,溶液,解决方案 be isolated from被与隔绝 either or或（者）或（者） for example例如 be dependent on依靠, 依赖,New Words and Expressions,Text 2,Te

14、chnical Terms a steam power plant蒸汽发电厂 an internal combustion engine 内燃机 the feed-water heater给水加热器 the feed-water pump(给水)泵 the steam condenser蒸汽冷凝器 the steam generator蒸汽发生器（锅炉） the steam turbine蒸汽轮机,Exercise(1),Answer the following questions according to the text. (1) How do we usually do when stu

15、dying a thermal engineering? (2) How can be the boundary of a system? (3) What is the solution of a system dependent on? (4) Based on the difference of the characteristic of the systems, how many the different systems are named? (5) How do we usually do when a studied object is a large and very comp

16、lex system? (6) What is the boundary of a studying object?,Exercise(2),Decide whether the following statements is true or false according to the text. (1) In the thermal engineering, the studied objects normally are isolated from one another and then try to analysis the change and interaction. (2) T

17、he boundary of a system can be either real or imaginary, but it can not be either fixed or movable. (3) In a thermodynamics system, we can solute it only by placing an imaginary envelope around the objects under consideration and not by using an actual envelope if it exists. (4) It is not very impor

18、tant and essential for us to specify the boundaries of the system carefully. (5) Then the performance of the entire system can be determined by the summation of the performance of the individual component systems.,Exercise(3),Put the following words into Chinese/English. (1) If the gas in a cylinder

19、 is the studying object, then it is the thermodynamic system. (2)研究缸内气体时，其（系统）边界在汽缸体外，系统则包含汽缸及缸内气体。以汽缸内表面为边界，系统则只包括（缸内）气体。 (3) In most cases, a studied object would be a large and very complex system. We can break down it into a lot of component parts and analyze every component parts. (4)因为当流体进入或离开

20、这些小系统时，各部均为开口系统且需如此分析。,Notes to the Text1.In the thermal engineering, the studied objects normally are isolated from one another and then we try to analysis the change and interaction, the studied objects isolated is named thermodynamic system. 句中the studied objects normally are isolated from one an

21、other与we try to analysis the change and interaction相并列。在热力工程中，通常将研究对象分离出来再分析其变化及（与外界）的相互作用，该对象即热力系统。2. The boundary of a system can be either real or imaginary, and either fixed or movable. If the gas in a cylinder is the studying object, then it is the thermodynamic system. 句中and either fixed or mo

22、vable.是省略句。全句为and it can also be either fixed or movable.3.we can do it either by placing an imaginary envelope around the objects under consideration or by using an actual envelope if it exists. eitheror结构，两个介词短语（by）相并列。,Text 1,4.when dealing with a gas in the cylinder where the boundaries are loca

23、ted on the outside of the cylinder, 分词短语做状语，全句为when we deal with 5.So it is very important and essential for us to specify the boundaries of the system carefully. 此句为it is for sb. to do sth.结构。6. The boundaries of a closed system may be either rigid or may expand or contract, 是eitheroror句。7. Then th

24、e performance of the entire system can be determined by the summation of the performance of the individual component systems. 可将之化整为零再逐件分析。则全系统的性能取决于各分系统之统和。,Text 2 General Characteristics of Heat Transfer,When study the course of the heat transfer carefully，we can find that the heat or thermal ener

25、gy is transferred from one region to another by three modes: conduction, convection and radiation. In fact，the heat transfer process is a combining of two or three. 1 在仔细研究热量传递的过程中，我们可以发现热量/能量由一个区域到另外一个时，通过三种方式进行传递：导热、对流和辐射。 事实上，热传递通常为（其中）两或者三种中的组合。,contents,Unit 1,New words,（1）Conduction is a proce

26、ss that the heat transfers from the parts of high temperature of the object to the low or from a warmer object to the cooler contacting with it. 2 导热即热量从物体的高温部向低温部或从热物体向与之接触的冷物体传递的过程。,Temperature is the driving force behind the heat transfer. The great the temperature difference, the greater the hea

27、t transfer rate is. And heat does not conduct at the same rate in different materials. 热传导的动力为温差。温差越大，传热率越高，并且不同物质的导热系数不同。,The heat transfer in conduction can be explained as the energy actually traveling from one molecule to another. The second law of thermodynamics states that thermal transfer occ

28、urs in the direction of decreasing temperature. In solid opaque bodies, the significant heat transfer is thermal conduction 导热可以解释为能量在分子之间的传递。根据热力学第二定律，热传递是发生在温度降低的方向。对于非透明固体而言，导热为其主要的热量传递方式。,（2）Thermal convection may occur from one location to another by means of current set up in a fluid medium. 4

29、 When heat is moved, it is normally transferred into some movable substance. The most common fluid mediums in convection process are air and water. 对流是借助于流体形成的介质来实现热量由某一区域到另一区域的传递。当热量传递时，往往传低于某种可移动的物质中。空气和水是最常见的两种热传递流体媒介。,Thermal convection involves energy transfer by eddy mixing and diffusion of th

30、e fluid in addition to conduction. Consider heat transfer to a fluid flowing inside a pipe， If the Reynolds number is sufficiently great, three different flow regions will exist. 除导热外，对流换热还借助于流体的涡旋洄流及流体碰撞混合过程予以实现。对于管内流动流体的传热，如果雷诺数足够大，则三种流动边界均会存在。,When fluid currents are produced by sources external

31、to the heat transfer region, for example, a blower or pump, the solid-to-fluid heat transfer is termed forced convection. If the fluid flow is generated internally by non-uniform densities caused by temperature variation, the heat transfer is termed free or natural convection.5 当流体产生于（源于）热传递区之外时，例如风

32、机或泵，则固液之间的热传递成为强制对流。如果流体是由于系统内部温度变化所导致的流体密度不同而产生的，则该热传递成为自由或自然对流。,（3）In conduction and convection, heat transfer takes place through matter. For radiant heat transfer, there is a change in energy form; from internal energy at the source to electromagnetic energy for transmission, then back to intern

33、al energy at the receiver. 6 对于导热和对流，其热量传递需借助物质实现。对于辐射换热过程，其需要一个能量形式的转换，既热源的内容转换为电磁能来实现传递，然后于接收处转换为内能。,Whereas conduction and convection are affected primarily by temperature difference and somewhat by temperature level, the heat transferred by radiation increase rapidly as the temperature increases

34、. 导热和对流主要受温差和物体的不同温度水平的影响，而辐射换热直接随温度的升高而加强。,Radiation is the only type of heat transfer that can travel through a vacuum, such as space, because radiation is not dependent on matter as a medium of heat transfer. 辐射是唯一可以在真空，如太空，进行热传递的形式，因为其无需依靠某种物质作为介质进行传热。,This is impossible with convection and cond

35、uction because they require some form of matter, like air or water, to be the transmitting medium. 而这对于对流换热和热传导是不可能发生的，因为他们需要诸如空气和水作为传热介质。,New Words and Expressions,blower n. 风机，风扇, 爱吹牛的人 characteristica. 特有的, 典型的; n.特性, 特征 collision n.碰撞, 冲突 conduction n. 传导 contact n.接触, 联系 vt.接触, 联系 convection n.

36、传送, 对流 eddy n.旋转, 漩涡v. (使)起漩涡 elastic a.弹性的 electromagnetic a.电磁的 internally ad.在内, 在中心,Text 2,mediumn.媒体, 方法, 媒介 a. 中间的, 中等 moleculen.化分子, 些微 non-uniform a.不一致的, 不均匀的 opaque n. 不透明物 a. 不透明的,不传热的,迟钝的 primarily ad.首先, 起初, 主要地, 根本上 radiationn. 发（光、热）, 辐射, 放射（线） region n区域, 地方,地区,领域, (大气)层,temperature

37、n.温度 transmissionn. 播送,发射,传动,传送,传输,转播 vacuum n. 真空, 真空吸尘器 a.(产生)真空的 vt. 用真空 variation n. 变更,变化,变异,变种,音变奏,变调 whereas conj.然而, 反之, 鉴于, 尽管, 但是 a combining of结合 by means of依靠 contact with与联系，与接触 takes place发生,Technical Terms elastic collision弹性碰撞 flow region 流动区域 temperature difference温差 the fluid flow液

38、体流动，液流 the heat transfer region传热区 the heat transfer传热 the Reynolds number 雷诺数 the second law of thermodynamics热力学第二定律,Text 2,Exercise (1),Answer the following questions according to the text. (1) How many modes are there in the heat transfer？ (2)What is the heat conduction process? (3)What is the s

39、ignificant heat transfer mechanism in a solid opaque body? (4)What are the most common fluid mediums in convection process? (5)Which is the only type of the heat transfer that can travel through a vacuum?,Exercise(2),Decide whether the following statements is true or false according to the text. (1)

40、 The heat transfer process is not net. (2) Temperature different is the driving force behind the heat transfer. (3) Thermal convection can not occur from one location to another by means of current set up in a fluid medium. (4) For radiant heat transfer, there is not a change in energy form. (5) Whe

41、n fluid currents are produced by sources external to the heat transfer region, for example, a blower or pump, the solid-to-fluid heat transfer is termed forced convection. (6) This is possible with convection and conduction because they require some forms of matter, like air or water, to be the tran

42、smitting medium.,Exercise(3),Put the following words into Chinese/English. (1) Conduction is a process that the heat transfers from the parts of high temperature of the object to the low or from a warmer object to the cooler contacting with it. (2)根据热力学第二定律，热传递指向温度降低的方向。 (3) Whereas conduction and c

43、onvection are affected primarily by temperature difference and somewhat by temperature level, the heat transferred by radiation increase rapidly as the temperature increases. (4) 辐射是唯一可以在真空（例如太空）进行的热传递（形式），因其可以不依赖（某种）物质进行传热。,Notes to the Text1. When study the course of the heat transfer carefully，we

44、 can find that the heat or thermal energy is transferred from one region to another by three modes:句中that the heat or thermal energy is transferred from one region to another by three modes是宾语从句。仔细研究热量传递过程，我们可以发现热量通过三种方式进行传递： 2. Conduction is a process that the heat transfers from the parts of high

45、temperature of the object to the low or from a warmer object to the cooler contacting with it.句中the low是省略句，完全形式应为the parts of low temperature of the object。that the heat transfers from the parts of high temperature of the object to the low or from a warmer object to the cooler contacting with it是表语

46、a process的定语从句，句中fromto为介词短语做状语。导热即热量从物体的高温部向低温部或从热物体向与之接触的冷物体传递的过程。3. In gases, conduction is a result of elastic collision of molecules. In liquids and electrically conducting solids, it is believed to be caused by longitudinal oscillations of the lattice structure. 句中it is believed to be caused b

47、y longitudinal oscillations of the lattice structure.是it isto 结构，it是形式主语，to be caused （by longitudinal oscillations of the lattice structure.）是真实主语。,Text 2,4. Thermal convection may occur from one location to another by means of current set up in a fluid medium.句中set up in a fluid medium.为分词短语，做curr

48、ent的定语。其中的set是分词形式。对流是借助于流体介质形成的介质流来实现热量传递任务的。5. If the fluid flow is generated internally by non-uniform densities caused by temperature variation, the heat transfer is termed free or natural convection.caused by temperature variation是分词短语做定语。如果液流乃是由于系统内部由于温度变化所导致的密度不同导致，则该热传递过程成为自由（自然）对流。6. For ra

49、diant heat transfer, there is a change in energy form; from internal energy at the source to electromagnetic energy for transmission, then back to internal energy at the receiver. 该句为省略句。from internal energy at the source to electromagnetic energy for transmission, then back to internal energy at th

50、e receiver.是fromto结构。而热辐射（过程的实现）有一能量形式的转换过程，即热源内能（先）转化为电磁能进行传递，再于接受处转化为内能形式。介词短语at the source，for transmission，at the receiver分别做三个energy的宾语。,Text 2,Text 3 Conduction,Conduction is that the heat transfer through one or more substances from a region of high temperature to a region of low temperature

51、by the exchange of energy between the molecules of the substance. 1 In the process of transferring heat by conduction is based on the movement of the molecules, but no bodily displacement of the molecules occurs. However, the electron movement in a metal greatly assists in the heat transfer by condu

52、ction. 导热即分子间的热量借助于一种或者多种物质从高温处向低温处进行的热量交换。导热是基于分子运动的过程，但无分子位移发生。但是，金属的电子运动十分有助于热传导。,contents,Unit 1,New words,In general, a simple conduction usually occurs in solid. Because the volume of the working fluid will be changed when its absorbing or releasing heat. After a lot of the studies, Fourier de

53、veloped and summarized the fundamental law of conduction. 一般情况下，导热发生于固体之间。因为流体在吸收或者释放热量时，其体积会发生变化。 经过大量研究，傅里叶建立了热传导基本定律。,Consider steady-state, unidirectional heat flow through a solid. Take a slab of the solid having a cross-sectional area A normal to the path of heat flow. Let the thickness of the

54、 slab be dx, and let the temperature difference across the slab be dt.2 Then (1.5) Where Q=heat flow per unit of time =proportionality factor, called the thermal conductivity A=the area of that the conduction occurs dt/dx=rate of change in temperature with distance in the direction of heat flow.3 假设

55、稳态下，热量单向流经某一固体，取固体热流截面积A，板厚为dx，温差为dt。,Through a lots extensive experimental investigations, the values of thermal conductivities of many substances and the effect of temperature on these conductivities have been established. We could find that the thermal conductivity of any metal is much higher tha

56、n any of gas. 通过广泛实验调查，我们建立了许多物质的热导率（表）以及温度对热导率的影响。结果显示，金属导热性远远好于气体。,The value of thermal conductivity of a metal is only valid for these metals of a given degree of purity. Particularly, for those metals they are the highest in the thermal conductivity. 4 The introduction of a slight amount of anot

57、her metal will cause a significant change in their thermal conductivity. 金属的热导率是对一定纯度的金属有效。尤其是对哪些具有高导热率的金属。即便微量其它金属，也会导致金属热导率出现重大的差异。,There are some methods to know the thermal conductivity of a solid. The process to obtain a fairly accurate value for the thermal conductivity of a given solid of spe

58、cified composition is easy. 5 But it is much more difficult for us to determine the thermal conductivity of a gas, a vapor or a liquid, since it is too hard to eliminate the heat transfer in convection, which occurs with the transferring process in conduct simultaneously. 有多种方法获得固体的热导率。获得某种固体的准确热导率值

59、相对容易。但是，对于获得某一气体、蒸汽或者液体的热导率却相对困难。因为在对流中消除同时发生的导热十分困难。,And there are also many difficulties in the accurate measurement of other factors. So they are perhaps 10 to 25 percent in reported values of the thermal conductivities of fluids. When conduction in a simple wall, it is always assumed that the width and height of the wall are so large in comparison with the thickness of the wall that the heat flow may be considered to be unidirectional.6 并且，还有气体影响因素难以准确测量，一般的流体的热导率有1025%的误差。 当研究墙壁的传热过程时，总是假设墙壁的宽度和高度相对于墙壁的厚度而言无限大，即热流可以认为是单向传递。,One