火电厂自动化 电气自动化毕业设计外文翻译

1、PAGE 毕 业 设 计计（论 文）外 文 文 献献 翻 译学 号： 姓 名： 所在院系： 专业班级： 指导教师： 原文标题： TThe baasics of stteam ggeneraation and uuse 2009年 4月 29日PAGE 17蒸发汽化的基础础和使用 The basics of steam generation and use1.1 为何需需要了解蒸汽汽对于目前为止最最大的发电工工业部门来说说，蒸汽动力力是最为基础础性的。若没没有蒸汽动力力，社会的样样子将会变得得和现在大为为不同。我们们将不得已的的去依靠水力力发电厂、风风车、电池、太太阳能蓄电池池和燃料电池池，这些

2、方法法只能为我们们平日用电提提供很小的一一部分。蒸汽是很重要的的，产生和使使用蒸汽的安安全与效率取取决于怎样控控制和应用仪仪表，在术语语中通常被简简写成C&II（控制和仪仪表）。此书书旨在在发电电厂的工程规规程和电子学学、仪器仪表表以及控制工工程之间架设设一座桥梁。作为开篇，我将将在本章大体体描述由水到到蒸汽的形态态变化，然后后将叙述蒸汽汽产生和使用用的基本原则则的概述。这这看似简单的的课题实际上上却极为复杂杂。这里，我我们有必要做做一个概述：这本书不是是内容详尽的的论文，有的的时候甚至会会掩盖一些细细节，而这些些细节将会使使热力学家和和燃烧物理学学家都为之一一震。但我们们应该了解，这这本书的

3、目的的是为了使控控制仪表工程程师充分理解解这一课题，从从而可以安全全的处理实用用控制系统设设计、运作、维维护等方面的的问题。，1.2沸腾：水水到蒸汽的状状态变化当水被加热时，其其温度变化能能通过某种途途径被察觉（例例如用温度计计）。通过这这种方式得到到的热量因为为在某时水开开始沸腾时其效果可被被察觉，因而被称为感热。然而，我们还需需要更深的了了解。“沸腾”究竟是什么么含义？在深深入了解之前前，我们必须须考虑到物质质的三种状态态：固态，液液态，气态。（当当气体中的原原子被电离时时所产生的等等离子气体经经常被认为是是物质的第四四种状态，但但在实际应用用中，只需考考虑以上三种种状态）固态态，物质由分

4、分子通过分子子间的吸引力力紧紧地靠在在一起。当物物质吸收热量量，分子的能能量升级并且且使得分子之之间的间隙增增大。当越来来越多的能量量被吸收，这这种效果就会会加剧，粒子子之间相互脱脱离。这种由由固态到液态态的状态变化化通常被称之之为熔化。当液体吸收了更更多的热量时时，一些分子子获得了足够够多的能量而而从表面脱离离，这个过程程被称为蒸发发（凭此洒在在地面的水会会逐渐的消失失）在蒸发的的过程中，一一些分子是在在相当低的温温度下脱离的的，然而随着着温度的上升升，分子更加加迅速的脱离离，并且在某某一温度上液液体内部变得得非常剧烈，大大量的气泡向向液体表面升升起。在这时时我们称液体体开始沸腾。这这个过程

5、是变变为蒸汽的过过程，也就是是液体处于汽汽化状态。让我们试想大量量的水装在一一个敞开的容容器内。液体体表面的空气气对液体施加加了一定的压压力，随着液液体温度的上上升，便会有有足够的能量量使得表面的的分子挣脱出出去，水这时时开始改变自自身的状态，变变成蒸汽。在在此条件下获获得更多的热热量将不会引引起温度上的的明显变化。所所增加的能量量只是被用来来改变液体的的状态。它的的效用不能用用温度计测量量出来，但是是它仍然发生生着。正因为为如此，它被称为是潜潜在的，而不不是可认知的的热量。使这这一现象发生生的温度被称称为是沸点。在在常温常压下下，水的沸点点为100摄摄氏度。如果液体表面的的压力上升，需需要更

6、多的能能量才可以使使得水变为蒸蒸汽的状态。换换句话说，必必须使得温度度更高才可以以使它沸腾。总总而言之，如如果大气压力力比正常值升升高百分之十十，水必须被被加热到一百百零二度才可可以使之沸腾腾。沸腾的水表面的的蒸汽据说为为饱和的，在在特定的压力力下，沸腾发发生时的温度度被成为饱和和温度。关于蒸汽在任何何混合的温度度和压强及其其他因素下的的信息都可以以在蒸汽表格格中查到，如如今我们可以以通过软件查查询而不是用用传统的表格格。这些秩序序表最初是在在1915年年由英国的物物理学家Huugh Loongbouurne CCallenndar出版版发行的。因因为知识以及及测量技术的的进步，作为为测量单位

7、改改变的结果，如如今出现了许许多版本的蒸蒸汽表，但是是它们都只能能查出一种结结果，在任何何压强下，饱饱和温度，每每单位液体的的热量，具体体的体积等等等。在发电厂控制系系统的设计过过程中，了解解蒸汽和蒸汽汽表是必不可可少的。例如如，如果一个个设计师需要要补偿蒸汽流流量的压力变变化，或者消消除在水位测测量中的密度度误差，参考考这些表是至至关重要的。 另一个与蒸汽有有关的词是界界定汽水混合合物中的蒸汽汽含量。在英国，即是是所谓的蒸汽汽干度（在美美国使用的术术语是蒸汽品品质）。这意味着，如如果每公斤的的混合物含有有0.9公斤斤蒸汽和0.11公斤的水，干干燥分数是00.9。在相同大气压下下，当它的温温度

8、超过了它它的饱和温度度时，水蒸气气就成为过热热蒸气。当它它沸腾之后收收集起来，通通过一个管道道将它远离流流体，然后加加入更多的热热量给它，这这一过程中进进一步给过热热蒸汽补充能能量，从而提提高热量转换换为电能的效效率。 如前所述,热量量补充给已开开始沸腾的水水不会引起温度度的进一步变变化。相反，它它却改变流体的状状态。一旦形形成了蒸汽，焓降有助于蒸汽的总热量的增加。这些显热再加上潜热用于增加每公斤流体过热程度。电厂的一个主要要目标是将投入使用的的燃料能量转转化为可用的热或发发电。在利益益经济和环境境效益同等重重要的情况下下，重要的是是在这一转换换过程获得最最高水平的经经济和环境效效益。当从蒸汽

9、中中获得尽可能能多的能量后后，液体变成冷冷却水，然后进行行再热，终于于回到了锅炉炉重新使用。1.3蒸汽的性性质：正如前言，这本本书介绍给用用户的锅炉及及蒸汽发生器器，以及他们们的工厂或住住房和其他复复合物，或驱驱动涡轮，这这些都是发电电机的原动力力。此书将这种种过程统称为为发电厂。在所有这这些工程中，蒸汽都是由加热水使其沸腾得到的，我们在开始研究发电厂C I之前，必须了解参与这一进程的机理和蒸汽本身。首先，我们必须须先考虑一些些基本的热力力过程。其中中两个是卡诺诺和朗肯循环环，虽然C I工程程师可能无法法直接利用它，但如何运用用它仍然是一个非非常必要的了了解。1.3.1卡诺诺循环电厂的主要功能

10、能是将某种形式式的燃料资源源转换成电力力能源。尽管管许多尝试，但但并没有证明明在未经中间间媒介的情况况下，可以直直接将化石燃料（或或原子核燃料）的能能量转换为电能。若若太阳能电池池和燃料电池池在未来的大大规模使用得得以实现，将将足以对化石燃料使使用产生影响响，但目前这这种电厂只限于小规模模的应用。水水涡轮机的水水力发电厂能能够产生大量量的电力，但但这种电厂有有一定限制的的地方，他们们必须有满足足使用这些机机器的足够高高的水位。因此，如果希望望从化石燃料料或从核反应应中获得大量量的电能，首首先必须从可可用资源中释释放能量，然后传传送到发电机机，这个过程程从头到尾需需要使用一种种介质来传递递能量。

11、此外，有有必要采用可可以使其相对对安全和提高高效率的介质。对对地球来讲，水水至少在一般般情况下是一一种丰富和廉廉价的介质。随随着技术的发发展，在二十十世纪，使用用其他媒介的可可能性也已被被考虑，如使使用水银，但但除了应用程程序(如全新新航天器的限限制和适用条条件),这些些已经达到了了积极的使用,和蒸汽一样样普遍适用于于电站。卡诺循环的两个个热力学定律律。第一，焦焦耳定律，与与机械能做功有有关：卡诺定律定定义了在热能能转换成机械械能的工程中中的温度关系系。他认为，如如果该进程是是可逆的，热热可以转化成成机械能，然后后提取和重复复使用，并使使其闭环。如图11.1，活塞塞没有遇到任任何摩擦，内内气缸

12、完全由绝缘材料制成成。活塞是由由“工作流体”驱动。气缸的的一端，可以以自由的从理理想导体切换换为绝缘体。外汽缸有两部分组成，其中之一可以提供热量而其本身的温度(T1)下降, 另一个是一个无底冷水槽温度(T2)是不变的。如图1.2所示示 ，显示了压力/容积关系的的流体在汽缸缸内的整个循循环周期。由于这一进进程是一个反反复循环的过过程，所以研研究可以从任何方方便的起点开开始，我们将将在A点开始始，在气缸盖盖（在这个时时候假定为是是一个理想导导体），使热热量从热源进进入气缸。结结果是，中期期开始扩大，如如果它被允许许自由扩大，玻玻意耳定律（其其中指出，在在任何温度之之间关系的压压力和容量是是常数）中

13、规规定的温度不不会上升，但但将留在其初初始温度（TT1） 。这这就是所谓的的等温膨胀。当介质的压力和和容积已达到到B点时，气缸盖由理理想导体转换换成一个绝缘缘体，而介质质允许继续扩扩大，而没有热的增减减，这就是所所谓的绝热膨膨胀。当介质质的压力和容容积已达到CC点时，气缸盖转变成理理想导体，但但外部热源被被散热器取而代之。活活塞开始驱动，然后压缩介质质。热流经头头部的散热片片，当温度达达到中等，在在散热片（点点D），缸盖再再次切换到理理想绝缘体，戒指指被压缩直至至到达初始条条件的压力和和温度，这个个周期便完成了了，在绝热情况况下对外做功功。1.3.2朗肯肯循环卡诺循环设定一一个汽缸绝缘缘墙和可

14、以随随意由导体转转换成绝缘体体的气缸盖，它可能仍然是一个科学的概念并没有实际应用中得到运用。在20世纪初，一名苏格兰的工程教授叫威廉林肯,他对卡诺循环提出了修改，在这个基础上发展形成的理论在火力发电厂被广泛使用。即使现在的联合循环电厂仍然使用他的两个阶段的操作。朗肯循环示意图图如图1.33。从A点开始，在在恒压条件下下，通过热源源使介质膨胀胀到B点，然后绝绝热膨胀发生生，直至达到到曲线图状态态点C，从这这里开始，在在恒温条件下下，介质的体体积减小直至至到达D点，最最后将其压缩缩回其初始条条件。The bassics oof steeam geenerattion and uuse1.1 Why

15、y an uundersstandiing off steaam is needeedSteam ppower is fuundameental to whhat iss by ffar thhe larrgest sectoor of the eelectrricityy-geneeratinng inddustryy and withoout itt the face of coontempporaryy sociiety wouldd be ddramatticallly diffferennt froom itss pressent oone. WWe wouuld bee forcc

16、ed to reely onn hydrro-eleectricc poweer plaant, wwindmiills, batteeries, solaar cellls annd fuel cellss, alll of wwhich are ccapablle of produucing only a fraactionn of tthe ellectriicity we usse.Steam iis impportannt, annd thee safeety annd effficienncy off its generrationn and use ddependd on tth

17、e appplicaation of coontroll and instrrumenttationn, oftten siimply referrred tto as C&I. The oobjecttive oof thiis boook is to prrovidee a brridge betweeen thhe disscipliine off poweer-plaant prrocesss engiineeriing annd thoose off electtroniccs, innstrummentattion aand coontroll engiineeriing.I sh

18、alll starrt by outliining in thhis chhapterr the changge of statee of wwater to steamm, folllowedd by aan oveervieww of tthe baasic pprinciiples of stteam ggeneraation and uuse. TThis sseeminngly ssimplee subjject iis exttremelly commplex. Thiss willl necesssarilly be an ovvervieew: itt doess not pr

19、eteend too be aa detaailed treattise aand at tiimes iit willl simmplifyy mattters aand glloss oover ssome ddetaills whiich maay even causee the thermmodynaamicisst or combuustionn physsicistt to sshuddeer, buut it shhould be unndersttood tthat tthe aiim is to prrovidee the C&I eengineeer wiith enoug

20、gh undderstaandingg of tthe suubjectt to ddeal ssafelyy withh praccticall conttrol-systeem desiggn, opperatiional and mmainteenancee probblems.1.2 Boiiling: the changge of statee fromm wateer to steammWhen waater iis heaated iits teemperaature risess in aa way that can bbe dettectedd (for exampple b

21、yy a thhermommeter). Thee heatt gainned inn thiss way is caalled sensiible bbecausse itss effeects ccan bee senssed, bbut att somee poinnt thee wateer staarts to booil. But herre we need to loook evven deeeper into the ssubjecct. Exxactlyy whatt is meantt by tthe exxpresssion boiliing? To sttudy tth

22、is wwe musst connsiderr the threee basicc stattes off mattter: ssolidss, liqquids and ggases. (A pplasmaa, prooducedd whenn the aatoms in a gas bbecomee ioniised, is offten rreferrred too as tthe foourth statee of matteer, buut forr mostt praccticall purpposes it iss suffficiennt to consiider oonly

23、tthe threee basiic staates.) In iits soolid sstate, mattter coonsistts of many moleccules tighttly boound ttogethher byy attrractivve forrces bbetweeen theem. Whhen thhe matteer abssorbs heat the eenergyy leveels off its moleccules increease aand thhe mean distaance bbetweeen thee moleeculess incrre

24、asess. As more and mmore hheat iis appliied thhese eeffectts inccreasee untiil thee attrractivve forrce beetweenn the moleccules is evventuaally oovercoome annd thee partticless becoome caapablee of movinng aboout inndepenndentlly of each otherr. Thiis chaange oof staate frrom soolid to liiquid is c

25、oommonlly reccognissed ass mellting.As moree heatt is aapplieed to the lliquidd, somme of the mmolecuules ggain enouggh eneergy tto esccape ffrom tthe suurfacee, a pprocesss callled eevaporrationn (wherreby aa pooll of lliquidd spillled oon a ssurfacce willl graaduallly dissappeaar). What is haappen

26、iing duuring the pprocesss of evapooratioon is that some of thhe moleccules are eescapiing att fairrly loow temmperattures, but as thhe temmperatture risess thesse esccapes occurr moree rapiidly aand att a ceertainn poinnt thee liquuid becommes veery aggitateed, wiith laarge qquantiities of buubbles

27、s risiing too the surfaace. IIt is at thhis tiime thhat thhe liqquid iis saiid to startt boiiling. It is inn the proceess off channging statee to aa vapoour, wwhich is a fluidd in aa gaseeous sstate.Let us consiider aa quanntity of waater tthat iis conntaineed in an oppen veessel. Here, the air ttha

28、t bblankeets thhe surrface exertts a ppressuure onn the surfaace off the ffluid and, as thhe temmperatture oof thee wateer is raiseed, ennough energgy is eventtuallyy gainned too overrcome the bblankeeting effecct of that presssure aand the wwater startts to changge itss statte intto thaat of a vapp

29、our (steamm). Fuurtherr heat addedd at tthis sstage will not ccause any ffurtheer dettectabble chhange in tempeeraturre: thhe eneergy aadded is ussed too channge thhe staate off the fluidd. Itss effecct cann no llongerr be ssensedd by aa therrmometter, bbut itt is sstill theree. Forr this reasoon it

30、 is caalled latennt, raather then sensiible, heat. The tempeeraturre at whichh thiss happpens iis callled tthe bboilinng poiint. At noormal atmosspheriic presssure tthe booilingg poinnt of waterr is 1100 C.If the presssure oof thee air blankket onn top of thhe watter weere too be increeased, moree e

31、nerrgy woould hhave tto be introoducedd it tto breeak frree. IIn othher woords, the ttemperraturee mustt be rraisedd furtther tto make it booil. TTo illlustraate thhis pooint, if thhe preessuree is iincreaased bby 10% abovee its normaal atmmospheeric vvalue, the tempeeraturre of the wwater must be r

32、aiseed to just abovee 102 C beefore boiliing occcurs.The steeam emmerginng froom thee boilling lliquidd is ssaid tto be saturrated and, for aany giiven ppressuure, tthe teemperaature at whhich bboilinng occcurs iis callled the ssaturaation tempeeraturre.The infformattion rrelatiing too steaam at any

33、 ccombinnationn of ttemperraturee, presssure aand otther ffactorrs mayy be ffound in stteam ttabless, whiich arre nowaddays aavailaable iin sofftwaree as wwell aas in the mmore ttradittionall papeer form. Thesse tabbles wwere ooriginnally publiished in 19915 byy Hughh Longgbournne Calleendar (18633-

34、19300), a Britiish phhysiciist. BBecausse of advannces iin knowlledge and mmeasurrementt techhnologgy, annd as a ressult oof chaangingg unitts of meeasureement, manyy diffferentt variiants of stteam ttabless are todayy in existtence, but they all eenablee one to loook upp, forr any presssure, the ss

35、aturaation tempeeraturre, thhe heaat perr unitt masss of ffluid, the speciific vvolumee etc.Understtandinng steeam annd thee steaam tabbles iis esssentiaal in many stagees of thhe dessign oof powwer-pllant ccontrool sysstems. For exampple, iif a ddesignner needss to ccompennsate a steeam-fllow meeas

36、ureement for cchangees in presssure, or to coorrectt for densiity errrors in a waterr-leveel meaasuremment, referrence to thesee tablles iss esseentiall.Anotherr termm relaating to stteam ddefinees thee quanntity of liiquid mixedd in with the vvapourr. In the UUK thiis is calleed thee drynness ffrac

37、tiion (iin thee USA the term used is stteam qqualitty). WWhat tthis mmeans is thhat iff eachh kiloogram of thhe mixtuure coontainns 0.99 kg oof vapouur andd 0.1 kg off wateer, thhe dryyness fracttion is 0.9.Steam bbecomees supperheaated wwhen iits teemperaature is raaised abovee the saturrationn tem

38、pperatuure coorresppondinng to its ppressuure. TThis iis achhievedd by colleectingg it ffrom tthe veessel in whhich tthe booilingg is ooccurrring, leadiing itt away from the lliquidd throough aa pipee, andd thenn addiing moore heeat too it. This proceess addds fuurtherr enerrgy too the fluidd, whiic

39、h immprovees thee effiicienccy of the cconverrsion of heeat too elecctriciity.As statted eaarlierr, heaat addded onnce thhe watter haas staarted to booil dooes not ccause any ffurtheer dettectabble chhange in teemperaature. Insttead iit chaanges the sstate of thhe fluuid. OOnce tthe stteam hhas foor

40、med, heatt addeed to it coontribbutes to thhe tottal heeat off the vapouur. Thhis iss the sensiible hheat pplus tthe laatent heat plus the hheat uused iin inccreasiing thhe temmperatture oof eacch killogramm of the ffluid throuugh thhe nummber oof deggrees of suuperheeat too whicch it has bbeen rais

41、eed.In a poower pplant, a maajor oobjecttive iis thee convversioon of energgy loccked up inn the inputt fuell intoo eithher ussable heat or ellectriicity. In tthe innteressts off econoomics and tthe ennvironnment it iss impoortantt to oobtainn the higheest to thhe watter too enabble possiible llevel

42、 of effficieency iin thiis connversiion prrocesss. As we haave allreadyy seen, the greattest eefficiiency is obbtaineed by maximmisingg the energgy levvel off the ssteam at thhe poiint off deliivery to thhe nexxt staage off the proceess. WWhen aas much energgy as possiible hhas beeen abbstraccted ff

43、rom tthe stteam, the ffluid reverrts too the form of coold waater, whichh is tthen wwarmedd and treatted too removve anyy air whichh may have becomme enttraineed in it beefore it iss finaally returrned tto thee boiller foor re-use.1.3 Thee natuure off steaamAs statted inn the Prefaace, tthe booilers

44、s and steamm-geneeratorrs thaat aree the subjeect off thiss bookk provvide ssteam to ussers ssuch aas inddustriial pllant, or housiing annd othher coomplexxes, oor to drivee turbbines that are tthe prrime moverrs forr elecctricaal genneratoors. FFor thhe purrposess of tthis bbook, such proceesses ar

45、e ggroupeed toggetherr undeer thee geneeric nname powerr plannt. IIn all tthese appliicatioons thhe steeam iss prodduced by appplyinng heaat to waterr untiil it booils, and bbeforee we eembarkk on oour sttudy oof powwer-pllant CC&I wee mustt underrstandd the mechaanismss invoolved in thhis prrocesss

46、 and the nnaturee of steamm itseelf.First, we muust paause tto connsiderr somee basiic theermodyynamicc proccessess. Two oof theese arre thee Carnnot annd Rannkine cyclees, annd altthoughh the C&I enginneer mmay noot makke usee of tthese direcctly, it iss neveerthelless uusefull to have a bassic unn

47、dersttandinng of what they are hhow thhey opperatee.1.3.1 TThe Caarnot cycleeThe priimary functtion oof a ppower plantt is tto connvert into electtricitty thee energgy loccked uup in some form of fuuel reesourcce. Inn spitte of many attemmpts, it haas nott provved poossiblle to generrate eelectrrici

48、tyy in llarge quanttitiess fromm the ddirectt convversioon of the eenergyy conttainedd in aa fosssil fuuel (oor eveen a nucleear fuuel) wwithouut thee use of a mediuum thaat actts as an inntermeediaryy. Solarr cellls andd fuell cellls mayy one day aachievve thiis aimm on aa scalle larrge enouggh to

49、make an immpact on foossil-fuel utiliisatioon, buut at preseent suuch plantts aree conffined to smmall-sscale appliicatioons. TThe waater tturbinnes off hydroo-elecctric plantts aree capaable oof genneratiing laarge qquantiities of ellectriicity, but ssuch pplantss are necesssarilly resstrictted too

50、 areaas wheere thhey arre plenttiful suppllies oof watter att heigghts ssufficcient for uuse byy thesse macchiness.Therefoore, iif onee wishhes too obtaain laarge qquantiities of ellectriicity from a fossiil fueel or from a nucclear reacttion iit is necesssary to fiirst rreleasse thee energgy thaat

51、is availlable withiin thaat ressourcee and then to trransfeer it to a generrator, and this proceess neecessiitatess the use oof a mmediumm to cconveyy the energgy froom souurce tto desstinattion. Furthhermorre, itt is nnecesssary tto empploy a meddium tthat iis reaadily availlable and wwhich can bbe

52、 useed witth rellativee safetty andd effiicienccy. Onn plannt Earrth, wwater is, aat leaast inn geneeral, a plenttiful and ccheap mediuum forr effeectingg suchh trannsferss. Witth thee deveelopmeent of teechnollogy dduringg the twenttieth centuury otther ppossibbilitiies haave been consiideredd, suc

53、ch as the uuse off merccury, but eexceptt for appliicatioons such as sppacecrraft wwhere entirrely nnew seets off limiitatioons annd connditioons applyy, nonne of thesee has reachhed acctive use, and ssteam is unniverssally used in poower sstatioons.Carnot frameed onee of tthe twwo lawws of thermmod

54、ynaamics. The firstt, Joulees laaw, haad rellated mechaanicall enerrgy too workk: Carrnotss law definned the ttemperraturee relaationss appllying to thhe connversiion off heatt enerrgy innto mechaanicall enerrgy. HHe saww thatt if tthis pprocesss werre to be maade reeversiible, heat couldd be cconve

55、rrted iinto wwork aand thhen exxtractted annd re-used to maake a cloosed lloop. In hiis conncept (Figuure 1.1), aa pistton mooves ffreelyy withhout encouunteriing anny friictionn insiide a cylinnder mmade oof somme perrfectlly inssulatiing materrial. The ppistonn is ddrivenn by aa worrking fluidd. T

56、hhe cyllinderr has a heaad at one eend thhat caan be switcched aat willl froom beiing a perfeect conduuctor to beeing aa perffect iinsulaator. Outsiide thhe cyllinderr are two bbodiess, one oof whiich caan delliver heat withoout itts ownn tempperatuure ( T1 ) faallingg, thee otherr beinng a bbottomm

57、less cold sink at a tempeeraturre (T22) whiich iss alsoo consttant.The opeeratioon of the ssystemm is sshown graphhicallly in figurre 1.22, whiich showss the presssure/vvolumee relaationsship oof thee fluiid in the ccylindder ovver thhe wholee cyclle. Ass the proceess iss a reepeatiing cyycle iits o

58、pperatiion caan be studiied from any cconvennient startting ppoint, and we shhall bbegin at thhe poiint A, wheree the cylinnder hhead (at thhis tiime asssumedd to bbe a pperfecct connductoor of heat), alllows hheat ffrom tthe hoot souurce tto entter thhe cyllinderr. Thee resuult iss that the mmedium

59、m begiins too expaand, aand iff it iis alllowed to exxpand freelly, Boylees laaw (whhich sstatess thatt at aany teemperaature the rrelatiionshiip betweeen prressurre andd voluume iss consstant) dicttates that the ttemperraturee will not rrise, but wwill sstay aat itss inittial ttemperraturee (Tl). T

60、hiis is calleed isoothermmal expannsion.When thhe preessuree and volumme of the mmediumm havee reacched tthe vaalues at pooint BB, thee cyliinder head is swwitcheed froom beiing a perfeect coonducttor too beingg a peerfectt insuulatorr and the mmediumm alloowed tto conntinuee its expannsion with no