燃气专业外语翻译

1.1 工程热力学基础thermodynamicsisa sciencein whichthestorage,transformation,and transferof energyare studied. energy is stored as internal energy (associated with temperature), kinetic energy (due tomotion), potential energy (due to elevation) and chemical energy (due to chemical composition); it is transformed from one of these forms to another; and it is transferred across a boundary as either heat or work.热力学是一门研究能量储存、转换及传递的科学。能量以内能（与温度有关）、动能（由物体运动引起）、势能（由高度引起） 和化学能（与化学组成相关） 的形式储存。 不同形式的能量可以相互转化， 而且能量在边界上可以以热和功的形式进行传递。in thermodynamics, we will derive equations that relate the transformations and transfers of energyto properties such as temperature, pressure, and density. substancesand their properties, thus, become very important in thermodynamics. many of our equations will be based on experimental observations that have been organized into mathematical statements or laws; the first and secondlaws of thermodynamics are the most widely used.在热力学中，我们将推导有关能量转化和传递与物性参数，如温度、压强及密度等关系间的方程。因 此，在热力学中，物质及其性质变得非常重要。许多热力学方程都是建立在实验观察的基础之上，而 且这些实验观察的结果已被整理成数学表达式或定律的形式。其中，热力学第一定律和第二定律应用最为广泛。1.1.1 thermodynamic system and control volume热力系统和控制体athermodynamicsystemisa fixedquantityofmattercontainedwithinsomeenclosure.the surface is usually an obvious one (like that surrounding the gas in the cylinder). however, it may bean imagined boundary (like the deforming boundary of a certain amount of mass as it flows througha pump).精品资料热力系统是一包围在某一封闭边界内的具有固定质量的物质。系统边界通常是比较明显的（如气缸内气体的固定边界）。然而，系统边界也可以是假想的（如一定质量的流体流经泵时不断变形的边界）。all matter and space external to a system is collectively called its surroundings. thermodynamics is concerned with the interactions of a system and its surroundings, or one system interacting with another. a system interacts with its surroundings by transferring energy across its boundary. nomaterialcrossestheboundaryof a system.if thesystemdoesnotexchangeenergywiththe surroundings ，it is an isolated system.系统之外的所有物质和空间统称外界或环境。热力学主要研究系统与外界或系统与系统之间的相互作用。系统通过在边界上进行能量传递，从而与外界进行相互作用，但在边界上没有质量交换。当系统与外界间没有能量交换时，这样的系统称为孤立系统。in many cases, an analysis is simplified if attention is focused on a particular volume in space into which, or from which, a substance flows. such a volume is a control volume. a pump, a turbine, and an inflating or deflating balloon are examples of control volumes. the surface that completely surrounds the control volume is called a control surface.在许多情况下，当我们只关心空间中有物质流进或流出的某个特定体积时，分析可以得到简化。这样的特定体积称为控制体。例如泵、透平、充气或放气的气球都是控制体的例子。包含控制体的表面称为控制表面。thus, we must choose, in a particular problem, whether a system is to be considered or whether a control volume is more useful. if there is mass flux across a boundary, then a control volume is required;otherwise, a system is identified.因此，对于具体的问题， 我们必须确定是选取系统作为研究对象有利还是选取控制体作为研究对象有利。如果边界上有质量交换，则选取控制体有利；反之，则应选取系统作为研究对象。1.1.2 equilibrium, process and cycle平衡、过程和循环when the temperature of a system is referred to, it is assumed that all points of the system have the same, or essentially the same, temperature. when the properties are constant from point topoint and when there is no tendency for change with time, a condition of thermodynamic equilibrium exists. if the temperature, say, is suddenly increased at some part of the system boundary, spontaneous redistribution is assumed to occur until all parts of the system are at thesame temperature.对于某一参考系统， 假设系统内各点温度完全相同。当物质内部各点的特性参数均相同且不随时间变化时，则称系统处于热力学平衡状态。当系统边界某部分的温度突然上升时，则系统内的温度将自发地重新分布，直至处处相同。whenasystemchangesfromoneequilibriumstateto another,the pathof successivestates through which the system passes is called a process. if, in the passing from one state to the next,the deviation from equilibrium is infinitesimal, a quasi-equilibrium process occurs,and each state intheprocessmaybeidealizedasanequilibriumstate.quasi-equilibriumprocessescan approximatemanyprocesses,such as thecompressionand expansionof gasesin an internal combustion engine, with no significant loss of accuracy. if the system goes from one equilibriumstateto another througha seriesof nonequilibriumstates(as in combustion), a nonequilibrium process occurs.当系统从一个平衡状态转变为另一个平衡状态时，系统所经历的一系列由中间状态组成的变化历程称为过程。若从一个状态到达另一个状态的过程中，始终无限小地偏离平衡态，则称该过程为准静态过程，可以把其中任一个中间状态看作为平衡状态。准静态过程可近似视为许多过程的叠加结果，而不会显著减小其精确性， 例如气体在内燃机内的压缩和膨胀过程。如果系统经历一系列不平衡状态（如燃烧），从一个平衡状态转变为另一个平衡状态，则其过程为非平衡过程。when a system in a given initial state experiences a series of process and returns to the initial state,the system goes a cycle. at the end of the cycle, the properties of the system have the same values they had at the beginning.当系统从一个给定的初始状态出发，经历一系列中间过程又回到其初始状态，则称系统经历了一个循环。循环结束时，系统中的各参数又与初始参数相同。the prefix iso-is attached to the name of any property that remains unchanged in aprocess. an isothermal process is one in which the temperature is held constant; in an iso-baric process, the pressure remains constant; an isometric process is a constant-volume process.在任一特性参数名称前加上前缀iso- ，表示该参数在整个过程保持不变。等温（isothermal ）过程中温度保持不变；等压（isobaric ）过程中压强恒定；等容（isometric ）过程中体积保持不变。1.1.3 vapor-liquid phase equilibrium in pure substance纯物质的气 -液相平衡consider as a system 1 kg of water contained in the piston/ cylinder arrangement shown in fig.1-1(a). suppose that the piston and weight maintain a pressure of 0.1 mpa in the cylinder and thattheinitialtemperatureis20 . as heatis transferredtothewater,thetemperatureincreases appreciably, the specific volume increases slightly, and the pressure remains constant. when the temperature reaches 99. 6, additional heat transfer results in a change of phase, as indicated in fig.1-1(b).thatis,someoftheliquidbecomesvapor,andduringthisprocessboththetemperature and pressure remain constant, but the specific volume increases considerably. whenthelastdropofliquidhasvaporized,furthertransferofheatresultsinanincreaseinboth temperature and specific volume of the vapor, as shown in fig.1-1(c).如图 1-1(a) 所示，由活塞和气缸组成的装置中装有1kg 水。假定活塞和其上的重物使气缸内压强维持在 0.1mpa ，初始温度 20 。当有热量开始传递给水时，缸内水温迅速上升，而比容略有增加，气缸内压强保持恒定不变。 当水温达到99.6 时， 如若再增加传热量， 水将发生相变， 如图 1-1(b) 所示。也就是说，一部分水开始气化变为蒸汽，在此相变过程中，温度和压强始终保持不变，但比容却有大幅度的增加。当最后一滴液体被气化时，进一步的加热将使蒸汽温度和比容均有所增加，如同1-1(c)所示。图 1-1液体在常压下的蒸发过程the term saturation temperature designates the temperature at which vaporization takes place at a given pressure. this pressure is called the saturation pressure for the given temperature. thus, forwaterat 99. 6 the saturationpressureis 0.1mpa,andfor waterat0.1 mpathesaturationtemperature is 99. 6.在给定压强下发生气化的温度称为饱和温度，压强称为给定温度下的饱和压强。因此，99.6 水的饱和压强是 0.1mpa ， 0.1mpa 水的饱和温度为99.6 。if a substanceexistsas liquidat the saturationtemperatureand pressure,itis calledsaturated liquid.if the temperatureof the liquidislowerthanthesaturationtemperaturefortheexisting pressure,itis calledeithera subcooledliquid(implyingthat thetemperatureislowerthanthe saturation temperature for the given pressure) or a compressed liquid (implying that the pressure is greater than the saturation pressure for the given temperature).如果某一工质为液态并处于其饱和温度和饱和压强下，则称该液体为饱和液体。如果液体温度低于当前压强下的饱和温度， 则称该液体为过冷液体（表明液体的当前温度低于给定压强下的饱和温度）或压缩液体（表明液体的当前压强大于给定温度下的饱和压强）。when a substance exists as part liquid and part vapor at the saturation temperature, its quality is defined as the ratio of the mass of vapor to the total mass. thus, in fig.1-1(b),if the mass of the vapor is 0. 2 kg and the mass of the liquid is 0.8 kg, the quality is 0.2 or 20%. quality has meaningonly when the substance is in a saturated state.若某一工质在饱和温度下以液、气共存的形式存在，则称蒸汽质量与总质量之比为干度。因此，如图1-1(b) 所示，若蒸汽质量为0.2kg ，液体质量为0.8kg ，则其干度为0.2 或 20% 。干度只有在饱和状态下才有意义。ifasubstanceexistsasvaporatthesaturationtemperature,itiscalledsaturatedvapor. (sometimes the term dry saturated vapor is used to emphasize that the quality is 100%). when thevapor is at a temperature greater than the saturation temperature, it is said to exist as superheated vapor. the pressure and temperature of superheated vapor are independent properties, since the temperature may increase while the pressure remains constant.若某一工质处于饱和温度下并以蒸汽形态存在，则称该蒸汽为饱和蒸汽（有时称为干饱和蒸汽，意在强调其干度为100% ）。当蒸汽温度高于其饱和温度时，则称之为过热蒸汽。过热蒸汽的压强和温度是彼此独立的，因为温度上升时，压强可能保持不变。letusplotonthetemperature-volumediagramoffig.1-2theconstant-pressurelinethat represents the states through which the water passes as it is heated from the initial state of 0.1mpaand 20 . let statea represent the initial state,b the saturated-liquid state (99. 6), and lineabthe process in which the liquid is heated from the initial temperature to the saturation temperature. point c is the saturated-vapor state, and linebc is the constant-temperature process in which the change of phase from liquid to vapor occurs. linecd represents in which the steam is superheated at constant pressure. temperature and volume both increase during this process.在图 1-2 所示的温度 -比容图上作等压线，表示水由初压0.1mpa 、初温 20 被加热的过程。点a 代表初始状态，点b 为饱和液态（ 99.6 ），线 ab 表示液体由初始温度被加热至饱和温度所经历的过程。点c 表示饱和蒸汽状态，线bc 表示等温过程，即液体气化转变为蒸汽的过程。线 cd 表示在等压条件下蒸汽被加热至过热的过程，在此过程中，温度和比容均增大。图 1-2温度-比容曲线表 1-1一些物质的临界参数in a similarmanner,a constantpressureof 10mpaisrepresentedby lineijkl , forwhichthe saturation temperature is 311. 1. at a pressure of 22.09mpa, represented by linemno ，we find,however, that there is no constant-temperature vaporization process. instead，point n is a point ofinflectionwithazeroslope.thispointiscalledthecriticalpoint.atthecriticalpointthe saturated-liquid and saturated-vapor states are identical. the temperature, pressure, and specificvolume at the critical point are called the critical temperature,critical pressure, and critical volume. the critical-point data for some substances are given in table 1-1.类似地，线ijkl表示压强为10mpa下的等压线，相应的饱和温度为311.1 。但是，在压强为22.09mpa条件下（线mno ），不存在等温蒸发过程。相反，点n 是个转折点，在该点上，切线斜率为零，通常把n 点称为临界点。在临界点处，饱和液体和饱和气体的状态都是相同的。临界点下的温度、压强和比容分别称为临界温度、 临界压强和临界比容。 一些工质的临界点数据如表1-1 所示。1.1.4 the first law of thermodynamicsthe first law of thermodynamics is commonly called the law of conservation of energy. in elementary physics courses, the study of conservation of energy emphasizes changes in kineticand potential energy and their relationship to work. a more general form of conservation of energy includes the effects of heat transfer and internal energy changes. other forms of energy could also be included, such as electrostatic, magnetic, strain, and surface energy.1.1.4 热力学第一定律通常把热力学第一定律称为能量守恒定律。 在基础物理课程中， 能量守恒定律侧重动能、 势能的变化以及和功之间的相互关系。 更为常见的能量守恒形式还包括传热效应和内能的变化。 当然，也包括其它形式的能，如静电能、磁场能、应变能和表面能。 the first law of thermodynamics was stated for a historically,cycle: the net heat transfer is equal to the net work done for a system undergoing a cycle.历史上，用热力学第一定律来描述循环过程：净传热量等于循环过程中对系统所做的净功。1.1.5 the second law of thermodynamicsthe second law of thermodynamics can be stated in a variety of ways. here we present two: the clausius statement and the kelvin-planck statement.1.1.5 热力学第二定律热力学第二定律有多种表述形式。在此列举两种：克劳修斯表述和凯尔文-普朗克表述。clausius statementit is impossible to construct a device that operates in a cycle and whose sole effect is the transfer of heat from a cooler body to a hotter body.克劳修斯表述：制造一台唯一功能是把热量从低温物体传给高温物体的循环设备是不可能的。图 1-3第二定律的违背this statement relates to a refrigerator (or a heat pump). it states that it is impossible to construct a refrigerator that transfers energy from a cooler body to a hotter body without the input of work; this violation is shown in fig.1-3(a).以冰箱（或热泵）为例，不可能制造一台不用输入功就能把热量从低温物体传给高温物体的冰箱，如图 1-3(a) 所示。it is impossible to construct a device that operates in a cycle and produces no other effect than the production of work and the transfer of heat from a single body.凯尔文-普朗克表述：制造一台从单一热源吸热和做功的循环设备是不可能的。in other words, it is impossible to construct a heat engine that extracts energy from a reservoir,doeswork,and doesnot transferheatto a low-temperaturereservoir.thisrulesout anyheatengine that is 100 percent efficient, like the one shown in fig.1-3(b).换句话说，制造这样一台从某一热源吸热并对外做功，而没有与低温热源进行换热的热机是不可能的。因此，该表述说明了不存在工作效率为100% 的热机，如图1-3(b) 所示。1.1.6 the carnot cyclethe heatenginethat operatesthemostefficientlybetweena high-temperaturereservoiranda low-temperaturereservoiristhecarnotengine.thisisanidealenginethatusesreversible processes to form its cycle of operation; such a cycle is carnot cycle. the carnot engine is veryuseful, since its efficiency establishes the maximum possible efficiency of any real engine. if the efficiency of a real engine is significantly lower than the efficiency of a carnot engine between the same limits, then additional improvements may be possible.1.1.6 卡诺循环卡诺机是低温热源和高温热源间运行效率最高的热机。卡诺机是一个理想热机，利用多个可逆过程组成一循环过程， 该循环称为卡诺循环。卡诺机非常有用， 因为它的运行效率为任何实际热机最大可能的效率。因此， 如果一台实际热机的效率要远低于同样条件下的卡诺机效率，则有可能对该热机进行一些改进以提高其效率。图 1-4卡诺循环theidealcarnotcycleinfig.1-4iscomposedoffourreversibleprocesses:12:isothermal expansion;23: adiabaticreversibleexpansion;34: isothermalcompression;41: adiabaticreversible compression. the efficiency of a carnot cycle is:note that the efficiency isincreased by raising the temperatureth at which heat is added or by lowering the temperaturetlat which heat is rejected.理想的卡诺循环包括四个可逆过程，如图1-4 所示： 12 等温膨胀； 23 绝热可逆膨胀； 34 等温压缩； 41 可逆绝热压缩。卡诺循环的效率为注意，提高th（提高吸热温度）或降低tl（降低放热温度）均可使循环效率提高。1.1.7 the rankine cyclethe first class of power cycles that we consider are those utilized by the electric power generating industry, namely, power cycles that operate in such a way that the working fluid changesphase fromaliquidto avapor.thesimplestvapor-powercycleiscalledtherankinecycle,shown schematically in fig.1-5(a). a major feature of such a cycle is that the pump requires very little workto deliver high-pressure water to the boiler. a possible disadvantage is that the expansion process in the turbine usually enters the quality region, resulting in the formation of liquid droplets that may damage the turbine blades.1.1.7 朗肯循环我们所关心的第一类动力循环为电力生产工业所采用的，也就是说， 动力循环按这样的方式运行：工质发生相变，由液态变为气态。最简单的蒸汽-动力循环是朗肯循环，如图1-5(a) 所示。朗肯循环的一个主要特征是泵耗费很少的功就能把高压水送入锅炉。其可能的缺点为工质在汽机内膨胀做功后，通常进入湿蒸汽区，形成可能损害汽轮机叶片的液滴。图 1-5朗肯循环the rankine cycle is an idealized cycle in which friction losses in each of the four components are neglected. the losses usually are quite small and will be neglected completely in initial analysis.the rankine cycle is composed of the four ideal processes shown on thet-s diagram in fig.1-5(b):12: isentropic compression in a pump; 23: constant-pressure heat addition in a boiler; 34: isentropic expansion in a turbine; 41: constant-pressure heat rejection in a condenser.朗肯循环是一个理想循环，其忽略了四个过程中的摩擦损失。这些损失通常很小， 在初始分析时可完全忽略。朗肯循环由四个理想过程组成，其t-s 图如图 1-5(b) 所示： 12 为泵内等熵压缩过程；23 为炉内定压吸热过程；34 为汽轮机内等熵膨胀做功过程；41为凝汽器内定压放热过程。the pumpis usedto increasethe pressureof the saturatedliquid.actually,states1 and 2 are essentially the same, since the high-pressure lines are extremely close to the saturation curve; theyareshownseparatedforillustrationonly.theboiler(alsocalledasteamgenerator)andthe condenser are heat exchangers that neither require nor produce any work.泵用于提高饱和液体的压强。事实上，状态1 和状态 2 几乎完全一样，因为由2 点开始的较高压强下的吸热过程线非常接近饱和曲线，图中仅为了解释说明的需要分别标出。锅炉（也称蒸汽发生器） 和凝汽器均为换热器，它们既不需要功也不产生功。if we neglect kinetic energy and potential energy changes，the net work output is the area under the t-s diagram, represented by area 1-2-3-4-1 of fig.1-5(b); this is true since the first law requires thatwnet =q net. the heat transfer to the working substance is represented by areaa-2-3- b-a. thus, the thermal efficiencyof the rankine cycle isthatis,thedesiredoutputdividedby theenergyinput(thepurchasedenergy).obviously,the thermal efficiency can be improved by increasing the numerator or by decreasing the denominator.thiscanbedonebyincreasingthepumpoutletpressurep2 ,increasingtheboileroutlet temperaturet3, or decreasing the turbine outlet pressurep4.如果忽略动能和势能的变化，输出的净功等于t-s 图曲线下面的面积，即图1-5(b) 中 1-2-3-4-1所包围的面积， 由用热力学第一定律可证明wnetqnet 。循环过程中工质的吸热量对应面积a-2-3-b-a 。因此，朗肯循环的热效率可表示为面积 12341 (1-2)面积 a23ba 即，热效率等于输出能量除以输入能量（所购能量）。显然，通过增大分子或减小分母均可以提高热效率。这可以通过增大泵出口压强p2 ，提高锅炉出口温度t3，或降低汽机出口压强p4 来实现。1.1.8 the reheat cycleit is apparent that when operating in a rankine cycle with a high boiler pressure or a low condenserpressureit isdifficultto preventliquiddropletsfromforminginthe low-pressureportionof the turbine. since most metal cannot withstand temperatures above about 600,the reheat cycle is often used to prevent liquid-droplet formation: the steam passing through the turbine is reheated atsome intermediate pressure, thereby raising the temperature to state 5 in thet-s diagram of fig. 1-6.thesteamthenpassesthroughthelow-pressuresectionoftheturbineandentersthe condenser at state 6. this controls or completely eliminates themoisture problem in the turbine.often, the turbine is separated into a high-pressure turbine and a low-pressure turbine. the reheatcycle does not significantly influence the thermal efficiency of the cycle, but it does result in a significant additional work output, represented in the figure by area 4-5-6-4 -4 of fig.1-6. the reheat cycle demands a significant investment in additional equipment ， and the use of such equipment must be economically justified by the increased work outp