1、,Instructor: Aigo X. School of Chemical Engineering and Pharmacy,WIT,P.R.ChinaMarch 8, 2009,Chemical Engineering Thermodynamics,Contents,第1章 衡算方程的一般形式1-1普遍化质量衡算方程1-2普遍化能量衡算方程1-3普遍化熵衡算方程1-4 普遍化有效能衡算方程,第2章 溶液热力学基础,2-1 偏摩尔量的特点2-2 热力学基本方法2-3 平衡条件与相律2-4 逸度及其关系式2-5 活度及其关系式2-6 状态方程2-7 气体混合物和纯气体逸度的计算2-8 纯液体
2、和固体逸度的计算2-9 液体混合物逸度的计算,第3章 相平衡原理的应用,3-1 相平衡原理3-2 气液平衡3-3 恒沸系统的热力学3-4 气体在液体中的溶解度3-5 液-液平衡3-6 液-固平衡3-7 超临界技术3-8 相平衡过程开发中的信息处理3-9 相平衡原理在过程分析中的应用,教学参考书,1 胡英.“流体的分子热力学”. 高等教学出版社.19832 J.M.Smith,H.C.Van Ness,M.M.Abbott. Introduction of Chemical Engineering Thermodynamics.McGraw-Hill, 7th edition,20053 T.E
3、.Daubert, Chemical Engineering Thermodynamics4 S.M. Walas,Phase Equilibria in Chemical Engineering 5 S.I.Sandler, Chemical and Engineering Thermodynamics6 M.modell,R.C. Reid, Thermodynamics and its Applications7 J.M.Prausnitz,et al. Molecular Thermodynamics of Fluid Phase Equilibria8 马沛生主编.化工热力学,化学工
4、业出版社,20059 郭天民,多元气液平衡和精馏,化学工业出版社,197610 童景山、李敬,流体热物理性质的计算,清华大学出版社,1982冯新、宣爱国等,化工热力学,化学工业出版社,2008,Preface,1 The Central Problemsof Thermodynamics(1) energyThermodynamics is the study of the changes in the state or condition of a substance when changes in its temperature, state of aggregation(聚集态),or
5、its internal energy are important. By internal energy we mean the energy of a substance associated with the motion,interaction, and bonding of its constituent molecules,rather than the external energy associated with the velocity and location of its center of mass,which is of primary interest in mec
6、hanics. Thermodynamics is a macroscope science .It deals with the average changes that occur among large numbers of molecules rather than the detaiked changes that occur in a single molecule.Firstly, the problem is concerned with computing the amount of work or the flow of heat either required or re
7、leased to accomplish a specified change of state of a system or,alternatively,the prediction of the change in thermodynamic state that occurs for given heat or work flows.-we refer to these problems as energy flow problems,Chemical Engineering Thermodynamics,Preface,1 The Central Problemsof Thermody
8、namics(2)equilibriaAn important concept in thermodynamics is the equilibrium state. If a system is not subjected to a continual forced flow of mass ,heat,or work, the system will eventually evolve to a time invariant state in which there are no internal flowsof heat or mass and no change in composit
9、ion as a result of chemical reactions. This state of the system is the equilibrium state. The precise nature of the equilibrium state depends on both the character of the system and the constraints imposed on the system by its immediate surroundings and its container(a constant volume containter,or
10、a thermostatic bath) Of particular interest here is the identification orprediction of the equilibrium state of system that initially is not in equilibrium. The most commom problem of this type the prediction of the new equilibrium state of a system that has undergone a change in the constraints tha
11、t had been maintaining it in a previous state.,Chemical Engineering Thermodynamics,Preface,2 Step on appling the principleof thermodynamics in the engineering(1) Simplifing and abstrating the real matter so that it is easily described in mathematics equation.(2) drew the thermodynamic relationship -
12、on energy(energy,entropy,exergy) -on equilibrium(phase equilibrium,chemical reaction)(3) Solving the equations on thermodynamic relationship -calculating the properties of materials by designing a mathematics method,Chemical Engineering Thermodynamics,Chapter1 A General Balance Equation and conserve
13、d quantities,1-1 the general balance equation of mass1 the basic concept Systemthe region under study ,which may be a specified volume in space or a quantity of matterSurroundingsthe rest of the universeThermodynamic stateas characterized by its density,refractive index ,composition,pressure,tempera
14、ture,or other variables Phasethe state of sgglomeration of the system(whether it is a gas,liquid,or solid)Isolated system it does not change as a result of changesin its surroundingsAdiabatic system-it is thermally isolated fromtheirsurroundings,or it is not in thermal contact,but may be in machanic
15、al contanctOpen system-mass , heat and work can flow into or out of a thermodynamic systemClosed systemno mass flows.but heat can be added to the systm,or work done on itSteady statethe time-invariant state(it occur frequently in continuous chenical and physical processing.and Steady state processes
16、 are of only minor interest.) In this course , we will discuss non- steady state,Chemical Engineering Thermodynamics,Chemical Engineering Thermodynamics,Chapter1 A General Balance Equation and conserved quantities,Chapter1 A General Balance Equation and conserved quantities,1-1 the general balance e
17、quation of mass2 the general balance equation of mass,Chemical Engineering Thermodynamics,为了使导出的衡算方程具有普遍意义,我们选择一个如图1-1所示的任意系统。这个系统的特点如下:a) 系统由单组分或多组分流体组成。通过界面有单股或多股质量 流进入或离开系统。b) 系统的整体可以是运动的,也可以是静止的;系统的边界可因压缩或膨胀而移动。c)系统与环境间有热与功的流动。除了在核分裂过程中,有部分质量转变为能量,以及在物体以接近光速运动时,有质量增加外,在通常的化工过程中质量是守恒的。,图1-1 有多股质量
18、流进出的任意系统,Chapter1 A General Balance Equation and conserved quantities,1-1 the general balance equation of mass2 the general balance equation of mass(1) 敞开系统质量衡算的一般形式 质量流是系统与环境间进行质 量交换的唯一方式。为简化起见,我们假定:所有通过边界进入或离开系统的质量流都是理想流体;流体的流动方向与边界垂直;在边界处流体的性质均匀。于是,微元过程的质量衡算方程可写为:,Chemical Engineering Thermodynam
19、ics,Chapter1 A General Balance Equation and conserved quantities,1-1 the general balance equation of mass2 the general balance equation of mass(2) 恒质量系统的质量衡算形式恒质量系统,摩尔数是守恒量。于是,微元过程的质量衡算方程可写为:,Chemical Engineering Thermodynamics,Chapter1 A General Balance Equation and conserved quantities,1-1 the gen
20、eral balance equation of mass2 the general balance equation of mass(3) 连续系统的质量衡算形式 对于连续系统,系统的性质在 空间是逐点连续变化的。于是, 微元过程的质量衡算方程可写为:,Chemical Engineering Thermodynamics,Chapter1 A General Balance Equation and conserved quantities,1-1 the general balance equation of mass2 the general balance equation of m
21、ass(4) 匀态不稳定过程的质量衡算形式 刚性容器的充气、放气或放液过程均属于这类过程。其特点是系统的状态随时间而变化。因此,进出系统的质量流率也随时间而变化。 但在任一瞬间,系统内的性质可看作是均匀的。 于是, 微元过程的质量衡算方程可写为:,Chemical Engineering Thermodynamics,Chapter1 A General Balance Equation and conserved quantities,1-1 the general balance equation of mass2 the general balance equation of mass(
22、5) 稳定流动过程的质量衡算形式 稳定流动的特点是系统内流体的流动情况不随时间而变化。各点的状态参数也不随时间而变化。 因此,系统内无质量和能量的积累。 于是, 微元过程的质量衡算方程可写为:,Chemical Engineering Thermodynamics,For example,Chapter1 A General Balance Equation and conserved quantities,1-1 the general balance equation of mass2 the general balance equation of mass(6) 封闭系统的质量衡算形式封
23、闭系统可认为是一个特殊的敞开系统。即所有进入或离开系统的质量流的速率均为零。 因此,无论系统内部进行的是流动过程、还是非流动过程,系统与外界无质量交换。 于是, 微元过程的质量衡算方程可写为:,Chemical Engineering Thermodynamics,Chapter1 A General Balance Equation and conserved quantities,1-2 the general balance equation of energy1 the open system,Chemical Engineering Thermodynamics,图1-1 有多股质量
24、流进出的任意系统,微元过程的能量衡算方程式为,Note: Q系统吸热为正、放热为负 W系统对环境做功为正、环境对系统做功为负,Chapter1 A General Balance Equation and conserved quantities,1-2 the general balance equation of energy 1 For the open system 在敞开系统的能量平衡方程式中,环境与系统所交换的总功包括流动功和净功:,Chemical Engineering Thermodynamics,若不考虑剪切功、电功、磁功和表面功等,净功仅包括轴功和边界移动功:,随着质量进
25、入系统和离开系统时要输入和输出流动功,故流动功总和为,Chapter1 A General Balance Equation and conserved quantities,1-2 the general balance equation of energy 1 For the open system 在敞开系统的能量平衡方程式中,环境与系统所交换的总功包括流动功和净功:,Chemical Engineering Thermodynamics,若不考虑剪切功、电功、磁功和表面功等,净功仅包括轴功和边界移动功:,随着质量进入系统和离开系统时要输入和输出流动功,故流动功总和为,稳定流动过程,基准
26、水平面,Chapter1 A General Balance Equation and conserved quantities,1-2 the general balance equation of energy 1 For the open system于是,敞开系统的能量平衡方程式为,Chemical Engineering Thermodynamics,上式表明,质量流所携带的能流,除内能和宏观的动能、位能外,还包括流体的流动功。对于恒组成系统,能量平衡方程式为,若在dt时间内变化,则能量平衡速率方程式为,Chapter1 A General Balance Equation and
27、conserved quantities,1-2 the general balance equation of energy 2 For the non-steady flow 这一过程的特点是系统在任一瞬间的性质都是均匀的。能量平衡方程式与前面的相同,Chemical Engineering Thermodynamics,若在dt时间内变化,则能量平衡速率方程式为,Chapter1 A General Balance Equation and conserved quantities,1-2 the general balance equation of energy 3 For the
28、steady flow 这一过程的特点是系统 无质量和能量的积累,系统的热力学性质也不随时间而变化。能量平衡方程式为,Chemical Engineering Thermodynamics,上式表明,在稳态流动过程中,离开和进入系统的质量流所携带的能流差是系统与环境交换的结果。而系统的能量变化为0.,积分之,可得,稳流系统热力学第一定律的简化及应用,1)流体流经压缩机、透平机、鼓风机、泵等设备,若设备散热很小,可近似看成绝热过程,则:,即系统与环境交换的轴功等于系统的焓变。若知道工作流体通过设备时进、出口状态下的焓值,即可求得该设备的轴功。,2)流体流经管道、换热器、吸收塔、精馏塔、混合器、反
29、应器等设备,上式是冷凝器、蒸发器、冷却器等热负荷确定的依据,因此在进行设备设计中进行的热量衡算,严格的讲应称为焓衡算。,3) 流体流经节流阀或多孔塞 当流体流经阀门或孔板等装置,,,即节流过程为等焓流动,4)流体流经蒸汽喷射泵及喷嘴,、喷管,喷管:作用是通过流体获得高速,而压强下降。,当入口流速音速,当出口流速音速时,用于拉法尔喷管 :,称为绝热稳定流动方程式。,流体流经喷射设备时,通过改变流动的截面积,将流体自身的焓转变为动能,从而获得较高的流速。,(2)扩压管:在流动方向上流速降低、压力增大的 装置称为扩压管。,根据此式前面的公式可计算流体终温、质量流速、出口截面积等,因此它是喷管和扩压管
30、的设计依据。,由热力学基本关系式可知,5)柏努利方程,不可压缩的流体在管道中的流动,若假设流体无粘性(无阻力,无摩擦),并且管道保温良好,流动过程中流体环境无热、无轴功的交换。,Chapter1 A General Balance Equation and conserved quantities,1-2 the general balance equation of energy 4 For the closed system特点: 无论系统 进行的过程是否流动,由质量流携带的能流项为0。能量平衡方程式为,Chemical Engineering Thermodynamics,Chapter
31、1 A General Balance Equation and conserved quantities,1-2 the general balance equation of energy 5 For Example 1-2 A 4 m3 storage tank containing 2 m3 of liquid is to be pressurized with air from a large high-pressure reservoir through a valve at the top of the tank to rapid ejection of the liquid(s
32、ee figure) .The air in the reservoir is maintained at 2.0 X106Pa and 300K. The gas space above the liquid contains initially air at 1 X105Pa and 280K. When the pressure in the tank reaches 5 X105Pa, the liquid transfer valve is opened and the liquid ejected at the rate of 0.2 m3/min while tank press
33、ure is maintained at 5 X105Pa. What is the air temperature when the pressure reaches 5 X105Pa and when the liquid has been drained completely? Neglect the interactions at the gas-liquid and gas tank boundaries. It may be assumed that the gas above the liquid is well mixed and that air is an ideal ga
34、swith a constant value of Cv = 20.9 J/molK. m(storage tank )=1000kg, Cp(storage tank )=448.0 J/molK.,Chemical Engineering Thermodynamics,Figure2 ( Example 1-2),Chemical Engineering Thermodynamics,Solution: Example 1-2,1 分析题意,画示意图2 假设a. 假设高压气柜的体积很大,在向储槽充气中,气柜中的温度和压力不变。b.气体为理想气体c.储槽中充气后以及排液后,其气体的温度与充气
35、、排液时的速度有关。 即与充气及排液过程中储槽中气体是否有足够的时间与钢制储槽壁作充分的热交换有关。 在缺乏实验数据的情况下,我们可以考虑两种极端情形:第一种情形充气和排液过程进行迅速,气体与储槽壁、液体没有热交换;第二种情形-充气和排液过程不快,气体已储槽壁有充分的热交换,气体与液体无热交换(液体的导热系数远小于金属),且气体的温度与储槽壁的温度相同。,Chemical Engineering Thermodynamics,Solution: Example 1-2,3 第一种情形充气和排液过程进行迅速,气体与储槽壁、液体没有热交换(绝热过程);a. 求充气过程结束时,储槽气体温度T2; 充
36、气过程是匀态不稳定流动过程, 取储槽液体上方的气体为系统,作质量衡算:,Chemical Engineering Thermodynamics,忽略动能变化、位能变化,根据已知条件,有,按题意,充入气体的状态参数不变,故Hin为常数。积分上式得,Chemical Engineering Thermodynamics,Chemical Engineering Thermodynamics,Solution: Example 1-2,3 第 一种情形充气和排液过程进行迅速,气体与储槽壁、液体没有热交换(绝热过程);b. 求放液后的气体温度T3;放液过程也是匀态不稳定流动过程, 仍取储槽液体上方的气
37、体为系统,作质量衡算:,Chemical Engineering Thermodynamics,忽略动能变化、位能变化,且不做轴功,根据已知条件,有,积分以上两个公式,得,Solution: Example 1-2,4 第二种情形 按有充分热交换的情况计算a.求充气过程结束时,储槽气体温度T2; 取储槽液体上方的气体为系统,设微元过程中气体与储槽壁间的传热量为Q, 作质量衡算:,Chemical Engineering Thermodynamics,积分以上两个公式,得,向储槽壁传热的结果将使储槽温度升高,且与气体温度相同,故,Chemical Engineering Thermodynami
38、cs,4 第二种情形 按有充分热交换的情况计算a. 求充气过程结束时,储槽气体温度T2;,Chemical Engineering Thermodynamics,积分以上两个公式,得,4 第二种情形 按有充分热交换的情况计算b. 求放液后的气体温度T3; 取储槽液体上方的气体为系统,作质量衡算:,Chapter1 A General Balance Equation and conserved quantities,1-3 the general balance equation of entropy1 the open system,Chemical Engineering Thermody
39、namics,图1-1 有多股质量流进出的任意系统,微元过程的熵衡算方程式为,Note: Q系统吸热为正、放热为负,进入物流 流出物流,物流熵差,与环境热量交换引起的熵变,过程不可逆引起的熵变,敞开系统熵平衡式即为:,Chemical Engineering Thermodynamics,熵(entropy)描述系统内分子无序热运动的状态函数,封闭系统的熵变,热源或系统的温度,系统与外界的热量交换会引起系统熵的变化,热力系统与外界环境所构成的孤立系统,熵变为:,表示总量,表示系统,表示环境,Chemical Engineering Thermodynamics,Chapter1 A Gener
40、al Balance Equation and conserved quantities,1-3 the general balance equation of entropy 2 For the constant composition system,Chemical Engineering Thermodynamics,Chapter1 A General Balance Equation and conserved quantities,1-3 the general balance equation of entropy 3 For the steady flow,Chemical E
41、ngineering Thermodynamics,4 For the adiabatic process,0,敞开系统稳流过程的熵平衡式,0 因为Q=0,当流体通过节流阀时,只有一股流体,故:,流体经过节流阀时熵的变化,不可逆绝热过程:,则有:,Chemical Engineering Thermodynamics,可逆绝热过程:,则有:,绝热可逆的稳流过程为等熵过程,即:,Chemical Engineering Thermodynamics,的空气流在绝热下相互混合,求混合过程的,熵产生量。设在上述有关温度范围内,空气的平均等压热容,空气稳流混合过程,两股气流混合为绝热稳流过程,并且在有
42、关温度、压力下的空气可视为理想气体。从质量守恒原理可得混合后质量流量,解,根据热力学第一定律,绝热混合过程Q=0,,因此,可求得混合后空气的温度,对于绝热稳流过程,由式(6-18)可得,由上述结果可知,对于绝热稳流混合过程,虽然敞开体系的熵变为零,且无熵流,但由于混合过程是不可逆的,内部必然有熵产生,因此流出混合器物料熵的总和大于流入物料熵的总和。,Chemical Engineering Thermodynamics,熵分析法在化工单元过程中的应用,分析各种不可逆因素引起的功损耗的原因和大小,提高过程热力学完善性的程度,提高能量利用效率,熵分析法的步骤,确定出入系统各种物流量和热流量、功流量
43、以及各种物流的状态参数,确定物流的焓变和熵变,对系统能量衡算,并计算系统变化过程的理想功,计算系统的熵产生量,计算系统的损耗功;计算过程的热力学效率,Chemical Engineering Thermodynamics,对于混合过程,理想功计算,对绝热混合器,假定混合后为理想溶液,若混合前后温度、压力不同,为计算方便,将混合过程分为二步进行,第步将系统温度、压力变化到混合器出口的温度与压力,第步同温同压下不同组分进行混合,即为理想溶液混合熵变,则混合过程总熵变为以上二步熵变之和,混合过程的理想功为,多组分混合过程,其理想功可写为,损耗功,根据熵衡算方程,对于等温等压的混合过程,其理想功可简化
44、为,说明混合过程的损失功在数量上等于理想功,不能得到有效地利用。,分离过程,分离过程能耗是大型化工、石化企业中所占能耗比例最高。,(1) 等温等压下混合物分离为纯度100%产品的过程,该条件下的分离过程为混合过程的逆过程。对理想气体,(2) 等温等压下混合物分离为纯度非100%产品过程,分离,A+B,nA,nB,Wid1,100A,100B,nA1A,nA2A,nB1B,nB2B,Wid2,Wid3,(nA1+nB1)A(B),(nB2+nA2)B(A),Wid4,Wid5,纯度低于100%含量产品分离理想功计算示意图,Chemical Engineering Thermodynamics,C
45、hapter1 A General Balance Equation and conserved quantities,1-4 the general balance equation of exergyy1 the open system,Chemical Engineering Thermodynamics,图1-1 有多股质量流进出的任意系统,微元过程的熵衡算方程式为,Note: Q系统吸热为正、放热为负 , Ws-系统做功为正、耗功为负,基本概念:,定义:体系由所处的状态变到基本态时所提供的理想功。,为了表达体系处于某状态的作功能力,必须确定基准态,,有效能,态时所具有的最大作功能力。
46、,Chemical Engineering Thermodynamics,规定体系的环境为基准态。环境是指人类活动的环境:大气、地球、水源,变到基准态包括两个概念:,(1)与基准态完全相同。,(2)与基准态达到完全平衡。,完全平衡,热平衡温度相等,力平衡压力相等,化学平衡组成相等或平衡聚集状态、 浓度达到化学平衡,我们规定环境的T、P化学组成不变(即恒定的),规定了T、p及化学组成的环境并不是自然环境,这种人为规定的环境即为环境模型。我们是以环境模型为基准态。系统处于基准态时,各部分有效能均为零。,基准态的规定原则:,能量的级别(品位),自然界能量,高级能量,低级能量,僵态能量,能量的贬质:,是指由高品位能量转化为低品位能量.,合理用能:,就是希望获得的功要多,消耗的功要少,损失的功要小。,节能:,实质对高级能量和低级能量而言,对于僵态能量,由于其不能转化为功,故无研究的必要。,能级:,单位能量所含的有效能称为能级,或称为有效能浓度,,