工程熱力學總復習ppt

1、總復習(Overall Review),系統(tǒng) (Thermodynamic System): A quantity of matter or a region in space chosen for study. （系統(tǒng)就是指被選做研究對象的物體或空間。）2. 平衡狀態(tài)(Equilibrium State) A system in equilibrium experiences no changes with ti

2、me when it is isolated from its surroundings. 所謂平衡狀態(tài)就是指在沒有外界影響的情況下，系統(tǒng)的狀態(tài)不隨時間而發(fā)生變化。,Basic Concept,3.準靜態(tài)過程(Quasi-static Process ) 在無限小勢差推動下的由連續(xù)平衡態(tài)組成的過程，就是準靜態(tài)過程。 When a process proceeds in such a manner th

3、at the system remains infinitesimally close to an equilibrium state at all times, it is called a quasi-static or quasi-equilibrium process.,4.可逆過程(Reversible process) 系統(tǒng)經(jīng)歷某一過程后，如果能使系統(tǒng)與外界同時恢復到初始狀態(tài)，而不留下任何痕跡，則此過程為可逆過程。

4、 A process that can reversed without leaving any trace on the surroundings. That is, both the system and the surroundings are returned to their initial states at the end of the reverse process.,自發(fā)過程(Spontaneous Proces

5、s)不需要任何外界作用而自動進行的過程。 Aprocess which can happy naturally without the interference from the surroundings.,,5.穩(wěn)態(tài)穩(wěn)定流動(Steady-flow process) A process during which a fluid flows through a control volume steadily.

6、 That is, the properties remain the same at a fixed point during the entire process.,6.循環(huán) (Cycle) If a system returns to its initial state at the end of the process, it is said a system have undergone a cycle. 系統(tǒng)經(jīng)

7、歷了一系列狀態(tài)變化過程，又回到了原來狀態(tài)，稱為熱力循環(huán)。,7.比熱容（Specific Heat)將單位物量的物質(zhì)溫度升高1K所需加入的熱量。 The energy required to raise the temperature of a unit quantity of a substance by one degree,8.分容積 ( component volume ) 假定混合氣體中組成氣體具有與混合氣

8、體相同的溫度及壓力時，單獨存在所占有的容積。9.分壓力（Component pressure） 假定混合氣體中組成氣體單獨存在，并具有與混合氣體相同的溫度及容積時的壓力,10.焓（Enthalpy）Enthalpy, a state function, is defined as follows, h= u + pv This energy is composed of two pa

9、rts: the internal energy of the fluid (u) and the flow work (pv) associated with pushing the mass of fluid across the system boundary. 對開口系統(tǒng)而言，焓指流動工質(zhì)所攜帶能量的一部分，這部分能量取決于熱力狀態(tài),11.飽和狀態(tài) Saturation state飽和狀態(tài)：汽化與凝結的動態(tài)平衡

10、12.蒸發(fā)（Evaporize）和沸騰（Boiling)13.干度（Dryness)14.汽化潛熱（Latent heat),15. 未飽和濕空氣(Unsaturated Air) Dry air+ Superheated water vapor 干空氣和過熱水蒸汽的混合物。飽和濕空氣(Saturated Air)Dry air+ Saturated water vapor 干空氣和飽和水蒸汽的混合物。,16.露點溫度(De

11、w-point Temperature) It is defined as the temperature at which condensation begins when the air is cooled at constant pressure.17.相對濕度φ (Relative Humidity of Air) It is defined as the ratio of the amount of mois

12、ture in the air to the maximum amount of moisture the air can hold at the same temperature. 濕空氣中實際包含的水蒸汽量與同溫度下最多能包含的水蒸汽量的百分比。,18.含濕量(Humidity ratio) 含濕量d：以干空氣為基準，包含1千克干空氣的濕空氣中中所含有的水蒸汽的質(zhì)量。 The mass of wa

13、ter vapor present in a unit mass of dry air is called humidity Ratio.,,19.馬赫數(shù)：（The Mach number） M, It is the ratio of the flow speed, c, to the velocity of sound in the same fluid at the same state. It is denoted as

14、M. (流體在某一點的運動速度和該點當?shù)芈曀僦? 以M表示),,20.滯止參數(shù)(Stagnation Properties) 氣體速度為零時的狀態(tài)稱為滯止狀態(tài),該狀態(tài)的參數(shù)稱為滯止參數(shù). Stagnation properties represent the enthalpy of a fluid when it is brought to rest adiabatically,,21.Critical

15、Pressure Ratio(臨界壓力比),22. 絕熱節(jié)流 (Adiabatically Throttling)　 流速為 的氣流,由于局部阻力使流體降壓膨脹的現(xiàn)象稱為節(jié)流, 因流速高,時間短,與外界換熱少,可視作絕熱,故稱絕熱節(jié)流.,Critical Point(關鍵點）:,1. Pressure (壓力）,Absolute pressure （絕對壓力）Relative pressure （相對壓力）Gage pr

16、essure （表壓力）Vacuum pressure （真空度）,絕對壓力與相對壓力,,當 p > pb,,表壓力 pe,,當 p < pb,,真空度 pv,,,,,,,pb,,pe,,p,,,pv,,p,relative pressure,absolute pressure,Gage pressure,Vacuum pressure,As shown in the following figure，it is know

17、n that pb=101325Pa, the height difference is H=300mm for mercury liquid. The gauge pressure of B is 0.2543MPa,Then what is the pressure for side A, and what is the value of Pg,A?已知大氣壓pb=101325Pa，U型管內(nèi) 汞柱高度差H=300mm，氣體表B讀

18、數(shù)為0.2543MPa，求：A室壓力pA及氣壓表A的讀數(shù)pgA,Exercise.1 (練習1）---壓力的測量,解：,,2. Equation of State for Ideal Gas （理想氣體的狀態(tài)方程的應用）,Pv=RT,Example. Determine the mass of air in a room whose dimensions are 4m× 5m× 6m at 100kPa and

19、 25℃,3.平均比熱 Mean specific heat,,,t,,,t2,t1,c(cp ,cv),,,,,,,c=f (t),,,,,求O2在100-500℃平均定壓熱容,4.理想氣體?u、? h和?s的計算,,,,,,,? W,,? Q,,,一般式,?Q = dU + ?W Q = ?U + W,?q = du + ?w q = ?u + w,單位工質(zhì),適用條件： 1）任何工質(zhì) 2) 任何過程,Point f

20、unction---Exact differentials--- dPath function---Inexact differentials--- ?,5.閉口系統(tǒng)能量方程,可逆閉口系能量方程,?w = pdv,簡單可壓縮系可逆過程,? q = Tds,?q = du + pdv,q = ? u + ? pdv,任何工質(zhì)、可逆過程,Tds = du + pdv,? Tds = ? u + ? pdv,熱力學恒等式,理想氣體、可逆過程

21、,6.  Corollaries of the First Law （熱力學第一定律的推論）(1)  Work done in any adiabatic (Q=0) process is path independent. (2) For a cyclic process heat and work transfers are numerically equal,,or,7. 穩(wěn)態(tài)穩(wěn)

22、定流動系統(tǒng)能量方程,,?q = dh-vdp,Exercise (練習),Correct the error in the following equations. (糾正下列各式中的錯誤)(1) (2)(3)(4)(5),,,,,,2. Make a statement of suitable conditions under which the following equations can be ado

23、pted. ( 敘述下列各公式的適用條件)(1)(2)(3)(4),,,,,3. Initially, there is m1 working fluid in an adiabatic and rigid container, its state is denoted as ‘1’.Then m2 working fluid of state ‘2’ is charged into t

24、he container. The process finished until the state of the working fluid reaches ‘3’ . Write out the energy equation for the process.,,,,,,,,,,,8.The procedures adopted (所采取的步驟),,Pv=RT,35,,,,(1) Work consumption (耗功量）If

25、it is isothermal compression, then(若壓縮過程為可逆定溫過程，則：)If it is isentropic compression, then(若壓縮過程為可逆絕熱壓縮，則: ),,,,,,9.單級壓氣機,If it is polytropic compression, then (若壓縮過程為可逆多變過程，則 : ),（2） Discharge Temperature (排氣溫度）,,

26、10. The influence of residual volume of inter-space. (余隙容積的影響)（1）The influence on discharge volume( 對排氣量的影響）,,,,（2） The influence on compression work（對耗功量的影響） There is no influence on compression work.(對

27、耗功量無影響),11. Multistage Compression with inter-cooling （多級壓縮、中間冷卻）,12. 克勞修斯表述,不可能將熱從低溫物體傳至高溫物體而不引起其它變化。,It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of hea

28、t from a lower-temperature body to a higher-temperature body.,Clausius statement,在相同的高溫熱源和相同的低溫熱源間工作的可逆熱機的熱效率恒高于不可逆熱機的熱效率； The efficiency of an irreversible heat engine is always less than that of a reversible one o

29、perating between the same two thermal reservoirs.,,,,,12.Carnot‘s Theorems (卡諾定理),,在相同的高溫熱源和相同的低溫熱源間工作的一切可逆熱機有相同的熱效率，而與工質(zhì)無關。 The efficiencies of all reversible heat engines operating between the same two thermal res

30、ervoirs are the same.,(1)卡諾定理指明了熱變功的最高效率 The Carnot Theorem indicates the maximum thermal efficiency of heat engine, which converts heat into work.,,13. The significance of the Carnot Theorems (卡諾定理的意義),

31、(2)卡諾定理指明可以通過提高高溫熱源的溫度,降低低溫冷源的溫度或減少過程的不可逆因素等方式來提高熱效率 The Carnot Theorem point out thermal efficiency can be improved by means of raising the temperature of high temperature thermal reservoir, lowering the temperature

32、 of lower temperature reservoir, or reducing irreversibilities.,(3) 卡諾熱效率表明了熱量的最大可用能 The Carnot thermal efficiency value reveals the maximum amount of high temperature thermal energy which can be converted to work.

33、(4)卡諾定理表明能量不僅有數(shù)量的差別，還有品質(zhì)的高低 The Carnot Theorem indicates that energy has quality as well as quantity.,熱源溫度越高，熱量的品質(zhì)就越高,其可轉(zhuǎn)化為的可用能就越大。 The higher the temperature, the higher the quality of thermal energy. (5) 基

34、于卡諾定理,才證明熵是一個狀態(tài)參數(shù) It is based on Carnot theorem that entropy is investigated to be a property.(),卡諾定理舉例,A 熱機是否能實現(xiàn),,,,,,,1000 K,300 K,A,,,,2000 kJ,800 kJ,1200 kJ,可能,,如果：W=1500 kJ,1500 kJ,不可能,,500 kJ,例題:,14.克勞修斯不等式,

35、∴ 對任意循環(huán),,= 可逆循環(huán) 不可能,,熱源溫度,熱二律表達式之一,克勞修斯不等式例題,A 熱機是否能實現(xiàn),,,,,,,1000 K,300 K,A,,,,2000 kJ,800 kJ,1200 kJ,,可能,,,如果：W=1500 kJ,1500 kJ,不可能,,500 kJ,(4). > , for irreversible process (不可逆過程)。

36、 =, for reversible process (可逆過程),,,15.The increase principle of Entropy (孤立系統(tǒng)的熵增原理),For isolated system The entropy of an isolated system during a process always increases or, in t

37、he limiting case of a reversible process remains constant. In other word, it never decreases. (孤立系統(tǒng)中的過程總是向著熵增大的過程進行,若為可逆過程,則熵不變。換句話說，即孤立系統(tǒng)的熵不會減小）,,,16. Entropy generation and Entropy flow (熵產(chǎn)與熵流)Entropy generation i

38、s caused by any irreversibility. ( 熵產(chǎn)是由不可逆因素引起的熵變),(2) Entropy Flow/Transfer (熵流),Entropy transfer by mass flow (質(zhì)量熵流),Entropy transfer by heat transfer (熱量熵流),For steady-flow system (對于穩(wěn)態(tài)穩(wěn)定流動系統(tǒng)）For single stream, ad

39、iabatic, steady flow （對于單股絕熱的穩(wěn)態(tài)穩(wěn)定流動系統(tǒng)）,For closed system (對于閉口系統(tǒng)),17. Significance of Entropy and its application (熵的意義及應用)1. Heat absorption and heat rejection during a

40、 reversible processcan be calculated by resorting to Entropy. (可逆過程中的吸熱或放熱量可借助熵來計算）2. Entropy generation indicates the direction of proce

41、ss in isolated System.(熵產(chǎn)是孤立系統(tǒng)中過程進行方向的標志）,heat transfer across a finite temperature difference（溫差傳熱） Free or unrestrained expansion（自由膨脹）3. Entropy is a measurement of the amount of thermal energy which can not be co

42、nverted to work. (熵是熱量不可用能大小的量度）4.Entropy Generation indicates the amount of loss in energy which can be converted to work. (熵產(chǎn)是做功能力損失的量度）,,,,,T,s,,,,TH,T0,s1,s2,18. Types of Property Tables (水蒸汽表的分類)

43、 1. Saturated water Tables (飽和水和飽和蒸汽表) Saturated water---T Tables(以溫度t為獨立變量排列) Saturated water---p Tables(以壓力p為獨立變量排列) 2. Subcooled water and Superheated vapor Table (未飽和水和過熱水蒸汽表) P and t are dependent variab

44、les (以p和t為自變量),,,,,,,4. Consulting property tables of water vapor to determine the state of each point and their h，s，x.(利用水蒸氣表判斷下列各點的狀態(tài)，并確定其h，s，x的值。),19. Thermodynamic Processes of Water Vapor (水蒸氣的熱力過程),,,,,,(1) Bas

45、ed on the given conditions, determine the initial state and its properties .(根據(jù)已知條件，確定初始狀態(tài)，查出其余參數(shù)。)(2) Based on the characteristics of the process and one of the properties of the final state, determine the final state

46、 and its properties. ( 根據(jù)過程特點和一個終態(tài)參數(shù)，確定終態(tài)，再查出其余終態(tài)參數(shù)。)(3) Based on the initial and final state, calculate the q、Δu、w during the process。(根據(jù)初、終態(tài)參數(shù)，計算q、Δu、w等。),(1) Constant Volume Process ( 定容過程, v=定值。),,,,Constant volu

47、me Process (定容過程),(2) Constant Pressure Process (定壓過程 p=定值),Constant Pressure Process (定壓過程),(3) Constant Temperature Process (定溫過程 T=定值),Isothermal Process (定溫過程),(4) Adiabatic Process ( 絕熱過程),Isentropic Process

48、 (定熵過程),Example: 1 kg water vapor, initially, ℃ undertakes an isentropic expansion process and reaches the final state of Calculate the amoun

49、t of work done by the water vapor during the process.,,,,,The atmospheric air is at ℃ . （１）If is relative humidity is equal to 60%, then calculate such properties as（２）If ℃