熱力學(xué)第一定律TheFirstLawofThermodynam.ppt

熱力學(xué)第一定律 （The First Law of Thermodynamics),能量守恒與轉(zhuǎn)換定律,能量之間數(shù)量的關(guān)系,回顧(Review),是否滿足能量守恒與轉(zhuǎn)換定律的過程一定都能自動發(fā)生?,A process must satisfy the first law of Thermodynamics to occur. (一個過程必須滿足熱力學(xué)第一定律才能發(fā)生),Satisfying the first law alone does not ensure that the process will actually take place. (但是，滿足熱力學(xué)第一定律的過程未必都能發(fā)生）,5.1自發(fā)過程的方向性） The Direction of Spontaneous Process 5.2熱力學(xué)第二定律的表述 Statement of the Second Law of Thermodynamics 5.3卡諾循環(huán)與卡諾定律 Carnot cycle and Carnot Theorem 5.4熵、熵增原理及熵方程 Entropy, The increase principle of Entropy and Entropy Equation 5.5熵的意義及應(yīng)用 Significance of Entropy and its application,Chapter 5.The Second Law of Thermodynamics （第五章 熱力學(xué)第二定律）,過程的方向性,溫差傳熱 (Heat Transfer under temperature difference) 自由膨脹 (Free Expansion),A,B,TA TB,A B,QA,QB,U1=U2,QA= QB,QA= QB,U1=U2,5.1 Spontaneous Process （自發(fā)過程）,溫差傳熱和自由膨脹均為不平衡勢差推動下的非準(zhǔn)靜態(tài)過程,也即不可逆過程,摩擦生熱 電容電阻電路,U2=U1+mc2/2,U1=U2+mc2/2,自發(fā)過程的方向性 (Direction of Spontaneous Process),自發(fā)過程：不需要任何外界作用而自動進(jìn)行的過程。 Such as (例如：) a. heat transfer driven by finite temperature difference (有限溫差傳熱) b. work is converted into heat by friction (通過摩擦功轉(zhuǎn)變?yōu)闊? c. Free or unrestrained expansion (空氣向真空自由膨脹)。 d. Mixing process of different substances (不同的流體混合),自發(fā)過程的方向性 (Direction of Spontaneous Process),功量,自發(fā)過程具有方向性、條件、限度,摩擦生熱,熱量,100%,熱量,發(fā)電廠,功量,40%,放熱,自發(fā)過程只能沿某一方向進(jìn)行，而不能反向自動發(fā)生,自然界自發(fā)過程都具有方向性,3.熱力學(xué)第二定律的任務(wù) Essence of the Second Law of Thermodynamics,能不能找出共同的規(guī)律性? 能不能找到一個判據(jù)?,自然界過程的方向性表現(xiàn)在不同的方面,熱力學(xué)第二定律,研究過程的方向性和補(bǔ)償限,5.2 Statement and Essence of the Second Law of Thermodynamics （熱力學(xué)第二定律的表述和實(shí)質(zhì)）,熱二律的表述有 60-70 種,傳 熱 熱功轉(zhuǎn)換,1851年 開爾文普朗克表述 熱功轉(zhuǎn)換的角度,1850年 克勞修斯表述 熱量傳遞的角度,1. 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 heat from a lower-temperature body to a higher-temperature body.,Clausius statement,克勞修斯表述,Clausius statement,Transfer heat from high temperature reservoir to low temperature ones is a spontaneous process. However it is irreversible. (從高溫物體向低溫物體的傳熱是一個自發(fā)過程,但是不可逆) Transfer heat from low temperature reservoir to high temperature ones is possible. However it will leave influence on environment. (從低溫物體向高溫物體的傳熱過程是可以實(shí)現(xiàn)的,但會給環(huán)境造成一定影響),空調(diào),制冷 (Air-Conditioning, Refrigerating),代價(jià)：耗功 (Cost: Energy Consumption),熱量不可能自發(fā)地、不付代價(jià)地從低溫物體傳至高溫物體。,2. 開爾文普朗克表述,不可能從單一熱源取熱，并使之完全轉(zhuǎn)變?yōu)橛杏霉Χ划a(chǎn)生其它變化。,KelvinPlanck Statement,It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work.,No heat engine can achieve a 100 percent thermal efficiency. (熱機(jī)的效率不可能達(dá)到100%) For a heat engine, the working fluid must exchange heat with the environment. (對于熱機(jī)來說,工質(zhì)必然和環(huán)境交換熱量),熱機(jī)不可能將從熱源吸收的熱量全部轉(zhuǎn)變?yōu)橛杏霉Γ仨殞⒛骋徊糠謧鹘o冷源。,開爾文普朗克表述,KelvinPlanck Statement,Heat reservoirs,Thermal Energy Source,冷熱源:容量無限大，取、放熱其溫度不變,但違反了熱 力學(xué)第二定律,第二類永動機(jī) perpetual-motion machine of the second kind,第二類永動機(jī)：設(shè)想的從單一熱源取熱并 使之完全變?yōu)楣Φ臒釞C(jī)。,這類永動機(jī) 并不違反熱力 學(xué)第一定律,第二類永動機(jī)是不可能制造成功的,環(huán)境是個大熱源,Perpetual motion machine of the second kind,鍋 爐,汽輪機(jī),發(fā)電機(jī),給水泵,凝汽器,Wnet,Qout,Q,Suppose we can construct a heat pump which transfers heat from a low temperature reservoir to a high temperature one without using external work. Then, we can couple it with a heat engine in such a way that the heat removed by the heat pump from the low temperature reservoir is the same as the heat rejected by the heat engine, so that the combined system is now a heat engine which converts heat to work without any external effect. This is thus in violation of the Kelvin-Planck statement of the second law.,3.克勞修斯說法與開爾文-普朗克說法等價(jià) Equivalence of Clausius and Kelvin-Planck Statements,Now suppose we have a heat engine which can convert heat into work without rejecting heat anywhere else. We can combine it with a heat pump so that the work produced by the engine is used by the pump. Now the combined system is a heat pump which uses no external work, violating the Clausius statement of the second law. Thus, we see that the Clausius and Kelvin-Planck statements are equivalent, and one necessarily implies the other.,兩種表述的關(guān)系,開爾文普朗克 表述,完全等效!,克勞修斯表述：,違反一種表述,必違反另一種表述!,熱一律否定第一類永動機(jī),熱機(jī)的熱效率最大能達(dá)到多少？ 又與哪些因素有關(guān)？,?,熱一律與熱二律,t 100不可能,熱二律否定第二類永動機(jī),t =100不可能,熱二律的實(shí)質(zhì), 自發(fā)過程都是具有方向性的 表述之間等價(jià)不是偶然，說明共同本質(zhì) 若想逆向進(jìn)行，必付出代價(jià),代價(jià)為多少方可進(jìn)行?,1.卡諾循環(huán) Carnot Cycle,法國工程師卡諾 (S. Carnot)， 1824年提出 卡諾循環(huán),熱二律奠基人,Carnot Cycle is a a particular cycle that has the best possible efficiency, which is important in practice. It sets an upper limit on what is possible for real engines.,5.3 Carnot Cycle and Carnot Theorem (卡諾循環(huán)及卡諾定理),p,V,Heat is transferred to the working fluid during 1-2 (Qh) and heat is rejected during 3-4 (Ql).,an isothermal expansion at high temperature Th （在高溫h 下的等溫吸熱過程） (2) an adiabatic expansion （可逆絕熱膨脹過程） (3) an isothermal compression at low temperature Tl （在低溫l下的等溫放熱過程） (4) an adiabatic compression （可逆絕熱壓縮過程）,卡諾循環(huán) Carnot Cycle,卡諾循環(huán)熱機(jī)效率,卡諾循環(huán)熱機(jī)效率,q1,q2,w,Thermal efficiency of Carnot Cycle,Applying first law,For Isothermal Process of Ideal gas: (對理想氣體的等溫過程),Thermal efficiency of Carnot Cycle (卡諾循環(huán)的熱效率),For ideal gas,在相同的高溫?zé)嵩春拖嗤牡蜏責(zé)嵩撮g工作的可逆熱機(jī)的熱效率恒高于不可逆熱機(jī)的熱效率； The efficiency of an irreversible heat engine is always less than that of a reversible one operating between the same two thermal reservoirs.,2.Carnots Theorems (卡諾定理),在相同的高溫?zé)嵩春拖嗤牡蜏責(zé)嵩撮g工作的一切可逆熱機(jī)有相同的熱效率，而與工質(zhì)無關(guān)。 The efficiencies of all reversible heat engines operating between the same two thermal reservoirs are the same.,2.Carnots Theorems (卡諾定理),Assumed that the work done by these two heat engines is the same. (假定兩個熱機(jī)所做的功相等),W,W,reversible,irreversible,卡諾定理的證明 (Investigation on the Carnot Theorem),For a Carnot engine, the efficiency simplifies to This is the highest efficiency a heat engine operation between the two thermal energy reservoirs at temperatures and can have. The thermal efficiencies of actual and reversible heat engines operating between the same temperature limits compares as follows,(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.,3. The significance of the Carnot Theorems (卡諾定理的意義),(2)卡諾定理指明可以通過提高高溫?zé)嵩吹臏囟?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 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. (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.,功量比熱量更可貴，因?yàn)樗梢?00%地轉(zhuǎn)化為熱量，而熱量只能部分轉(zhuǎn)化為功 Work is a more valuable form of energy than heat since 100 % of work can be converted to heat, but only a fraction of heat can be converted to work.,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(jī)是否能實(shí)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:,T,s,4.工作在相同溫限范圍內(nèi)的任意可逆循環(huán)與卡諾循環(huán) For any reversible cycle and Carnot cycle working between the same temperature difference,T1,T2,TM1,TM2,s2,s1,5. Entropy (熵),p a 1 2 2 b v,For every small Carnot cycle,Then, Entropy is defined as,. Clausius Inequality (克勞修斯不等式),p a 1 2 2 b v,For every small irreversible cycle,克勞修斯不等式,克勞修斯不等式的研究對象是循環(huán)方向性的判據(jù),正循環(huán) 逆循環(huán) 可逆循環(huán) 不可逆循環(huán),克勞修斯不等式的推導(dǎo),克勞修斯不等式的推導(dǎo),（2）不可逆循環(huán),1、正循環(huán)（卡諾循環(huán)）,T1,T2,R,Q1,Q2,W,吸熱,假定 Q1=Q1 ，tIR tR，WW,可逆時(shí),IR,W,Q1,Q2,克勞修斯不等式的推導(dǎo),（1）可逆循環(huán),2、反循環(huán)（卡諾循環(huán)）,T1,T2,R,Q1,Q2,W,放熱,克勞修斯不等式的推導(dǎo),（2）不可逆循環(huán),2、反循環(huán)（卡諾循環(huán)）,T1,T2,R,Q1,Q2,W,放熱,假定 Q2 = Q2 WW,可逆時(shí),IR,W,Q1,Q2,克勞修斯不等式推導(dǎo)總結(jié),可逆 = 不可逆 ,正循環(huán)（可逆、不可逆）,吸熱,反循環(huán)（可逆、不可逆）,放熱,僅卡諾循環(huán),?,克勞修斯不等式, 對任意循環(huán),= 可逆循環(huán) 不可能,熱源溫度,熱二律表達(dá)式之一,克勞修斯不等式例題,A 熱機(jī)是否能實(shí)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,5.3 The increase principle of Entropy and Entropy Equation （熵增原理與熵方程） Performance of Entropy (熵的性質(zhì)) (1) we define Entropy is a state property. Any substance possesses this property . ( 熵是一個狀態(tài)參數(shù)，任何物質(zhì)都具有熵這個參數(shù)） It depends only on state. (它僅取決于狀態(tài)） (2) Entropy is an extensive property. It possess addition (熵是一個廣延參數(shù)，具有可加性） (3) Heat absorption during reversible process can be calculated by the following equation. ( 可逆過程的吸熱量可用下列公式計(jì)算）,Entropy of a substance increases as it absorbs heat.(可逆過程吸熱，則導(dǎo)致熵增大） Entropy decreases as it rejects heat.（可逆過程放熱，則導(dǎo)致熵減?。?(4) , for irreversible process (不可逆過程)。 =, for reversible process (可逆過程),For Example. Initially, a system with air , undertakes an isothermal expansion process and reaches . undertake a adiabatic process and reaches . Calculate the change in entropy.,2.孤立系統(tǒng)的熵增原理 The increase principle of Entropy,we know For isolated system The entropy of an isolated system during a process always increases or, in the 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(jìn)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?。?Why does not entropy of isolated system decrease? (為什么孤立系統(tǒng)的熵不會減少？） Only irreversibilities can lead to the increase in entropy of an isolated system.（不可逆性是導(dǎo)致孤立系統(tǒng)熵增大的唯一原因） Such as heat transfer across a finite temperature difference（溫差傳熱） friction（摩擦） Free or unrestrained expansion（自由膨脹） mixing of two fluids（液體的混合） electric resistance（電阻） inelastic deformation of solid（固體的塑性變形） chemical reactions（化學(xué)反應(yīng)） 3.Entropy generation and Entropy flow (熵產(chǎn)與熵流) Entropy generation is caused by any irreversibility. ( 熵產(chǎn)是由不可逆因素引起的熵變), , for irreversible process (不可逆過程)。 =, for reversible process (可逆過程) (2) Entropy Flow/Transfer (熵流) Entropy can be transferred to or from a system by two mechanisms: heat transfer and mass flow. Entropy transfer by heat transfer (熱量熵流) The direction of entropy transfer is the same as that of heat transfer. (熱量熵流的方向與熱流的方向相同) Energy is transferred by both heat and work,whereas, entropy is only transferred by heat. No entropy is transferred by work. (能量可以由熱量和功量的交換實(shí)現(xiàn)傳遞,但是, 熵流卻只能有熱量傳遞引起,做功不引起熵的流動),Entropy transfer by mass flow (質(zhì)量熵流) Mass contains energy as well as entropy. Both entropy and energy are carried into or out of system by streams of matter.(物質(zhì)具有能量和熵的屬性,隨著物流的遷移,能量和熵都會被帶進(jìn)或帶出系統(tǒng)) The rates of energy and entropy transport into or out of a system is proportional to the mass flow rate. (能量及熵流率與質(zhì)量流率成正比.) The entropy of a system increases by when mass in the amount of enters and decreases by the same amount when the same amount of mass at the same amount leaves the system. (當(dāng)質(zhì)量為 的物質(zhì)進(jìn)入系統(tǒng)時(shí),系統(tǒng)的熵將增大 ; 當(dāng)當(dāng)質(zhì)量為 的物質(zhì)離開系統(tǒng)時(shí),系統(tǒng)的熵將減少 ),4. Entropy Equation (熵方程),(1) Entropy balance of any system undergoing any process can be expressed as (任何系統(tǒng)經(jīng)過任何過程的熵平衡可表達(dá)為) (2) For closed system (對于閉口系統(tǒng)) The entropy change of a closed system during a process is equal to the sum of the net entropy transferred through the system boundary by heat transfer and the entropy generation within the system boundaries. (經(jīng)過一個過程,閉口系統(tǒng)的熵變等于通過邊界的熱量熵流與系統(tǒng)內(nèi)部的熵產(chǎn)之和),For adiabatic closed system For any closed system and its surroundings,(2) For Open System (對于開口系統(tǒng)) The entropy change of a Open system during a process consists of （經(jīng)過一個過程,開口系統(tǒng)的熵變由下列部分組成） the net entropy transferred through the system boundary by heat transfer (通過邊界的熱量熵流) B. the net entropy transfer into the system by mass flow (進(jìn)入系統(tǒng)的凈質(zhì)量熵流) C. the entropy generation within the system bo