大學(xué)化工專業(yè)英語Lesson 3.doc

The Second Law of Thermodynamics熱力學(xué)第二定律Thermodynamics is concerned with transformation of energy, and the laws of thermodynamics describe the bounds within which these transformation are observed to occur. 熱力學(xué)討論的是能量的轉(zhuǎn)換，熱力學(xué)定律描述了這些轉(zhuǎn)變能夠發(fā)生的邊界條件。The first law, stating that energy must be conserved in all ordinary processes, has been the underlying principle of the preceding chapters. 第一定律指出了在一般過程中，能量是守恒的，它是前面章節(jié)遵循的根本原則。The first law imposes no restriction on the direction of energy transformation. 第一定律對(duì)能量轉(zhuǎn)換的方向性沒有限制。Yet, all our experience indicates the existence of such a restriction. 然而，我們的經(jīng)驗(yàn)表明這種限制的存在。To complete the foundation for the science of thermodynamics, it is necessary to formulate this second limitation. Its concise statement constitutes the second law. 為了完善熱力學(xué)的科學(xué)基礎(chǔ)，有必要規(guī)定第二個(gè)限制條件，它簡(jiǎn)潔的內(nèi)容構(gòu)成了第二定律。The differences between the two forms of energy, heat and work, provide some insight into the second law. 兩種形式的能量：熱和功之間的不同，為第二定律提供了一些見解。These differences are not implied by the first law. 這些不同是第一定律中沒有提到的。In an energy balance both work and heat are included as simple additive terms, implying that one unit of heat, such as a joule or BTU, is equivalent to the same unit of work. 在能量平衡中，功和熱作為簡(jiǎn)單的加和項(xiàng)，表明了，一個(gè)單位的熱，如1J或1BTU，等于相同單位的功。Although this is true with respect to an energy balance. 雖然這是真正的能量平衡。Experience teaches that there is a difference in quality between heat and work. 經(jīng)驗(yàn)告訴我們，熱和功之間有一個(gè)質(zhì)量的差異。This experience can be summarized by the following facts. 這方面的經(jīng)驗(yàn)可以從以下事實(shí)中總結(jié)出來。First, the efficiency of the transformation from one form of work to another such as electrical to mechanical as accomplished in an electric motor, can be made to approach 100 percent as closely as is desired. 首先，使得從一種形式的功向另一種形式的功的轉(zhuǎn)換效率盡可能的接近于我們所向往的100%，比如，從電能到機(jī)械能的轉(zhuǎn)換能夠通過電動(dòng)機(jī)來實(shí)現(xiàn)。One needs merely to exert more and more care in eliminating irreversibilities in the apparatus. 我們僅僅需要越來越關(guān)心裝置設(shè)備中不可逆性的消除。On the other hand, efforts to convert energy transferred to a system as heat into any of the forms of work show this regardless of improvements in the machines employed. 另一方面，將轉(zhuǎn)移到系統(tǒng)中的熱量轉(zhuǎn)換成任何一種形式的功表明，這與所使用機(jī)器的改進(jìn)無關(guān)。The conversion is limited to low values（40 percent is an approximate maximum）. 這種轉(zhuǎn)換率是被限制在一個(gè)較小的值內(nèi)（40%大約是最大值）。These efficiencies are so low, in comparison with these obtained for the transformation of work from form to another, that there can be no escape from the conclusion that there is an intrinsic difference between heat and work, in the reverse direction, the conversion of work into heat with 100 percent efficiency is very common. 與不同形式的功之間轉(zhuǎn)換的效率相比，這些效率是太低了，以至于得出一個(gè)不可逃避的結(jié)論：熱與功之間有一個(gè)本質(zhì)的不同，在相反的方向上，功向熱轉(zhuǎn)換的效率為100%，這是非常普通的。Indeed, efforts are made in nearly every machine to eliminate this conversion, which decrease efficiency of operation. 事實(shí)上，為了消除這種轉(zhuǎn)變，我們?cè)谂Ω倪M(jìn)幾乎每臺(tái)機(jī)器，這降低了操作效率。These facts lead to the conclusion that heat is a less versatile or more degraded form of energy than work. 從這些事實(shí)中可以得出一個(gè)結(jié)論，熱與功相比，沒有那么多變，沒有更多能量的退化形式。Work might be termed energy of a higher quality than heat. 功可以被稱為是比熱具有更高質(zhì)量的能量。To draw further upon our experience, we know that heat always flows from a higher temperature level to a lower one, and never in the reverse direction. 為了進(jìn)一步的總結(jié)我們的經(jīng)驗(yàn)，我們知道從高溫到低溫將會(huì)產(chǎn)生熱量，然而在相反的方向上不會(huì)有熱量產(chǎn)生。This suggests that heat itself may be assigned a characteristic quality as well as quantity, and that this quality depends upon temperature, the relation of temperature to the quality of heat is evident from the increased in efficiency with which heat may be converted into work as the temperature of the source is raised. 這表明，熱本身可能被分配了一定的質(zhì)量和數(shù)量，這個(gè)質(zhì)量取決于溫度，從增加的效率來看，溫度和熱的質(zhì)量的關(guān)系是明顯的：在這樣的效率下，隨著原始材料溫度的升高，熱能夠轉(zhuǎn)化成功。For example, the efficiency, or work output per unit of fuel burned, of a stationary power plant increases as the temperature of the steam in the boiler and superheater rises. 例如，一個(gè)固定式發(fā)電站的效率，或者燃燒每單位燃料的輸出功，隨著鍋爐或過熱器中蒸汽溫度的升高而增加。Statements of the Second Law第二定律的陳述The observations just described are results of the restriction imposed by the second law on the direction of actual processes. Many general statements may be made which described this restriction and hence, serve as statements of the second law. Two of the most common are: 剛剛描述的觀察結(jié)果是第二定律對(duì)實(shí)際過程在方向上的限制的結(jié)果。許多通用的語句能夠描述這個(gè)限制，因此，這些描述可以作為第二定律的陳述。最常見的兩個(gè)是：1. No apparatus can operate in such a way that its only effect（in system and surroundings）is to convert heat absorbed by a system completely into work. 1. 沒有設(shè)備能夠僅僅產(chǎn)生這樣一種影響：實(shí)現(xiàn)將系統(tǒng)吸收的熱量全部轉(zhuǎn)化成功。2. Any process which consists solely in the transfer of heat from one temperature to a higher one is impossible. 任何一個(gè)從低溫到高溫的過程僅僅包含熱量的轉(zhuǎn)移是不可能的。Statement 1 does not imply that heat cannot be converted into work, but does mean that changes, other than those resulting directly from the conversion of heat into work, must occur in either the system or surroundings. 陳述1并不意味著熱量不能轉(zhuǎn)化為功，但是意味著，除了由熱轉(zhuǎn)化成功直接產(chǎn)生的變化之外，在系統(tǒng)或環(huán)境中一定有其他的變化發(fā)生。Consider the case of an ideal gas in a cylinder and piston assembly expanding reversibly at constant temperature. 考慮理想氣體恒溫下在活塞氣缸內(nèi)可逆膨脹。Work is produced in the surroundings（consider the gas as the system）equal to the integral of the pressure times the change in volume. 將氣體考慮為系統(tǒng)，對(duì)環(huán)境做的功等于壓力乘以體積變化的積分。Since the gas is ideal, u=0 then, according to the first law the heat absorbed by the gas from the surrounding is equal to the work produced in the surroundings because of the reversible expansion in the gas. 由于氣體是理想氣體，所以u(píng)=0，根據(jù)第一定律，氣體從周圍環(huán)境吸收的熱量等于周圍環(huán)境所做的功，因?yàn)闅怏w膨脹是可逆的。At first this might seem to be a contradiction of statement 1, since in surroundings the only result has been the complete conversion of heat into work. 乍一看，這好像與陳述1相矛盾，由于在環(huán)境中，唯一的結(jié)果是由熱到功的完全轉(zhuǎn)變。However the second law statement requires that there also be no change in the system, a requirement which has not been met in this example. 然而，第二定律要求在系統(tǒng)中也沒有任何變化，在這個(gè)例子中，并沒有滿足這個(gè)要求。Since the pressure of the gas decreased, this process cannot be continued indefinitely. 由于氣體壓力下降，這個(gè)過程不能無限地繼續(xù)下去。The pressure of the gas would soon reach that of the surroundings, and further expansion would be impossible. 氣體的壓力很快就會(huì)達(dá)到環(huán)境的壓力，進(jìn)一步的膨脹是不可能的。Therefore, a method of continuously producing work from heat by this method would fail, if the original state of the system were restored in order to comply with the requirements of statements 1, it would be necessary to take energy from the surroundings in the form of work in order to compress the gas back to its original pressure. 因此，這樣由熱來連續(xù)生產(chǎn)功的方法是失敗的，為了符合陳述1的要求，如果系統(tǒng)的初始狀態(tài)被恢復(fù)，為了壓縮氣體回到原始?jí)毫Γ苡斜匾獜沫h(huán)境中以功的形式獲得能量。At the same time energy as heat would be transferred to the surroundings in order to maintain constant temperature. 同時(shí)，為了保持恒溫，熱量將會(huì)轉(zhuǎn)移到環(huán)境中。This reverse process would require just the amount of work gained from the expansion; hence the net work produced would be zero. 這種反轉(zhuǎn)過程僅僅要求膨脹時(shí)獲得的功的量；因此，產(chǎn)生的凈功是等于0。From this discussion it is evident that statement 1 might be expressed in an alternative way, viz: la. it is impossible to convert the heat absorbed completely into work in a cyclical process. 從這個(gè)討論中，可以很明顯地看出，陳述1可能有另外一種表達(dá)方式，即，1a. 在一個(gè)循環(huán)過程中不可能將吸收的熱量全部轉(zhuǎn)化為功。The term cyclical requires that the system be restored periodically to its original state. 這一術(shù)語周期性要求系統(tǒng)定期恢復(fù)到原來的狀態(tài)。In the previous example the expansion and compression back to the original state constitute a complete cycle. 在前面的離子中