熱力學(xué)第一定律thefirstlawofthermodynamics-在線瀏覽
2024-08-30 00:36本頁面
【正文】 It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lowertemperature body to a highertemperature 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(gè)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(huì)給環(huán)境造成一定影響 ) 空調(diào) ,制冷 (AirConditioning, 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 。 Kelvin－ Planck Statement It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a 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(duì)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?，而必須將某一部分傳給冷源 。 這類永動(dòng)機(jī) 并不違反熱力 學(xué)第一定律 第二類永動(dòng)機(jī)是不可能制造成功的 環(huán)境是個(gè)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 W 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 bined system is now a heat engine which converts heat to work without any external effect. ? This is thus in violation of the KelvinPlanck statement of the second law. 普朗克說法等價(jià) Equivalence of Clausius and KelvinPlanck Statements ? Now suppose we have a heat engine which can convert heat into work without rejecting heat anywhere else. ? We can bine it with a heat pump so that the work produced by the engine is used by the pump. ? Now the bined 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 KelvinPlanck 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(dòng)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(dòng)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 ? 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. 效率最高 167。 The efficiencies of all reversible heat engines operating between the same two thermal reservoirs are the same. rethreth , ?? ?‘s Theorems (卡諾定理 ) T 1 T 2 Q 1 Q 2A Q 2B Q 1 Assumed that the work done by these two heat engines is the same. (假定兩個(gè)熱機(jī)所做的功相等 ) W W reversible irreversible 39?？ㄖZ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 pares as follows HLT
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