【正文】 二定律做出了與可逆過(guò)程的區(qū)別和量化了只在不可逆中發(fā)生的過(guò)程。不可逆的比率指的是由不可逆性產(chǎn)生的熵占總熵的比率。 熱力學(xué)第二定律在制冷循環(huán)中的應(yīng)用，顯示了在相同條件下，一個(gè)完整的可逆循環(huán)可能擁有的最大 COP。176。BenedictWebbRubin Strobridge(1962)建議修改關(guān)系 ,在更高的密度 ,可以收到良好的效果用于 pvT 表面延伸到液相。理想氣體常數(shù) R 的定義是 (21) (pv)T 是壓力和體積的等溫線(xiàn) ,Ttp 是定義三相點(diǎn)的溫度水 ,是 176。 COP≡外部提供的凈能量 制冷能力 (14) 對(duì)于蒸氣壓縮系統(tǒng)來(lái)說(shuō)，提供的凈能量通常是以功、機(jī)械能或電能的形式出現(xiàn)，并且還包括壓縮機(jī)、風(fēng)機(jī)、水泵所需要的能量。 dI 由于不可逆引起的熵 (總是正的 ) 公式 (8)說(shuō)明了在系統(tǒng)中所有的熵變。 幾乎所有的熱力學(xué)過(guò)程都是以穩(wěn)流為模型的。一個(gè)閉式的制冷過(guò)程就是一個(gè)循環(huán)。 流動(dòng)功是由在系統(tǒng)外部產(chǎn)生的流動(dòng)流經(jīng)過(guò)系統(tǒng)界面而帶入的能量，從而把流體帶入這個(gè)系統(tǒng)。第二部分和第三部分講述了壓縮和吸收式兩種制冷循環(huán)，兩種最尋常的能量轉(zhuǎn)換形式。 lbf/(lb mole 勢(shì)能是由分子間的吸引或者是系統(tǒng)位置被提升而產(chǎn)生的。其定義如下： pvuh ?? (4) 其中： u 是 單位質(zhì)量的內(nèi)能。 當(dāng)蒸氣的溫度高于它的飽和溫度時(shí)，此時(shí)的蒸氣被稱(chēng)為過(guò)飽和蒸氣。不可逆產(chǎn)生的原因包括壓力的線(xiàn)性下降，在熱交換過(guò)程中熱交換器的熱量損失，以及各種不可避免的機(jī)械摩擦。 公式 (11)通常用于同質(zhì)量流進(jìn)同質(zhì)量流出的系統(tǒng)中，沒(méi)有功，可以忽略動(dòng)能、勢(shì)能。此基礎(chǔ)上的一個(gè)基本方程是維里方 程。 熱力學(xué)使用分區(qū)或分布函數(shù)來(lái)確定維里系數(shù) 。密集的液體 ,許多高階術(shù)語(yǔ)是必要的 ,既不能令人滿(mǎn)意地預(yù)測(cè)從理論也不能確定從實(shí)驗(yàn)測(cè)量。,等 ,和 B,C,D,等等 ,都是維里系數(shù)。因此，在同等的條件下，任何制冷循環(huán)中不管是理論還是實(shí)際中，可逆過(guò)程的功與實(shí)際的功會(huì)變?yōu)椋? ??? ITWW r e v e r s i b l ea c tu a l 0 (13) 制冷循環(huán)的熱力學(xué)分析 制冷循環(huán)是把熱能從一個(gè)低溫的區(qū)域傳遞到另一個(gè)高溫的區(qū)域。在沒(méi)有不可逆性時(shí)，這個(gè)系統(tǒng)達(dá)到最大理想效率。在室內(nèi)的溫度和壓力下，氣體一般都是過(guò)飽和蒸氣。 系統(tǒng)中任何一個(gè)參數(shù)變化了，就可以確定整個(gè)系統(tǒng)發(fā)生了變化。其表達(dá)式如下： 22mVKE? (2) 式中： V—— 流體流過(guò)邊界面的速度 化學(xué)能是由組成分子的原子的排列產(chǎn)生的。 R).The quantity pv/RT is also called the pressibility factor。這個(gè)章節(jié)講述了工程熱力學(xué)在制冷循環(huán)中的應(yīng)用。機(jī)械功或者軸功是由機(jī)械裝置傳出或者傳入的能量。 一個(gè)循環(huán)是經(jīng)過(guò)一個(gè)過(guò)程或幾個(gè)過(guò)程，系統(tǒng)的初狀態(tài)與末狀態(tài)是相同的。 進(jìn)入系統(tǒng)的凈能量 =系統(tǒng)儲(chǔ)存能的凈增量 或者 進(jìn)入的能量 — 流出的能量 =系統(tǒng)儲(chǔ)存能的增量 圖 1 表明一個(gè)熱力學(xué)系統(tǒng)能量的流進(jìn)與流出。 eesm? 由質(zhì)量的流出引起的熵減。這個(gè)過(guò)程在以下的幾個(gè)章節(jié)中會(huì)講到。維里系數(shù)是溫度的函數(shù) ,的值在方程 (19)和相應(yīng)的系數(shù) (20)是相關(guān)的。數(shù)字計(jì)算機(jī)允許使用非常復(fù)雜的狀態(tài)方程在計(jì)算 pvT 價(jià)值觀 ,甚至高的密度。也就是說(shuō) ,Z = pv / RT 或 維里形成的一個(gè)優(yōu)勢(shì)是統(tǒng)計(jì)力學(xué)被用來(lái)預(yù)測(cè)低階系數(shù) 并提供物理維里系數(shù)的意義。對(duì)于多級(jí)循環(huán)，每一個(gè)階段都可以由一個(gè)可 逆循環(huán)來(lái)描述。 ??? ??? s ur rinout T QmsmsI )()( (11) 公式 (6)可以用來(lái)代替熱交換量。一種方法可以用在開(kāi)式系統(tǒng)里熵流的概念和過(guò)程的不可逆性來(lái)描述。干度只有在飽和狀態(tài) (飽和溫度與飽和壓力 )下才有意義。其他的熱力學(xué)參數(shù)包括熵、內(nèi)能和焓。系統(tǒng)越復(fù)雜，熵就越大；一個(gè)有序簡(jiǎn)單系統(tǒng)的熵就會(huì)很小。 an orderly or unmixed configuration is one of low entropy. Energy has the capacity for producing an effect and can be categorized into either stored or transient forms. Stored Energy Thermal (internal) energy is caused by the motion of molecules and/or intermolecular forces. Potential energy (PE) is caused by attractive forces existing between molecules, or the elevation of the system. mgzPE? (1) where m =mass g = local acceleration of gravity z = elevation above horizontal reference plane Kiic energy (KE) is the energy caused by the velocity of molecules and is expressed as 2 2mVKE? (2) where V is the velocity of a fluid stream crossing the system boundary. Chemical energy is caused by the arrangement of atoms posing the molecules. Nuclear (atomic) energy derives from the cohesive forces holding protons and neutrons together as the atom’s nucleus. Energy in Transition Heat Q is the mechanism that transfers energy across the boundaries of systems with differing temperatures, always toward the lower temperature. Heat is positive when energy is added to the system (see Figure 1). Work is the mechanism that transfers energy across the boundaries of systems with differing pressures (or force of any kind),always toward the lower pressure. If the total effect produced in the system can be reduced to the raising of a weight, then nothing but work has crossed the boundary. Work is positive when energy is removed from the system (see Figure 1). Mechanical or shaft work W is the energy delivered or absorbed by a mechanism, such as a turbine, air pressor, or internal bustion engine. Flow work is energy carried into or transmitted across the system boundary because a pumping process occurs somewhere outside the system, causing fluid to enter the system. It can be more easily understood as the work done by the fluid just outside the system on the adjacent fluid entering the system to force or push it into the system. Flow work also occurs as fluid leaves the system. Flow work =pv (3) where p is the pressure and v is the specific volume, or the volume displaced per unit mass evaluated at the inlet or exit. A property of a system is any observable characteristic of the system. The state of a system is defined by specifying the minimum set of independent properties. The most mon thermodynamic properties are temperature T, pressure p, and specific volume v or density ρ. Additional thermodynamic properties include entropy, stored forms of energy, and enthalpy. Frequently, thermodynamic properties bine to form other properties. Enthalpy h is an important property that includes internal energy and flow work and is defined as pvuh ?? (4) where u is the internal energy per unit mass. Each property in a given state has only one definite value, and any property always has the same value for a given state, regardless of how the substance arrived at that state. A process is a change in state that can be defined as any change in the properties of a system. A process is described by specifying the initial and final equilibrium states, the path (if identifiable), and the interactions that take place across system boundaries during the process. A cycle is a process or a series of processes wherein the initial and final states of the system are identical. Therefore, at the conclusion of a cycle, all the properties have the same value they had at the beginning. Refrigerant circulatin