【正文】 lutions are monly used in vapor absorption refrigeration systems 基本吸收式系統(tǒng)的主要組成部分如圖 52所示，和圖 51的左半部分相比可以看到在兩種循環(huán)中冷凝器，膨脹閥和蒸發(fā)器是相同的，而機(jī)械式壓縮機(jī)被一個(gè)熱壓縮機(jī)所代替了，這個(gè)熱壓縮機(jī)包括吸收器，溶液泵，發(fā)生器（或鍋爐）和液體閥。在世界上有大量不同形式的熱能，比如太陽(yáng)能，地?zé)崮?，各種廢熱和生物能等。 reversible heat rejection at pc=const. desuperheating and condensation to saturated liquid, (from point 2 to point 3)。 Ref. 24。 In mechanical refrigeration, the pressor is the heart of the system. It produces a difference of pressure on the two sides of the expansion valve, thereby causing a steady and positive flow of the refrigerant through that valve. It keeps fluid circulating in the system, thus maintaining continuous refrigeration. [1] 壓縮機(jī)是機(jī)械驅(qū)動(dòng) 蒸氣 壓縮制冷循環(huán)的心臟。 the refrigerants used in the cycle in Chapters 7 and 8. 機(jī)械驅(qū)動(dòng) 蒸氣 壓縮制冷循環(huán)是本書(shū)最主要的內(nèi)容， 蒸氣 壓縮制冷的循環(huán)分析將在第六章予以討論，循環(huán)的主要部件，包括壓縮機(jī)、冷凝設(shè)備、蒸發(fā)器以及流量控制閥將會(huì)在第十章到第十三章進(jìn)行討論。 1937年， . Berestneff研制了水 /氯化鋰制冷系統(tǒng)。 In lithium bromidewater absorption refrigeration systems, water is the refrigerant and lithium bromide is the absorbent. This explains that the lithium bromide absorption system is strictly limited to evaporation temperatures above 0186。在圖表中同樣可以看見(jiàn)純水線，即相當(dāng)于 0?? 的溶液，右邊不管是橫坐標(biāo)還是縱坐標(biāo)，在純水線上的點(diǎn)都有相同的溫度。高溫高壓的制冷劑蒸氣以狀態(tài)點(diǎn) 1離開(kāi)發(fā)生器流入冷凝器，并在冷凝器中冷卻和冷凝。 , specific enthalpy of solutions of LiBr in water 圖 溴化鋰水溶液的比焓 (3) Steadyflow analysis (3) 穩(wěn)流分析 Assume a lithium bromide system operating at the following conditions: 假設(shè)溴化鋰系統(tǒng)在以下工況下運(yùn)行： Evaporation: 5℃ (pe= mbar), Condensation: 50℃ (pc= mbar), Generator: 110℃ , Absorption: 40℃ . 蒸發(fā)器： 5℃ (pe= mbar): 冷凝器 : 50℃ (pc= mbar), 發(fā)生器 : 110℃ , 吸收器 : 40℃ . Assuming equilibrium states leaving the generator and the evaporator, no pressure drops, and plete heat exchange, . the strong solution leaves the exchanger at 40℃ . 假設(shè)發(fā)生器和蒸發(fā)器處于平衡狀態(tài)，沒(méi)有壓降，并且熱交換完全，也就是說(shuō)，濃溶液離開(kāi)換熱器時(shí)是 40℃ 。但是雙效要求由氣體 火焰或高壓 蒸氣 直接驅(qū)動(dòng)。而且，腐蝕所形成的碎片使噴淋水頭，換熱器等的通道變窄。 Some disadvantages associated with lithium bromide absorption refrigeration systems are: the risk of crystallization of solution at high concentrations。多效吸收裝置中，在被排放到環(huán)境之前，這些熱量中的一些用來(lái)產(chǎn)生更多的制冷劑蒸氣。由于在吸收過(guò)程中，溶液中的溴化鋰質(zhì)量不變，因此有以下關(guān)系存在： ? ? ws ???? 1?? (59) Hence: 因此： wsw?? ?? ?? (510) For example, if ?w? and ?s? , the circulation factor λ is , by eq. (510). 比如說(shuō)，如果 ?w? ， ?s? ，由式 510可得循環(huán)倍率 λ為 。在吸收過(guò)程中放的熱 (Qa)被排向環(huán)境。由混合前后 LiBr 質(zhì)量不變可得 ： ? ? 2211321 ??? mmmm ??? (57) And: 321321 ?? ?? ???mm (58) 3. Vapor pressure of LiBrwater solution 3. LiBrwater溶液的蒸氣壓力 The vapor pressure of aqua lithium bromide solution is determined by its temperature and mass fraction. Their relationship is shown in . The abscissa is temperature in linear scale。在發(fā)生器，濃溶液被加熱至沸騰，放出的蒸氣被精餾至幾乎為純氨蒸氣并被送入冷凝器。 —Vapor Absorption Refrigeration Refrigeration plants based on the principles of vapour absorption have been around for many years. The early development on this system can be dated back over 100 years ago. In 1823, J. Leslie constructed a vacuum/absorption freezing apparatus in England. And in 1878, the first refrigerated mue was built in Paris using F. Carr233。單位質(zhì)量制冷量可按下式求出： kgkJhhq 1e / ??? (53) The coefficient of performance of the cycle can be calculated as: 循環(huán)的性能系數(shù)（ COP）可以按下面計(jì)算： ?????? kgkJ kgkJhh hhwqCO P ine (54) If the mass flow rate of the refrigerant R134a through this cycle is m=, then the refrigeration capacity, the condensing load and the work of pression can be gotten as: 如果循環(huán)中制冷劑 R134a的質(zhì)量流量 m=，那么制冷能力、冷凝負(fù)荷及壓縮功可計(jì)算如下： ?? ee mqQ ?? cc mqQ ?? inin mwW In the vapor pression refrigeration cycle, there are some methods of increasing refrigeration capacity for small systems such as subcooling and superheating. They will be analyzed in Chapter 6. The multistage vapor pression systems, cascade and autocascade vapor pression systems will also be discussed in that chapter. 對(duì)于 蒸氣 壓縮制冷循環(huán)，有一些方法可以提高小型系統(tǒng)的制冷能力，如過(guò)冷和過(guò)熱。 reliability, safety, and flexibility in operation。機(jī)械功驅(qū)動(dòng) 蒸氣 壓縮制冷循環(huán)的原理在 22部分已經(jīng)做了簡(jiǎn)單的描述，整個(gè)循環(huán)的流程將會(huì)在本章做詳細(xì)的說(shuō)明。所以單位質(zhì)量制冷劑的冷凝負(fù)荷為： 1 7 1 .1 kJ/kghhq 32C ??? (52) The process 34 is an irreversible throttling process, in which the temperature and pressure of refrigerant both decrease at constant enthalpy: 過(guò)程 34是制冷劑的不可逆節(jié)流過(guò)程，制冷劑此過(guò)程中溫度和壓力都得以降低，節(jié)流前后的焓值相等。這些循環(huán)利用了在 蒸氣 制冷壓縮循環(huán)的技術(shù)；比如說(shuō)節(jié)流蒸發(fā)和冷凝。吸收器提供用來(lái)吸收氨蒸氣的含有大量水的稀溶液。 The refrigerants and absorbent in H2OLiBr system and NH3–H2O system 表 51, H2OLiBr系統(tǒng)和 NH3–H2O系統(tǒng)中的制冷劑和吸收劑 吸收式循環(huán) 制冷劑 吸收劑 H2O–LiBr 系統(tǒng) H2O LiBr solution NH3–H2O 系統(tǒng) NH3 H2O 2. Composition of mixtures Calculation of absorption refrigerators requires some knowledge of the thermodynamics of solutions and of how their properties depend on the position. 吸收式制冷機(jī)的計(jì)算要用到一 些溶液熱力學(xué)和混合物成分特性的知識(shí)。接著蒸氣被吸收器中的吸收劑在低溫低壓下吸收。吸收式循環(huán)系統(tǒng)中一個(gè)重要的量是濃溶液的質(zhì)量流量，濃溶液是用來(lái)吸收來(lái)自蒸發(fā)器中的蒸氣，這個(gè)量叫做循環(huán)倍率 λ。 , a doubleeffect absorption cycle [10] 圖 雙效吸收式循環(huán) If vapor temperature leaving the generator (boiler) is high, the vapor can be used to heat other generators. In the absorption industry, ―effect‖ is used to refer how many times the heat energy is utilized. In a singleeffect absorption chiller, the heat carried away by the vapor evolved from the generator is rejected in the condenser, where heat is only use once. In a multipleeffect absorption chiller, some of this energy is used to generate more refrigerant vapor before rejected to the surrounding. The more vapor generated per unit of heat or fuel input, the greater the cooling capacity, hence, the higher the overall operating efficiency. Multipleeffect chillers are more efficient than singleeffect chillers, but they require high temperature heat source. Singleeffect chillers may be dr