【正文】 lithium bromide absorption refrigeration systems are: the risk of crystallization of solution at high concentrations。制冷循環(huán)是常規(guī)的 ，從冷凝器來的高壓制冷劑進入接收器，接著通過膨脹閥和發(fā)生吸熱過程的蒸發(fā)器 。而且，腐蝕所形成的碎片使噴淋水頭，換熱器等的通道變窄。用像城市煤氣這樣的高溫熱源來加熱發(fā)生器，在吸收過程中被逐級吸收，所以其熱力系數(shù)或制冷系數(shù)比雙效的高。但是雙效要求由氣體 火焰或高壓 蒸氣 直接驅(qū)動。間接加熱的裝置用外部鍋爐或發(fā)生系統(tǒng)產(chǎn)生的 蒸氣 或熱水。 , 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: 假設溴化鋰系統(tǒng)在以下工況下運行： 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℃ . 假設發(fā)生器和蒸發(fā)器處于平衡狀態(tài)，沒有壓降，并且熱交換完全，也就是說，濃溶液離開換熱器時是 40℃ 。以溴化鋰吸收系統(tǒng)為例，吸收前后的質(zhì)量分數(shù)分別表示為 s? 和 w? 。高溫高壓的制冷劑蒸氣以狀態(tài)點 1離開發(fā)生器流入冷凝器，并在冷凝器中冷卻和冷凝。溴化鋰 —水吸收式制冷基本循環(huán)包括 8個 主要部分，除了在機械驅(qū)動制冷循環(huán)中可以見到的蒸發(fā)器，冷凝器和膨脹閥，其余五個部分是完成熱壓縮的溶液泵，吸收器，發(fā)生器，換熱器和一個閥 , a scheme of a basic absorption refrigeration system 圖 54, 基本吸收式制冷系統(tǒng)體系 In the evaporator, the heat (Qe) from low temperature source (To) is transferred to the refrigerant which changes its state from liquid to vapor at low pressure from state 3 to state 4. The vapor is then absorbed by the absorbent LiBr in the absorber at low pressure and temperature. During the absorption, the vapor changes into liquid state 5. The absorption is an exothermic process. The heat (Qa) released during the absorption process is rejected to the surroundings. The weak solution is delivered by the pump to the generator (G) at high pressure at the state 7. The solution in the generator is heated to boil off the refrigerant (water) with heat (Qb) from the high temperature source so that the solution is concentrated. Solution in the generator bees strong and leaves the generator at state 8. The high pressure and temperature refrigerant vapor at state 1 leaves the generator and flows to the condenser where the refrigerant is cooling down and condensed. The condensing heat (QC) is rejected to the surroundings. The liquid refrigerant then expands through the expansion valve (RV1) from state 2 to state 3. This pletes the refrigerant cycle. The strong solution leaving the generator flows back to the absorber after passing through the valve (RV2) and changing its state from state 9 to 10 to plete the solution circulatio n. It worth noting that the pression done by the pump in the absorption system only consumes a small amount of mechanical work (Wp). 在蒸發(fā)器中，制冷劑在低壓下吸收低溫熱源 (To)的熱量 (Qe)，并由狀態(tài)點 3 的液態(tài)變?yōu)闋顟B(tài)點4的蒸氣。在圖表中同樣可以看見純水線，即相當于 0?? 的溶液，右邊不管是橫坐標還是縱坐標，在純水線上的點都有相同的溫度。而在運行工況下，溴化鋰（一種吸濕性鹽）是幾乎不揮發(fā)的，所以不需要精餾。 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。 In an ammoniawater absorption system, ammonia is used as the refrigerant and water as the absorbent. The absorber is fed with weak solution rich with water which absorbs the ammonia vapor. The absorption of ammonia by water is an exothermic process. The strong solution formed in the absorber is pumped to the generator at higher pressure. In the generator, the strong solution is boiled by heating, and the vapor given off is rectified to nearly pure ammonia and delivered to the condenser. There is a heat exchanger interposed between the generator and absorber. The hot weak solution from the generator transfers the heat to the strong solution from the absorber. To maintain the difference in pressures between the generator and absorber, a valve is installed in the pipe [4, 5] 在氨水吸收式系統(tǒng)中，氨做制冷劑，水做吸收劑。 1937年， . Berestneff研制了水 /氯化鋰制冷系統(tǒng)。它們是：吸收式制冷系統(tǒng)，吸附式制冷系統(tǒng)和蒸氣 噴射式制冷系統(tǒng)。 the refrigerants used in the cycle in Chapters 7 and 8. 機械驅(qū)動 蒸氣 壓縮制冷循環(huán)是本書最主要的內(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、冷凝設備、蒸發(fā)器以及流量控制閥將會在第十章到第十三章進行討論。 For the case of evaporating temperature Ctte ???? 201 and condensing temperature Cttc ??? 403 , the thermal parameters of the states could be found from the diagram or table of the refrigerant R134a as below: 對于蒸發(fā)溫度 Ctte ???? 201 ，冷凝溫度 Cttc ??? 403 ， R134a 的熱力參數(shù)可以從 Ph 圖或熱力性質(zhì)表查取，查取結(jié)果如下： Evaporating pressure MPape ? 蒸發(fā)壓力 MPape ? Condensing pressure MPapc ? 冷凝壓力 MPapc ? The specific enthalpies of these states are: 這些狀態(tài)點的比焓為： kJ/kgh1 ? kJ/kgh2 ? kJ/kgh3 ? kJ/kghh 34 ?? , Schematic and a log ph diagram for a basic vapor pression cycle 圖 51，基本 蒸氣 壓縮循環(huán)的示意圖以及在 log ph圖上的 表示 The process 12 is a reversible, adiabatic (isentropic) pression of the refrigerant. So the specific work input by the pressor is: 過程 12為制冷劑的可逆絕熱壓縮過程，壓縮機輸入功為： 4 2 .6 kJ/kghhw 12in ??? (51) The process 23 is an internally reversible constant pressure heat rejection process, in which the refrigerant is desuperheated and then condensed to a saturated liquid at point 3. During this process, the refrigerant rejects heat to condensing media. So the specific condensation heat load per unit mass flow rate of refrigerant is: 過程 23為定壓放熱過程，在此過程中制冷劑先降溫然后被冷凝至飽和液體狀態(tài) 3，制冷劑向冷凝媒介放熱。 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] 壓縮機是機械驅(qū)動 蒸氣 壓縮制冷循環(huán)的心臟。循環(huán)中驅(qū)動裝置的目的是完成整個循環(huán)，在機械功驅(qū)動 蒸氣 壓縮制冷循環(huán)中，此驅(qū)動裝置就是 蒸氣 壓縮機。 Ref. 24。 relative simplicity of its maintenance。 reversible heat rejection at pc=const. desuperheating and condensation to saturated liquid, (from point 2 to point 3)。這些將會在第六章進行分析，同時，多級 蒸氣 壓縮系統(tǒng)、復疊式