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专业外文翻译英文题目：Theoretical analysis of low-temperature hot source driven two-stage LiBr/H20 absorption refrigeration system中文题目：低温热驱动双级LiBr/H2O吸收式制冷系统的理论分析学院：万方科技学院专业：机械设计制造及其自动化班级：机设08-2班姓名： 刘 松学号：0828070147指导老师：邓 乐Theoretical analysis of low-temperature hot source driven two-stage LiBr/H20 absorption refrigeration systemW. B. MaGuangzhou Institute of Energy Conversion, Chinese Academy of Sciences,81CentralMartyrs Road, Guangzhou, ChinaS. M. DengDepartment of Building Services Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong KongReceived 19 December 1994; revised 6 June 1995Abstract: A detailed theoretical analysis is presented for a two-stage LiBr/H20 absorption refrigeration system, which consists of an evaporator, a low-pressure absorber, a low-pressure generator, a high-pressure absorber, a high-pressure generator, a condenser, a low-pressure heat exchanger and a high-pressure heat exchanger, driven by a low-temperature hot source. A comparison of results from the theoretical analysis and preliminary experiment indicates that the theoretical analysis developed can represent a real system with a reasonable accuracy, and is useful for future development.Keywords: absorption； water-lithium ；bromide；two-stageLiterature on absorption refrigeration systems driven by a low-grade energy source such as solar energy or waste heat in industries has been presented 1-5. These systems can in general be classified into two types according to the different working fluids: absorption refrigeration systems, using water-lithium bromide (LiBr/H20), water-ammonia (H20/NH3), water-lithium chloride (LiCI/H20); and adsorption systems, using ammonia calcium chloride (CaCI2/NH3), water-silica-gel, water zealot, activated charcoal-methanol (CH3OH). However, only absorption refrigeration systems using water lithium bromide as working fluid have been operated successfully and have found commercial applications.A single-stage LiBr/H20 absorption refrigeration system generally consists of an evaporator, absorber, generator, condenser and solution heat exchanger. This system operates with water as refrigerant and lithium bromide as absorbent, and the heat source required to run such a system should have at least a temperature of over 86C in order to achieve a reasonable COP 6. However, there exists a large amount of low-temperature heat source of less than 86C, such as waste heat in industries, solar energy and geological heat. If these low temperature heat sources can be used or reused, it will not only improve the overall system energy efficiency, but decrease the heat pollution to the environment as well.A two-stage LiBr/H20 absorption refrigeration system, with water as refrigerant and lithium bromide as absorbent, can however be operated with a lower temperature heat source from 75 to 86C, and a coefficient of performance (COP) of above 0.38 for such a system can be achieved when the condenser cooling water temperature is 32C and the chilled water supply temperature is 9C, notably when the outlet temperature of the heat source is lower than 64 C 7. Therefore a two-stage LiBr/H20 absorption refrigeration system is useful and significant in recovering low temperature waste heat in industries, and in applying solar energy and geological heat. Research work for simulating single-stage absorption refrigeration systems, double-effect absorption refrigeration systems and absorption heat pumps has been reported by a number of researchers, including Bogart 8, Vilest et al 9, and Grossman et al 1-12, but little research for two-stage LiBr/H20 absorption refrigeration systems has been presented. This paper describes the theoretical analysis for the performance of a two-stage absorption refrigeration system under different operating conditions, and a comparison between the theoretical analysis and preliminary experimental results is presented.AssumptionsThe following assumptions were made in the course of analysis.1. The temperature and concentration of LiBr aqueous are in equilibrium at the saturated pressure of LiBr aqueous.2. Heat loss to outside the system is neglected.3. The LiBr fraction pressure is neglected: i.e. the pressure in the vapor phase is equal to the saturated pressure of water.System descriptionThe two-stage LiBr/H20 absorption refrigeration system shown schematically in Figure 1 consists of an evaporator, low-pressure (LP) absorber, LP generator, LP solution heat exchanger, high-pressure (HP) absorber, HP generator, HP solution heat exchanger, condenser and two solution pumps. The pressure in the evaporator is equal to that in the LP absorber, Pe. The pressures in the LP generator and the HP absorber are equal (Pm) as are the pressures in the HP generator and the condenser (Pc). The order of these pressures is Pe PmPc The refrigeration process is described below.The refrigerant water is circulated through the evaporator, LP absorber, LP generator, HP absorber, HP generator and condenser. After water vapor has condensed in the condenser, it returns to the evaporator through an expansion valve. However, the absorbent LiBr aqueous solution is circulated within two separate cycles: a low-pressure cycle between the LP absorber and the LP generator, and a high-pressure cycle between the HP absorber and the HP generator.Figure 2 shows the two-stage LiBr/H20 absorption refrigeration cycle on a log P-T diagram. The cycle indicated by 21-71-51-41-81-91-21 is the low-pressure stage, and that by 2h-7h-5h-4h-8h-9h-2 h is the high pressure stage, corresponding to points in Figure 1. As compared with a single-stage absorption refrigeration system, there are two additional components, is the HP absorber and LP generator, in a two-stage system. These are used to concentrate the LiBr aqueous solution in the LP stage cycle so that it is possible to produce 7-9C chilled water in the evaporator.Theoretical analysis of the absorption cycleLow-pressure cycleWater vaporized in the evaporator is absorbed by the concentrated solution of LiBr from the LP generator through the LP solution heat exchanger; then the LiBr aqueous solution changes to the weak solution. The outlet temperature and concentration (T12 and Xl,) of the LiBr solution are determined based on the pressure Pe and temperature Twi of the cooling water： The weak solution is then pumped to the LP generator through the LP solution heat exchanger, in which it exchanges heat with the concentrated solution from the LP generator. In the LP generator, weak solution is heated to T4 and concentrated to strong solution Xlr. T14 and Xlr are in equilibrium at pressure Pm： Then strong solution returns to the LP absorber to form the low-pressure cycle.High-pressure cycleThe strong solution Xhr in the HP absorber from the HP generator through the HP solution heat exchanger absorbs vapor generated in the LP generator. The weak solution) (ha is then pumped to the HP generator through the HP solution heat exchanger. Similarly, Xh, and Th2 are determined by the temperature Twi of the cooling water and Pro： The weak solution in the HP generator is heated to Th4 by the heat source and concentrated to strong solution Xhr. Th4 and Xhr are in equilibrium at pressure Pc： The strong solution concentrated in the HP generator then returns to the HP absorber, forming the high pressure cycle.Mass and energy balanceEvaporator： LP absorber： LP generator： LP heat exchanger： (19)HP absorber： HP generator： HP solution exchanger： (26)Condenser： Total input heat： Total output heat： Total energy balance： Coefficient of performance (COP)： State variables, temperatures, concentrations and enthalpies of LiBr aqueous solution at points 1-9 were calculated by literature 13-19.The temperature differences (T) between two fluids at the exits of the heat exchangers in the system were determined based on the operating parameters and heat exchanger structure in different heat exchangers. For example, in the evaporator, the temperature differences between the chilled water and refrigerant at the entrance and exit are 7 and 2C respectively.ResultsAnalysis results were obtained using low-temperature hot water as heat source and are discussed below：Effect of hot water temperatureFigure 3 shows the effect of the temperature of the hot water on the coefficient of performance (COP). It is clear that the two-stage LiBr absorption refrigeration cannot be operated if the outlet temperature of the LiBr aqueous solution, Th4 or Tl4, in the HP generator and LP generator is below 58C, under the condition when the temperature of chilled water is 7c and that of the condenser cooling water is 32c. If the temperature difference between the inlet temperature of the hot water and the outlet temperature of the LiBr aqueous solution, Th4 or T14, in the HP generator and LP generator is assumed to be 15C, then a two-stage LiBr/H20 absorption refrigeration system cannot be operated when the temperature of the hot water Thi, is under 73 C. The COP of a two-stage LiBr/H20 absorption refrigeration system increases with the temperature of the hot water, but when the temperature Thi, is above 87 C, or Th4 and T14 are above 72 C, the increase of COP is very small. Because the heat loss increases when the temperature of the heat source, Thi, is increased, the temperature of the heat source Thi above 87 C is not advantageous for a two-stage LiBr/H20 absorption refrigeration system. Figure 3 shows that the best temperature range of the heat source is between 75 C and 87 C for a two-stage LiBr/H20 absorption refrigeration system.Effect of chilled water temperature, Tch oThe influence of different chilled water temperature Tcho on the COP of a two-stage LiBr/H20 absorption refrigeration system is shown in Figure 4. A two-stage LiBr/H20 absorption refrigeration system is more suitable for supplying chilled water of over 9 C for air conditioning or other applications. If the temperature of the chilled water is under 7 C, the COP is very small when the temperature of the cooling water is 32 C.Effect of the temperature of cooling water, TwiThe temperature of the condenser cooling water, Twi, is one of the factors affecting the COP of a two-stage LiBr/H20 absorption refrigeration system. The COP of a two-stage LiBr/H20 absorption refrigeration system decreases with increase of the temperature of the cooling water (Figure 5).Comparison with preliminary experimental resultsPreliminary experimental results for a two-stage LiBr absorption refrigeration system were obtained on a 6 kW experimental prototype, whose schematic is identical to that shown in Figure 1. The design parameters as were listed in Table 1.From Figure 6, as compared with the preliminary experimental results, the COP obtained from the theoretical analysis is 10-13% larger. It is believed that the main reason for this might be that heat losses were ignored in the analysis. After adding these heat losses, the computed results are in good agreement with the experimental results, as indicated by the dashed line in Figure 6. Other possible reasons for the discrepancy might be in part due to some assumptions in the calculation, which could however be identified when sufficient experimental data are available.Temperature differences in various heat exchangers were also in agreement with those used in the theoretical analysis.The comparison with the preliminary experimental results indicated that the theoretical analysis for such a two-stage LiBr/H20 absorption system could represent the real system with a reasonable accuracy. This analysis is expected to be further improved with more available experimental data from continued experimental work. Nevertheless, the analysis presented is useful in understanding the complex heat and mass transfer taking place in a two-stage absorption refrigeration system, and in system design in order to achieve the maximum system efficiency.ConclusionsThe theoretical analysis for a two-stage LiBr/H20 absorption refrigeration system driven by a low temperature source is presented, and the analysis results are compared with the preliminary results from a 6 kW experimental prototype. It is concluded that the analysis can represent a real system with a reasonable accuracy and is useful for future research development work of two-stage absorption refrigeration machines. While the experimental work is continuing, the theoretical analysis presented will be subject to further experiment validation.Figure 5 The effect of cooling water temperature on COPFigure 1 Schematic description of a two-stage absorption refrigeration system: C, condenser; Gh, high-pressure generator; Ah, high-pressure absorber; Gb low-pressure generator; At, low-pressure absorber; E, evaporator; HEXL, low-pressure solution exchanger; HEXH, high-pressure solution exchangerFigure 3 The effect of hot-water temperature on COP for a two-stage LiBr absorption refrigeration system when the outlet chilled water temperature Tch o = 7C and the cooling water temperature Twi = 32C原文翻译低温热驱动双级LiBr/H2O吸收式制冷系统的理论分析W. B. Ma 广州能源研究所、中国科学院、中央大道81号,中国广州S. M. Deng 屋宇设备工程系,香港理工大学九龙区,香港 1994年12月19日收到;修改于1995年6月6日摘要：一份详细的理论分析,提出了两级libr/h20吸收制冷系统,是由一个蒸发器、低压吸收器、低压发生器、高压吸收器、高压发生器、冷凝器、低压热交换器和高压热交换器组成.是通过低温热源驱动的. 由理论分析和初步实验比较结论表明,发展理论分析体系可以合理准确地描述一个实际系统,并且今后的有广阔的发展前途。关键字:吸收；溴化锂-水溶液；双级文献著作上的吸收式制冷系统是由低品位的能量驱动的,例如:太阳能,工业废热.图1-5说明这些系统按照不同的工质一般分为两种类型:吸收式制冷系统,利用水和溴化锂工质对,氨水工质对,水-氯化锂工质对;吸附系统,使用氯化物和氨吸附剂,水-硅胶,水合物,活性炭-甲醇.但是,只有吸收式制冷系统利用水合溴化物作为工质对得以成功运作并已投入商业使用中。单级溴化锂吸收式制冷系统通常是由一个蒸发器,一个吸收器,一个发生器,一个冷凝器和一个热交换器组成.这个系统的运作中,水作为制冷剂,溴化锂作为吸收剂,并且热源要求至少要在摄氏86度以上,为了达到一个合理的制冷系数(COP)。然而,存在大量小于86摄氏度的低温热源,例如:工业废热,太阳能和地热.如果这些低温热源能被利用或再利用,它不但可以提高能源系统的整体效率,而且还可以减少对环境的热污染。双级溴化锂制冷系统,以水作为制冷剂,溴化锂作为吸附剂,然而它的运行要求75到86摄氏度的热源即可并且它的制冷系数(COP)在0.38以上,这样的系统可以达到当冷凝水是32摄氏度并且得到9摄氏度的冷冻水的制冷过程,尤其是低温热源的出口温度可以降到64摄氏度以下.因此,双效溴化锂吸收式制冷系统在工业废热的回收,太阳能,地热能利用方面有重要意义和用途.双效溴化锂制冷系统的研究是通过模拟单级溴化锂制冷系统进行的. 双效溴化锂吸收式制冷系统和吸收式热泵已经报道过一些研究其中包括马龙,Vliet森Al、格罗斯曼森等,但到目前为止很少研究双级溴化锂吸收式制冷系统. 本文的理论分析阐明了双级吸收制冷系统在不同的工况条件下的性能,并对理论分析和初步实验结果进行比较。 术语表COP制冷系数c冷凝器h焓(kj/kg)ch冷冻水m表面张力(kg/s)E蒸发器P压力(pa)G发生器Q热量(kw)H高压q热导率(kj/kg)I入口T温度(C)L低压X吸收率（%）O出口流体传热温差（C）r浓溶液下面是设备a吸收器；稀溶液1-9状态点w冷却水1,，3,，m相对蒸发压力Pc,Pc,Pm下列是假设过程中所作的假设分析:1. 溴化锂溶液的浓度和温度都在溴化锂溶液饱和压力下。 2. 系统热损失忽略不记。3. 溴化锂溶液的压力忽略,即:在容器的压力等于饱和水蒸汽的压力。系统过程介绍：双级溴化锂吸收式制冷系统通过大略显示在图表1是由一个蒸发器,低压(LP)吸收器、低压发生器,低压溶液热交换器,高压吸收器,高压发生器,高压热交换器,冷凝器和两个溶液泵组成.蒸发器中的压力与低压吸收器中的压力相等(Pe),低压发生器中的压力和高压吸收器中压力相同(Pm)也正如高压发生器中压力与冷凝器中压力相等(Pc).这些压力的关系是PePmPc.制冷过程描述如下:冷冻水循环是通过蒸发器,低压吸收器,低压发生器,高压吸收器,高压发生器和冷凝器进行的.之后水蒸气在冷凝器中凝结,然后通过一个膨胀阀节流后进入蒸发器.而吸收剂溴化锂溶液是通过内部两个独立的循环:一个是低压循环在低压吸收器和低压发生器之间进行;另一个是高压循环在高压吸收器和高压发生器之间进行。图2是双级溴化锂吸收制冷循环P-T图上的表示.其中21-71-51-41-8191-21循环是低压阶段,而2h-7h-5h-4h-8h-9h-2h是高压阶段的循环,相当于图形1上的各点.与单级溴化锂吸收制冷系统相比,双级溴化锂吸收制冷系统存在两个额外部件,即高压吸收器和低压发生器.它们是用来在低压循环阶段收集溴化锂稀溶液以至于在蒸发器制得7-9的冷冻水。吸收循环的理论分析低压循环蒸发器中吸热汽化的水蒸汽被通过低压热交换器来自低压发生器的溴化锂浓溶液吸收之后,溴化锂浓溶液变为溴化锂稀溶液.溴化锂溶液出口的温度(T12)和浓度(X1)是根据冷却水的压力(Pe)和温度(Twi)测定的。 (1) (2)溴化锂稀溶液通过泵的作用进入低压发生器然后通过低压热交换器,通过低压发生器稀溶液和浓溶液进行热交换.在低压发生器中稀溶液被加热到T14和浓度为X1r.温度T14和浓度X1r处于压力Pm下的平衡状态。 (
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