外文翻译吸收式制冷

1、吸收式制冷简介吸收循环是一个过程，制冷效果被通过使用两种流体和一些热量输入产生, 而不是如同在更熟悉的蒸汽压缩循环里的电输入。蒸汽压缩和吸收冷却循环在较高的压力经过制冷剂的压缩到一个低的压力和余热经过制冷剂的蒸发完成热的移动。 创造压力差并且循环这种致冷剂的方法是在两个循环之间的主要差别。 蒸汽压缩循环利用一台机械压缩机建立必要循环制冷的压力差。 在吸收系统，一种二元溶液或者吸收质用来循环制冷。 因为温度需求为循环在中低温热水范围内, 并且对于电能储蓄有重要的潜能，吸收制冷好像是地热的应用的一种好前景。 吸收机器在两个基本的构造今天是市场上可买到的。对于应用来说超过32F( 主要是空气调节)

2、,循环使用溴化锂作为有吸收剂，水作为制冷剂。 对低于32F的应用来说，氨水/水循环使用氨作为制冷剂，水作为吸收剂。 溴化锂/ 水循环机器图1显示一台典型的溴化锂/ 水机器(溴化锂/ 水)的图解。 过程在两个容器或者壳发生。 上面壳包含发生器和冷却器； 下面的壳，包含吸收剂和蒸发器。 热量供应在含有溴化锂/ 水溶液发生器中。 这一热量引起致冷剂在这一容器水中沸腾溶液到蒸馏状态。水蒸汽进入冷凝器部分在那里一个冷却的介质来把蒸汽冷凝到液态。水然后流动到蒸发器它经过在筒上方含有流体被冷却的区间。为了维持吸收器- 蒸发器壳的一个最低压，水在一个非常低的温度沸腾。这沸腾引起水从介质中吸收热被冷却,因此,降

3、低它的温度。蒸发了水然后进入吸收器它被和在含水量中的非常低的溴化锂/ 水溶液混合的区间之内经过。这浓溶液 ( 浓溴化锂/ 水溶液) 容易吸收来自蒸发器区间的蒸汽形成稀溶液。这就是给循环取名吸收的原因。稀溶液然后被抽到发生机区间重复循环。如图1中所示，有三种流体循环外面的连接中: a)发生器热输入量,b)冷却水 , c)冷凝水 。由于每一个这些循环是一种特性机器额定下的温度。因为单级单位, 这些温度是 :0.12MPa的蒸气 (等效热的水) 进入发生器， 85F的冷却水，44F留下的冷凝水(制冷和空调工程师学会, 1983)。在这些状态之下,一个制冷系数 (COP) 大约可能在 0.65 到 0

4、.70 (制冷和空调工程师学会,1983)。制冷系数可能被想到如机器效率的一种指标。它可以由所需要的热输入量除于冷却产量计算。举例来说，在一个 0.70 的制冷系数操作一个 500吨的吸收冷却器会需要:(500 x 12,000 Btu/h)/0.70=8,571,429 Btu/h 热输入量。这热输入量相当于0.12MPa 9,022 磅/小时的蒸气，或者1,008 gpm 240F 水在17F D T.双级机器能有效的提高机器的制冷系数。然而,温度需求为这些进入发电量温差范围内提供了很好的要求(350 F)。结果，双级机器会或许不被应用到地热应用。措施基于已经被发展 (Christen,1

5、977) 描述单级吸收机的措施反应式,图 2 显示出在制冷系数和容量 (冷却出量) 与热水温度输入量的效应。进入热水小于220 F 的温度实际上造成设备容量的减少。温度造成设备容量减少的原因自然和输入到吸收式循环中的热量相关。在发生器中，热输入量在吸收剂/冷剂混合物中引起沸腾发生。 因为压力在发生器中总是不变的,固定在沸腾温度下。结果，那个进入热水温度的一个还原反应引起在热的流体和沸腾混合物之间的温差一个还原反应。 因为热传递直接地因温差而改变 ,由于进入热水温度在吸收致冷容量中有一个几乎线性的减少。在过去几年中，一个制造厂商已经为在较低的进水口温度增加措施修正小的容量单位 (2 到 10吨)

6、 。然而,在大量输出中被修正机器的低温不仍然有效, 会可以应用在制度和工业型方案中。虽然制冷系数和容量也被其他的参数改变, 像冷凝器和冷凝水温度和流度估计,发生器热输入量在生产中有最大的影响。这是特别地重要的考虑关于地热应用。因为许多240 F和高于此范围的地热资源正在被调查因为使用有机的郎肯循环 (ORC) 的发电量方案, 空气调节应用在这个温度之下是有可能的。结果，在 180 到 230 F 范围中操作的冷却器 (依照图 2) 不得不在 400 和 20% 之间特大号中选择。同传统的系统相比这会容易增加资本支出而且减少回报。资本支出的增加会从较大的冷却塔成本出现，它起因于吸收设备的低制冷系

7、数。单效设备的制冷系数大约是0.7。在相同的状态下面的蒸汽压缩机器的制冷系数可能是 3.0 或更高。结果，为每个单位的制冷，一个蒸汽压缩系统会必须在冷却塔释放 1.33个热量单位。对于一个吸收系统，在一个 0.7 的制冷系数， 2.43个热量单位一定在冷却塔被释放。这为吸收系统在冷却塔和附件增加重要的成本。为了要维持发生器中的热传递,唯一的温差可能在热水蒸气中被忽略。这是事实的一个结果机器本来设计来作蒸气的进量。热传递从那个浓缩蒸汽是一个常数温度过程。 结果,为了要有相等的效果，进入的热水温度会有高于饱和的温度在以定格的状态符合到进水口汽压。这要考虑到热水循环中的一些T。在锅炉中加倍了实施,这

8、对工作费是小的影响。然而，因为T直接地影响流量率和抽泵能量,这是地热应用的主要考虑。举例来说,假如0.54的制冷系数和 15个t的一个大的离心机(只有压缩机消费).小的温差和高流动率在空气调节应用中关于吸收冷却器使用估计指出另外的考虑。 承担一个地热系统要设计一个新的建筑物的加热和冷却。因为供热系统与冷却器的在比较中可能被设计为了相当大的温差, 吸收应用的逐渐增加的成本会必须使用比较高花费和泵花费的需求。 一个第二应用为空气供暖需求设计而且使用一个较小的吸收机承担基本负荷。在这一应用，第二的电冷却器会使用到达好的效果。 从另一方面来说，成本支出会是增加的。大的吨数设备成本图 3 列举了一些在空

9、间净化应用中一般大的吨数 (100个吨) 冷却设备的成本。图中显示出的吸收冷却器 (Abs。 chlr.),离心式冷水机 (Elec。 chlr.),冷凝器设备附件(冷却塔，冷却水抽水机和冷却水砂眼)的成本为了吸收冷却器附件 (Abs。 twr.)和离心式冷水机附件(Elec。 twr.)。 如图所示，吸收设计同电驱动冷却器冷却器相比它本身和它的冷凝器附件设备成本要高的多。 这些是最初的资本支出差别在一个地热实施中不得不节约。图 3. 电动和吸收冷却器和辅助设备的成本 .(Means,1996)小的吨数设备据目前我们所知,现在只有一家公司制造小的吨数 (100 tons) cooling eq

10、uipment for space conditioning applications. The plot shows the installed costs for both absorption chillers (Abs. chlr.), centrifugal chillers (Elec. chlr.), and auxilliary condenser equipment (cooling tower, cooling water pumps and cooling water piping) for both absorption chillers (Abs. twr.) And

11、 centrifugal chillers (Elec. twr.). As shown, both the chiller itself and its auxilliary condenser equipment costs are much higher for the absorption design than for electric-driven chillers. These are the primary capital cost differences that a geothermal operation would have to compensate for in s

12、avings.Figure 3. Chiller and auxiliary equipment costs - electric and absorption (Means, 1996).SMALL TONNAGE EQUIPMENTTo our knowledge, there is only one company (Yazaki, undated) currently manufacturing small tonnage (20 tons) lithium bromide refrigeration equipment. This firm, located in Japan, pr

13、oduces equipment primarily for solar applications. Currently, units are available in 1.3, 2, 3, 5, 7.5, and 10 ton capacities. These units can be manifolded together to provide capacities of up to 50 tons.Because the units are water cooled chillers, they require considerably more mechanical equipmen

14、t for a given capacity than the conventional electric vapor compression equipment usually applied in this size range. In addition to the absorption chiller itself, a cooling tower is required. The cooling tower, which is installed outside, requires interconnecting piping and a circulation pump. Beca

15、use the absorption machine produces chilled water, a cooling coil and fan are required to deliver the cooling capacity to the space. Insulated piping is required to connect the machine to the cooling coil. Another circulating pump is required for the chilled water circuit. Finally, hot water must be

16、 supplied to the absorption machine. This requires a third piping loop.In order to evaluate the economic merit of small absorption equipment compared to conventional electric cooling, Figure 4 was developed. This plot compares the savings achieved through the use of the absorption equipment to its i

17、ncremental capital costs over a conventional cooling system. Specifically, the figure plots cost of electricity against simple payback in years for the five different size units. In each case, the annual electric cost savings of the absorption system (at 2,000 full load hours per year) is compared t

18、o the incremental capital cost of the system to arrive at a simple payback value. The conventional system to which absorption is compared in this case is a rooftop package unit. This is the least expensive conventional system available. A comparison of the absorption approach to more sophisticated c

19、ooling systems (VAV, 4-pipe chilled water, etc.) would yield much more attractive payback periods.Figure 4. Simple payback on small absorption equipment compared to conventional rooftop equipment.The plot is based on the availability of geothermal fluid of sufficient temperature to allow operation a

20、t rated capacity (190F or above). In addition, other than piping, no costs for geothermal well or pumping are incorporated. Only cooling equipment related costs are considered. As a result, the payback values in Figure 4 are valid only for a situation in which a geothermal resource has already been

21、developed for some other purpose (space heating and aquaculture), and the only decision at hand is that of choosing between electric and absorption cooling options.Figure 4 also shows that the economics of small tonnage absorption cooling are attractive only in cases of 5 to 10 ton capacity requirem

22、ents and more than $0.10 kW/h electrical costs. Figure 4 is based on an annual cooling requirement of 2,000 full load hours per year. This is on the upper end of requirements for most geographical areas. To adjust for other annual cooling requirements, simply multiply the simple payback from Figure

23、4 by actual full load hours and divide by 2,000.The performance of the absorption cooling machine was based on nominal conditions in order to develop Figure 4. It should be noted that, as with the larger machines, performance is heavily dependent upon entering hot water temperature and entering cool

24、ing water temperature. Ratings are based on 190F entering hot water, 85F entering cooling water and 48F leaving chilled water. Flow rates for all three loops are based upon a 9F delta T.Figure 4 illustrates the effect of entering hot water temperature and entering cooling water temperature on small

25、machine performance. At entering hot water temperatures of less than 180F, substantial derating is necessary. For preliminary evaluation, the 85F cooling water curve should be employed.COMMERCIAL REFRIGERATIONMost commercial and industrial refrigeration appli-cations involve process temperatures of

26、less than 32F and many are 0F. As a result, the lithium bromide/water cycle is no longer able to meet the requirements, because water is used for the refrigerant. As a result, a fluid which is not subject to freezing at these temperatures is required. The most common type of absorption cycle employe

27、d for these applications is the water/ammonia cycle. In this case, water is the absorbent and ammonia is the refrigerant.Use of water/ammonia equipment in conjunction with geothermal resources for commercial refrigeration applications is influenced by some of the same considerations as space cooling

28、 applications. Figure 5 illustrates the most important of these. As refrigeration temperature is reduced, the required hot water input temperature is increased. Because most commercial and industrial refrigeration applications occur at temperatures below 32F, required heat input temperatures must be

29、 at least 230F. It should also be remembered that the required evaporation temperature is 10 to 15F below the process temperature. For example, for a +20F cold storage application, a 5F evaporation temperature would be required.Figure 5. Small tonnage absorption equipment performance.Figure 5 sugges

30、ts a minimum hot water temperature of 275F would be required. There is not a large number of geothermal resources in this temperature range. For geothermal resources that produce temperatures in this range, it is likely that small scale power generation would be competing consideration unless cascad

31、ed uses are employed. Figure 5 indicates another consideration for refrigeration applications. That is the COP for most applications is likely to be less than 0.55. As a result, hot water flow requirements are substantial. In addition, the cooling tower requirements, as discussed above, are much larger than for equivalently sized vapor compression equipment.CONCLUSIONIn conclusion, it is necessary to evaluate the following factors when considering a geothermal/absorption cooling application f