暖通空调专业-毕业设计外文翻译(共13页).doc

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1、精选优质文档-倾情为你奉上Refrigeration System Performance using Liquid-Suction Heat ExchangersS. A. Klein, D. T. Reindl, and K. BroWnellCollege of EngineeringUniversity of Wisconsin - MadisonAbstractHeat transfer devices are provided in many refrigeration systems to exchange energy betWeen the cool gaseous refr

2、igerant leaving the evaporator and Warm liquid refrigerant exiting the condenser. These liquid-suction or suction-line heat exchangers can, in some cases, yield improved system performance While in other cases they degrade system performance. Although previous researchers have investigated performan

3、ce of liquid-suction heat exchangers, this study can be distinguished from the previous studies in three Ways. First, this paper identifies a neW dimensionless group to correlate performance impacts attributable to liquid-suction heat exchangers. Second, the paper extends previous analyses to includ

4、e neW refrigerants. Third, the analysis includes the impact of pressure drops through the liquid-suction heat exchanger on system performance. It is shoWn that reliance on simplified analysis techniques can lead to inaccurate conclusions regarding the impact of liquid-suction heat exchangers on refr

5、igeration system performance. From detailed analyses, it can be concluded that liquid-suction heat exchangers that have a minimal pressure loss on the loW pressure side are useful for systems using R507A, R134a, R12, R404A, R290, R407C, R600, and R410A. The liquid-suction heat exchanger is detriment

6、al to system performance in systems using R22, R32, and R717.IntroductionLiquid-suction heat exchangers are commonly installed in refrigeration systems With the intent of ensuring proper system operation and increasing system performance.Specifically, ASHRAE(1998) states that liquid-suction heat exc

7、hangers are effective in:1) increasing the system performance2) subcooling liquid refrigerant to prevent flash gas formation at inlets to expansion devices3) fully evaporating any residual liquid that may remain in the liquid-suction prior to reaching the compressor(s)Figure 1 illustrates a simple d

8、irect-expansion vapor compression refrigeration system utilizing a liquid-suction heat exchanger. In this configuration, high temperature liquid leaving the heat rejection device (an evaporative condenser in this case) is subcooled prior to being throttled to the evaporator pressure by an expansion

9、device such as a thermostatic expansion valve. The sink for subcooling the liquid is loW temperature refrigerant vapor leaving the evaporator. Thus, the liquid-suction heat exchanger is an indirect liquid-to-vapor heat transfer device. The vapor-side of the heat exchanger (betWeen the evaporator out

10、let and the compressor suction) is often configured to serve as an accumulator thereby further minimizing the risk of liquid refrigerant carrying-over to the compressor suction. In cases Where the evaporator alloWs liquid carry-over, the accumulator portion of the heat exchanger Will trap and, over

11、time, vaporize the liquid carryover by absorbing heat during the process of subcooling high-side liquid.BackgroundStoecker and Walukas (1981) focused on the influence of liquid-suction heat exchangers in both single temperature evaporator and dual temperature evaporator systems utilizing refrigerant

12、 mixtures. Their analysis indicated that liquid-suction heat exchangers yielded greater performance improvements When nonazeotropic mixtures Were used compared With systems utilizing single component refrigerants or azeoptropic mixtures. McLinden (1990) used the principle of corresponding states to

13、evaluate the anticipated effects of neW refrigerants. He shoWed that the performance of a system using a liquid-suction heat exchanger increases as the ideal gas specific heat (related to the molecular complexity of the refrigerant) increases. Domanski and Didion (1993) evaluated the performance of

14、nine alternatives to R22 including the impact of liquid-suction heat exchangers. Domanski et al. (1994) later extended the analysis by evaluating the influence of liquid-suction heat exchangers installed in vapor compression refrigeration systems considering 29 different refrigerants in a theoretica

15、l analysis. Bivens et al. (1994) evaluated a proposed mixture to substitute for R22 in air conditioners and heat pumps. Their analysis indicated a 6-7% improvement for the alternative refrigerant system When system modifications included a liquid-suction heat exchanger and counterfloW system heat ex

16、changers (evaporator and condenser). Bittle et al. (1995a) conducted an experimental evaluation of a liquid-suction heat exchanger applied in a domestic refrigerator using R152a. The authors compared the system performance With that of a traditional R12-based system. Bittle et al. (1995b) also compa

17、red the ASHRAE method for predicting capillary tube performance (including the effects of liquid-suction heat exchangers) With experimental data. Predicted capillary tube mass floW rates Were Within 10% of predicted values and subcooling levels Were Within 1.7C (3F) of actual measurements.This paper

18、 analyzes the liquid-suction heat exchanger to quantify its impact on system capacity and performance (expressed in terms of a system coefficient of performance, COP). The influence of liquid-suction heat exchanger size over a range of operating conditions (evaporating and condensing) is illustrated

19、 and quantified using a number of alternative refrigerants. Refrigerants included in the present analysis are R507A, R404A, R600, R290, R134a, R407C, R410A, R12, R22, R32, and R717. This paper extends the results presented in previous studies in that it considers neW refrigerants, it specifically co

20、nsiders the effects of the pressure drops,and it presents general relations for estimating the effect of liquid-suction heat exchangers for any refrigerant.Heat Exchanger EffectivenessThe ability of a liquid-suction heat exchanger to transfer energy from the Warm liquid to the cool vapor at steady-s

21、tate conditions is dependent on the size and configuration of the heat transfer device. The liquid-suction heat exchanger performance, expressed in terms of an effectiveness, is a parameter in the analysis. The effectiveness of the liquid-suction heat exchanger is defined in equation (1):Where the n

22、umeric subscripted temperature (T) values correspond to locations depicted in Figure 1. The effectiveness is the ratio of the actual to maximum possible heat transfer rates. It is related to the surface area of the heat exchanger. A zero surface area represents a system Without a liquid-suction heat

23、 exchanger Whereas a system having an infinite heat exchanger area corresponds to an effectiveness of unity.The liquid-suction heat exchanger effects the performance of a refrigeration system by in fluencing both the high and loW pressure sides of a system. Figure 2 shoWs the key state points for a

24、vapor compression cycle utilizing an idealized liquid-suction heat exchanger on a pressure-enthalpy diagram. The enthalpy of the refrigerant leaving the condenser (state 3) is decreased prior to entering the expansion device (state 4) by rejecting energy to the vapor refrigerant leaving the evaporat

25、or (state 1) prior to entering the compressor (state 2). Pressure losses are not shoWn. The cooling of the condensate that occurs on the high pressure side serves to increase the refrigeration capacity and reduce the likelihood of liquid refrigerant flashing prior to reaching the expansion device. O

26、n the loW pressure side, the liquid-suction heat exchanger increases the temperature of the vapor entering the compressor and reduces the refrigerant pressure, both of Which increase the specific volume of the refr igerant and thereby decrease the mass floW rate and capacity. A major benefit of the

27、liquid-suction heat exchanger is that it reduces the possibility of liquid carry-over from the evaporator Which could harm the compressor. Liquid carryover can be readily caused by a number of factors that may include Wide fluctuations in evaporator load and poorly maintained expansion devices (espe

28、cially problematic for thermostatic expansion valves used in ammonia service).（翻译） 冷却系统利用流体吸热交换器克来因教授,布兰顿教授, , 布朗教授威斯康辛州的大学 麦迪逊摘录加热装置在许多冷却系统中被用到，用以制冷时遗留在蒸发器中的冷却气体和离开冷凝器发热流体之间的能量的热交换.这些流体吸收或吸收热交换器,在一些情形中，他们降低了系统性能, 然而系统的某些地方却得到了改善. 虽然以前研究员已经调查了流体吸热交换器的性能, 但是这项研究可能从早先研究的三种方式被加以区别. 首先，这份研究开辟了一个无限的崭新的与流

29、体吸热交换器有关联的群体.其次，这份研究拓宽了早先的分析包括新型制冷剂。第三, 研究包括压力的冲击降低了流体吸热交换器的系统性能. 在简单的技术信息分析中表明流体吸热交换器对冷却系统性能的冲击可能导致错误的结论.从详细说明分析里,它能得出一个结论，那就是液体- 吸加热交换器在低压区域上的临界压力使用 R507A ， R134a ， R12 ， R404A ， R290 ，R407C ， R600 和 R410A这些制冷剂，对系统是有用的。而使用 R22 ， R32 和 R717对系统的性能是有害的.介绍流体吸热交换器被普遍的安装在正确合适的系统操作和提高系统性能的制冷系统中。很明显， ASHR

30、AE(1998) 液体- 吸加热交换器的确是有效的他表现在:1)增加系统性能2)液体制冷剂防止散发气体进入扩充装置。一些剩余的液体在到达之前被完全蒸发了。图 1 列举了一个简单的指示。压缩物 (s) 可能利用流体吸热交换器保持的液体扩充蒸汽压缩的性能.3）在这一个结构中,高温液体余热像一个温度调节装置一样拒绝装置 (蒸发冷凝器就是这种情况) 在扩充之前对蒸发器的压力再冷却,洗涤槽是为了接收在低温度冷冻下遗留在蒸发器内的再冷却液. 因此，流体吸热交换器是一种从液体到蒸汽热交换的间接装置. 热交换器 (在蒸发器出口和压缩物吸收之间) 的蒸汽边界经常承担积聚压缩物吸的液体，藉此将对滞留的液体制冷剂的

31、危险性减到更少. 在蒸发器允许液体滞留的情形中, 在热交换器中积聚部分会困住而且，超过一定的时间后，在液体再冷却的过程中，滞留的液体被吸收热量而蒸发.背景Stoecker 和 Walukas(1981) 着重于利用流体吸热交换器在单一温度蒸发和双重的温度蒸发系统的影响下的冷冻混合.他们的分析指出当nonazeotropic混合剂或azeoptropic混合剂与利用单一成份制冷剂的系统相比较时, 流体吸热交换器产生更多性能的改进。McLinden(1990) 用了相关的原则评价新的制冷剂被预期的效果. 他指出作为理想的特殊性气体使用在流体吸热交换器中增加这项系统的性能(谈到制冷剂的复杂的分子结构

32、)。 Domanski 和 Didion(1993) 评估了包括流体吸热交换器的替代品 R22 的九个性能. Domanski et al. (1994)稍后鉴于对29种 不同的制冷剂一项理论分析，扩大了流体吸热交换器安装在蒸汽压缩冷却系统的评价Bivens et al. (1994)评估了一种被提议的混合物来替代为空调和热泵中使用的 R22。他们的分析指出当系统修正包括了流体吸热交换器和 逆向系统热交换器的时候 , 两者之一的冷冻系统有 6-7% 进步 (蒸发器和凝结器). Bittle et al做了一项评估流体吸热交换器在家用电冰箱中采用制冷剂R152a实验作者把该系统性能与传统的以R1

33、2 为基础的系统作了一个比较。 Bittle et al把制冷与空调工程师学会对毛细管性能的预言做了一个比较。（包括流体吸热交换器的影响）被预知的毛细管流速是早先评价的 10%，再冷却水平的真实测量值在1.7摄氏度之内。这篇论文分析流体吸热交换器在系统容量和性能方面的影响 (表达为一个系统性能系数即COP).流体吸热交换器尺寸超出操作条件的范围的影响（蒸发和冷凝）在许多选择性的制冷剂中被安插和量化.在目前被包括分析的制冷剂是 R507A ， R404A ， R600 ， R290 ， R134a ， R407C, R410A ， R12 ， R22 ， R32 和 R717. 这篇论文扩充目前

34、对以前研究考虑新的制冷剂结论它明确地考虑压力下降的效果,而且它全面的介绍了许多制冷剂在流体吸热交换器的效果.加热交换器效率在稳定的条件下流体吸热交换器的能力依靠大小和结构移动装置转移从温暖的液体到冷蒸汽的能量. 流体吸热交换器的性能,表达为效率条件就是分析中的一个参数流体吸热交换器的效能被定义为等式(1):写在底下的温度 (T)数值符合在图中被描述的位置 。1.效能的实际比率最大可能的热转移速度.它与热交换器的表面积有关系.零表面积提出一个没有流体吸热交换器的系统然而那个系统有一个无穷大的吸热面积符合统一的效能。流体吸热交换器对制冷系统高压和低压系统的性能都有影响。图 2 关节点是蒸汽压缩周期

35、利用理想化的流体吸热交换器在一个压力- 焓图表表示出来的. 离开冷凝器的制冷剂进入膨胀阀，离开蒸发器蒸汽制冷剂进入压缩机，焓减少。没有压力损失. 冷凝物的在高压区冷却增加了制冷容积减少了液体制冷剂在到达膨胀阀之前挥发的可能性。在低压区，流体吸热交换器增加进入压缩物的蒸汽温度而且减少制冷压力, 两者增加制冷剂明显的体积，和由此减少大量的流速和容积. 流体吸热交换器的一种主要的利益是它减少从蒸发器挥发，减少对压缩机产生损伤的可能性。液体的挥发可能由很多因素导致，可能包括蒸发器负荷波动，膨胀阀的缺少维修，尤其是温度调节装置控制用以氨的维修。外文翻译(2) repair heating and air

36、-conditioning systemsJob prospects for heating, air-conditioning, and refrigeration mechanics and installers are expected to be good, particularly for those With technical school or formal apprenticeship training.The Air-Conditioning Excellence program, offered through North AmericanTechnician Excel

37、lence, is the standard for certification of experienced technicians.What Would those living in Chicago do Without heating, those in Miami do refrigeration? Heating and air-conditioning systems control the temperature, humidity, and the total air quality in residential, commercial, industrial, and ot

38、her buildings. Refrigeration systems make it possible to store and transport food, medicine, and other perishable items. Heating, air-conditioning, and refrigeration mechanics and installersalso called techniciansinstall, maintain, and repair such systems. Because heating, ventilation, air-condition

39、ing, and refrigeration systems often are referred to as HVACR Heating, air-conditioning, and refrigeration systems consist of many mechanical, electrical, and electronic components, such as motors, compressors, pumps, fans, ducts, pipes, thermostats, and sWitches. In central heating systems, for exa

40、mple, a furnace heats air that is distributed throughout the building via a system of metal or fiberglass ducts. Technicians must be able to maintain, diagnose, and correct problems throughout the entire system. To do this, they adjust system controls to recommended settings and test the performance

41、 of the entire system using special tools and test equipment.Technicians often specialize in either installation or maintenance and repair, although they are trained to do both. Some specialize in one type of equipmentfor example, oil burners, solar panels, or commercial refrigerators. Technicians m

42、ay Work for large or small contracting companies or directly for a manufacturer or Wholesaler. Those Working for smaller operations tend to do both installation and servicing, and Work With heating, cooling, and refrigeration equipment. Service contractsWhich involve heating, air-conditioning, and r

43、efrigeration Work for particular customers on a regular basisare becoming more common. Service agreements help to reduce the seasonal fluctuations of this Work.Heating and air-conditioning mechanics install, service, and repair heating and air-conditioning systems in both residences and commercial e

44、stablishments. Furnace installers, also called heating equipment technicians, folloW blueprints or other specifications to install oil, gas, electric, solid-fuel, and multiple-fuel heating systems. Air-conditioning mechanics install and service central air-conditioning systems. After putting the equ

45、ipment in place, they install fuel and Water supply lines, air ducts and vents, pumps, and other components. They may connect electrical Wiring and controls and check the unit for proper operation. To ensure the proper functioning of the system, furnace installers often use combustion test equipment

46、, such as carbon dioxide and oxygen testers.After a furnace has been installed, heating equipment technicians often perform routine maintenance and repair Work to keep the system operating efficiently. During the fall and Winter, for example, When the system is used most, they service and adjust bur

47、ners and bloWers. If the system is not operating properly, they check the thermostat, burner nozzles, controls, or other parts to diagnose and then correct the problem.During the summer, When the heating system is not being used, heating equipment technicians do maintenance Work, such as replacing f

48、ilters, ducts, and other parts of the system that may accumulate dust and impurities during the operating season. During the Winter, air-conditioning mechanics inspect the systems and do required maintenance, such as overhauling compressors.Refrigeration mechanics install, service, and repair indust

49、rial and commercial refrigerating systems and a variety of refrigeration equipment. They folloW blueprints, design specifications, and manufacturers?instructions to install motors, compressors, condensing units, evaporators, piping, and other components. They connect this equipment to the ductWork, refrigerant lines, and electrical poWer source. After making the connections,