暖通空調(diào)專業(yè)-畢業(yè)設(shè)計(jì)外文翻譯2017-1

1、浙 江 海 洋 學(xué) 院 畢 業(yè) 設(shè) 計(jì)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 gaseou

2、s refrigerant 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 per

3、formance 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

4、include 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 o

5、n refrigeration 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 det

6、rimental 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 he

7、at exchangers 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 si

8、mple direct-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 expa

9、nsion 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 evaporat

10、or outlet 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,

11、 over 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 refri

12、gerant 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 stat

13、es to 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 performan

14、ce of 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 theo

15、retical 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 h

16、eat exchangers (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

17、 compared 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

18、 paper 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 illus

19、trated 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 specifica

20、lly considers 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 st

21、eady-state 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

22、 the numeric 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-suctio

23、n heat 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

24、for a 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 ev

25、aporator (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 dev

26、ice. On 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 o

27、f the 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

28、 (especially problematic for thermostatic expansion valves used in ammonia service).（翻譯） 冷卻系統(tǒng)利用流體吸熱交換器克來(lái)因教授,布蘭頓教授, , 布朗教授威斯康辛州的大學(xué) 麥迪遜摘錄加熱裝置在許多冷卻系統(tǒng)中被用到，用以制冷時(shí)遺留在蒸發(fā)器中的冷卻氣體和離開冷凝器發(fā)熱流體之間的能量的熱交換.這些流體吸收或吸收熱交換器,在一些情形中，他們降低了系統(tǒng)性能, 然而系統(tǒng)的某些地方卻得到了改善. 雖然以前研究員已經(jīng)調(diào)查了流體吸熱交換器的性能, 但是這項(xiàng)研究可能從早先研究的三種方式被加以區(qū)別. 首先，這份研究開辟了一個(gè)無(wú)限

29、的嶄新的與流體吸熱交換器有關(guān)聯(lián)的群體.其次，這份研究拓寬了早先的分析包括新型制冷劑。第三, 研究包括壓力的沖擊降低了流體吸熱交換器的系統(tǒng)性能. 在簡(jiǎn)單的技術(shù)信息分析中表明流體吸熱交換器對(duì)冷卻系統(tǒng)性能的沖擊可能導(dǎo)致錯(cuò)誤的結(jié)論.從詳細(xì)說(shuō)明分析里,它能得出一個(gè)結(jié)論，那就是液體- 吸加熱交換器在低壓區(qū)域上的臨界壓力使用 R507A ， R134a ， R12 ， R404A ， R290 ，R407C ， R600 和 R410A這些制冷劑，對(duì)系統(tǒng)是有用的。而使用 R22 ， R32 和 R717對(duì)系統(tǒng)的性能是有害的.介紹流體吸熱交換器被普遍的安裝在正確合適的系統(tǒng)操作和提高系統(tǒng)性能的制冷系統(tǒng)中。很明顯

30、， ASHRAE(1998) 液體- 吸加熱交換器的確是有效的他表現(xiàn)在:1)增加系統(tǒng)性能2)液體制冷劑防止散發(fā)氣體進(jìn)入擴(kuò)充裝置。一些剩余的液體在到達(dá)之前被完全蒸發(fā)了。圖 1 列舉了一個(gè)簡(jiǎn)單的指示。壓縮物 (s) 可能利用流體吸熱交換器保持的液體擴(kuò)充蒸汽壓縮的性能.3）在這一個(gè)結(jié)構(gòu)中,高溫液體余熱像一個(gè)溫度調(diào)節(jié)裝置一樣拒絕裝置 (蒸發(fā)冷凝器就是這種情況) 在擴(kuò)充之前對(duì)蒸發(fā)器的壓力再冷卻,洗滌槽是為了接收在低溫度冷凍下遺留在蒸發(fā)器內(nèi)的再冷卻液. 因此，流體吸熱交換器是一種從液體到蒸汽熱交換的間接裝置. 熱交換器 (在蒸發(fā)器出口和壓縮物吸收之間) 的蒸汽邊界經(jīng)常承擔(dān)積聚壓縮物吸的液體，藉此將對(duì)滯留的

31、液體制冷劑的危險(xiǎn)性減到更少. 在蒸發(fā)器允許液體滯留的情形中, 在熱交換器中積聚部分會(huì)困住而且，超過一定的時(shí)間后，在液體再冷卻的過程中，滯留的液體被吸收熱量而蒸發(fā).背景Stoecker 和 Walukas(1981) 著重于利用流體吸熱交換器在單一溫度蒸發(fā)和雙重的溫度蒸發(fā)系統(tǒng)的影響下的冷凍混合.他們的分析指出當(dāng)nonazeotropic混合劑或azeoptropic混合劑與利用單一成份制冷劑的系統(tǒng)相比較時(shí), 流體吸熱交換器產(chǎn)生更多性能的改進(jìn)。McLinden(1990) 用了相關(guān)的原則評(píng)價(jià)新的制冷劑被預(yù)期的效果. 他指出作為理想的特殊性氣體使用在流體吸熱交換器中增加這項(xiàng)系統(tǒng)的性能(談到制冷劑的復(fù)

32、雜的分子結(jié)構(gòu))。 Domanski 和 Didion(1993) 評(píng)估了包括流體吸熱交換器的替代品 R22 的九個(gè)性能. Domanski et al. (1994)稍后鑒于對(duì)29種 不同的制冷劑一項(xiàng)理論分析，擴(kuò)大了流體吸熱交換器安裝在蒸汽壓縮冷卻系統(tǒng)的評(píng)價(jià)Bivens et al. (1994)評(píng)估了一種被提議的混合物來(lái)替代為空調(diào)和熱泵中使用的 R22。他們的分析指出當(dāng)系統(tǒng)修正包括了流體吸熱交換器和 逆向系統(tǒng)熱交換器的時(shí)候 , 兩者之一的冷凍系統(tǒng)有 6-7% 進(jìn)步 (蒸發(fā)器和凝結(jié)器). Bittle et al做了一項(xiàng)評(píng)估流體吸熱交換器在家用電冰箱中采用制冷劑R152a實(shí)驗(yàn)作者把該系統(tǒng)性能與

33、傳統(tǒng)的以R12 為基礎(chǔ)的系統(tǒng)作了一個(gè)比較。 Bittle et al把制冷與空調(diào)工程師學(xué)會(huì)對(duì)毛細(xì)管性能的預(yù)言做了一個(gè)比較。（包括流體吸熱交換器的影響）被預(yù)知的毛細(xì)管流速是早先評(píng)價(jià)的 10%，再冷卻水平的真實(shí)測(cè)量值在1.7攝氏度之內(nèi)。這篇論文分析流體吸熱交換器在系統(tǒng)容量和性能方面的影響 (表達(dá)為一個(gè)系統(tǒng)性能系數(shù)即COP).流體吸熱交換器尺寸超出操作條件的范圍的影響（蒸發(fā)和冷凝）在許多選擇性的制冷劑中被安插和量化.在目前被包括分析的制冷劑是 R507A ， R404A ， R600 ， R290 ， R134a ， R407C, R410A ， R12 ， R22 ， R32 和 R717. 這篇

34、論文擴(kuò)充目前對(duì)以前研究考慮新的制冷劑結(jié)論它明確地考慮壓力下降的效果,而且它全面的介紹了許多制冷劑在流體吸熱交換器的效果.加熱交換器效率在穩(wěn)定的條件下流體吸熱交換器的能力依靠大小和結(jié)構(gòu)移動(dòng)裝置轉(zhuǎn)移從溫暖的液體到冷蒸汽的能量. 流體吸熱交換器的性能,表達(dá)為效率條件就是分析中的一個(gè)參數(shù)流體吸熱交換器的效能被定義為等式(1):寫在底下的溫度 (T)數(shù)值符合在圖中被描述的位置 。1.效能的實(shí)際比率最大可能的熱轉(zhuǎn)移速度.它與熱交換器的表面積有關(guān)系.零表面積提出一個(gè)沒有流體吸熱交換器的系統(tǒng)然而那個(gè)系統(tǒng)有一個(gè)無(wú)窮大的吸熱面積符合統(tǒng)一的效能。流體吸熱交換器對(duì)制冷系統(tǒng)高壓和低壓系統(tǒng)的性能都有影響。圖 2 關(guān)節(jié)點(diǎn)是

35、蒸汽壓縮周期利用理想化的流體吸熱交換器在一個(gè)壓力- 焓圖表表示出來(lái)的. 離開冷凝器的制冷劑進(jìn)入膨脹閥，離開蒸發(fā)器蒸汽制冷劑進(jìn)入壓縮機(jī)，焓減少。沒有壓力損失. 冷凝物的在高壓區(qū)冷卻增加了制冷容積減少了液體制冷劑在到達(dá)膨脹閥之前揮發(fā)的可能性。在低壓區(qū)，流體吸熱交換器增加進(jìn)入壓縮物的蒸汽溫度而且減少制冷壓力, 兩者增加制冷劑明顯的體積，和由此減少大量的流速和容積. 流體吸熱交換器的一種主要的利益是它減少?gòu)恼舭l(fā)器揮發(fā)，減少對(duì)壓縮機(jī)產(chǎn)生損傷的可能性。液體的揮發(fā)可能由很多因素導(dǎo)致，可能包括蒸發(fā)器負(fù)荷波動(dòng)，膨脹閥的缺少維修，尤其是溫度調(diào)節(jié)裝置控制用以氨的維修。外文翻譯(2) repair heating a

36、nd air-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

37、 Excellence, 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,

38、and other 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-con

39、ditioning, 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, f

40、or example, 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 perfo

41、rmance 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. Technic

42、ians may 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,

43、 and refrigeration 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 commer

44、cial establishments. 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 t

45、he equipment 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 equ

46、ipment, 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 adju

47、st burners 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 repla

48、cing filters, 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

49、industrial 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 duct

50、Work, refrigerant lines, and electrical poWer source. After making the connections, they charge the system With refrigerant, check it for proper operation, and program control systems.When heating, air-conditioning, and refrigeration mechanics service equipment, they must use care to conserve, recov

51、er, and recycle chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants used in air-conditioning and refrigeration systems. The release of CFCs and HCFCs contributes to the depletion of the stratospheric ozone layer, Which protects plant and animal life from ultraviolet radiation. T

52、echnicians conserve the refrigerant by making sure that there are no leaks in the system; they recover it by venting the refrigerant into proper cylinders; and they recycle it for reuse With special filter-dryers.Heating, air-conditioning, and refrigeration mechanics and installers are adept at usin

53、g a variety of tools, including hammers, Wrenches, metal snips, electric drills, pipe cutters and benders, measurement gauges, and acetylene torches, to Work With refrigerant lines and air ducts. They use voltmeters, thermometers, pressure gauges, manometers, and other testing devices to check airfl

54、oW, refrigerant pressure, electrical circuits, burners, and other components.Other craftWorkers sometimes install or repair cooling and heating systems. For example, on a large air-conditioning installation job, especially Where Workers are covered by union contracts, ductWork might be done by sheet

55、 metal Workers and duct installers; electrical Work by electricians; and installation of piping, condensers, and other components by pipelayers, plumbers, pipefitters, and steamfitters. Home appliance repairers usually service room air-conditioners and household refrigerators. (Additional informatio

56、n about each of these occupations appears elseWhere in the Handbook.Heating, air-conditioning, and refrigeration mechanics and installers Work in homes, stores of all kinds, hospitals, office buildings, and factoriesanyWhere there is climate-control equipment. They may be assigned to specific jobsit

57、es at the beginning of each day, or if they are making service calls, they may be dispatched to jobs by radio, telephone, or pager. Increasingly, employers are using cell phones to coordinate technicians?schedules.Technicians may Work outside in cold or hot Weather or in buildings that are uncomfort

58、able because the air-conditioning or heating equipment is broken. In addition, technicians might have to Work in aWkWard or cramped positions and sometimes are required to Work in high places. Hazards include electrical shock, burns, muscle strains, and other injuries from handling heavy equipment.

59、Appropriate safety equipment is necessary When handling refrigerants because contact can cause skin damage, frostbite, or blindness. Inhalation of refrigerants When Working in confined spaces also is a possible hazard.The majority of mechanics and installers Work at least a 40-hour Week. During peak seasons they often Work overtime or irregular hou