暖通空调专业-毕业设计外文翻译2017-1

Refrigeration System Performance using Liquid-Suction Heat Exchangers

S. A. Klein, D. T. Reindl, and K. BroWnell

College of Engineering

University of Wisconsin - Madison

Abstract

Heat transfer devices are provided in many refrigeration systems to exchange energy betWeen the cool gaseous 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 performance 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 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 on 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 detrimental to system performance in systems using R22, R32, and R717.

Introduction

Liquid-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 exchangers are effective in:

1) increasing the system performance

2) subcooling liquid refrigerant to prevent flash gas formation at inlets to expansion devices

3) fully evaporating any residual liquid that may remain in the liquid-suction prior to reaching the compressor(s)

Figure 1 illustrates a simple 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 expansion 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 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, over time, vaporize the liquid carryover by absorbing heat during the process of subcooling high-side liquid.

Background

Stoecker and Walukas (1981) focused on the influence of liquid-suction heat exchangers in both single temperature evaporator and dual temperature evaporator systems utilizing refrigerant 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 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 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 theoretical 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 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 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 1.7 C (3 F) of actual measurements.

This 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 illustrated 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 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 Effectiveness

The ability of a liquid-suction heat exchanger to transfer energy from the Warm liquid to the cool vapor at steady-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 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-suction 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 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 evaporator (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. 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 of 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 (especially 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， ASHRAE(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)。 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R12 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-CONDITIONING SYSTEMS

Job 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 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, 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 installers—also called technicians—install, maintain, and repair such systems. Because heating, ventilation, air-conditioning, 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 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 performance 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 equipment—for example, oil burners, solar panels, or commercial refrigerators. Technicians 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 contracts—Which involve heating, air-conditioning, and refrigeration Work for particular customers on a regular basis—are 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 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 the 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 equipment, 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 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 replacing 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 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 ductWork, 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, recover, 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. Technicians 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 using 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 airfloW, 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 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 information 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 factories—anyWhere there is

climate-control equipment. They may be assigned to specific jobsites 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 uncomfortable 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. 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 hours. Maintenance Workers, including those Who provide maintenance services under contract, often Work evening or Weekend shifts and are on call. Most employers try to provide a full WorkWeek year-round by scheduling both installation and maintenance Work, and many manufacturers and contractors noW provide or even require service contracts. In most shops that service both heating and air-conditioning equipment, employment is stable throughout the year.

Heating, air-conditioning, and refrigeration mechanics and installers held about

249,000 jobs in 2002; almost half Worked for cooling and heating contractors. The remainder Was employed in a variety of industries throughout the country, reflecting a Widespread dependence on climate-control systems. Some Worked for fuel oil dealers, refrigeration and air-conditioning service and repair shops, schools, and stores that sell heating and air-conditioning systems. Local governments, the Federal Government, hospitals, office buildings, and other organizations that operate large air-conditioning, refrigeration, or heating systems employed others. About 15 percent of mechanics and installers Were self-employed.

（翻译）空调和制冷系统的维修

暖气、空调和冷冻技术工人和安装工人的就业前景一直都被看好，特别是对那些具有技术学校和受正规学徒训练的人来说更是如此。

由北美优秀技术人员组织提供的空调技术卓越计划已经作为技术人员是否有经验

的衡量标准。

设想那些生活在芝加哥的人没有暖气怎么办，生活在迈阿密的人没有空调怎么办，或者全国各地的血库没有冷冻技术怎么办？暖气和空调系统控制着温度、湿度和整个居住区、商业区、工业区及其他建筑物内的空气质量。冷冻系统使储存和运输事物、医药和其他易变质的东西成为可能。暖气、空调和冷冻技术工人和安装人员—也就是所谓的技术人员---负责安装、保养和维修这些系统。由于暖气、通风、空调和冷冻系统经常被称为HVACR系统，这些工人也因此可被叫做HVACR技术人员。

暖气、空调和冰箱设备有很多机械的、电子的和电子元件组成，如发动机、压缩机、水泵，风扇、水管、可调温龙头和开关等。比如，在暖气系统核心中，熔炉是通过铁片或玻璃纤维将整个室内的空气变暖。技术人员必须能够维护、诊断和纠正整个系统的问题。要做到这一点，他们将系统控制调节到优化配置并利用特殊的工具和检测设备来检测整个系统的性能。

尽管技术人员被训练成同时在安装和维修两个领域都比较擅长，但实际上他们往往只在其中某个领域具有专长。一些人比较擅长操作某种设备，比如燃油炉, 太阳电池板或商用冷冻机。技术人员可能为一些大型或小型的承包公司工作，或者直接为厂商或批发商业工作。而那些负责小型工程的人则常常用暖气、冷气和冷冻设备同时从事安装和服务工作。那种为特定客户的暖气、空调和冷冻工作提供常规化服务的服务合同正变的越来越普遍。这些服务协议有助于减少这种工作季节性波动的影响。

暖气和空调技术工人同时在居住区和商业区安装和维修暖气和空调系统。熔炉安装工人，也就是所谓的暖气设备技术人员，根据设计图或其它说明书安装燃油、天然气、电子、固体燃料和复合燃料暖气系统。空调技术人员安装和维护空调核心装置。在把设备安装完成后，他们安装燃料和水力供应管道，通风管，水管和其他部件。他们可能把电线和控制器连接起来然后检查各个部件是否正常操作。为了确保系统的正常的运转，熔炉安装技术人员经常使用检测设备，比如二氧化碳和氧气检测仪。

在熔炉安装完成后，暖气设备技术人员经常进行常规性的保养和维修工作以保持系统有效运转。比如，在秋冬季节，当系统使用最频繁的时候，他们维护和调整油炉,鼓风机。如果系统不能正常的运转，他们就检查温度计, 燃烧喷嘴，控制器或其他部件以诊断和纠正问题。

在夏天，当暖气系统不再需要使用时，暖气设备技术人员就做维护工作。例如更换过滤器、通风管和其他系统部件，因为这些部件在平时机器运转的时候可能积累了一些垃圾和杂质。同样的，在冬天，空调技术人员进行检测系统及做一些必要的维护工作，如检查压缩机

冷冻技术人员安装、护理和维修工业和商业用的冷冻系统及各种各样的冷冻设备。他们根据设计图纸，设计说明和安装指南来安装发动机、压缩机、蒸发器，管道和其他

部件。他们把这些设备与管道系统,冷冻生产线和电源连接起来。连接后，他们用制冷剂给系统充电，检查系统是否正常操作和设计控制系统程序。

当暖气,空调和冷冻技术人员维护这些设备时,他们必须仔细保存,回收再利用在空调和冷冻系统中使用的CFC和HCFC制冷剂。制冷剂的释放会造成臭氧层的损耗,这保护了动植物免受紫外线的照射.技术人员通过确保系统没有渗漏来保存制冷剂,然后通过把制冷剂排入相应的汽缸中来回收制冷剂,最后他们用特殊的过滤干燥器进行再利用.

暖气,空调和制冷技术工人和安装工人擅长使用各种各样的工具,包括铁锤, 扳手,金属剪刀,电钻, 切管机和弯曲机,标尺和手电筒等.他们用这些工具操作冷冻线和排风管.工人们用伏特计, 温度计,压力计和其他检测设备来检测气流,冷冻压力,电流,电炉和其他组件.其他技术工人有时也安装或维修冷气和暖气系统,例如,在一个大型的安装工程中,特别是在这些工程中工人承担了多项合同,这样管道工作往往由管道安装工人负责,技术人员负责与电力有关的工作,还有铺管工,管道维护工人和蒸汽安装工人负责其他的相关工作.家具维修人员通常室内空调机和家用冷冻机的服务工作.(有关每种职业的额外分工信息在手册的其他地方都有说明)。

暖气,空调和冷冻技术工人和安装工人的工作场所包括家庭,各种商店,医院,办公室和工厂,凡是有环境控制设备的地方都是他们的工作场所.他们可能在一天开始的时候被分配到某个工作地点,或者如果他们提供电话服务的时候,可用电波、电话和信使等手段指派工作.现在,越来越多的雇主用手机调配技术人员和工作安排.

在寒冷或炎热的季节，技术人员可能在室外工作。或者在条件很差的室内（如那里空调或致热设备已经损坏）工作,.除此之外,技术人员还有可能必须在肮脏或拥挤的地方工作,有时还必须在高空工作.他们面临很多危险,包括电击,烫伤,肌肉压力和其他来自操作设备的伤害.

所以当操作冷冻设备时,适当的安全设施是必要的,因为接触设备可能造成皮肤损伤,冻伤或失明. 当然在狭窄的地方吸入制冷剂也是一种可能的危险.

大部分的技术人员和安装人员每周至少工作40小时。在高峰时节,他们经常加班加点或没作息规律的工作。维修工人（包括那些根据工作合同提供服务的工人）,经常加夜班或周末加班,并且随时听从电话的安排.大部分雇主设法通过安排安装和维护时间表将全年的工作时间安排的满满的。并且现在许多厂家和承包商提供服务合同，有些甚至要求服务合同.在大部分同时销售暖气和空调设备的商店,全年的人员安排都是稳定的.

在2002年,大概有249,000个岗位从事暖气,空调和冷冻技术和安装工作.几乎半数的岗位为冷气和暖气承包商工作，其余的人员在全国各种各样的工业部门工作,这一现象反映了对环境控制系统的普遍依赖性.这其中一些人为燃油供应商,冷冻和空调服务商、维修店,学校,销售暖气和空调设备的商店工作. 另一些为那些具有大型空调\冷冻和暖气设备的当地政府,联邦政府,医院、办公楼和其他组织工作.还有大约15%的技术人员和安装工人则是自主谋业.

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中文3696字本科毕业论文外文翻译出处：Infosys Strategic Vision 原文： Insights from Banking Simple By Ashok Vemuri Introduction “A simpler way of banking.We treat with you respect. No extraneous features. No hidden fees.” For the unini tiated, this is the mantra of BankSimple, a Brooklyn-based startup which has positioned itself as a consumer-friendly alternative to traditional banks. BankSimple pushes a message of user experience—sophisticated personal finance analytics, a single “do-it-all” card, superior customer service, and no overdraft fees.Though branchless and primarily online-based, BankSimple is also planning to provide some traditional customer service touches, including phone support and mail-in deposits. Interestingly, BankSimple will also likely not be a bank—at least not in the technical, FDIC sense of the word. Rather, BankSimple’s strategy is to be a front-end focused on the customer experience. The back-end core “bank” component will be FDIC-insured partner banks. Unfettered by years of IT investments and entrenched applications, BankSimple’s team has the freedom to build an innovative, user-friendly online interface, customer service program, and the associated mobile and social bells and whistles that more and more consumers are demanding. One way to look at it is as a wrapper insulating the consumer from the accounting, compliance, and technology challenges that many banks face. Like personal finance sites https://www.360docs.net/doc/8b672596.html, and Wesabe before it, BankSimple is looking to tap into a perceived gap between what major banks provide and what consumers want. A recent survey by ForeSee Results and Forbes found that consumers view online banking as more satisfying than banking done offline. Though good news for the industry as a whole, the survey also found that the five largest banks in the country scored the lowest in the study. Cheaper and more customer friendly, digital banking is the future—but many consumers are finding it is better done with credit unions, community banks, and (down-the-road) startups like BankSimple. As you read, significant investments are being made by banks to improve their online, mobile, and IVR customer-friendliness. Major banks are embracing these channels, and customer satisfaction will likely improve over time. Even so, startups like Bank- Simple should be viewed as a learning opportunity. Their ideas are disruptive and often highlight pain points that need to be addressed. BankSimple’s first two stated philosophies are a good place to start: “A simpler way of banking” and “We treat you with respect.”

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机械类毕业设计外文翻译

本科毕业论文(设计) 外文翻译学院：机电工程学院专业：机械工程及自动化姓名：高峰指导教师：李延胜 2011年05 月10日教育部办公厅 Failure Analysis，Dimensional Determination And

Analysis，Applications Of Cams INTRODUCTION It is absolutely essential that a design engineer know how and why parts fail so that reliable machines that require minimum maintenance can be designed．Sometimes a failure can be serious，such as when a tire blows out on an automobile traveling at high speed．On the other hand，a failure may be no more than a nuisance．An example is the loosening of the radiator hose in an automobile cooling system．The consequence of this latter failure is usually the loss of some radiator coolant，a condition that is readily detected and corrected．The type of load a part absorbs is just as significant as the magnitude．Generally speaking，dynamic loads with direction reversals cause greater difficulty than static loads，and therefore，fatigue strength must be considered．Another concern is whether the material is ductile or brittle．For example，brittle materials are considered to be unacceptable where fatigue is involved． Many people mistakingly interpret the word failure to mean the actual breakage of a part．However，a design engineer must consider a broader understanding of what appreciable deformation occurs．A ductile material，however will deform a large amount prior to rupture．Excessive deformation，without fracture，may cause a machine to fail because the deformed part interferes with a moving second part．Therefore，a part fails(even if it has not physically broken)whenever it no longer fulfills its required function．Sometimes failure may be due to abnormal friction or vibration between two mating parts．Failure also may be due to a phenomenon called creep，which is the plastic flow of a material under load at elevated temperatures．In addition，the actual shape of a part may be responsible for failure．For example，stress concentrations due to sudden changes in contour must be taken into account．Evaluation of stress considerations is especially important when there are dynamic loads with direction reversals and the material is not very ductile． In general，the design engineer must consider all possible modes of failure，which include the following． ——Stress ——Deformation ——Wear ——Corrosion ——Vibration ——Environmental damage ——Loosening of fastening devices

毕业设计外文翻译附原文

外文翻译专业机械设计制造及其自动化学生姓名刘链柱班级机制111 学号1110101102 指导教师葛友华

外文资料名称： Design and performance evaluation of vacuum cleaners using cyclone technology 外文资料出处：Korean J. Chem. Eng., 23(6), (用外文写) 925-930 (2006) 附件： 1.外文资料翻译译文 2.外文原文

应用旋风技术真空吸尘器的设计和性能介绍吉尔泰金，洪城铱昌，宰瑾李，刘链柱译摘要：旋风型分离器技术用于真空吸尘器 - 轴向进流旋风和切向进气道流旋风有效地收集粉尘和降低压力降已被实验研究。优化设计等因素作为集尘效率，压降，并切成尺寸被粒度对应于分级收集的50％的效率进行了研究。颗粒切成大小降低入口面积，体直径，减小涡取景器直径的旋风。切向入口的双流量气旋具有良好的性能考虑的350毫米汞柱的低压降和为1.5μm的质量中位直径在1米3的流量的截止尺寸。一使用切向入口的双流量旋风吸尘器示出了势是一种有效的方法，用于收集在家庭中产生的粉尘。摘要及关键词：吸尘器; 粉尘; 旋风分离器引言我们这个时代的很大一部分都花在了房子，工作场所，或其他建筑，因此，室内空间应该是既舒适情绪和卫生。但室内空气中含有超过室外空气因气密性的二次污染物，毒物，食品气味。这是通过使用产生在建筑中的新材料和设备。真空吸尘器为代表的家电去除有害物质从地板到地毯所用的商用真空吸尘器房子由纸过滤，预过滤器和排气过滤器通过洁净的空气排放到大气中。虽然真空吸尘器是方便在使用中，吸入压力下降说唱空转成比例地清洗的时间，以及纸过滤器也应定期更换，由于压力下降，气味和细菌通过纸过滤器内的残留粉尘。图1示出了大气气溶胶的粒度分布通常是双峰形，在粗颗粒（>2.0微米）模式为主要的外部来源，如风吹尘，海盐喷雾，火山，从工厂直接排放和车辆废气排放，以及那些在细颗粒模式包括燃烧或光化学反应。表1显示模式，典型的大气航空的直径和质量浓度溶胶被许多研究者测量。精细模式在0.18?0.36 在5.7到25微米尺寸范围微米尺寸范围。质量浓度为2?205微克，可直接在大气气溶胶和 3.85至36.3μg/m3柴油气溶胶。

STC89C52处理芯片-毕业论文外文翻译

中文翻译 STC89C52处理芯片电气工程的研究和解决方案中心（ceers）艾哈迈德为吉.波特首要性能：与MCS-51单片机产物兼容、8K字节在系统可编程视频存储器、1000次擦拭周期，全静态操作：0Hz~33Hz、三级加密程序存储器，32个可编程I/O接口线、三个16位定时器（计数器），八个中断源、低功能耗空闲和掉电模式、掉电后间断可唤醒，看门狗定时器、双数值指针，掉电标示符。关键词：单片机，UART串行通道，掉电标示符等前言可以说，二十世纪跨越了三个“点”的时代，即电气时代，电子时代和现已进入的电脑时代。不过，这种电脑，通常指的是个人计算机，简称PC机。还有就是把智能赋予各种机械的单片机（亦称微控制器）。顾名思义，这种计算机的最小系统只用了一片集成电路，即可进行简单的运算可控制。因为它体积小，通常都是藏在被控机械的内部里面。它在整个装置中，起着有如人类头脑的作用，他出了毛病，整个装置就会瘫痪。现在，单片机的种类和适用领域已经十分广泛，如智能仪表、实施工控、通讯设备、导航系统、家用电器等。各种产品一旦用上了单片机，就你能起到产品升级换代的功效，常在产品名称前冠以形容词——“智能型”，如智能洗衣机等。接下来就是关于国产STC89C52单片机的一些基本参数。功能特性描述: STC89C52单片机是一种低功耗、高性能CMOS8位微控制器，具有8K在系统可编程视频播放存贮器使用高密度非易失性存储器技术制造，与工业80C51 产物指令和引脚完全兼容。片上反射速度允许程序存储器在系统可编程，也适用于常规的程序编写器。在其单芯片上，拥有灵敏小巧的八位中央处理器和在线系统可编程反射，这些使用上STC89C52微控制器为众多嵌入式的控制应用系统提供高度矫捷的、更加有用的解决方案。STC89C52微控制器具有以下的标准功效：8K字节的反射速度，256字节的随机存取储存器，32位I/O串口线，看门狗定时器，2个数值指针，三个16 为定时器、计数器，一个6向量2级间断结构，片内晶振及钟表电路。另外，STC89C52可降至0HZ静态逻辑操作，支持两种软件可选择节电模式、间断继续工作。空闲模式下，CPU停止工作，允许RAM、定时器/计数器、串口、间断继续工作。掉电保护体式格局下，RAM内容被生成，振动器被冻结，单片机一切的工作停止，直到下一个间断或者硬件复位为止。8位微型控制器8K字节在系统中可编程FlashSTC89C52.。

外文翻译--浅谈建筑环境与暖通空调能耗

中文2300字 Shallow talk the building environment an air condition to can consume with the warm Summary: The research constructs environment, understanding a warm an air condition to carry output reason and influencing factor, can be more and reasonably put forward solve problem of method. Keyword: Constructing a warm of environment an air condition can consume Shallow talk the building environment an air condition to can consume with the warm The energy provided motive for the development of the economy, but because of various reason, the development of the energy is a usually behind in economy of development. In the last few years, the growth rate maintenance of citizen's total output value of China are in about 10%, but the growth rate of the energy only have 3% ～s 4%.Such situation's requesting us has to economize on energy. The comparison that constructs the energy depletion in the society always the ability consume compares greatly, the building of the flourishing nations' use can have to the whole country generally and always can consume of 30% ～s 40%;China adopts the town population of the warm area although only 13.6% that have national population, adopt warm use an ability but have a whole country and always can consume of 9.6%.Construct the economy energy is the basic trend of the building development, is also a new growth of[with] the contemporary building science technique to order. The necessity of the modern building constitutes a part of warm, the air condition realm has already received the influence of this kind of trend as well, warm the economy energy within air condition system is cause a warm the attention of the air condition worker, and aims at different of the adopt of energy characteristics and the dissimilarity building of the nation, region is warm, well ventilated, the air condition request develop a related economy energy technique .The research constructs environment, understanding a warm an air condition to carry output reason and

金融学毕业论文外文翻译中英文全

Improve the concept of financial supervision in rural areas1 Xun Qian Farmers in China's vast population, has some large-scale production of the farmers, but also survival-oriented farmers, huge differences between the financial needs of rural finance intermediation makes complex, together with agriculture itself is the profit low, natural and market risks high risk decision to weak agricultural industry characteristics, resulting in the cost of rural financial transactions is far higher than the city, also decided to organize the rural financial system in terms of operation or in the market has its own special characteristics. 20 years of financial reform, financial development while the Chinese city made impressive achievements, but the rural finance is the entire financial system is still the weakest link. Insufficient supply of rural finance, competition is not sufficient, farmers and agricultural enterprises in getting loans and other issues is also very prominent, backward rural financial system can no longer effectively support the development of modern agriculture or the transformation of traditional agriculture and the building of new socialist countryside, which to improve the rural financial supervision new topic. China's rural financial regulatory problems (A) the formation of China's financial regulatory system had "a line three commission " (People's Bank, the Securities Regulatory Commission, Insurance Regulatory Commission and the Banking Regulatory Commission) financial regulatory structure. Bank These stringent requirements, different management and diversification of monitoring has its positive role, but it also had some negative effects. First, inefficient supervision, supervision of internal consumption of high costs, limited financial industry business development and innovation space. Second, the regulatory agencies, regulatory bodies and the information asymmetry between central banks, banking, securities, and insurance mechanisms of coordination between regulatory bodies are not perfect. Information between central banks and regulatory agencies is difficult to share, is difficult to create effective monitoring force. Basically between the various 1American Journal of Agricultural Economics，2009.