龙设计终版翻译

1、山东建筑大学毕业设计外文文献及译文- 外文翻译Evaluation of energy and exergy losses in district heating networkAbstractIn this paper, energy and exergy losses forming in the heat distribution network of district heating systems were evaluated. For this purpose, equations of energy and exergy losses were identified and by

2、 using them, heat distribution network of the university campus which has a heating network of pipes 11,988m in length and 65250 mm in diameter was analyzed. It was found that exergy losses forming during heat distribution were about 16% of total exergy in the system and temperature of hot water sup

3、plied and returning was found to be the most important factor affecting these exergy losses.Keywords: Energy loss; Exergy loss; District heating network1. IntroductionFaster urbanization caused by industry revaluation made to emerge the idea finding a remedy to human needs from a centre in addition

4、to the social services like water supply, sewer system public transportation and district heating system. The first district heating system was built at Lockport (New York, USA) in 1877 1. Since then it has been spread on the various Country of Europe. The district heating systems have been used inc

5、reasingly in Germany, Denmark, Holland, Belgium, and especially in Sweden and Russia since at the beginning of 20th century. For example, the pipe network of district heating system in Moscow is about 600 km 2. As district heating and cooling systems spend great quantities of fuel at national econom

6、ies level to provide heating cooling and domestic hot water in buildings. These systems attracted great attention in the literature 17.District heating is important not only because of the use of energy sources more efficiently but also being received with energy need more regularly, sufficiently an

7、d cheaper than other ways. In district heating system, heat generated in a plant is transported to the consumers in an extensive area. Thus, it is provided to heat a region consisting of many buildings and hot water from a centre. The district heating system, transport from the heat plant by using p

8、rimary pipe net work, via substation, to secondary pipe network where heat is finally distributed to consumer.In this system, energy and exergy losses are form in distribution pipes owing to carrying off the heat through large distances. Energy and exergy losses because of pipeline highly affect the

9、 advantages of heating systems economically. Hence, heat losses from pipelines should be reduced to minimum level. Heat losses in heat distribution network were computed 810% with a study carried out by Poredos and Kitonovski 8.Energy and exergy analyses are performed recently to show where energy e

10、fficiencies occur within processes, donated as energy and exergy losses. Energy and exergy losses can directly be translated to an increase in primarily fuel consumption. Energy analysis is based on the first law of thermodynamics, which is concerned with the conversation of energy. Exergy analysis

11、is based onsecond law of thermodynamics. Many researchers propose that the thermodynamic performance of a process is best evaluated with exergy analysis 9.From the thermodynamics point of view, exergy is defined as the maximum amount of work, which can be produced by a system, or a flow of matter or

12、 energy as it comes to equilibrium with a reference environment. Unlike energy, exergy is not subject to a conservation law (except for ideal, or reversible, processes). Rather, exergy is consumed or destroyed, due to irreversibilities in any real process. The exergy consumption during a process is

13、proportional to the entropy created due to irreversibilities associated with the process. Exergy analysis is a method that uses the conservation of mass and conservation of energy principles together with the second law of thermodynamics for the analysis, design and improvement of energy and other s

14、ystems. The exergy method is a useful tool for furthering the goal of more efficient energy-resource use, for it enables the locations, types, and true magnitudes of wastes and losses to be determined 10.In this study, energy and exergy losses in the heat distribution network of Ataturk university c

15、ampus were analysed. In the University, heating and domestic hot water in building of supplied heat is produced by district heating. Ataturk University is in the Erzurum which is one of the coldest cities in Turkey. In one season, approximately 10,000 tons fuel-oil is consumed in theheating system.

16、Because the pipe network is about 12 km, which is assumed to be quite long, there have been energy and exergy losses considerably in the heating network system.2. System description and analysisThe system consists of a branched pipeline network for distributing the heat from the heating plant to the

17、 consumer. The essential element of such a system is the pipeline, which enables the transport of energy and which is the source of the heat losses. Another important part of the system is the heat stations, where the heat is transferred from a high to a low temperature medium, resulting in decrease

18、d heat quality. In the analysis, the pipeline network was the insulated pipes with diameter from 65 to 250 mm. The total length of the pipeline network is 11,988 m.The average pressure in the primary network , was 15 bar, while in the secondary network, the pressure depended on the atmosphere pressu

19、re.Heat transfer from the primary to the secondary network in heat stations was via shell-tube heat exchangers.2.1. Energy balance The heat supplied to the consumer is (1)where, Qi shows the heat transferred to the water by heating plant, Wp is work which has been done by the pump for the circulatio

20、n of hot water though pipelines, Qc, the heat provided forconsumers and Qloss indicates heat losses in pipe network. Pipes are in the channel which is under the ground . Below, heat loss formed in a channel with two pipes at a certain instant of time is indicated by using the model . According to th

21、is model, heat loss formed in channel of unit length is expressed as (2) Temperature of pipeline is assumed to be the arithmetic average of and , , is daily average outer temperature and R is the thermal resistance . Glass wool of average 8 mm thickness was used in the pipeline analysed. Channel was

22、 manufactured from the mixture of stone and concrete. Channel circumference length CC, the channel thickness tc and thermal conductivity kc were taken as 5 m, 10 cm,2.5 W/mK, respectively. Thermal conductivity ks was taken as 0.91 W/mK for soil with moisture 13.2.2 Exergy balanceExergy balance may b

23、e written as (3) where Ex;i is hot water exergy, Ex;w is the electrical exergy given for the pump, Ex;c is the exergy provided for consumers. Exergy losses, Ex;lossA, Ex;loss B, Ex;lossC, are explained below.2.2.1. Exergy losses formed from heat losses Ex;loss AHeat losses during the transport of ho

24、t water through pipes cause exergy losses. From theknown equation Ex;lossA can be defined as 14Ex;lossA =（1- (4)2.2.2. Exergy losses due to hot water transportation Ex;loss BThe heat is transported from the heating to the consumers using hot water with a particular enthalpy value. Electrically-drive

25、n pumps are used to create a flow of water. Electrical energy represents pure exergy and this exergy is used to overcome the flow resistance in the pipeline network, through which istransformed into heat. The exergy of the heat at a temperature Tw ismuch lower than the exergy of the work Wp. As a re

26、sult, the exergy losses 8 are E x;loss B =Wp - (5)2.2.3. Exergy losses during heat transfer in heat exchanger Ex:loss CHeat transfer in a heat exchanger is an irreversible process, therefore exergy losses occur. The total exergy losses comprise the losses from the irreversible heat transfer and the

27、losses due to the friction of both follows. According to the findings of Kotas 15, the exergy losses due to friction for the liquid flow (small specific volume) are relatively small, so the exergy losses during heat transfer are (6)The temperatures of the both water flows in the heat exchanger vary,

28、 and so, Eq. (6) is in a differential form. The calculation of exergy losses for the heat exchanger can also be in an integralform, with the temperatures of both fluids (Tw and Tcw ? eTc;s t Tc;rT=2) determined by the thermodynamic average temperature 8. (7) 3. Results and discussionEnergy losses in

29、 pipelines which are used for the distribution of heat from the heating plant to the exchanger in heating systems are very important. Heat losses in pipelines were calculated using daily average outer temperature values. Heatlosses due to the network Qloss is about 8.62% of the energy provided by he

30、ating plant, Qi.Thickness of thermal insulation materials is the most effective factor which causes reduction of heat losses in pipes. Heat losses decrease by increasing thickness of insulation. Especially, an increase up to a thickness of 20 cm results in an important decrease in heat losses. Varia

31、tion of heat losses due to the insulation thickness can be seen in reference. It would be a decrease of about25% in heat losses if an insulation thickness of 20 cm was used instead of 8 cm in pipes. Moreover, channel circumference length has a reduction effect of heat losses although it is small.The

32、 supply and return water temperatures are 140180 C and 105135 C, respectively, which therefore have been taken in to account in the analysis in this paper. Exergy losses in hot water distribution pipes, in heat exchanger and from the circulation of hot water, change with the temperature of hot water

33、 supplied and returning. variation of exergy losses in hot water distribution pipes due to the change of supplied and returning water temperature may be seen in reference. Exergy losses increase with an increase of Ts while it decreases with an increase of Tr. Electrical energy is supplied to the sy

34、stem to drive the circulating pumps. With a constant demand for the amount of thermal energy to be supplied, the mass flow of the water varies and, therefore, so does the amount of supplied electrical energy. It shows that this is greater with lower temperature differences between the supplied and r

35、eturning hot water.4. ConclusionIn this paper, the energy and exergy losses occurring in the district heating network system have been investigated; regarding the supply and return water temperatures. The analysis exergy loss which occurs during the transport of thermal energy to consumers indicates

36、 that this loss is large and primarily dependent on the temperature of the hot water. The total exergy losses increase 0.75% with increasing the supply water temperature about 10 C, which is the case for the return water temperature. This analysis shows that this loss during heat transfer in distric

37、t heating network can be reduce, by reducing the consumption of electrical energy during the transport of hot water to the consumer and by reducing heat loss in pipelines.These heat losses should be kept at a minimum, which is possible by lowering the supply temperature from the plant and by increas

38、ing of thermal insulation thickness in pipes. However,lowering the supply temperature could result in unacceptably low temperature levels at the customers.Furthermore, if the supply temperature is reduced, the water flow in the system increases,resulting in higher pumping costs. 中文译文区域供热网络中的能源和火用损失的

39、评价摘要在本文中，对能源和火用损失形成的分布区域供热热网系统进行了评估。为此，需要确定能源和火用损失方程和能够使用它们，如对一个有一个长11988米直径为65-250毫米供热管道的大学供热分配网络进行分析。结果发现，在热成型火用损失约占总系统总能量的16%,并且发现供水温度和回水温度是影响火用损失的最重要因素。关键词：能源损失;火用损失;区域热网1简介由于工业再评价造成的迅速城市化使得人们产生一个节能的想法，即寻找到一个补救人们需要的的像供水社会服务中心，下水道系统，公共交通和区域供热系统社会服务中心。第一个区域供热系统建于1887年洛克波特（美国纽约）1。从那时起，它已经开始被铺设在欧洲的各

40、个国家。该区域供热系统已越来越多地用于在德国，丹麦，荷兰，比利时，尤其是在20世纪初瑞典和俄罗斯。例如区域供热管网系统在莫斯科约600公里2。由于区域性加热和冷却系统花费占国家重要经济部分的燃料来提供在建筑物供暖制冷及生活用热水中。因此这些系统引起了极大关注在文献1-7。区域供热不仅是因为能源使用效率，更重要是能够得到更多的比其他方法更定期的，充分的和便宜的能量。在区域供热系统，热生成在一个工厂而被运到消费者的广泛区。因此，它提供热给一个地区的许多建筑物并且热水来自一个中心。该区域供热系统，从工厂运输的热利用主要管网，通过换热站，在二级热管网中最终分配给消费者。在这个系统中，在分配管道中能量和

41、火用损失是由于热量通过较长的距离。能源和管道火用损失高度影响供暖系统的经济优势。因此，从管道中损失的热应减少到最小程度。由Poredos和Kitonovski 8进行的研究表明在分配热网中热损失以8-10进行计算。能源和火用分析，表明在最近进行的发生在内部流程的能源效率中，能源和火用损失的消耗。能源和火用损失可直接转换为一个主要的燃料消费的增加。能源分析是基于热力学第一定律，火用分析的基础是热力学第二定律。许多研究者建议，一个过程的热力性能，是最好的火用分析与评价9。从热力学的角度来看，火用的定义是工作的最高限额，它可以由一个系统或物质流或能量流产生，当它达到一个均衡状态在一个参考环境。与能量

42、不同，火用不遵循守恒状态（除理想，或可逆流程）。相反，火用消耗或损失，由于不可逆过程存在于任何真实际的过程。由于与进程有关的不可逆性，在一个进程的火用消费是熵产生成正比的。火用分析的方法是使用质量和能量守恒原则与热力学第二定律在一起进行的分析，设计以及能源和其他系统的改进。该火用方法为进一步推动更有效的能源资源利用的有用工具，因为它能够真正计算出地点类型和程度的浪费和损失10。在这项研究中，对阿塔特乌尔克大学校园热分布网络的能量和火用损失进行了分析。在这所大学，供暖和生活热水供应热是由集中供热提供。阿塔特乌尔克大学是建在土耳其最冷的城市埃尔祖鲁姆。在一个供暖期间中，约有10000吨燃油消耗在供

43、暖系统。因为管网12公里左右，这是假设相当长，有相当高的能源和火用损失在热网系统中。2 系统描述和分析 该系统由从热源分配热量到热用户的供热管网分支组成。这样一个系统的基本组成部分是管道，它能够增强热量运输，并且是热源损失的主要来源。该系统的另一个重要组成部分是换热站，在这里热量从较高温度转移到较低温度的介质中，导致热量品质减少。在分析中，绝热管网管道直径从65到250毫米。该管网总长度为11988米 。在主网络，平均为15bar的压力，而在二级网络，压力为大气压力。 热站热量从主转移到辅助网络是通过壳管热交换器。2.1能量平衡提供给热用户的热量是 （1）其中表示通过热电厂传递给热水的热量，表

44、示水泵为热水在管网中的循环所做的功，表示提供给热用户的热量，表示在管道中的损失的热量。管道布置在底下的渠道，除此之外，在一个通道中有两个管子产生的热损失在一个特定的时刻产生，每单位长度管道形成的热损失表现为 （2）管道温度假设为的和Tr的算术平均数。是每日平均温度，R是表一中各种类型的热阻。平均8毫米厚度的玻璃棉是用于管道分析。渠道是由石头和混凝土混合物制造成的。管道计算周长，管道厚度TC和导热系数KC分别取为5米，10厘米，2.5 W / mK。土壤与水分的混合物的导热系数被取为0.91W/mK13。2.2火用平衡火用平衡可描写为 （3）其中E x;i为热水的火用，E x;w为被提供给水泵的电能的火用，Ex;c为提