龍設(shè)計終版翻譯

1、山東建筑大學(xué)畢業(yè)設(shè)計外文文獻(xiàn)及譯文- 外文翻譯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. 中文譯文區(qū)域供熱網(wǎng)絡(luò)中的能源和火用損失的

39、評價摘要在本文中，對能源和火用損失形成的分布區(qū)域供熱熱網(wǎng)系統(tǒng)進(jìn)行了評估。為此，需要確定能源和火用損失方程和能夠使用它們，如對一個有一個長11988米直徑為65-250毫米供熱管道的大學(xué)供熱分配網(wǎng)絡(luò)進(jìn)行分析。結(jié)果發(fā)現(xiàn)，在熱成型火用損失約占總系統(tǒng)總能量的16%,并且發(fā)現(xiàn)供水溫度和回水溫度是影響火用損失的最重要因素。關(guān)鍵詞：能源損失;火用損失;區(qū)域熱網(wǎng)1簡介由于工業(yè)再評價造成的迅速城市化使得人們產(chǎn)生一個節(jié)能的想法，即尋找到一個補救人們需要的的像供水社會服務(wù)中心，下水道系統(tǒng)，公共交通和區(qū)域供熱系統(tǒng)社會服務(wù)中心。第一個區(qū)域供熱系統(tǒng)建于1887年洛克波特（美國紐約）1。從那時起，它已經(jīng)開始被鋪設(shè)在歐洲的各

40、個國家。該區(qū)域供熱系統(tǒng)已越來越多地用于在德國，丹麥，荷蘭，比利時，尤其是在20世紀(jì)初瑞典和俄羅斯。例如區(qū)域供熱管網(wǎng)系統(tǒng)在莫斯科約600公里2。由于區(qū)域性加熱和冷卻系統(tǒng)花費占國家重要經(jīng)濟(jì)部分的燃料來提供在建筑物供暖制冷及生活用熱水中。因此這些系統(tǒng)引起了極大關(guān)注在文獻(xiàn)1-7。區(qū)域供熱不僅是因為能源使用效率，更重要是能夠得到更多的比其他方法更定期的，充分的和便宜的能量。在區(qū)域供熱系統(tǒng)，熱生成在一個工廠而被運到消費者的廣泛區(qū)。因此，它提供熱給一個地區(qū)的許多建筑物并且熱水來自一個中心。該區(qū)域供熱系統(tǒng)，從工廠運輸?shù)臒崂弥饕芫W(wǎng)，通過換熱站，在二級熱管網(wǎng)中最終分配給消費者。在這個系統(tǒng)中，在分配管道中能量和

41、火用損失是由于熱量通過較長的距離。能源和管道火用損失高度影響供暖系統(tǒng)的經(jīng)濟(jì)優(yōu)勢。因此，從管道中損失的熱應(yīng)減少到最小程度。由Poredos和Kitonovski 8進(jìn)行的研究表明在分配熱網(wǎng)中熱損失以8-10進(jìn)行計算。能源和火用分析，表明在最近進(jìn)行的發(fā)生在內(nèi)部流程的能源效率中，能源和火用損失的消耗。能源和火用損失可直接轉(zhuǎn)換為一個主要的燃料消費的增加。能源分析是基于熱力學(xué)第一定律，火用分析的基礎(chǔ)是熱力學(xué)第二定律。許多研究者建議，一個過程的熱力性能，是最好的火用分析與評價9。從熱力學(xué)的角度來看，火用的定義是工作的最高限額，它可以由一個系統(tǒng)或物質(zhì)流或能量流產(chǎn)生，當(dāng)它達(dá)到一個均衡狀態(tài)在一個參考環(huán)境。與能量

42、不同，火用不遵循守恒狀態(tài)（除理想，或可逆流程）。相反，火用消耗或損失，由于不可逆過程存在于任何真實際的過程。由于與進(jìn)程有關(guān)的不可逆性，在一個進(jìn)程的火用消費是熵產(chǎn)生成正比的?；鹩梅治龅姆椒ㄊ鞘褂觅|(zhì)量和能量守恒原則與熱力學(xué)第二定律在一起進(jìn)行的分析，設(shè)計以及能源和其他系統(tǒng)的改進(jìn)。該火用方法為進(jìn)一步推動更有效的能源資源利用的有用工具，因為它能夠真正計算出地點類型和程度的浪費和損失10。在這項研究中，對阿塔特烏爾克大學(xué)校園熱分布網(wǎng)絡(luò)的能量和火用損失進(jìn)行了分析。在這所大學(xué)，供暖和生活熱水供應(yīng)熱是由集中供熱提供。阿塔特烏爾克大學(xué)是建在土耳其最冷的城市埃爾祖魯姆。在一個供暖期間中，約有10000噸燃油消耗在供

43、暖系統(tǒng)。因為管網(wǎng)12公里左右，這是假設(shè)相當(dāng)長，有相當(dāng)高的能源和火用損失在熱網(wǎng)系統(tǒng)中。2 系統(tǒng)描述和分析 該系統(tǒng)由從熱源分配熱量到熱用戶的供熱管網(wǎng)分支組成。這樣一個系統(tǒng)的基本組成部分是管道，它能夠增強熱量運輸，并且是熱源損失的主要來源。該系統(tǒng)的另一個重要組成部分是換熱站，在這里熱量從較高溫度轉(zhuǎn)移到較低溫度的介質(zhì)中，導(dǎo)致熱量品質(zhì)減少。在分析中，絕熱管網(wǎng)管道直徑從65到250毫米。該管網(wǎng)總長度為11988米 。在主網(wǎng)絡(luò)，平均為15bar的壓力，而在二級網(wǎng)絡(luò)，壓力為大氣壓力。 熱站熱量從主轉(zhuǎn)移到輔助網(wǎng)絡(luò)是通過殼管熱交換器。2.1能量平衡提供給熱用戶的熱量是 （1）其中表示通過熱電廠傳遞給熱水的熱量，表

44、示水泵為熱水在管網(wǎng)中的循環(huán)所做的功，表示提供給熱用戶的熱量，表示在管道中的損失的熱量。管道布置在底下的渠道，除此之外，在一個通道中有兩個管子產(chǎn)生的熱損失在一個特定的時刻產(chǎn)生，每單位長度管道形成的熱損失表現(xiàn)為 （2）管道溫度假設(shè)為的和Tr的算術(shù)平均數(shù)。是每日平均溫度，R是表一中各種類型的熱阻。平均8毫米厚度的玻璃棉是用于管道分析。渠道是由石頭和混凝土混合物制造成的。管道計算周長，管道厚度TC和導(dǎo)熱系數(shù)KC分別取為5米，10厘米，2.5 W / mK。土壤與水分的混合物的導(dǎo)熱系數(shù)被取為0.91W/mK13。2.2火用平衡火用平衡可描寫為 （3）其中E x;i為熱水的火用，E x;w為被提供給水泵的電能的火用，Ex;c為提