機械類外文翻譯

1、xx大學(xué)機械工程學(xué)院畢業(yè)設(shè)計The app licati on of Acoustic Emissi on for detect ingincipient cavitati on and the best efficie ncy point of a60KW cen trifugal pump; case studyL. Alfaye z, D. Mba, G. Dyson July 2005AbstractPumps p lay a sig nifica nt role in In dustrial plants and n eed continu ous mon itori ng to m

2、inimize loss of production. To date, there is limited published information on the application of Acoustic Emission (AE)to incipient pump cavitation. This paper presents a case study where AE has bee n app lied for detect ing incipient cavitati on and determ ining the best efficiency point (BEP)of a

3、 60KW centrifugal pump. Results presented are based onNPSH (Net Positive Suctio n Head)a nd p erforma nee tests. I n con clusi on the AE tech nique was show n to offer early detect ion of incipient cavitati on, furthermore, the tech nique has dem on strated the ability to determ ine the BEP of a pum

4、pKeywords:Acoustic Emissi on; best efficie ncy point; cavitati on; con diti on mon itori ng;Pump p erforma nee1. IntroductionTypically the pump manufacturer will undertake performanee and NPSH(Net PositiveSuction Head)tests on supplied pumps, the significanee of the latter is to determine the 3%dr o

5、p in head at which serious cavitati ons will occur. The NPSH can be exp ressed as the differe nee betwee n the suct ion head and the liquids vapour head. The concept of NPSH was developed for the purpose of comparing inlet condition of the system with the inlet requireme nt of the pump. Cavitati on

6、causes a loss of pump efficie ncy and degradati on of the mecha ni cal in tegrity of the pump. It must be no ted that cavitati on starts to devel op before the第45頁共57頁xx大學(xué)機械工程學(xué)院畢業(yè)設(shè)計（論文）3%dr op in head. It is gen erally acce pted that the critical p ressure for incep ti on of cavitati on is not con s

7、ta nt and varies with op erati on fluid p hysical prop erties and the surface rough ness of the hydraulic equipment.App licati on of the high freque ncy Acoustic Emissi on (AE)tech nique in con diti on mon itori ng of rotating machinery has been growing over recent years1-9.Typical frequencies assoc

8、iated with AE activity range from 20 KHz to 1MHz.The most commo niy used method for ide ntify ing the p rese nee of cavitati on is based on observati ons of the drop in head. Whilst other techniques such as vibration analysis and hydrophone observations for pump fault diag no sis are well establishe

9、d, the app licati on of AE to this field is still in its infancy. In additi on, there are a limited nu mber of p ublicati ons on the app licati on of AE to pump health and cavitati on mon itori ng. Derakhsha n et al 10i nv estigated the cavitati on bubble colla pse as a source of acoustic emission a

10、nd commented that the high amplitude pressure puIse associated with bubble colla pse gen erated AE. With the AE sen sor was pl aced on the actual specimen experiencing cavitation Derkhshan observed increasing AE r.m.s levels with in creased p ressure of flow and cavitati on. However, with the AE sen

11、 sor moun ted on the tank wall the reverse was observed, decreasing AE r.m.s levels with increasing pressure and cavitati on. This was attributed to a visible bubble cloud that in creased with p ressure. It was comme nted that this cloud atte nu ated the AE sig nature p rior to reach ing the tran sd

12、ucer on the wall cas ing. Neill et al11,12assessed the p ossibility of early cavitati on detecti on withAE and also no ted that the colla pse of cavitatio n bubbles was an imp ulsive eve nt of the type that could gen erate AE. It was observed that whe n the pump was un der cavitati on the AE operati

13、onal background levels dropped in comparison to non-cavitating conditions. In conclusion Neill stated that loss in NPSH before the 3%drop-off criterion was detectable with AE and evide nee of incipient cavitati on was detectable in the higher freque ncy ban d(0.5 to 1MHz).The papers reviewed above h

14、ave clearly associated AE with the collapse of cavitation bubbles. The p rese nee of cavitati on has bee n show n to in crease or decrease op erati onal AE no ise levels10,11,12.This paper p rese nts a case study to ascerta in the app licability of theAE tech nique for detect ing incipient cavitati

15、on, and, to access the opportun ities offered by the AE tech nique for determ ining the best efficie ncy poin t(BE P)of a pump.第46頁共57頁xx大學(xué)機械工程學(xué)院畢業(yè)設(shè)計（論文）2. Exp erimental set upA series of p erforma nee and NPSH tests were un dertake n on a two stageDavidBrow n 60KW ce ntrifugal pump (Model DB22)with

16、 a maximum cap acity of 20m3/h at an efficie ncy of 70.6%.These tests were un dertake n using a closed loop arra ngeme nt with a vacuum facility in accorda nee with BS 9906.It must be no ted that best en deavours were un dertake n to reduce the time take n to reach the required flow rate duri ng p e

17、rforma nee andNPSH tests.Acoustic Emissi on sen sors were located at a dista nee of 0.5 m from sucti on flan ge; at the sucti on flan ge; on the pump cas ing in the vic in ity of imp eller sucti on eye; on the cas ing in the vici nity of the imp eller discharge tip; 0.5m from discharge flan ge, see

18、figure 1.3. Data acquisition systemsThe AE sen sors used for all of the exp erime nts were broadba nd type sen sors with a relative flat response in the region between 100 KHz to 1MHz (Model:WD, PhysicaAcousticsCorpo rati on ).The out put siefnOn the AE sen sors was p re-a mp lified at 40dB.Co ntinu

19、 ousAE r.m.s values were calculated in real time by the An alogue to Digital Conv erter(ADC).The sampling rate for acquisition was set at 100ms for all tests and the time constant for calculati ng the AE r.m.s was also set at 100 ms.4. Exp erimental results and observation4.1 Performance testFigure

20、2 details the performanee characteristics of the pump, highlighting the BEP at394.5m/hr. The p erforma nee test were un dertake n twice to en sure rep eatability. Observati ons of AE r.m.s activity duri ng the p erforma nee test are dis played in figure 3.Duri ng the performanee test, AE activity fr

21、om the sensor located in the vicinity of impeller on pump cas ing was found to have the largest magn itude, pro vid ing the best po siti on for correlati ngAE activity to pump performanee. It was observed that the minimum AE r.m.s value wasobta ined for a flow rate of 94.5m/hr. At this flow rate the

22、 AE acuitygen erated from the fluid flow with in the pump and pipes was lowest in comp aris on to other flow rates. Either side of this flow rate resulted in in creas ing AE r.m.s activity with in creased flow rates. Basedon these observati ons it was con eluded that the BEP must occur where there w

23、as mini mals performanee test and was found tflow turbulenee in the system, and hence minimum AE activity. The predicted efficiency point of 94.5m/hr was checked with the manu facturer be accurate. In teresti ngly this is the first known correlatio n betwee n AE activity and the BEP and agrees with

24、observations of McNulty 13, though McNulty Svestigation was centred at freque ncies in the audible ran ge; lower tha n the AE ran ge. The adva ntage offered by theAE tech nique is the in here nt reject ion of typi cal mecha ni cal and p rocess op erati onal backgro und no ise(less tha n 20 KHz)4.2 N

25、PSH testA total of three NPSH tests were un dertaken at flow rates of 101,141 and 180m/hr, see figure4. As with the p erforma nee tests, the best AE sig nature res ponse was located on the pump cas ing in the vic in ity of the imp eller eyeFigures 5 to 7 detail the associated AE r.m.s levels for the

26、 three flow rates con sidered.The follow ing observati ons were no ted:At a flow rate of 101m/h an in crease of 165%i n AE r.m.s levels was observed from an NPSH value of 8.2m to 7m.Relatively constant levels followed until an NPSH of 5.8 m when a rap id decrease in AE r.m.s levels was no ted. With

27、further reducti ons in NP SH, sp ikes in AE r.m.s sig nal vels associated with cavitatio n was also observed by Neill11.Observati ons ofAE levels from the suct ion and discharge pipes mirrorthis observati on.a flow rate of 141m/h an in crease of 43% in AE r.m.s was observed at NPSH value of 12.7m to

28、 9.3m.A rap id decrease in level was no ted at an NPSH of 9.3m.With further reducti ons inNP SH, sp ikes in AE r.m.s sig nal were observed as with the test a flow rate of 101m/hr. Aga in, observati ons of AE levels from the sucti on and discharge pipes mirrored this observati on.At a flow rate of 18

29、1m/h an in crease in AE r.m.s of 223%was observed at NPSH value of 11m to 7.3m.A gradual decrease in the AE levels followed to an NPSH of 1.7 m, where an in crease in the r.m.s value was observed.5. Discussions5.1Performance testThe observations of AE activity during the performanee test were very e

30、ncouraging. The ability to predict a systems BEP by observing variations in the AE r.m.s response offer p rocess engin eers a po werful tool for mon itori ng plant p erforma nee. Whilst further research is still required the opportunities offered by such a tool could be applied to determining system

31、 BEP irres pective of the type of medium (liquid, gases, semi-solids, etc )in the system.The observati ons no ted in this inv estigatio n correlate with hydr ophone measureme nts un dertake n by McNulty 13,where the minimum sound inten sity coin cided with the pumpBEP.5.2 NPSH testIt is esse ntial t

32、o un dersta nd the cavitati on seque nee if it is to be correlated to observed AE activity. Once the sucti on p ressure starts to decrease, vortexes start to occur at the imp eller blade ti ps. With further reduct ion in p ressure these vortexes take the form of travelli ng bubbles in the liquid. Th

33、ese bubbles are in itially created in lower p ressure area on the suct ion surface of the blades. Eventually the bubbles move to higher-pressure areas where they colla pse. With eve n further reduct ion in the suct ion p ressure, the bubbles comb ine into larger cavities. These cavities are usually

34、formed on the imp eller blade sucti on surface.For all NPSH tests an in crease in AE r.m.s levels was no ted as values of NPSH started to decrease. A maximum level of AE r.m.s was reached after which further reducti ons in NPSH resulted in a decrease in AE r.m.s levels. This was also observed on the

35、 sen sors located on the suction and discharge flanges. It is postulated that at the start of the NPSH test the in crease in AE r.m.s levels was attributed to the on set of cavitati on. The drop in AE r.m.s with decreasing NPSH values was attributed to the attenuation caused by bubble clouds.Followi

36、 ng the creati on of bubbles, and the eve ntual formatio n of the bubble cloud, the AE r.m.s levels were exp ected to drop. The loss in AE stre ngth due to the p rese nee of cavitati on and the bubble cloud was n oted by Neill11,12a nd Derakhsha n 10res pectively.5.3 ConclusionsThe results from acou

37、stic emissi on an alysis have show n a clear relati onship betwee n AE activity measured from the pump casing, suction and discharge pipes, and incipient cavitati on. At a relatively high NPSH value, whe n incipient cavitati on is known to occur, an in crease in AE r.m.s levels was observed.However,

38、 as cavitati on devel oped a reduct ion in AE r.m.s levels due to atte nu ati on was no tedThis would suggest that the AE tech nique is more suited to detect ing incipient, and not devel op ed, cavitatio n.AE was also found to have eno rmous poten tial in determ ining the BEP of a pump an d/or p roc

39、ess employing pumps though further research on this observati on is required.6. References1. Mba, D. and Bannister, R.H.(1999).Condition monitoring of low-speed rotating machi nery usi ng stress waves: Part1 and P artPToc Inst Mech En grs 213(3), Part E,153-185.2. Morha in, A, Mba, D, Beari ng defec

40、t diag no sis and acoustic emissi on Journal ofEngineering Tribology, I Mech E, Vol 217,No.4, Part J,p257-272,2003.ISSN1350-6501Mba,D.(20023. Mba,D.(2002).Applicability of acoustic emissions to monitoring the mechanicalin tegrity of bolted structures in low sp eed rotati ng machi nery: case study. N

41、DT andEln ternati on al35(5),293-3004. D. Mba, A. Cooke, D. Roby ,G. Hewitt, Detectio n of shaft-seal rubb ing in large-scalepo wer gen erati on turb ines with Acoustic Emissi ons; Case study. Journal of Po wera ndEn ergy-Part A,I Mech E, Vol 218,No.2 ,Part A,p 71-82,March 2004.ISSN0957-6509.5. Tout

42、o un tzakis, T. and Mba, D.(2003).Observati on of Acoustic Emissi on Activity duri ngGear Defect Diag nosis. NDT and E In ternatio nal.36 ,471-477.6. Kristoffer Bruzelius D. Mba(2004),A n in itial in vestigation on the pote ntialA pp licability of Acoustic Emissi on to rail track fault detecti on. N

43、DT&EIn ternatio nal ,37(7),507-516.7. L. D. Hall and D. Mba,(2004)Diag no sis of con ti nu ous rotor -stator rubb ing in largescaleturbi ne un its using acoustic emissio nSJItraso ni cs,41(9),765-773.8 .L. D. Hall and D. Mba,(2004),Acoustic emissi ons diag no sis of rotor-stator rubsusing the KS sta

44、tistic,Mecha nical Systems and Sig nal P rocessin,g8(4),849-868.9. D. Mba,N, Jamalud in, Mon itori ng extremely slow rolli ng eleme nt beari ngs: Part landll,NDT and E In ternatio nal,35(60),349-366,2002.10. O. Derakhsha n, J.Richard Houghto n, R. Keith Jon es(1989).Cavitation Mo nitori ng ofHydro t

45、urb ines with RMS Acoustic Emissi on Measureme nts. World Meeti ng onAcoustic Emissio n,p305-315,March 1989.11. G D Neill, R L Reube n, P M San dford (1997).Detection of In ci pie nt cavitatio n in PumpsUsi ng Acoustic Emissi on. Journal of P rocess Mecha ni cal Engin eeri ng,ImechE,211(4),267.12. G

46、 D Neil, et al.(1996)Detection of In ci pie nt cavitation in Pumps Usi ng AcousticEmissio n. In proceed ings of COMADEM 96.Sheffield Uni versity, July16-18,391-401.13. P.J. McNulty(1981)Measureme nt Techni ques and An alysis of Fluid-Borne Noise inPumps. Nati onal Engin eeri ng Laboratory. NEL Repor

47、t No第50頁共57頁XX大學(xué)機械工程學(xué)院畢業(yè)設(shè)計（論文）聲發(fā)射檢測初生空化及其應(yīng)用60KW離心泵最佳效率點案例研究L.法浦亞斯，D.姆巴，G.戴森 2005 年7月摘要泵在工業(yè)領(lǐng)域發(fā)揮著顯著的作用，需要持續(xù)監(jiān)控，以盡量減少生產(chǎn)損失。到 目前為止，將聲發(fā)射技術(shù)（AE應(yīng)用于泵初生空化的信息依然很有限。本文介紹 了一個聲發(fā)射技術(shù)（AE已應(yīng)用于檢測初生空化和確定 60KW離心泵的最佳效率點（BEP的研究案例。該案例的結(jié)果是基于 NPSH（汽蝕余量）和性能測試得到的?？傊?，聲發(fā)射技術(shù)被證明可以提供初生空化的檢測， 此外，該技術(shù)已還證明, 聲發(fā)射具有確定泵的最佳效率點（BEP的能力。關(guān)鍵字:聲發(fā)射；最

48、佳效率點；空化； 狀態(tài)監(jiān)測；泵性能1介紹泵廣泛的應(yīng)用于我們的生活和工業(yè)當(dāng)中。 泵的制造商會提供說明泵在給定條 件下的性能特性曲線。這些曲線表明泵的放電能力，泵的揚程，功率和工作效率 之間的關(guān)系。一臺泵的理想工作點被稱為最佳效率點（BEP。在這一點，泵的流量和壓頭相結(jié)合，使泵達到最佳效率。如果泵在最佳效率點（BEP外運行，不 僅將使泵的效率受到影響，而且會加劇磨損，降低泵的使用壽命。 通常情況下, 泵制造商將對泵進行性能和 NPSH（汽蝕余量）測試，后者的意義在于確定揚程下降3%時將發(fā)生嚴(yán)重的氣穴現(xiàn)象。汽蝕余量（NPSH可以表示為總水頭和液體 汽化時的壓力頭之間的差。NPSH的概念是因比較泵的入

49、口條件與泵的入口要求 而提出的。氣蝕引起泵的效率和泵機械完整性降低。必須指出，空化開始發(fā)生于 揚程下降3%之前。人們普遍認(rèn)為初生空化的臨界壓力不是恒定的，而且與工作 流體的物理性質(zhì)及液壓設(shè)備的表面粗糙度的變化有關(guān)。聲發(fā)射技術(shù)在回轉(zhuǎn)機械狀態(tài)監(jiān)測中的應(yīng)用一直在增長。聲發(fā)射的范圍從20KHz到1MHz最常用的用于識別汽蝕存在的方法是觀測泵揚程的下降。雖然振動 分析及泵故障診斷水聽器觀測等技術(shù)已經(jīng)非常成熟，聲發(fā)射技術(shù)在這一領(lǐng)域的應(yīng) 用尚處于起步階段。此外，將聲發(fā)射技術(shù)應(yīng)用到泵的性能和空化監(jiān)測的出版物的 數(shù)量仍十分有限。德拉哈思漢等人研究認(rèn)為空化泡破裂是聲發(fā)射的一種來源，并認(rèn)為與泡沫破 裂相關(guān)的高振幅壓

50、力脈沖產(chǎn)生了聲發(fā)射。 通過放置在空化實驗樣品中的聲發(fā)射傳 感器，德拉哈思漢觀察到 AE有效值、水平流動和空化壓力都增大了。然而，將AE傳感器安裝在實驗箱箱壁上卻得到了相反的結(jié)果，AE有效值、水平與空化壓力都下降了。這是由一個隨著壓力增大的可見的氣泡云造成的。 這就是說，氣泡 云產(chǎn)生的AE在到達實驗箱箱壁上的AE傳感器之前在不斷地衰減。尼爾等人評估 了利用AE檢測早期氣蝕的可能性，并且指出，空化氣泡的破裂所產(chǎn)生的脈沖可 以產(chǎn)生聲發(fā)射。據(jù)觀察，泵在空化條件下的 AE水平比在無空化條件下的要低?？傊釥柋硎?， 比標(biāo)準(zhǔn)低3 %的汽蝕余量是可以被聲發(fā)射檢測到的，并且，初 生空化的證據(jù)在較高的頻帶（0.5

51、至1MHZ也是可檢測的。上文已明確表明AE與空化氣泡的破裂有關(guān)。汽蝕的存在已被證明增加或減 少AE水平。本文介紹了一個案例研究，以確定聲發(fā)射技術(shù)檢測初生空化的適用 性，并利用聲發(fā)射技術(shù)確定泵的最佳效率點（BEP。2. 實驗裝置一系列的性能和汽蝕余量的測試將分兩個階段進行。大衛(wèi)布朗的60KW離心泵（型號DB22，最大流量為204n3/h，效率為70.6 %。這些試驗在BS9906標(biāo)準(zhǔn) 的真空封閉設(shè)備中進行。必須指出的是，在泵的性能和汽蝕余量測試實驗中， 實 驗人員盡了最大的努力，從而降低了泵達到實驗所要求的流量所需的時間。 聲發(fā) 射傳感器分別被安裝在距吸入口法蘭0.5m處，葉輪入口附近的殼體上，

52、葉輪放電 尖端附近殼體上及距出口法蘭0.5m處。參見圖1。3. 數(shù)據(jù)采集系統(tǒng)實驗中的聲發(fā)射傳感器均是工作范圍為 100 kHz至1MHZ勺（型號：WD物理聲學(xué)公司）傳感器。AE傳感器的輸出信號將預(yù)放大為 40dB,連續(xù)的聲發(fā)射有效值將會被數(shù)字轉(zhuǎn)換器（ADC實時計算。所有測試的采樣率均為100毫秒，計 算聲發(fā)射有效值的時間也是100毫秒。4. 實驗結(jié)果4.1性能測試圖2詳細(xì)描述了泵的性能特征，表明泵的最佳效率點在流量為94.5m3/h時。泵的性能測試進行了兩次，以確保其可重復(fù)性。AE有效值測試結(jié)果如圖3所示。AE活動的峰值出現(xiàn)在泵殼葉輪附近從設(shè)在葉輪上的泵殼體附近，AE的相關(guān)活動為泵的性能提供了

53、最佳的位置。據(jù)觀察，在流量為94.5m3/h時AE的有效值最低。相比于其他流量下流體在泵和管道內(nèi)產(chǎn)生的聲發(fā)射，在94.5m3/h的流量下所產(chǎn)生的聲發(fā)射最低。高于或低于這個流量都將會導(dǎo)致AE活動的增加?；谶@些觀察可以得出結(jié)論，最佳效率點（BEP）定出現(xiàn)在系統(tǒng)湍流最小點，也就是聲發(fā)射活動最低點。預(yù)測的最佳效率點94.5m3/h是制造商通過性能測試的得到的，并且該點被證明是正確的。有趣的是，這第一次證明了的AE活性和最佳效率點存在相關(guān)性并且和麥克納爾蒂的觀察相符合， 雖然麥克納爾蒂的調(diào)查集中在 比AE范圍低的可聽頻率范圍內(nèi)。AE技術(shù)的優(yōu)點是降低了傳統(tǒng)的機械噪音（低 于20千赫）04.2汽蝕余量測試實驗分別測試了流量分別為101、141、180m3/h時的汽蝕余量。如圖4所示。由性能測試實驗可知，最好的 AE信號出現(xiàn)在葉輪入口附近的泵殼處。圖5到圖7詳細(xì)的表明了在三種不同流量下的聲發(fā)射有效值觀察結(jié)果表明：1）在流量為101n3/h，汽蝕余量為7m至8.2m時，AE有效值增加了 165%當(dāng)汽蝕余量為5.8m時，AE有效值會急劇增大。隨汽蝕余量繼續(xù)降低，AE有效值會出現(xiàn)尖峰，此時泵的揚程下降了 3%尼爾也觀察到了這種和空化有關(guān)的AE有效值的變化，泵吸入口和排出口處的 AE有效值變化也印證了這種現(xiàn)象。2）在流量為141n3/h，汽蝕余量為9.3m至12.7m時，AE有效值增加了 43%當(dāng)