機(jī)械類外文翻譯--聲發(fā)射檢測(cè)初生空化及其應(yīng)用60kw離心泵最佳效率點(diǎn)案例研究

1、第 45 頁(yè) 共 57 頁(yè)中文 中文 2940 字出處： 出處：NDT case studyL. Alfayez, D. Mba, G. Dyson July 2005AbstractPumps play a significant role in Industrial plants and need continuous monitoring to minimize loss of production. To date, ther

2、e is limited published information on the application of Acoustic Emission (AE)to incipient pump cavitation. This paper presents a case study where AE has been applied for detecting incipient cavitation and determining t

3、he best efficiency point (BEP)of a 60KW centrifugal pump. Results presented are based on NPSH (Net Positive Suction Head)and performance tests. In conclusion the AE technique was shown to offer early detection of incipie

4、nt cavitation, furthermore, the technique has demonstrated the ability to determine the BEP of a pumpKeywords:Acoustic Emission; best efficiency point; cavitation; condition monitoring;Pump performance1. IntroductionTypi

5、cally the pump manufacturer will undertake performance and NPSH(Net Positive Suction Head)tests on supplied pumps, the significance of the latter is to determine the 3%drop in head at which serious cavitations will occur

6、. The NPSH can be expressed as the difference between the suction 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 requirement

7、of the pump. Cavitation causes a loss of pump efficiency and degradation of the mechanical integrity of the pump. It must be noted that cavitation starts to develop before the 3%drop in head. It is generally accepted tha

8、t the critical pressure for inception of cavitation is not constant and varies with operation fluid physical properties and the surface roughness xx 大學(xué)機(jī)械工程學(xué)院畢業(yè)設(shè)計(jì)（論文）第 47 頁(yè) 共 57 頁(yè)A series of performance and NPSH tests wer

9、e undertaken on a two stage ‘ DavidBrown’60KW centrifugal pump(Model DB22)with a maximum capacity of 204m³/h at an efficiency of 70.6%.These tests were undertaken using a closed loop arrangement with a vacuum facili

10、ty in accordance with BS 9906.It must be noted that best endeavours were undertaken to reduce the time taken to reach the required flow rate during performance and NPSH tests.Acoustic Emission sensors were located at a d

11、istance of 0.5 m from suction flange; at the suction flange; on the pump casing in the vicinity of impeller suction eye; on the casing in the vicinity of the impeller discharge tip;0.5m from discharge flange, see figure

12、1.3. Data acquisition systemsThe AE sensors used for all of the experiments were broadband type sensors with a relative flat response in the region between 100 KHz to 1MHz (Model:WD,‘Physical Acoustics Corporation’).The

13、output signal from the AE sensors was pre-amplified at 40dB.Continuous AE r.m.s values were calculated in real time by the Analogue to Digital Converter(ADC).The sampling rate for acquisition was set at 100ms for all tes

14、ts and the time constant for calculating the AE r.m.s was also set at 100 ms.4. Experimental results and observation4.1 Performance testFigure 2 details the performance characteristics of the pump, highlighting the BEP a

15、t 94.5m/hr. The performance test were undertaken twice to ensure repeatability. Observations of AE r.m.s activity during the performance test are displayed in figure 3.During the performance test, AE activity from the se

16、nsor located in the vicinity of impeller on pump casing was found to have the largest magnitude, providing the best position for correlating AE activity to pump performance. It was observed that the minimum AE r.m.s valu

17、e was obtained for a flow rate of 94.5m/hr. At this flow rate the AE activity generated from the fluid flow within the pump and pipes was lowest in comparison to other flow rates. Either side of this flow rate resulted i