机械类外文翻译--声发射检测初生空化及其应用60kw离心泵最佳效率点案例研究(编辑修改稿)

机械类外文翻译--声发射检测初生空化及其应用60kw离心泵最佳效率点案例研究(编辑修改稿)内容摘要：

rease of 165%in AE levels was observed from an NPSH value of to constant levels followed until an NPSH of m when a rapid decrease in AE levels was noted. With further reductions in NPSH, spikes in AE signal vels associated with cavitation was also observed by Neill[11].Observations of AE levels from the suction and discharge pipes mirrorthis observation. a flow rate of 141m/h an increase of 43%in AE was observed at NPSH value of to rapid decrease in level was noted at an NPSH of further reductions in NPSH, spikes in AE signal were observed as with the test a flow rate of 101m/hr. Again, observations of AE levels from the suction and discharge pipes mirrored this observation. At a flow rate of 181m/h an increase in AE of 223%was observed at NPSH value of 11m to gradual decrease in the AE levels followed to an NPSH of m, where an increase in the value was observed. 5. Discussions xx 大学机械工程学院毕业设计（论文） 第 49 页 共 57 页 test The observations of AE activity during the performance test were very encouraging. The ability to predict a systems BEP by observing variations in the AE response offer process engineers a powerful tool for monitoring plant performance. Whilst further research is still required the opportunities offered by such a tool could be applied to determining system BEP irrespective of the type of medium (liquid, gases, semisolids, etc )in the system. The observations noted in this investigation correlate with hydrophone measurements undertaken by McNulty [13],where the minimum sound intensity coincided with the pump BEP. NPSH test It is essential to understand the cavitation sequence if it is to be correlated to observed AE activity. Once the suction pressure starts to decrease, vortexes start to occur at the impeller blade tips. With further reduction in pressure these vortexes take the form of travelling bubbles in the liquid. These bubbles are initially created in lower pressure area on the suction surface of the blades. Eventually the bubbles move to higherpressure areas where they collapse. With even further reduction in the suction pressure, the bubbles bine into larger cavities. These cavities are usually formed on the impeller blade suction surface. For all NPSH tests an increase in AE levels was noted as values of NPSH started to decrease. A maximum level of AE was reached after which further reductions in NPSH resulted in a decrease in AE levels. This was also observed on the sensors located on the suction and discharge flanges. It is postulated that at the start of the NPSH test the increase in AE levels was attributed to the onset of cavitation. The drop in AE with decreasing NPSH values was attributed to the attenuation caused by bubble clouds. Following the creation of bubbles, and the eventual formation of the bubble cloud, the AE levels were expected to drop. The loss in AE strength due to the presence of cavitation and the bubble cloud was noted by Neill[11,12]and Derakhshan [10]respectively. 6 Conclusions The results from acoustic emission analysis have shown a clear relationship between AE xx 大学机械工程学院毕业设计（论文） 第 50 页 共 57 页 activity measured from the pump casing, suction and discharge pipes, and incipient cavitation. At a relatively high NPSH value, when incipient cavitation is known to occur, an increase in AE levels was observed. However, as cavitation developed a reduction in AE levels due to attenuation was noted This would suggest that the AE technique is more suited to detecting incipient, and not developed, was also found to have enormous potential in determining the BEP of。