الفهرس 
GENERAL INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
A special test rig for study of cavitation in centrifugal pump is designed and constructed in the laboratory of Prof. Bassyouni Ahmed Khalifa at Faculty of Engineering Shibin El-Kom. The rig was designed so that the flow rate ratio (pump flow rate/ optimum flow rate), suction pressure, pump rotational speed and water temperature could be varied independently under cavitating condition. The pump suction side and front shroud of its impeller are made from transparent perspex to permit visual cavitation inception.
An experimental study of circulatory flow in the pipe immediately in the front of the pump impeller at varies pump rotational speeds and flow rates is presented. The distribution of velocity at low flow rates is measured at impeller inlet. The onset and structure of the flow recirculation at the inlet are investigated experimentally. The results showed that the recirculating flow appeared for flow rate ratios Q/Qopt < 0.8 and there is no recirculating flow for flow rate ratios Q/Qopt ≥ 0.8. On the basis of the velocity distribution an empirical formula is obtained to describe the relation between the ratio of meridional velocity with recirculation flow to the meridional velocity without recirculation flow (Cm΄/Cm) and the flow rate ratio (Q/Qopt).
The effects of flow rate ratio, pump rotational speed and water temperature on performance and cavitation inception of a centrifugal pump are presented experimentally. The tests were carried out at different flow rate ratios and different rotational speeds and different water temperature. The ratio of flow rate to optimum flow rate was varied from 0.3 to 1.1, while the speed and temperature were varied from 1500 rpm to 3000 rpm and from 20°C to 90°C respectively.
The results showed that the visual inception net positive suction head (NPSHi,v) decreases with the increase of flow rate ratio till reaches a minimum then started increases with increase of flow rate ratio. The visual inception NPSHi,v is found to increase with increase of the pump rotational speed. The visual inception net positive suction head (NPSHi,v) is found to increase with temperature up to about 40°C and reached a maximum and then decreases again. This trend of the variation of NPSHi with temperature is found to be the same for all values of flow rate ratios and speeds.
Visual observation of cavitation showed that the 3% DROP in head cannot be regarded as a low for inception point. The visual inception NPSHi,v is well correlated with the net positive suction head corresponding to 3% DROP in head (NPSH3%) directly which is independent of the flow rate and the rotational speed.
A special theoretical model has been predicted considering many parameters such as flow conditions (flow rate ratio, rotational speed, water temperature), thermodynamic properties of water, nuclei and gas content and off-design phenomenon and its effect on meridional velocity, relative velocity and incidence angle. Comparison between the calculated NPSHi from the present model and those measured for all the present data and other investigators data showed a good agreement.