Experimental and Numerical Investigations of the Effect of Net Positive Suction Head on Water Hammer In Pipeline Systems
Maher Abdul Ameer1, Audai Hussein Al-Abbas2
1Maher Abdul Ameer, Pumps Eng. Dept, Al-Musaib Technical College, Foundation of Technical Education, Babylon, Iraq.
2Audai Hussein Al-Abbas, Pumps Eng. Dept, Al-Musaib Technical College, Foundation of Technical Education, Babylon, Iraq.
Manuscript received on September 21, 2013. | Revised Manuscript received on October 18, 2013. | Manuscript published on October 30, 2013. | PP: 86-91  | Volume-3, Issue-1, October 2013. | Retrieval Number:  A2149103113/2013©BEIESP

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Abstract: In the present paper, the effect of the Net Positive Suction Head (NPSH) for the centrifugal pump in a simple pipeline system has been carried out eliminating water hammer. Both the experimental tests and numerical calculations were performed in this study to investigate the transient flow effects when the discharges change abruptly in the system. The phenomenon of transient flow is generally occurred when the sudden opening of the downstream valves are used in the pumping station or due to introducing additional parallel branches of pipelines that contain pumps. Experimentally, two operational tests with different NPSH were conducted to show the relations between the head (H) and discharge (Q). The results of these tests showed two different types of H-Q curves. The first test produced a flat H-Q curve when the water surface level in the suction tank was 4 m above the center line of the pump. While in the second test the operational case created a steep H-Q curve when the pump was used to lift 6 m from the suction tank. That is likely happened due to the decrease in a cut-off discharge point. The numerical calculations on hypothec simple pipeline system have been done for the transient flow after determining the shape of the characteristics H-Q curves produced from the experimental tests. The Darcy-Waysbach equation was used to calculate the friction losses and obtain the system resistance curve. The classical method of characteristics, which is based on the methodological analysis of the finite difference method, was executed to propagate the wave pressure in each cases examined. The numerical results were clearly showed that the wave pressure produced in the pipeline system with the flat H-Q curve is smaller than that produced in the pipeline with the steep H-Q curve. This means that the first case is significantly reduced the possibility of occurrence the water hammer phenomenon.
Keywords: Transient flow, Net positive suction head, Pipeline system, Water hammer, Centrifugal pump.