Cavitation Experiment

ABSTRACT
Pumps are an essential part of any system where the movement of fluids is needed. In this experiment, pump curves, pumps in parallel and series as well as the phenomenon of cavitation were investigated. The objectives for the experiment were: to determine a characteristic pump curve of a single centrifugal pump and compare it to the manufacturer’s pump curve; to confirm that the overall pump curve for pumps in series and parallel can be obtained from the individual pump curves and finally to demonstrate the phenomenon of cavitation and determine the effects of volumetric flow rate and suction static head on cavitation. These were achieved by making use of a centrifugal pump apparatus and adjusting valves accordingly to focus on specific

When this happens, bubbles form at the suction side of the pump where the pressure is lowest and as they pass through the pump they burst. This causes noise, a loss of efficiency and damage to the impeller blades through erosion (Cengal and Cimbala, 2014). Cavitation must be avoided in a pipe system by specifying criteria for the inlet of the pump, such as ensuring the suction pressure is greater than the vapour pressure of the fluid. This is measured using a parameter called net positive suction head (NPSH). It is defined by Cengal and Cimbala as the change in a pump’s inlet stagnation pressure head and the head of vapour pressure. NPSH is shown in Equation [8] in Appendix C. The required NPSH for a particular pump at different flow rates can be calculated and plotted. The point where the required NPSH and the system NPSH curves cross is the maximum flow rate that pump can operate at in order to avoid

The overall pump curves for pumps in series and pumps in parallel were obtained and compared to theory and from this it was concluded that when two identical pumps are connected in series the overall head is doubled at a constant flow rate. Also, when two identical pumps are connected in parallel the flow rate at a particular head is doubled. The phenomenon of cavitation was demonstrated and the effects of fluid flow rate and suction static head on cavitation were observed. It was concluded that as the fluid flow rate decreased, more bubbles appeared and thus the chances of cavitation increased. Furthermore, because of the decrease in inlet pressure due to a decrease in flow rate, the suction static head also decreased.

6. RECOMMENDATIONS
If this experiment were to be repeated, the following is recommended in order to improve on the accuracy of the results obtained