EXPERIMENTAL ANALYSIS OF SILT EROSION IN PUMP AS TURBINE

Abstract

Silt erosion is a phenomenon of mechanical wear of components. This is due to the dynamic action of sediment flowing along with water impacting against a solid surface of hydraulic components. However, the mechanism of erosion is complex due to interaction of several factors viz, particles size, shape, hardness, concentration, velocity, impingement angle, and properties of material. The silt laden water passing through the turbine is the root cause of silt erosion of turbine components which consequently leads to a loss in efficiency. This affects output, abetting of cavitation, pressure pulsations, vibrations, mechanical failures and frequent shut downs. Since silt erosion damage is on account of dynamic action of silt with the component, properties of silt, mechanical properties of the component in contact with the flow and conditions of flow. Therefore, these are jointly responsible for the intensity and quantum of silt erosion. Silt erosion is one of the most important technical problem for hydro-electric power stations experienced in silt laden water, and the pumping plants to be employed in diversion of solid particle-liquid two phase flow in many industrial and agricultural sectors. In regard to hydropower, micro hydro power (MHP) is gaining importance since it is a clean and alternative source of energy. The only problem in MHP is the high cost of turbine, for which Pump as Turbine (PAT) is an outstanding solution. Hence, it is important to study the impact of silt erosion in PAT and the related parameters which affects the efficiency of PAT. An objective of present study is to investigate the mechanism of silt erosion in Pump as Turbine (PAT) using numerical and experimental method. In numerical method, 2 phase flows has been simulated in Ansys simulation package and erosion model has been implemented to study the effect of silt concentration on erosion. An experimental setup has also been developed to analyze the effect of silt erosion in PAT. In experimental analysis, high impact areas `hotspdts' have been identified and the effect of silt concentration on the quantum of silt erosion has been studied. Hub has been identified as most erosion prone area of impeller in PAT. The maximum mass loss rate is 2.02 x 10-3 milligrams at 7500 ppm and minimum mass Ioss rate has _been. found as 1.35 x 10-3 milligrams at 3500 ppm. The results of the simulation have also been validated by the experimental analysis. Finally, an attempt has been made to develop a correlation for the silt erosion and the concentration of silt particles.