Parametric Studies on Sediment Erosion on Pump as Turbine

Abstract

Sediment erosion is the most affecting factor in the hydraulic turbines particularly in hilly area. Sediment ow may lead to increase in the maintenance cost, damage of turbine parts and on the long run it may even result in the complete failure of the turbine. Sediment erosion is the cause of dynamic actions of silt which ow along with the water; hence the complete removal of sediment from the water is not feasible. The objective of the present study is to carry out parametric studies on silt erosion effect on Pump as Turbine. The effects of specific silt size (700-1000 µm) was studied at three different concentrations viz. 0.5%, 0.75% and 1%. The experiments were performed at rated speed of 1400 rpm for three different time interval viz. 18 hours, 36 hours and 54 hours. As impeller material SS 304 is selected. To study the effects of silt erosion, 12 no.s of specimen cut from SS 304 sheet (0.25 mm thickness) were glued on the impeller on the blades as well as shrouds. The effects of silt erosion are studied using various approaches viz. visual inspection, mass reduction due to wear, increased in surface roughness, optical microscope and scanning electron microscope (SEM) image comparison. It was found that, due to silt erosion the roughness increased and mass of impeller decreased with increment in concentration and time of run. The roughness is increased by 367%, 411% and 422%; whereas the average mass loss in specimen was found as 0.60%, 1.44% and 1.65%. with silt concentrations of 0.5%, 0.75% and 1% after running the setup for 54 hours. From the SEM images of specimen, it was found that silt erosion leads to plowing, indentation and lip formation at different locations. Due to silt erosion the efficiency was decreased by 2 to 3% at different ow rates.