Effects of Silt Erosion on Pump Running in Turbine Mode

Abstract

One of the most affecting factors for the life of hydro machines is sediment erosion. Sediment erosion occurs mainly due to high concentration of silt particles present in the water. Due to sediment erosion all the water passage parts may be adversely affected and sometimes may lead to the failure of the whole machine as well. It also increases the maintenance as well as running cost of the plant. In the present study, effects of silt erosion are studied on the performance of service pump (used for artificial head generation) as well as pump running as turbine. The silt of specific size (250 μ -500 μ) was mixed with the water by 5% (by weight) in the underground tank. The agitator was designed, developed and installed on the underground tank for proper mixing of silt with water. The agitator (material: SS 304, impeller diameter: 55 cm, number of blades: 3, speed: 80 rpm) coupled with gear box and motor (capacity: 1.5 hp) was installed on the water tank (L X B X H: 2.5 m x 2 m x 1.5 m). The effects of silt erosion were studied in terms of change in mass and roughness of impeller, comparison of microscopic images taken using Scanning Electron Microscope (SEM) as well as effect on hydraulic performance of PAT. From the SEM images of PAT impeller, it was found that silt erosion led to indentations and plowing in the blade passages. The surface roughness of the impeller was increased from 1.371 μm to 1.962 μm . The silt erosion resulted in decrease in mass of impeller, power output and PAT efficiency by 0.26 %, 3-4% and 2-3 % respectively at different operating conditions.