Experimental Investigation of Silt Erosion

Abstract

Erosion of underwater components by silt comprised water bodies is one of the biggest and most irritating situations in hydro turbines. Silt erosion problems are present for all types of hydraulics like runner, pump, guide vanes,etc. Erosion of hydro components depends on various parameters like silt size, concentration, hardness,water flow velocity, component material, operational time etc. Due to such problems arise decrease in efficiency and economic losses. During heavy rainfall, situation become hazardous as silt concentration reaches higher which may extend to turbine failure and setup breakdown. Complete nullification of silt from the water is not possible. Focus of this study is to carry out parametric studies of silt laden water on PAT at different concentration, time intervals and silt sizes. In the first phase of study, experiments were perfromed at different speeds and the maximum efficiency was found to be 57.17 % at 1200 rpm. To study the effects of silt erosion, SS 304 material sheets were embedded on the impeller. Experiments with silt water were done at at 1200 rpm at different concentrations of 0.5% and 0.75% at three different time intervals viz. 18, 36 and 54 hours. To observe behaviour of silt erosion 36 numbers of SS 304 strips were cut and glued on blades and shroud of impeller. Damages caused by silt erosion were analysed on the basis of 4 parameters i.e. mass loss, roughness variation in strips, optical microscopy, scanning electron microscopy. Because of silt erosion mass of steel strips decreased and roughness of strips increased as concentration & time interval proggressed. SEM images showed detailed view of SS 304 strips which gave information about indentation, plowing, lip formation. With 0.5% silt concentration, the roughness was increased by 151.5%, 152.7%, 154.1% after 18, 36, 54 hrs. The corresponding mass loss was found as 0.0459%, 0.0473%, 0.0507%.