The Effect of Backward Curved Back Vanes and Back Channels on Fiber Entry Into the Back Shroud Cavity of a Wastewater Pump

Abstract In this paper, the influence of different back vanes (BVs) and back channels (BCs) on fiber entry into the back shroud cavity is experimentally investigated. Vane and channel contours correspond to backward curved blades of a semi-open two-channel impeller. The configurations feature varying axial gap widths between back shroud and rear housing wall. Vane height and channel depth are also changed throughout the tests. Vane and channel width as well as number are constant. The axial gap width between rear housing wall and back vane top or channel ground is constant as well. For each configuration, the operating points part load, best efficiency point, and overload are examined. Tested configurations are compared to unmodified reference configurations regarding fiber dry mass accumulated in a defined area within the back shroud cavity after a test duration of 60 min. The experiments demonstrate that selected back vane configurations reduce fiber entry by up to 100%, causing minor decreases in operating point-averaged overall efficiency of 0.8% and less. The back channel configuration investigated at minimum axial gap width eliminates the minor fiber entry of the reference configuration, decreasing operating point-averaged overall efficiency by 0.9%. In contrast, mean fiber entry is significantly increased by the back channels at larger gap widths by up to 0.679 g. Except for one back channel configuration with minor fiber entry of up to 0.046 g, none of the presented back vane or back channel configurations shows fiber entry at part load.