PIV Measurement of Flow Conditions Near Casing Tongue of Mini Centrifugal Pump

Abstract

Flow conditions near the casing tongue have a significant impact on the performance and stable operation of the centrifugal pump, so the internal flow conditions have been measured by the experiment and PIV measurement. The internal flow conditions of mini centrifugal pumps especially smaller than 100mm are less measured by PIV measurement and its flow conditions near the casing tongue are not clarified yet. Therefore, PIV measurement was conducted near the casing tongue for the mini centrifugal pump having 55mm impeller diameter. The two-dimensional open impeller with the large blade outlet angle  2 =60° was selected as the test impeller. FlowMaster Stereo-PIV by LaVision was used for the PIV measurement and the whole test section was made of the acrylic resin including the test impeller. Two CCD cameras with its resolution 2048×2048 pixels were used and velocity vector and contour were calculated by the PIV measurement software DaVis(Lavision). The internal flow conditions near the casing tongue were focused in this research. The PIV measurement results at different flow rates were shown and the tongue flow angle was defined to clarify the flow condition near the casing tongue with the impeller rotation. With the increase of the flow rate, the tongue flow angle increases which means the flow near the casing tongue is discharged to the casing throat. In the present paper, the internal flow near the casing tongue is clarified by PIV measurement results and the flow conditions with the impeller rotation are discussed. the dynamic head difference of the sectional averaged axial velocity to the corresponding measured static head difference. The rotor was driven by the motor. The flow rate Q was obtained by a magnetic flow meter KEYENCE FD-UH25G, measurement accuracy ±0.5%, installed far downstream of the pump and the torque was measured by a torque meter ONO SOKKI SS-010, measurement accuracy ±0.2%. The shaft power was calculated by the torque and rotational speed measured by a rotational speed sensor ONO SOKKI MP-981. The shaft power was evaluated by the torque eliminating the mechanical loss and disc friction loss using a disc without the impeller in this performance test. Then, the hydraulic efficiency of the pump  was calculated as the ratio of the water power to the shaft power.