A Study Comparing the Subsurface Vortex Characteristics in Pump Sumps

The vortex generated around the suction region of the pump sump causes problems such as damage to the pump, increased maintenance costs, and failure to supply coolant smoothly. Therefore, analyzing vortices is essential in pump sump design. However, the CFD analysis alone is insufficient in pump sumps vortex analysis since the reliability of the results is doubtful in scaled model tests. This study conducted the model test to validate a suitable CFD simulation method by identifying the Type 2 vortex among the three types of subsurface vortices. The dye test and PIV technology were used to visualize the Type 2 subsurface vortices, whereas the PIV vorticity results were then compared to the CFD results. The average vorticity of 60.2 (1/s) was identified as the reference level of Type 2 subsurface vortices formation by mapping the dye test results with the PIV vorticity results. Furthermore, the average vorticities of 84.63 (1/s) and 85.15 (1/s) were recorded in the presence of Type 2 subsurface vortices in PIV and CFD, respectively, and these values can be applied to the designing of pump sumps.

The Influence of Hydrodynamic Changes in a System with a Pitched Blade Turbine on Mixing Power

This paper presents an analysis of hydrodynamics in a tank with a 45° and 60° pitched blade turbine impeller operating while emptying the mixer and with an axial agitator working during axial pumping-down of water at different water levels above the impeller. Measurements made with the PIV method confirmed the change in direction of pumping liquid after the level dropped below the critical value, with an almost unchanged liquid stream flowing through the mixer. It was found that an increase in the value of the tangential velocity in the area of the impeller took place and the quantity of this increase depended on the angle of the blade pitch and the rotational frequency of the impeller. Change in this velocity component increased the mixing power.

Hydraulic Design and Power Characterization of Closed Turbine-Type Agitator

Designs of impeller as an agitator with alteration and modification of a conventional turbine type impeller were proposed to improve the power characteristics and to provide a favorable efficiency. For development of the turbine type impeller, a concept of the alterative design was for the impeller blades to transmit fully energy. This impeller has shrouds structurally and was named “closed impeller”. For baffled vessels agitated by the closed impellers, the internal liquid flow as well as the bulk liquid flow were examined to be analyzed for energy consideration. The closed impeller being modified, its internal flow was observed to be appreciably smooth along the blade surfaces. In evaluation in terms of hydraulic and energetic efficiencies indicating the phenomenon in the impeller swept region and that in the rest, respectively, the closed impellers were demonstrated to have improved power characteristics as an increased transmission and consequent uniformized dissipation.

Optimization design of submerged propeller in oxidation ditch by computational fluid dynamics and comparison with experiments

The operating condition of a submerged propeller has a significant impact on flow field and energy consumption of the oxidation ditch. An experimentally validated numerical model, based on the computational fluid dynamics (CFD) tool, is presented to optimize the operating condition by considering two important factors: flow field and energy consumption. Performance demonstration and comparison of different operating conditions were carried out in a Carrousel oxidation ditch at the Yingtang wastewater treatment plants in Anhui Province, China. By adjusting the position and rotating speed together with the number of submerged propellers, problems of sludge deposit and the low velocity in the bend could be solved in a most cost-effective way. The simulated results were acceptable compared with the experimental data and the following results were obtained. The CFD model characterized flow pattern and energy consumption in the full-scale oxidation ditch. The predicted flow field values were within -1.28 ± 7.14% difference from the measured values. By determining three sets of propellers under the rotating speed of 6.50 rad/s with one located 5 m from the first curved wall, after numerical simulation and actual measurement, not only the least power density but also the requirement of the flow pattern could be realized.