Mixed Flow Pump Impeller Reference Book a Guide to Design, Modelling and Analysis

The mixed flow pumps are generally being used in large thermal power plants for cooling water duties. The mixed flow pump is a unification of radial and axial characteristics. The design of mixed flow impellers of high specific speed is a direct extension of the well-established empirical methods of the designing of radial flow impellers. The extension of similar methods serves for the design of mixed flow impellers, but the introduction of near diagonal flow layout at a still larger specific speed stimulated the incorporation of axial pump impeller design techniques in mixed flow pump technology.

The usual industrial practice of mixed flow pump impeller design starts with the estimation of approximate meridional streamlines by dividing the annulus by the equal area method. Empirical co-efficient depending on the specific speed are used to fix the inlet and outlet blade angles. Similar co-efficient are used to determine overall impeller layout before the meridional streamlines are estimated. The inlet and outlet angles being fixed in this manner, the blade sections are laid out on the developed stream surfaces. The shape of the composite blade is controlled by adjusting the shape of the blade sections on the adjusted stream surfaces.

The above industrial method is basically based on some empirical co-relations and design constants. The industrial design method often ignores the actual happening within the pump flow passage and is consequently a poor guide when the question of a new design and development of pumps comes to picture. In the above design process the designer has less control than desirable over events. The lack of clear cut rational basis also inhibits the correction of manufacturing of shortfalls in expected performance.

To overcome the above difficulties, one has to formulate a rational basis for the designing of impellers starting from basic principles, such that the use of empirical co-relations is minimized. Such a design from the basic principles has advantages that the designer will have more control over the outcome of his design, while keeping the physical principle constantly in view and enables him to rectify any faults in the performance of the pump.

In view of the above, it is decided to design a mixed flow pump impeller using the basic principles of fluid mechanics and turbo machinery. Finally, after the design of the impeller is completed, modeling software is used to draw the 3-Dimensional model of that impeller, ANSYS analysis software is used to estimate the stress under uniformly distributed and uniformly varying load and as well as natural frequency is calculated, simulation of the same has been carried out to find out the design acceptability. Last but not the least artificial neural network method used to validate the results of impeller blades i.e. acceptability of inlet inclined position blade is a better choice than regular trapezoidal positioned blades.