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Chemical Pump Designing a New Chemical Pump for the Global Market

Author / Editor: Norbert Kastrup / Dominik Stephan

A chemical pump must meet a variety of standards. Against the background of these standards, it seems very difficult to generate additional value for the customer that is not already explicitly covered in the standards’ scope. Nevertheless, designing a new chemical pump opens up new opportunities if expertise concerning application and experience in the field is taken as the basis for improvements.

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Back vanes (left) and balancing holes in conjunction with a throttling device (right) are two options to reduce axial thrust caused by different pressure profiles at the front and the rear impeller shroud.
Back vanes (left) and balancing holes in conjunction with a throttling device (right) are two options to reduce axial thrust caused by different pressure profiles at the front and the rear impeller shroud.
(Picture: KSB)

KSB’s decision to substitute the 45-year-old ISO 2858 pump type CPK/ CPKN with the new chemical pump type Mega CPK was driven by the recognition that the chemical industry is an increasingly global industry whose requirements exceed those stipulated in worldwide standards.

The following paper tries to quantify customers’ technical benefits concerning the efficiency, hydraulic selection chart, variant flexibility, reliability, ease of maintenance and feedback to the installation by, as far as possible, only applying the variation of materials and shape. It should be noted that the quantitative values are obtained from tests and are not based on estimates or extrapolations.

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Efficiency of Chemical Pumps

Testing is still regarded as a reliable method for investigating the flow inside a pump. However, it is a disadvantage of all experimental studies that they are timeconsuming and expensive. Therefore, stateof- the-art tools such as computational fluid dynamics (CFD) are used. Computer-based simulations can provide detailed insights into the complex flow processes inside a pump, for example in terms of their efficiency and performance curve.

Any computer-based simulation starts with the three-dimensional geometry of the component. In preparation for the flow simulation, the flow-guiding surfaces must first be digitized; i.e. the components (for example the impeller) are provided with a surface mesh. The resulting volume is addressed in a step called ‘pre-processing’, during which a computational 3D grid is generated.

Computer Based Simulation for Pump Design

The quality of the 3D grid is largely responsible for the quality of the simulation results. While surface grids are partly generated manually, the spatial 3D grid is generated automatically. Defining the requirements of specific boundary conditions for the operating point (speed, flow rate), the physical properties of the fluid (density, viscosity) and the computational mode complete the pre-processing stage.

After formulating the inlet and outlet boundary conditions, the actual computerbased simulation procedure begins. Here, the computer operates automatically and without user intervention. The resulting solution is evaluated, analyzed and documented. If the result does not fulfill expectations, the geometry of the model is modified and the process begins again.

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