Characteristics of Centrifugal Pumps with Low Specific Speed

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Name of Student
Institution Affiliation
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RESEARCH METHODOLOGY
Abstract
This study presents the characteristics of the centrifugal water pump with low specific
speed. The relationships between the vane exit angle, impeller diameter and blade width at the
exit are studied in order to evaluate the characteristics of the centrifugal pump. Discharge is
highly affected by outlet conditions, flow resistance and the impeller and casing design
parameters since this particular pump is a non-positive type. Thus, it is important to obtain the
working conditions and design parameters that consume little power to produce optimal output
and give the highest efficiency. This report aims at the evaluation of the performance of a
centrifugal pump for the above-mentioned specifications. It is a common knowledge that varying
certain design parameters is what leads to the development of various models of pumps.
Experimental design optimization (DoE) uses response surface method (RSM), computational
fluid dynamics (CFD) optimization and analysis are performed on the ready-made models to
virtually simulate the performance and compare with results obtained from experiments. The
response surface method helps to formulate the optimal design of the pump. The objective
functions of the centrifugal pump are given by the total head and the total efficiency at the design
rate of flow.
Background information
The scope of centrifugal pumps application is wide for, industrial, domestic, institutional
and other fields. However, the existence of a big number of geometric parameters has made the
processes of their design and prediction of performance a challenging task. Therefore, pump
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manufacturers have resorted to trial-and-error methods of testing prototypes to predict and
optimize performance. However, this method is time-consuming and costlier to the
manufacturers leading to higher cost of production, hence lower profit margins. Owing to that,
many manufacturers have begun embracing computational fluid dynamics in hydrodynamic
design to do prototyping and analysis for various types of pumps (Baloni et al, 2015).
Centrifugal pumps have been widely used for a long time for water supply plants,
irrigation, steam power plants, chemical plants, oil refineries, mines, food processing and
hydraulic power services due to their suitability in practice of any service. Many African and
Arabian countries are facing great challenges of drought due to the global warming effect. Hence
it is very important to find out the working conditions and design parameters that deliver ideal
output and greatest efficiency with the minimal power consumption to ensure that better
centrifugal pumps have been developed to aid in the irrigation and water supply. Many of the
projects which have been initiated by their governments and other international Humanitarian
organization have significantly failed due to the high cost of running the projects
In the recent past, the application of computational fluid dynamics analysis has
dramatically gained grounds in the design of the centrifugal pumps. With the help of the
computational fluid mechanics approach, the internal flow of fluids in the pump impellers can,
therefore, be easily predicted (Ajay et al, 2017). The centrifugal pumps are known to deliver
essential energy to the fluid which is to be pumped greatly through the velocity changes which
occurs in the centrifugal pump. It involves conversion of mechanical energy to hydrodynamic
energy of the handling fluid needed to get the fluid to the required height or place by the impeller
blade or centrifugal force. The input energy of the hydraulic pump is mechanical such as a
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mechanical motor or a small engine, but the output energy is the hydrodynamic energy of the
fluid which is being raised (Jung et al, 2016). The previous modifications which have been done
to the centrifugal pump have yielded very little regarding improving the efficiency of the
centrifugal pumps. I propose that the performance of the centrifugal pumps can be improved by
decreasing the impeller outlet width, increasing the impeller outlet diameter, increase the
impeller outlet blades height, increase the impeller blade outlet angle and increase the number of
blades on the impeller. In this project, I want to come up with the ways through which the design
of the centrifugal pump can be optimized to achieve high efficiency by use of computational
fluid mechanics and other computer software.
It is significant to analyze the performance of a centrifugal pump since it is widely used
in various fields for large-scale pumping systems. In addition, it is one of the most useful and
mechanical rotordynamic machines for fluid works. Similarly, it is important to note that
centrifugal pumps are used in applications with moderate head and discharge requirements
(Škerlavaj et al, 2017). Currently, a lot of research is being conducted to increase its efficiency,
performance improvement as well as to reduce the losses associated with it such as losses due to
impeller, disk and volute friction, losses of recirculation, shock losses, and turbulence losses as
well as power consumption issues. Time-consuming, costly and limited scope experimental
investigation procedures have been conducted on pumps for years. To curb this problem or
decrease the number of experiments, computational fluid dynamics software offers a platform
where virtual analysis can be used to predict the performance of various pump models (Cao &
Zhang, 2017).
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This study was primarily carried out to identify the design parameters as well as
modifying them with an aim of improving the characteristics of the pump performance. This
paper was done in with two software. Two software was used for the optimization of the
performance of the centrifugal pump. The first part employs the services of computational fluid
dynamics (CFD) and part two uses the response surface method (RSM) software for
optimization. The fundamental design parameters are put into consideration for the numerical
and experimental analysis of performance where computational fluid dynamics was used to
evaluate the design parameters along with an intensive study of experiments. The ANSYS-
FLUENT code will also be applied in the (RSM) to give numerical solutions to the equations as
well as to carry out numerical simulations. Figure 1 below gives a detailed discussion of the
methodology used to optimize the design parameters.
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Figure 1. Research methodology (Cellek & Engin, 2016)
Literature review
Centrifugal pumps refer to a sub-category of dynamic axisymmetric turbomachinery.
They pump fluids by converting rotational kinetic energy to hydrodynamic energy of the fluid
flow. An electric motor or a fuel engine provides the rotational energy. There is an impeller
which accelerates the velocity of the fluid as it radially flows into a volute chamber (diffuser).
The fluid acquires pressure and velocity as it passes the impeller. The volute further increases the
pressure while decelerating the fluid flow (Najafi et al, 2017).
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