Sample Engineering Paper on Computation Fluid Dynamics; Improving the Efficiency of the Impeller of Centrifugal Pumps

Abstract

The paper looks at centrifugal pumps, its composition and how its different parts help it achieve the intended purpose. Consequently, the paper will look at its uses and applications in easing workloads. Basically, the paper will look at centrifugal pumps from four key sections; introduction, methodology, literature review, discussion and conclusion. The introduction will introduce the pumps giving the key components, use and how they operate while the methodology will present the data methods used in collecting data on its usage and analysis. Accordingly, the literature review will provide an in-depth analysis of the research initiatives conducted in the centrifugal pumps using the CFD, with the discussions providing the analysis of the use and application of the pumps, while the conclusion will give deductions concerning the pumps, its properties and applications.

Table of Contents

Abstract 1

Table of Contents. 2

Introduction. 3

Centrifugal Pump. 3

Computational fluid dynamics (CFD) 5

Methodology. 6

Literature Review.. 6

Performance Prediction. 6

Parametric Study. 8

Cavitation Analysis. 9

CFD in Enhancing the Efficiency of Centrifugal Pumps. 9

Discussion. 11

Conclusion. 13

Works Cited. 15

Introduction

Centrifugal Pump

A centrifugal pump is composed of impellers, which are a set of rotating vanes enclosed in a casing. The rotation of the impellers allows flow of fluid from inner to outer radius. This process allows for the creation of suction at the eye of the impeller hence facilitating continuous lifting of fluid from pump to pump. The process facilitates the conversion of kinetic energy into pressure energy and the development of head from the fluid emanating from the delivery pipe (Wen- Guang 119-120). The growth and acceptance of centrifugal pumps is attributable to industrial developments and advances in combustion machines, steam turbines, and high-speed electric motors. Centrifugal pumps are hydrodynamic machines fitted with rotating impellers that continuously transmit mechanical work from the driving machine to fluid. The ability to convert kinetic energy into pressure energy makes it necessary to enhance their efficiency of the impellers and volute casing used in these pumps using computational fluid dynamics (Wen-Guang 120).

Figure 1.0 Working principle of centrifugal pump

Research and development initiatives targeting centrifugal pumps have resulted in improvement in their performance. They have also ensured the introduction of new construction materials, which have necessitated an expansion of their field of applicability. In the contemporary construction field, it is common to find efficiencies of 90%+ for large centrifugal pumps and better than 50% for small fractional horsepower units. In centrifugal pumps, electrically operated motor helps in the production of mechanical energy. The water or fluid, which is operated by motor, is forced by the pump into the expectation of the desired work, which results in the production of hydraulic energy. Centrifugal pumps are part of the hydrodynamic machines, which use rotating impellers in the transmission of mechanical work from the driving machine to fluid; this allows for the conversion of kinetic energy into pressure energy.

Computational fluid dynamics (CFD)

Applied mathematics, physics, and computation software are encompassed in the dynamics of computational fluid, as well as their effect on the objects they move along. CFD is based on the Navier-Strokes equations that provide descriptions of the relationship between the temperature, density, velocity, and pressure of a moving fluid. CFD has been used as a tool for analysis of data, especially in understanding the thermal properties and modeling of fluid flow. For its functioning, CFD software uses layout, size, and content to the data center information to create a three-dimensional mathematical model on a grid. This can be viewed by rotation from varying angles. This approach to CFD modeling enables an administrator to engage in effective identification of hotspots, thus learning of where there is a mixture of fluids. By changing variables, it is possible for an administrator to visualize the flow of fluid under different circumstances. This information can be helpful in the optimization of the efficiency of an existing infrastructure and engage in effective prediction of the efficacy of a particular layout of information technology equipment. This is because CFD has the ability of stimulating changes that help administrators in understanding areas in need of necessary adjustments in a cost-effective manner.

CFD plays instrumental role in the prediction of pump performance when functioning at different rotational speeds. The analysis of mechanical behavior is often facilitated by numerical simulation. When integrated as part of centrifugal pump operationalization, CFD provides an accurate and cost-effective alternative in scaling model testing using variation on the simulation being performed. CFD employs discretization, a numerical methodology in the development of approximations that govern equations of fluid mechanics in the fluid area of interest (Aman et al. 60).

Methodology

Data collection throughout the research was defined by extensive research of secondary data concurring the use of computational fluid dynamics in improving the effectiveness and efficiency of the impellers of centrifugal pumps. This involved in-depth review of multiple research studies of computational fluid dynamics and centrifugal pumps. The methods, result, and conclusions of the secondary sources of data were analyzed and used in the synthesis of a conclusion and development of recommendations on the topic.

Literature Review

The dynamics and demand charge pump engineers with the responsibility of providing machines that can operate more proficiently, unobtrusively, and consistently at affordable costs. In an attempt to meet this dynamic demand of the market, engineers have been involved in the application of CFD as a numerical simulation tool to conduct varieties of investigations on ways of improving on the efficiency of impellers of the centrifugal pumps. This section provides an in-depth analysis of the research initiatives conducted in the centrifugal pumps using the CFD approach.

Performance Prediction

Centrifugal pumps are used in many applications and this explains why the pump system may be required to operate over a wide range of applications. Efforts have been made focused on the design of state-of-the-art pumps. With the incorporation of CFD, it has become possible to study the complex flows through different components of pumps operating in different conditions with the objective of improving their performance at off-design conditions. In their numerical simulation research on the internal flow in a backwards curve vanned centrifugal pump, Mentzoset et al. (22-31) assert that the MRF approach in taking into consideration the impeller-volute interaction was a complete failure. This is because of its fixed coupling formulation. Despite this failure, this approach was successful in recommending for the development a foundational understanding of flow at various operating points. Furthermore, it enhanced the use of the transient analysis as an instrument for understanding the interface between spiral casing and impeller.

Figure 2.0: (a) Centrifugal pump in a three-dimensional computational model and (b) the inert pressure contours a centrifugal pump.

Using the MRF approach, Mentzos et al. (32) replicated the flow through the impeller of the centrifugal pump using finite volume methodology. This was used in collaboration with a structured grid system for a solution to the discretized governing equation. Their approach also emphasized on the application of the CFD methodology in flow patterns prediction, distribution of pressure distribution, and head capacity curve. Their studies report that despite the insufficiency of the grid size in facilitating an operative examination of the local boundary layer variables, they were able to capture the comprehensive variables. The aim of the approach was to advocate for the development of basic understanding of the flow of fluid at various operating points.

Parametric Study

CFD helps in predicting the flow behavior in different parts of any hydraulic machine before commencing with the manufacturing process. In cases whereby modification of the existing system is necessary, the process can be incorporated in a numerical model, and its impact can be predicted prior to the implementation process. This means that through the CFD process, it is possible to study the effects of various factors from an independent approach or through the formation of non-dimensional groups on the performance of pumps. In his analysis of the performance of pumps, Bacharoudis et al. varied the outlet blade angles by maintaining the same outlet diameter (77-78). This analysis process also included the incompressible Navier-Strokes equations and the 3D numerical simulation using a commercial CDF finite volume code. The analysis reveal that at a trifling capacity, especially by increasing the outlet angle from 20°-50°, there was more than a 6% increase in head and 4.5% reduction in hydraulic efficacy. Nevertheless, at high flow rates, increasing the outlet flow angle resulted in significant improvement of the hydraulic efficiency.

From this analysis, Anagnostopoulos developed a numerical model for the simulation of the 3D turbulent flow into the centrifugal pump impeller with the objective of solving the RANS equation (763-764). The representation of the impeller geometry characterizes this model. Characterization occurs using varieties of manageable project variables that provide the ability of amending the shape of the impeller with the objective of testing different configurations. According to the resulst of the parametric study, there was a remarkable gain in hydraulic efficiency, which was realized through the optimization of the impeller geometry.

In their numerical study on the effects of changing the stator angle and hub curve profile in mixed flow pump at operation point and at part load, Patel and Ramakrishnan concluded that the nature of power and head versus capacity curves obtained was similar to that of standard mixed flow pump (22). Furthermore, they also concluded that the reduction of pump efficiency was possible within a +5% range at duty point. However, in their study, there was an observation of more variation at off-design conditions and this led to the conclusion that there was a 1%+ improvement after changing hub curve profile and matching of stator angle.

Cavitation Analysis

Cavitation is a possible occurrence at different regions of the pump, especially when the vapor pressure, which corresponds to fluid temperature, is above the local pressure. While using the multi-phase CFD methodology in the analysis of the performance of centrifugal pump performance under cavitation conditions, Lindau, Adam, and Laura used the homogenous two-phase RANS equation in the solving volume continuity and mixture continuum equations together with vapor volume fraction (377-380). This study involved an observation of the blade cavitation and performance trends of partial discharge. Through quantitative comparison with experimental results, the objective was to assess the effects of cavitation on pump performance. From the study, it was concluded that at high flow rates, there were cavitation bubbles at the pressure side, which resulted in gradual reduction of head. The multiphase CFD model was able to predict the gradual drop despite the inconsistencies of the computations.

CFD in Enhancing the Efficiency of Centrifugal Pumps

According to Jin et al., the popularity of centrifugal pumps is attributable to its increased use in various applications in the industrial field (110-114). These include the petroleum, chemical, pharmaceutical industries, and in space technology. The gradual development of the centrifugal pump was to accommodate ultra-low specific speed whereby the pump speed is high with a low flow rate. The GSB20-380 is a hydraulic model of centrifugal pump developed with ultralow speed. Its design parameters were focused on the volute part. For the effectiveness of this hydraulic machine, the design adopted the 3D solid model characterized by five blade impellers. To improve on its efficiency, the design process ensured that the speed calculation and boundary conditions for the area were uniform. The impeller intended sign is the rotating boundary while the thermal insulation is the solid wall boundary condition. This is an indication that through the incorporation of the CFD simulation in the development of hydraulic model, it is possible to enhance the efficiency of the centrifugal pump considering that the head and efficacy of the resulting product is higher than that of similar product performance.

Figure 3.0: The effect of periodic upkeep on pump efficacy

For improved efficiency of the centrifugal pump, it is possible to redesign the major components such as casing or impeller using the inverse design with singularity method. According to Wen-Guang, this is considered possible through the establishment of a cubic Bezier curve used in the expression of mathematical density function of bound density vortex intensity along the blade camber line (125). Through this curve, it becomes possible to acquire smooth, well-loaded, and carefully controlled blades. The curve facilitates the valuation of the loading constant and differences in pressure across blades in the original impeller. This ensures that it is greater than the remodeled impeller. According to Wen-Guang, the findings from CFD analysis assert a 5%+ improvements in the efficiency of the impeller hydraulic (123).

CFD can also play a critical role in the prediction of the performance of a centrifugal pump when testing occurs against the complex internal flow. This is enhanced through the incorporation of the SIMPLEC algorithm and the standard k-€ turbulence model for the prediction process. Furthermore, the process can also be facilitated by the organization of fundamental equation of fluid dynamics in rotating and stationary reference frames. Aman et al., argue that it is possible by understanding the flow passage through the display of velocity distributions, the trajectory, and curve plot of pressure (61). Upon such display, an analytical formula is used in the comparison and simulation of results for head and flow rate. The process thus leads to the development of the conclusion that the flow patterns that define the operationalization of centrifugal pump can be described through the movement of turbulence model and reference frame.

Discussion

There is a wide application of centrifugal pumps in different industries. In typical industrial operations, the diameters and concentration of solid particles are dependent on the type of slurry for a particular application. Dense slurry flow inside a centrifugal pump casing using the Eulerain multiphase model is characterized by a mixture of the k-€turbulence model essential in modeling turbulence. The process of validating existing predictions is through the comparison of experimental data with published numerical results. The verification of the results of concentration distribution and velocity occurs against rigorous mesh dependence coupled by validation of results in case pump casing using FEM based numerical results (Pagalthivarthi et al. 254-255).

Centrifugal pumps are categorized in the group of turbo machines which are engaged in large-scale industrial operations at industrial levels. This means that the main objective in redesigning centrifugal pumps based on CFD approaches is to increase their efficacy while decreasing the net positive suction head. For this to be realized, it becomes important to investigate centrifugal pumps using numerical approaches such as the Genetically optimized Group Method of Data (GMDH). This is a Numeca software that is used in obtaining polynomial models for the effect of geometrical parameters of the centrifugal pump on both efficiency and net positive suction head (Safikhani, Khalkhali, and Farajpoor 37-40). This approach focuses on the metamodelling of CFD results that allows for iterative optimization techniques for optimal designs. This is an indication that simple polynomial approaches used in a multi-objective optimization model can assist in finding the best combination for net positive suction head and efficiency.

Research is often concerned with the rise of head, which is affected by changes in the angle of the outlet blade. Through systematic research in the effects of the existing design elements of centrifugal pumps, it is possible to assess how their performance in different ranges of flow rates can be improved through experiments and numerical predictions. This is founded on the understanding that when the angle of an outlet blade increases, the performance of the impellers also increases. This is because the performance curves become flatter and slicker throughout the flow rates. When centrifugal pumps are operating at a normal capacity, there is 6%+ gain in the head and a decrease of 5%+ in their hydraulic efficiency. Moreover, when there is at high flow rates, the angle of the outlet blades increases. This often results in substantial enhancement of hydraulic efficacy especially when the calculation of the minimum radial pressure or forces is done from the best efficiency point.

Using a CFD code such as FLUENT, it is possible to conduct the flow analysis of two or more centrifugal pumps in a comparative manner. Through this approach, it becomes possible to develop solutions for the calculations or equations for the analysis of turbo machinery flow. Through the incorporation of Sliding Mesh (SM), multiple references frame (MRF), and Mixing Plane (MP), it is possible to solve steady and unsteady flow equations comparatively. This is because while the SM provides better results, MRF and MP methodologies give physical approximations and results that are far from the best efficiency point (Dick 579-580). With the help of CFD, it is possible to predict the complex internal flow in the horizontal split case pump. This process facilitates the design of the centrifugal pump. Through CFD, it is possible to determine the most effective impeller diameter and the techniques of modifying the volute design to give better efficiency (Kadam et al. 1-4).

Conclusion

CFD simulation has the ability of verifying the influence of the outlet blade angle on the performance of centrifugal pumps. This was facilitated by the realization that at high flow rates, and by increasing the angle of the outlet blade, there is often a substantial improvement in the efficacy of the centrifugal pumps. The optimization of the hydraulic design of the impeller of centrifugal pumps is possible through trial and error methodologies or through the introduction of changes in the input designs of the impellers. Through CFD results, it is possible to assess the mechanical behavior of impeller parts using numerous parameters such as velocity contours. This can be used in the prediction and in the optimization of the designs of the centrifugal pumps that are to be manufactured or modified. 

Works Cited

  1. Aman, Abdulkadir, Kore, Sileshi and Dribssa, Edessa. “Flow Simulation And Performance Prediction Of Centrifugal Pumps Using CFD-tool,” Journal of EEA, Volume 28, 2011, 59-65.
  2. Anagnostopoulos, John S. “CFD analysis and design effects in a radial pump impeller.” Wseas Transactions on fluid mechanics 1.7 (2006): 763.
  3. Bacharoudis, E. C., et al. “Parametric study of a centrifugal pump impeller by varying the outlet blade angle.” Open Mechanical Engineering Journal 2.5 (2008): 75-83.
  4. Dick, Eric, et al. “Performance prediction of centrifugal pumps with CFD-tools.” Task quarterly 5 (2001): 579-594.
  5. Jin, Jie, et al. “Design and analysis on hydraulic model of the ultra-low specific-speed centrifugal pump.” Procedia Engineering 31 (2012): 110-114.
  6. Kadam, V. S., et al. “Design and development of split case pump using computational fluid dynamics.” Institute of technology, Nirma University, Ahmedabad (2011): 1-4.
  7. Pagalthivarthi, Krishnan V., et al. “CFD predictions of dense slurry flow in centrifugal pump casings.” International Journal of Aerospace and Mechanical Engineering 5.4 (2011).
  8. Wen-Guang, L. I. “Inverse design of impeller blade of centrifugal pump with a singularity method.” Jordan Journal of Mechanical and Industrial Engineering 5.2 (2011): 119-128.
  9. Lindau, Jules W., Adam M. Yocum, and Laura L. Pauley. “Performance analysis of cavitating flow in centrifugal pumps using multiphase CFD.” (2002).
  10. Patel, Kiran, and N. Ramakrishnan. “CFD analysis of mixed flow pump.” International ANSYS Conference Proceedings. 2006.
  11. Safikhani, H., A. Khalkhali, and M. Farajpoor. “Pareto based multi-objective optimization of centrifugal pumps using CFD, neural networks and genetic algorithms.” Engineering Applications of Computational Fluid Mechanics 5.1 (2011): 37-48.