Impeller Trimming Research Articles

Optimal selection of parallel pumps running as turbines for energy harvesting in water transmission lines considering economic parameters

The need for energy is growing due to concerns about development and well-being, but the traditional methods of energy production harm people and the environment. This impact can be reduced by using renewable energy sources like hydropower. Since the cost of electromechanical equipment in small hydroelectric power plants accounts for a large percentage of the capital cost, applying the pump as turbine (PAT) is recommended. In this research, an effort has been made to select the optimal arrangement of PATs for a water transmission line without the need for control systems. The selection optimization process involves selecting the model of the pump as turbine and the number of turbines in parallel simultaneously. The optimization process relies on economic parameters, aiming to maximize the Net Present Value (NPV) of the power plant. In addition, the financial analysis of the project has been carried out. As a first step to achieve this objective, a database including single and double-suction pumps based on available pumps is needed. To cover a wider range of heads and flow rates, impeller trimming relationships for the pumps are considered. The Brute-Force algorithm has been used for the optimization process and two different objective functions (OF) have been investigated. First, it is based on economic optimization, and the NPV function is used as the OF; then, the Multi-Criteria Decision Making (MCDM) method is used as the second OF. The case study of this research is a water transmission line between two cities in Iran. A MATLAB code has been developed to perform all the steps of this study. The results demonstrate that by considering impeller trimming for pumps in the database and using NPV as OF, the number of pumps used for the power plant decreased from 12 to 6 and the capital cost decreased by about 10%. By implementing impeller trimming, the NPV and energy production of the PAT power plant are increased. Comparing the two desired objective functions leads to the recommended appropriate OF for applications. It is worth mentioning that the harvested energy from this water transmission line is about 9 GWh/year. The economic analysis results show that the PAT power plant payback period (PP) for this water transmission line is less than one year.

Enhancing Hydropower Generation through Pump as Turbine (PAT) System Optimization

Abstract: Pump as Turbine (PAT) systems, operating in reverse mode to transform mechanical energy into hydraulic energy, pose unique challenges in the pursuit of optimal performance for hydropower generation. This research leverages the power of ANSYS CFD/CFX simulations to delve into the impact of various impeller trimming configurations on the efficiency and effectiveness of PAT systems in the context of hydropower generation. The research involves a systematic approach that includes CAD modeling and meshing to analyze three base models: PAT Case 1 (Ø255 mm, 6 blades), PAT Case 4 (Ø230 mm, 6 blades), and PAT Case 7 (Ø215 mm, 6 blades). To validate the simulations, a comparison is made with reference models (PAT reference Ø255 and 6 blade configuration, PAT reference Ø230 and 6 blade configuration, PAT reference Ø215 and 6 blade configuration). The findings of this study show that increasing the number of blades from 6 to 7 results in significant improvements in head, power output, and efficiency. However, further increases to 8 blades demonstrate diminishing efficiency gains. Moreover, reducing the impeller diameter proves to be a beneficial factor in enhancing overall system performance. Among the configurations tested, the Ø215 mm diameter with 7 blades stands out as the top-performing option. This design offers promising potential for maximizing pump efficiency in practical hydropower applications.

Effect of Impeller Trimming on the Energy Efficiency of the Counter-Rotating Pumping Stage

Developing ways to increase centrifugal pumps’ pressure and power characteristics is a critical problem in up-to-date engineering. There are many ways to resolve it, but each has advantages and flaws. The presented article aimed to ensure higher energy efficiency indicators by using a counter-rotating pumping stage with trimming. During the research, the comprehensive approach was based on CFD modeling and the Moore–Penrose pseudoinverse approach for overestimated systems. According to the obtained data, pumps with a counter-rotating stage allowed the pressure head to be significantly increased compared with the standard design of the flow part. Notably, for pumping units CPS 180/1900 with a basic stage, the pressure head of 127 m was reached. However, when using a counter-rotating stage, the pressure head could be increased up to 270 m, which was 2.1 times higher. Therefore, to ensure unchanged characteristics when using centrifugal pumps with the counter-rotating stage, the weight and size indicators can be significantly reduced compared to the traditional design scheme. The proposed numerical and analytical approaches allow estimating the highest pressure and energy characteristics values.

Studying the variation of the slip factor when trimming the impeller of centrifugal pumps

It is well-known that one of the reasons for reducing the head of a centrifugal pump, when trimming its impeller, is the reduction of the slip factor. There are various methods used to determine it, but there is lack of information on whether they are applicable in case that a pump with a trimmed impeller operates. In the present work, a comparative experimental study concerning the applicability of some of the methods used to determine the slip factor, on two centrifugal pumps with different specific speed of rotation, is performed. Based on the experimental data, CFD models of the impellers of the two pumps have been validated and a numerical simulation study concerning the change of the slip factor during trimming, has also been performed. The impact of the rate of impeller trimming on the the slip factor variation has also been established. Based on the results found, concerning the performed numerical study, equations describing the relationship between the slip factor and the rate of trimming of the studied pumps are obtained.

Performance Prediction and Geometry Optimization for Application of Pump as Turbine: A Review

Pump as Turbine (PAT) is a technically and economically effective technology to utilize small/mini/micro/pico hydropower, especially in rural areas. There are two main subjects that influence the selection and application of PAT. On the one hand, manufacturers of pumps will not provide their characteristics under the turbine mode, which requires performance prediction methods. On the other hand, PAT efficiency is always slightly lower than that of pump, which requires further geometry optimization. This literature review summarized published research studies related to performance prediction and geometry optimization, aimed at guiding for selection and optimization of PAT. Currently, there exist four categories of performance prediction methods, namely, using BEP (Best Efficiency Point), using specific speed, loss modeling, and polynomial fitting. The using BEP and loss modeling methods are based on theoretical analysis, while using specific speed and polynomial fitting methods require statistical fitting. The prediction errors of published methods are within ±10% mostly. For geometry optimization, investigations mainly focus on impeller diameter and blade geometry. The influence of impeller trimming, blade rounding, blade wrap angle, blade profile, blade number, blade trailing edge position, and guide vane number has been studied. Among published methods, the blade rounding and forward-curved impellers are the most effective and feasible techniques.

Effect of Impeller Trimming on Centrifugal Pump

Pumps, especially centrifugal pumps, play an important role in engineering application, such as petroleum and petro-chemical industries, agricultural industries, portland cement industries etc. To obtain the best performance of the pumps, one has to operate the pumps at their design conditions. In some circumstances, however, the pumps must operate lower than their design conditions and result in the decrease in their performances. In such cases, it is possible to replace the pump impeller with the smaller impeller diameter or to cut its original impeller to smaller size as necessary. The cut of the impeller, or it is frequently referred to as impeller trimming, in some extence is preferable than replacing with new impeller or even by replacing with new pump with smaller head and capacity. In this study, we examine the effect of the pump impeller trimming to the pump performaces. The study was performed in the Fluid Mechanics Laboratory, Mechanical Engineering Department of ITS, Surabaya. The pump impellers were cut up to approximately 19 percent of its original pump impeller diameter, where the original pump impeller diameter is 129 mm. The pump has the maximum capacity of 100 liters/min and the total head of 31.5 m. The pump is powered by a 300 Watt electrical motor. Parameters to be studied in this research include pump capacity, pump head, pump power, and pump efficiency. The results of this study show that all data are in good agreement with the pump affinity laws. Pump capacity, pump head, and pump power decresase as the pump impeller diameter decreases. The pump efficiency is, however, in some extent, increases as the pump impeller diameter decreases. The maximum increase in pump efficiency is obtained when the ratio between the trimmed impeller to its original pump impeller diameter is approximately 89 percent (i.e. D2/D1 = 0.89), with the increase in pump efficiency of approximately 20 percent.

Energy Loss and Radial Force Variation Caused by Impeller Trimming in a Double-Suction Centrifugal Pump.

Impeller trimming is an economical method for broadening the range of application of a given pump, but it can destroy operational stability and efficiency. In this study, entropy production theory was utilized to analyze the variation of energy loss caused by impeller trimming based on computational fluid dynamics. Experiments and numerical simulations were conducted to investigate the energy loss and fluid-induced radial forces. The pump’s performance seriously deteriorated after impeller trimming, especially under overload conditions. Energy loss in the volute decreased after trimming under part-load conditions but increased under overload conditions, and this phenomenon made the pump head unable to be accurately predicted by empirical equations. With the help of entropy production theory, high-energy dissipation regions were mainly located in the volute discharge diffuser under overload conditions because of the flow separation and the mixing of the main flow and the stalled fluid. The increased incidence angle at the volute’s tongue after impeller trimming resulted in more serious flow separation and higher energy loss. Furthermore, the radial forces and their fluctuation amplitudes decreased under all the investigated conditions. The horizontal components of the radial forces in all cases were much higher than the vertical components.

Effects of Impeller Trimming on Performance in a Double-suction Centrifugal Pump

In order to research the relationship between impeller trimming and performance in a double-suction centrifugal pump, impellers were trimmed 11mm and 22mm respectively. Numerical methods were applied combined with the original one, and experimental validation was also carried out on original and 11mm model. The performance and difference of total pressure between volute inlet and outlet was calculated, meanwhile, distributions of velocity and turbulence eddy dissipation on volute middle section were analyzed. The results indicate that the head drops with the trimming process and discontinuity appears when trimmed 22mm. The impeller trimmed 11mm is the most efficient under part-load and design conditions, while the original model has the lowest efficiency. Efficiency in trimmed cases decreases dramatically under over-load condition, especially when trimmed 22mm. Duo to rotor-stator interaction between impeller and volute receded by the enlarged clearance, the head losses inside the volute decrease with impeller trimming but increase significantly under 1.4Qd when trimmed 22mm. The extremely high shock losses resulting from exaggerated impeller outlet flow angle and dissipation near volute tongue account for it. Moreover, the losses in volute diffuser channel increase due to the vortexes generated by flow separation and backflow. The losses in volute will be improved by impeller trimming within reasonable limits in a double-suction pump. This research provides theoretical foundation for impeller trimming in double-suction centrifugal pumps.

Affinity laws for impellers trimmed in two partial emission pumps with very low specific speed

Partial emission pumps or open impeller pumps or tangent pumps with very low specific speed at either fast or conventional speed have found extensive applications in aircraft, liquid rockets, cryogenic fluid systems, chemical and petroleum-chemical industries, energy and food processing systems, etc. Usually, impeller trimming of rotodynamic pumps serves as an effective tool to meet required hydraulic performance of a liquid transport system and also to improve the entire system energy utilization efficiency. However, the affinity laws for the impeller trimming in a partial emission pump have been unavailable so far. In the paper, such affinity laws in terms of constant and variable exponents were established for flow rate, head, efficiency, flow coefficient and head coefficient based on the existing experimental data of two partial emission pumps at best efficiency points. It was shown that the affinity laws differ from the counterparts for centrifugal pumps, especially the exponent of around 2 for flow rate and the exponent of approximately 1.5 for head in comparison with nearly 1.5 for flow rate and about 2 for head in centrifugal pumps. The underlying mechanism for this effect was disclosed in terms of the ratios of the hydraulic, volumetric and mechanical efficiencies after trimming to the efficiencies before trimming analytically. The hydraulic loss, leakage flow rate and recirculation flow rate in two pumps were estimated according to the elements of fluid mechanics. It was identified that the hydraulic loss in the volute is more dominant than in the impeller and responsible for the rise of hydraulic efficiency with the trimming in progress. Moreover, the significant increase of recirculation flow rate between the volute tongue and the impeller outlet contributes to the substantial reduction in flow rate after impeller trimming.

Methods of regulating the work of units at irrigation pumping stations

Irrigation pumping stations are one of the main elements of irrigation systems and the main consumer of electricity in the agricultural sector of the Republic of Uzbekistan. Therefore, the question of choosing a method for regulating the operation of pumping units is very important. Most irrigation pumping stations in the Republic of Uzbekistan are equipped with centrifugal pumps of type “D”. The main types of regulation for such pumps are: impeller trimming, changing the frequency of rotation of the impeller, the pumping unit switching on and off control method. The specific features of the operating modes of irrigation pumping stations revealed are. The analysis of various methods for regulating pumping units during the operation of irrigation pumping stations showed that, according to the degree of coverage of the water consumption schedule, the most optimal methods are valve control and a change in the rotational speed of the impeller shaft. Regulation by changing the speed of rotation and the pumping unit switching on and off control method more suitable according to the economy criterion. Calculations for the pumping stations “Ulugbek II”, “Kizil-Bayrak”, “Ittifok”, “Navoi” and “Turkiston” showed that with a change in the diameter of the impeller, the energy savings can reach 21.1-63.5%. When using a frequency converter at the same pumping stations, energy savings can reach 16.5-35.4 5%. It must be taken into account that, when turning, regulation is possible only in the direction of decreasing parameters.

CFD Analysis of Impeller Trimming

Impeller trimming is a key impeller modification. It allows the best efficiency point (BEP) to be moved towards the region of lower flowrate and height, thus optimizing pump performance for specific piping systems. The paper deals with prediction of trimming results using CFD methods. Experience shows that modification of the BEP position depends on the trimming method as well as on the pump type and its specific speed. The analysed pump is of diagonal type with a specific speed of nb = 0.168. Its impeller is of a 4-blade design and a spiral casing is used as a volute. Seven cases of trimming are presented (including a non-trimmed original version). The paper compares CFD obtained data and data measured on an experimental stand. Additionally, the approach to CFD analysis, as well as the use of a turbulence model and characteristics of internal pump volume meshing are described.

Compendious Review on “Internal Flow Physics and Minimization of Flow Instabilities Through Design Modifications in a Centrifugal Pump”

Centrifugal pumps are one of the significant consumers of electricity and are one of the most commonly encountered rotodynamic machines in domestic and industrial applications. Centrifugal pumps operating at off-design conditions are often subject to different periodic flow randomness, which in turn hampers functionality and performance of the pump. These limitations can be overcome by modification in the conventional design of different components of a centrifugal pump, which can assuage flow randomness and instabilities, reconstitute flow pattern and minimize hydraulic flow losses. In this article, flow vulnerabilities like pressure and flow inconsistency, recirculation, boundary layer separation, adverse rotor–stator interaction, and the effects on operation and performance of a centrifugal pump are reviewed. This article also aims to review design modification attempts made by different researchers such as impeller trimming, rounding, geometry modification of different components, providing microgrooves on the impeller and others. Based on the findings of this study, it is concluded that some design modifications of the impeller, diffuser, and casing result in improvement of functionality, efficiency, and reduction in pressure fluctuations, flow recirculation, and vibrations. Design modifications should improve the performance without hampering functionality and useful operational range of the pump. Considerable research is still necessary to continue understanding and correlating flow physics and design modifications for the pump impeller, diffuser, and casing.

Numerical Study of Impeller Trimming on a Centrifugal Pump Test Unit

Centrifugal pumps have an essential role in various industries. Impeller trimming is often performed to optimize the pump performance at a particular operating point. Impeller trimming refers to a reduction in the impeller outer diameter and thus causes a change in the velocity triangle on the impeller of a centrifugal pump. Three-dimensional, unsteady simulations were conducted numerically using moving mesh. This centrifugal pump has a backward-curved impeller with six blades, with an outer diameter of 120 mm and an outlet angle of 10◦ , which will be trimmed to a diameter of 114 mm. Trimming the impeller reduced the outer diameter so that the outlet angle of the relative velocity to the tangential direction, β2, automatically changed according to the blade shape. The simulation was done by varying the pump discharge. The simulation results were compared with the experimental results. The results obtained in this study include quantitative data and qualitative data. Qualitative data was the appearance of velocity profiles, velocity vectors, and pressure contours. Meanwhile, the quantitative data were in the form of suction pressure, discharge pressure, head calculation, and hydraulic power. The comparison of the results of the numerical simulation with the experimental results have the same trend, although the simulation tended to underestimate the head and hydraulic power. A decrease in head and hydraulic power of the pump due to trimming the impeller from the lowest discharge to the highest discharge is as much as 13% to 24%.

Prediction of the Effect of Impeller Trimming on the Hydraulic Performance of Low Specific-Speed Centrifugal Pumps

The effect of trimming of radial impellers on the hydraulic performance of low specific-speed centrifugal pumps is studied. Prediction methods from literature, together with a new prediction method that is based on the simplified description of the flow field in the impeller, are used to quantify the effect of trimming on the hydraulic performance. The predictions by these methods are compared to measured effects of trimming on the hydraulic performance for an extensive set of pumps for flow rates in the range of 80% to 110% of the best efficiency point. Of the considered methods, the new prediction method is more accurate (even for a large impeller trim of 12%) than the considered methods from literature. The new method generally overestimates the reduction in the pump head after trimming, and hence results less often in impeller trims that are too large when the method is used to determine the amount of trimming that is necessary in order to attain a specified head.

Protočne karakteristike centrifugalne pumpe kod primene različitih metoda korigovanja radnog kola

Protočne karakteristike centrifugalne pumpe kod primene različitih metoda korigovanja radnog kola

Impact of Auxiliary Equipments’ Consumption on Electricity Generation Cost in Selected Power Plants of Pakistan

This study focuses on higher generation cost of electricity in selected TPPs (Thermal Power Plants) in Sindh, Pakistan. It also investigates the energy consumed by the auxiliary equipment of the selected TPPs in Sindh, Pakistan. The AC (Auxiliary Consumption) of selected TPPs is compared with that in UK and other developed countries. Results show that the AC in selected TPPs in Sindh, Pakistan exceeds the average AC of the TPPs situated in developed countries. Many energy conservation measures such as impeller trimming and de-staging, boiler feed pump, high voltage inverter, variable frequency drive, and upgrading the existing cooling tower fan blades with fiber reinforced plastic are discussed to overcome higher AC. This study shows that harnessing various available energy conservative measures the AC and unit cost can be reduced by 4.13 and 8.8%; also adverse environmental impacts can be mitigated. Results show that the unit cost of electricity can be reduced from Rs.20 to19/kWh in JTPP (Jamshoro Thermal Power Plant), Rs.9 to 8.8/kWh in GTPS (Gas Turbine Power Station) Kotri and Rs. 11 to 10.27/kWh in LPS (Lakhara Power Station). Thus, electricity production can be improved with the existing capacity, which will eventually assist to manage the current energy crisis and ensure its conservation.

Energy Savings through Pipe Header Optimization on a Cooling Tower Pumping Station

ABSTRACTEnergy savings in fluid pumping systems mainly rely on decreasing the flow rate of the fluid being pumped, in which case there are a few tried-and-tested solutions such as impeller trimming, variable speed drive (VSD) installations, replacing larger pumps with smaller pumps to match the system requirements, etc., but what can one do to optimize a system in which the flow rate of the fluid cannot be reduced?When the electrical components of the system cannot be modified to increase the efficiency of the system, one needs to look at optimizing other parts in the system. In this specific application, the main pipe header of the pumping system was optimized, thereby improving the systems flow rate and thus the energy savings was realized by switching off one 75 kW pump during production time to achieve a power reduction of 18.5% with a payback of four months.This article presents a case study in which a cooling tower pumping system originally operating using three 75-kW centrifugal pumps to circulate ...

Effect of impeller trimming on performance

Impeller trimming can improve the performance of a centrifugal pump and expand its application range. This article compares special impeller trimming methods, providing a scientific basis for trimming, and outlines the most effective methods for different flow rates.

Effects of Impeller Trimming Methods on Performances of Centrifugal Pump

AbstractImpeller trimming can improve the hydrodynamic performances of the centrifugal pump and expand the application range of the pumps. However, most researches focus on single-impeller cutting method; the literature slightly lacks a comparison of the different impeller trimming methods, which is very important in deciding on an impeller trimming method. In this paper, by taking the centrifugal pump as the research object, the accuracy of computational fluid dynamics (CFD) was verified by comparing experimental results and those of the numerical simulation. On the basis of impeller straight trimming, miscut, and triangle trimming methods, a new unconventional parabolic impeller trimming method was put forward. In different trimming sizes and operating conditions, performance curves of four impeller trimming methods were compared to get several different trimming models. By researching the flow field of centrifugal pump, the change reasons of centrifugal pump’s performance curves were further revealed. ...

Effects of impeller diameter and rotational speed on performance of pump running in turbine mode

The major limitations of mini/micro hydropower schemes is the higher cost of small capacity hydro turbines. Also, it is very cumbersome, time consuming and expensive to develop the site specific turbines corresponding to local site conditions in mini/micro hydro range. In such plants, small centrifugal pumps can be used in turbine mode by running in the reverse direction. The efficiency of pump as turbines (PATs) is usually lower than the conventional hydro turbines; however, there may be substantial decrease in the capital cost of the plant.Hydropower plants usually runs at part load for several months in a year due to insufficient water availability for the power generation. The application range of PAT can be widened if its part load and/or maximum efficiency can be improved. In the present study, experimental investigations are carried out on centrifugal pump running in turbine mode to optimize its geometric and operational parameters e.g. impeller diameter and rotational speed. The experiments were performed in the wide range of rotational speeds varying from 900 to 1500rpm with original (∅ 250mm), 10% trimmed (∅ 225mm) and 20% trimmed (∅ 200mm) impellers. Impeller trimming led to improvement in efficiency at part load operating conditions. The performance of PAT was found better at the lower speeds than that at the rated speed. The effects of blade rounding were studied in all the cases and it led to 3–4% rise in efficiency at rated speed with the original impeller. The empirical correlation is also developed for prediction of efficiency in terms of impeller diameter and rotational speed in non-dimensional form.