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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.

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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. [ABSTRACT FROM AUTHOR]

Influences of different impeller trimming methods on flow characteristics of a centrifugal pump have been studied numerically and experimentally in this research. Different cases of trimmed impellers include straight trimmed impeller with and without remained shrouds, oblique trimmed impeller, triangular trimmed impeller, semi-circular trimmed impeller and polygon-shaped trimmed impeller. Verification of computational results has been investigated through comparison of experimental and numerical data as maximum deviation of 5.4 per cent has been observed. Results revealed that impeller trimming method has profound impact on the centrifugal pump performance as the highest head value has been achieved by employing the impeller with polygon-shaped trimmed shrouds at all flow rates, which is by 5 per cent higher than that of the conventional trimmed impellers (straight trimmed ones). Furthermore, it is also seen that the efficiency of polygon-shaped trimmed impeller was reduced by 3.6 per cent at BEP (Best Efficiency Point).

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.

Impeller 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. The turbulent kinetic energy distribution and pressure distribution of the four trimming methods at best efficiency points (BEPs) were compared. The results showed that impeller trimming can improve pressure distribution of the impeller outlet, decrease shaft power, and increase energy saving. [ABSTRACT FROM AUTHOR]

Centrifugal impeller blade trimming can be used to modify an existing impeller design to meet a new flow or pressure ratio design point. In flow trimming, the passage area is reduced from inlet to outlet along the entire meridional length of the impeller to reduce the flow coefficient of the impeller while maintaining the pressure ratio of the untrimmed impeller. Axial trimming is a method of reducing the blade height at the impeller exit while maintaining the shroud profile of the original impeller in order to reduce the head coefficient of the impeller while maintaining the original flow range. In this work, computational fluid dynamics was employed to numerically model four impellers of varying geometries, speeds, and performance characteristics to study the performance effects and limits of modifying the impeller geometry by either flow or axial trimming. Flow trimming was found to be capable of reducing the flow coefficient by between 20 and 50% while maintaining the pressure ratio and efficiency of the baseline impeller. The suitability of an impeller for flow trimming was found to correlate strongly with flow incidence angle. Reducing the exit blade height of a centrifugal impeller by trimming the blades axially may be used to reduce the pressure ratio of a compressor while maintaining flow range; however, the amount of pressure ratio reduction was limited to between 9 and 13% before choking in the passage reduced the choked flow rate. Impeller performance was found to respond differently to axial trimming based on the diffusion ratio of the baseline impeller. [ABSTRACT FROM PUBLISHER]

Centrifugal compressor blade trimming can be used for the purpose of changing the performance characteristics of an impeller or allowing a single impeller design to be used for a range of operating conditions. There are different methods of impeller blade trimming that may be employed to change the impeller flow rate, the pressure ratio, or both. In this study, computational fluid dynamics is used to model the effects of two different methods of blade trimming on a single centrifugal compressor design. Impeller performance characteristics and analysis of the flow field are presented for a series of trims. Trimming the passage area from inlet to outlet along the meridional length reduced the flow rate of the impeller and narrowed the effective operating range. The head coefficient and efficiency relative to the choked flow coefficient remained unchanged as the passage area is reduced; however, the flow rate is reduced by a greater amount than the inlet area is reduced. Trimming the impeller blades by shifting the shroud profile in the axial direction caused the head coefficient to be reduced while maintaining a constant flow coefficient. This method of trimming is limited by choking in the radial portion of the passage, and the head coefficient for the impeller studied was able to be reduced by up to 15% before further trimming limited the choked flow rate. [ABSTRACT FROM AUTHOR]

Very high flow coefficient centrifugal compressor stages are mostly applied as the first stages of multistage compressors. The performance of this type of stages is critical to the entire centrifugal compressors, but surprisingly little related information is available in the open literature. A centrifugal compressor with high inlet flow coefficient of 0.2, presenting a narrow operating range and unstable running situation even at design speed during the test, is investigated here. To reveal flow details in this centrifugal compressor, numerical simulations have been carried out and indicate that excessive impeller flow diffusion results in the poor performance of this centrifugal compressor. With the same inlet flow coefficient, six redesign cases coming from an in-house one-dimensional analysis program are proposed together with impeller trimming and equal flow area design method for corresponding vaneless diffuser. Performance comparison among these redesign centrifugal compressors is presented and the most suitable one is recommended for test in the future. In addition, three redesign cases with lower inlet flow coefficient developed by means of flow trimming are shown in the end to satisfy potential application areas. Finally, the results in this study can provide valuable reference information for multistage centrifugal compressor design. [ABSTRACT FROM AUTHOR]

A multistage deep-well centrifugal pump (DCP) with different impeller rear shroud radius have been investigated both numerically and experimentally under multiconditons, which aims at studying the influence of impeller rear shroud radius to the axial force and pump hydraulic performance. During this study, a two-stage DCP equipped with three different impellers was simulated employing the commercial computational fluid dynamics (CFD) software ANYSY-Fluent to solve the Navier-Stokes equations for three-dimensional steady flow. High-quality structured grids were meshed on the whole computational domain. Test results were acquired by prototype experiments, and then compared with the predicted pump performance and axial force. The static pressure distribution in the pump passage obtained by numerical simulation was analyzed. The results indicated that the appropriate impeller rear shroud radius could improve the pump performance and lower the axial force significantly. [ABSTRACT FROM AUTHOR]

Abstract: Centrifugal pumps as inevitable part of any desalination plant are significant consumers of energy. Due to high capacities of desalination plants, efficient operation of all their components, including centrifugal pumps is very important. It is often found that centrifugal pumps do not operate in their optimal points for various reasons. One of the methods to improve efficiency of centrifugal pump is proposed here. Impeller trimming is a common practice performed by pump manufacturers and users when it is necessary to adjust the centrifugal pump head and flow to the actual needs. The trimmed pump is not strictly similar to the initial pump because only a few parameters are modified, while all the others remain unchanged. In spite of this, the assumption of valid similarity was made here and examined through a series of experiments. A centrifugal pump impeller of low specific speed (n sp =19,745r.p.m.m0. 75 s−0.5) was trimmed and tested successively. For this particular pump, the influence of disregarded similarity can be estimated to ±3.94% for the pump head and to ±5.24% for the power, both with a 95% statistical certainty. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]