Disk Friction Losses Research Articles

Centrifugal pump performance improvement using back cavity filling

Centrifugal pumps consume majority of energy used by the electric motor driven systems among all end users of the industrial sector. Only in European region, a 1% improvement in efficiency (η) of the centrifugal pump is capable enough to reduce CO2 emissions by at least 572 tons per day. The prime motive of this research is to assess the applicability of the novel back cavity filling (BCF) in reducing the disk friction losses of centrifugal pumps without changing the pump's original design. By adding a solid ring to the bearing housing's back-cover plate, the BCF was applied to a medium specific speed pump (Ns = 54 rpm), resulting in a 1 mm back axial clearance from 13 mm. Numerical simulations and experiments were carried out to investigate the effect of BCF on pump performance under two conditions: with and without BCF at best efficient point (BEP) and various partload conditions for 1450 rpm (rated) as well as 1000 rpm. Pump performance characteristics were enhanced by BCF at both rpms for the whole flow rate range. At 1450 rpm, BCF resulted in an average 0.74% increment in total head, 2.08% reduction in input torque, and 2.70% increment in overall efficiency over the flow rate range. While an average 2.04% improvement in total head, 1.33% reduction in input torque, a 3.30% enhancement in overall efficiency were obtained at 1000 rpm. Performance parameter enhancement was higher at lowest part load compared to the BEP on rated rpm.

Reduction of Disk Friction Loss by Applying a Fin to the Back of a Centrifugal Impeller

Abstract It is well known that the ratio of disk friction loss of low specific speed pumps is large. When the specific speed is 100 min−1, m3/min, m or less, the disk friction loss increases remarkably. In this study, focusing on the clearance flow from the diffuser outlet to the impeller outlet (This is called the outward flow) behind the centrifugal pump, a fin was installed on outer diameter side of the rotating wall on the back side of a centrifugal pump as a countermeasure, and the influence of changes in velocity distribution near the wall on disk friction loss was investigated by torque measurements, velocity measurement, and computational fluid dynamics (CFD) analysis. As a result, it was clarified that disk friction loss is decreasing by installing the fin in both torque measurements and CFD results, because the clearance flow is separated by fin and circumferential velocity is increased in the wake region of the fin in both measurements and CFD. In addition, it was clarified that disk friction coefficient (normalized torque) can be expressed as a function of the inlet swirl ratio and Reynolds number. Also, prediction equation is derived for each shape (with and without fin). According to the equation, it was found that disk friction loss reduction effect by installing a fin becomes larger when Reynolds number and the inlet swirl ratio are small.

Effect of parasitic losses on the design optimization of inward flow radial supercritical CO2 turbines

Inward flow radial (IFR) supercritical CO2 (sCO2) turbines are smaller in size and operate at considerably higher speeds in comparison to similar capacity conventional gas or steam turbines. The compact size and high speed of IFR turbines result in significant parasitic (leakage and disk friction) losses at the rotor backface. This paper presents CFD investigations to understand the mechanism of parasitic losses of IFR turbines in the kW to MW power scales. The first part of the paper presents a parametric study to quantify the effect of backface flowpath dimensions, rotor inlet radius, and rotational speed on the magnitude of parasitic losses. Subsequently, the paper proposes the implementation of a radial labyrinth seal on the rotor backface to curtail the parasitic losses. The second part of the paper examines how the power scale of the turbine and its design parameters, specific speed and velocity ratio, influence the magnitude of parasitic losses. The investigation reveals that parasitic losses cause an efficiency drop of 8%–15% for 100 kW and 4%–9% for 1 MW IFR sCO2 turbines. In addition, IFR turbines designed for low specific speeds and high velocity ratios result in notably higher parasitic losses, leading to a decline in turbine efficiency. Finally, the paper presents optimal turbine design parameters accounting for the parasitic losses to maximize turbine efficiency.

Super antiwear properties of polytetrafluoroethylene (PTFE) induced by MeV proton irradiation

In this paper, the surface of polytetrafluoroethylene (PTFE) was modified by 1 MeV proton beam at high temperature. The changes of wear resistance and hardness of PTFE before and after irradiation were evaluated by ball/pin disk friction loss tester and nanoindentation tester, respectively. The results showed that the wear resistance of PTFE irradiated by proton at high temperature has been significantly enhanced. The mass wear rate decreases from 2.75 × 10−6 g/Nm to 0.39 × 10−6 g/Nm, and the wear depth decreases from 29.9 μm to 8.2 μm, respectively. Proton irradiation could be a simple and effective method for PTFE surface modification and can significantly improve the wear resistance. The potential chemical reaction mechanism for the improvement of wear resistance of irradiated PTFE in terms of microstructure was discussed. Crosslinking induced by proton irradiation enhanced the interaction force among PTFE molecules, thus the mechanical properties were improved.

Investigation of a centrifugal pump for energy loss due to clearance thickness while pumping different viscosity oils

The clearance between the stationary volute and rotating impeller of a centrifugal pump is crucial; however, it affects the internal flow and deteriorates the pump performance. This study performed a flow investigation through a numerical simulation to understand the effect of clearance and pumping fluid viscosity under the design and off-design conditions of a centrifugal pump. Numerical simulations were conducted by solving unsteady Reynolds-averaged Navier-Stokes (URANS) equations and validated using experimental results. Five three-dimensional centrifugal pump flow domains were created, by varying the clearance thickness, and simulated with three different fluid properties. Consequently, the numerical simulation results aided in understanding the internal flow pattern and estimating energy loss due to disk friction and leakage through the clearance. It was found that the disk friction and leakage losses, which cause secondary losses in the pump, were highly affected by the fluid properties and clearance thickness. The clearance thickness drastically affected both the volumetric and hydraulic efficiencies to leakage; however, beyond a particular value, it became less significant. Furthermore, the viscous oils caused a high disk friction loss; however, the leakage loss was less affected by the clearance thickness.

Thermodynamic analysis of open-air Brayton cycle to predict radial turbine aerodynamic performance

• A novel radial turbine design approach based on blade loss coefficient correction. • A system-turbine coupled evaluation method for the open-air Brayton cycle. • Turbine rotational consideration in turbine performance prediction. • Optimization of correlative coefficients in turbine geometrical design. The separated performance evaluation of the system and turbine leads to low accuracy in overall system performance prediction for the open-air Brayton cycle. To achieve the coupling analysis of system and turbine performance prediction and improve the accuracy of parameters optimization, this paper focuses on the improvement of the system and turbine performance evaluation approach. An improved turbine design approach based on blade loss coefficient correction is proposed to promote accuracy in turbine design. Meanwhile, an improved system-turbine coupled evaluation method for the open-air Brayton cycle is established by coupling the system performance prediction with the improved turbine design approach. The overall system performance analysis of the open-air Brayton cycle is performed to present the superiorities of the improved system-turbine coupled evaluation method. Furthermore, the parameters optimization of turbine design is carried out with the system performance evaluation and the rotational speed consideration to obtain optimum turbine isentropic efficiency. The results indicate that the improved turbine design approach can significantly decrease the relative error of turbine isentropic efficiency in one-dimension design to less than 1.85%. The improved system-turbine coupled method can decrease the relative deviation by 12.96% in system thermal efficiency compared with the conventional approach. In addition, the higher residual velocity loss, the lower disk friction loss, and the higher blade velocity coefficient are caused by the higher turbine rotational speed. Ultimately, the maximum thermal efficiency of the open-air Brayton cycle is 40.35% and the corresponding optimum turbine isentropic efficiency is 89.14% under the given system conditions. It is of great significance for parameter setting and optimization for the open-air Brayton cycle, and offers the support for the energy sustainability utilization.

Effect of the number of blades on diffuser unsteady loss of centrifugal pump

Abstract In recent years, an unshrouded impeller is being developed for rocket turbopumps to reduce production costs and disk friction losses. However, the internal flow structure in a diffuser influenced by an impeller has not been clarified yet. In this study, we focused on the investigation of unsteady flow in turbopumps with unshrouded impellers and vaned diffusers by experiments and CFD. Furthermore, we investigated the effect of changing the number of blades of the impeller and diffuser on the unsteady losses in the diffuser. First, we measured the static pressure at the shroud side in the impeller and the velocity at the diffuser inlet and outlet. Second, we confirmed the accuracy of the CFD by comparing CFD results with experimental results. Third, we investigated unsteady losses in diffusers by CFD. We could confirm increased entropy at the suction surface and shroud side because of the tip leakage and the vortex. Finally, we changed the number of impeller blades or diffuser blades. In conclusion, the loss region at the suction surface and the high-pressure region at pressure surface in the unshrouded impeller were mixed and caused unsteady losses through the diffuser. And diffuser efficiency decreased because channel width in diffuser became narrower by the number of diffuser blades increasing.

Effects of the Balance Hole Diameter on the Flow Characteristics of the Rear Chamber and the Disk Friction Loss in the Centrifugal Pump

This paper studies the flow characteristics and disk friction loss of the rear chamber in a centrifugal pump at a design flow condition with six values of the balance holes at diameters from 0 to 12 mm. The results show that the turbulent boundary layer in the rear chamber is greatly affected by the leakage flow. When the balance hole diameter increases, the flow characteristics of the rear chamber is mainly restricted by the mainstream flow field of the volute. However, when the balance hole diameter is larger than the design value, the disk friction loss of the rear chamber remains basically unchanged. On the contrary, when the balance hole diameter is smaller than the design value, the larger the balance hole diameter the smaller the friction loss of the disk in the rear chamber area. The results of this paper provide a reference for reducing axial force and stable operation of a centrifugal pump.

Flow inside impeller sidewall gaps and disk friction of radial centrifugal pump

Disk friction losses can significantly influence the overall pump effciency. It is most pronounced in the case of machines with low or moderate specific speed, which has to be kept in mind during a design process of a pump. However, analyses using computational fluid dynamics (CFD) often completely neglect the sidewall gaps geometry. Correctly solved flow in the sidewall gaps can have a great impact on the whole flow pattern inside the pump and therefore it can considerably influence the calculated effciency. The paper is focused on the precise simulation of the flow in the spaces between impeller shrouds and casing. CFD study using embedded Large Eddy Simulation (LES) approach in order to achieve accurate insight into the flow in sidewall gaps and reasonable computational time was performed. Obtained results are compared with data from experimental measurements.

Sensitivity analysis of centrifugal compressors aerodynamic losses using 1D-mean streamline prediction technique

One-dimensional modeling and prediction of the centrifugal compressor performance are challenging as they require conservation equations and empirical and semi-empirical correlations. Therefore, there is a need to perform a consolidated study of the compressor aerodynamic loss models to conclude the importance of each loss to the compressor performance modeling. Accordingly, the purpose of this paper is to examine the effect of each aerodynamic loss on the compressor performance and explore more about which loss could have a negligible effect on the compressor performance. A MATLAB code was developed to predict the performance of five different small turbocharger centrifugal compressors at different geometric and operating conditions. The developed code was validated using the available experimental data of the investigated compressors. A sensitivity analysis methodology was performed using the validated code to check the effect of ten aerodynamic losses for the impeller and volute sections on the compressor performance. This paper concludes that impeller disk friction, blade loading, and clearance losses have a negligible effect on the small turbocharger vanless diffuser compressor performance.

Investigation of Flow Structure in a Narrow Clearance of a Low Specific Speed Centrifugal Impeller

Abstract The disk friction loss is remarkably large in low specific speed centrifugal pumps, and an effective reduction method has not been established. Therefore, to develop the method, the loss mechanism was investigated. To grasp the internal flow structure in the narrow clearance, both experimental and computational approaches were used. An experimental apparatus that imitates clearance between a rotating impeller disk and a stationary casing disk was used and the static pressure distribution in the radial direction was measured. The internal flow where the disk friction loss occurs was investigated. In the case of outward flow, the static pressure decreased because the influence of the centrifugal force lessened toward the outer diameter of the disk, as the flow rate surged. For this reason, the pressure gradient became steep. According to the computational fluid dynamics (CFD) analysis, there was a vortex in the cross section of the clearance. This vortex encouraged flow recirculation and promoted the increase in the circumferential velocity in the potential core. When the flow rate grew, the vortex diminished. The circumferential velocity gradient and the shear stress intensified. As a result, the disk friction escalated. In the case of inward flow, the pressure gradient became steep as the flow rate increased. There was a vortex in the clearance, the size of which lessened when the flow rate surged. The disk friction had a minimum value at the flow rate was 6 × 10−4 m3/s. This research clarified that the vortex in the clearance has a remarkable effect on reducing the disk friction.

Investigation of Internal Flow in Centrifugal Pump Diffuser using Laser Doppler Velocimetry (LDV) and Computational Fluid Dynamics

An unshrouded impeller is being developed for high head pumps to reduce costs and disk friction losses. On the other hand, research of internal flow in a diffuser did not clearly reveal flow structure. In this experiment, we measured the velocity distribution at the diffuser inlet and outlet plane using laser doppler velocimetry (LDV) to capture the flow from the unshrouded impeller. The relation between the total pressure and velocity distribution was evaluated. The circumferential velocity and meridian velocity were measured by short-focus LDV (Diode Laser, 74mW) about the circumferential and the height direction of the vane direction. Operating conditions in this steady measurement are at the design point flow rate. The result was compared with computational fluid dynamics (CFD) simulations carried out in steady conditions at the previously defined operation points. In this experiment, a phenomenon that the streamline moved toward the shroud side was confirmed. There was also a region where the static pressure increased on the shroud side at the diffuser inlet. This phenomenon was caused by the influence of the tip leakage flow of the unshrouded impeller downstream and the gap of the impeller’s main plate. Furthermore, two high velocity regions on the hub and shroud side at the diffuser outlet were observed because of the secondary flow in the diffuser. From the above studies, it was clarified that the ununiform flow in the diffuser was caused by the influence of the secondary flow in the unshrouded impeller.

Flow Inside the Sidewall Gaps of Hydraulic Machines: A Review

The paper critically reviews the current state of the art in flow inside sidewall gaps of hydraulic pumps and turbines. It describes the consequences of the presence of this type of flow in turbomachinery and then relates it to other physical phenomena that determine the behavior, operating characteristics, and overall performance of the machine. Despite the small dimensions of the rotor-stator spaces, the flow in these regions can significantly affect the overall flow field and, consequently, efficiency. The circulation of the fluid inside the gaps and secondary flow that is caused by rotating elements influences the disk friction losses, which is of great importance, especially in the case of low specific speed pumps and turbines. The flow pattern affects the pressure distribution inside a machine and, thus, generates axial thrust. The presence of secondary flow also significantly changes the rotordynamics and can bring about undesirable vibrations and acoustics issues. This article aims to review and summarize the studies that were conducted on the mentioned phenomena. Experimental and numerical studies are both taken into consideration. It proposes some requirements for prospective research in order to fill current gaps in the literature and reveals the upcoming challenges in the design of hydraulic machines.

Numerical simulation and experimental study on the comparison of the hydraulic characteristics of an axial-flow pump and a full tubular pump

An axial-flow pump impeller is designed on the basis of plane cascade theory, which is based on surface element method, to study the influence of impeller rotor on the hydraulic performance of the a full tubular pump. Then, the performance of the full tubular and axial-flow pumps has been compared and analyzed through CFD and model test, respectively. First, two-dimensional plane cascade theory is used for the hydraulic design of pump impeller blades according to the design condition of an axial-flow pump. Second, the CFD calculations of full tubular pump and axial-flow pumps are performed using numerical simulation software. Finally, the reliability of the numerical simulation is verified by using a model test. Results show that under the design condition of the axial-flow pump, the head, efficiency, and maximum efficiency correspond to 3.30 m, 86.3%, and 86.69%, respectively. In the design condition, the head of the full tubular pump is 3.12 m and decreases by 5.5%, and the hydraulic efficiency is 78.54% and declines by 7.76%. The hydraulic loss caused by clearance backflow and the disc friction loss caused by rotor housing mainly caused the reduction in the hydraulic performance of the full tubular pump. Meanwhile, the decrease in the maximum operating head of the full tubular pump is greater than that of the axial-flow pump. Moreover, the safe and stable operation area of the full tubular pump is only 82.43% of that of the axial-flow pump. This work has important theoretical and guiding significance in the design and practical engineering application of the full tubular pump.

Influence of Critical Wall Roughness on the Performance of Double-Channel Sewage Pump

The numerical method on a double-channel sewage pump was studied, while the corresponding experimental result was also provided. On this basis, the influence of wall roughness on the pump performance was deeply studied. The results showed that there was a critical value of wall roughness. When the wall roughness was less than the critical value, it had a great influence on the pump performance, including the head, efficiency, and shaft power. As the wall roughness increased, the head and efficiency were continuously reduced, while the shaft power was continuously increased. Otherwise, the opposite was true. The effect of wall roughness on the head and hydraulic loss power was much smaller than that on the efficiency and disk friction loss power, respectively. With the increase of wall roughness, mechanical efficiency and hydraulic efficiency reduced constantly, leading to the decrement of the total efficiency. With the increase of flow rate, the effect of wall roughness on the head and efficiency gradually increased, while the influence on the leakage continuously reduced. The influence of the flow-through component roughness on the pump performance was interactive.

Effect of molten salt properties on internal flow and disk friction loss of molten salt pump

Computational fluid dynamics is used to study the effect of temperature on flow structure and disk friction loss for different working fluids in a high temperature molten salt pump, which is used for concentrating solar power, the velocity profile and pressure distribution in the first stage of the pump model and the effect of the fluid property on the ring leakage, disk friction loss as well as the shear stress distribution on shroud are analyzed for the pure water and the molten salt with temperature 300?C and 565?C respectively. The main findings can be concluded as: the working fluids have little effect on pump performance and internal velocity distribution whereas the pressure of the flow field would increase with the fluid density, with the increase of the fluid viscosity, the shear stress inside the ring also increases and the total leakage can be eliminated evidently, the increase of the fluid density and viscosity show the significant responsibility for the disk friction loss, in which the fluid viscosity also increases the disk friction loss, and the viscosity is one of the most influential factors for the shroud shear stress and it can be observed that the shear stress on front shroud is higher than that on the rear shroud. It is believed that the present work can deep the understandings of the fluid structures inside the molten salt pump, which can provide some guidelines to improve the pump performance and optimize the pump structure.

CFD를 이용한 머드 펌프의 성능 예측

A commercial CFD code is used to caculate the 3-D viscous flow field within the centrifugal pump impeller. Design conditions are changed by pump inlet diameter(203.2㎜) and pump outlet diameter(152.4㎜). Numerical calculation was performed by changing flow rate from 7 to 12m 3 /min. Working fluids are clean water and muddy water. The viscosity of muddy water is measured by the unsteady capillary of the viscometer. The pump performance is predicted well through the computer simulation. The results are summarized as follows: the pump characteristics of the total pressure, efficiency and shaft power with high viscosity fluids by muddy water was different from those clean water. When the viscosity of the applied fluid increased, the total pressure, and efficiency more decreased than those of clean water. The decreasing gradients of the total pressure and the efficiency were larger than water due to the increased disk friction losses at the duty operation point. The shaft power of clean water and muddy water increased. This study shows that the calculated results agree well with the analysis results of design condition.

Influence of clearance flow on disk friction loss in low specific speed hydraulic machines

Generally, in industrial applications, multi-stage pumps are used to obtain high working pressure. However, utilizing these pumps requires larger body size and longer shafts which will lead to substantial costs. As a result, a low specific speed machine is needed to minimize costs. In such case, energy can be saved and manufacturing costs can be reduced by increasing the efficiency of these low specific speed machines disk friction loss is one important cause of friction in low specific speed machines. It is caused by fluid friction occurring in the clearances between the shroud and back-shroud of the impeller and the casing. This loss is not directly related to the energy conversion in turbo machines, however it is related to the main characteristics of a machine. It will be increased proportionally with the impeller diameter and decreased with its specific speed. In this research, a test apparatus for measuring friction torque on a rotating disk was established, including a pressure resistant tank and boost pump connected in a closed loop using water as the working fluid. The sample rotating disk simulated the leakage flow path between the back-shroud and the casing of a centrifugal pump. Disks with different clearances were prepared, and fluctuations of torque were studied as a function of flow rate and Reynolds number. As a result, an optimum value for disk clearance with the minimum torque was observed to exist under each flow condition. CFD analysis was performed using a model simulating the disk clearance to understand the internal flow structure. For purpose of validation, the radial distribution of static pressure on the stationary wall was simulated by CFD and compared to experimental results. The CFD analysis agreed with the experimental distribution of wall static pressure in an acceptable manner, therefore it is proved that CFD model can reliably be used in evaluation of disk friction loss. Moreover, disk friction loss variation as a function of flow rate was investigated with inward and outward flow directions. It is seen that for both directions, disk friction loss decreases with flow rate. However, a vortex structure was observed at the inlet of the disk clearance for inward flow direction. Size of the vortex structure changes as a function of flow rate and has an influence on disk friction loss. The occurrence of this vortex structure may increase the efficiency of actual low specific speed machinery.

A step forward: IEC 62097-Edition 2 - “Hydraulic Machines, Radial and Axial – Methodology for Performance Transposition from Model to Prototype”

Advances in the technology of hydraulic machines for hydroelectric power plants provided the background for updating and revising the efficiency scale effect methodology of IEC 60193. The fundamental step forward in IEC 62097 is the standardization of scalable losses in specific hydraulic energy, leakage losses and disk friction losses. The transposition of the hydraulic performance is driven by the dependence of friction losses on Reynolds number Re and the effect of surface roughness Ra. Since the roughness of the actual machine components differs from part to part, the performance scale effect is evaluated for each individual part separately and then is finally summed up to obtain the overall performance transposition for a complete machine. After the release of IEC 62097 Edition 1 in 2009, comments on this standard were received and open or unclear topics identified. As a result, the new innovative concepts were introduced and developed, and editorial changes were implemented in Edition 2. This paper presents the significant improvements implemented in the release of IEC 62097 Edition 2 related to the performance transposition methodology for hydraulic machines through: a) addressing the shift in nED and QED in the performance scaling from the model to prototype; b) identifying two-step efficiency transposition as the primary method for deriving prototype efficiency based on the model test results; c) specifying recommended roughness measurement techniques and minimum prototype roughness values; d) readjusting scalable losses and leakage losses for models with peak efficiency exceeding the assumed maximum hydraulic efficiency specified in the standard; e) improved structure of the IEC 62097 standard document and “Excel” workbook providing clear and user friendly guidelines for the performance transposition calculations. The release of Edition 2 is a clear step forward in advancing the performance transposition methodology for radial and axial hydraulic machines.

Performance of a submerged impulse hydro turbine

This study is focused on performance of a developed submerged impulse turbine, which is suitable for small hydropower generation in drinking water pipelines around mountainous region. The turbine works as a pressure reducing valve and can be generated electricity. Loss for submerged operation of the runner should be clarified to estimate accurately the turbine performance. The performance tests were conducted with changing the casing pressure, supplying flow rate and number of nozzles. As a result, turbine performance for submerged operation drops down comparing that for non-submerged operation. The water jet issuing from the nozzle occurrs cavitation. The cavitation degradates turbine performance. The cavitation phenomenon can be suppressed by increase the casing pressure. It is also revealed that the number of nozzles is important for the turbine performance. This is because of that the input energy from the nozzle is increased with the number of nozzles, on the other hand disc friction and mixing loss on the runner is only depended on the runner rotation speed.