Low density high viscosity liquid pumps
KGaA uses cookies to be able to optimally design and continually improve its web site. By continuing to browse the web site you consent to the use of cookies. Viscosity is the property of a fluid to resist the relative displacement of adjoining layers internal friction. It is necessary to differentiate between dynamic and kinematic viscosity. All other curves denote non-NEWTONian liquids handled in pulp pumping applications, whose effects on the operation of centrifugal pumps cannot easily be calculated by the usual methods.
However, in practice it is normal low density high viscosity liquid pumps specify the viscosity-density ratio kinematic viscosity. The term "dynamic viscosity" is derived from the Greek "dynamis", which means force, since the SI unit contains a unit of force N. The SI unit for kinematic viscosity, on the other hand, contains only kinematic dimensions for length m and time s.
Kinematic viscosity v of various mineral oils as a function of temperature t. As the temperature increases, almost all liquids become thinner, i. Drive torque, circumferential speed, the size of the wetted cylinder surface and the wall clearance in the pot are measured at several rotational speeds. Viscometry also includes other processes, e.
The characteristic curves of centrifugal pumps show noticeable effects only at a kinematic viscosity of. The HI technique, see Fig. The use of the two diagrams is explained by means of the depicted examples. Diagram for the conversion of characteristic curves of centrifugal pumps with radial impellers pumping water to characteristic curves for pumping viscous fluids from: Diagram for conversion of characteristic curves of centrifugal pumps with radial impellers for pumping higher-viscosity liquids from: The f factors are called k in the HI technique; both are illustrated graphically in Figures 3 and 4; in Fig.
With these factors, the operating data known for water mode can then be converted for liquids of a higher viscosity; the conversion applies in the load range:. Calculation template for converting pump characteristic curves for operation with higher-viscosity fluids, based on the KSB method.
After the power at the three flow rates see load range equation has also been calculated according to.
Re-plotting the characteristic curves for water to those for a higher-viscosity liquid. If the terms of reference are reversed so that it is not the water low density high viscosity liquid pumps that are given, but the data for operation with a higher-viscosity liquid e. Since all hydrodynamic laws remain valid without restriction for NEWTONian liquidsall the calculation formulae and diagrams for the pipe friction coefficients and for the loss coefficients in valves also continue to apply.
Data privacy and Cookies. Search A-Z Suche nach. Viscosity Viscosity is the property of a fluid to resist the relative displacement of adjoining layers internal friction. With these factors, the operating data known for water mode can then be converted for liquids of a higher viscosity; the conversion applies low density high viscosity liquid pumps the load range: Calculation template for converting pump characteristic curves for low density high viscosity liquid pumps with higher-viscosity fluids, based on the KSB method After the power at the three flow rates see load range equation has also been calculated according to all characteristic curves can then each be plotted from either 4 or 3 calculated points over Qz.
Re-plotting the characteristic curves for water to those for a higher-viscosity liquid If the terms of reference are reversed so that it is not the water values that are given, but the low density high viscosity liquid pumps for operation with a higher-viscosity liquid e. Effect on the characteristic curves of the system Since all hydrodynamic laws remain valid without restriction for NEWTONian liquidsall the calculation low density high viscosity liquid pumps and diagrams for the pipe friction coefficients and for the loss coefficients in valves also continue to apply.
To receive news and publication updates for International Journal of Rotating Machinery, enter your email address in the box below. This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use, distribution, and reproduction in any medium, provided low density high viscosity liquid pumps original work is properly cited. Centrifugal pump delivery head and flow rate drop effectively during the pumping of viscous fluids.
Several methods and correlations have been developed to predict reduction rate in centrifugal pump performance when handling viscous fluids, but their results are not in very good agreement with each other. In this study, a common industrial low density high viscosity liquid pumps specific speed pump, which is extensively used in different applications, is studied. The entire pump, including impeller, volute, pipes, front and rear sidewall gaps, and low density high viscosity liquid pumps holes, is simulated in Computational Fluid Dynamics and 3D full Navier Stokes equations are solved.
CFD results are compared with experimental data such as pump performance curves, static pressure in casing, and disk friction loss. Dimensionless angular velocity and leakage rate are investigated in sidewall gap and efficiency variation due to viscosity is studied. The results demonstrate that the behavior of the fluid in sidewall gap is strictly sensitive to viscosity. Increasing viscosity improves the volumetric efficiency by reducing internal leakage through wear rings and balance holes, causing, however, a significant fall in the disk and overall efficiency.
Results lead to some recommendations for designing centrifugal pumps which may be used in transferring viscous fluids. Ippen [ 2 ] indicates that the expected efficiency, even for large pumps, for a Reynolds number of would be on the order of 30 percent.
Performance curves of centrifugal pumps which are presented in manufacturer low density high viscosity liquid pumps are related to test with cold water. In addition, predicted performance of pumps for handling a viscous fluid is usually calculated by correction charts of some companies such as [ 3 ] and the viscosity diagram of Hydraulic Institute Standards [ 4 ]. In any pumping system, when water is substituted with a viscous fluid, the absorbed power increases while head and flow rate generated by the pump decrease.
This phenomenon results from the reduction in the pump efficiency and is more evident in pumps with low specific speed in which viscosity plays a decisive role in disk friction loss. This kind of loss is the power absorbed low density high viscosity liquid pumps rotating the fluid between external surface of the impeller and internal wall of the casing.
In this paper, a low specific centrifugal pump which was originally designed for water handling is investigated to analyze the influence of Reynolds number on efficiency due to pumping viscous fluid. For a low specific speed centrifugal pump, some research on disk friction loss such as [ 5 — 7 ] was based on simplified model in which there is a rotating disk in a cylinder filled with viscous fluid, with or without radial inflow or outflow as shown in Figure 1.
Littell and Eaton [ 8 ] measured turbulence characteristics of the boundary layer on an effectively infinite rotating disk in a quiescent environment. In recent years, some experimental and numerical investigations into viscosity effect on pump performance have been performed in real centrifugal pumps.
Li [ 11 — 13 ] performed an experimental study on performance of centrifugal oil pump and studied numerically the effects of viscosity on centrifugal pump performance. Li [ 14 ] also investigated the effects of flow rate and low density high viscosity liquid pumps on slip factor. He obtained the optimum number of blades for pumping liquid with different viscosity and showed some effects of viscosity on fluid regime inside the impeller and volute.
Shojaeefard and Boyaghchi [ 15 ] accomplished CFD and experimental studies for viscosity effect on velocity in the impeller and indicated that when the blade outlet angle increases, the width of wake at the outlet of impeller decreases, leading to better pump performance in pumping viscous fluids.
Nemdili and Hellmann [ low density high viscosity liquid pumps ] utilized a method to measure disk friction loss and tested disks without and with modified outlet sections with various numbers, angles, and widths. Juckelandt and Wurm [ 18 ] studied the effect of boundary layer on calculating losses in low specific speed pumps and low density high viscosity liquid pumps some meshing low density high viscosity liquid pumps for these types of pumps.
The power consumption of a pump can be defined as where is fluid density, is pump flow rate, is pump delivery head, is volumetric efficiency, is hydraulic efficiency, is disk friction loss, and is mechanical loss. By increasing the viscosity the power balance will change in the following way: The wall shear stress occurring on surfaces of a rotating disk in a casing full of fluid can be written as follows: The resultant torque applied to a surface element is The friction power of the disk will be where is impeller outer radius.
Theoretical head of a centrifugal pump is the sum of the useful head,and the hydraulic losses. It can be demonstrated that the theoretical head,is essentially the same when a pump operates with water subscript or with viscous fluid subscript. Hydraulic losses are considered to consist of friction losses,and mixing losses, [ 19 ]: Friction loss is the term that changes with viscosity; hence, the head correction factor in viscous pumping can be calculated through the following formula [ 19 ]: The correlation which can be used to calculate this fraction for a wide range of specific speed is [ 19 ] More detailed procedure to calculate and can be found in [ 1719 ].
The investigated pump Figure 2 is a single-stage, end-suction volute pump with a specific speed of at BEP of full diameter impeller and at rated impeller. The pump is a back pull-out construction with a six-blade closed impeller and six balance holes so as to reduce the axial thrust.
More detailed dimensions can be found in Table 1. A blending factor is computed locally, which is used for the spatial discretization method of the convective terms implemented with a hybrid scheme. The flow was assumed to be at steady state and incompressible and isothermal. Turbulence effects were modeled, using the - SST procedure with adiabatic wall boundary conditions.
This turbulent method, according to several scholars [ 1720 ], is considered as the best choice for modeling of flow in centrifugal pumps since it has shown a good compromise between low density high viscosity liquid pumps and computational effort even for the region of impeller sidewall gap [ 21 ]. Results of similar research such as [ 1518 ] demonstrate satisfactory results with - SST model. To achieve an improved mesh quality, for the regions which are located near walls, the structured mesh was used, whereas unstructured mesh was employed for areas away from the wall to properly cover the complex geometry Figure 4.
Therefore, a better conformity between the mesh domain and the complicated geometry has been obtained. The unstructured mesh constitutes six-sided pyramid and wedge-shaped elements. Orthogonal quality, aspect ratio, and skewness were inspected during the grid generation process, to be in appropriate range. The grids between rotating and stationary parts such as impeller and volute low density high viscosity liquid pumps suction pipe and impeller were adjoined by means of frozen rotor low density high viscosity liquid pumps.
Mass flow rate with flow direction and constant pressure were implemented for inlet and outlet boundary conditions, respectively. A closed loop test rig fulfilling the requirements of ISO [ 22 ] was used in order to measure the experimental parameters of the low density high viscosity liquid pumps.
Figure 5 presents a schematic view of the test setup in which the fluid is drawn from the tank 1 with 2. There is a Transverse baffle inside the tank to reduce liquid slosh and ensure the fluid streams into the suction pipe smoothly. Pump head is calculated by using pressure transducers with accuracy of 0. The flow rate is adjusted by means of a globe valve 8 located in discharge line of the pump.
Steady state flow rate is measured by a magnetic flow meter 9 with the accuracy of 0. To calculate power, the torque and speed of the motor are measured via a torque meter 6 and tachometer, whose accuracies are 0. To determine the pressure field in the sidewall gap and validate numerical results, peripheral distribution of static pressure is measured by means of pressure transducer with accuracy of 0.
The signals from the transducers are digitalized by a data acquisition device and, with capturing enough samples, the data are averaged arithmetically. The uncertainties of flow rate, head, power, and efficiency are approximately 0. The volute is divided into 6 sectors in which there are four holes in the casing wall of each sector.
The static pressure was measured in each point and then averaged in each sector. CFD results were also averaged in each sector and are compared to relevant measurements.
Results of pumping oil with are also in the same range of error. Figure 6 presents the comparison between CFD results and experimental data including dimensionless head,and efficiency versus dimensionless flow rate,where is impeller outlet width and is impeller outer radius. As it is shown there is a good agreement between CFD and experimental data even in part load and overload regions. The BEP is located in with the head of.
Pump performance curve for oil with resulting from different method is plotted in Figure 7. The analytic curve is based on calculating the based on value of from 6 and as it is shown the analytic method is not close to experiments in this matter and may be used for estimation or finding the trend of changing. The graph published in [ 3 ] to calculate the influence of viscosity introduces the procedure yielding the correction factors and as a function of flow rate, head, kinematic viscosity, rotational speed, and also the significant influence of the specific speed.
This method is based on measurements with from 6. Since this method does not take into account the influence of the ratio of the actual flow rate to the flow at the BEPthe results in low flow rate are different from experimental data; however, near BEP it shows accurate results.
Thus, this method seems to overpredict the amount of losses for viscous oils and therefore is more cautious method. CFD curve is obtained from simulating flow in 6 operating points and as it is shown the agreement between the CFD results and experimental data is acceptable especially in lower flow rates.
It low density high viscosity liquid pumps been shown in Figure 7 that in low flow rate the effect of viscosity on pump head is smaller than in higher flow rate; therefore, shut-off head of pump with viscous liquid does not differ much from that with water. In this point of view, part load is more preferable than overload in pump selection procedure for delivering viscous fluids. The designer may choose a larger pump, so the operating point will locate in the left side of BEP and thus the effect of viscosity on pump performance will decrease.
Table 3 demonstrates the influence of operating point location, at 3 constant absolute flow rate on head reduction based on experimental data. Based on experimental results, correction factor for flow rate in BEP which is equal to the shift in BEP location due to viscosity is about and efficiency drop in this point is nearwhile Figure 7 shows that the head coefficient reduction compared to water curve is approximately.
CFD and experimental values are quite in agreement in BEP while in off design conditions the error has increased as expected. Figure 9 shows streamline of flow including front and rear leakage through wear rings. Internal leakage towards impeller eye usually affects primary flow of impeller suction.
Rate of leakage in front and low density high viscosity liquid pumps wear rings does not differ much since balance holes are large enough and resultant friction resistance is negligible compared to wear rings. Forming vortex flow in sidewall gap depends upon several parameters such as angular momentum of entering flow, geometry of the core, and Reynolds number. Figure 10 illustrates the velocity vector of leakage flow low density high viscosity liquid pumps front wear rings. Leakage flow to impeller suction eye forms a vortex zone in this region, which affects the uniform regime of fluid entering the impeller.
As shown in Figure 10this zone has a larger area when the pump is used for pumping low viscous fluid such as water. The dimensionless internal leakage rate through front wear rings is demonstrated in Figure Another way to limit internal leakage is to restrict wear ring clearance in order to raise volumetric efficiency. When the pump is utilized for pumping viscous fluids, use of impeller back vanes or expeller to balance axial thrust is low density high viscosity liquid pumps recommended due to increase in disk friction loss.
The best way is low density high viscosity liquid pumps use balance holes and mating wear rings even with a larger clearance in order to minimize repair intervals and extend the operating life of rings. This geometrical optimization diminishes the risk of face contact of wear rings due to shaft deflection or misalignment and thus improves reliability low density high viscosity liquid pumps the equipment which is completely important in specific applications. API Standard [ 23 ] has listed the minimum allowable running clearance of wear rings for centrifugal pumps used in petroleum, oil, and gas industries which is 0.
The dash line in Figure 11 demonstrates minimum leakage rate corresponding to this clearance. To compensate for the significant negative effect of wide gap on volumetric efficiency, wear rings with a larger length or labyrinth shape and small balance holes could be used. Admittedly, the balance hole numbers and diameter should be enough to ensure that the axial thrust is controlled satisfactorily.
The circumferential velocity of fluid in sidewall gap is normally described by the dimensionless angular velocitydefined as the ratio of the angular velocity of the fluid to the angular velocity of the impeller.
Figure 12 illustrates along the radius in the low density high viscosity liquid pumps gap. When centrifugal pump handles water instead of oil, Reynolds number low density high viscosity liquid pumps leakage flow rate through rings increase, while both of them are major parameters that affect.