How Is The Shear Rate Of An Impeller Calculated

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Simple Method for Determining Stress and Strain Constants for

er to determine a value for the rpm-shear rate conver - sion factor k1 since P ~ k1(n-1). By measuring the power input required to agitate several power law fluids, k1can be determined graphically. This method was used by Rao [9] to determine the effective shear rate of a flag impeller and later referred to this method as the RN

stock preparation Total Stock Chest Mixing

on the relation between shear rate and viscosity. This is typically expressed as Power Law, but in the case of a high concentration of paper pulp, it does not correlate. The data that correlates viscosity with impeller shear rates was obtained via calibrated impeller test (CIT). Paper pulp of a known consistency was mixed at different RPM using

Impeller Design for Liquid-Liquid Dispersion Using VisiMix

Max shear rate (1/sec) Shear Stress Near Impeller (N/sq.m) RC-1 with PB impeller at 1000 rpms PVM baffle (experimental set up) 281 30800 54.6 RC-1 with PB impeller at 1000 rpms 4 flat blade baffles 259 7220 12.8 RC-1 with PB impeller at 2000 rpms * 4 flat blade baffles 171 20500 36.2 RC-1 with 6 blade RDT impeller at 1000 rpms

Impeller Mixing Simulations of Transitional Flow

Simulations were carried out for an A200 impeller in a baffled tank. The tank and impeller geometries are depicted in Figure 1. The tank had four evenly-spaced baffles, and the impeller consisted of four flat blades pitched at a 45° angle, with a diameter of 7 in. The geometry for the A200 impeller was provided by SPX Flow.

Modelling of Shear Sensitive cells in a stirred tank reactor

Figure 2-3: Effect of averaging on the periodic velocity calculated using the SAS-SST turbulence model with 1° time-step and a mesh with 2.138×106 nodes at a dimensionless radial distance r R of 1.07 from the impeller axis at the axial height of the impeller disk. 20 Figure 2-4.

Bakker A., Gates L.E. (1995) Viscous Mixing. Chemical

the viscosity will vary with shear rate throughout the volume of the tank. To calculate the average viscosity experi- enced by the impeller, an effective shear rate is calculated by Metzner Pitched-blade turbine NP High-efficiency impeller N Pitched-blade turbine High-efficiency impeller 100 Reynolds Number 10,000 Figure 2.

inite lement Analysis of Vane eometry for Shear Thinning

values (viscosity at shear rate 1.0 s-1), adding more fibres to the suspension logically increased the viscosity of the system. The model was run with different angular velocities of the impeller between 0 and 200 rpm. Tangential velocity magnitudes (√𝑢 2 +𝑢 2) at a

Melt Pelletization of a Hygroscopic Drug in a High Shear

increases in the granule growth rate were observed for all meltable binders tested, when the binder amount and the impeller speed were increased. Factorial designs with all three binders were performed under the same conditions. In these experiments, no correlation existed between the granule growth rate and the viscosity of the different binders.

PM0509 26 37 MIXING

shear rate at the same impeller speed. If shear sensitivity is a concern, radial flow impellers should not be used. In the case of hydrofoils, scaleup will always result in a lower shear rate. All small-scale mixers operate at high impeller speeds: the typical bench top mixer may run at over 1,000 rpm, while large industrial-scale mixers may

Performance characteristics of centrifugal pumps when

cients were calculated to modify the shear rate, s, and then the Rabinowitsch-Mooney transform was again used to determine the corrected true shear rate, it,. Figure 4 shows the rheograms of the coal slurry. Both the yield stress and plastic viscosity can be seen to increase with mixture concentration. Figures 5, 6 and 7

Cell Culture Scale-Up in Stirred-Tank Single-Use Bioreactors

parameters such as filling rate, aeration rate, and type of gassing device and pressure). Stirredt ank BioreactorS The stirred-tank bioreactor design is relatively easy to describe with classical engineering approaches (Figure 1). Parameters to describe this vessel geometry include impeller diameter, vessel diameter, liquid height, and ratios

Design and Fabrication of impeller for Single Suction

procedure of impeller for single section centrifugal pump. The pump type is single stage centrifugal pump with close impeller type. This impeller develops a head of 20 m and delivers 0.9 m3 /min of water. The designed impeller has 97 mm inlet diameter, 226 mm outlet diameter, 20˚ inlet vane angle and 23 outlet vane ˚ angle.

Research Article Fluidization Characteristics of Medium-High

F : Mesh generation ((a): vessel and (b) details of impeller). Shear rate ( s 1) 5,000 10,00015,00020,00025,00030,00035,00040,00045,000 Onset of turbulent regime 6.62 % 8% 11 % 12.5 % 14 % 700 800 900 1000 1100 1200 1300 1400 1500 1600 Shear stress (Pa) F : Shear stress versus shear rate of waste tissue pulp and several mass concentrations.


calculated by measuring the absolute static pressure at a point where the diameter is twice that of the inlet and outlet flanges. The flow rate and torque are measured with an accuracy of ±0.2% using a magnetic flowmeter and a torque meter, respectively. The flow rate is controlled using a gate valve.

Rotor-Stator Mixers

3. Shear Rate Whenever there is relative motion between liquid layers shearing forces exist that are related to the velocity gradient. Metzner and Otto (1957) showed that the average shear rate around the impeller can be calculated as a product of rotational speed and a proportionality parameter, KS, which depends on the impeller geometry. The best

Variability of Energy Dissipation and Shear Rate with

Energy dissipation rate (ε in W/kg) and shear rate (γ in 1/s) on different geometric parameters have been calculated by using visimix® software at different impeller rotational speed. 2.1. Dissipation Rate of Turbulent Kinetic Energy, ε A characteristic feature of turbulent flow is the presence of a wide range of eddy sizes, rang-


The impeller shear rate was computed by means of the Robertson y Ulbrecht correlation (23), which was developed for Rushton turbines in the 100 < Re < 2.9.104 range, In Eq. 3, ν is the kinematic viscosity calculated with the zero-shear viscosity, η o. Eq. 3 yielded that a


symmetry of the impeller discharge stream, the impeller pumping capacity can be calculated from the equation () () = ∫ = ∫ / 2 0. d 2 ( ) d. d ax S QP ax uax S ax u r r r ax π. (2) Example of the radial profile of dimensionless axial component of the mean velocity uax uax. nd *. = in the impeller discharge stream leaving the impeller

Blending of Newtonian and Shear-Thinning Fluids in a Tank

The global circulation rate Q. c, is the flow rate driven by the circulation loop which is created by the impeller. It may be determined by integrating the axial velocity at a horizontal plane corresponding to the circulation centre. The non-dimensional circulation number N. Qc. is calculated in a similar manner to the pumping number: N Q. Qc

Numerical Simulation and Analysis of Power Consumption and

to this correlation, the mean shear rate can be related to the impeller speed by γ avg s kN, (6) where k s is Metzner-Otto constant and it is assigned a value of 11.5 for the radial flow impeller[18], γ avg is mean shear rate. The mean shear rate can be used to evaluate the apparent viscosityηa


under the 3rd impeller (impeller discharge stream section). (b) Axial mean velocity profile 30 mm from the surface of the tank. 3.2. Intermig impellers Intermig impellers were designed to be up- and down-pumping at the same time. The inner part of the impeller pumps the fluid upwards while the outer part of the impeller pumps the fluid downwards.

Shear flow curve in mixing systems A simplified approach

on the calculation of the shear stress shear rate relationship from the torque and rotational speed of mixing probe. Different methods have been developed for estimating the shear rate in the impeller zone (Steffe, 1992). From the power consumption method in laminar regime,

Communication to the Editor - Wiley

rine impeller. The results indicated that there was an op- timum range of shear rate; i.e., an average shear rate of 20 to 30 s- or an impeller tip speed of 5 to 8 dmis, which maximized all the values of the following parameters: the specific growth rate, the maximum cell concentra-

J. Zheng - Columbia

C is specific to the impeller/tank geometry tested but independent of scale. p=a/y.;;Kya-l [8] The average liquid shear rate 'Y in an agitated vessel can be related to the impeller speed N by the Results of Stirring Tests with NeMonian liquids eqttation (Metzner and Otto. 1.957) y=aN {9) In order to determine the C term foc a partiallar


Figure 6. Calculated value of torque moment. 2. Calculation of shear characteristics in zone around the blades see Figures 7-10. Figure 7. Sub-menu of shear parameters in the impeller zone. Figure 8. Maximum shear rate in the impeller zone.

Numerical Calculation of the Flow in a Centrifugal Pump

volume flow rate through the impeller and g the gravity acceleration, while the subscripts 1 and 2 denote impeller inlet and exit conditions, respectively. The right-hand side integral is approximated by a summation over the radial flow rates δq at all grid cells facing the inlet or the exit circumference of the impeller.


assumption that the average liquid shear rate is proportional to impeller speed (Metzner and Otto. 1957). the effective viscosity can be obtained: MILL DYNAMICS WITH MEDIA ONLY Power charaderistics of stirred media mill have been studied by an approach developed from wOr ( on stirred reactors and under

Tutorial Tackling the Challenge of Scalability

monly used to calculate the impeller power consumption per liquid volume (P/V [W/m3]). Maintaining constant P/V between vessels is another of the most accepted strategies for scale-up. Np can be calculated from the im-peller torque using equation (1) in Fig-ure 2. The impeller torque was exper-imentally determined from the direct-


that are calculated using CFD software. The result shows that the shear rate is high on the front end portion of the stirrer. The maximum shear rate tend to a stable behaviour after the stirring time of 2 second. The relation between the speed and the maximum shear rate is in the form of linear equation. 1. Introduction

p U e l a c S d n a n g i s e D Mixing Systems

dict local shear rate, γ, at the impeller region. They discovered that γ in the direct vicinity of an impeller is propor-tional to the shaft speed. γ= ⋅k NMO (9) where kMO, the Metzner-Otto constant, depends on the im-peller design. Using the im-peller shear rate, the local vis-cosity can be calculated from Equation (6) or (8). The local


an open impeller pump is analyzed and Ye et al. (2015) in which the laminar/turbulent transition inside an open impeller pump is studied. In this case, the authors put the attention on the effects of shear stress, pump speed and fluid rheology. NUMERICAL MODEL In this work two centrifugal pumps are considered. Both machines have an open

Mechanical Agitator Power Requirements for Liquid Batches

2 = velocity of the impeller blade tip. D = diameter of the impeller, feet. N = rotational speed of the impeller. The volumetric flow rate through the radial sweep of the impeller, see Figure 6, is expressed as: q = V r2 * A p ( 2 ) where: V r2 = radial component velocity of the liquid leaving the blade tip. A

Design Calculation of Impeller for Axial Flow Pump

flow. Thus, the impeller forces the liquid into a rotary motion by impeller action. This study relates to the impeller design of axial flow pump that can develop a head of 3 m and deliver 0.3 m3/s of water at the speed of 1000 rpm. In the design impeller, outlet diameter is 350 mm, entrance vane angle

Process Parameters Affecting the Synthesis of Natural Flavors

impeller). The maximal shear rate (gmax) in the stirred bioreactor was calculated to characterize the mechanical stress according to the following equation [10]: gmax = 3.3N1.5D rL mL 0.5 (3) where N = agitation speed (s 1), D = impeller diameter (m), rL= the density of the medium (kg/m3), and mL= viscosity of the fluid (Pa s). 2.5.

Experimental investigation of hydrate formation, plugging and

helical blades impellers. They observed that impeller pitch and blade width did not affect the shear rate coefficient (the constant of proportionality between shear rate and rotational speed). For anchor and helical blades impellers, laminar flow can still be achieved at Reynolds numbers above 100 (La Fuente et al. 1998).

Computational Fluid Dynamics Modeling of Scalable Stirred

Figure 3 7: Velocity (A), shear rate (B), and energy dissipation rate (D) at different fluid heights in 100 ml bioreactor model. Cut plane 1 (z=0.03 m) on the left side is the

A new model of cavern diameter based on a validated CFD study

Shear-thinning phenomenon is the most common deviation from the Newtonian behavior of fluids. Shear-thinning fluids, e.g. polymer solutions and melts, suspensions, emulsions and even food products are found in almost all industries. High shear forces occur near an impeller during stirring. With highly shear-thinning fluids in that region an

Mixing Fundamentals - Mixing Fundamentals

shear. The power P consumed by an impeller is related to the volumetric circulation rate Q (pumping capacity) and the velocity Head Delta H from the impeller by: The pumping capacity of an impeller is defined as the volumetric flow rate normal to the impeller discharge area. The pumping capacity of an impeller is proportional

Mixing: Impeller Performance in Stirred Tanks

Po is the impeller s power number and it is a drag coef-ficient that is determined by the geometry of the impeller (blade width, blade angle, number of blades and so on.). The primary flow generated by an impeller is calculated from Equation (2): Q=Fl N D3 (2) Fl is the impeller s flow, or pumping number.