Impellers power consumption

D IMPELLER DIAMETER N IMPELLER ROTATIONAL SPEED p LIQUID DENSITY 

the 8-inch impeller with standard blades was more effective than the 8-inch impeller with narrow blades. These results all indicate that in this range of impeller-size-to-tank-size ratio, pumping capacity is more important than fluid shear rate for this particular criterion of physical dispersion. 

Looking now at some actual published mass transfer rates. Fig. 29 shows the results of some experiments reported previously and Figs. 30 through 33 show some additional experiments reported which give further clarification to Fig. 29. 

At the far right of Fig. 29 is shown high mixer power levels relative to the gas rate, and it can be seen that D/T makes no difference to the mass transfer. This occurs in some types of hydrogenation, carbonation, and chlorination. In those cases, the power level is so high relative to the amount of gas added to the tank tiiat flow to shear ratio is of no importance. 

This has led to the common practice today of using the distribution of power in a three-impeller system, for example, 40% to the lower impeller and 30% to each of the two upper impellers. Fig. 35. 

Impeller power draw is the power transfer from the impeller to the fluid causing fluid motion. This power is eventually dissipated by viscous dissipation into heat within the fluid. Power dissipation is often termed power consumption and is equal to the power draw at steady state according to a global or macro scale kinematic energy balance. 

Several approaches have been applied estimating the power consumption. The traditional approach is to use dimensional analysis, creating power laws based on experimental data on torque [87]. The power or Newton number has the same function as the pumping number, accounting for various effects on power consumption. 

Impeller power consumption, P, is primarily a function of system characteristics like impeller speed, N, impeller diameter, P, impeller design, physical properties of fluid, vessel size and geometry, impeller location and baffle design. Through extensive experimental work, correlations determining the 

The power number in (7.4) is usually determined from suitable param-eterizations which are functions of Re3molds number, Fronde number, and geometry. 

Fundamental momentum and energy analyzes can be used to verify the relationships obtained by dimensional analysis. The theory might be of more general interest thus a brief outline is presented in this section. 

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Not only is the type of flow related to the impeller Reynolds number, but also such process performance characteristics as mixing time, impeller pumping rate, impeller power consumption, and heat- and mass-transfer coefficients can be correlated with this dimensionless group. 

Power Consumption of Impellers Power consumption is related to fluid density, fluid viscosity, rotational speed, and impeller diameter by plots of power number (g P/pN Df) versus Reynolds number (DfNp/ l). Typical correlation lines for frequently used impellers operating in newtonian hquids contained in baffled cylindri-calvessels are presented in Fig. 18-17. These cui ves may be used also for operation of the respective impellers in unbaffled tanks when the Reynolds number is 300 or less. When Nr L greater than 300, however, the power consumption is lower in an unbaffled vessel than indicated in Fig. 18-17. For example, for a six-blade disk turbine with Df/D = 3 and D IWj = 5, = 1.2 when Nr = 10. This is only about... 

On the reverse, how does the presence of particles affect local and global flow features in the vessel such as the vortex structure in the vicinity of the impeller, power consumption, circulation and mixing times, and the spatial distribution of turbulence quantities more specifically colliding particles have an impact on the liquid s turbulence (Ten Cate et al., 2004) while local particle concentrations affect the effective (slurry) viscosity which may be useful in the macroflow simulations ... 

Oyama and Endoh (012) studied the solution of sugar in water in 6.7- and 10.8-in. baffled vessels using paddles and flat-blade turbines. They report a mass-transfer coefficient which was proportional to the cube root of the particle diameter and to the cube root of the impeller power consumption per unit mass of agitated liquid. 

Rate of impeller rotation could be used as some indication of the work being done on the material. As the motor or impeller power consumption is proportional to the product of torque and speed, the latter is an important factor in evaluating the corresponding load. 

Impeller power consumption can be calculated as a product of the direct torque, rotational impeller speed, and a coefficient (usually equal to 2n times a unit conversion factor, if required). 

Zega, J. Lee, D. Shiloach, A. Erb, D. Scale-up of the wet granulation process for a dicalcium phosphate formulation using impeller power consumption. AAPS Meeting November, 1995. 

Power Consumption of Impellers Power consumption is related to fluid density, fluid viscosity, rotational speed, and impeller diameter by plots of power number (g P/pN Df) versus Reynolds number (D Np/p). Typical correlation lines for frequently used impellers operating in newtonian liquids contained in baffled cylindrical vessels are presented in Fig. 18-17. These curves may be used also... 

Nusselt number, Nu = hl/k (—) origo, an arbitrary reference point in space impeller power consumption (W) wave period associated with Taylor hypothesis (s) function in MWR example laminar impeller pitch (m) pressure (Pa)... 

Impeller power consumption determines the horsepower and impeller diameter required for a given mixing proce.ss. 

As already discussed in context with the single-phase simulations, boundary conditions at the impeller are predicted from measured data of the averaged velocities. The gassed linear liquid velocities differ from the ungassed velocities because impeller power consumption and pumping capacity of the impeller decrease due to gassing. 

AP net impeller power consumption (motor power consumption minus the dry blending baseline level)... 

Nusselt dimensionless number impeller power consumption [J s ]... 

Correlations for Impeller Power Consumption under Gassed Conditions. The gassed power consumption is one of the most important parameters in the successful design and scale-up of stirred tank bioreactors since it influences numerous mixing parameters whose interactions are complex. However, a major weakness of scale-up at constant Pg/V is in the estimation of the... 

Origo, an arbitrary reference point in space Impeller power consumption (W)... 

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