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Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[energy, fluid dynamics, mechanics] Dimensionless number indicating the ratio of the net drag force to the net inertial force pertaining to rotational systems, where Pw = ΔW/Δt (i.e., rate of change in work) is the power consumed or produced by the device, ωN the rotational rate of change, cNP a dimensional constant, ρ density, and L characteristic length. The Power number relates to momentum transfer in for instance agitators, pumps, and fans as well as power consumption.
Physical Processes
Published in Ralph L. Stephenson, James B. Blackburn, The Industrial Wastewater Systems Handbook, 2018
Ralph L. Stephenson, James B. Blackburn
In the viscous range, the expected result of power number being inversely proportional to Reynolds number is also confirmed by experimental data. A logarithmic plot of the relation between power number and Reynolds number has a slope of −1 in the viscous range.
Interactions of mixing and reaction kinetics of depolymerization of cellulose to renewable fuels
Published in Chemical Engineering Communications, 2018
Palmqvist et al. have reported that the mixing speed needed to attain complete fluid motion was initially (at 10% insoluble solids) as high as 300–400 rpm. As the hydrolysis proceeds, the viscosity of the material decreases, which leads to reduced power consumption. Thus, viscosity reduction results in increase in Reynolds number, which in turn leads to a decrease in power number. It was clear from the observations that the total dissipated energy at the beginning of the hydrolysis increases drastically with the increase in mixing speed in the vessel. It was recommended that, by increasing the enzyme concentration, the energy demand of the process can be reduced to the greater extent, because of the attainment of higher rates of hydrolysis of the biomass. Therefore, it is highly possible to attain same conversions at different mixing energy input by altering other operational parameters—residence time, mixing speed, and/or enzyme concentration. It was also seen that significant amount of energy was required to achieve even a slightly high level of conversion during the later stages of hydrolysis (Palmqvist et al., 2011).
Application of Eulerian-Eulerian-Lagrangian hybrid model to simulate liquid-liquid drop size distribution in stirred tank reactors
Published in Journal of Dispersion Science and Technology, 2020
Reza Farzad, Stefan Pirker, Simon Schneiderbauer
Experimental data for the velocity profiles together with the DSD in STRs rarely exists in the literature. The prediction of the impeller’s power number (Np) is a common way to characterize the flow in STRs which is used especially to validate the flow field in the CFD simulations (e.g.[23,72]). The power number can be calculated from the torque applied to the impeller
Performance intensification of a stirred bioreactor for fermentative biohydrogen production
Published in Preparative Biochemistry and Biotechnology, 2018
E. I. Garcia-Peña, C. Niño-Navarro, I. Chairez, L. Torres-Bustillos, J. Ramírez-Muñoz, E. Salgado-Manjarrez
The power number is one of the most frequently used parameters in the design of mixing processes. In the context of the drag force due to the power, some researchers assume that the power number NP depends on the impeller tip speed, but it mainly depends on the projected area of the blades, which is a function of the impeller diameter and the width and length of the paddle (W and L).[13]