Results For Impellers Research Articles

Experimental Study on Scale-Up of Solid–Liquid Stirred Tank with an Intermig Impeller

The scale-up of a solid–liquid stirred tank with an Intermig impeller was characterized via experiments. Solid concentration, impeller just-off-bottom speed and power consumption were measured in stirred tanks of different scales. The scale-up criteria for achieving the same effect of solid suspension in small-scale and large-scale vessels were evaluated. The solids distribution improves if the operating conditions are held constant as the tank is scaled-up. The results of impeller just-off-bottom speed gave X = 0.868 in the scale-up relationship ND X = constant. Based on this criterion, the stirring power per unit volume obviously decreased at N = N js, and the power number (N P) was approximately equal to 0.3 when the solids are uniformly distributed in the vessels.

Characterization of hydromechanical stress in aerated stirred tanks up to 40 m(3) scale by measurement of maximum stable drop size.

BackgroundTurbulence intensity, or hydromechanical stress, is a parameter that influences a broad range of processes in the fields of chemical engineering and biotechnology. Fermentation processes are often characterized by high agitation and aeration intensity resulting in high gas void fractions of up to 20% in large scale reactors. Very little experimental data on hydromechanical stress for such operating conditions exists because of the problems associated with measuring hydromechanical stress under aeration and intense agitation.ResultsAn indirect method to quantify hydromechanical stress for aerated operating conditions by the measurement of maximum stable drop size in a break-up controlled dispersion was applied to characterize hydromechanical stress in reactor scales of 50 L, 3 m3 and 40 m3 volume with a broad range of operating conditions and impeller geometries (Rushton turbines). Results for impellers within each scale for the ratio of maximum to specific energy dissipation rate ϕ based on measured values of maximum stable drop size for aerated operating conditions are qualitatively in agreement with results from literature correlations for unaerated operating conditions. Comparison of data in the different scales shows that there is a scale effect that results in higher values for ϕ in larger reactors. This behavior is not covered by the classic theory of turbulent drop dispersion but is in good agreement with the theory of turbulence intermittency. The data for all impeller configurations and all aeration rates for the three scales can be correlated within ±20% when calculated values for ϕ based on the measured values for dmax are used to calculate the maximum local energy dissipation rate. A correlation of the data for all scales and all impeller configurations in the form ϕ = 2.3∙(ϕunaerated)0.34∙(DR)0.543 is suggested that successfully models the influence of scale and impeller geometry on ϕ for aerated operating conditions.ConclusionsThe results show that besides the impeller geometry, also aeration and scale strongly influence hydromechanical stress. Incorporating these effects is beneficial for a successful scale up or scale down of this parameter. This can be done by applying the suggested correlation or by measuring hydromechanical stress with the experimental method used in this study.

811 ガイドベーン中の振動遠心羽根車に働く非定常力の解析(関東支部 茨城講演会)

Lateral fluid forces acting on a rotating centrifugal impeller in whirling motion were analyzed by using unsteady potential flow theory. Impellers operating in diffusers with vanes were modeled and the fluid forces were calculated. Results of fluid forces were converted to mass, damping, stiffness matrices by the Fourier Integral and least square method. The results for impellers with guide vanes showed that the time averaged values of fluid forces remained almost unchanged, while there were significant instantaneous fluctuations due to the impeller/guide vane interactions. And it was found that the elements of matrices for impeller with guide vanes were usually greater than those for impeller without guide vanes.