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Research Papers: Flows in Complex Systems

Investigation of the Flow Field in a Rectangular Vessel Equipped With a Side-Entering Agitator

[+] Author and Article Information
C. Gómez1

Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, BC, V6T 1Z3, Canadaclara@chbe.ubc.ca

C. P. J. Bennington, F. Taghipour

Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, BC, V6T 1Z3, Canada

1

Formerly Ford.

J. Fluids Eng 132(5), 051106 (May 06, 2010) (13 pages) doi:10.1115/1.4001575 History: Received July 23, 2009; Revised March 23, 2010; Published May 06, 2010; Online May 06, 2010

Abstract

The hydrodynamics of stirred vessels with side-entering impellers, which are used in numerous process industries including petroleum, foods, and pulp and paper manufacturing, have received limited attention. In the present work, the flow in a reduced size rectangular tank equipped with a side-entering axial flow impeller, scaled down from the industrial agitation of low consistency pulp fiber suspensions, was investigated using particle image velocimetry (PIV) and computational fluid dynamics (CFD), in the laminar regime $(18≤Re≤120)$. Tuning of the PIV measuring parameters for an optimum capture of valid velocity vectors within a representative portion of the vessel is described. A detailed description of the construction and refinement of the grid and quantification of the discretization error in the CFD results is also presented. The simulation predictions were extensively evaluated by comparing the measured planar flow patterns and velocity fields at various locations in the mixing vessel. Very good agreement was found between PIV measurements and computed velocities confirming the efficiency of CFD in the analysis of mixing systems. The prediction of global mixing parameters was also evaluated. The computed impeller torque and impeller power number agreed very well with experimental measurements over the range of Re studied.

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Figures

Figure 1

(a) Schematic of the experimental setup showing the front view of the mixing vessel, the PIV acquisition system, triggering device used, and photograph of the impeller (upper right corner). (b) Location and size of the measuring areas. The dashed lines illustrate the locations at which the velocity profiles were evaluated. The horizontal line is located at impeller height and the vertical line is located at a distance d cm (varied from 3 cm to 10 cm) in front of the impeller. (c) PIV Illumination planes. (d) Schematic of the large-scale flow patterns over a photograph of the PIV illumination plane aligned with the impeller tip.

Figure 10

CFD and PIV results for vertical profiles of normalized axial and vertical velocity components for a vertical line at x∗=0.48; d=10 cm (see Fig. 1), spanning the PIV image height, in a plane aligned with the blade tip (z=−5.25 cm). Results are shown for N=118 rpm, Re=36 and N=267 rpm, Re=82. The error bars indicate the standard deviation for a series of three measurements.

Figure 2

Profile of the mean (a) axial and (b) vertical velocities at a line located at x∗=0.37; d=6 cm (see Fig. 1) in the measurement plane aligned with the impeller tip (z=−5.25 cm), at N=118 rpm, Re=36

Figure 3

Effect of Δt on the mean value of the axial velocity measured at a line located at x∗=0.33; d=4.5 cm (see Fig. 1) in the measuring plane aligned with the impeller tip. (a) N=118 rpm, Re=36. (b) N=267 rpm, Re=83.

Figure 4

Effect of the impeller angular position α (at two different angles 90 deg apart from each other) on the mean value of the axial velocity measured at a line located at x∗=0.29; d=3 cm (see Fig. 1), in the measuring plane aligned with the impeller tip. N=267 rpm, Re=83.

Figure 5

Computed vertical profiles of axial velocity in a plane aligned with the blade tip (a) for a vertical line at x∗=0.29; d=3 cm (see Fig. 1) and (b) for a vertical line at x∗=0.48; d=10 cm (see Fig. 1). N=327 rpm, Re=101.

Figure 6

Mean planar velocity fields for Re=101 in the three vertical planes of measurement: (a) midplane (z=0 cm); (b) plane aligned with the impeller tip (z=−5.25 cm) and (c) plane located 2 cm away from the vessel wall (z=−10.25 cm). Velocity vectors colored by velocity magnitude (m/s).

Figure 7

Experimental (left) and CFD (right) planar velocity fields in the center plane of measurement for (a) Re=36, (b) Re=82, and (c) Re=101. Velocity vectors colored by velocity magnitude (m/s).

Figure 8

CFD and PIV results for horizontal profiles of normalized axial and vertical velocity components for a horizontal line located at the impeller center (see Fig. 1), and covering the full length of the PIV image, in a plane aligned with the blade tip (z=−5.25 cm). Results are shown for N=386 rpm, Re=120 and N=118 rpm, Re=36. The error bars indicate the standard deviation for a series of three measurements.

Figure 9

CFD and PIV results for vertical profiles of normalized axial and vertical velocity components for a vertical line at x∗=0.34; d=5 cm (see Fig. 1), spanning the PIV image height, in a plane aligned with the blade tip (z=−5.25 cm). Results are shown for N=118 rpm, Re=36 and N=267 rpm, Re=82. The error bars indicate the standard deviation for a series of three measurements.

Figure 11

CFD and PIV results for vertical profiles of normalized axial and vertical velocity components at Re=82; (a) for line at x∗=0.34; d=5 cm (see Fig. 1) in the midplane of measurement (z=0 cm), and (b) for line at x∗=0.48; d=10 cm (see Fig. 1) in the measurement plane located 2 cm away from the vessel wall (z=−10.25 cm). The error bars indicate the standard deviation for a series of three measurements.

Figure 12

Comparison of NP versus Re for experimental and computational tests. The error bars are based on the accuracy with which the torque was measured (±0.002 N m).

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