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TECHNICAL PAPERS

# Blade Angle Effects on the Flow in a Tank Agitated by the Pitched-Blade Turbine

[+] Author and Article Information
Yeng-Yung Tsui1

Department of Mechanical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan R. O. C.yytsui@mail.nctu.edu.tw

Jian-Ren Chou, Yu-Chang Hu

Department of Mechanical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan R. O. C.

1

Corresponding author.

J. Fluids Eng 128(4), 774-782 (Jan 24, 2006) (9 pages) doi:10.1115/1.2201636 History: Received May 01, 2005; Revised January 24, 2006

## Abstract

This paper presents a study of the influence of the blade angle on the flow in a tank stirred by the pitched-blade turbine. The flow induced by the pitched-blade turbine is usually described as an axial type with a principal ring vortex dominating the flow structure. However, it is known that as the blade becomes vertical, i.e., as the pitch angle of the blade becomes $90deg$, the flow is of the radial type, with two main ring vortices occupying the tank. Thus, a transition of flow type must take place when the blade angle is varied. This motivates the current study. A computational method was developed, which incorporates the unstructured grid technique to deal with the complex geometry in the tank. Multiframe of reference was employed to handle the rotation of the impeller. The results show that the transition from the axial type to the redial type is not progressive, but occurs all of a sudden at a particular angle, depending on the configuration. This critical angle decreases as the off-bottom clearance and the impeller size are increased. Its influences on the flow angle of the discharge stream, the power requirement, the induced flow rate through the impeller, and the pumping efficiency are discussed. The mechanism to cause the sudden change of flow type is addressed through observing the flow on the surface of the turbine blade.

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## Figures

Figure 1

Multiframe of reference

Figure 2

Illustration of a control volume

Figure 3

A sketch of a stirred tank

Figure 4

A typical computational grid

Figure 5

Comparison of predictions with measurements

Figure 6

Flow streamlines for D=T∕3, C=T∕3

Figure 7

Limiting streamlines on the surface of the blade for α=75deg and 76deg. The sketches on the left are referred to the front surface and those on the right to the back surface.

Figure 8

Pressure contours on the surface of the blade for α=75deg and 76deg. The sketches on the left are referred to the front surface and those on the right to the back surface.

Figure 9

Flow streamlines for D=T∕3, C=T∕2

Figure 10

Flow streamlines for D=T∕2, C=T∕3

Figure 11

Define flow angle of the discharge stream

Figure 12

Variation of the flow angle against the pitch angle of the blade for (a)D=T∕3, and (b)D=T∕2

Figure 13

Variation of the power number against the pitch angle of the blade for (a)D=T∕3, and (b)D=T∕2

Figure 14

Variation of (a)k* and (b)ε* against the pitch angle of the blade for D=T∕3

Figure 15

Variation of the pumping number against the pitch angle of the blade for (a)D=T∕3, and (b)D=T∕2

Figure 16

Variation of the pumping efficiency against the pitch angle of the blade for (a)D=T∕3, and (b)D=T∕2

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