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A new method for better and faster mixing

Two or more different types of granular material are mixed using mixers, in large amounts to produce a uniform mixture in the paint, fertilizer, and pharmaceutical industries. A common problem with these mixers is that particulates or granules of dissimilar size, shape and density tend to segregate and separate out as clumps.

Prof. D. V. Khakhar and his student of Department of Chemical Engineering have devised specially designed impellers to the central shaft of the rotating drums used for such mixing. Impellers are similar to blades of a fan which protrude out from the shaft of the rotor. They actively churn the flow of the material near the drum axis and also disperse the heavy material that tends to accumulate near the central axis.

The researchers have demonstrated the efficacy of this improvisation by a novel experiment, where glass beads of two different size and colors (red and colorless) were loaded into a horizontal drums, one with impeller and one without, and rotated. The drum with impeller showed superior mixing along both the axial (along the length of the drum) and radial (across the circular cross section of the drum) directions. The impeller was designed to have 'inverse S' shape. Best results were obtained when the impeller was rotated at a considerably higher speed compared to that of the drum and in the same direction as that of the drum.

Although uniform dispersion of the beads of different colours could be clearly visualized in snapshots of the rotating drum, quantitative measurements confirmed that the mixing index was high and segregation index was low. In particular they found that for certain size of the impeller blades, the distribution of smaller particles varies rather uniformly across the cross-section and thus core formation was prevented. This invention will result in more efficient industrial mixers.

Indian patent application no. 809/MUM/2003 Patent grant no. 213856
Inventors: D V Khakhar and S Hajra


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