The purpose of this letter is to present an improved version of the eruption-like flow demonstration device that I had reported on in this publication.1 The earlier version dealt with only one granular material, ceramic microsphere (CMS). The improved version contains CMS and sand side by side for comparison as shown below. Their average grain sizes differ by approximately an order of magnitude.

Overall dimensions of the device are the same as before, but a vertical plate divides each of the lower and upper chambers into two equal bins, allowing for separation of the two granular materials. The separating disk between the upper and lower chambers has symmetrical holes on both sides of the vertical divide.

When the cylinder is turned upside down, sand and CMS flow through identical geometries but very differently. The sand flows quickly and uniformly, as shown in the video,2 while the CMS, as...

Supplementary Material

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