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This study was carried out to investigate the break up of nanoparticle clusters in a liquid using an in-line rotor stator. Two types of fumed silica particles were dispersed in distilled water: Aerosil 200 V, which is hydrophilic, has a primary particle size of 12 nm and Aerosil R816 which is based on Aerosil 200 V and surface modified to render it hydrophobic. The article reports on the rheology of the dispersions, particle size analysis, the effect of concentration, and processing conditions such as the rotor speed, that is, the specific power input, and flow rate, that is, the residence time.

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It has been unclear whether bubbles are required to induce particle velocity fluctuations in gas fluidized beds (FBs). We show that bubbles are not necessary by applying diffusing-wave spectroscopy to particles whose minimum bubbling velocity is approximately 5 times that of the minimum fluidization velocity. Fluctuations are first observed at or just above fluidization and increase in magnitude with superficial velocity. The distribution of velocity fluctuations in the bed is also presented: they are symmetrical about the centreline where they are maximal and increase with height above the distributor.