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The behaviour of agitated submerged granular media is of wide relevance technologically and in nature. Recent modelling of such systems has invoked a kinetic theory description. Such descriptions involve the so-called granular temperature, which is directly related to the mean-square of the velocity fluctuations about the mean flow velocity. The better formulation of these models and their subsequent validation demand the experimental elucidation of the dynamics and granular temperature of submerged granular media undergoing excitation. Such elucidation, based on the non-invasive optical technique of diffusing wave spectroscopy (DWS), is reported here. The particle dynamics and granular temperature have been studied for a periodically forced submerged granular bed as a function of the forcing conditions. Rather unexpectedly, it was found that the granular temperature scaled with the square of the acceleration of the forcing rather than the square of the peak forcing velocity as in dry vibro-fluidized beds. It was also observed that the granular temperature increased with distance above the base of the bed where the forcing was applied.

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.

We report granular temperature and solid fraction fields for a thin rectangular bed (20×200 mm crosssection and 500 mm high) of glass particles (mean diameter of 165 m and density of 2500 kg/m 3 ) fluidized by water for superficial velocities ranging from 0.05U t , which is approximately double the minimum fluidization velocity, to 0.49U t , where U t is the particle terminal velocity estimated by fitting the Richardson-Zaki correlation to the bed expansion data. At superficial velocities below 0.336U t , the solid fraction and granular temperature are uniform throughout the bed. At higher superficial velocities, the solid fraction tends to decrease with height above the distributor, whilst the granular temperature first increases to a maximum before decaying towards the top of the bed. Correlation of the mean granular temperature with the mean solid fraction and the local granular temperature with the local solid fraction both suggest that the granular temperature in the liquid fluidized bed can be described solely in terms of the solid fraction. The granular temperature increases monotonically with solid fraction to a maximum at ≈ 0.18 where it then decreases monotonically as approaches the close-packed limit.

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