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A fibre optic probe has been used to measure voidage profiles in the fountain, spout and annulus of spouted beds. The voidage in most of the annulus was found to be somewhat higher than the loose‐packed voidage and increased with increasing spouting gas flow rate, contrary to usual assumptions. There is a denser region in the annulus where the voidage was a little lower than the loose‐packed bed voidage. In the core of the fountain, the voidage decreased with height for low spouting gas flow rate, consistent with the model of Grace and Mathur (1978); however, at higher gas flow rate, it first increased with height and then decreased towards the fountain top. The radial profiles of local voidage were roughly parabolic in the lower portion of the spout and blunt in the upper portion.

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