Study of bubble dynamics in gas-solid fluidized beds using ultrashort echo time (UTE) magnetic resonance imaging (MRI)

•Ultrashort echo time MRI was used to image the dynamics of a gas-solid fluidised bed.•Measurements performed at a resolution of 1 mm × 1 mm × 2 mm in 25 ms.•Images were used to track bubbles as they rise through the bed.•Observed in-plane bubble coalescence, bubble wake evolution and lateral drift of bubbles.•Vertical images show approximately 1D perturbations in voidage collapsing into bubbles.

A narrow column, gas-solid fluidized bed was studied using ultrashort echo time (UTE) magnetic resonance imaging (MRI) for particles of diameter 0.44 mm, 0.72 mm, and 1.5 mm. UTE enables 1D and 2D images to be acquired of an individual bubble as it rises through the sample with higher spatial resolution than has previously been possible with MRI. One-dimensional images allow calculations of bubble rise velocity and bubble frequency. They also show leading-trailing bubble coalescence. Images of bubbles in the axial plane were obtained in 2D, with the location of images adjusted to track bubbles as they rise. These measurements were used to observe the wake region of a bubble, lateral drift as the bubble rises, and in-plane bubble coalescence. Images in the vertical plane were used to study the stability of a 1D perturbation in voidage. The perturbation collapsed rapidly with particles <1 mm in diameter, but for the 1.5 mm diameter particles the perturbation was often stable throughout the imaging region.