Magnetic resonance imaging (MRI) of jet height hysteresis in packed beds

• Magnetic resonance imaging is used to image jets and spouts in packed beds.
• We study the role of particle type, bed size and fill on the jet–spout transition.
• We propose a criterion to predict hysteresis in the jet–spout transition.
• The effect of particle sphericity on the minimum spouting velocity is shown.

The hysteresis in the jet–spout transition in packed beds was systematically investigated using magnetic resonance imaging (MRI) and pressure measurements. Specifically, the hysteresis in the jet height as a function of the orifice velocity was studied as a function of particle type, bed dimension and fill level. In order to compare the hysteresis of different experimental configurations, a hysteresis coefficient h=(Usf−Ums)/Usfh=(Usf−Ums)/Usf was introduced. It was observed that an increase in the fill level or the bed dimensions resulted in higher values of h. It was also found that the hysteresis is most pronounced for non-spherical particles, whereas no hysteresis was observed for the most spherical particles when placed in the smallest bed. In addition, pressure measurements were used to explore the relationship between the pressure drop and the jet height.

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