A model for the interpretation of the bed collapse experiment

The bed collapse technique was first reported by Rietema in 1967. It is one of the standard techniques commonly used for the characterization of the fluidization quality of powders. It is particularly useful for fine fluidized particles or more generally for powders belonging to group A of the Geldart classification. The bed collapse experiment is used to measure the time required for the de-aeration of the particle suspension and, by extrapolating the linear portion of the collapse curve, the dense phase voidage. These should be dependent only on the particle and fluid properties, but it has long been recognised that the system configuration will affect these results. We present a new model that can be used to predict the bed collapse curve, the bubble escape time, and the de-aeration times taking into account the system configuration. This can be achieved from the knowledge of the initial conditions, the dense phase voidage, and the superficial velocity in the dense phase. The model can be used to predict under which conditions the 1-valve or 2-valve configuration will yield the correct extrapolation to obtain the dense phase voidage from the experimental curve. The model has been validated using experimental bed collapse curves for a set-up that can be operated in the 1-valve and 2-valve configuration. Excellent agreement between experiment and simulations was obtained. (c) 2004 Elsevier B.V. All rights reserved.