Prediction ability of a new minimum bubbling criterion

The recently developed minimum bubbling criterion of Brandani and Zhang [19] for a prediction of the minimum bubbling point was validated using an experimental determination of the minimum bubbling points of spherical rigid non-porous powders with various particle size distributions. These powders include a narrow size cut powder, a “natural” size distribution powder and a “bimodal” size distribution powder. The minimum bubbling points were correctly identified using the εd and Ud characteristic curves, obtained from a correct interpretation of 1-valve and 2-valve bed collapse curves using the bed collapse model, developed by Cherntongchai and Brandani in [21]. In order to enhance the prediction ability of the stability criterion, an appropriate drag force correlation was introduced into the criterion. Then, it was pointed out that the characteristic parameter of the criterion has a strong dependence on the voidage term as an exponential function. As a result, a simple empirical correlation is proposed. The new stability criterion was, then, tested against a detailed comparison of 700 minimum bubbling points taken from literature. The criterion can very well predict the minimum bubbling voidage for various operating conditions of rigid non-porous materials and predict fairly well the minimum bubbling velocity.

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► Accurate minimum bubbling points were obtained from εd and Ud expansion curves.
► Brandani and Zhang stability criterion was validated, using this data points.
► A modified drag force correlation was proposed.
► A characteristic length was found to be an exponential function with voidage.
► Modified Brandani and Zhang stability criterion was proposed.