Linear stability analysis of gas-fluidized beds for the prediction of incipient bubbling conditions

This work focuses on the development of a novel linear stability criterion for the state of homogeneous fluidization regime, based on a new mathematical model for gas-fluidized beds. The model is developed starting from the well-known particle bed model. A mono-dimensional momentum balance is derived leading to a set of equations which explicitly include voidage-gradient dependent terms (elastic force) for both solid and fluid phases. A fully predictive criterion for the stability of homogeneous fluidization state is here proposed, based on the well-known Wallis' linear stability analysis. The criterion requires the choice of an appropriate averaging distance, which in the present development is found to be bed-voidage dependent. The linear stability criterion resulted in turn in a simple, yet fully predictive, relationship for incipient bubbling voidage. Validation was carried out analyzing the influence of all physical properties and sensitivity to closure relations, showing substantial agreement with literature data