Gas-solid suspensions flowing through a granular bed

Investigations are presented concerning a gas-particle mixture flowing through a fixed granular bed. Solids hold-up and pressure drop have been measured for various gas and solids flow rates. The main results are the following. (i) Transitions between regimes can be observed by means of diagrams already valid for free fluidization; a transport velocity and a critical velocity can be evaluated from them. (ii) The concentration of powder in the flowing suspension is strictly proportional to the powder flow rate at a fixed gas velocity. An average velocity of the solids can then be calculated; this velocity is a linear function of the gas velocity. (iii)) The pressure gradient minus the pressure gradient for the gas alone is strictly proportional to the powder concentration at a given gas velocity. In contrast to the free fluidization situation, this 'net' pressure gradient is always lower than the volumetric weight of the solids present in the suspension.