ABSTRACT
General comments While uidization by liquids results in an expansion of the bed with smooth internal movement of the individual particles of the suspension in a owing stream of the liquid, uidization by gas breaks up the owing gas into bubbles (i.e., individual voids) at or soon after the onset of uidization. These two patterns of behavior are referred to as particulate or homogeneous and aggregative or heterogeneous uidization, respectively. As the gas density increases, and/or the solid density decreases, the behavior approaches that of particulate uidization (even if the uid is not a liquid), and vice versa. The following criteria can be used to roughly distinguish between the two modes of uidization (i.e., for dening the so-called quality of uidization):
( )( ) , ; ,Fr
g L dmf mf
T Re′
−
< >
r r 100 100particulate aggregative
(9.1)
where Frmf = u2mf/gdp (Froude group at minimum uidization) and Re′mf = dpumfρG/μ (Reynolds number at minimum uidization). Although a number of studies, of varying degrees of rigor, have added to our understanding of uidization over the last 60 years, six developments of a very general nature stand out as signicant-providing the basic structure of uid-bed reactor analysis and design.
