Slug properties such as average slug vertical length, slug rising velocity and slug frequency in a fluidized bed (0.38 m-ID and 4.4 m height) of polymer powders have been determined by measuring pressure flunctuations The effects of excess fluidization velocity (0.3-0.9 m/s), particle size ($600-1200 \mum$), bed height (0.65-1.15 m) and distributor type (perforated plate and bubble cap type) have been determined.
The slug frequency decreases slightly with increasing excess fluidization velocity but slug rising velocity, vertical slug length and the maximum bed height increase linearly with increasing excess fluidization velocity.
As the initial static bed height increases the slug frequency decreases slightly but slug rising velocity and vertical slug length increase. The increasing rate of slug rising velocity decreases with increasing gas velocity.
The slug frequency appears to be independent of the type of particles used but there are two slug types can be observed, namely square-nose slug with LLDPE and round-nose slug with PP.
The Slug frequency is higher with the opening higher area ratio, however, there is no effect of the opening area ratio on slug rising velocity. With the same opening area ratio, the number of orifice and the distributor shapes have no effect on slug rising velocity. Therefore, the slug rising velocity is calculated from the following correlation equation.
$U_S = 0.6(U_o-U_{mf}) + 0.18 \sqrt{gD}$
With the bubble cap distributor, the slug frequency is higher than that with the perforated plate distributor but the decreasing rate of slug frequency with the bubble cap type is higher than that with the perforated plate. Therefore, slug frequency is nearly same with the two distributor at higher excess fluidization velocity ($U_o-U_{mf}$).
The obtained slug frequency has been correlated with the excess fluidization velocity, bed height and column diameter. The obtained correlation equation as
$\frac{fH_{mf}}{\mu-\mu_{mf}} = 0.08\left[\frac{gD}{(\mu-\mu_{mf})^2}\right]+0.07$
The obtained vertical slug length has been correlated with the excess fluidization velocity, bed height and column diameter as
$\frac{L{{(DH_{mf})^}1/2}} = 1.82\frac{\mu-\mu_{mf{{{\sqrt}gD}}-0.13$
