HYDRODYNAMICS IN EXTERNAL-LOOP AIRLIFT BIOREACTORS WITH STATIC MIXERS

Liquid circulation superficial velocity and gas holdup behaviours were investigated in an external-loop airlift bioreactor of 0.170 m(3) liq uid volume in gas-induced and forced-circulation-loop operation modes, in the presence of static mixers made of corrugated stainless steel p ieces, resulting in packets with the height-to-diameter ratio equal to unity and using non-Newtonian starch solutions as liquid phase. The s tatic mixers were disposed In the riser in three blocks, each with thr ee mixing packets, successively turned 90 degrees to the adjacent mixi ng element. It was found that in the presence of static mixers and for ced-loop operation mode, liquid circulation superficial velocity in th e riser section was significantly diminished, while gas holdup increas ed in a great measure. It was considered that static mixers split the fluid into individual streams and break up the bubbles, resulting in s mall bubble sizes with a relative homogeneous bubble distribution over riser cross section. They act as supplementary resistances in liquid flow, reducing riser cross sectional area, equivalent with A(D)/A(R) a rea ratio diminishing.