CONCENTRIC-TUBE AIRLIFT BIOREACTORS PART III - EFFECTS OF GEOMETRY ONMASS-TRANSFER

Mass transfer coefficients were measured in three concentric-tube airl ift reactors of different scales (RIMP, V-L = 0.07 m(3); RIS-1, V-L = 2.50 m(3) RIS-2, V-L = 5.20 m(3)). The effects of top and bottom clear ance and flow resistances at downcorner entrance were studied in water -air system. Experimental results show that h(s), h(B) and A(d)/A(R) r atio affect K(L)a values as a result of their influence on gas holdup and liquid velocity. The gas-liquid mass-transfer coefficients for all the geometric variables were successfully correlated as Sherwood numb er with Froude and Galilei numbers, the bottom spatial ratio (B = h(B) /D-R), the top spatial ratio (T = h(s)+D-R/D-R), the gas separation ra tio (Y = h(s)+D-R/D-s) and the downcomer flow resistance ratio (R = A( d)/A(R)). The proposed empirical model satisfactorily fitted the exper imental data obtained in large airlift reactors and some data presente d in literature.