Most authors publishing numerical calculations for the how field claim
that scientific progress on liquid mixing in bubble columns must be b
ased on the fluid dynamics. In a previous paper (Millies, M. and Mewes
, D., 1995, Calculation of circulating flows in bubble columns. Chem.
Engng Sci. 50, 2093-2106) a calculation method was presented, which al
lows the prediction of the flow field including several consecutive ci
rculation cells. The conclusions for liquid mixing are drawn in the pr
esent paper. The main transport resistance of mixing of liquid phase i
s located between the circulation cells, a region which was completely
neglected up to now. A structured model and even the one-dimensional
dispersion model may be obtained from simplifying the transport equati
on of tracer under certain assumptions. Thus, the coefficients of the
structured model and the one-dimensional dispersion model are obtained
as results of the numerical calculation. Even though the stirred tank
model appears convincing on first view, it is shown to fail as a link
between the fluid dynamics and the liquid mixing.