The liquid phase mixing is considerably complicated when two
other dispersed phases are present at the same time, such as the
cases in gas–liquid–solid, liquid–liquid–solid and gas–liquid-liquid systems. Among three-phase systems in stirred tanks, the
gas–liquid–solid system is the most investigated one. The critical
agitator speed and the corresponding power consumption for
solids suspension and gas dispersion are the popular subjects.
Relatively limited work addressed the mixing time in three-phase
stirred reactors. measured the mixing time
in a single-impeller gas–liquid–solid agitated contactor using the
conductivity method, and reported that the mixing time behavior
was different as compared to the solid–liquid system and much
similar to the gas–liquid system. Longer mixing time in the gas–
liquid–solid system than that in the solid–liquid and gas–liquid
systems was observed in their measurements. They found that
the variation of mixing time with impeller speed in the aerated
solid–liquid suspension was a useful indication to determine the
critical solid suspension speed at the gassed condition (Njsg) ) investigated liquid-phase mixing time by
transient pH measurements in a single-impeller gas–liquid–solid
stirred tank with non-Newtonian fluids as the continuous phase.
The presence of either gas or solids increased the mixing time in
non-Newtonian fluids, and the gas made more substantial contribution to the increased mixing time compared with that in
pure water at lower speeds. Multi-impeller gas–liquid–solid
agitated tanks were more covered in the literature.) investigated the mixing in a three-impeller (four pitched
blade downflow-four pitched blade downflow-Pfaudler type
impeller) gas–liquid–solid stirred tank, and found that the mixing
time increased with superficial gas velocity to 0.016 m/s, after
which the mixing time decreased in the case of melamine
suspension. Generally, solid particles have been found to extend
liquid phase mixing time, but for small glass beads drew no generalized and quantitative relationship for the
mixing time.observed that the mixing time
in the solid–liquid case at higher solid concentrations (up to 40%
w/w) was much greater when compared to the situation without
solids, but for the gas–liquid–solid three phase system the
increase was relatively small, especially with Scaba and 6MFU
impellers. used the mixing time
variation method to determine Njsg in four-impeller gas–liquid–
solid three phase systems.