Experimental study and numerical simulation of local void fraction in cold-gassed and hot-sparged stirred reactors

Local void fraction distributions of different superficial gas velocities at 24, 54, 68, and 81 °C were measured with an electric conductivity probe in a fully baffled, dished base stirred vessel of 0.48 m diameter holding 0.145 m3 of liquid. A 6-elliptical-blade disk turbine (HEDT) was used as the bottom impeller to disperse the incoming gas, with two down pumping 4-blade hydrofoil impeller (WHD) above. Results showed that the averaged local void fraction at of 81 °C was about 20% lower than that at ambient temperature, though the profiles were similar in both cases. The local void fraction increased with increasing superficial gas velocity. The standard Eulerian–Eulerian formulation of the k–ε turbulence model with multiple frames of the reference (MFR) was used in the simulation. The population balance model (PBM) combined with MUSIG model was implemented in the commercial CFX code. The simulated local void fraction profiles at N=4, 6, and 8 s−1 at the same superficial velocity of Vs=0.0156 m/s and at the location of r/R=0.85 are in reasonable agreement with the measurements.

► Both cold-gassed and hot-sparged systems have similar local void fraction distributions.
► The averaged void fraction in the hot system of 81 °C is about 20% lower than that at ambient temperature.
► The simulated void fraction profiles are in reasonable agreement with the measurements.