Measurement of gas-liquid mass transfer in an agitated vessel - A comparison between different impellers

Measurement of mass transfer rate was carried out in an agitated vessel with gas sparging. The performance of mass transfer of several commonly used impellers (i.e. Lightnin A315 and A310, 45 degrees pitched blade turbine, concave blade turbine, Rushton turbine, and Rushton turbine with holes) were examined systematically under the same fluid and tank conditions. A dynamic gassing-out method was used to measure the mass transfer rate of oxygen from gas to the de-ionised water. The variation of the dissolved oxygen concentration of the water was measured by a polarographic dissolved oxygen probe (ORION PCM800). The present data shows reasonable agreement with that in previous publications such as those of Linek et al. (1987), Hickman (1988), Warmoeskerken and Smith (1989), Martin et al. (1994), and Chen and Chen (1999). All the data collected here shows that van't Riet's (1979) expression, i.e.: k(L)a = alpha (P/V)U-0.4(s)0.5 represents reasonably well (to within +/- 30%) the correlation of k(L)a with specific power P/V and superficial gas velocity US. However, the present data seem to indicate that the radial now impellers provide slightly higher (17%) mass transfer rate than the axial flow impellers.