Mass transfer between different phases in a mechanicallystirred vessel and its comparison with that in a gas-stirred one

In order to understand effect of operating conditions on mass transfer between different phases in a mechanically stirred vessel, cold model study was carried out with liquid paraffin as a dispersion phase and ion-exchanged water as a continuous phase. Inner diameter of vessel, D, was varied in conjunction with both depth, H₀, as D=H₀=400 and 300 mm. Rotation speed, N, was changed between 50-240 rpm, volume ratio, V_oil/V _w, of dispersed to continuous phase was 5.9×10^-2 and 1.2×10^-1. Liquid/liquid mass transfer rate showed characteristic trend depending on liquid/liquid mixing pattern. It was kept nearly constant at lower level in the region I, monotonically increased in the region II except near the region III and its increasing rate decreased in the region II near the region III. Liquid/liquid mixing pattern was grouped into three regimes. I: the region where liquid/liquid interface did not arrive at the impeller, II: the region where liquid/liquid interface attained at impeller position, III: the region where gas/liquid interface touched impeller. Under the same supply rate of mixing energy, liquid/liquid mass transfer rate of mechanical stirring corresponded to that of gas stirring at a point in the region II. In the region I and the first half of II, liquid/ liquid mass transfer rate of gas stirring is larger than that of mechanical stirring, whereas that of gas stirring is smaller than that of mechanical stirring in the region III and the latter half of II. Gas/liquid mass transfer rate increased remarkably with an increase in N in the region III.