1992 Volume 33 Issue 10 Pages 927-936
Synthesized Cu–Bi and Cu–Bi–Pb alloys were vacuum-melted at 1446 K while being stirred with Stirrers A and B, which could produce predominantly tangential flow (low surface renewal rate) and axial flow (high surface renewal rate), respectively. The stirrers were rotated at different speeds up to 230 rpm. The observed rates of removal of bismuth and lead were expressed by a first-order rate equation. The overall mass-transfer coefficient (K) and liquid-phase mass-transfer coefficient (KL) for both elements were determined and then their dependence on the rotational speed of each stirrer was observed.
In Cu–Bi alloy, for stirring with Stirrer A at 36 to 156 rpm, K and KL for bismuth were almost independent of the rotational speed but at 225 rpm became smaller and for stirring with Stirrer B at 63 to 148 rpm, they increased with increasing rotational speed. In Cu–Bi–Pb alloy, for stirring with Stirrer A, K and KL for both elements tended to decrease with increasing rotational speed and for stirring with Stirrer B at 65 to 151 rpm, they increased with increasing rotational speed. Until about 100 rpm for Cu–Bi alloy and 150 rpm for the Cu–Bi–Pb alloy, for each element, K and KL for stirring with Stirrer A were greater than those for stirring with Stirrer B, respectively. This relation for KL is contrary to predictions from the film-penetration theory. This observation suggests that the mechanisms of the liquid-phase mass-transfer under the present experimental conditions are different from those based on the theory.
At any fixed rotational speed of each stirrer, it was found that K(Cu–Bi)<K(Cu–Bi–Pb) and KL(Cu–Bi)<KL(Cu–Bi–Pb) for bismuth and KL(Bi)\simeqKL(Pb) for Cu–Bi–Pb alloy. At about 60 and 100 rpm, the square root of KL(Cu–Bi–Pb)/KL(Cu–Bi) of bismuth for stirring with Stirrer A equals the ratio for stirring with Stirrer B.
