13.14 Design of Mixer-Settlers

Extraction systems have design conditions that often compete with each other. First, we would like a high surface area between the continuous and discontinuous phases (large number of small drops) to give a high mass transfer rate, and we want vigorous mixing to increase the continuous phase mass transfer coefficient. On the other hand, we would like a rapid settling (or rising if discontinuous phase is less dense) velocity for drops so that we can operate at higher flow rates. Since settling velocity is proportional to the drop diameter squared [shown later in Eq. (13-57)], large drops settle faster. Settling velocity is also directly proportional to the density difference between the two phases and is inversely ...

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