Micro-Mixing in a Continuous Flow Reactor : Coalescence and Redispersion Models

Abstract

For the fluid mixing which occurs in a continuous flow reactor, two different mechanisms must be considered. The one is macro-mixing resulting from the difference in residence time of outflowing fluid and the other is micro-mixing caused by the mass exchange between fluid elements. In this paper new models for the micro-mixing are presented as follows : The incoming fluid is broken up into discrete fragments of equal volume which are small enough compared to the reactor size. A fragment of fluid comes into contact and coalescence with another l/tc times per unit time on an average, and is immediately rebroken into two fragments of equal volume. The concentration in the fragments becomes uniform at the instant of coalescence. From the above assumptions, the basic design equations are derived, and for the ideal perfect macro-mixing reactor, the effect of micro-mixing on the conversion of zero, first, and second order reactions is considered. In the case of first order reactions the micro-mixing has no effect on the conversion. In the case of reactions of zero and second order, the conversion is caluculated by equations (24), (36) and (30), (38), respectively. And the validity of these equations for second order reaction is discussed using a reaction which takes place in liquid droplets dispersed in an inert phase.