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Reaction in Mixed or Segregated Systems

In order to visualize physically what is meant by molecular-level or micromixing, consider a point volume element of fluid within the reactor that is just large enough to possess the average value of an intensive property such as concentration at the particular location considered [P.V. Danckwerts, Chem. Eng. Sci., 8, 93 (1958)]. All molecules within a point-volume element have zero age when entering the reactor, and all have zero time to remain within the reactor (life expectancy) when the element exits. The degree of micromixing defines what happens to the individual molecules within a point-volume element in the time between its entrance and exit from the reactor. [Pg.232]

Now just what is the importance of micromixing in chemical reaction systems The question is perhaps best answered using a famous example from the paper of Danckwerts cited above. Consider the isothermal, second-order irreversible reaction A + B C, carried out homogeneously and at constant volume. The initial concentrations of A and B, Cao and Cbo, are set in the ratio [Pg.232]

If the system is in a state of maximum mixedness, after a fraction /of A is reacted, the concentrations are [Pg.232]

At the opposite end of the spectrum of micromixing, let us consider the same system, but now consisting of two segregated portions having differing degrees of conversion of A,/i, and /2, with the volumes of the two portions in the ratio a to (1-a). The concentrations of A in the two portions are, [Pg.232]

These two rates are not the same. Comparing equations (4-5) and (4-7) gives [Pg.233]


See other pages where Reaction in Mixed or Segregated Systems is mentioned: [Pg.232]   


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