Mass diffusion cascade

In mass diffusion, separation of isotopes occurs throu diffusion of the li t isotope of a gas mixture into a condensible vapor at higher rate than diffusion of the heavy isotope. Mass diffusion separation has been canied out in a cascade of individual mass diffusion stages and in a mass diffusion column. 

Table 14.21. Isotopes separated by cascade of mass diffusion stages...

Because the separation obtainable in a mass diffusion stage is even smaller than in a gaseous diffusion stage, a practical degree of separation requires either a multistage cascade, such as the 48-stage cascade used by Hertz [H3] to separate neon isotopes, or a mass diffusion column. 

Separation of Uranium Isotopes by Cascade of Mass Diffusion Stages... 

With such a small fractional mass difference between the isotopes, the separation obtained by diffusion through a single barrier is very small, and a practical gaseous diffusion plant must consist of a very large number of barrier stages arranged in a diffusion cascade. The cascade principle is illustrated diagrammatically in Fig. 5.1. 

Besides the dispersion model, the tanks in series model is the other onedimensional model widely used to represent non-ideal flow. Here the fluid is thought to flow through a series of equal-size ideal stirred tanks, and the parameter in this model is the number of tanks in the cascade (iV q). The RTD curves and moments of this model are easy to obtain, since problems of proper boundary conditions and method of tracer injection and measurement do not intrude. need not be an integer for curve-fitting purposes. It is strictly empirical, and no theoretical justification, such as Taylor diffusion, or theoretical estimates of the model parameter, are generally possible. This model starts from the mass balance equation for a series of i stirred vessels with 1 < i < iV, and AT, the number of vessels in the series (or the number of equivalent stages,... 

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