Nairobi Spreading of Tracer Dispersion Model and Segregated Flow Model


Question Description

Models are useful for representing flow in real vessels, for scale up, and for diagnosing poor flow. These models apply to turbulent flow in pipes, laminar flow in very long tubes, flow in packed beds etc. An ideal pulse of tracer is introduced into a reactor and the pulse spreads as it passes through the vessel, and to characterize the spreading according to various models. Illustrate the spreading of tracer using dispersion model and segregated flow model with suitable diagram.


The answer will be

  • paraphrase
  • minimum 1000 words for Dispersion model With suitable diagram
  • minimum 1000 words for segregated flow model With suitable diagram
  • Harvard Referencing
  • Provide some figures/pictures with reference

Please refer the attached books which you can use for answer the questions.

Tutor Answer

School: New York University


Dispersion Model And Segregation Model 1

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Dispersion Model And Segregation Model 2
The spreading of tracer using dispersion model
Supposing a model pulse of a tracer is initiated into the fluid getting into the container or
vessel (Swamee, Pathak, and Sohrab, 2000, p. 23). The pulse spreads while it goes through the
container and to portray the spreading in line with the model, it is assumed a diffusion-like
procedure is super-imposed on the plug flow. This is what is called dispersion or longitudinal
dispersion to differentiate it from the molecular diffusion. D is the dispersion coefficient which
represents the spreading procedure (Swamee, Pathak, and Sohrab, 2000, p. 26). As a result:
Large D denotes quick spreading of the tracer curve
Small D denotes slow spreading
D = 0 denotes no spreading, therefore plug flow.
The tracer spreading consistent with the dispersion method

(Swamee, Pathak, and Sohrab, 2000, p. 30)

Dispersion Model And Segregation Model 3

(Swamee, Pathak, and Sohrab, 2000, p. 32).

Considering the plug flow of a liquid, on top of which is overlaid at a given level of
backmixing, the extent of which is does not rely on the position within the vessel (Cimorelli et al,
2005, p. 43). This condition means that there are no stagnant pockets and no short-circuiting or
gross bypassing of fluid inside the vessel. This is what is termed as the dispersed plug flow
model or just the dispersion model. It is good to realize that the changing turbulence intensities
or intermixing the calculations of this ideal should array from plug flow at one side to mixed
flow on the other extreme or side. Therefore the reactor volume for the model will rest between
those predicted for the mixed flow and plug flow. Since the mixing procedure entails a shuffling
of material redistribution either through eddies or slippage, and given that this is replicated very
many times in the course of the fluid flow through the vessel, the disturbance may be deemed
statistical in nature somewhat like in molecular diffusion (Cimorelli et al, 2005, p. 51). For the
molecular diffusion within the x-direction, the leading differential equation is given through the
Fick’s Law:

Representation of the dispersion model –dispersed plug flow

Dispersion Model And Segregation Model 4

(Cimorelli et al, 2005, p. 53)
Fitting the dispersion model for small extents of Dispersion
For small dispersion extents, the spreading tracer curve does not considerably alteration
in shape while it goes through the measuring point (Irwin and Hanna, 2005, p. 22). Luckily, for
small levels of dispersion several simplifications and estimations within the analysis of curves
are likely. Foremost, the shape or form of the shape curve is insensitive to the limit condition
imposed on the vessel whether open or close...

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