Dr. Nagarani Ponakala

The theory of dispersion of a contaminant in fluid flows has wide application in chemical engineering, biomedical engineering, physiological fluid dynamics and environmental science. The basic principle underlying the dispersion theory is the spreading of a solute (any substance dissolved in a given solution) in a flowing fluid due to combined action of molecular diffusion and non- uniform velocity distribution.

APPLICATIONS OF DISPERSION

In chemical engineering, the dispersion of a gaseous tracer injected into a flowing stream of a second gas, is studied under conditions where the tracer gas can also be exchanged by diffusion within a stagnant gaseous zone held in a porous solid. The dispersion of salt and other materials in estuaries are studied through models of dispersion of a passive contaminant in a two dimensional open channel.

Publication by Dr. Nagarani Ponakala et al
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EXAMPLES OF DISPERSION MODELS IN BLOOD FLOW

Numerous examples are available in biological systems where dispersion plays an important role. Since many intravenous medications are therapeutic at low concentration but toxic at high concentration, it is important to know the rate of dispersion of drugs in blood flow of the circulatory system. In particular, in the indicator dilution technique, it is a common practice to introduce a quantity of a dye into the blood stream and to measure its concentration at some down-stream point as it moves along the blood flow.

USE OF CATHETERS

Catheters are used to inject the dye and to withdraw blood samples for the purpose of measurements. Catheters are long cylindrical tubes at the tip of which various functional tools are positioned. The insertion of a catheter into an artery leads to the formation of an annular gap between the artery wall and catheter wall. Dr. Ponakala is interested in understanding the effects of catheter insertion in fluid flow in the cardiovascular system. The introduction of a catheter into blood vessels can be a potent cause of disturbance of natural fluid flow and mixing of blood. The sampling system always introduces some distortion in the time–concentration curve, so that the recorded curve is not of the same shape as the original time-concentration relation at the withdrawal site. Hence, the aim of this study is to provide a correction to the values measured when a catheter is inserted in the artery, based on the concept of dispersion theory.

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RESULTS AND APPLICATIONS

Considering the wall absorption characteristics, the entire dispersion process is characterized by the three transport coefficients viz. absorption coefficient, convection coefficient and dispersion coefficient. The results that we obtained are discussed in applications to a catheterized artery and compared with the case of normal artery where there is no catheter. The coefficients of convection and dispersion are found to be affected significantly by the presence of a catheter and property of the fluid (yield stress). The yield stress is found to have no effect on the absorption coefficient. The combined effect of the presence or increase in the radius of the catheter and yield stress is found to inhibit the dispersion coefficient. It is seen that the presence of a catheter and increase in the catheter size helps in the dyes or other solutes to get off the blood vessels for all values of the absorption parameter. The coefficients of convection and dispersion are found to be affected significantly by the presence of a catheter and the yield stress of the fluid. Although the present study brings out the effects of wall absorption and yield stress on dispersion in a catheterized artery, the model has to be further redefined for the analysis of dispersion process when the catheter is not centrally positioned in the artery, which will be more realistic and that work is under progress.