Effect of molecular configuration of Xanthan gum drage reduction

Rochefort, Skip; Middleman, Stanley

doi:10.1063/1.35522

Cited by 7 publications

(5 citation statements)

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“…When we for example correct the data of Virk & Wagger (1990) for the increase in viscosity due to the dissolved polymers, their results for the type-B case show a delay in transition to a Reynolds number of approximately 6500 (a fact which they do not mention themselves). A delay in transition has also been found for Xanthan gum Singh 1988 andRochefort &Middleman 1985), which has a rigid helical structure. Other examples are asbestos fibres (Vaseleski & Mezner 1974) and surfactants that form so-called rod-like micelles (Bewersdorff 1990).…”

Section: Introductionmentioning

confidence: 69%

“…For instance, delay in transition for polymer solutions has been mainly reported in small diameter pipes, usually smaller than 1 cm (e.g. Castro & Squire 1967;White & McEligot 1970;Chung & Graebel 1972;Rochefort & Middleman 1985;Bewersdorff & Singh 1988). These results were found both for extended as well as coiled polymers.…”

Section: Main Conclusion and Discussionmentioning

confidence: 95%

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Laminar–turbulent transition in pipe flow for Newtonian and non-Newtonian fluids

1998

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A cylindrical pipe facility with a length of 32 m and a diameter of 40 mm has been designed. The natural transition Reynolds number, i.e. the Reynolds number at which transition occurs as a result of non-forced, natural disturbances, is approximately 60 000. In this facility we have studied the stability of cylindrical pipe flow to imposed disturbances. The disturbance consists of periodic suction and injection of fluid from a slit over the whole circumference in the pipe wall. The injection and suction are equal in magnitude and each distributed over half the circumference so that the disturbance is divergence free. The amplitude and frequency can be varied over a wide range.First, we consider a Newtonian fluid, water in our case. From the observations we compute the critical disturbance velocity, which is the smallest disturbance at a given Reynolds number for which transition occurs. For large wavenumbers, i.e. large frequencies, the dimensionless critical disturbance velocity scales according to Re−1, while for small wavenumbers, i.e. small frequencies, it scales as Re−2/3. The latter is in agreement with weak nonlinear stability theory. For Reynolds numbers above 30 000 multiple transition points are found which means that increasing the disturbance velocity at constant dimensionless wavenumber leads to the following course of events. First, the flow changes from laminar to turbulent at the critical disturbance velocity; subsequently at a higher value of the disturbance it returns back to laminar and at still larger disturbance velocities the flow again becomes turbulent.Secondly, we have carried out stability measurements for (non-Newtonian) dilute polymer solutions. The results show that the polymers reduce in general the natural transition Reynolds number. The cause of this reduction remains unclear, but a possible explanation may be related to a destabilizing effect of the elasticity on the developing boundary layers in the entry region of the flow. At the same time the polymers have a stabilizing effect with respect to the forced disturbances, namely the critical disturbance velocity for the polymer solutions is larger than for water. The stabilization is stronger for fresh polymer solutions and it is also larger when the polymers adopt a more extended conformation. A delay in transition has been only found for extended fresh polymers where delay means an increase of the critical Reynolds number, i.e. the number below which the flow remains laminar at any imposed disturbance.

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Section: Introductionmentioning

confidence: 69%

Section: Main Conclusion and Discussionmentioning

confidence: 95%

Laminar–turbulent transition in pipe flow for Newtonian and non-Newtonian fluids

1998

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“…Figure 4.101 shows how the profile of the flow curve changes with increasing polymer concentration in scleroglucan aqueous systems [513]. When oscillatory and steady shear behaviors of xanthan systems are compared, the traces 1]*(00) and 1](Y) are almost parallel, with 11*(00) sensibly higher than 1](y) [318,517].…”

Section: Steadyflow Behaviormentioning

confidence: 99%

Rheology of polysaccharide systems

Lapasin

Pricl

1995

Rheology of Industrial Polysaccharides: Theory and Applications

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The transport properties and, specifically, the rheological behavior of real and complex materials such as polysaccharide systems can be significantly affected by several factors, mainly related to molecular and supermolecular features. Most of these factors are common to all polymeric systems, as they have universal character; others are peculiar to carbohydrate polymers. If we bear in mind the concepts discussed in §1.4, we can easily imagine for polysaccharides a variety of structural conditions much wider than that generally observed for synthetic polymers. On both molecular and supermolecular scales, polysaccharides possess special characteristics that reflect specific behavior so that different classes of materials can be identified.Let us consider the molecular scale first: at this level, the polymer backbone and its related features, such as its length in solution, shape, stitfuess and the eventual presence of ionizable groups, playa major role in determining the macroscopic properties of the system, including its rheology. Many of these molecular parameters correlate among themselves (e.g. chain stitfuess and length); others must be combined with external factors such as, for instance, the characteristics of the solvent medium. These latter may, in turn, exert an influence on the conformation adopted by the macromolecule in the medium itself, as well as on the possibility of forming supermolecular structures. In other words, changes in ionic strength, the nature of counterions, temperature or other solvent parameters may induce a conformational transition, thus modifying the hydrodynamic resistance of the macromolecule to flow. Also, if the polymer concentration is high enough, the variations described above may promote structural changes at a supermolecular level and, accordingly, modifications in the rheological behavior. Before leaving this brief comment on solvent characteristics we must mention the viscosity although, R. Lapasin et al. (eds.), Rheology of Industrial Polysaccharides: Theory and Applications

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“…Studies of the drag-reducing characteristics of Xanthan gum showed that this is indeed a good example of a type-B fluid. 43 Because of the relatively low molecular weight of Xanthan gum, the solution viscosity is necessarily higher than water viscosity if significant levels of drag reduction are to be achieved. Figure 13 shows results of shear viscosity measurements for both Xanthan gum solutions used in our tests, as measured in capillary tubes with diameters of 0.723 and 2 mm.…”

Section: Type-b Drag Reducer "Xanthan Gum…mentioning

confidence: 99%

Measurement of temperature profiles in turbulent pipe flow of polymer and surfactant drag-reducing solutions

2007

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A device was built to measure temperature profiles of turbulent pipe flows of various drag-reducing fluids. It is easy to use and reliable. We measured temperature profiles over a range of conditions leading to accurate measurements down to y + Ϸ 10, for tests carried over Reynolds numbers ͑Re͒ between 10 000 and 90 000. The effects of high heat fluxes and buoyancy, in particular, were quantified to ascertain the parameter range for accurate measurements. Temperature profiles measured for type-A polymer solution and for cationic surfactant solutions allowed us to see strong similarity between velocity and temperature profiles for drag-reducing surfactant solutions. A comparison between the slopes of the thermal and velocity buffer layers resulted in calculated turbulent Prandtl numbers between 6 and 9 for those drag-reducing solutions. We also used this tool to investigate drag reduction for a nonionic surfactant solution, which showed a significantly different fan-type profile, and also for a type-B drag-reducing polymer solution ͑Xanthan gum͒.

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Effect of molecular configuration of Xanthan gum drage reduction

Cited by 7 publications

References 0 publications

Laminar–turbulent transition in pipe flow for Newtonian and non-Newtonian fluids

Laminar–turbulent transition in pipe flow for Newtonian and non-Newtonian fluids

Rheology of polysaccharide systems

Measurement of temperature profiles in turbulent pipe flow of polymer and surfactant drag-reducing solutions

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