Flow Of Polymer Solutions Research Articles

Group Analysis of the Boundary Layer Equations in the Models of Polymer Solutions

The famous Toms effect (1948) consists of a substantial increase of the critical Reynolds number when a small amount of soluble polymer is introduced into water. The most noticeable influence of polymer additives is manifested in the boundary layer near solid surfaces. The task includes the ratio of two characteristic length scales, one of which is the Prandtl scale, and the other is defined as the square root of the normalized coefficient of relaxation viscosity (Frolovskaya and Pukhnachev, 2018) and does not depend on the characteristics of the motion. In the limit case, when the ratio of these two scales tends to zero, the equations of the boundary layer are exactly integrated. One of the goals of the present paper is group analysis of the boundary layer equations in two mathematical models of the flow of aqueous polymer solutions: the second grade fluid (Rivlin and Ericksen, 1955) and the Pavlovskii model (1971). The equations of the plane non-stationary boundary layer in the Pavlovskii model are studied in more details. The equations contain an arbitrary function depending on the longitudinal coordinate and time. This function sets the pressure gradient of the external flow. The problem of group classification with respect to this function is analyzed. All functions for which there is an extension of the kernels of admitted Lie groups are found. Among the invariant solutions of the new model of the boundary layer, a special place is taken by the solution of the stationary problem of flow around a rectilinear plate.

Растворы полимеров и их математические модели

Mathematical models for the motion of weak solutions of polymers have been studied over the past 50 years. The initial model (Voitkunskii, Amfilokhiev, and Pavlovskii, 1970) contains two key parameters - relaxation viscosity and shear stress relaxation time. In the limiting case, when the last parameter is small, the Pavlovskii model (1971) arises. Its equations are close to second-grade fluid equations (Rivlin and Eriksen, 1955). The paper contains an overview of the works on all three models and new results related to the Pavlovskii model. The solution to the problem of the un-steady layered flow of an aqueous polymer solution in a layer with a free boundary, the boundary condition on which includes the time derivative of the desired function is constructed. We derive the equations that describe the motion of a polymer solution in a laminar boundary layer near a rectilinear plate. The parameter included in equations characterizes the ratio of the thickness of the Prandtl boundary layer to the thickness of the relaxation boundary layer. We study the influence of this parameter on the motion picture by the example of a stationary flow near a critical point.

Special Features of Nonlinear Behavior of a Polymer Solution on Large Periodic Deformations

Study of the behavior of polymer solution flows in the region of nonlinear viscoelasticity allows one to more accurately evaluate the adequacy of rheological models and to describe the rheological properties of a material in more detail. The nonlinear viscoelastic properties manifesting themselves in the process of studying the behavior of a polymer material on significant deformations were investigated with the aid of time dependences of shear stresses calculated at different amplitudes. The present work considers the applicability of the modified Vinogradov–Pokrovskii rheological model to describing the oscillating shearing of polymer fluids with a large amplitude. It has been established that on increase of the deformation amplitude, the shear stresses cease to be a true harmonic, and one observes the appearance of a "step" on their left front, which speaks of the substantial nonlinearity in the behavior of the sample. The obtained theoretical dependences are compared with experimental data for a 5% solution of polyethylene oxide in dimethyl sulfoxide. The comparison was made as by plotting the time dependences of normalized stresses, so by analyzing Lissajous figures. Despite the simplicity, the modifi ed Vinogradov–Pokrovskii rheological model adequately describes the behavior of polymer materials on significant periodic deformations.

Flow and heat transfer in drag-reducing polymer solution flow through the corrugated tube and circular tube

Flow and heat transfer characteristics of xanthan gum (XG) solutions are experimentally studied to compare the drag reduction (DR) and heat transfer reduction (HTR) behavior in the corrugated tube with that in the circular tube. Effects of XG concentration (C) and bulk velocity (v) on drag enhancement (DE), heat transfer enhancement (HTE) and comprehensive performance index (ξ) in the corrugated tube are also examined. The results show that the DR in the corrugated tube increases and then decreases until becomes negative with increasing bulk velocity under the intense turbulent disturbance of the corrugated wall, which is different from the DR behavior in the circular tube, and the onset of DR is found to occur earlier. In addition, the variation trend of HTR is consistent with that of DR’s absolute value, which is closely related to the interaction between drag reduction property and high viscosity property of XG solutions. Furthermore, the HTE and ξ increase with increasing XG concentration and decreasing bulk velocity, and the maximum HTE and ξ can be up to 25 and 1600, which proves the corrugated tube has a specific applicability in terms of energy saving and heat transfer enhancement for high-concentration XG solutions at low velocity.

Fluid Rheological Effects on the Flow of Polymer Solutions in a Contraction-Expansion Microchannel.

A fundamental understanding of the flow of polymer solutions through the pore spaces of porous media is relevant and significant to enhanced oil recovery and groundwater remediation. We present in this work an experimental study of the fluid rheological effects on non-Newtonian flows in a simple laboratory model of the real-world pores—a rectangular sudden contraction–expansion microchannel. We test four different polymer solutions with varying rheological properties, including xanthan gum (XG), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and polyacrylamide (PAA). We compare their flows against that of pure water at the Reynolds () and Weissenburg () numbers that each span several orders of magnitude. We use particle streakline imaging to visualize the flow at the contraction–expansion region for a comprehensive investigation of both the sole and the combined effects of fluid shear thinning, elasticity and inertia. The observed flow regimes and vortex development in each of the tested fluids are summarized in the dimensionless and parameter spaces, respectively, where is the normalized vortex length. We find that fluid inertia draws symmetric vortices downstream at the expansion part of the microchannel. Fluid shear thinning causes symmetric vortices upstream at the contraction part. The effect of fluid elasticity is, however, complicated to analyze because of perhaps the strong impact of polymer chemistry such as rigidity and length. Interestingly, we find that the downstream vortices in the flow of Newtonian water, shear-thinning XG and elastic PVP solutions collapse into one curve in the space.

Bistability in the unstable flow of polymer solutions through pore constriction arrays

Polymer solutions are often injected in porous media for applications such as oil recovery and groundwater remediation. As the fluid navigates the tortuous pore space, elastic stresses build up, causing the flow to become unstable at sufficiently large injection rates. However, it is poorly understood how the spatial and temporal characteristics of this unstable flow depend on pore space geometry, which can vary widely between different porous media. We investigate this dependence by systematically varying the spacing between pore constrictions in a one-dimensional ordered array. We find that when the pore spacing is large, unstable eddies form upstream of each constriction, similar to observations of an isolated constriction. By contrast, when the pore spacing is sufficiently small, the flow in the different pores exhibits a surprising bistability, stochastically switching between two distinct unstable flow states. We hypothesize that this unusual behaviour arises from the interplay between elongation and relaxation of polymers as they are advected through the pore space. Consistent with this idea, we find that the flow state in a given pore persists for long times; moreover, flow states are strongly correlated between neighbouring pores. Thus, the characteristics of unstable flow are not determined just by injection conditions and the geometry of the individual pores, but also depend on the spacing between pores. Ultimately, these results help to elucidate the rich array of behaviours that can arise in polymer solution flow through porous media.

The Research on Dilute Polymer Solutions Cavitating Flow through Venturi and Cavitation Induced Vibration Acceleration Characteristics

The present work deals with an original study of vibration signals induced by unsteady cavitating flow of polymer solutions through a Venturi section. A blow-down Venturi experimental rig was utilized to generate cavitation in polymer solutions. The cavitating flows through the Venturi tunnel were captured by high-speed photography. The accelerometer was mounted on the upper wall of Venturi tunnel to gather the cavitation induced vibration accelerations. Results show that the morphologies of cavitation bubbles in polymer solutions are different from that of filtered water. Cavitation bubbles with bigger size and less number are observed in polymer solutions cavitating flow. It is observed that the peak value, kurtosis and the root-mean-square of vibration acceleration increase in polymer solutions. Meanwhile, a broader frequency band and a higher power spectral density level is observed in spectrogram of polymer solutions. It is inferred that the collapse of the vaporous cavity clouds with high void fraction developed in polymer solutions is responsible for this alteration.

Asymmetric flow of polymer solutions around microfluidic cylinders: Interaction between shear-thinning and viscoelasticity

Viscoelastic flow around a cylinder is a model problem representing a wide range of relevant industrial processing and biological applications. Reducing the cylinder to microscopic dimensions conveniently enables the problem to be examined in the absence of inertia. Recently, we have developed glass microfluidic geometries containing long and slender, yet rigidly fixed, microfluidic cylinders, which present a low blockage ratio β=2r/W=0.1, where r=20μm is the cylinder radius and W=400μm is the channel width. Using a shear-banding viscoelastic wormlike micellar (WLM) solution, we showed how the flow around such a cylinder could destabilize beyond a critical Weissenberg number (Wi=λU/r, where λ is a characteristic time of the fluid and U is the average flow velocity), resulting in the asymmetric division of the fluid around either side of the cylinder [Haward et al, Soft Matter15:1927]. In the present work we investigate this flow instability in greater detail using a range of polymer solutions formulated from hydrolyzed poly(acrylamide) (HPAA) dissolved at different concentrations in deionized water. The test fluids present a range of shear-thinning responses under steady shear, and also a wide variety of characteristic times. At low HPAA concentrations, the flow around the cylinder remains essentially symmetric for all Wi, but as the concentration increases, so does the maximum degree of the flow asymmetry observed with increasing Wi. Interestingly, at intermediate concentrations, the flow can resymmetrize at very high Wi. We understand these effects by considering simultaneously both the degree of shear-thinning of the fluid and the imposed Wi, and our analysis shows that both strong shear-thinning and high elasticity are required for the formation of strongly asymmetric flows. Our results represent the first report of this highly asymmetric flow state in polymer solutions, showing that it is a general phenomenon and not only specific to WLM. Our analysis provides a clear insight into the origins of this unusual flow state and may also be relevant to understanding other instances of asymmetries arising in shear-thinning viscoelastic flows.

Early transition, relaminarization and drag reduction in the flow of polymer solutions through microtubes

Experiments are performed to investigate the onset of early transition and drag reduction in the flow of polymer (polyacrylamide and polyethylene oxide) solutions through rigid microtubes of diameters in the range 0.49–2.84 mm. We measure friction factor variation with Reynolds number for varying polymer concentrations and tube diameters, and the Reynolds number, , at which the experimental data deviate from the laminar value represents the onset of transition. Crucially, owing to the high shear rates encountered in our experiments, we show that it is important to account for shear thinning of the fluid in the theoretical estimation of the friction factor in the laminar regime. We accomplish this using a Carreau model, and show that the use of laminar friction factor calculated without shear thinning leads to an erroneous overestimation of . The obtained from friction factor data in the present study is in good agreement with that inferred using micro particle image velocimetry analysis in Chandra et al. (J. Fluid Mech., vol. 844, 2018, pp. 1052–1083). For smaller concentrations of the added polymer, there is a marginal delay in the onset of turbulence, but as the concentration is increased further, the transition Reynolds number decreases much below , the usual value at which transition occurs in Newtonian pipe flows. Thus, the present study further corroborates the phenomenon of early transition leading to an ‘elasto-inertial’ turbulent state in the flow of polymer solutions. For concentrations such that there is a delay in transition, if is maintained above the for Newtonian fluids, the flow is transitional or turbulent in the absence of polymers. At such a fixed , if the concentration of the polymer is increased gradually, the friction factor decreases and the flow relaminarizes. With further increase in polymer concentration, the flow undergoes a transition due to elasto-inertial instability. The effect of addition of small amounts of polymer on turbulent drag reduction in the flow of water through microtubes is also investigated. Increase in polymer concentration, molecular weight and decrease in tube diameter causes an increase in drag reduction. The friction factor data for different polymer concentrations, molecular weights, tube diameters and , when plotted with , show a reasonable collapse, where is the Weissenberg number defined as the product of the longest relaxation time of the polymer solution and the average shear rate in the tube and is the ratio of solvent to total solution viscosity. Interestingly, the onset of the maximum drag reduction asymptote, for experiments using varying tube diameters and polymer concentrations, appears to occur at .

Prediction of Drag Reduction Rate in Turbulent Channel Flow Based on BP Neural Network

The technology of turbulent drag reduction by viscoelastic additives cannot be widely applied in practical engineering due to the difficulty in judging the effect of drag reduction. To solve this problem, the experiment of drag-reducing channel flow of polymer solution was carried out based on the comprehensive analysis of the factors affecting the drag reduction rate. Abundant drag reduction rate data were obtained. A three-layer BP neural network prediction model was established with polymer solution concentration, Reynolds number and injection flow rate as input parameters. Based on the test results, the prediction accuracy on drag reduction rate of the model was analysed. The prediction and model validation of drag reduction rate are carried out further according to the historical data in literature. The results show that the predicted drag reduction rate of BP neural network is close to the real drag reduction rate in the drag-reducing flow of polymer solution. The prediction is with high accuracy and with good generalization ability. It is expected to be applied to practical projects and to promote the development of turbulent drag reduction technology by additives.

Elastic turbulence in two-dimensional cross-slot viscoelastic flows

We report evidence of irregular unsteady flow of two-dimensional polymer solutions in the absence of inertia in cross-slot geometry using numerical simulations of Oldroyd-B model. By exploring the transition to time-dependent flow vs. both the fluid elasticity and the polymer concentration, we find a periodic behaviour close to the instability threshold and more complex flows at larger elasticity, in agreement with experimental findings. For high enough elasticity we obtain dynamics pointing to elastic turbulence, with temporal spectra of velocity fluctuations showing a power-law decay, of exponent between –3 and –2, and probability density functions of velocity fluctuations that weakly deviate from Gaussianity while high non-Gaussian tails characterise those of local accelerations.

Oscillations of a cantilevered micro beam driven by a viscoelastic flow instability

The interaction of flexible structures with viscoelastic flows can result in very rich dynamics. In this paper, we present the results of the interactions between the flow of a viscoelastic polymer solution and a cantilevered beam in a confined microfluidic geometry. Cantilevered beams with varying length and flexibility were studied. With increasing flow rate and Weissenberg number, the flow transitioned from a fore-aft symmetric flow to a stable detached vortex upstream of the beam, to a time-dependent unstable vortex shedding. The shedding of the unstable vortex upstream of the beam imposed a time-dependent drag force on the cantilevered beam resulting in flow-induced beam oscillations. The oscillations of the flexible beam were classified into two distinct regimes: a regime with a clear single vortex shedding from upstream of the beam resulting in a sinusoidal beam oscillation pattern with the frequency of oscillation increasing monotonically with Weissenberg number, and a regime at high Weissenberg numbers characterized by 3D viscoelastic instabilities where the frequency of oscillations plateaued. The critical onset of the flow transitions, the mechanism of vortex shedding and the dynamics of the cantilevered beam response are presented in detail here as a function of beam flexibility and flow viscoelasticity.

A Computational Systems Approach to Rational Design of Nose-to-Brain Delivery of Biopharmaceutics

In this work, a computational systems approach, comprising models at different time and length scales, is developed to elucidate the fundamental chemical, physical, transport, and biological processes in relation to the design of a novel nose-to-brain drug delivery system for the treatment of neurodegenerative diseases. In particular, a kinetic model is established to describe the formation of a hydrogel patch, via the enzymatic cross-linking of tyramine-modified hyaluronic acid, on the olfactory cleft. A fluid transport model is employed to describe the flow of a cross-linkable viscoelastic polymer solution through an applicator in terms of tube and reactive fluid characteristics (e.g., tube geometry, volumetric flow rate, and viscosity). The spreading of the deposited HA droplet on a mucus substrate is modeled via the development of a dynamic droplet deformation model. Subsequently, a dynamic drug release model is formulated to quantify the release rate of an active pharmaceutical ingredient (e.g., long-acting insulin analogues) from a distributed population of drug-loaded polymeric carriers embedded into a hydrogel matrix in terms of molecular and morphological properties of the hydrogel–drug carriers system. Finally, the drug flux from the hydrogel–mucosa interface to the olfactory bulb via the epithelium and lamina propria olfactory sublayers is modeled with a series of dynamic mass transport models. The various mathematical models are integrated together following a multiscale modeling approach to aid the identification of key design system parameters and material properties that can lead to the optimization of the complex drug carriers–hydrogel, droplet deposition, film formation, and drug delivery system to achieve a desired therapeutic effect over a two-week delivery time.

Onset of transition in the flow of polymer solutions through deformable tubes

Experiments are performed to investigate laminar-turbulent transition in the flow of Newtonian and viscoelastic fluids in soft-walled microtubes of diameter ∼400 μm by using the micro-particle image velocimetry technique. The Newtonian fluids used are water and water-glycerine mixtures, while the polymer solutions used are prepared by dissolving polyacrylamide in water. Using different tube diameters, elastic moduli of the tube wall, and polymer concentrations, we probe a wide range of dimensionless wall elasticity parameter Σ and dimensionless fluid elasticity number E. Here, Σ = (ρGR2)/η2, where ρ is the fluid density, G is the shear modulus of the soft wall, R is the radius of the tube, and η is the solution viscosity. The elasticity of the polymer solution is characterized by E = (λη0)/R2ρ, where λ is the zero-shear relaxation time, η0 is the zero-shear viscosity, ρ is the solution density, and R is the tube radius. The onset of transition is detected by a shift in the ratio of centerline peak to average velocity. A jump in the normalized centerline velocity fluctuations and the flattening of the velocity profile are also used to corroborate the onset of instability. Transition for the flow of Newtonian fluid through deformable tubes (of shear modulus ∼50 kPa) is observed at a transition Reynolds number of Ret ∼ 700, which is much lower than Ret ∼ 2000 for a rigid tube. For tubes of lowest shear modulus ∼30 kPa, Ret for Newtonian fluid is as low as 250. For the flow of polymer solutions in a deformable tube (of shear modulus ∼50 kPa), Ret ∼ 100, which is much lower than that for Newtonian flow in a deformable tube with the same shear modulus, indicating a destabilizing effect of polymer elasticity on the transition already present for Newtonian fluids. Conversely, we also find instances where flow of a polymer solution in a rigid tube is stable, but wall elasticity destabilizes the flow in a deformable tube. The jump in normalized velocity fluctuations for the flow of both Newtonian and polymer solutions in soft-walled tubes is much gentler compared to that for Newtonian transition in rigid tubes. Hence, the mechanism underlying the soft-wall transition for the flow of both Newtonian fluids and polymer solutions could be very different as compared to the transition of Newtonian flows in rigid pipes. When Ret is plotted with the wall elasticity parameter Σ for different moduli of the tube wall, by taking Newtonian fluids of different viscosities and polymer solutions of different concentrations, we observed a data collapse, with Ret following a scaling relation of Ret ∼ Σ0.7. Thus, both fluid elasticity and wall elasticity combine to trigger a transition at Re as low as 100 in the flow of polymer solutions through deformable tubes.

Fabrication, Characterization, and Biological Evaluation of Airbrushed Gelatin Nanofibers.

Gelatin nanofibers have gained significant attention for different biomedical applications, as they provide a suitable environment for cell attachment, growth, and proliferation compared to the other biopolymers and synthetic polymers. Airbrushing/solution-blow-spinning could overcome the limitation of the conventional electrospinning method of nanofiber preparation. The present study reports the fabrication of nano/microfibers from commercially available low-molecular-weight gelatin of animal origin as a first-time study. The effect of various airbrushing parameters, namely, the concentration of gelatin solution, air pressure, and polymer solution flow rate on the fiber quality, morphology, and diameters, was studied. Finally, the biological evaluation of the airbrushed gelatin nanofibers was performed using human bone marrow-derived mesenchymal stem cells (hBMSCs). Gelatin nanofibers exhibit excellent biocompatibility and support the growth of hBMSCs similar to electrospun gelatin nanofibers. Our airbrushing technique is an easy, low-cost, and scalable method to fabricate the gelatin nanofibers for different biomedical applications such as tissue engineering, wound healing, and substrate for delivery of bioactive molecules.

Pore-Scale Flow Characterization of Polymer Solutions in Microfluidic Porous Media.

Polymer solutions are frequently used in enhanced oil recovery and groundwater remediation to improve the recovery of trapped nonaqueous fluids. However, applications are limited by an incomplete understanding of the flow in porous media. The tortuous pore structure imposes both shear and extension, which elongates polymers; moreover, the flow is often at large Weissenberg numbers, Wi, at which polymer elasticity in turn strongly alters the flow. This dynamic elongation can even produce flow instabilities with strong spatial and temporal fluctuations despite the low Reynolds number, Re. Unfortunately, macroscopic approaches are limited in their ability to characterize the pore-scale flow. Thus, understanding how polymer conformations, flow dynamics, and pore geometry together determine these nontrivial flow patterns and impact macroscopic transport remains an outstanding challenge. This review describes how microfluidic tools can shed light on the physics underlying the flow of polymer solutions in porous media at high Wi and low Re. Specifically, microfluidic studies elucidate how steady and unsteady flow behavior depends on pore geometry and solution properties, and how polymer-induced effects impact nonaqueous fluid recovery. This work thus provides new insights for polymer dynamics, non-Newtonian fluid mechanics, and applications such as enhanced oil recovery and groundwater remediation.

Steady laminar plume generated from a heated line in polymer solutions

From the theoretical viewpoint, governing equations are derived for a steady laminar plume generated from a heated line in polymer solutions, in which similarity variables and the single polymer chain model are introduced. The resolved solutions imply that polymers promote the velocity in the centerline-near region but suppress that in the region far from the centerline. The equivalent effect of polymers is understood as producing two space-dependent source terms, which can explain the interaction between polymers and fluid flow from the viewpoint of energy transport. There exists a critical Weissenberg number (Wi) beyond which the promotion effect in the centerline-near region disappears, which results from the competition of stretching and relaxation of the polymer chain. Meanwhile, the corresponding modification of similarity velocity and heat transport are illustrated and validated numerically by single plume flow in polymer solutions. This work thus may contribute to the understanding of the polymer effect on single plume flow and further the heat transport enhancement mechanism in the bulk flow of turbulent Rayleigh-Bénard convection with polymers.

The Peculiarities of Oil Displacement in the Process of Oscillating Injection of Polymer Solution into the Bed with Layered Heterogeneity

The authors study the filtration flow of polyethylene oxide (PEO) water solutions of molecular weights 4∙106 and 6∙106 within the concentration range from 0 to 0.05% when exposed to an oscillating hydrodynamic field. Photographs characterizing the displacement of oil (with a viscosity of 10 to 50 mPa. s) with PEO water solutions from model porous formations with layered heterogeneity have been obtained. They have made it possible to specify the effectiveness of different oil displacement modes. It is shown that pumping a polymer solution into porous heterogeneous strata, while exposing it to oscillating hydrodynamic field, proved to yield a higher oil displacement ratio, as compared with a stationary oil displacement mode. The authors find out the conditions providing the positive influence on elastic deformations effects in the process of enhanced oil recovery by using polymer solutions. If elastic deformations take place, the filtration flow of polymer solutions should be carried out in the oscillating mode, whereas the frequency of the oscillating effect on the filtration flow should correspond to the dissipative function maximum. The stated results of the polymer solution flow research, under model conditions of a porous bed, have confirmed the nonlinearity mechanism of the polymer solutions filtration flow. In essence, the molecular and macromolecular non-linearity mechanism of the polymer solutions filtration flow means that in a porous medium under the influence of quasi-regular longitudinal velocity gradients, there arise self-sustained oscillations of reversible macromolecular deployment; the deployed macromolecules, in turn, influence the structure of the filtration flow, both on the molecular and macromolecular levels. Deformation oscillations of macromolecules and dissolubility of dynamic macromolecular structures formed under the influence of tensile currents result in the energy dissipation increase and the filtration flow nonlinearity. The nonlinearity of polymer solutions filtration flow ensures the alignment of the frontal advance of the polymer solutions within a porous bed with a layered heterogeneity and, consequently, higher oil displacement efficiency.

Simulation of semidilute polymer solutions in planar extensional flow via conformationally averaged Brownian noise.

The dynamics and rheology of semidilute polymer solutions in strong flows are of great practical relevance. Processing applications can in principle be designed utilizing the relationship between nonequilibrium polymer conformations and the material properties of the solution. However, the interplay between concentration, flow, hydrodynamic interactions (HIs), and topological interactions which govern semidilute polymer dynamics is challenging to characterize. Brownian dynamics (BD) simulations are particularly valuable as a way to directly visualize how molecular interactions arise in these systems and are quantitatively comparable to single-molecule experiments. However, such simulations are often computationally intractable and are limited by the need to calculate the correlated Brownian noise via decomposition of the diffusion tensor. Previously, we have introduced an iterative conformational averaging (CA) method for BD simulations which bypasses these limitations by preaveraging the HI and Brownian noise in an iterative procedure. In this work, we generalize the CA method to flowing semidilute solutions by introducing a conformation dependent diffusion tensor and a strain dependent approximation to the conformationally averaged Brownian noise. We find that this approach nearly quantitatively reproduces both transient and steady state polymer dynamics and rheology while achieving an order of magnitude computational acceleration. We then utilize the CA method to investigate the concentration and flow rate dependence of polymer dynamics in planar extensional flows. Our results are consistent with previous experimental and simulation studies and provide a detailed view of broad conformational distributions in the semidilute regime. We observe interconversion between stretched and coiled states at steady state, which we conjecture occur due to the effect of concentration on the conformation dependent polymer drag. Additionally, we observe transient flow-induced intermolecular hooks in the startup of flow which lead to diverse and unique stretching pathways.

Instability driven by shear thinning and elasticity in the flow of concentrated polymer solutions through microtubes

Polymers make flow in a tube unstable at low Reynolds numbers. An investigation shows that laminar flows of polymer solutions in a tube become unstable, unlike Newtonian fluids, at a Reynolds number as low as 10. This occurs because of the elastic and shear-thinning nature of polymer solutions.