Fluid Rheological Effects Research Articles

Fluid rheological effects on streaming dielectrophoresis in a post-array microchannel.

Recent studies have demonstrated the strong influences of fluid rheological properties on insulator-based dielectrophoresis (iDEP) in single-constriction microchannels. However, it is yet to be understood how iDEP in non-Newtonian fluids depends on the geometry of insulating structures. We report in this work an experimental study of fluid rheological effects on streaming DEP in a post-array microchannel that presents multiple contractions and expansions. The iDEP focusing and trapping of particles in a viscoelastic polyethylene oxide solution are comparable to those in a Newtonian buffer, which is consistent with the observations in a single-constriction microchannel. Similarly, the insignificant iDEP effects in a shear-thinning xanthan gum solution also agree with those in the single-constriction channel except that gel-like structures are observed to only form in the post-array microchannel under large DC electric fields. In contrast, the iDEP effects in both viscoelastic and shear-thinning polyacrylamide solution are significantly weaker than in the single-constriction channel. Moreover, instabilities occur in the electroosmotic flow and appear to be only dependent on the DC electric field. These phenomena may be associated with the dynamics of polymers as they are electrokinetically advected around and through the posts.

Insulator-based dielectrophoretic focusing and trapping of particles in non-Newtonian fluids.

Insulator-based dielectrophoretic (iDEP) microdevices have been limited to work with Newtonian fluids. We report an experimental study of the fluid rheological effects on iDEP focusing and trapping of polystyrene particles in polyethylene oxide, xanthan gum, and polyacrylamide solutions through a constricted microchannel. Particle focusing and trapping in the mildly viscoelastic polyethylene oxide solution are slightly weaker than in the Newtonian buffer. They are, however, significantly improved in the strongly viscoelastic and shear thinning polyacrylamide solution. These observed particle focusing behaviors exhibit a similar trend with respect to electric field, consistent with a revised theoretical analysis for iDEP focusing in non-Newtonian fluids. No apparent focusing of particles is achieved in the xanthan gum solution, though the iDEP trapping can take place under a much larger electric field than the other fluids. This is attributed to the strong shear thinning-induced influences on both the electroosmotic flow and electrokinetic/dielectrophoretic motions.

Study of wellbore heat transfer considering fluid rheological effects in deep well acidizing

Real-time understanding of the wellbore temperature is a prerequisite for the acidizing treatment design. Fluid flow regime variation caused by fluid rheological property has a great influence on wellbore temperature distribution. According to the physical situation in the acidizing process, the wellbore and formation heat transfer model considering fluid rheological effects is established, the validity of the model is verified by comparing with monitoring data and previous research results. The results indicate that fluid rheology will cause the transition of flow regime, which leads to the variation of heat transfer efficiency. Considering wellbore original water is benefit for accurately predicting bottom-hole temperature. Injection rate has a great influence on fluid flow regime. A critical injection rate with the highest cooling efficiency exists in the low range of pumping rate condition. The findings above can provide theoretical insights for the deep well acidizing, and the model built in this paper is applied in field wellbore temperature simulation.

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.

Elastic instabilities in the electroosmotic flow of non-Newtonian fluids through T-shaped microchannels.

Electroosmotic flow (EOF) has been widely used to transport fluids and samples in micro- and nanofluidic channels for lab-on-a-chip applications. This essentially surface-driven plug-like flow is, however, sensitive to both the fluid and wall properties, of which any inhomogeneity may draw disturbances to the flow and even instabilities. Existing studies on EOF instabilities have been focused primarily upon Newtonian fluids though many of the chemical and biological solutions are actually non-Newtonian. We carry out a systematic experimental investigation of the fluid rheological effects on the elastic instability in the EOF of phosphate buffer-based polymer solutions through T-shaped microchannels. We find that electro-elastic instabilities can be induced in shear thinning polyacrylamide (PAA) and xanthan gum (XG) solutions if the applied direct current voltage is above a threshold value. However, no instabilities are observed in Newtonian or weakly shear thinning viscoelastic fluids including polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), and hyaluronic acid (HA) solutions. We also perform a quantitative analysis of the wave parameters for the observed elasto-elastic instabilities.

Electroosmotic flow of non-Newtonian fluids in a constriction microchannel.

Insulator-based dielectrophoresis has to date been almost entirely restricted to Newtonian fluids despite the fact that many of the chemical and biological fluids exhibit non-Newtonian characteristics. We present herein an experimental study of the fluid rheological effects on the electroosmotic flow of four types of polymer solutions, i.e., 2000 ppm xanthan gum (XG), 5% polyvinylpyrrolidone (PVP), 3000 ppm polyethylene oxide (PEO), and 200 ppm polyacrylamide (PAA) solutions, through a constriction microchannel under DC electric fields of up to 400 V/cm. We find using particle streakline imaging that the fluid elasticity does not change significantly the electroosmotic flow pattern of weakly shear-thinning PVP and PEO solutions from that of a Newtonian solution. In contrast, the fluid shear-thinning causes multiple pairs of flow circulations in the weakly elastic XG solution, leading to a central jet with a significantly enhanced speed from before to after the channel constriction. These flow vortices are, however, suppressed in the strongly viscoelastic and shear-thinning PAA solution.

Fluid rheological effects on particle migration in a straight rectangular microchannel

There has recently been a significantly increasing interest in the passive manipulation of particles in the flow of non-Newtonian fluids through microchannels. However, an accurate and comprehensive understanding of the various fluid rheological effects on particle migration is still largely missing. We present in this work a systematic experimental study of both the individual and the combined effects of fluid inertia, elasticity, and shear thinning on the motion of rigid spherical particles in a straight rectangular microchannel. We first study the sole effect of each of these rheological properties in a Newtonian fluid, purely elastic (i.e., Boger) fluid, and purely shear-thinning (i.e., pseudoplastic) fluid, respectively. We then study the combined effects of two or all of these rheological properties in a pseudoplastic fluid and two types of elastic shear-thinning fluids, respectively. We find that the fluid elasticity effect directs particles toward the centerline of the channel while the fluid shear-thinning effect causes particle migration toward both the centerline and corners. These two effects are combined with the fluid inertial effect to understand the particle migration in inertial pseudoplastic and viscoelastic fluid flows.

A thermodynamically consistent formulation of magnetoporoelasticity

The dynamical theory of a porous, elastic, and magnetically inert solid body infiltrated by a ferromagnetic liquid is formulated. This type of magnetoporoelastic material opens a wide range of technical applications, such as controlled vibration dampers, sensors, and adaptive mirrors. The irreversible deformation and nonlinear coupling among the solid elastic, fluid rheological, and magnetic effects is derived based on the Biot–Frenkel theory with thermodynamic considerations. The thermal effect, however, is not considered in this paper. A linearized version of constitutive equations and the dynamic equations are introduced.

Fluid rheological effects in sliding elastohydrodynamic point contacts with transient loading: Traction : D. M. Sanborn and W. O. Winer, JOLT, Ser. F 93 (3) (1971) 342–348; 7 figs., 1 table, 17 refs.

Fluid rheological effects in sliding elastohydrodynamic point contacts with transient loading: Traction : D. M. Sanborn and W. O. Winer, JOLT, Ser. F 93 (3) (1971) 342–348; 7 figs., 1 table, 17 refs.

Fluid rheological effects in sliding elastohydrodynamic point contacts with transient loading : D. M. Sanborn and W. O. Winer, JOLT, Ser. F, 93 (2) (1971) 262–271; 11 figs., 2 tables, 21 refs.

Fluid rheological effects in sliding elastohydrodynamic point contacts with transient loading : D. M. Sanborn and W. O. Winer, JOLT, Ser. F, 93 (2) (1971) 262–271; 11 figs., 2 tables, 21 refs.

Fluid Rheological Effects in Sliding Elastohydrodynamic Point Contacts With Transient Loading: 2—Traction

This paper describes the results of the traction measurements obtained in the experiment discussed in the companion paper entitled “Fluid Rheological Effects in Sliding Elastohydrodynamic Point Contacts With Transient Loading: I.—Film Thickness.” Under the conditions investigated, the traction values appear to be primarily a function of the sliding velocity. Large variations in fluid composition and inlet viscosity had little influence on the tractive force. It was also found that rapid application of the normal load had a negligible effect on the traction.

Closure to “Discussions of ‘Fluid Rheological Effects in Sliding Elastohydrodynamic Point Contacts With Transient Loading: 2—Traction’” (1971, ASME J. Lubr. Technol., 93, pp. 346–347)

Closure to “Discussions of ‘Fluid Rheological Effects in Sliding Elastohydrodynamic Point Contacts With Transient Loading: 2—Traction’” (1971, ASME J. Lubr. Technol., 93, pp. 346–347)

Fluid Rheological Effects in Sliding Elastohydrodynamic Point Contacts With Transient Loading: 1—Film Thickness

This paper describes an experimental investigation of the elastohydrodynamic problem. The investigation was limited to a study of nominal point contacts in pure sliding motion. The profile of the lubricant film separating the bearing surfaces was determined during a transient of the normal load. During this transient the Hertzian contact stresses were increased from zero to a maximum of 150,000 lbf/in2 in approximately 45 milli-secs. The sliding velocities used in this study were varied from 13.7 to 92.1 ips. The resulting mean shear rate, however, was typically 107 reciprocal seconds. Both pure and polymer-blended naphthenic and paraffinic oils, in addition to several synthetic fluids, were studied. On the basis of the film thickness profiles obtained for the polymer-blended oils, it was concluded that the ambient value of viscosity often used in theoretical considerations does not characterize the behavior of the system. It was also found that the rapid application of the normal load had a negligible effect on the film thickness profile. During this investigation the contact traction was also measured. The results of those measurements are reported in the companion paper, “Fluid Rheological Effects in Sliding Elastohydrodynamic Point Contacts With Transient Loading: II—Traction.”