Column size effects of DER fluids

Advances in Physics, 2003

Electrorheological (ER) fluids are a class of materials whose rheological properties are controllable by the application of an electric field. A dielectric electrorheological (DER) fluid is the simplest type of ER fluid, in which the material components follow a linear electrostatic response. We review and discuss the progress of the studies on physics of this type of material. A first-principles theory of DER fluids, along with relevant experimental verifications, are presented in some detail. In particular, the properties presented include static equilibrium structure, shear modulus, static yield stress and its variation with applied electric field frequency, and structure-induced dielectric nonlinearity. Contents page 1. Introduction 344 2. Formulation 345 3. Effective dielectric constant evaluation 347 4. Structure in the DER fluid 355 5. Static yield stress of the DER fluid 358 6. Upper bounds of the yield stress and shear modulus 361 7. Comparison with experiments 363 7.1. Mesostructure of the DER fluid 364 7.2. The yield stress of dry glass-oil DER fluids 364 7.3. Structure-induced dielectric nonlinearity 367 8. Summary and discussion 371 Acknowledgements 371 Appendix A. Basis functions 372 A.1. Spherical particles 372 A.2. Spherical shell inclusion 373 Appendix B. Matrix elements of theĜ G operator 374 Appendix C. Proof of an expansion formula 378 Appendix D. Ewald sums 379 References 382

Applied Physics Letters, 1998

Smart Materials and Structures, 2009

A home-made electrorheological (ER) fluid, known as ETSERF, has been created with suspension-based powders dispersed in silicone oil. Because of the special structure of their particles, ETSERF suspensions present a complex behavior. In the absence of an electric field, the ETSERF fluid manifests a near-Newtonian behavior, but when an electric field is applied, it exhibits a pseudoplastic behavior with yield stress. The ER effect under DC electric fields has been experimentally investigated using both hydrous and anhydrous ER fluids. The ER properties are strongly dependent on the dielectric properties of ETSERF suspensions, and hydrous ER fluids have a high dielectric constant and a high relaxation frequency which show a strong electrorheological effect. The relationship between the electrorheological effect and the permittivity of ER fluids has also been extensively studied. Experimental results show that the interfacial polarization plays an important role in the electrorheological phenomenon. The ageing of ETSERF fluids was also studied and it was found that the dielectric properties (mainly the dielectric loss tangent) and ER properties are strongly related to the duration of ageing. A fresh ETSERF suspension exhibits high relaxation frequency and high dielectric constant. These results are mainly explained by the effect of interfacial polarizations.

Physical Review E, 2012

A dielectric measurement method has been proposed to apply to the study of the microstructure of electrorheological (ER) fluids. To test our measurement method the dielectric permittivity increment caused by pair and chain formation was measured in dilute Brownian ER fluids composed of silicone oil and nanosized silica particles. The critical values of the electric field required to induce structure formation were experimentally determined from the electric field dependence of the measured permittivity increment. From the electric field induced time evolution of the relative permittivity of ER fluids, the characteristic times of the pair and chain formation were calculated. Our experimental results for the time constants are in good agreement with the corresponding theoretical data obtained from the Eyring theory.

Physical Review E, 2002

Electrorheological ͑ER͒ fluid based on zeolite and silicone oil under elongation, compression, and shearing was investigated at room temperature. Dc electric fields were applied on the ER fluid when elongation and compression were carried out on a self-constructed test system. The shear yield stress, presenting the macroscopic interactions of particles in the ER fluid along the direction of shearing and perpendicular to the direction of the electric field, was also obtained by a HAAKE RV20 rheometer. The tensile yield stress, presenting the macroscopic interactions of particles in the ER fluid along the direction of the electric field, was achieved as the peak value in the elongating curve with an elongating yield strain of 0.15-0.20. A shear yield angle of about 15°-18.5°reasonably connected tensile yield stress with shear yield stress, agreeing with the shear yield angle tested well by other researchers. The compressing tests showed that the ER fluid has a high compressive modulus under a small compressive strain lower than 0.1. The compressive stress has an exponential relationship with the compressive strain when it is higher than 0.1, and it is much higher than shear yield stress.

1998

Mechanical properties of electrorheological uids under various dynamical loading conditions have been studied using a computer simulation model. The model assumes electrostatic point-dipole interaction between particles with or without multipolar corrections and the interaction with the base uid due to viscous laminar ow is described with Stokes drag. The mechanical loading is introduced as constant rate shear, compression or elongation to a system of particles set initially to a single chain, a column of body centered tetragonal (BCT) unit cells, a thick BCT-structure or to a structure grown with electric eld from originally random con guration. Results show that the relative strength of the single chain structure is usually largest. Electrorheological systems under compressive loading were found to transmit largest force from one plate to another. Under elongation loading a thick BCT-structure seemed surprisingly weak compared with the system under compression or shear. In addition, the response of a BCT-structure under sinusoidally alternating shear or tensile straining have been studied. It was found that under tensile loading the ability of the system to transfer force is dependent on oscillation frequency much more than under shear loading.

An Electrorheological (ER) process occurs when the viscosity of fluid with dispersed particles is modified by the application of an electric field. The Electrorheological flowable dispersed fluids can be currently used for fixing of materials responding to mechanical loads and, as working media for dampers and dielectric actuators. The present investigation has been undertaken with the aim of studying the parameters that effect on the apparent viscosity of low–concentration ER-fluid (diatomite in transformer oil). Results demonstrate increases in the viscosity by applying electric field. It is shown that the viscosity behavior can be reasonably modeled as a power–low fluid, with the viscosity equal to a consistency index, K, multiplied by the shear rate raised to the power n-1. Results indicate that both the consistency index K and the exponent n are influenced by voltage and temperature, where K has linear and n has exponential relation with temperature. The variation of the appare...

IRJET, 2022

Since last three decades, ER fluid has major importance in science, medical and engineering problems, which include vibration reduction and suspension. Electrorheological fluids are smart materials whose rheological properties are controllable through the applications of an external electric field. These rheological properties of ER fluid can be exploited in ERF devices for advanced technological applications. The optimal design of ERF devices requires proper mathematical modeling and basic governing equations. This paper presents the working principles, governing equations and mathematical framework for ER fluids. Also in this paper recent progress of ER devices and their applications have been discussed.

Physical Review E, 2015

We have determined the response time of dilute electrorheological fluids (ER) in drag flow from the dynamic dielectric response. On the basis of a kinetic rate equation a new formula was derived to approximate the experimental time-dependent dielectric permittivity during the temporal evolution of the microstructure. The dielectric response time was compared to the standard rheological response time extracted from the time-dependent shear stress, and a good agreement was obtained. We found that the dielectric method is more sensitive to detect any transient during the chain formation process. The experimental saturation value of the dielectric permittivity corresponding to the equilibrium microstructure was estimated on the basis of formulas derived from the Clausius-Mossotti equation.

International Journal of Multiphase Flow, 2013

The steady state electrohydrodynamics of a leaky dielectric fluid column in confined domains is investigated. The governing electrohydrodynamic equations are solved, in a plane normal to the column axis, for Newtonian and immiscible fluids in the framework of leaky-dielectric theory and for creeping flow regime. The domain confinement strengthens or weakens the electric field, depending on R > 1 or R < 1, respectively, R = r i /r o being the ratio of electric conductivity of the column to that of the surrounding fluid. Similarly, the flow intensity decreases for R < 1, but it remains unchanged or increases for R > 1, depending on the interplay of electric and hydrodynamic effects. An expression for the interface deformation for small distortion from the circular shape is found using the domain perturbation technique. It is shown that below a threshold domain size the confinement effect will lead to the reversal of the tendency of the net normal hydrodynamic stress in deforming the interface to an oblate or a prolate shape, and that below a critical domain size the necessary condition for having an oblate column will transfer from R < S to R > S, where S = i / o is the permittivity ratio.