Electrorheological Flows

Tsukiji, T. Utashiro, T. Flow Characterisation of E. R. Fluids Between Two Parallel Plate Electrodes. Proc. ASME Int. Congress and Expo., San Francisco, Developments in Electrorheological flows FED Vol. 235, MD Vol. 71 (Nov. 1996), pp. 37-42... 

The electroviscous effects are observed as variations of viscosity upon application of outer electric fields, and as build-up of potential gradients upon flow of such fluids. See also -> electroconvection, electrorheological... 

Electrorheological properties of fluids, in this case PS/MWCNT suspensions in silicone oil, can be demonstrated in the form of flow curves obtained from measurements on a rotational rheometer in the absence and presence of external electric field (21). The flow curves expressing shear stress vs. shear rate dependence are... 

Fig. 8-1). If one attempts to slide one electrode relative to the other the particle chains resist with a force that increases roughly as (Winslow 1949 Klingenberg and Zukoski 1990). Electrorheological fluids were discovered and patented by W. M. Winslow (1947, 1949) some 50 years ago. Since then, Winslow and others have dreamed of widespread applications of these fluids in fast clutches, actively controlled shock absorbers, variable-flow pumps, and robotic activators.

Electrorheological Fluid A dispersion of microscopic particles suspended in a low permittivity, low conductivity liquid such that the dispersion s flow properties change in the presence of electric fields. Also termed ER fluids the electrorheological effect is also termed the Winslow effect. When an electric field is applied to an ER fluid, the polarizable particles become electric dipoles and can align to form chains and more complex structures as a result the fluid becomes more viscous and may form a gel. Example cornstarch dispersed in corn oil and subjected to an electric field gradient of about 10,000 V/cm. See also reference 18. 

M. Stenicka, V. Pavlinek, P. Sahci, N.V. Bhnovci, J. Stejskal, O. Quadrat, Effect of hydrophihcity of polycuiiline pcuticles on their electrorheology, steady flow cuid dyncunic behaviour, /. Colloid Interface Sci., 2010,346, 236. 

Materials that allow an intelligent or smart structure to adapt to its environment are known as actuators. These materials have the ability to change the shape, stiffness, position, natural frequency, damping, friction, fluid flow rate, and other mechanical characteristics of adaptronic structures in response to changes in temperature, electric field, or magnetic field. The most common actuator materials are shape memory alloys, piezoelectric materials, mag-netostrictive materials, electrorheological fluids, and magnetorheological fluids [2]. Actuators with these materials will be described in detail in Sects. 6.2 to 6.6 therefore you will find only a brief overview below. 

An electrorheological fluid (dispersion type), as defined for this purpose, is a mixture of micron-sized, high dielectric constant particles carried in an insulating base oil. When an electric field is applied transverse to the direction of any motion of the fluid, it causes an interaction between the particles, the field and the dispersant, and this results in an increase in the resistance to the flow of the mixture. 

Perhaps the most problematic area that obstructs the control of these changes by the use of electrorheological fluids is the particle mechanics or continuum conundrum for characterizing the flow of the dense slurry (unexcited) or yielding plastic (excited). Whilst many years have been spent in computer analysis... 

Retroactive Effects on the Power Electronics. The operating modes of electrorheological actuators are classified into three types flow mode (or valve mode), shear mode and squeeze mode. The former two modes do not exhibit any retroactive effects, whereas the squeeze mode can generate high voltages when the distance between the capacitor plates are altered quickly. When an actuator is operated in squeeze mode, extra precautions must be taken to protect the amplifier from damage. 

Liquid crystals and their electrorheological properties under flows with a constant shear rate over the height of the channel have been treated in a number of papers. However, in all of these papers the studies have focused on situations in which the anchoring was the same at all boundaries. Only recently, a systematic study of the influence of different boundary conditions on the shear flow was treated together with the influence of an applied electric field. 

In Fig. 21 we present the average viscosity as a function of Afl. Notice that the electrorheological effed is less pronounced for larger values of the shear flow since the cylinder s rotation turns the nematic perpendicularly to the electric field and as a consequence its influence is reduced. 

Medina, J.C. Mendoza, C.l. (2008). Electrorheological effect and non-Newtonian behavior of a homogeneous nematic cell under shear flow Hysteresis, bistability, and directional response. EPL Europhysics Letters, Vol. 84, pp. 16002-pl-16002-p6... 

Reyes, J.A. Manero, O. Rodriguez, R.F. (2001). Electrorheology of nematic liquid crystals in uniform shear flow. Rheologica Acta, Vol. 40, pp. 426-433... 

Electrorheological Behavior. Electrorheological (ER) fluids are colloidal suspensions whose properties change strongly and reversibly upon application of an electric field. AVhen an electric field is applied to an ER fluid, it responds by forming fibrous or chain structures parallel to the applied field. These structures greatly increase the viscosity of the fluid, by a factor of 10 in some cases. At low shear stress the material behaves like a solid. The material has a yield stress, above which it will flow, but with a high viscosity. 

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