Structure evolution in electrorheological fluids flowing through microchannels

Abstract

Enhanced knowledge of the transient behavior and characteristics of electrorheological (ER) fluids subject to time dependent electric fields carries the potential to advance the design of fast actuated hydraulic devices. In this study, the dynamic response of electrorheological fluid flows in rectilinear microchannels was investigated experimentally. Using high-speed microscopic imaging, the evolution of particle aggregates in ER fluids subjected to temporally stepwise electric fields was visualized. Nonuniform growth of the particle structures in the channel was observed and correlated to field strength and flow rate. Two competing time scales for structure growth were identified. Guided by experimental observations, we develop a phenomenological model to quantitatively describe and predict the evolution of microscale structures and the concomitant induced pressure gradient.

Yield Hardening of Electrorheological Fluids in Channel Flow

“…On the other hand, in shear mode, they note that the aggregation of chains into columns is the dominant process. This is in agreement with recent studies by Qian et al [17] on structure evolution in channel flow of ER fluids.…”

“…To measure the rheological response under flow mode, a rectangular microchannel is fabricated [17] (shown in Fig. 1).…”

“…9 in Appendix C) indicating that wall slip plays a negligible role in our measurements for the range of the shear rates tested. For the case of channel flow, Video 1 in Appendix C taken using the imaging setup described by Qian et al [17] demonstrates the absence of slip at the walls for a low-volume fraction fluid (ϕ ¼ 0.02) at an applied of field of E ¼ 4 kV=mm and an imposed flow rate Q ¼ 30 μL= min.…”

“…By averaging over a series of peaks, we obtain an average value of the yield pressure differential at yield for the channel at each imposed mass flow rate. In the lubrication limit (L ≫ h, W), the field-dependent pressure difference at yield ΔP y ðE; ϕÞ can be related to the Bingham yield stress using the following relation obtained via a global force balance on the system [17,26]:…”

Stimuli-Responsive Polymers and Colloids under Electric and Magnetic Fields

“…The field-induced structures restrict the free flow of dispersed particles in ER/MR suspensions, thereby inducing significant variations in their rheological and viscoelastic properties including yield stress, flow curve, enhanced apparent viscosity, creep, recovery, and dynamic moduli [26,27]. The interesting smart electro/magneto-responsive characteristics of fine tuning and the quick response make them appropriate candidates in broad engineering areas, such as clutches, seismic vibration dampers, breaks, optical finishing systems, medical therapies, artificial muscle stimulators, actuators, haptic master, micro-fluidic control, and viscosity reduction of crude oil [24,[28][29][30][31][32][33][34][35]. Nevertheless, compared to conventional ER fluids, MR suspensions generally exhibit a higher field-induced effect and are in less demand by electric providers.…”