CHAPTER 9. Magnetorheological Fluids Flowing Through Porous Media: Analysis, Experimental Evaluation, and Applications

Abstract

The behavior of magnetorheological (MR) fluids flowing through porous media is evaluated analytically and experimentally. In the porous media, tortuous channels exist within a packed bed of particles. As MR fluid flows through tortuous channels in the porous media, a magnetic field can be applied in the axial direction by a solenoid wrapped around the valve holding the porous media. Since the fluid direction deviates from the axial direction as the MR fluid passes through the porous media, a field-dependent yield stress develops in the fluid in addition to a shear-rate dependent viscous force. The active length of this configuration can be nearly as long as the MR valve, whereas in conventional MR devices, the active region occupies a small fraction of the valve length. Placing the electromagnetic coil externally also allows for improved heat dissipation and accessibility for maintenance. The key elements affecting MR flow in the porous media are identified using flow analysis in porous media, such as porosity, tortuosity and shape. A detailed analysis focuses on determining how these parameters lead to improvements in performance. A hydraulic device using a by-pass porous valve is developed for experimental evaluation. Different configurations of porous media are tested. Each composed of packed beds of metallic rods or spheres, and performance is compared at varying velocities. To fully understand the interaction between the MR fluid and the magnetic field in the porous media, a mathematical model ispresented and is validated through experimental results.