Introducing the thermal field into multi-physics coupling for the modeling of MR fluid-based micro-brake

Miniaturization of magnetorheological (MR) fluid-based actuator, as an essential building block of miniature electromechanical systems, is of significant importance. Since the feature size of miniature electromechanical systems 1–10 mm, the heat generation and dissipation process in the MR fluid would dramatically affect the speed reduction mechanism of micro-brake. The objective of this manuscript is to propose a model for the MR fluid-based micro-brake with high accuracy by introducing the thermal field into the multi-physics coupling. The temperature- and field-dependent rheological properties of MR fluid are investigated and the data is presented. The rheological behavior of MR fluid under the comprehensive effect of temperature field, magnetic field and flow field is modeled by introducing the Arrhenius equation. A COMSOL Multiphysics-based simulation method, which includes two heat sources, is proposed to calculate the thermal distribution of the miniature turbine generator under the multi-physics coupling. The influence of temperature on the yield stress τ_y and the influence of shear rate γ˙ on viscosity η are also introduced into the MR fluid-based micro-brake to obtain a torque calculation model with high precision. The miniature turbine generator was driven with an initial rotational speed of 18,200 r/min. The temperature ranged from 41 to 123 °C as a current from 0.3 to 1.5 A was applied to the micro-brake. Results show that the accuracy has been improved more than 12.9% by introducing thermal analysis to the micro-brake model. We believe this work is significant for realizing the high precision control of MR fluid-based micro-brake at high rotational speeds.