RESPONSE TIME OF MAGNETORHEOLOGICAL (MR) FLUID AND MR VALVES UNDER VARIOUS FLOW CONDITIONS

The response time of magnetorheological (MR) fluids to an external magnetic field is a few milliseconds. However, the overall response time in MR devices under a magnetic field is a function of electromagnetic parameters, the capabilities of the driving electronics, as well as, the operation conditions. Therefore, the overall response time of a MR device depends on the internal device design parameters. In this work, the response times of MR fluid and MR fluid valves have been studied under various flow configurations. Two types of valving geometries; annular flow, and radial flow are considered in the MR fluid valve designs. The transient pressure response of MR fluid valves are evaluated by using a diaphragm pump with a constant volume flow rate. The performance of each MR valve is characterized using a voltage step input, as well as, a current step input while recording the activation electric voltage/current, magnetic flux density, and pressure drop as a function of time. The variation of the response time of the MR valves under constant volume flow rate is experimentally investigated. The system's time constant is determined under induced pressure changes. In order to obtain the response time of the MR fluid a Maxwell model with a time constant is employed to describe the field induced pressure behavior of MR fluid under a steady flow. The results demonstrate that the pressure response times of the MR fluid and the MR valves depend on the designs of the electric parameters and the valve geometry. MR valves in annular flow geometry have a slow falling response time compared to their rising response time. MR valves in radial flow geometry result in faster pressure response times both in rising and falling states.