Measurements of shear stress in ER/MR fluids used in valves by adapting centrifugal force

The article introduces a new flow rheometer of a simple structure, designed to determine the blocking stress in valves with electrorheological (ER) and magnetorheological (MR) fluids. It combines the advantages of rotary and flow rheometers. In this rheometer, a flow of a small ER/MR fluid sample placed in a revolving channel, is forced by the centrifugal force. The designed rheometer has a characteristically simple structure due to the lack of components such as pistons or pumps used to induce the flow of ER/MR fluid, and it does not have the basic disadvantage of flow rheometers, which is the necessity to analyse a large sample of fluid. The results of measurements conducted with the new rheometer were compared with results from two standard rheometers: A flow rheometer and a rotary rheometer. In order to adjust the measurement results from the new rheometer to these obtained from standard rheometers, the research featured a method of selecting numerical coefficients occurring in formulas used to calculate shear stress. The method is based on optimization method and it minimizes the differences between measurements for the same values of electric or magnetic field strength.