Development of a wireless electrical resistance detector for real-time particle volume fraction measurement in centrifuges

A wireless electrical resistance detector has been developed to measure the real-time particle volume fraction in a high speed centrifuge. The detector is composed of an AC (alternating current) generation device, a measurement circuit and a wireless transmission device. The square wave alternating AC signal is generated from batteries. To test the measurement accuracy, the developed detector is attached around a lab-scale centrifuge with a limited rotational velocity. With the developed detector, the real-time volume fraction of polymer pellets with an elliptic cylindrical shape in sodium chloride solution is measured at different positions under various rotational velocities and particle supply rates. The measurement results are compared with a numerical simulation by the volume-of-fluid (VOF) method for validation. A parabola-shaped phase boundary between particle and sodium chloride solution is detected. As the rotational velocity increases, more and more particles are pushed outward and raised along the cylindrical vessel because of the increased centrifugal force, which causes an increase of the particle volume fraction near the wall. Moreover, as the initial particle loading height increases, the parabola-shaped phase boundary shifts upward and increases the particle volume fraction near the wall.