Analysis of factors affecting the rotation speed of axial-flux free-rotor electromagnetic stirrer

Abstract

In this study, a new PIC (programmable – integrated - circuit) microcontroller controlled electromagnetic stirrer is designed. The electromagnetic stirrer system consists of axial-flux permanent-magnet synchronous motor-based rotating magnetic field source (stator), heater, a cup for the liquid to be stirred and a magnetic stir bar (magnetic fish-rotor) which is immersed into the liquid to stir it by rotating with the rotary magnetic field. The rotary magnetic field source is constituted of 3 identical winding groups which are connected in star. For ensuring the rotary magnetic field, square wave-shaped voltage signals are applied to the 3 winding groups with 120° phase differences between each couple of signals. The frequency of the square waves which directly affects the stirring speed is controlled by a PIC microprocessor-based supplier circuit. Magnetic stir bar iron core is produced from a magnetically oriented sample. In this study, the parameters which especially affect the rotation speed of the electromagnetic stirrer, the effects of the magnetic stir bar size on the stirring process, the principles of the supplier circuit, the effects of the liquid parameters like volume, viscosity, etc., are studied and discussed. Our previous studies on electromagnetic stirrers were carried out for small-volume liquids and 3% Si-Fe sheet metals were used for the magnetic stir bar core. In this study, easily magnetisable and bigger size cores are used for stirring bigger-volume liquids.