A simple μ-PTV setup to estimate single-particle charge of triboelectrically charged particles

Triboelectric separation is a useful phenomenon that can be used to separate fine powders. To design technical devices or evaluate the potential of powders to be triboelectrically separated, knowledge about the charge distribution on a single-particle level has to be obtained. To estimate the single-particle charge distribution in an application-oriented way, a simple μ-PTV system was developed. The designed setup consists of a dispersing and a charging unit using a Venturi nozzle and a tube, respectively, followed by a separation chamber. In the separation chamber, a homogenous electrical field leads to a deflection of the particles according to their individual charge. The trajectories of the particles are captured on single frames using microscope optics and a high-speed camera with a defined exposure time. The particles are illuminated using a laser beam combined with a cylindrical lens. The captured images enable simultaneous measurement of positively and negatively charged particles. The charge is calculated assuming a mean particle mass derived from the mean particle size. Initial experiments were carried out using starch of different botanical origins and protein powder. Single-component experiments with starch powders show very different charge distributions for positively and negatively charged particles, whereas protein powder shows bipolar charging. Different starch-protein mixtures show similar patterns for positive and negative charge distributions.