Abstract
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.
Highlights
Triboelectric charging occurs everywhere in nature from child rubbing a balloon on their hair to industrial powder handling
Triboelectric charging is predominately described as a problem, rather than an opportunity
Triboelectric charging is an exciting but so far not completely understood phenomenon. It has been investigated in many fields of research, such as contact electrification in dust devils (Farrell, 2004; Mareev and Dementyeva, 2017), in clouds after volcanic eruptions (Anderson et al, 1965; Mather and Harrison, 2006), in the formation of planets (Yair et al, 2008; Wang et al, 2017), and in almost every application dealing with fine and dry powders
Summary
Triboelectric charging occurs everywhere in nature from child rubbing a balloon on their hair to industrial powder handling. Triboelectric charging is an exciting but so far not completely understood phenomenon. It has been investigated in many fields of research, such as contact electrification in dust devils (Farrell, 2004; Mareev and Dementyeva, 2017), in clouds after volcanic eruptions (Anderson et al, 1965; Mather and Harrison, 2006), in the formation of planets (Yair et al, 2008; Wang et al, 2017), and in almost every application dealing with fine and dry powders. Triboelectric charging is seen as a problem in industrial applications if particles are to be moved because charged particles tend to agglomerate and adhere on surfaces (Wong et al, 2015). Triboelectric charging of particles and surfaces is a desirable effect in electrophotography (Schein, 1999), nanogenerators (Wang, 2013; Jiang et al, 2018), and particle separation (Eichas and Schönert, 1992; Wu et al, 2013; Wang et al, 2015; Tabtabaei et al, 2016; Landauer and Foerst, 2018; Landauer et al, 2019)
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