A Novel Apparatus For Particle-Particle Single Contact Electrification Experiments

TL;DR

This work introduces a novel apparatus that combines pneumatic conveying and acoustic levitation to achieve electrically and physically isolated, high-speed particle-particle collisions with a high collision success rate ($93\%$). The design enables precise control over incident pre-contact charge, trajectory, speed, and impact angle, while using a target held in an acoustic trap and Faraday cups to measure pre- and post-contact charges. Electrical tests reveal that charge transfer is a stochastic process, not solely governed by pre-contact potential differences, necessitating large datasets to resolve underlying statistics. The apparatus provides a platform to study triboelectrification more rigorously and to refine models for industrial mitigation of charge transfer hazards.

Abstract

The experiment of a single contact between two sub-centimeter high-speed particles is often difficult to execute, especially if the collision must be physically and electrically isolated, as is the case for triboelectrification studies. Apparatuses designed for this type of experiment fall short of providing high-speed isolated collisions with a high probability of contact. In this article, we propose a novel apparatus that combines pneumatic conveying and acoustic levitation to provide an electrically and physically isolated, high impact speed collision between two sub-centimeter particles with a collision success rate of 93 %. We can control the pre-contact charge, material, and size of both particles, and the impact speed and angle. Test results show that charge transfer between two insulator particles is not solely driven by contact potential difference; it is a stochastic process that requires large datasets to resolve and understand. Our new apparatus can efficiently generate these datasets and provide new insights on the stochastic nature of charge transfer, and the effect of each of the collision parameters mentioned earlier on particle-particle charge transfer.

Figures (6)

• Figure 1: Schematic of our apparatus. The pre-contact section propels an incident particle, with controlled speed, trajectory, and pre-contact charge, towards a target particle held stationary in the contact section. After the collision, the post-contact charge of both particles is measured by Faraday cups in the post-contact section. This apparatus combines pneumatic conveying and acoustic levitation to provide an electrically and physically isolated, high impact speed collision between two sub-centimeter particle with a collision success rate of 93. We can precisely control the incident pre-contact charge, incident trajectory, impact speed, impact angle, and target pre-contact charge.
• Figure 2: Mean incident particle trajectory (with one standard deviation as shaded region) for 3.97 nylon sphere through reducers with different outlet diameters shown in (A). The precision of the trajectory increases as $\lambda$ decreases, and the precision is the same in all planes (B). The red dot in (B) represents a 3mm target particle 50mm away from the reducer outlet. The spread of the incident trajectory is less than the particle diameter, so the incident particle has a near-perfect chance of hitting this target particle. This result confirms that we have precise control the incident particle trajectory towards the target particle.
• Figure 3: Overlapped frames of a collision of a 3.97 nylon sphere (incident particle in green) and a 3.17 nylon sphere (target particle in brown). The borders of the Faraday cups are highlighted consistently with the colour of the particle the cup catches. The precision of the incident particle trajectory allows us to control the impact angle and post-contact trajectories.
• Figure 4: (A) Incident pre-contact charge measurement via the sensing device for a neutralized 3.97 nylon sphere conveyed with zero coils in the pre-contact charger. The incident pre-contact charge is equal to the difference between the mean charge value after exit of the incident particle and the mean charge value during residence of the incident particle in the sensor. (B) Comparison between incident pre-contact charge measurements from the sensing device and a Faraday cup for the same 3.97 nylon sphere conveyed with a one or two coils at different gas velocities. All data points fall on the identity line, confirming that the sensing device precisely and accurately measures the incident pre-contact charge.
• Figure 5: (A) Particle charge of a 3.17 nylon sphere after neutralization for different durations. The magnitude and error of the post-neutralization charges (0.4$\pm$0.4) confirm that we can precisely control the target pre-contact charge. (B) Incident pre-contact charge as a function of particle velocity and number of coils in the pre-contact charger. The data shows that we can precisely control the incident pre-contact charge with a maximum deviation of 20.