arXiv subjects

Simon Jantač

Publications and source records attributed to Simon Jantač.

10 recordsLinked to original sources

arXiv2026

Divergent Impact Charging of Polymer Particles

When a particle contacts a surface of another material, it is commonly believed that the particle acquires an impact charge that scales inversely with its pre-impact charge and whose polarity is set by the materials. We show that this belief holds for conductive particles but fails for polymers. For polymers, the impact charge increases linearly with the particle's pre-impact charge. Its polarity is not determined by the materials but by the pre-impact particle charge relative to a divergence point at which the net charge transfer reverses. We attribute this divergence to the attraction of surrounding ions to the particle surface. These attracted ions carry polarity opposite to that of the particle, and their amount scales with the particle charge. They transfer to the opposing surface during contact, thereby defining the impact charge. We propose a phenomenological model for the divergent impact charge arising from this mechanism. Finally, we reexamine previous measurements and show that they support this mechanism.

cond-mat.soft↗

arXiv2026

ML enhanced measurement of the electrostatic charge distribution of powder conveyed through a duct

The electrostatic charge acquired by powders during transport through ducts can cause devastating dust explosions. Our recently developed laser-optical measurement technique can resolve the powder charge along a one-dimensional (1D) path. However, the charge across the duct's complete two-dimensional (2D) cross-section, which is the critical parameter for process safety, is generally unavailable due to limited optical access. To estimate the complete powder charge distribution in a conveying duct, we propose a machine learning (ML) approach using a shallow neural network (SNN). The ML algorithm is trained with cross-sectional data extracted from four different three-dimensional direct numerical simulations of a turbulent duct flow with varying particle size. Through this training with simulation data, the ML algorithm can estimate the powder charge distribution in the duct's cross-section based on only 1D measurements. The results reveal an average $L^1$-error of the reconstructed 2D cross-section of 1.63 %.

physics.flu-dyn↗

arXiv2025

Unifying same- and different-material particle charging through stochastic scaling

Triboelectric charging of insulating particles through contact is critical in diverse physical and engineering processes, from dust storms and volcanic eruptions to industrial powder handling. However, many experiments over the years have consistently revealed counterintuitive charging patterns, including variable impact charge under identical conditions, charge sign reversal with repeated impacts, and bipolar charging of differently sized particles. Existing computational models cannot predict these patterns; they either rely on oversimplified heuristics or require inaccessible detailed surface properties. We present a stochastic scaling model (SSM) for particle charging that unifies same-material (particle-particle) and different-material (particle-wall) charging in a single theoretical framework. The model grounds in a physics-based stochastic closure by the mean, variance, skewness, and minimum impact charge measured in a highly-controlled reference experiment. To test the SSM, we implemented it in an open-source Lagrangian-Eulerian CFD solver. When simulating 300 000 insulating particles transported by turbulent wall-bounded flows, the SSM takes less than 0.01% of the CPU time. By scaling the statistical parameters of the reference impact to each collision, the new model reproduces the complex charging patterns observed in experiments without requiring surface-level first-principles inputs. The SSM offers a physically grounded route to large-scale simulations of electrostatic effects across many fields of particle-laden flows.

physics.comp-ph↗

arXiv2025

A Novel Apparatus For Particle-Particle Single Contact Electrification Experiments

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.

physics.ins-det↗

arXiv2025

Triboelectric Charging Model for Particles with Rough Surfaces

The triboelectric charging of particles depends on the contact area of the particle and the contacting surface. Even though the surface topology determines the real contact area, particle charging models do not account for surface roughness. In this paper, we combine contact mechanics and triboelectrification models to predict the charging of rough particles. First, a laser confocal microscope measured the statistical descriptors of polyethylene (PE) particles surface topology. Then, we descriptors particle surfaces by distributing spheroidal asperities on the smooth particle core until the surface roughness reaches the measured value. The Hertz contact mechanics model predicts the deformation of the asperity-covered particle and the resulting real contact area in dependence on impact velocity. Finally, we introduced the real contact area into the condenser model for triboelectric particle charging. The accuracy of the new model predictions was demonstrated by comparing it to a more complex surface reconstructions that account for the fractal surface topology. Furthermore, the model's predicted particle saturation charges agree well with our shaker experiments and with experimental data in the literature on the charging of plane surfaces. The developed triboelectric charging model for particles with rough surfaces is simple and requires only standard descriptors of the surface topology; thus, it suits large-scale simulations of electrifying powder flows.

cond-mat.soft↗

arXiv2024

Unmasking hidden ignition sources: A new approach to finding extreme charge peaks in powder processing

Powders acquire a high electrostatic charge during transport and processing. Consequently, in the aftermath of dust explosions, electrostatic discharge is often suspected to be the ignition source. However, definite proof is usually lacking since the rise of electrostatic charge cannot be seen or smelled, and the explosion destroys valuable evidence. Moreover, conventional methods to measure the bulk charge of powder flows, such as the Faraday pail, provide only the aggregate charge for the entire particle ensemble. Our simulations show that, depending on the flow conditions, contacts between particles lead to bipolar charging. Bipolar charged powder remains overall neutral; thus, a Faraday pail detects no danger, even though individual particles are highly charged. To address this gap, we have developed a measurement technology to resolve the powder charge spatially. The first measurements have revealed a critical discovery: a localized charge peak near the inner wall of the conveying duct is 85 times higher than the average charge that would be measured using the Faraday pail. This finding underscores the possibility of extremely high local charges that can serve as ignition sources, even though they remain undetected by conventional measurement systems. Our new technology offers a solution by spatially resolving the charge distribution within powder flows, unmasking hidden ignition sources, and preventing catastrophic incidents in the industry.

physics.app-ph↗

arXiv2024

Spatially resolved measurement of the electrostatic charge of turbulent powder flows

This article reports on measurements of the electrostatic charge of particles in a turbulent duct flow. In contrast to previous charge measurements, which do not apply to turbulent flows or give only the sum of all particles' charges, the new method resolves the charge of a turbulent powder flow spatially. The experiment consists of a Particle Tracking Velocimetry (PTV) system and electrode plates that generate an electric field. By comparing particle velocities and accelerations with and without the electric field, the time-averaged local particle charge profile is derived. Spatially resolving the charge profiles unveiled bipolar particle flow. The average of the charge profiles agreed well with a conventional Faraday pail measurement, demonstrating the accuracy of our measurements. However, the peak value of the charge profiles was 76 times higher than the average of the particles' charge.

physics.flu-dyn↗

arXiv2024

Suppression and Control of Bipolar Powder Charging by Turbulence

Current models predict particles of the same material but different sizes to charge bipolar upon contacts; the resulting charge peaks endanger process safety. However, we found wall-bounded turbulence to suppress the powder's electrostatic charging. Aerodynamic forces skew the collision frequency and narrow the charge distribution's bandwidth. Bipolar charging reduces, especially in moderately polydisperse systems of a low Stokes number. Not the smallest but mid-sized particles charge most negatively. Moreover, turbulence separates charge, producing pockets of high electric potential in low-vorticity regions.

physics.flu-dyn↗

arXiv2024

Influence of the Reynolds number from $Re_τ= 150$ to $210$ on size-dependent bipolar charging

We recently found wall-bounded turbulence to suppress and control bipolar triboelectric charging of particles of identical material. This control is due to fluid modifying the motion of light particles. Thus, the particles' charge distribution depends on their Stokes number distribution. More specifically, fluid forces narrow the bandwidth of the charge distribution, and bipolar charging reduces dramatically. Consequently, not the smallest but mid-sized particles collect the most negative charge. However, the influence of the Reynolds number or particle concentration on bipolar charging of polydisperse particles is unknown. This paper presents the charging simulations of same-material particles the in different wall-bounded flows. In a comprehensive study, we vary the Reynolds number from $Re_τ=$ $150$ to $210$ and the particle number density from $4 \times 10^9 \ \mathrm{m}^{-3}$ to $1 \times 10^{10} \ \mathrm{m}^{-3}$ to further explore the influence of the carrier flow on bipolar charging. We model charge transfer based on the balance of transferable charge species. Such species can represent adsorbed ions transferred during collisions or free electrons captured into a lower energy state on the other surface. The turbulent flow is modeled via Direct Numerical Simulations (DNS) and is coupled to the particulate phase modeled via the Discrete Element Method (DEM). Overall, our multiphysics approach couples the fluid dynamics, electric field, triboelectric charging, and particle momentum into one complex simulation.

physics.flu-dyn↗

arXiv2022

Recent progress in CFD modeling of powder flow charging during pneumatic conveying

Thus far, Computational Fluid Dynamics (CFD) simulations fail to predict the electrostatic charging of particle-gas flows reliably. The lack of a predictive tool leads to powder operations prone to deposits and discharges, making chemical plants unsustainable and prime candidates for explosions. This paper reviews the rapid progress of numerical models in recent years, their limitations, and outlines future research. In particular, the discussion includes CFD models for the physics and chemistry of particle electrification. The condenser model is most popular today in CFD simulations of powder flow electrification but fails to predict most of its features. New experiments led to advanced models, such as the non-uniform charge model, which resolves the local charge distribution on non-conductive particle surfaces. Further, models relying on the surface state theory predicted bipolar charging of polydisperse particles made of the same material. While these models were usually implemented in CFD tools using an Eulerian-Lagrangian strategy, recently Eulerian methods successfully described powder charging. The Eulerian framework is computationally efficient when handling complete powders; thus, Eulerian methods can pave the way from academic studies to application, simulating full-scale powder processing units. Overall, even though CFD models for powder flow charging improved, major hurdles toward a predictive tool remain.

physics.flu-dyn↗