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We are presenting highly porous ethyl cellulose (EC) nanostructured films for triboelectric nanogenerator (TENG) contact layer material with high performance for converting mechanical energy to electricity. Homogeneous porous EC films were deposited on conductive substrate in less than one minute without need for specific equipment. EC triboelectric layer material was contacted with tin doped In2O3, polydimethylsiloxane (PDMS) and polymethyl methacrylate. In system where EC was contacted against PDMS three orders of magnitude higher power density was observed comparing to other systems, demonstrating that prepared EC is a superior triboelectric layer material for using in TENG devices in conjunction with PDMS.

A relationship between triboelectric charge and contact force for two triboelectric layers is presented, by combining the theories of insulator contact charging and contact mechanics. Experimental verification has been successfully performed using contact-mode triboelectric nanogenerators (TENGs) in two cases: (a) under varying contact forces while keeping the surface roughness profile constant, and (b) under varying surface roughness profiles while keeping the contact force constant. The theory presented here can serve as an important guide in the design of triboelectric systems, particularly of a contact-mode TENG structure for specific applications and self-powered systems.

A single impact triboelectric charging experimental setup has been used to investigate the antistatic effect of two additives coated at the surface of beads on impact charges resulting from impact between a glass bead and a polyurethane (PU) target, at various additive concentrations and two different RH conditions. Three configurations of additives have been studied exhibiting different behaviours with RH, underlining the importance of humidity conditions in antistatic properties. Results for additive A, an organic oil, showed almost no impact charge decrease at RH 1% while results for additive B, a quaternary ammonium salt, presented no difference between RH 1% and 45%. This behaviour could be explained by a difference in surface water desorption dynamic when placed in a low humidity environment. In a second part, additional measurements analysing the effect of RH and temperature in the same glass/PU impact configuration in absence of additives are discussed. No significant variation of impact charge was observed on glass/PU triboelectric charging, confirming that previous results were indeed related to the presence of additives at the surface of the beads. A comparison with another triboelectric pairing, glass/PTFE, also shows the likeliness of different charge transfer mechanisms being involved in glass/PU and glass/PTFE as well as a general effect of temperature on impact charge which could be connected to relaxation mechanisms.

Particle–particle collisions play a crucial role in the triboelectric charging in particle-laden flows. However, the mechanism of the charging pattern is still poorly understood. In the present work, electrostatic charging experiments of particle–particle collisions were conducted to explore the charge transfer with different-sized particles. The experimental results show that the polarity of the transferred charge varies with the material type. The influence of the initial charges on the charge transfer was observed, and the influence degree was compared for different materials. The charging behaviors were analyzed based on the charge transfer model driven by the electric potential difference. Through electrostatic analysis, the electric potential difference arising from the electric field of the preexisting surface charges was numerically calculated for the dielectric materials with polarization effects and the ideal non-polarizable material. It was revealed that the potential difference alters significantly owing to the surface charge redistribution of dielectric materials. Dielectric polarization was numerically investigated by varying particle size and relative permittivity of the material. The numerical results explain the discrepancies in the charging tendency of various materials in the experiments.

In this paper, we investigate the variability of dynamic triboelectric charging of both particulate emissions (smoke, unburned propellant and other debris) and projectiles launched from a 9 mm Beretta pistol. We measured charge transients both at the weapon muzzle and at a location 10 m downrange using cylindrical charge sensors to characterize the charge associated with the muzzle blast and that of the projectile. We derive an analytical expression for the time-domain voltage response of cylindrical charge sensors, and use it to quantify the charge present on the projectiles. Our results indicate that the magnitude and polarity of charge present on a given projectile depends strongly on the ammunition type, even if the primer and propellant chemistries are identical. Projectiles, on average, carry a charge opposite in polarity to that of the particulates present in the muzzle blast. We hypothesize that the relative motion of the gas-solids flow in the annulus between the barrel and the projectile leads to charge transfer between the particulates and the projectile, resulting in the case of oppositely charged projectiles and particulates.

Numerous research studies have been made on the electrostatic separation of granular insulating materials, with many industrial applications in the area of waste electric and electronic equipment (WEEE) recycling. However, very few investigators have studied the separation of finely-ground matter (i.e., granule diameter

Granular materials, when fluidized by air or other gaseous medium, acquire electrostatic charge by particle-particle and particle-wall collisions. The effectiveness of particle tribocharging achieved with such fluidization process is crucial for establishing the feasibility of electrostatic separation of mixed granular solid wastes in the recycling industry. The aim of the present work is to introduce a simple mathematical model for simulating the outcome of a novel tribo-aero-electrostatic separation process involving mixture of three granular materials. The process is characterized by the fact that the charging of the granules is produced in a fluidized bed device, in the presence of an electric field. The mathematical model in this case assumed that the probability of a granule to be separated can be expressed using the normal distribution law, as a function of the number of impacts with granules belonging to the other classes of materials. The effect of the presence of a third species of particles was taken into account. Thus, it was possible to calculate the evolution over time of the mass of granules separated at the electrodes for different compositions of the granular mixture. The calculated results are in good agreement with the experiments.

Application of the measurements of a charge induced on the flat electrode placed at the bottom of a container, for the determination of total accumulated charge is discussed in the paper. The value of correction factor K Q , important for the numerical linking of both (accumulated and induced) charges, was determined numerically and experimentally. The values of K Q factors determined by various methods differ as 1:1.7, however application of the method of "open" Faraday cage in technological conditions is fully justified.

The contacts of particles with a device wall as well as mutual particle collisions cause the redistribution of charge in systems with powder particles. This, usually undesirable phenomenon known as triboelectric charging, leads to operational problems and safety risks in industrial systems, e.g., in fluidized-bed polymerization reactors. We focus on the charging of polyethylene powder particles caused by the particle-particle interactions. Our model utilizes the Discrete Element Method (DEM) for the description of the particle motion and involves the balance of transferable charged species to quantify the triboelectric charging of particles in contact. The model predicts the charging dynamics of polyethylene powder particles in systems of various particle size distributions (PSD) and addresses the influence of segregation of particles on charging. Our simulation results are in agreement with two general trends in charging that are often observed in both industrial and naturally-occurring particulate systems: (i) Charging is most pronounced in systems with wide PSD and (ii) small particles charge mostly negatively, whereas big particles typically carry positive charge. Subsequently, our results suggest that particle segregation plays an important role in the charging dynamics of particulate systems, as segregation of particles of different sizes can alter PSD locally. It is important to include electrostatic forces in charging models, especially in systems that exhibit significant charging. Specifically, electrostatic attraction among unlike charged particles leads to the ‘orbiting motion’ of particles that is followed by the formation of particle aggregates.

Glass substrates for displays are insulating materials capable of generating and maintaining high levels of triboelectric charges posing a risk of electrostatic discharge (ESD) damage to electronic display components. In this work, an apparatus for triboelectric charging characterization of display glass during the roller transfer process was designed and fabricated. In order to establish the reliability of the characterization, the triboelectric charge and the electrostatic potential distribution measurement system was automated. The preconditioning process of the glass and the rollers was also addressed. In order to analyze the measurements' results, a multiphysics model that considered both electrical and mechanical properties was proposed. The test parameters that were expected to affect the triboelectric charging characteristics are defined and discussed, as well as some of the characterization results such as the effects of acceleration/deceleration and maximum velocity, relative humidity and moisture on the glass and the rollers, and the conductivity of the rollers. The peak-to-peak deviation of the de-embedded triboelectric charges, due to a steady-state velocity period with different combinations of acceleration/deceleration and maximum velocities, was 14.2%. The triboelectric charges increased as the relative humidity increased from 30% to 50% with the same temperature. They also increased when the insulating rollers were replaced with dissipative rollers.

A prototype direct current Triboelectric Generator (DC-TEG) has been demonstrated to generate dc voltages by converting rotational mechanical energy into electrical energy. The generator primarily consists of four rotating wheels (two copper electrodes and two triboelectric wheels) utilizing polytetrafluoroethylene (PTFE) tape and nylon fabric as the triboelectric materials in its design. Once subjected to mechanical rotation, the interaction between the two triboelectric materials generates equal, but opposite charges and deposits them on the copper electrodes resulting in a dc voltage across an external load resistor. The power performance of the generator, with changes in angular frequency, has been measured. The DC-TEG can generate a dc voltage of about 1.5 mV across an external load of 15.14 kΩ at a rotational speed of 10 rev/sec. The dependences of current and power on the angular frequency have also been measured. Preliminary results suggest that the relationship between the dc voltage and angular frequency of rotation is quadratic, however further measurements at relatively higher angular frequencies are needed before a proper mathematical model may be established. The work here presents a new, cost-effective DC-TEG design for power scavenging from any naturally or artificially occurring rotational mechanical motion facilitated by either wind or flowing water for self-powered systems.

The aim of this paper is to point out the influence of dielectric barrier discharge treatment on tribocharging of granular insulating materials. Particles of Polyvinyl Chloride (PVC) and Polypropylene (PP) were subjected to an AC dielectric barrier discharge (DBD) plasma treatment in ambient airprior to tribocharging in a vibratory device. The charge to mass ratio was measured for treated and untreated materials. Electrostatic separation of a mixture of granular materials (PVC and PP) to measure the effectiveness of DBD treatment was evaluated by processing treated and untreated PVC/PP granular mixtures in a free-fall electrostatic separator. The obtained results clearly indicate that DBD has the capability to influence surface charging proprieties of polymer granular materials. In case of short treatment time, typically less than 3 s, a marked increase in the charge to mass ratios was observed for both PVC (about 35%) and PP (roughly 45%). In the same way, the quantity of DBD-treated materials, recovered after electrostatic separation, was increased by about 104% and 30% for PVC and PP, respectively, as compared to untreated case. The DBD treatment time is a key factor to increase the tribo electric effect.

This work deals with development, characterization, and application of triboelectrically charged nonwoven electrets. The electrets were prepared using wool and polypropylene fibers and employing needlepunched nonwoven technology. It was observed that the magnitude and duration of electret charge increased with a decrease in diameter of wool and polypropylene fibers. The charge was found to decay double exponentially, presumably due to quick decay of surface charge and slow decay of bulk charge. The charge in tribocharged electrets was utilized to capture hazardous particles from the air stream very efficiently. The electret media exhibited remarkably higher filtration efficiency than the uncharged media.

Water flowing through tubes of different materials and collected in a Faraday cup contains net electric charge. Water charge is always positive but its magnitude depends on the material position in most triboelectric series. On the other hand, water acquires net negative electric charge when falling through air but its charge is modified after it passes through an electric field. Thus, water is located on the top of the triboelectric series and its charge is a robust and reliable way to organize materials within the triboelectric series, giving due attention to its surface properties.

The cause of electron transfer in contact electrification is one of the most hotly debated physical problems today. In this study, the electron transfer is hypothesized to be partly driven by the surface dipole induced potential during contact. This phenomena is demonstrated by a combination of atomistic field theory (AFT) and molecular dynamics (MD) simulation. A representative contact system of carbon and silicon dioxide was chosen for its excellent tribo-tunneling power output performance. The results reveal the existence of a nonlinear potential field as well as the existence of a separation dependent potential barrier at the contact interface. Possible scenarios of triboelectric charge transfer are discussed in light of these results. These results are critical to the fundamental understanding of contact electrification.

The charge-accumulation and sensitivity towards external stimuli are the challenging issues for explosives, in which an accidental electrostatic discharge. Deep eutectic solvent (DESs) were used to reduce the tribocharging of energetic materials (EMs). Five DESs were selected to coat on cyclotetramethylenetetranitramine (HMX) as a useful nitramine-based material via the simple wet-mixing. Thoroughly tribocharging measurements of the samples showed a dramatic reduction of charge-accumulation, in which the most charge reduction belonged to Gly-ChCl. Also, our experiments showed that the charge-accumulation decreased from 3600 nC kg−1 to less than 50 nC kg−1 when HMX was coated with only 0.3 wt% of Gly-ChCl.

Experiments on same-material granular tribocharging in bidisperse mixtures have demonstrated a clear size dependence in the polarity of charge on each species. These experiments typically involve charging via fluidization or shaking in air or similar environments, and frequently measure only overall polarity rather than individual grain charge. These experiments require discrete size species in each mixture, and may include additional environmental influences on the charging process that remain poorly understood. Using our methodology for charging in high vacuum and measuring individual grain charge, we have examined mixtures of zirconia-silica grains with two primary size species combined in varying quantities. We have explored the accuracy of a variety of charging models compared to the charge distributions observed in our experiments. Our experimental results will inform future theoretical models for the charge transfer mechanism in dielectric grains.

Triboelectric charging of small particles is a common problem in industrial processes because it can lead to various undesired consequences such as electric discharges or surface adhesion. Despite the many studies on the phenomenon, there remains significant gaps in understanding regarding the charge transfer mechanisms responsible for triboelectric charging, impeding the ability to make predictions regarding a contact between two dielectric materials. An experimental setup measuring the charge generated during a single impact between a dielectric particle and a dielectric target under well controlled conditions is used to investigate the triboelectric charging of a glass bead against polymer targets. Mechanical parameters such as the normal and tangential velocities and their influence over the charge generated at impact are studied statistically against a Polytetrafluoroethylene (PTFE) and a Polyurethane (PU) target, and two different behaviours are exhibited. Additional tests were performed on beads of different diameter in order to enrich the observations previously made on mechanical properties.

Commonly used liquids have a powerful effect on producing electrostatic charges, from laboratory routines to industry processing and everyday activities. In many situations, electrostatic charges are not desirable, mostly in the presence of flammable liquids or for electronic devices that are susceptible to electrostatic discharge (ESD). Recently, liquid water was successfully allocated in the triboelectric series and it was shown that it can acquire great amounts of charge when flowing through different materials or even by a simple micropipetting. Here, we have developed a simple but robust protocol to suppress and control electrostatic charges during the pipetting of water, common alcohols and solutions. Using glass containers instead of plastic ones, charge is highly suppressed and its sign and magnitude can be controlled with external electrical fields. Finally, drops arising from a micropipette ended in a grounded metallic needle have roughly zero net charge, regardless the presence of external electrical fields. This protocol faces a very challenging problem of electricity formation while handling common liquids and it could be helpful to avoid electrostatic charge in many systems.

Electrostatic charging is a ubiquitous but poorly understood phenomenon. One of the difficulties with studying electrostatics is separating the different types of charging (triboelectric, inductive, or gas phase ion adsorption). We constructed an experiment to test how liquid film evaporation affects the charge on an insulator surface. Our results showed that when a liquid evaporates in an electric field, it leaves a charge on the substrate surface. It was also determined that the magnitude and polarity of the charge depends on the local electrostatic potential of the substrate and sufficient charge buildup leads to a dielectric breakdown of air, a potential source of hazardous sparks. We reveal through careful experiments that the charge is transferred via induction from electrical ground through the liquid film and onto the substrate's surface. Ambient fields were shown to be able to cause this type of charging, suggesting that failing to account for this phenomenon may explain the lack of reproducibility in previous electrostatic charging studies.

The studies reported show that measurements of atmospheric electric fields by pole mounted electrostatic fieldmeters can match measurements by a horizontal antenna wire. Some differences were experienced early in the tests that cannot yet be explained. The differences are tentatively attributed to tribocharging actions during initial set up of the antenna system and by wind blown airborne particulates at the antenna wire. Pole mounted fieldmeters provide opportunity for long term unattended measurements in quite adverse weather conditions with continuous checking of operational health against debris, spider's webs, etc.

Many studies have been reported for contact electrification based on the electron transfer from donors to acceptors. However, the chemical structures of donors and acceptors have not been identified. Here we calculated the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of model structures of mechano anions, mechano cations and mechano radicals which were produced by the heterogeneous and homogeneous scissions of covalent bonds comprising polymer main chain in vacuum at 77 K. We identified the donors are mechano anions(HOMO) and mechano radicals(HOMO), and the acceptors are mechano cations(LUMO) and mechano radicals(LUMO). The contact electrification is due to the electron transfer from the donors to the acceptors during contacting on the friction surface, and produces mosaic nano-scopic domains with opposite sign. The sign of the net charge of polymer was deduced from the number of paths of electron acceptance reaction. The relative sign of charge and position on the triboelectric series were deduced from their chemical structure.

Dry triboelectric separation of coal depends on tribocharge difference of the coal and gangue mineral. The coal samples of different density fraction prepared by sink-and-float method were pretreated by chemicals and their effects on the tribocharge performance with stainless steel were studied by measuring the charge-to-mass and relative dielectric constant. The results show the tribocharging performance of middle density fraction coal is the worst compared with other density fractions. The charge of lower density fraction was increased by chemical conditioning with light diesel oil, ammonia, and kerosene, while the charge of higher density fraction was decreased with ethanol and lignin.

The paper presents the results of experiments upon the influence of tribocharging of PAO and PAG synthetic motor base oils blended with different additives—friction modifiers (FM) and antiwear agents (AW)—and the effect of an external DC electric field on the braking torque. The experiments are carried out in a rotating shaft–oil–lip seal system which represents a specially built experimental facility to be a simplified model of an engine crankcase in the interior of which a metal shaft rotates. The research is especially aimed at the braking torque of a rotating shaft sealed with a lip seal and a possibility of reduction in the torque under external DC electric fields. DC voltage is applied between the stiffening ring of lip seal and a rotating, earthed shaft. The braking torque of rotating shaft is measured as a function of the oil–additive blend's temperature, the shaft's angular velocity, and the absolute value of the external DC voltage. In general, it is found that an external DC electric field causes the braking torque to change with the increasing DC voltage. The change depends on the additives and base oils used in their blends which in turn causes the torque to increase in the case of the PAO–additive blends or to decrease for the PAG–additive blends.

The triboelectric effect describes electrical charging when bringing different materials into contact. We report on the generation of hard X-ray radiation by peeling various adhesive tapes under medium vacuum conditions. Beside vacuum housing and pumps as instrumentation only an electric motor, two rolls and a metal foil as target material are necessary. The spectral distribution of generated X-rays was analyzed using an energy-dispersive detector. Depending on peeling speed, pressure and choice of material combination, electrons with energies sufficient to excite emission in the hard X-ray region are produced. The results are discussed in terms of triboelectric separation of charge carriers.

Numerical simulation has proved to be a powerful tool in the research and development of new electrostatic processes. In a previous paper, the authors have introduced a simple mathematical model for simulating the outcome of a novel tribo-aero-electrostatic separation process for binary mixtures of granular materials. The mathematical model assumed that the probability of a granule to be separated can be expressed as a function of the number of impacts with granules belonging to the other class of materials. The process is characterized by the fact that the charging of the granules is produced in a fluidized bed device, in the presence of an electric field. The aim of the present paper is to simulate the continuous operation of such a device at various feed rates. The evolution in time of the mass of granules collected at the electrodes has been computed for various compositions of the granular mixture. The effect of the walls was taken into account. The computed results were in good agreement with the experiments. They demonstrate that open-loop continuous operation of the separator is possible for a range of feed-rates that depends on the composition of the materials to be separated.

The aim of study was to evaluate the effectiveness of a new facility for recycling of plastics from granular waste electrical and electronic equipment. The installation consists of two sections, the products of a first tribo-aero-electrostatic separator being subsequently treated in two free-fall electrostatic separators. The tests were performed on a mixture of polycarbonate (PC) and polyamide (PA). Analysis of the purity of the products obtained was performed using a program of image processing in MATLAB. Products of very high purity (roughly 95% for both PC and PA) were obtained at a recovery rate higher than 70%.

Identification of the optimal operating conditions is a critical issue for the industrial application of tribocharging techniques. The aim of this paper is to formulate a set of recommendations regarding the choice of tray length, vibration amplitude and material feed-rate values for a vibratory-type tribocharger. The study was carried out on a laboratory vibratory feeder with granular plastics originating from waste electrical and electronic equipment. Several one-factor-at-a-time experiments followed by a composite factorial experiment were performed based on a two-step strategy: 1) identifying the domain of variation of the controlled variables; 2) finding the best choice of the set point.

Triboelectric separation is of increasing importance in a number of industries. The initial tribocharging process is poorly understood, with tribocharger design and operation dominated by trial and error. Better physical understanding of tribocharger operation would be invaluable for the optimization of triboelectric separation processes. Cylindrical pneumatic cyclones are highly suitable for continuous-flow mineral separation applications. Charge measurements, trajectory modelling and high-speed video footage of particle motion have been combined to understand charging in terms of particle dynamics in a cylindrical cyclone. These observations are interpreted in terms of cyclone tribocharger design and operation.

We address electrostatic charging of unstrained and strained latex rubber sheets contacted with a series of materials: polytetrafluoroethylene (PTFE), polyurethane (PU) and stainless steel (SS). For PTFE, strain causes a reversal in the direction of charge transfer. For PU, the direction of charge transfer is reversed after repeated contacts due to material transfer, and strain increases the number of contacts needed for this reversal. For SS, strain reduces the frequency of electrical discharges occurring. These effects may be explained by strain either changing material properties relevant to triboelectric charging, or changing the nature of contact between the surfaces.

Triboelectrification for a rolling contact between hardwood and softwood spheres and a polytetrafluoroethylene (PTFE) plane is studied. For a variety of experimental parameters, the saturation charge developed on the spheres was measured. The results are compared with those reported previously where PTFE spheres were rolled on wood planes. The observations suggest that different principles are involved in the two experimental situations; however, in both cases the saturation charge developed depends on the apparent area of contact.

The distribution of charge within the wall fouling region and bulk of a fluidized bed reactor was investigated. Experiments were conducted in a 0.1 m in diameter carbon steel fluidization column under atmospheric conditions. Polyethylene particles were fluidized with extra dry air at 1.5 the minimum fluidization velocity (bubbling flow regime) for 1 h. Using an online Faraday cup measurement technique, the net charge-to-mass ratio ( q / m ), as well as the size distribution of all particles adhered to the column wall and those in the bulk of the bed was determined. The wall particles were found to be predominantly negatively charged while those which did not adhere to the wall were predominantly positively charged. The charge distribution within each region was then investigated by a custom made charged particle separator that separated the particles according to their charge magnitude and polarity. It was determined that although the net charge of the wall layer particles was negative, a significant amount of positively charged particles existed within each sample and therefore the entire wall particle layer. This suggests that the wall layer was formed through layering between positively and negatively charged particles. Particles in the bulk of the bed also consisted of bipolarly charged particles.

Triboelectric particle charging features in many industrial processes. Dynamic particle-surface contact is the key charging mechanism in many types of particle tribocharger. Models of dynamic charging have tended to assume that the particle is spherical, but experiments have shown that particle shape can strongly influence the charging behaviour. We review some experimental work, then present a simple two-dimensional model of the dynamic contact charging of an elliptical particle, of varying roundness ratio, with a flat surface. A rich variety of contact modes (sliding, rolling, tumbling) are captured, each producing distinctive charging behaviour.

Electrostatic separation has already proved to be an effective means for the recycling of granular plastics from industrial wastes. The aim of the present work was to optimize the operation of a novel device that could ensure effective triboelectric charging of such materials prior to their selective sorting in a high-intensity electric field. The experiments were performed on two sorts of mm-size granular materials Acrylonitrile Butadiene Styrene and High Impact Polystyrene, originating from the processing of waste electric and electronic equipment. The samples were introduced in a Polyvinyl Chloride cylinder, where a co-axial propeller entrained the plastic granules into a helical motion that favored their triboelectric charging by combining the mechanical and aerodynamical effects. The experimental design methodology was employed for the modeling and optimization of the tribocharging process.

This paper demonstrates the tribolelectricity by the flow of water in an insulating pipe. A theoretical analysis showing the relation between the electric discharge and the system hydromechanical parameters is developed. Based on the macroscopic RC-circuit modeling of the system understudy, techniques allowing to minimize the discharge effect are introduced. With two different demonstrators, as predicted in theory, a voltage variation up to 300 mV is observed by using pipes having mm-diameter and pure water with 45 cm 3 s −1 flow rate. Finally, an application for the risk prevention caused by the explosion for the gas filling of engine fuel tank is discussed.

The charging that occurs when a pair of insulating surfaces of identical chemical composition are rubbed (i.e. triboelectric charging) remains poorly understood. It is believed that asymmetry in contact plays an important role in this charging. To study this phenomenon, we have developed an experimental methodology that asymmetrically rubs two surfaces by contacting a rotating cylinder with a stationary cylinder – the rubbing is asymmetric in that the contacting area is much greater on the rotating cylinder than on the stationary cylinder. We find that the charge transfer occurs with a spatial distribution of charge, in terms of magnitude and polarity, on the contacted area. The direction of the average charge transfer is material dependent: for Teflon–Teflon contact, the surface with the larger contacting area charges positively, but for Nylon–Nylon contact the surface with the larger contacting area charges negatively. This difference is interpreted as being due to a negatively-charged species transferred in the case of Teflon (electrons or negative ions), but a positively-charged species transferred in the case of Nylon (positive ions).

Although several investigations had been carried out to explore the triboelectrification of powders, only few data are available on the experimental procedures and set-ups required to obtain reliable data. The present study deals with the development of a pneumatic test to characterise the tribocharging of fine powders. An experimental device was set up allowing on-line monitoring of the charge of both particles and transport pipes. Experiments were carried out using two types of powder (fine sugar and PVC) coupled with two types of pipe materials (Teflon and nylon). Results showed the extreme importance of the control of the relative humidity, the initial charge of particles and the charge dissipation of the walls to obtain pertinent data. Furthermore, the results showed that solids loadings higher than 1 (kg of solids/kg of air) are not proper to achieve reliable measurements. However, at very dilute solids loading (∼0.001) the time evolutions of the electrostatic charge and the mass of the powder follow similar trends so that the tribocharging becomes independent of the solids mass flowrate. This allows accurate assessment of the tribocharging of cohesive powders for which a regular flow cannot be guaranteed.

Electrostatic charge generation poses significant problems in some commercial gas–solid fluidized bed reactors such as those in gas-phase polyolefin production. Understanding the contributing factors to charge generation is important in determining the charge generation mechanisms, leading to the development of methods to reduce or prevent this phenomenon. This work focused on determining the effect of fluidization time on particle charging and the amount of particle adhesion on the fluidization column wall in both the bubbling and slugging flow regimes. The charging effect was investigated for particles in three regions of the fluidized bed: elutriated fines, bulk particles inside the bed, and particles adhered to the column wall. The particles size distribution, mass and charge were measured for all three regions. Fluidization was carried out with polyethylene resins from an industrial reactor; times of 15, 30, 60, 120, 180, and 360 min were evaluated. Increased fluidization time decreased the amount of particles mass collected in the bulk region and increased those adhered to the column wall during the velocities tested in the bubbling flow regime. Whereas the quantity of particles in each region was not affected by fluidization time for the velocities examined in the slugging flow regime. Bipolar charging was observed with relatively smaller particles becoming predominately positively charged and larger particles becoming predominately negatively charged. Each region of the bed affected the magnitude of net q/m, with elutriated fines having the largest magnitude, followed by those adhered to the column wall, and finally those in the bulk of the bed. Charge saturation was attained for fluidization times greater than 60 min for particles in the bulk and along the column wall for all gas velocities. However, extended fluidization times were required with the entrained fines in bubbling flow; whereas charge saturation of fines in slugging flow occurred shortly after the onset of fluidization. Mean particle diameter for each measurement region was not impacted by the fluidization time for any of the gas velocities tested. The bed hydrodynamics was found to definitely have an impact on the particle–wall fouling where the particle layer continued to develop on the inner column wall as fluidization time increased for those velocities in the bubbling regime while comparatively less impact on particle layer growth was observed in the slugging flow regime. In addition, the bubbling flow regime resulted in particle layers formed on the column wall to be longer and thinner whereas those formed in the slugging flow regime were shorter and thicker.

By means of statistical modelling and measurement, the triboelectric current noise spectral density is evaluated for shielded cables in body-borne wired network subjected to mechanical stresses. Assuming a shot noise model, an expression for the current spectral density of the noise is derived. The efficiency of the methodology is demonstrated by measuring the triboelectric current noise in two shielded cables subjected to bending. Thereafter the parameters of the noise pulses' waiting time and amplitude probability density functions are extracted from measurement, thus enabling the computation of the current spectral density of the noise induced mechanically in body-borne wired networks.

In a previous work, the addition of basic screened Coulombic electrostatic forces to an existing commercial discrete element modeling (DEM) software was reported. Triboelectric experiments were performed to charge glass spheres rolling on inclined planes of various materials. Charge generation constants and the Q/m ratios for the test materials were calculated from the experimental data and compared to the simulation output of the DEM software. In this paper, we will discuss new values of the charge generation constants calculated from improved experimental procedures and data.

The paper presents the results of experiments on tribocharging of different mineral, semisynthetic, and synthetic base oils and their blends with additives. An antiwear additive ZDDP (zinc dialkyldithiophosphate) is tested when added to base oils in different percentages by weight. Experiments are carried out on the specially built experimental facility to be a simplified model of an engine crankcase in whose interior an earthed metal shaft rotates at given angular velocities. The potential of a stiffening ring of a lip seal is measured directly with an electrometer. The potential is a measure of tribocharging in a rotating shaft–oil–lip seal system, friction junction, and especially between both interfaces: shaft surface–oil and oil–lip of a lip seal. The experimental results are presented in the form of some characteristics that are relationships of the potential induced in the stiffening ring with oil's temperature for different angular shaft's velocities and additives, contents. The oil's temperature ranges from 60 to 110 °C and is controlled automatically. The angular velocities of a shaft used are 500 and 1500 rpm. The additive contents in the blends with different base oils are 0.1 and 0.2%. The pure base oils of all the types and some lip seals are also examined. Moreover, the influence of an external DC electric field applied between the earthed shaft and the stiffening ring on the braking torque of the shaft is examined for a range of temperatures of the pure oils and their blends with the additive used, angular velocities, and additive contents. The electric field is produced while applying the high DC voltage of both polarities between the shaft and the ring. The absolute value of the voltage is in a range from 500 to 1500 V.

A critical challenge for experimental studies of triboelectric charging is to generate reproducible and unambiguous data that can be linked to theoretical concepts. We have developed a methodology to investigate the triboelectric charging of granular materials due solely to particle–particle interactions (i.e. no particle–wall interactions). The methodology is based on a particle flow apparatus that generates a fountain-like flow in which the particles contact only other particles, but no equipment surfaces. Non-contact methods of measuring charge and separating particles by charge are employed so that probe-particle charging does not occur.

A rotating shaft, rotary lip seal, and oil creating a film between the surfaces of a shaft and of a lip of the seal sets up a system, which is relatively simple geometrically, but complex physically and electrochemically. Such a system is characteristic of all machinery, engines, etc. where rotating parts and seals occur. In the experiments and tests performed to date different real commercial motor oils, original base oils, additives to base oils (antiwear and extreme pressure additives), lip seals, and shafts with different roughness have been used for a range of oil temperatures and shaft angular velocities. Tribocharging in the interfacial system: rotating shaft–oil–lip seal (the friction junction) is observed and analysed. Other experiments were performed to compensate for the electric field generated in the system applying an external DC electric field and to find its effect on friction and the braking torque of the shaft. The results show that tribocharging can exert influence on the braking torque of a rotating shaft. The reduction of the braking torque under the action of an external DC electric field is also observed. The similar experiments are repeated with the use of pure base oils and additives including zinc dialkyldithiophosphate (ZDDP). Tribocharging is evident in the case of pure base oils and when these are blended with ZDDP. The external DC electric field also reduces the braking torque while applying the DC voltage to the system. Here the authors try to interpret the former and last research results in their physical aspect and to answer some questions.

A triboelectrostatic separation system consists of a tribo-charging of materials and a separation of the charged materials in an electric field. Selective charging and optimum charge density (charge-to-mass ratio: nC/g) of materials in tribo-charging are the most important parameters for separation efficiency. In this study, a new tribo-charger set was made by combining a vertical reciprocator and various charger materials, and then the triboelectric series and charging properties of the plastics was estimated. The charge density of particles was confirmed to depend on the relative humidity ( 250 Hz) and the retention time (>300s) in the vertical-reciprocation charger. In addition, the charge density of mixed samples (PMMA: PVC = 1:1) was experimentally validated to be higher than that of a single sample, because of contacting or colliding in combination with particle–particle and particle–charger surface. Triboelectric series and charging properties of plastics can be used to predict material separation for the recycling of waste plastic in triboelectrostatic separation.

Particle dynamics simulations are carried out to study triboelectric charging in granular systems composed of a single insulating material. The simulations implement a model in which electrons trapped in localized high energy states can be transferred during collisions to low energy states in the other particle. It is shown that this effect alone can generate electrostatic charging in the system, and cause net electron transfer from larger particles to smaller particles. The magnitude of charging is small for systems of a single particle size but becomes much greater for a system with polydispersal particle sizes, due to the net electron transfer from larger to smaller particles. The negative charge of smaller particles, and positive charge of larger particles has been observed in field studies and laboratory experiments of granular systems.

Theoretical and experimental work has been performed pursuant to incorporating electrostatic forces into a commercial Discrete Element Modeling (DEM) software package. This DEM software is used to model the trajectories of large numbers of particles for industrial applications and processes. Electrostatic forces due to the triboelectrification of the particles will be included in the model in addition to existing kinematic forces enhancing the fidelity of the calculation. In this paper, we will present an overview of the theoretical calculations and experimental data and their comparison to the results of the DEM simulations.

Expressions for the voltage generated by tribocharging between a cable's dielectric and outer conductor, and the maximum voltage across a resistive load of a cable, are derived as a function of time. For a reasonably large load resistance and cable capacitance, the expressions reduce to simple single-time-constant equations that can be used to estimate the highest frequency of interest of the generated noise. The derived expressions can also assist the designer in weighing the tradeoffs associated with changing the ohmic resistance and capacitance of low-noise cables.

In offset printing, the printouts experience various complicated processes and operations before the final product is ready to be sent forward. In addition to the actual printing, these unit operations involve cutting, folding, stacking, labelling and various other operations which all include some kind of frictional contact either between the printed sheets themselves, or between the sheets and the machinery. In these contacts, charge exchange takes place which often leads to problems in the handling of lightweight prints. Machine speeds are ever increasing which has increased the importance of electrostatic problems. In this study, we present various measurements which have been performed on coating powders and coated papers both in a laboratory and in a pilot-scale facility.