Electrostatic Charge Generation Research Articles

Carbon nanotube microbeads for enhanced gas heating in a fluidized bed solar air collector

A novel approach utilizing vertically-aligned carbon nanotube (VACNT) as solar heat absorbers is proposed for efficient gas heating in a concentrated fluidized bed solar air collector (FBSAC). The VACNT powder was fabricated into CNT beads suitable for fluidized bed applications through macronization and densification. The CNT bead showed an increase in size and a 6.8 times increase in apparent density. The increase in sphericity and a significant decrease in the repose angle indicated improved particle fluidity. The prepared CNT beads demonstrated an absorptivity similar to VACNT, along with increased thermal conductivity and specific heat capacity, indicating superior thermophysical properties compared to conventional CNTs. Moreover, the reduced electrostatic charge generation minimizes the issue of particle attachment on the transmission window. The heat absorption characteristics of air in FBSAC (50 mm i.d. × 150 mm height) with CNT microbeads were determined. The FBSAC achieved a maximum gas temperature of approximately 150 °C. The CNT bead achieved a higher temperature difference of the gas per irradiance and a more comprehensive operating range of gas velocities up to 0.16 m/s than VACNT. The FBSAC with CNT beads exhibited a maximum thermal efficiency of 30.3 % and higher efficiency of 8–21 % than CNT powders at gas velocity of 0.11 m/s. A correlation was proposed to predict the thermal efficiencies of the FBSACs with different particles from dimensionless numbers considering particles dynamics and thermophysical properties.

Particle movement mode effect on electrostatics

In this work, particle electrostatics was studied by experiment methods. A single particle was tested for charge generation through moving along a metal inclined plate. It is found that particle movement mode does an important role in determining electrostatics generation. The sequence of particle movement mode to generate electrostatic charge from high to low is sliding, sliding-rolling and rolling. Particle sphericity determines the mode of particle movement along the inclined plate. The electrostatics generated decreases with increasing sphericity. Such trend becomes less from sliding to rolling and decreases with increasing the plate inclination. The electrostatics generated decreases with increasing the inclined angle of the plate, which causes particles more rolling and less sliding. The effect of inclined angle of the plate on the electrostatic charge generation is more significant for a particle with low sphericity than that for a particle with high sphericity. In addition, a granular pneumatic conveying system was set up to measure the electrostatics generated by multiple particles, where particle movement mode is found to make an obvious effect on electrostatic charge generation. Due to particle–wall contact area being large, sliding particles can generate more electrostatic charge than rolling particles do. It is found that electrostatics increases with particle size, particle loading and pipe length.

Validation of a Textile Material’s Electrostatic Characterization Device for Different Parameters and Their Effect on the Electrostatic Charge Generation

This research aims to validate an electrostatics characterization device to better understand the process of static charge generation in textile materials and to see how different factors affect it. This electrostatic device offers a variety of settings for controlling sample electrostatic activation and has a sample size range of up to one square meter. It can move in both horizontal and vertical directions in a controlled manner, providing a variety of possibilities for testing the effect of various movement features on electrostatic charge formation. Not only the textile polymer but also the motion characterizations influence the generation of electrostatic charges in textiles. The influence of frequency, pressure, dwell time between moves, test duration, effect of different sample sizes, and amplitude of movement on electrostatic charge generation was studied in greater detail. Two different parameters of the electrostatic waveform (peak voltage and peak-to-peak voltage) were investigated. The generation of electrostatic charges is proportional to the peak voltage and peak-to-peak voltage of the electrostatic waveform. Overall electrostatic charge generation increases with increasing frequency, stepping height, applied pressure at the same frequency, and sample size, but decreases with increasing dwell time between moves at the same frequency. The charge also increases with test duration until a saturation point is reached.

Effect of temperature on triboelectrifcation of polyethylene particles in a pilot-scale pressurized gas-solid fluidized bed

In this work, the influence of temperature on electrostatic charging behaviour of polyethylene (PE) particles and their degree of fouling in a pilot-plant fluidized bed was studied at two pressure levels. PE resin received from a commercial reactor was fluidized in a 0.15 m stainless-steel column at two pressures of 101 and 2600 kPa while the operating temperatures was varied from 24 to 58 °C. The amount of wall fouling and particles charge distribution in various regions of the bed were measured. Overall, it was found that at similar operating conditions, increasing pressure gave rise to a larger amount of wall fouling. At atmospheric pressure, the fouling declined by approximately 30%, when the average bed temperature was doubled from 24 °C. At 2600 kPa, a similar trend was observed although the influence of temperature was significantly greater, with 72.5% decline at the highest temperature tested. The particles within the bulk of the bed acquired less net specific charge (Q/m) at higher temperatures, signifying a lower electrostatic charge generation within the bed with the increase in temperature.

Risks and limitations of steam curtains protection in case of flammable gases leakage

AbstractRefinery and petrochemical production facilities process and produce gaseous and liquid hydrocarbons. In case of any failure, improper design, or human error, flammable or toxic substances can be released into the environment. In such cases, vapor barriers of steam curtains are used in the chemical industry to primarily dilute the released gases as well as to divert the gases to the safe area away from a potential source of ignition. When steam is ejected from a nozzle in the pipe wall, the medium rubs against the edge of the nozzle, liquid water impinges on the wall of the nozzle, and an electrostatic charge can therefore be expected. From the above description, it can be deduced that if the operation of the steam curtains is associated with the generation of electrostatic charge and the possibility of its discharge and the generation of electrostatic sparks, the activation of the steam curtains during the discharge of flammable gases paradoxically represents a certain risk. From the point of view of assessing the potential risks in the operation of vapor barriers, the magnitude of the electric charge energy generated is a crucial issue. Measuring the electric charge on the flowing steam from the nozzles is complicated with a large scatter of measured values. However, with reference to the experience gained from repeated measurements, the experimentally measured values and the obtained results can at least be seen as an expert estimate. This paper focuses on the evaluation of experimental measurements of the magnitude of the generated electrostatic charge on real steam curtains of an ethylene plant. Based on the measured results, risks are defined and appropriate measures are taken.

Water Penetration and Abrasion Resistance of Functional Nonwoven Fabrics Produced Using Recycled Cotton and Acrylic Fibers

ABSTRACT In this investigation, an engineered loop-bonded nonwoven fabric was developed using recycled cotton and recycled acrylic blended fibers with polyester thread for warping in Arachne stitch bonding machine by varying the fabric weight, blend ratio, and course spacing in different levels of treatment combinations. Acrylic and cotton fibers were extracted by recycling weft knitted cut pieces (garment waste). The developed loop-bonded nonwoven fabrics were tested for its abrasion resistance, water penetration resistance in hydrostatic pressure, and air permeability behavior. The air permeability decreased with the increase in cotton content in the blending composition, thickness, stitch density, and fabric weight. The abrasion resistance increased with the increase in thickness, fabric weight, and thread density with optimum level. The investigated cotton/acrylic blended nonwoven have attractive properties for its better absorbency, lower electrostatic charge generation, superior comfort, disposability and sanitation value, faster drying properties, better durability, a highly-desirable luxurious soft hand, improved thermal resistance, air permeability and moisture vapor transmission, higher productivity, lower production costs and shorter production cycles.

Experimental and Simulation Investigation of the Nanoscale Charge Diffusion Process on a Dielectric Surface: Effects of Relative Humidity

Electrostatic charge generation and diffusion on the nanoscale were studied by atomic force microscopy and Kelvin probe microscopy. The charge diffusion coefficients were obtained by matching exper...

Complete Prevention of Contact Electrification by Molecular Engineering

Summary Electrostatic charges are easily generated on surfaces during contact electrification. Although these invisible charges have emerged as a new dimension in mediating the functions of surfaces, such as energy conversion, liquid transport, reactivity, and adsorbability, the accumulation of charges on surfaces can also pose many undesirable consequences. Despite notable progress, existing approaches in engineering antistatic surfaces suffer from limitations such as the need to modify bulk materials or for delicate control of patterning on surfaces that rely on the neutralization of generated charges. Herein, we report a general toolbox for designing antistatic coatings by leveraging on chemically heterogeneous components with electron-donating and electron-accepting functions, i.e., N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and 1H,1H,2H,2H-perfluorooctyl trimethoxysilane, to molecularly engineer the surface potential to achieve an electrostatic homogeneity and completely prevent charge generation. Our approach is general, which allows the facile fabrication of antistatic coatings on various materials, even flexible and curved, with good re-writability and transparency.

Electrostatic charge generation on material surfaces from the evaporation of liquids

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.

Prevention of Electrostatic Charge Generation in Filtration of Low-Conductivity Oils by Surface Modification of Modern Filter Media

The electrostatic charging behavior of filter elements operating in various hydraulic and lubricating fluids has been re-examined from the perspective of fundamental material properties of the two materials participating in the event. In contrast to the previously proposed mechanisms that focused predominantly on fluid and material conductivities, new evidence strongly suggests that the relative placement of the substrates in the triboelectric series must be taken into account. The positions occupied in the triboelectric series account for the donor/acceptor tendencies exhibited by the materials when brought close together in close proximity (≤10 nm). Nevertheless, this behavior is only an outward manifestation of the deeper underlying characteristics that include material surface energies and, looking even deeper, the associated electron work functions of the interacting materials. Herein we provide several examples of the enhanced understanding of the electrostatic charging/discharging (ESC/ESD) phenomena as they occur in the course of filtration of hydraulic and lubricating fluids through modern filter elements constructed of synthetic glass fiber and polymer materials.

Hospital flooring – why is that an issue today?

Control of electrostatics has been considered important in hospitals since the advent of anesthesia chemicals for surgical procedures. Now that anesthetics are for the most part not flammable, hospital designers in the United States are rarely considering electrostatics. Since flammable situations are much less likely in hospitals, the US organization, the National Fire Protection Association (NFPA), has removed any mention of electrostatic control from the Health Care Facility Standard, NFPA 99[1]. This document had always been important for consideration in hospital design, especially surgical suites. The elimination of a requirement for conductive flooring and appropriate footwear have brought about serious consequences regarding electrostatic charge generation and accumulation. Accumulated charge has led to discharge issues resulting in personal injury, electronic equipment damage and loss of significant amounts of data. Figure 1 is an example of recorded voltage on a person while pushing a metal cart in the hospital discussed in Incident three below.

Electrostatic Charge Generation in Pneumatic Conveying Process: Effect of Particle Properties

One of the main concerns in particle pneumatic conveying process is the possibility of hazards for operation safety due to the electrostatic charge generation as a result of collisions between particles and the equipment wall. Indeed, the electrostatic discharge can occur in the equipment leading to fire or explosion. Simulation of these kinds of processes plays an important role in understanding the various aspects of the system in order to production loss prevention. This paper deals with the simulation of particle pneumatic conveying process inside an inclined tube using a particular method. In this method, the electrification of particles inside the tube is influenced by the vertical collision velocity against the tube wall. Simulation of the particle movements inside the tube, generation of electrostatic charges over the particle surfaces as well as the possibility of fire as a result of discharging the electrostatic energy are investigated. The possibility of fire is investigated by comparing the amount of electrostatic energy with minimum ignition energy (MIE) of the particles. The effect of particle properties including the size and mechanical ones in the simulation is studied. Finally, several solutions are proposed to manage the risk of fire and explosion. As results, the electrostatic energy (E) is beyond the MIE, and the electrostatic discharge can occur leading to explosion for the diameters more than 2 mm and also for elasticity constants lower than 140 MPa. Eventually, there is no hazard of fire and explosion, since all calculated electrostatic energy for the change of Particle Poisson’s ratio varying from 0.1 to 0.9 is less than the MIE value for the air flow rate of 10 m3/h.

Effect of Fluidization Pressure on Electrostatic Charge Generation of Polyethylene Particles

Electrostatic charge generation in gas–solid fluidized beds results in operational challenges in some industrial processes such as polyethylene production. Such reactors operate at elevated pressures, and thus, the aim of this work was to investigate fluidized bed electrification at pressurized conditions. The degrees of particles’ charging and wall coating in a pressurized pilot-scale gas–solid fluidized bed of polyethylene resin was studied from atmospheric pressure to 2600 kPa (abs), while the gas bubble dynamics was concurrently measured by an optical fiber probe. The average gas bubble size was found to be larger at atmospheric condition along with the frequency of large bubbles, resulting in a larger degree of particle-wall contacts. The degree of fluidized bed wall coating increased with the increase of pressure. This finding was related to the decline in the gas bubble size and the increase in frequency of small bubbles found at elevated pressures, which promoted particle–particle contacts, and th...

Comparison of electrostatic charge generation in gas-solid fluidized beds in turbulent versus pre-turbulent flow regime

In this work, the effect of gas velocity on the electrostatic charge generation in gas-solid fluidized beds was studied with a specific focus on the transition to turbulent flow regime. Experiments were conducted at a pressure of 2600kPa (abs) with fluidizing gas velocities of 1.5, 3, and 5 times of Umf (pre-turbulent regimes) and 7.5 times of Umf (turbulent regime). Increasing the gas velocity and transitioning to the turbulent flow regime improved particle-wall contacts; and thus, augmented the extent of wall fouling, which indicates the increase in bed electrostatic charge generation. The amount of fouling was approximately five times larger in turbulent flow regime (7.5Umf) in comparison to that for the lowest gas velocity examined in bubbling flow regime (1.5Umf). The particles coating on the column wall consisted of a thick bottom layer which extended to a height of approximately 1m above the distributor plate, and a thin top layer which extended to the top of the column near the outlet. The particles net specific charge in the top and bottom layers did not vary with the increase in gas velocity. However, the net charge of these particles increased. The fine particles entrained from the bed had a net negative charge resulting in a net positive charge to be left behind in the bed contributing to the increase in the magnitude of wall fouling at higher gas velocities, especially in turbulent flow regime.

Investigation of granular surface roughness effect on electrostatic charge generation

Electrostatic charge generation is a multivariable and complex issue whose working mechanism has never been fully understood. The objective of this paper is to investigate the effect of granule surface roughness on electrostatic charge generation. Two kinds of granule material, Polyvinyl chloride (PVC) and polypropylene (PP) were used with the granule size of 4mm diameter, 2mm height and the shape was cylinder or semi-cylinder. The working surfaces were grounded and roughness ranged from 0.140 to 8.600μm. It was found that uneven surfaces tended to give rise to voids between two solids, where air stored in the voids was able to accelerate discharging. With the same roughness, PVC tended to generate more electrostatic charge than PP by one order of magnitude. For both materials, electrostatic charge generation first increased with surface roughness and then decreased. The maximum electrostatic charge generated was found to occur when the effects of interaction, contact area and voids discharging were at equilibrium. With the combined effect of humidity, surface roughness and contact area, highest electrostatics generation occurred near the mid-roughness tested in this work. Humidity had more effect on electrostatic charge generation as the granule working surface had lower roughness.

Experimental bench for studying the relation between the dynamic characteristics of the frictional motion and the electric potential at the surface of polymer slabs in sliding conformal contact

Quantifying the triboelectric charging that occurs at polymer-on-polymer contact is crucial in the appropriate design of sliding or rolling components of various mechanisms. The paper describes the key devices and instrumentation of a laboratory bench developed for the accurate study of the tribocharging characteristics of polymer slabs in frictional sliding conformal contact. The bench enables the adjustment of several factors that affect the electrostatic charge generation (relative sliding speed, normal contact force, and number of back-and-forth cycles), and is equipped with sensors for the continuous monitoring of sample displacement, as well as of both normal and tangential forces. The triboelectric charge is evaluated by non-contact 2-D mapping of the electric potential at the surface of the samples at the end of the frictional process. The experimental methodology includes appropriate filtering of the signals provided by the sensors, before being recorded and interpreted. The cartography of the surface potential is put in relation with the dynamic characteristics of the frictional motion. The effectiveness of the laboratory bench is illustrated by the study of the electric potential generated by frictional sliding conformal contact between rectangular slabs of Polyvinyl Chloride (PVC) and Acrylonitrile Butadiene Styrene (ABS).

Simultaneous measurement of electrostatic charge and its effect on particle motions by electrostatic sensors array in gas-solid fluidized beds

Repeated particle-particle and particle-wall collisions and frictions lead to the generation and accumulation of electrostatic charges in the gas-solid fluidized beds. Variations of electrostatic signals are a rich source of information on particle motions and charging, which have rarely been explored and interpreted. To gain a more comprehensive understanding of the induced electrostatic signals in the fluidized beds, an array of arc-shaped induced electrostatic sensors were attached to the outer wall of a fluidized bed. Combined with cross-correlation method, induced electrostatic voltage signals and correlation velocity of particles were measured simultaneously. It was found that electrostatic charges accumulation restrained the particle motions while the average correlation velocity of particles increased with the amount of injecting liquid antistatic agent. Based on the analyses of induced electrostatic signals, the particle correlation velocity, and the particles charge-to-mass ratio under different charging levels, a predictive model of the average particles charge-to-mass ratio was established. Compared with the results obtained from Faraday cup, the estimated results showed a relative error no more than 40%. Simultaneous measurement of particle correlation velocity and particles charge-to-mass ratio were complemented by arc-shaped induced electrostatic sensors array combined with cross-correlation method.

Mechanism of particle build-up on gas-solid fluidization column wall due to electrostatic charge generation

Particle build-up on gas-solid fluidization column wall due to electrostatic charging causes significant operational challenges including reactor shutdown in industrial processes such as gas-phase ethylene polymerization to produce polyethylene. It is well acknowledged that in fluidization process electrostatic charges are generated as a result of continuous particle-particle and particle-vessel wall contacts. However, the mechanism of charged particle attraction towards the fluidization column wall and their adhesion has received minimal attention. This work proposes a mechanism for particle build-up on the column wall by experimentally investigating the fouled particles charge distribution using a charged particle separator apparatus. The experiments were carried with two types of linear low-density polyethylene resins in a pressurized pilot-scale gas-solid fluidization system. Experimental results showed that the polyethylene layer built-up on the column wall contained both positively and negatively charged particles. A mechanism was proposed indicating that charged particle migration towards the metallic column wall was due to the image and electrostatic forces. The image forces were attributed to the particle-wall contacts while the electrostatic forces were between the charged particles fouled on the column wall and those oppositely charged within the bulk of the bed. In addition, the net space charge of the bulk particles contributed to the migration of the particles towards the column wall.

Effect of Human Activities and Environmental Conditions on Electrostatic Charging

The generation of electrostatic charge is considered for the cases of standing up from a chair and removing a garment at dew points with temperature and relative humidity (RH) of −13.1 °C (5 °C, RH 25%), −10 °C (27 °C, RH 8%), −8.9 °C (18 °C, RH 15%), −1.7 °C (38 °C, RH 8%), 5 °C (27 °C, RH 25%), 5.6 °C (18 °C, RH 45%), and 13.9 °C (27 °C, RH 45%). Using ESD mitigation shoes/floors rather than non-ESD can reduce the voltages by a factor of ∼2 to 5 for garment removal and ∼2 to 7 for standing up from a chair. For the garment removal, the charge voltage will drop to 100 V within ∼0.5 to 6 s and within ∼1 to 30 min when ESD and non-ESD mitigation shoes/floors are used, respectively. For the standing-up form a chair, the corresponding times are ∼0.5 to 3 s and ∼1 to 4 min, respectively. For the extreme case at 22 °C, RH 5%, the voltage can surpass +/− 20 kV. Finally, it is shown that the voltages a person will charge up to may vary by +/− 30% just because of different capacitances to ground. Residential home settings will lead to the highest voltages (60 pF test person to ground, U.S. wood frame house), while standing on a concrete floor only half of the voltage may be reached (120 pF).

Investigation of granule electrostatic charge generation with normal stress effect

The mechanism of electrostatic charge generation is significant to understand relevant granular electrostatics occurred in granule handling systems. However, the knowledge about single granule charge generation is far from completion. In this work, electrostatic charge generation of single granule sliding along a metal plate was measured and the effects of normal stress in combination with the humidity, saturation and contact area on electrostatics generation were studied. It was found that the electrostatics generated in the process increased with normal stress, which was independent of granule material and humidity. Humidity decreased electrostatics generation but such effect was found to be reduced as the normal stress was increased. In this work, all sampled granules had almost the same increasing rate of electrostatics with time to reach the state of electrostatics saturation. Normal stress was found to be a significant factor effect on the contact area of granule-metal plate.