Plasma Jet Array Research Articles

Experimental investigation of a spanwise plasma jet array in a turbulent boundary layer for skin-friction drag reduction

Three different types of particle imaging velocimetry (PIV) measurements, namely planar-PIV, micro-PIV, and stereo-PIV, are integrated to provide a full picture of the interaction between a spanwise plasma jet array and a turbulent boundary layer (TBL) at Reθ = 1208. Quiescent-flow characterization reveals that the plasma actuator array induces a wavy jet. With increasing duty cycle (DC), the peak jet velocity grows yet the height of the jet body decreases. When the TBL is actuated by such a plasma jet array, the spanwise distribution of the relative drag variation exhibits two regions with opposite signs, and the formation of these two regions can be attributed to the upwash and the downwash effects of the plasma-induced vortex, respectively. After spatial-averaging in the plasma actuation zone, net drag reduction (DR = 3.2%) is only achieved at the lowest DC of 10%. Although, by increasing the duty cycle, more drag reduction can be obtained in the upwash zone, the accompanying drag increase in the downwash zone is even prominent.

Visualization of electrical interaction among close-packed atmospheric pressure plasma jets

Plasma jet arrays can flexibly generate large-scale plasma in ambient air for surface treatment. Close arrangement of plasma jets inevitably induces a complex electrical interaction, which reshapes plasma plumes and destabilizes the treatment process. Understanding electrical interaction is a prerequisite for optimizing parameters in surface treatment. In this study, we employ a linear electro-optic technique to visualize the electrical interaction on the cross section perpendicular to plume trajectories. The strength of the interaction is featured by the density of the deposited surface charge. Results show that plasma jet arrays can simultaneously deposit like-charged groups onto the substrate. However, the electrical interaction is proven to behave with a tendency toward convergence rather than the repulsion caused by electrostatic interaction. It is inferred that electrons at the head of ionization waves (IWs) shield electrostatic repellence between positive charge groups. The collision ionization by electrons in the interval guides the coalescence of adjacent IWs. This study clarifies the electrical interaction between multiple jets, which is instructive for stable control of large-scale non-thermal plasmas for surface treatment.

Enhancing CFRP laminates with plasma jet arrays: A study of interlaminar mechanical properties

AbstractThis study delves into the efficacy of plasma jet array treatment in bolstering the interlaminar toughness of Carbon Fiber Reinforced Polymer (CFRP) prepregs, a crucial parameter for their deployment in high‐performance domains. Employing high‐frequency pulsed microsecond plasma jet arrays for surface modification, this research not only demonstrated a 19.49% upsurge in peak load capacity but also a remarkable 29.94% enhancement in Mode I interlaminar fracture toughness, as evident from Double Cantilever Beam (DCB) tests. Furthermore, the surface wettability improvements were underscored by a substantial decrease in water contact angle from 108.33° to 31.45° and a total surface energy augmentation from 12.20 to 64.16 mN/m, post a 1‐min plasma treatment. X‐ray Photoelectron Spectroscopy (XPS) results indicated an appreciable rise in oxygen functionalities, suggesting enhanced resin‐fiber bonding. Additionally, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) analyses revealed notable decreases in surface roughness and microscale defects, contributing to smoother surfaces conducive to better adhesive bonding and reduced manufacturing defects. These multifaceted improvements, stemming from alterations in surface chemistry and topography, underpin the significant potential of plasma treatment in advancing CFRP laminate applications requiring superior durability and mechanical resilience.Highlights A plasma jet arrays method to enhance CFRP's interlaminar properties was studied. The influence mechanism of plasma modification was revealed in detail. The interlayer toughening mechanism of CFRP after plasma modification is proposed.

Experimental investigation of a grid plasma jet array in a turbulent boundary layer for skin-friction drag reduction

Toward turbulent skin-friction drag reduction, a novel layout of plasma actuator with a grid anode is devised (grid edge length: L), capable of producing an array of wall-normal plasma jets. The characteristics of this plasma jet array and its interaction with a turbulent boundary layer are investigated experimentally with a particle imaging velocimetry. Results show that the quiescent flow field of the plasma actuator is dominated by a standing vortex ring attached at the inner sides of the square grid, a wall-normal jet flow issued from the grid center, and a downwash flow between adjacent grids. When a tandem array of 11 plasma jets are issued into the cross flow, an equilibrium stage is reached after the third jet. In this stage, the main body of the wall-normal jet bends noticeably to the cross flow, and its leeward side hosts a reverse flow zone, extending downstream to form a slender low-speed wedge (LSW). Two vortical structures are prominent: the streamwise counter-rotating vortex pair residing in the two sides of the jet body, and the arch-shape negative spanwise vortex situated on the LSW root. In the grid-middle plane, the production of turbulence is enhanced across the entire boundary layer, and a second production peak is identified at y+=26. Reduction of the spanwise-averaged wall shear stress is achieved downstream of plasma actuation at x/L≥19.4, and part of the drag reduction fruit earned by ejection is offset by the spanwise transportation of high-velocity fluids toward the middle plane.

In situ measurement of dynamic surface charge on dielectrics interacted with plasma jet arrays

As a flexible tool to generate large-scale non-thermal plasma in ambient air, plasma jet arrays have attracted academic attention from multiple fields of biomedicine and material surface sciences. Optimization of plasma processing that heavily relies on trial-and-error experiments requires quantitative in situ diagnostics of plasma–surface interaction. This study focuses on the fundamental surface charge evolution in quartz dielectric deposited by plasma jet arrays. The thin quartz plate is attached to an electro-optic BSO crystal that is conductive and grounded in the back. These jet arrays are driven by a positive microsecond pulsed voltage with kHz frequency. Special attention is paid to the properties and mechanisms of the intriguing convergence of multiple adjacent surface charge patterns. The measured 1D and 2D jet arrays verify the trend of homopolar charge fusion at the plasma–surface interface, which was initially thought to be repulsive under electrostatic forces. The fusion of surface charges is considerably enhanced when more charges are transported onto targeted dielectrics, as well as at smaller separations. The simulation results reveal the mechanism of charge fusion that occurs when surface ionization waves (IWs) are in close proximity, and the high electric field between their heads provides a cluster of high-energy electrons that forces two IWs to merge until they connect. In the case of extremely small separations, the close-in IWs directly merge in bulk before touching the target. Quantitative in situ measurements of surface charges and the corresponding simulations provide fresh insight into the electrical interaction in large-scale atmospheric-pressure plasma jets. The properties of charge fusion can help with manufacturing and optimizing large-area uniform plasma jet sources for various dielectric materials.

Nanostructured Polyaniline Films Functionalized through Auxiliary Nitrogen Addition in Atmospheric Pressure Plasma Polymerization

Polyaniline (PANI) was synthesized from liquid aniline, a nitrogen-containing aromatic compound, through the atmospheric pressure (AP) plasma process using a newly designed plasma jet array with wide spacing between plasma jets. To expand the area of the polymerized film, the newly proposed plasma jet array comprises three AP plasma jet devices spaced 7 mm apart in a triangular configuration and an electrodeless quartz tube capable of applying auxiliary gas in the center of the triangular plasma jets. The vaporized aniline monomer was synthesized into a PANI film using the proposed plasma array device. The effects of nitrogen gas addition on the morphological, chemical, and electrical properties of PANI films in AP argon plasma polymerization were examined. The iodine-doped PANI film was isolated from the atmosphere through encapsulation. The constant electrical resistance of the PANI film indicates that the conductive PANI film can achieve the desired resistance by controlling the atmospheric exposure time through encapsulation.

Improvement of atmospheric jet-array plasma uniformity assisted by artificial neural networks

Atmospheric pressure plasma jet (APPJ) arrays have shown a potential in a wide range of applications ranging from material processing to biomedicine. In these applications, targets with complex three-dimensional structures often easily affect plasma uniformity. However, the uniformity is usually crucially important in application areas such as biomedicine, etc. In this work, the flow and electric field collaborative modulations are used to improve the uniformity of the plasma downstream. Taking a two-dimensional sloped metallic substrate with a 10° inclined angle as an example, the influences of both flow and electric field on the electron and typical active species distributions downstream are studied based on a multi-field coupling model. The electric and flow fields modulations are first separately applied to test the influence. Results show that the electric field modulation has an obvious improvement on the uniformity of plasma while the flow field modulation effect is limited. Based on such outputs, a collaborative modulation of both fields is then applied, and shows a much better effect on the uniformity. To make further advances, a basic strategy of uniformity improvement is thus acquired. To achieve the goal, an artificial neural network method with reasonable accuracy is then used to predict the correlation between plasma processing parameters and downstream uniformity properties for further improvement of the plasma uniformity. An optional scheme taking advantage of the flexibility of APPJ arrays is then developed for practical demands.

A conical assembly of six plasma jets for biomedical applications

A conical assembly of six plasma jets arranged in a rectangular pattern for biomedical applications is presented. The conical configuration increases the separation distance between individual tubes within the assembly that reduces interference between individual plasma jets and enables the jets to converge at the output, facilitating more uniform treatment as opposed to plasma jet arrays operated in parallel. Electrical and optical diagnostics of the plasma discharges and measurements of H2O2 and NO2− production in de-ionized water are used to characterize the potential suitability of the device for biomedical applications. Particularly, it was found that the efficiency in H2O2 (an important bacterial disinfection agent) production by the conical assembly of six plasma jets was more than nine-fold higher compared to its single plasma jet counterpart and that this could be achieved at a biocompatible temperature of below 300 K. Therefore, the device may find use in biomedical applications, particularly where larger area treatments are required such as for certain wounds and cancer tumors that can span areas of tens of cm2.

Plasma activated medium prepared by a bipolar microsecond-pulsed atmospheric pressure plasma jet array induces mitochondria-mediated apoptosis in human cervical cancer cells.

Plasma activated medium (PAM) was prepared by a bipolar microsecond-pulsed atmospheric pressure plasma jet (APPJ) array source and was utilized for cancer cell treatment. APPJ array-produced plasma were characterized. APPJ array treatment of three different solutions (deionized water (DW), HBSS (serum-free Hanks’ balanced salt solution), and DMEM (Dulbecco’s Modified Eagle Medium) + 10% FBS (fetal bovine serum)) were performed to induce the changes in the concentration of reactive oxygen and nitrogen species (RONS) as functions of the operating parameters. Human cervical cancer cells (HeLa) injected with plasma-treated media were investigated for changes in cell viability using MTT assay. It was observed that PAM-induced ROS can regulate the protein expression associated with mitochondria, and PAM causes apoptosis through Cyto C/JNK/p38 signaling on human cervical cancer cells.

Effect of HMDSO Addition on Discharge Characteristics and Uniformity of Nanosecond-Pulsed Plasma Jet Array

Atmospheric-pressure plasma jet (APPJ) array is considered as an efficient method to enlarge treatment and improve treatment efficiency. With the addition of precursors containing Si, the APPJ array can be used for improving the surface hydrophobicity and insulating performance of insulating materials. In this article, the influence of hexamethyl disiloxane (HMDSO) addition on the discharge characteristics and uniformity of a 1-D nanosecond-pulsed jet array in Ar has been investigated through electrical and optical methods. It is found that the addition of HMDSO in a small amount can promote the plume length, discharge power, transported charge, and emission intensity through the Penning effect. When the HMDSO content is higher than 0.04%, the discharge of jet array is weaken, especially the middle unit, which results in the decrease of the uniformity, plume length, discharge power, transported charge, and emission intensity. With the intensified charge-coupled device (ICCD) measurement of the ionization wave propagations of jet arrays in pure Ar, 0.04%, and 0.50% HMDSO, it shows that the 0.04% HMDSO enhances the spatial electric field strength in jet array and promotes plasma bullets propagation. However, more HMDSO addition reduces the space charges and plasma bullets propagation speed. The competition of Penning effect and electron absorption by the HMDSO addition results that the Ar jet array has maximum values of plume length, discharge power, transported charge, and emission intensity at 0.04% HMDSO content.

Modification of PMMA surface hydrophobic properties using an atmospheric-pressure plasma jet array for the enhancement of flashover voltage

Modification of PMMA surface hydrophobic properties using an atmospheric-pressure plasma jet array for the enhancement of flashover voltage

Uniform deposition of silicon oxide film on cylindrical substrate by radially arranged plasma jet array

In this work, the SiOx film was deposited on a cylindrical substrate by a radially arranged plasma jet array generated by an AC power supply. The properties of deposited SiOx film were studied systematically, including surface morphology, film thickness, elemental composition and chemical structure. Besides, the effect of surface modification on insulation improvement in a gas insulated transmission line (GIL) system was verified. The discharge uniformity of the plasma jet array was improved by adding ballast resistor in the series circuit. Our results showed that the SiOx films were composed with Si-O-Si group dominated by network structure along with a small amount of Si-OH group and inorganic groups (-CH2, Si-CH3). The film deposited by plasma jet array showed good uniformity on thickness and element composition. The lift-off voltage of metal particle improved by about 120.88% after SiOx film deposition. Our results provide a universal surface modification method for cylindrical substrate under mild conditions.

Discharge Characteristics of Fusion Plasma Jet Array and its Influencing Factors

Discharge Characteristics of Fusion Plasma Jet Array and its Influencing Factors

The Combination of Low-Temperature Plasma and Tripterygium wilfordii Hook F on Ameliorating Imiquimod-Induced Psoriasiform Dermatitis in Mice

Improving the transdermal delivery efficiency of medicine is a crucial measure to improve the treatment efficiency of psoriasis. This paper developed a low-cost, highly active, and large-action-area low-temperature plasma (LTP) jet array. The two components of plasma—the high concentration of reactive oxygen and nitrogen species and the strong electric field—easily changed the structural integrity of the stratum corneum, which enhanced the transdermal delivery of the medicine. Tripterygium wilfordii Hook F (TwHF) is a medicine used to treat autoimmune and inflammatory conditions. The enhanced transdermal delivery of TwHF significantly alleviated the severed psoriasiform dermatitis induced by the imiquimod. Unlike the TwHF treatment alone, the LTP + TwHF treatment was more efficient at suppressing epidermal thickening and inhibiting systemic inflammation without noticeable side effects. LTP + TwHF treatment provides a potential new solution for psoriasis treatment.

Mode transition in 1D He plasma jet arrays dominated by hydrodynamic interaction

As an emerging technology for flexibly generating large-area atmospheric plasma, jet arrays are facing an urgent problem to control discharge modes caused by jet-to-jet interactions, apart from issues of stability and uniformity. Here, two modes in one-dimensional ns-pulsed He plasma jet arrays are reported, namely coupling and collimated modes. Discharge characteristics and transition rules of the two modes are explored by optical, electrical, spatial-temporal resolved and Schlieren methods. Results reveal that the coupling mode appears only when multiple conditions are satisfied, including low gas flow rate, high voltage frequency and small jet separation. Fluid dynamics and intensified charged-coupled device images prove that the mode transition mainly depends on the hydrodynamic interaction, which exceeds the effect of electrostatic repellence between ionization waves. Shrinkage of He flows is visualized to be enhanced at coupling mode, contributing to inward deflection of outmost plasma jets. Eddies on both sides of jet array and low-pressure regions near nozzles are generated by electric winds, promoting the transversal momentum transfer and gas fusion among adjacent He flows, thus tending to jet couplings. Some fresh insights are provided in this work about jet coupling and generation of controllable large-area plasma sources. The results could help to understand the importance of hydrodynamic interaction among proximal plasma jets, and plasma action on adjacent gas flows.

Deposition of charged aerosols by E × B enhanced low‐temperature plasma jet array

AbstractIn this paper, an efficient plasma jet array based on the E × B enhancement was developed. The direction of the magnetic field was the same as the propagation direction of the plasma jet, and the direction of the electric field was perpendicular to the plasma jet. The E × B enhancement increased the length of the plasma jet from 0.5 to 1.8 cm, the discharge current peak by 37.8%, and the plasma power by 11.1%, compared with the control case. Three‐dimensional simulation of electrons movement indicates that the confinement of electrons in the high argon concentration region was the main reason for the E × B enhancement. The stronger discharge based on the E × B enhancement increased the ion density in the open air significantly. The charged aerosols were generated through the diffusion charging mechanism. The image charge electric force between charged and neutral aerosols increased the collision rate between aerosols, therefore, the larger aerosols were generated, and 108% more deposition of aerosols than the natural settlement case were achieved.

An investigation of plasma-driven decomposition of per- and polyfluoroalkyl substances (PFAS) in raw contaminated ground water

Per- and polyfluoroalkyl substances (PFAS) are contaminants of emerging concern owing to their ability to bioaccumulate in the body and subsequently cause cancer. PFAS, while recalcitrant to advanced oxidation, can be degraded by plasma action. In this work, we investigate the efficacy of two plasma reactors on degrading PFAS in ground water derived from two different contaminated sites. The reactors included an array of underwater plasma jets and a dielectric barrier discharge (DBD) with water dielectric barriers. While both reactors showed effectiveness in removing PFAS, the DBD with water barriers was most efficient with regard to the rate of degradation and power consumed. This better performance was attributed to the increased plasma–liquid contact area. Experiments indicate that air is a suitable working gas alternative to argon, and both AC and ns-pulsed power sources can generate the plasmas for these reactors. Furthermore, it was found that for both reactors, the removal rate for low and high PFAS concentration in ground water was the same, suggesting that the reactors are most efficient at treating heavily contaminated water. In this respect, a concentration step followed by plasma treatment may be a cost-effective means to treat the PFAS-contaminated water.

Numerical studies on downstream uniformity of atmospheric pressure plasma jet array modulated by flow and electric multi-field coupling control

Atmospheric pressure plasma jets (APPJs) have potential applications in many aspects ranging from traditional surface treatment to growing biomedicine. An array structure of such APPJs is the most efficient way to enlarge the treatment area. Nevertheless, the majority of APPJ arrays have shown mottled patterns downstream, a disadvantage for applications. Particularly, in biomedicine and certain other areas, improving the plasma homogeneity downstream of APPJ arrays is crucially needed. In this work, we numerically study synergistic effects of APPJ arrays on plasma propagation and homogeneity downstream based on a model coupling electric, flow, and temperature fields. Taking a two-dimensional three-tube APPJ array as an example, we study the influence of gas velocity and component, as well as applied voltages on plasma distributions. In addition, essential strategies for merging plasma bullets are acquired. Results show that the ionization rate between adjacent jets is important to provide electrons for jet merging. The helium mole fraction controls the plasma distribution and thus directly decides whether adjacent jets merge. After merging, the plasma bullets affect each other through the electric field to control the homogeneity downstream. Therefore, the plasma distribution is a result of the synergy of flow and electric fields. Then, a homogeneous plasma distribution downstream can be realized by the fine control of both fields, which provides an effective way to uniform the plasma downstream in plasma processing.

The Enhanced Water Vapor Condensation by Negative Air Plasma Jet Array

Rain enhancement is the main activity field of weather modification in the countries that suffer from water stress. The charged aerosol is a new man-made condensation nucleus to enhance the water vapor condensation. In this article, the negative-polarity air plasma jet array with plasma volume larger than 2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> was used to generate the charged aerosols. Aerosols are mainly charged in the unipolar atmosphere. The averaged charge number of charged aerosols was measured to be 5818e. The attractive electric force of charged aerosols was more than ten times higher than the sum of thermophoretic forces and diffusophoretic forces. These charged aerosols accelerated the collision-coalescence process inside the cloud chamber, generated large droplets in the range of 40- 70 μm, and increased the settling amount of moisture by 58.8%.

Comparison of spatial distribution of active substances and sterilization range generated by array of printed-circuit-board plasma jets

By copper deposited in the holes of two perforated printed circuit boards to form copper rings with a radius and width of 1.5 mm as electrodes, a 4 × 4 plasma-jet-array device equipped with ring-ring electrode structure can realize stable and synchronous discharge of each unit. On the other hand, the transposition of the active substances on the agar plate produced by atmospheric-pressure plasma-jet array was visualized using a KI-starch reagent. It showed that the shape of the distribution of active substances can change from a ring to a solid circle when the gas-flow rate was reduced below 8 slm. In particular, the inactivation range of Escherichia coli at 90 s and inactivation range of Staphylococcus aureus at 180 s using this device were both close to twice the array area when the gas-flow rate was 5 slm. • A two-dimensional 4 × 4 array atmospheric pressure plasma jet device was manufactured by using PCB technology. • The transposition of the active substances on the agar plate was visualized using a KI-starch reagent. • The distribution shape of active substances can change from ring to solid circle when the gas flow rate was reduced. • The spatial distribution of active substances and sterilization range are good fit.