In this paper, experimental and simulation investigations have been carried out for the characterization of the dielectric barrier discharge based cold atmospheric pressure plasma jet (C-APPJ) for a unique geometry in which argon gas is used at different flow rates along with pulsed DC supply at different frequencies. A tapered structure has been fabricated for acquiring sufficient velocity of the gas at a low flow rate. The typical V–I characteristic of the C-APPJ has been presented for a wide range of flow rates (1–5 SLM) and frequencies (10–25 kHz). On increasing the gas flow rate and frequency, discharge sustains for the lower potential of 5 kV and requires low power. It has been observed that the power dissipation for the formation of the plasma jet increases on increasing frequency at a constant flow rate. Also, the analysis of discharge current is presented for each combination of the flow rate and operating frequencies. Furthermore, the investigation has been carried out for the analysis of electron density, velocity distribution of gas, and distribution of the electric field in the C-APPJ for the same experimental geometry through the simulation tool COMSOL Multiphysics. The maximum electric field of 3.22 × 10 6 V / m and the maximum electron density of 3.38 × 10 19 1 / m 3 have been observed during the propagation of the plasma jet at 1 SLM flow rate. Such qualitative analysis of jet formation along the electric field distribution in a wide range of operating parameters would certainly be helpful in the development of dielectric barrier discharge based C-APPJ sources suitable for the biomedical and food related applications.

Experimental and simulation analysis of dielectric barrier discharge based pulsed cold atmospheric pressure plasma jet

Continuous gas temperature measurement of cold plasma jets containing microdroplets, using a focussed spot IR sensor

Computational study of plasma-induced flow instabilities in power modulated atmospheric-pressure microwave plasma jet

The diode-pumped metastable rare gas laser (DPRGL) is showing potential for high-power operation. A key issue in developing this concept is to produce high-density metastables in a large volume. To achieve this goal, we propose a new, to the best of our knowledge, architecture by extracting laser power from a diode-pumped plasma jet. In this scheme, the discharge and gain regions are separated, avoiding the negative effects of discharges in confined regions. A diode-pumped plasma jet-type Ar laser is demonstrated with 466-mW output and 33% slope efficiency. The gain volume can be increased with multi-jets, providing a better scaling potential for the DPRGL system.

Demonstration of a diode-pumped plasma jet-type rare gas laser.

In this article, the investigation has been carried out for the characterization of the proposed tapered geometry of dielectric barrier discharge (DBD)-based cold atmospheric pressure plasma jet (C-APPJ) on the basis of optical emission spectroscopy (OES) and imaging for different operating parameters, such as argon gas flow rates, applied voltages, and frequencies. The detailed characteristics for the formation of the plasma plume using argon as a working gas have been presented for a wide range of flow rates [1–3 standard liter per minute (SLM)] and frequencies (15–25 kHz). Increasing the pulse frequency, the length and the diameter of the plasma plume increase, while the length of the plasma plume increases when increasing the gas flow rate up to 2 SLM. Time-integrated images have been captured using the intensified charge couple device (ICCD) camera, which illustrates that the plasma plume comprises different emission layers of definite patterns. The propagation dynamics and formation of different emission layers of the plasma plume have also been investigated using the COMSOL Multiphysics simulation. It has been observed that the local electric field of 6 kV/cm is responsible for the propagation of the plasma bullet and the generation of the electron with an average energy of ~9 eV. OES has also been performed to understand the plasma chemistry and identify the reactive species in the C-APPJ. The discharge analysis and characteristics performed through experiment and simulation would certainly be helpful for the design and development of C-APPJ sources.

Analysis of Discharge Characteristics of Cold Atmospheric Pressure Plasma Jet

The design, performance, and characteristics of a low-temperature microwave-driven atmospheric pressure plasma jet (MAPPJ) are presented. The MAPPJ is based on a complex coaxial transmission line structure, and the gas is discharged by a continuous-wave microwave. By inputting two channel gas through inner and outer coaxial transmission lines, respectively, the gas flow can be restricted and the plasma jet open to atmospheric air could be long and straight without quartz tube. A 28.6 mm long straight low-temperature plasma jet is observed in the experiment. This MAPPJ device shows high efficiency in a wide operation range, and a maximum efficiency of 89.6% is measured in the experiment without a microwave matching network. This approach can be an initiation toward the commercialization of low-temperature MAPPJs.

A high efficiency low-temperature microwave-driven atmospheric pressure plasma jet

Conductive polymer composites (CPCs) based on polycarbonate/multi-walled carbon nanotubes (PC/MWCNT) were fabricated by melt mixing. By selecting the PCs with different molecular weights, three kinds of PC/MWCNT composites were obtained. The CPCs containing low viscous PC (lPC) had the lowest percolation threshold (0.06 vol%) as compared to those of medium viscous PC (mPC) (0.07 vol%) and high viscous PC (hPC) (0.13 vol%), which was attributed to the best MWCNT dispersion in matrix. Light microscopy images also demonstrated that lPC/MWCNT composite had the smallest undispersed filler agglomerates than the other two corresponding PC/MWCNT composites with the same filler loading (0.25 wt%). In terms of rheological measurements, rheological percolation occurred at a lower filler content for lPC/MWCNT than mPC/MWCNT and hPC/MWCNT composites. The chemo-resistive properties of composites towards organic vapors were investigated by measuring relative resistance change of CPCs upon vapor immersion-drying cycles. CPCs exhibited different sensing tendencies towards different organic vapors. lPC based CPCs exhibit higher relative resistance change as compared to mPC and hPC based CPCs because of their loosely overlapped conductive network, which are easily changed under polymer swelling. Besides, sample thickness is another factor that determined the vapor sensing performance of CPCs. Furthermore, relative resistance change of composites is found to be closely related with vapor concentration. This work presents a new thought in understanding filler dispersion in PC with different molecular weights, which has implication of turning conductive network structure and sensing performance of composites. 

The effect of polymer molecular weights on the electrical, rheological, and vapor sensing behavior of polycarbonate/multi‐walled carbon nanotube nanocomposites

The vortex rope in the draft tube is considered as the major contributor to pressure pulsation at partial load (PL) conditions, which causes the hydro unit to operate unstably. Based on the prototype Francis turbine HLA551-LJ-43 in the laboratory, J-grooves are designed on its conical section in this paper. We used numerical simulation to study the effect of the J-grooves on vortex suppression and energy dissipation in the draft tube. Four typical operating conditions were chosen to analyze the vortex suppression; the corresponding flow ratios Q* are 100%, 82%, 69%, and 53%, respectively. Entropy production theory is used to calculate the energy losses and assess the effect of the J-groove on energy dissipation under part-load conditions. By comparing entropy production, circumferential and axial velocity components, swirl intensity, pressure pulsation, and vortex distribution in a draft tube with and without J-grooves at different operating conditions, it can be concluded that the entropy production on the wall containing a conical section with J-grooves is obviously smaller than that without J-grooves, the effects of J-grooves on reducing circumferential velocity component Vu, pressure pulsation, and weakening vortex intensity and vortex rope in the conical section are obvious, especially at part load and deep part-load operating conditions. Using J-grooves shows better performance on vortex control and energy dissipation in the draft tube of a Francis turbine at partial load conditions.

https://www.mdpi.com/1996-1073/15/5/1707/pdf?version=1645777837

The Effect of J-Groove on Vortex Suppression and Energy Dissipation in a Draft Tube of Francis Turbine

The invention discloses a composite double-coaxial-line atmospheric-pressure low-temperature microwave plasma jet source, which comprises an external coaxial line and an internal coaxial line. The internal coaxial line is arranged in the external coaxial line. The external coaxial line comprises a pipe body. The pipe body is internally provided with a metal pipe. The bottom portion of the metal pipe is provided with a short-circuiting piston. The internal coaxial line comprises a needle electrode. The needle electrode is arranged in the metal pipe. The pipe body is provided with a gas input port 1. The gas input port 1 is communicated with the pipe body and the metal pipe. The bottom portion of the metal pipe is provided with a gas input port 2. The gas input port 2 is communicated with the metal pipe and the needle electrode. The pipe body is also provided with a microwave input port. The microwave input port is connected with the metal pipe. The atmospheric-pressure low-temperature microwave plasma jet source realizes emission of a stable and length-width-controllable low-temperature plasma jet flow, and improves the defects of high temperature, large excitation power, large size, unstable plasma jet flow, difficulty in adjustment and non-hand-held operation and the like in the prior art.

Composite double-coaxial-line atmospheric-pressure low-temperature microwave plasma jet source

Herein, immiscible poly(vinylidene fluoride)/poly(lactic acid) (PVDF/PLA) blends filled with multi-walled carbon nanotubes (MWCNT) were fabricated by a facile solution flocculation method. A co-continuous structure was formed at the blend ratio of 50v/50v. By extracting PLA, MWCNTs were found wrapped on the surface of porous PVDF. The electrical percolation threshold of porous composites is 0.25 wt.%, which is much lower than compact composites (2 wt.%). By comparing the electromagnetic interference shielding effectiveness (EMI SE) between compact and porous composites, the EMI SE of compact composites containing 15 wt.% MWCNT is ca. 30 dB, whereas 60 dB for the porous composites at the same filler loading. The enhanced shielding performance is derived from the porous structure and densely packed MWCNT on the PVDF surface that facilitates the multiple reflections of electromagnetic waves. This work provides a new thought in fabricating high performance EMI material by effectively tuning filler distribution in polymer blends. 

Enhanced electrical and electromagnetic interference shielding performance of immiscible poly(vinylidene chloride)/poly(lactic acid)/multi‐walled carbon nanotube composites via constructing filler‐wrapped porous structure

Cong Nie

Papers

A high efficiency low-temperature microwave-driven atmospheric pressure plasma jet

The effect of polymer molecular weights on the electrical, rheological, and vapor sensing behavior of polycarbonate/multi‐walled carbon nanotube nanocomposites

The Effect of J-Groove on Vortex Suppression and Energy Dissipation in a Draft Tube of Francis Turbine

Composite double-coaxial-line atmospheric-pressure low-temperature microwave plasma jet source

Enhanced electrical and electromagnetic interference shielding performance of immiscible poly(vinylidene chloride)/poly(lactic acid)/multi‐walled carbon nanotube composites via constructing filler‐wrapped porous structure