Effects Of Discharge Frequency Research Articles

Experimental and numerical investigations into the fabrication of alumina ceramic surface microchannel by electrochemical discharge machining

The electrochemical discharge machining (ECDM) is an advanced and promising technology for fabricating micro structures. This method is effectively applicable for non-conductive hard and brittle materials micromachining, such as glass and ceramics. However, the ceramics high melting point and intense heat exchange effects during microchannel fabrication lead to the easy dissipation of thermal energy and the difficulty in processing. To address this issue and expanded the ECDM processing range. This paper dedicated to the investigation of the material removal mechanism and process characteristics for the alumina ceramic surfaces microchannels preparation. Firstly, this study explained the difference of the ECDM critical applied voltage and gas film generation mechanism by analyzing the volt-ampere characteristic curve of 20 wt% NaOH electrolyte with a tool immersed depth of 2 mm and 10 mm respectively. Then, a thermal removal finite element model (FEM) for ECDM was developed. The heat cumulative and intermittent cooling effects applied on the alumina ceramic surface dominated the materiel removal. Additionally, it can be found that the microchannel machining accuracy and bottom surface quality depended on the Gaussian heat source characteristics, gas film formation mechanism, heat accumulation effect, and temperatures spatial and temporal distribution. And a series of single factor experiments for evaluating the parametric studies such as the effect of discharge frequency, applied voltage, duty ratio and tool feed rate on the fabricated microchannel performance are executed. Finally, the complex three-dimensional structures of cross microchannel grid and zigzag microchannel array with variable depth were successfully fabricated on aluminum oxide ceramic surface. Notably, the results highlighted and enriched the ECDM stability, consistency and applicability for alumina ceramic surface microchannel fabrication.

Fast simulation of the E–H mode transition in Ar/O2 inductively coupled plasmas

In this work, an analytical hybrid model, which consists of an analytical electromagnetic model and a global model, is developed to investigate the E to H mode transition in a planer inductively coupled plasma. By employing the hybrid model, the effect of discharge frequency, oxygen content, and gas pressure on the E to H mode transition is investigated. The results show that the electron density increases rapidly with coil current when the discharge shifts to the H mode, and the mode transition becomes smoother and occurs at lower current when the driving frequency is higher. As oxygen content increases, the electron density declines, and the threshold current for the mode transition exhibits a rising trend. The evolution of the threshold current with pressure is nonlinear; i.e., it decreases first and then increases, and the minimum value varies with discharge frequency. In addition, the plasma composition also changes during the E to H mode transition; i.e., all the charged species densities increase with coil current, except the O− density, which varies nonlinearly, and this indicates the decreasing electronegativity in the H mode. The results obtained in this work are helpful for understanding the effect of different discharAr/O2ge parameters on the E to H mode transition in Ar/O2 inductive discharges.

Influence of Working Surface Temperature on Area Effect in Electrical Discharge Machining Process

In this paper, we discuss the effects of working surface temperature on the material removal rate and tool electrode wear rate in sinking electrical discharge machining (EDM) process in order to clarify machining phenomena referred to as the area effect. First, the material removal rate, tool electrode wear rate and effective discharge frequency were measured for a 5mm-square rod tool electrode, and measured results were compared with those for 10mm-square rod tool electrode and 15mm-square rod tool electrode. Although the area effect is conventionally explained as the effect of discharge frequency, the measured results could not be explained in terms of only the dischargef requency. Then, the material removal rate and tool electrode wear rate for butt machining were compared with those of sinking machining, and the working surface temperature of the tool electrode were estimated using the measured temperature. It was found that the material removal rate and tool electrode wear rate are affected not only by the discharge frequency but also by the working surface temperature. It was also found that the tool electrode wear rate in a small working area can be reduced by lowering the working surface temperature.

Experimental assessment of a plasma-catalyst hybrid reformer for hydrogen production via partial oxidation of dimethyl ether

In this work, hydrogen is produced from partial oxidation reforming of dimethyl ether (DME) by a plasma-catalyst hybrid reformer under atmospheric pressure. The plasma-catalyst hybrid reformer which includes both plasma and catalyst reactors is designed. A spark discharge is used as a non-equilibrium plasma source, and it is used to ionize the mixture of DME and air. The performances of the reformer are characterized experimentally in terms of gas concentrations, hydrogen yield, DME conversion ratio, and specific energy consumption. The effects of discharge frequency, reaction temperature, air-to-DME ratio and space velocity are investigated. The experimental results show that the plasma-catalyst hybrid reformer enhances hydrogen yield when reaction temperature drops below 620 °C. At 450 °C, hydrogen yield of hybrid reforming is almost three times that of catalyst reforming. When space velocity is 510 h−1, hydrogen yield is 67.7%, and specific energy consumption is 12.2 kJ/L-H2.

Mathematical Modeling of Chemical Conversion in Thin-Layer Exothermic Mixtures under Periodic Electric-Spark Discharges

The dynamics of coating production using a reaction mixture with thermoreactive electric‐spark strengthening is studied numerically. It is shown that the main parameter that determines the thermal regime of coating is the initial thickness of the mixture layer. The parameter ranges for the process in a combustion regime and in a quasivolume conversion regime are determined. The effect of discharge frequency and the thermal characteristics of the reaction mixture and the substrate being strengthened on coating time is investigated. It is established that for a particular reaction mixture, the characteristic conversion temperature can be controlled by varying the electric discharge power and, hence, the heat flux at the active stage of the process, and for coating formation at this characteristic temperature, it is necessary that the thickness of the active layer be lower than a certain critical value.

Effects of discharge frequency on plasma characteristics and etching characteristics in high density Cl/sub 2/ plasma: comparison of ultrahigh-frequency plasma and radio-frequency plasma

We investigated the effects of discharge frequency on the characteristics of polycrystalline-silicon etching rates and on the etching selectivity on the gate oxide (SiO/sub 2/). An ultrahigh-frequency (UHF) plasma excited at 500 MHz was found to possess a wider process window for highly selective polycrystalline silicon etching than did an inductively coupled plasma excited at 13.56 MHz. The ionization rate in the UHF plasma is nearly constant at discharge pressures from 3-20 mtorr because the discharge frequency is higher than the electron-collision frequency in that plasma.