Enhancement Of Electric Field Strength Research Articles

Research on CH4-CO2 reforming over Ni-Fe catalyst enhanced by electric field

CH4-CO2 reforming is an important way to prepare syngas, but it is often difficult to achieve both high conversion rate and low energy consumption at the same time. High-voltage electric fields can provide high-density energy, and it helps to improve the catalytic effect as well as effectively reduce the reaction temperature. Based on the Ni-Fe catalytic supported on active carbon(AC), a high-voltage electric field was added to the reforming system in this paper. The effects of temperature, electric field strength, and catalytic performance of the catalyst were investigated, then the promotion effect of high voltage electric field on the reforming reaction was revealed. The results show that the Ni-Fe/AC catalyst has better catalytic performance than the single-metal component catalyst, and the comparatively best catalytic effect can be achieved with 10% component loading. After adding a 9 mA electric field at 400 °C, the conversion of CH4 increased from almost 0–19.6%, which was 9 times higher than that of 1 mA, and the conversion of CO2 also increased to 29.3%. This indicated that the enhancement of electric field strength could effectively promote the reforming reaction. Finally, according to the catalyst characterization analysis, it is speculated that the electric field can stimulate the AC support to generate a large amount of active substance, which facilitates the entire catalytic process.

Numerical design of SERS-active substrate for analyte detection using gold-hexagonal patterns

Surface enhanced Raman spectroscopy (SERS) is a rapid, sensitive, and efficient tool for detection/analysis of molecules based on enhancement of its Raman signals. Raman active molecules can be detected in trace quantities using SERS by coupling the electromagnetic energy at optical frequency. In this study, design of a robust SERS-active substrate has been proposed that is composed of gold hexagonal nano-patterns on SiO2. High enhancement of electric field strength (≈1010) was demonstrated using optimised substrate with standard laser sources (λ = 632 nm, and λ = 785 nm) for illumination. The proposed SERS substrate was found to respond to different analytes such as water, urea, and blood, with high sensitivity (Enhancement factor≈ 108-109). It is a versatile design that may find its application in bioanalysis/bio diagnostics, explosive detection, food adulteration etc. It was observed that variation of sharpness of corners of hexagonal patterns does not degrade the enhancement factor immensely. Fabrication of the proposed SERS substrate can be done by using existing nano-lithography tools such as e-beam lithography, focussed ion beam etc.

Plasma-Assisted Fuel Atomization and Multipoint Ignition for Scramjet Engines

Estimates of energy and power requirements for shortening the ignition delay time in hydrocarbon-fueled scramjet engines using nonequilibrium plasma generation of radicals show that the uniform volumetric plasma ignition would be associated with extremely high power budget and substantial losses of total pressure. A multipoint plasma ignition scheme based on electron beams is proposed that would emulate the volumetric ignition while reducing the power budget by several orders of magnitude. The paper also explores an approach where the fuel is injected into the core flow as a liquid jet, and low-power electron beams are used to electrostatically charge the droplets and thus to control droplet breakup, atomization, mixing, and ignition. With a subcritical microwave field applied to the injection region, local enhancement of electric field strength at the surface of droplets, together with seed electrons and ions produced by the electron beam, would create subcritical microwave discharges and thus initiate combustion in multiple spots. The multispot ignition would help in spreading the flame across the combustor. Additionally, the initiation of combustion at the droplet surface, where local equivalence ratio is high, could help ignite lean (in average) mixtures.

The Application of Atmospheric Pressure Dielectric Barrier Discharge Plasma on the Cleaning of Photovoltaic Panels

Plasma surface modification plays a significant role in the field of surface treatment, and the dielectric barrier discharge in air is an important method to generate plasma. With the widespread use of photovoltaic (PV) power generation, the impact of PV panel dust deposition had on power generation efficiency could not be ignored. The traditional method of cleaning PV panel is a waste of water and not environmental, which makes it urgent to find a simple and effective cleaning method. Based on the specific scene of PV generation and the structure of PV panel, a special uneven electrode was designed to discharge and generate plasma to treat the PV panel. Meanwhile, to treat the PV panel with stubborn dusts adhering on the surface for a long time, a method that discharges in wet condition was proposed. The simulation in wet condition confirms the enhancement of electric field strength and the experiment verified its treatment effect. The treatment on clean PV panels made it the property of preventing dust from adhering; the treatment in wet condition removed most of the dusts; eventually, the experiment under sunshine proved that the electrodes designed had little impacts on PV panels' generation.

A thermodynamic analysis for heterogeneous boiling nucleation under an external electric field

A generalized expression of chemical potential under external electric fields is derived based on the non-equilibrium thermodynamics theory. Using Gibbs free energy equilibrium condition, a thermodynamic model is developed for homogeneous and heterogeneous boiling nucleation under external fields. Taking into consideration the effects of electric fields strength, contact angle, and the temperature gradient in the superheated liquid layer, analytical solutions in integral forms for critical radius and availability are obtained for onset of heterogeneous boiling nucleation on a superheated wall. It is found that both the critical radius and availability increase with the enhancement of electric field strength, indicating that nucleation becomes more difficult to occur under an externally imposed electric field.

Separation of nanocolloids driven by dielectrophoresis: A molecular dynamics simulation

The nonequilibrium molecular dynamics (MD) method was used to model the nanocolloids and the solvent particles. By introducing a non-uniform electric field, colloids were polarized to have opposite polarities. Separation of colloids driven by dielectrophoresis (DEP) could be seen clearly under a strong electric field at low temperatures. Analyzing the ratio of DEP velocities of colloids to thermal velocities of neutral solvent particles showed that when the ratio was correspondingly big, collision between colloids and solvent particles would be intense, making the DEP velocity of colloids fluctuate frequently. By changing the electric field strength, it was found that the enhancement of electric field strength would quicken the separation of colloids. But when the electric field strength increased to a certain degree, the separation motion would be slow because of the strong friction resistance of the solvent particles to the colloids. Moreover, studying the separation reason of colloids based on the potential energy showed that after colloids were polarized, the attractive potential energy among the colloids would be weaker than before, while the increase of temperature would reduce the attractive potential energy and increase the repulsive potential energy, which accorded with the DLVO theory.

Molecular dynamics simulation for aggregation phenomena of nanocolloids

Nonequilibrium molecular dynamics (MD) method was used to study the dielectrophoresis (DEP) motion of nanocolloids in non-uniform electric field. By changing the electric field strength and system temperature, aggregation phenomena of nanocolloids was analyzed. Simulation results showed that at normal temperature, though the Brownian force can affect the motion of colloids, the attractive force will increase quickly with the distance between colloids down to 12 σ, which makes colloids aggregate. When the Brownian force is weak to colloid’s motion, for the enhancement of electric field strength, the DEP force of colloid will increase and so did the attractive force, which finally quickens the aggregate speed. Simulation results also showed that the temperature’ enhancement will increase the Brownian force of colloids, hence disturbing the colloids aggregation. Moreover, the DLVO theory was used to study the motion of a pair of interactional colloids, both the potential energy and the attractive force versus distance of colloids were presented, then the latter graph was used to compare with another graph elicited by MD method. Results showed that the two graphs were nearly the same, indicating the MD model accorded with the theory.

Tip‐enhanced Raman microscopy: practicalities and limitations

AbstractThe feasibility of apertureless scanning near‐field Raman microscopy, exploiting the local enhancement in Raman scattering in the vicinity of a silver or gold tip, was investigated. Using the finite difference time domain method we calculated the enhancement of electric field strength, and hence Raman scattering, achieved through the resonant excitation of local modes in the tip. By modelling the frequency‐dependent dielectric response of the metal tip we were able to highlight the resonant nature of the tip‐ enhancement and determine the excitation wavelength required for the strongest electric field enhancement, and hence Raman scattering intensity, which occurs for the excitation of modes localized at the tip apex. It is demonstrated that a peak Raman enhancement of 107‐fold should be achievable with <5 nm spatial resolution. We show that surface‐enhanced Raman scattering from carbon contamination on a silver or gold tip can be significant. However, we find for a tip of radius of curvature 20 nm that the Raman enhancement should decay totally within 20 nm from the tip. Hence withdrawal of the tip by this distance should lead to the disappearance of the tip‐enhanced signal, leaving only that from carbon contamination on the tip itself and the intrinsic signal from the sample. Copyright © 2003 John Wiley & Sons, Ltd.