Research On Dielectric Barrier Discharge (DBD) In Two Phase Of Mixture (TPM)

Dielectric barrier discharge (DBD) has a large number of industrial applications since DBD is an important feasible method to produce atmospherical pressure non-equilibrium plasma, and DBD has been studied extensively in theoretical and experiments. However, due to the development of industrial applications including the activation of desulfurization catalyzer for flue gas by discharge plasma, materials handling, food preservation, and so on, there are more DBDs in two phase of mixture (TPM), which not only in the pure gas. At present, there are a few researches on DBD in TPM.The paper mainly carried out theoretical and experimental researches on DBD in TPM, the result are as follows:For the strong coupling TPM, the paper built an approximate dipole-energy model to calculate the local field distribution. The dipole-energy model is simple and effective, and its results are better than the ideal dipole model. If TPM has a large particle volume fraction or dielectric mismatch, the interaction between particles is large too. In this case, the ideal dipole model is invalid and the dipole-energy model is valid. Based on the dipole-energy model, a correction formula to calculate the saturation charge of particles in TPM is obtained. The formula shows that when the dielectric mismatch is large enough, the saturation charge mainly depends on particle volume fraction. Besides, according to the application of dipole-energy model on calculation of ionic flow field under high voltage transmission lines, dipole-energy model is verified to be feasible and effective in the complex problem, which provides the foundation for application of dipole-energy model on DBD in TPM in further.For the discharge in TPM, the paper proposed the physical mechanism of discharge in TPM and the analytical formula to calculate the breakdown voltage of TPM. The results show that the particle size affects on the breakdown characteristics of TPM. There are three factors which affect the process of discharge in TPM:the field distortion; the particle captures electrons and hinders the development of avalanche; the particle absorbs photons. Based on the existing theories of gas discharge, the paper built the model of charge particles in avalanche; combined with the dipole-energy model, an analytical formula to calculate the short-gap breakdown voltage in TPM is derived. Calculations show that when particle size is large, breakdown voltage in TPM is lower than pure air; when particle size is smaller (micron), breakdown voltage in TPM is higher than pure air. Particle size also affects on the discharge form:when particle size is large, avalanche breaks on the particle surface, the discharge only occurs between particle and electrode; if the particle volume fraction is small, avalanche may jumps over the particle due to the photons; when particle size is small, avalanche can through the particle as surface discharge.For DBD in TPM, the paper built a simple particle simulation model which takes into account multi-avalanche and electrostatic repulsion. The results show that the competition in the effects of particles on discharge. Plasma particle simulation is characterized by tracking the movement of a large number of individual microscopic particles and the statistical average to reflect the macroscopic physical properties of substances. The method can avoid the complexity of solving the fluid equations, however, the amount of calculation remains high. According to the approximation of model, the calculation of discharge in TPM is greatly reduced. The calculations show that in pure gas gap, the speed of avalanche changes to streamer can be accelerated by charge accumulated on dielectric plate and space charge; in TPM, the amount of charge on dielectric plate increases due to the field distortion by particles, so the effect of acceleration is strong; in TPM, due to the charge of particles, the effect of electrons capture is stronger than field distortion by space charge, the acceleration of space charge is weak, which is benefit for amalgamation of avalanches. Besides, the speed of avalanche on particle is higher than avalanche in gas between particles; due to the faster avalanche on particle, polarization and charge of particles, the filed in gas between particles is greatly reduced, then avalanche is difficult to develop. Whether in pure gas or in TPM, multi-avalanche accelerates the speed of avalanche changes to streamer, multi-streamer accelerates the speed of development of streamer.For DBD in TPM, experimental results show that particles size and volume fraction affect the discharge form, and the surface discharge suppresses the filament discharge. In TPM, the Lissajous figure is a shuttle, which is different from the parallelogram shape in air. In TPM, there are two discharge forms:surface discharge and filament discharge, which can occur at the same time, but the different place. Surface discharge suppresses filament discharge, which means the discharge on particle suppresses the discharge in gap between particles. Experimental result is consistent with simulation, which also denies the conclusion of Nomura that surface discharge and filament discharge can occur at the same place and time, but provides the explanation to results of Murphy and Rajanikanth. When particle size is small or volume fraction is large, surface discharge suppresses filament discharge more. If particle size gets small, the onset voltage of surface discharge is reduced. Besides, experimental result shows that if particle size is large, discharge only occur at the place between particle and electrode; if particle is small, discharge can be through particle; this is the evidence of effect of particle size on discharge form.