【作者】 汪宇；

【导师】 李晓东； 陆胜勇；

【作者基本信息】 浙江大学 ， 工程热物理， 2011， 硕士

【摘要】 滑动弧放电是一种低温等离子体发生方式,由于具有较高的能量利用率,并且同时兼具高非平衡度、高电子密度和电子温度,在环境化工和能源等领域有广泛应用前景。大量的工业应用研究已经尝试中,但是控制滑动弧等离子体发展的物理化学机制尚没有得到准确而系统的描述。基于此背景,本文采用数值模拟并辅助实验的方法来研究滑动弧放电的物理化学特性,主要研究内容如下：(1)等离子体的电弧温度场、电场和导电区域尺寸是确定电子温度、电子密度、化学反应速率以及能量效率的重要参数。对气流量为1.43L/min和6.42L/min时50Hz交流滑动弧放电的电参数进行了测量；用瞬态的电弧模型描述滑动弧的能量传递,并用近似的介质电导率和热扩散系数对模型进行简化,解决了由于电弧结构变化所导致的移动边界问题；模拟求得等离子体的电弧结构、电场强度和动态温度场等参数的演化。其中,电弧电场的模拟值与实验值基本吻合,计算得到电弧轴心温度可以达到5700-6700K。研究结果表明,气流直接影响电弧结构和电流密度进而影响电弧电场和温度分布,在一个放电周期中电场呈先减小后增大的趋势。(2)将电弧等离子体瞬态Elenbaas-Heller模型与麦克斯韦方程组联立,建立一个描述大气压交流滑动弧等离子体放电的非线性模型。通过分析电参数的变化规律探索交流滑动弧放电的自磁特性。研究结果表明,气流量的增加会改变自磁场的演化。气流和自磁场联合作用决定了弧柱结构的变化。具有较小弧半径和较大轴向曲率的电弧段的局部磁场强度和自磁压力会高于其他弧段,这会加剧等离子体放电的不稳定性。(3)滑动弧等离子体的电子温度、电子密度和非平衡度是表征等离子体热力学性质的重要参数。根据较高电流时AlⅠ396.1nm的Stark展宽求得电离子体电子密度沿反应器轴线的分布情况；用瞬态的双温度模型描述等离子体放电的能量传递。模拟条件下电子密度可以达到1021～1022m-3数量级,电子密度变化情况符合实验结果；电子温度在一个放电周期的中间60%时间可以大体保持在1.3-1.8eV,并呈现先减小后增大趋势,与根据文献提供的公式的计算结果一致；等离子体的非平衡度和电子温度与电弧电场强度变化趋势相似,增大气流量并不能显著提高非平衡度。(4)在假设的温度分布的基础上建立一个描述气液两相滑动弧反应动力学的数学模型。模拟求得的OH粒子分布规律符合光谱诊断结果；研究结果表明较高的温度适于产生OH,并且OH生成量沿反应器轴线有先增大后减小的趋势；模型能较为准确地预测H2O2和H2的生成量；固定氧气流量时,增大水流量可以提高H2O2和H2的生成量。(5)以模拟有机污水正丁酸溶液为研究对象,研究了系统参数对降解效果的影响。并进行了滑动弧等离子体分别与TiO2光催化和H2O2联合降解有机污水的研究。结果表明,较高的氧气流量对降解有促进作用；TiO2含量为0.5mg/L时,协同效果最明显；提高H2O2投加量并拉长放置时间,会提高降解效果。更多还原

【Abstract】 Gliding arc discharge is a low-temperature plasma with high energy efficiency, electron temperature and density and has broad application prospects in the field of environment and energy. Although numerous industrial applications have been attempted, the physical and chemical mechanisms governing the gliding arc evolution are not yet accurately and comprehensively understood. In this dissertation the physical and chemical properties of gliding arc are researched based on numerical simulation and experiments. The main objectives of the current research included as following:(1) The arc temperature field, electric field and size of conducting zone of gliding arc plasma are important parameters to determine temperature and density of the electrons, chemical reactions rates and energy efficiency. Electrical parameters of a 50Hz ac gliding arc discharge were measured at two gas flow rate conditions, 1.43L/min and 6.42L/min. An instantaneous model which was used to describe the energy transfer of gliding arc discharge was simplified by using an approximate expression for the electrical conductivity and diffusivity of plasma, which raveled out the moving boundary in the gliding arc simulation resulted by variation of arc structure. The current density, electric field, dynamic temperature field and the structure of ac gliding arc was calculated. The electric field strength from the simulation result of the model was in agreement with the experimental data. According to the calculational result, the temperature in the axis of arc reached as far as 5700-6700K. It showed gas flow directly affected the arc structure and current density, thus affected the electric field strength and temperature distribution. The electric field strength increased firstly and then decreased during a discharge period.(2) A nonlinear model of ac gliding arc discharges in atmosphere-pressure is developed based on the combination of the transient Elenbaas-Heller model and Maxwell’s equations. According to the calculation results of discharge parameters, the self-magnetic properties of an ac gliding arc discharge is investigated. The numerical results indicate that the increase in the gas flow rate could change the evolution of the magnetic field. The conjunct effect of gas flow and self-magnetic field determines the arc column structure. Zones with smaller arc radius and larger axial curvatures in the plasma region have larger local magnetic field intensity and self-magnetic pressure, which accelerates the instability of discharges.(3) The electron temperature, electron density and degree of non-equinibrium are the important parameters that characterize the thermodynamics properties of gliding arc. According to the Stark broadening of the AlⅠ396. 1nm in a high electric current the distribution of the electrone density along the axis of the reactor is obtained. A transient two-temerature model is used to described energy transfer of the plasma discharge. The electrode density can achieve at 1021～1022m-3 orders of magnitude under the simulation conditions. The evolution of the electrode density is consistent with the experimental results. The electron temperature is in the range of 1.3～1.8eV in the middle 60% of a discharge cycle and first decreases and then increases, which is in agreement with results of the formula from literature. The development trend of the non-equilibrium degree of plasma is similar with that of the electric field strength. The increase of the gas flow rate could not evidently increase the non-equilibrium degree.(4) A mathematical model describing the chemical-reaction kinetics for gas-liquid gliding arc discharge is developed based upon assumed temperature profiles and chemical reactions. The distribution of OH from simulation agrees with the results from optical emission spectroscopy. The results indicate much higher temperature is in favor of the production of OH. The formation of the OH first increase and then decrease along the axis. The model can accurately predict the production of H2O2 and H2. Increasing the water flow rate leads to higher H2 and H2O2 production at fixed inlet oxygen carrier flow rates.(5)Using butyric acid solution as objective pollutant, the influences of the system parameters on the degradation of wastewater are studied. The respective combination of H2O2 and TiO2 photocatalytic with gliding arc are researched. The results shows a higher oxygen flow rate can promote the degradation of organic contamination. When the concentration of the TiO2 is 0.5g/L, the synergistic effect becomes most significant. Increasing the amount of H2O2 could improve degradation rate.更多还原