Characteristic studies on positive and negative streamers of double-sided pulsed surface dielectric barrier discharge

The mechanisms of streamer generation and propagation in double-sided pulsed surface dielectric barrier discharge (SDBD) on both sides have been analyzed and investigated by experiment and numerical simulation. The fully exposed asymmetric SDBD has two discharge processes located on the high voltage electrode (HVE) side and the ground electrode (GE) side. Discharge images of the HVE side and GE side are taken by a digital camera under continuous pulse and ICCD (Intensified Charge Coupled Device) is utilized to diagnose the generation and propagation of streamers in single pulse discharge. In order to understand the physical mechanisms of streamer evolution more deeply, we establish a 2D simulation model and analyze it from the aspects of electron density, ion density, reduced electric field and electron impact ionization source term. The results show that the primary and secondary discharges on the HVE side and the GE side of the double-sided SDBD are composed of positive streamer and negative streamer, respectively. On the HVE side, the accumulation of positive charges on the dielectric surface causes the direction of the electric field to reverse, which is the principal factor for the polarity reversal of the streamer. On the GE side, both the negative charges accumulated on the dielectric surface and the falling voltage are the key factors for the streamer polarity switch.     

Experimental and simulated investigation of microdischarge characteristics in a pin-to-pin dielectric barrier discharge (DBD) reactor

Both experimental and simulated studies of microdischarge (MD) are carried out in a dielectric barrier discharge with a pin-to-pin gap of 3.5 mm, ignited by a sinusoidal voltage with a peak voltage of 10 kV and a driving frequency of 5 kHz. Statistical results have shown that the probability of the single current pulse in the positive half-period (HP) reaches 73.6% under these conditions. Experimental results show that great luminous intensity is concentrated on the dielectric surface and the tip of the metal electrode. A 1D plasma fluid model is implemented by coupling the species continuity equations, electron energy density equations, Poisson equation, and Helmholtz equations to analyze the MD dynamics on the microscale. The simulated results are in good qualitative agreement with the experimental results. The simulated results show that the MD dynamics can be divided into three phases: the Townsend phase, the streamer propagation phase, and the discharge decay phase. During the streamer propagation phase, the electric field and electron density increase with the streamer propagation from the anode to the cathode, and their maximal values reach 625.48 Td and 2.31 × 1019 m−3, as well as 790.13 Td and 3.58 × 1019 m−3 in the positive and negative HP, respectively. Furthermore, a transient glow-like discharge is detected around the anode during the same period of streamer propagation. The formation of transient glow-like discharge is attributed to electrons drifting back to the anode, which is driven by the residual voltage in the air gap.     

中国茶叶品质危害因素分析及对策研究进展

近年来中国茶产业发展迅速,但因受不完善茶业体制和机制等因素影响,中国茶业一直未能完全摆脱来自农药残留、重金属、微生物及生物毒素等方面的安全危害,造成茶叶出口量和出口产值与国内茶叶资源在国际茶叶市场占有额不对称。本文围绕茶场生态环境、茶园管理、茶叶加工及贮运等方面阐述当前中国茶业发展中所面临的一些品质危害问题,并通过对茶叶质量安全法律体系、标准体系、危害评估和风险预警体系、质量控制体系、监管机制及人才培养等宏观体制、机制方面建设阐述解决目前存在问题的几点建议,旨在为未来中国茶业良性、快速、可持续发展提供一定理论参考依据。     

Pulsed gas–liquid discharge plasma catalytic degradation of bisphenol A over graphene/Cd S: process parameters optimization and O3 activation mechanism analysis

In the present work, pulsed gas–liquid hybrid discharge plasma coupled with graphene/Cd S catalyst was evaluated to eliminate bisphenol A(BPA) in wastewater. The optimization of a series of process parameters was performed in terms of BPA degradation performance. The experimental results demonstrated that nearly 90% of BPA(20 mg l^-1) in the synthetic wastewater(p H = 7.5,σ = 10 μS m^-1) was degraded by the plasma catalytic system over 0.2 g l^-1 graphene/Cd S at 19...     

平行磁场对脉冲针–板介质阻挡放电物理化学特性的影响EI北大核心CSCD

为在大气压下产生高强度的介质阻挡放电(dielectric barrier discharge,DBD)等离子体,该文利用永磁铁产生平行于电场方向的磁场,用于增强纳秒脉冲针–板DBD等离子体的物理化学活性,并探究不同脉冲参数下磁场对等离子体特性的影响规律和机制。考察平行磁场辅助脉冲针–板DBD等离子体的动态演化特性,并从电学、光学和臭氧生成特性等方面研究了脉冲电压幅值、上升沿时间和下降沿时间等参数对平行磁场辅助脉冲针–板DBD特性的影响规律。实验结果表明:平行磁场通过磁化电子改变DBD等离子体特性;施加平行磁场后,针–板DBD中空间流光放电及介质表面流光放电强度增强;不同脉冲放电参数下,施加平行磁场对放电强度及臭氧产量均显示出增强效果,在短脉冲上升沿时间条件下平行磁场的增强效果尤为显著。     

Generation of air discharge plasma in the cavities of porous catalysts: a modeling study

A study of the behaviors of air discharge plasma inside a catalyst’s pores is important to understand the plasma catalysis mechanism; however, few articles have reported the generation characteristics of air plasma in the pores of catalysts. The production of air microdischarge in a pore was studied by a two-dimensional fluid model, mainly focusing on the effect of pore size and applied voltage. The results show that an increase in the pore size in the range of 20–100 μm facilitates the occurren...     

三电极脉冲沿面介质阻挡放电等离子体特性及除冰研究

风力发电机和飞机在低温潮湿环境下运行时存在表面覆冰问题，进而影响装备的正常工作，严重时甚至危害人身财产安全。已有文献发现两电极沿面介质阻挡放电(surface dielectric barrier discharge,SDBD)在除冰方面有潜在的应用前景，但仍存在温升小和效率低等问题。为有效提高SDBD表面温度和除冰效率，该文将一接地电极安装在高压电极同侧，构成三电极SDBD结构，研究三电极脉冲SDBD等离子体特性及除冰过程与效果。结果表明：在相同的放电条件下，与两电极脉冲SDBD相比，三电极脉冲SDBD在放电能量、表面温度、发射光谱强度和除冰效果等方面表现出更为优异的能力。在20kV脉冲电压作用下，13mm间隙的三电极SDBD比两电极SDBD的放电能量增加了约1.95倍，最高温度提高了8℃。数值模拟结果也进一步表明：通过脉冲快速加热，三电极SDBD温升范围广和热量空间分布均匀，在除冰方面有很大的潜力。研究结果可为脉冲放电等离子体除冰及相关应用提供参考。