The effects of gas flow pattern on the generation of ozone in surface dielectric barrier discharge

Ozone production utilizing surface dielectric barrier discharge (SDBD) was experimental studied for different flow patterns considering the influences of transversal flow, lateral flow and different lateral flow positions. Results show that the flow patterns have a remarkable impact on the ozone yield by affecting the uniformity and turbulence of gas flow. Meanwhile, distributing the O₂ flow rate according to the intensity of the plasma reaction would also increase the generation efficiency of SDBD for ozone production. By improving the uniformity and introducing the lateral flow to the transversal flow, the highest ozone yield was obtained in flow pattern ‘F’. In this case, the ozone yield increased by 28.4% to 131 gkWh ⁻¹ from 102.8 gkWh⁻¹ in flow pattern ‘A’.     

细颗粒物声波团聚的微观机理研究

为拓展声波团聚机理,对声波团聚过程中的声流与声涡作用进行了理论和实验研究。利用声流测试系统,发现在0～1 kHz低频与5 kHz高频时,团聚室内声流现象较为明显;并通过可视化测试,在7 kHz高频时观察到明显的漩涡。结果表明,流场中的声流与声涡对颗粒团聚会产生很大的影响,声流或声涡越强,团聚效果越好。在0～1 kHz低频与5 kHz高频时,声流产生的切应力带动气溶胶颗粒发生碰撞团聚;高频时声涡力矩较大,其产生的轨道角动量带动粒子发生圆周和自旋运动;当声压级大于132 dB时,声涡团聚开始发挥作用,与声流一起促进颗粒团聚,且声压级越大团聚效果越强;与波节相比,波腹处的声流速度更大,声涡现象更明显,团聚效果也更好。     

空气源高频圆管型DBD臭氧产生的实验研究

电源频率和放电管长度是介质阻挡放电(DBD)臭氧产生的两个重要影响因素,在前期的研究基础上,采用合适的放电管长度和电源频率进行实验研究。实验研究了干空气源放电管长度、放电电压和气体流量对臭氧产生的影响,并进行了系统优化。研究结果表明:放电管长度由500 mm变为200 mm,在几乎不降低臭氧浓度下放电平均功率约降低了60%;臭氧浓度随放电电压和气体流量的增大先增大后降低;当流量为200 L/h、放电电压为2 698 V时,臭氧浓度与臭氧产率同时达到相对较高值,此时,臭氧浓度为5.3 g/m3时,臭氧产率为43.62 g/kWh。     

一种新型高温热电偶性能测试系统的研制

热电偶在高温使用时容易受到材料相容性、氧化等多种因素的影响,产生显著的不均匀性,需要对其进行性能测试,以进一步判断其测温准确度。研制了一种新结构的高温管式炉,控温热电偶布置方式有利于提高恒温段温度均匀性;在此基础上,搭建了一套高温热电偶测试系统,并对系统性能进行了理论模拟和实验研究。测试结果显示,在400~1000℃范围内,测试系统的温度稳定性优于±0.25℃;长度为150mm的恒温段的温度均匀性优于±0.35℃,表明测试系统的性能够满足热电偶性能测试的需求。     

混合放电臭氧发生器中臭氧产生过程的传热数值模拟

为揭示混合放电臭氧高效发生的电能转换和传热机理,采用有限体积法数值求解质量、动量和能量守恒方程,实现对混合放电臭氧发生进行传热分析,并实验验证了该方法的可行性。研究结果表明:气体进入两放电间隙后温度逐渐升高,且两放电间隙温度相差较大,内放电空间平均温度比外放电空间平均温度平均高6.38 K;中心电极、内电介质、外介电质和外电极各部分内部径向温差较小;混合放电仅36.14%的电能转换为热能,其中气体从3根放电管中携带的热量分别为9.85%,7.39%和4.78%,气体经过3根放电管后最高温度仅为313.2 K。混合放电电能转化率高、气体温度相对较低,是一种非常有前途的臭氧发生形式。     

SF6对介质阻挡放电臭氧生成的影响（英文）

The influence mechanism of a small amount of SF6 on ozone generation in oxygen or air discharge is investigated.Some results are obtained by probing into the number of the high-energy electrons,which have the sufficiency energy for generating ozone.Introducing a small amount of SF6 into oxygen sharply decreases the number of high-energy electrons,because the electron density decreases sharply while the mean electron energy remains constant due to higher breakdown voltage and lower discharge power,and some high-energy electrons are consumed by the excitation and attachment of SF6.In contrast,when a small amount of SF6 is added into dry air discharge,despite the consumption of the excitation and attachment of SF6,the number of high energy electrons increases sharply,which is attributed to the higher mean electron energy and electron density resulted from higher breakdown voltage and discharge power.When the volume fraction of SF6 increases from 0 to 2.22%,the ozone mass concentration and the ozone yield increase by 45.7% and 29.7%,respectively.Therefore,though the oxygen source should avoid the presence of SF6,adding a small amount of SF6 can improve the ozone mass concentration and the efficiency of ozone generation.     

Electron Transport Coefficients and Effective Ionization Coefficients in SF6-O2 and SF6-Air Mixtures Using Boltzmann Analysis

The electron drift velocity, electron energy distribution function （EEDF）, densitynormalized effective ionization coefficient and density-normalized longitudinal diffusion velocity are calculated in SF6-O2 and SFs-Air mixtures. The experimental results from a pulsed Townsend discharge are plotted for comparison with the numerical results. The reduced field strength varies from 40 Td to 500 Td （1 Townsend=10-17 V.cm2） and the SF6 concentration ranges from 10% to 100%. A Boltzmann equation associated with the two-term spherical harmonic expansion approximation is utilized to gain the swarm parameters in steady-state Townsend. Results show that the accuracy of the Boltzlnann solution with a two-term expansion in calculating the electron drift velocity, electron energy distribution function, and density-normalized effective ionization coefficient is acceptable. The effective ionization coefficient presents a distinct relationship with the SF6 content in the mixtures. Moreover, the E/Ncr values in SF6-Air mixtures are higher than those in SF6-O2 mixtures and the calculated value E/Ncr in SF6-O2 and SF6-Air mixtures is lower than the measured value in SFB-N2. Parametric studies conducted on these parameters using the Boltzmann analysis offer substantial insight into the plasma physics, as well as a basis to explore the ozone generation process.