Sterilization of Staphylococcus Aureus by an Atmospheric Non-Thermal Plasma Jet

An atmospheric non-thermal plasma jet was developed for sterilizing the Staphylococcus aureus （S. aureus）. The plasma jet was generated by dielectric barrier discharge （DBD）, which was characterized by electrical and optical diagnostics. The survival curves of the bacteria showed that the plasma jet could effectively inactivate 10 6 cells of S. aureus within 120 seconds and the sterilizing efficiency depended critically on the discharge parameter of the applied voltage. It was further confirmed by scanning electron microscopy （SEM） that the cell morphology was seriously damaged by the plasma treatment. The plasma sterilization mechanism of S. aureus was attributed to the active species of OH, N 2 ＋ and O, which were generated abundantly in the plasma jet and characterized by OES. Our findings suggest a convenient and low-cost way for sterilization and inactivation of bacteria.

Numerical study of the effect of coflow argon jet on a laminar argon thermal plasma jet

The effects of the velocity and width in coflow argon jet inlet on the flow characteristics of laminar argon thermal plasma jet flowing into the cold air have been studied by the large eddy simulation methods. The Kelvin–Helmholtz instability between argon thermal plasma jet and coflow argon jet causes the transition from a laminar jet to a turbulent jet in the presence of coflow argon jet. Moreover, increasing the velocity and width in coflow argon jet inlet can enhance turbulent transport and provoke coherent structure in the downstream of thermal plasma jet. And the mixing characteristics between argon thermal plasma, coflow argon and ambient air are strengthened. In addition, the width in coflow argon jet inlet has a significant effect on the distribution of temperature in the upstream of thermal plasma jet. It was also found that the transition occurs in advance with the increase of velocity and width in coflow argon jet inlet.

Large eddy simulation on the flow characteristics of an argon thermal plasma jet

Large eddy simulations based on the CFD software Open FOAM have been used to study the effect of Reynolds number and turbulence intensity on the flow and mixing characteristics of an argon thermal plasma jet.Detailed analysis was carried out with respect to four aspects:the average flow field,the instantaneous flow field,turbulence statistical characteristics and the selfsimilarity.It was shown that for the argon thermal plasma jet with low Reynolds number,increasing the turbulence intensity will increase the turbulent transport mechanism in the mixing layer rather than in the jet axis,leading to the faster development of turbulence.The effect of the turbulent transport mechanism increases with increasing Reynolds number.However,the characteristics of flow and mixing are not affected by turbulence intensity for high Reynolds number situations.It was also found that the mean axial velocity and mean temperature in the axis of the turbulent thermal plasma jet satisfy the self-similarity aspects downstream.In addition,decay constant K is 1.25,which is much smaller than that(5.7-6.1)of the turbulent cold gas jet and has nothing to do with the Reynolds number or turbulence intensity in the jet inlet.

Application of CCD Cameras to Investigations of Mixing on Boundaries of a Thermal Plasma Jet

Mixing of a thermal plasma jet with the surrounding atmosphere was studied using two CCD cameras （PCO SensiCam） situated detecting simultaneously the radiation of argon and nitrogen. The evaluation of image differences between two records showed that the location of regions on plasma jet boundaries characterised by stronger nitrogen radiation changes with the plasma flow rate. Close-to-laminar flow results in a small mixing rate and consequently low nitrogen optical emission on plasma jet boundaries. The increase of the flow rate leads to the formation of a relatively thick and stable layer on the boundaries characterised by strong nitrogen radiation. Further enhancement of the flow rate results in the formation of unstable regions of excited nitrogen molecules moving along the jet.

Quasi-direct numerical simulations of the flow characteristics of a thermal plasma reactor with counterflow jet

Three-dimensional quasi-direct numerical simulations have been performed to investigate a thermal plasma reactor with a counterflow jet. The effects of the momentum flux ratio and distance between the counterflow jet and the thermal plasma jet on the flow characteristics are addressed. The numerical results show that the dimensionless location of the stagnation layer is significantly affected by the momentum flux ratio, but it is not dependent on the distance.Specifically, the stagnation layer is closer to the plasma torch outlet with the increase of the momentum flux ratio. Furthermore, the flow regimes of the stagnation layer and the flow characteristics of the thermal plasma jet are closely related to the momentum flux ratio. The characteristic frequencies associated with the different regimes are identified. The deflecting oscillation flow regimes are found when the momentum flux ratio is low, which provokes axial velocity fluctuations inside the thermal plasma jet. By contrast, for cases with a high momentum flux ratio, flapping flow regimes are distinguished. The thermal plasma jets are very stable and the axial velocity fluctuations mainly exist in the stagnation layer.

Effects of deposition parameters on microstructure and thermal conductivity of diamond films deposited by DC arc plasma jet chemical vapor deposition

The uniform diamond films with 60 mm in diameter were deposited by improved DC arc plasma jet chemical vapor deposition technique. The structure of the film was characterized by scanning electronic microcopy(SEM) and laser Raman spectrometry. The thermal conductivity was measured by a photo thermal deflection technique. The effects of main deposition parameters on microstructure and thermal conductivity of the films were investigated. The results show that high thermal conductivity, 10.0 W/(K·cm), can be obtained at a CH4 concentration of 1.5% (volume fraction) and the substrate temperatures of 880-920 ℃ due to the high density and high purity of the film. A low pressure difference between nozzle and vacuum chamber is also beneficial to the high thermal conductivity.

Bacteria Inactivation Using DBD Plasma Jet in Atmospheric Pressure Argon

A coaxial dielectric barrier discharge plasma jet was designed, which can be operated in atmospheric pressure argon under an intermediate frequency sinusoidal resonant power supply, and an atmospheric pressure glow-like discharge was achieved. Two kinds of typical bacteria, i.e., the Staphylococcus aureus （S. aureus） and Escherichia coil （E. coil）, were employed to study the bacterial inactivation mechanism by means of the non-thermal plasma. The killing log value （KLV） of S. aureus reached up to 5.38 with a treatment time of 90 s and that of E. coil up to 5.36 with 60 s, respectively. According to the argon emission spectra of the plasma jet and the scanning electron microscope （SEM） images of the two bacteria before and after the plasma treatment, it is concluded that the reactive species in the argon plasma played a major role in the bacterial inactivation, while the heat, electric field and UV photons had little effect.

Experimental study on bacteria disinfection using a pulsed cold plasma jet with helium/ oxygen mixed gas

Cold atmospheric plasma jet is widely used in many fields due to the reactive oxygen species and low temperature for heat-sensitive products. This paper presents the inactivation of bacteria via a pulsed plasma jet with He/O2 mixed gas. To evaluate the disinfection performance, Staphylococcus aureus was used as an indicator bacteria for experiments. When the plasma jet dealt with agar plates spraying bacteria, it was found that mixed gas has a better performance than pure inert gas, indicated by the disinfection area. The increment of oxygen gas addition was beneficial to the disinfection ability of the plasma jet, while the gas had an opposite effect on the length of jet production. The experiments showed the efficacy of Staphylococcus aureus disinfection could reach up to 99.47% via a helium/oxygen （2%） plasma jet.

Influence of the Laminar Plasma Torch Construction on the Jet Characteristics

Based on two typical laminar plasma torches （LPT）, i.e. a multi-electrode plasma torch （MEPT） with segmented anode structure and a two-electrode plasma torch （TEPT） with conventional structure, this paper studied the influence of the LPTs construction on the jet characteristics. Experiments were designed to measure their arc voltage, jet length, thermal efficiency and specific enthalpy using a home-made data acquisition system. With them, the jet characteristics of the two different LPTs were compared in detail. Results show that different plasma torch construction leads to distinctively different characteristics of the generated plasma jet. Based on the different jet characteristics, a plasma torch with appropriate construction could be used to meet the different application requirements.

Efficacy of Atmospheric Pressure Plasma as an Antibacterial Agent Against Enterococcus Faecalis in Vitro

Enterococcus faecalis （E. faecalis） is a microorganism that can survive extreme challenges in obturated root canals. The aim of this study was to evaluate the efficacy of a non-thermal atmospheric pressure plasma plume against E. faecalis in vitro. A non-thermal atmospheric pressure plasma jet device which could generate a cold plasma plume carrying a peak current of 300 mA was used. The antibacterial efficacy of this device against E. faecalis and its biofihn un- der different conditions was detected. The antibacterial efficacy of the plasma against E. faecalis and Staphylococcus aureus （S. aureus） was also evaluated. After plasma treatment, the average diameter of inhibition zone on S. aureus and E. faecalis was 2.62±0.26 cm and 1.06±0.30 cm, respectively （P 〈 0.05）. The diameter was increased with prolongation of the treatment dura- tion. The diameters of inhibition zone of the sealed Petri dishes were larger than those of the uncovered Petri dishes. There was significant difference in colony-forming units between plasma group and control group on E. faecalis biofilm （P 〈 0.01）. The transmission electron microscopy revealed that the ultrastructural changes eytoderm of E. faecalis were observed after treatment for 2min. It is concluded that the non-thermal atmospheric pressure plasma could serve as an effective adjunct to standard endodontie microbial treatment.

等离子体射流产生与特性的实验研究

本文报道热等离子体射流产生及射流特性的实验研究结果。采用同一个直流等离子体发生器,工作气体流量小时产生出层流等离子体长射流,射流长度随气体流量或弧电流的增加而明显增加;工作气体流量大时则产生出湍流等离子体短射流,此时射流长度几乎与工作气体流量或弧电流无关;在层流与湍流等离子体射流工况之间,存在一个流动状况不稳定的过渡区,此时等离子体射流的平均长度随气流量的加大而减小,但随弧电流的加大而明显加大。层流等离子体长射流有相当好的刚性。

热等离子体射流温度与放电功率和气体流量的定标关系

利用氮系统的高温热力学函数Cp,m,结合热量计算公式及能量平衡关系,在理论上得到热平衡等离子体射流温度与放电功率和气体流量的定标关系。结果表明,该过程满足相似性原理,射流温度不是功率和流量的一般二元函数,而是比值Peff/f的一元函数。并对结果进行了相关的分析和讨论,为热等离子体的应用提供了参考数据。

Ar气中1维等离子体射流阵列的实验研究

为获得大面积射流等离子体,建立了大气压Ar气中1维等离子体射流阵列产生装置。通过电压电流波形、发光图像以及发射光谱等手段诊断了其放电特性,研究了外加电压幅值、气体流速和电源频率等对射流阵列产生的影响,得到了阵列最优工作条件,并获得此条件下阵列的放电功率和传输电荷和活性粒子等参数,进而分析了放电的排斥和耦合机制。发光图像拍摄的结果表明:外加电压幅值为8.5 k V,气体体积流量为20 L/min,电源频率20 k Hz时,射流阵列等离子体喷出管口最长,各管间排斥作用和耦合作用最小,放电最强烈,此时放电功率为101.85 W,传输电荷为1 716 n C。阵列中各管间彼此存在Coulomb力和Lorentz力,出现一定偏移是这2个力综合作用的结果。

大气压Ar/H_2O等离子体射流的放电特性

为促进大气压Ar／H2O等离子体射流放电在材料表面改性、等离子体医学及环境工程等方面的应用，研究了大气压Ar／H2O等离子体射流放电模式和放电参量。测量了这种射流在不同外加电压下的电气特性、发光特性及光谱特性，并据此计算得到主要放电参量，如放电功率、传输电荷、电子激发温度、分子振动温度以及转动温度等随外加电压的变化规律。结果表明：随着外加电压的增大，大气压Ar／H2O等离子体射流放电模式可分为电晕放电、介质阻挡放电和射流放电3个阶段，并可通过电压电流波形图和发光图像进行区分。Ar／H2O等离子体射流产生的粒子主要有Ar、OH以及少量的O和N2等。随着外加电压的增大，放电功率、传输电荷及主要粒子（包括OH）的谱线强度都随着外加电压的增大而增大。当外加电压从7kV增加到9．5kV时，分子振动温度和转动温度随着外加电压的增大而增大，其变化范围分别为1000－2200K和350-550K。当外加电压为9．5kV时，电子激发温度为0．646eV。

热等离子束照射工业纯钛快速渗氮制备表面氮化层

以热等离子束作为等离子源,以氮气、氢气混合气体作为工作气体,对工业纯钛进行表面渗氮处理,并利用显微硬度仪、X射线衍射仪、扫描电镜、金相显微镜分别对氮化后试样进行显微硬度测定、相结构及断面形貌分析。结果表明:在等离子束对试样进行15min的照射后即可在工业纯钛(TA_2)表面获得具有一定厚度的硬度较高的氮化层。

减压直流等离子体射流电子温度的双静电探针测量

建立了一套双静电探针诊断系统,用于检测在气流量为4.2 slm、弧电流为80 A、真空室压力为165Pa的条件下纯氩直流非转移弧等离子体射流的电子温度及其分布。结果表明:发生器出口处射流中心的电子温度约为14 500 K,射流中电子温度随离开发生器出口的轴向或径向距离的增加而单调降低;径向电子温度梯度约为263 K/mm,轴向电子温度梯度为69 K/mm;射流中电子温度随弧电流增加而单调上升。

层流与湍流等离子体冲击射流特性比较

本文采用数值模拟方法,对层流与湍流氩等离子体射流在空气环境中冲击平板时的流动与传热特性进行了对比研究。结果表明,在平板和射流进口间的距离较大时,平板的存在只对其附近的射流参数分布有较大影响,层流等离子体冲击射流的温度与轴向速度的轴向梯度明显小于湍流等离子体冲击射流情形;由于在平板表面形成的径向壁面射流对引射的附加贡献,层流和湍流等离子体冲击射流对环境空气的引射量明显增加。

高超飞行器表面热效应地面模拟实验研究

文章深入分析高超飞行器与临近空间大气相互作用的基本物理过程,激波加热及粒子碰撞产生等离子体的物理机制,并利用磁热屏蔽效应在高超飞行器模拟器与高速定向流间建立磁化等离子体鞘层,大幅降低中性激波气体向飞行器的能流传递,从而为高超飞行器提供有效的热防护作用。通过两次比对实验验证了磁热屏蔽效应的有效性及工程实施的可行性,为今后研制高韧性、超轻质、可重复使用热防护复合材料提供了实验数据,奠定了技术基础。实验中利用层流等离子体源作为高能流密度热源是热防护实验装备上的创新,层流等离子体源能流截面大、能流密度高,可以针对高超飞行器表面热效应进行全尺寸的模拟实验。

毛细管放电及其对发射药作用的仿真模型综述

为深入研究毛细管放电等离子体特性及其与发射药的相互作用机理,综述了电热化学发射系统中的相应仿真模型,从毛细管放电,等离子体射流和等离子体与发射药相互作用3个角度,介绍了烧蚀模型、毛细管等离子体磁流体动力学模型、等离子体射流模型、等离子体与发射药作用的传热学模型和化学动力学模型,并比较了不同模型的优缺点。结果表明:综合考虑温度与压强影响的动力学烧蚀模型可准确描述毛细管放电中的瞬态烧蚀过程;毛细管放电等离子体发生器的出口温度和密度在径向呈显著的不均匀分布,因此需要2维的毛细管放电模型;在等离子体射流模型和等离子体与发射药相互作用模型中,等离子体与空气和发射药的化学反应不能忽略。在下一步的研究中,磁流体动力学模型与化学动力学模型的结合,可准确预测电热化学发射系统中发射药的点火特性。

热等离子条件下Fe_2O_3催化裂解甲烷制备纳米炭纤维

以Fe2O3粉末为催化剂,N2,H2混合气体为等离子工作气,常压条件下裂解甲烷制得不同类型的纳米炭纤维。利用SEM、TEM、热重、XRD和拉曼光谱等表征手段揭示甲烷流量对纳米炭纤维(CNFs)形貌、纯度和结晶度的影响。结果表明:甲烷流量为0.3m3/h时,产物形貌为结晶度良好的空心套杯状纳米炭纤维,甲烷流量加大至0.5m3/h后,所得产物掺杂有大量的竹节状纳米炭纤维和带有颗粒的空心管,所得的纳米炭纤维的纯度下降。