Xian-Jun Shao

Effect of Low-Temperature Plasma on Microorganism Inactivation and Quality of Freshly Squeezed Orange Juice

Dielectric barrier discharge is used to generate low temperature plasma (LTP) for the treatment of freshly squeezed orange juice, which was inoculated with and without three kinds of microorganisms, respectively. Four experiments were designed and conducted: 1) When freshly squeezed orange juice samples inoculated with either Staphylococcus aureus, Escherichia coli, or Candida albicans were treated with LTP for 12,8, and 25 s, respectively, the numbers of each microorganism decreased more than 5 logs; 2) when orange juices without the aforementioned microor ganism inoculation were treated with LTP for inactivating original microorganisms inside and then stored at 4°C refrigeration, the total plate count and the proliferation rate of original microor ganism were both reduced significantly (counting per each 4-d during storage); 3) when orange juice samples without microor ganism inoculation were treated with LTP, the LTP treatment had insignificant effect on the values of vitamin C, total acid, turbidity,°Brix, and pH of orange juice; 4) when orange juice samples were inoculated with S. aureus, E. coli, or C. albicans, respectively, and their pH values were slightly decreased by adding HC1 (similar to that after LTP treatment), there was no obvious inactivation effects due to the reduction of pH values. It was proposed that microorganism inactivation was mainly due to reactive species and charged particles instead of slight pH reduction, and LTP treatment was able to effectively inactivate microbes and maintain the quality of orange juice.

Comparative study on the atmospheric pressure plasma jets of helium and argon

Formation mechanisms for atmospheric pressure plasma jets (APPJ) of He and Ar are investigated by comparing the discharge current, light emission from jet, and time-resolved image of the discharge. A longer jet of He (Ar) is available with active (ground) electrode sitting at downstream side. The jet of He outside active electrode arises from corona discharge, while that of Ar outside ground electrode results from charge overflow, and can be diffusive or filamentous in different phases of the applied voltage. The underlying mechanisms are discussed. These results can be helpful for the further mechanism investigation and implementation of APPJs.

Research on Surface Modification of Polytetrafluoroethylene Coupled With Argon Dielectric Barrier Discharge Plasma Jet Characteristics

An argon dielectric barrier discharge (DBD) atmospheric-pressure plasma jet (APPJ) is designed and employed for surface modification of polytetrafluoroethylene (PTFE). The plasma diagnostics and dielectric surface analysis are coupled together to investigate the mechanisms of plasma modification. The discharge power is obtained by Lissajous figure, and electron excitation temperature (EET) is measured through an optical emission spectrum and calculated by a Boltzmann diagrammatic method. The surface properties of modified PTFE samples are characterized by the static contact angle, surface resistivity, scanning electron microscope (SEM), and X-ray photoelectron spectroscopy. The results show that the discharge power, EET, and surface wettability increase with the Ar flowing rate, and a slight decrease of surface resistivity is revealed after plasma treatment. The surface roughness of PTFE is enhanced, and the oxygen-containing hydrophilic groups are incorporated by the impacts of APPJ radical species. Moreover, the hydrophilicity of PTFE can be improved by a surface presanding process, particularly after APPJ treatment. Finally, the surface modification mechanisms of APPJ on PTFE are discussed.

Experimental and Numerical Investigation on the Interaction Between Ar Flow Channel and Ar Plasma Jet at Atmospheric Pressure

In this paper, the interaction between Ar flow channel and atmospheric pressure plasma jet (APPJ) is investigated quantitatively by combining 3-D species transport simulation and optical schlieren observation together. The turbulence model, gravity force, and electrostatic force model are included into the Ar flow channel simulation. It is found that, with the increment of the Ar flow rate, the plasma plume reaches the maximum length at 3.5 L/min and then decreases sharply, which is corresponding to the Ar flow status. The simulations of the Ar flow channel show good agreement with the captured schlieren images. At small flow rates, the Ar flow channel bends downward due to the gravity. Under laminar flow, the high Ar mole fraction region near the axis of the Ar flow channel increases with the flow rate. However, the Ar flow presents as twist and radial diffusion, and the Ar mole fraction decreases rapidly when the Ar flow transits into turbulence, which leads the length of the Ar plasma plume to decrease sharply correspondingly. The plasma plume bestows the Ar flow channel a forward momentum, which decreases the curvature of bending downward and reinforces the twist and instability of the Ar flow channel under turbulence flow. By coupling the optical emission spectra and flow channel investigation together, it is revealed that Ar APPJ propagates along the core of the conelike flow channel. The Ar mole fractions at the head of the plasma plume are about 0.985 and 0.45 under laminar and turbulence flow, respectively.

Investigation on Spurt Length of Atmospheric-Pressure Plasma Jets

Three kinds of electrode configurations are employed for studying the spurt length of atmospheric-pressure plasma jets (APPJs). The influences of Ar flow rate, applied voltage, and electrode width on APPJ length are investigated. It is found that, for all the electrode configurations, the maximal length of the APPJ is achieved at 3 L/min of flow rate. With the increase of the applied voltage, the length of the APPJ increases and gradually tends to saturation. Furthermore, the APPJ propagation turns shorter under a wider wrapped electrode. It is considered that the variation of the APPJ length is attributed to the combination effects of Ar flow status, the amount of high-energy particles at the ionization front, and the memory effect of charges on dielectric surfaces.

Localization of multiple partial discharge sources in air-insulated substation using probability-based algorithm

Ultra-high-frequency (UHF) sensing technique has been introduced to detect and localize partial discharge (PD) sources in air-insulated substation (AIS). This paper presents a probability-based algorithm to localize multiple PD sources which may occur simultaneously in different power equipment. Assuming that the time difference of arrival (TDOA) between all pairs of antennas in a array are normally distributed, the probability density function (PDF) of PD source coordinates can be obtained by substituting the linearized form of time difference equations into PDFs of TDOAs. When large number of PD signals are recorded, the joint PDF (JPDF) can be calculated from the product of PDF of each TDOA. Then the PD coordinates to be solved are regarded as with highest probability, and can be solved by taking the derivative of JPDF. In the case of multiple PD sources, mixed UHF signals are separated by clustering the TDOA vectors with K Means clustering method. PD experiments are performed to test the presented algorithm, and the localization accuracy of proposed algorithm is compared with other typical methods such as Newton-Raphson, Particle Swarm Optimization and plane intersection method. The results indicate that the probability-based localization algorithm reasonably integrates the TDOAs of continuous signal sequence, which can effectively reduce the influence of TDOA estimation errors and improve the localization accuracy.

One-Dimensional Modeling of Dielectric Barrier Discharge in Xenon

A 1-D fluid model coupled with an external circuit is proposed to study the Xe dielectric barrier discharge (DBD) under a 50-kHz ac sinusoidal voltage. The impact of ions and photons on barrier surfaces and the thermal motion of charged particles in the sheath are taken into account in this model. The spatial and temporal distributions of electrons, ions, and excited, resonance, and metastable particles are investigated. The experimental investigations on discharge current densities under different voltage source amplitudes are analyzed and compared with simulation results. The results reveal that, with the increment of voltage source amplitudes, the waveforms of gas gap voltage and discharge current all move forward the applied voltage, showing a gradually decreased phase shift, which is in good agreement with the experimental observations. The evolution of surface charges accumulated on dielectric barriers can be divided into six stages during an ac cycle, and they play a key role in the ignition and extinction of the discharge. It is concluded that, while the charge difference between the surfaces of a two-side dielectric is up to a certain value and the applied voltage is low enough, the gas breakdown will occur. The spatiotemporal variations of particle densities and electric field indicate that the Xe DBD under the conditions considered in this paper is a typical glow discharge. Furthermore, the electron emission brought by impact of photons on dielectric surfaces can accelerate gap breakdown and strengthen the intensity of the discharge, and the sheath phenomenon is more obvious under the consideration of thermal motion of charged particles in boundary conditions.

Cathode-like luminescence from vacuum-dielectric interface induced by self-stabilizing secondary electron emission

A kind of interesting luminescence phenomenon from vacuum-dielectric interface under high electric field is presented in this Letter. It is visible, steady, and continuous, occurring before or accompanied with flashover across dielectric, which is quite different from general electroluminescence from insulator surface reported before. By investigating its optical and electrical characteristics, we consider it as cathode-like luminescence, which is initialized by the field electron emission from cathode triple junction and finally generated by the process of radiative recombination due to the self-stabilizing secondary electron emission and collision on insulator surface.

Partial discharge signals separation using cumulative energy function and mathematical morphology gradient

Partial discharge (PD) measurement and interpretation have become a powerful tool for condition monitoring and failure risk assessment of high voltage power equipment insulation. The occurrence of multiple discharge sources affects interpretation accuracy. This paper presents a PD signal separation algorithm using cumulative energy (CE) function parameters clustering technique. The waveform of PD signals are acquired by digital detection instruments with high sampling rate. Cumulative energy functions in time domain (TCE) and frequency domain (FCE) are calculated from PD waveforms and their FFT spectrums, respectively. Mathematical morphology gradient (MMG) operation is applied to the TCE and FCE to describe their variation characteristics. The feature parameters including width, sharpness and gravity are extracted from CEs and MMGs in both time and frequency domain, and compose a six-dimension feature space. The improved density-based spatial clustering of applications with noise (IDBSCAN) clustering algorithm is adopted to discover clusters in the feature space. The proposed separation algorithm is examined with mixed current impulse signals acquired from PD experiments on artificial multi-defect models and an on-site transformer. The separation results indicate that the proposed algorithm is effective for separating mixed PD signals initiated from multiple sources.

Effect of Low-Temperature Plasma on Deactivation of Hepatitis B Virus

In recent years, low-temperature plasma (LTP) has been widely applied in biological and medical fields. This paper is aimed to investigate the deactivation effect of LTP on hepatitis B virus (HBV). Dielectric barrier discharge (DBD) is employed to generate the atmospheric-pressure LTP for treatment of HBV. HBV serum collected from hepatitis B patients with HBsAg, HBeAg, and anti-HBc positive is used as the treatment model. LTP treatment time intervals are set as 10, 20, 30, and 40 s, respectively. Concentrations of HBsAg and S/N value for each different treatment are calculated. The liver function and HBV deoxyribonucleic acid (DNA) copy number are also detected. It is found that, compared with the control group, the concentrations of HBsAg and HBV DNA copy number of different treatment groups have statistically significant differences. With time going of LTP treatment, both the concentration of HBsAg and the copy number of HBV DNA gradually decrease, and all the S/N values are less than 2.1, indicating that HBsAg becomes negative after LTP treatment. Comparing the liver functions (i.e., enzymatic, proteinic, and bilirubin indicators) before and after LTP treatment, all the data are in the range of normal reference values. It is concluded that LTP induced by DBD is effective for HBV deactivation, and the liver function is kept normal during the process of plasma killing HBV.