|
|
Study of Sterilization Effects Initiated by Dielectric Barriere Discharge
Slámová, Jitka ; Pekárek, Stanislav (referee) ; doc. RNDr. Karol Hensel, Ph.D., oponent (referee) ; Krčma, František (advisor)
The overall goal of the presented dissertation thesis was to study the sterilization efficiency of dielectric barrier discharge operated at atmospheric pressure. The fungi Aspergillus niger, gram-positive bacteria Bacillus subtilis and in some experiments also gram-negative bacteria Escherichia coli were used as a bio-indicator enabling to evaluate the effect of plasma assisted microbial inactivation. The samples of microorganism were placed on paper Whatman 1 or PET foil and exposed to plasma. The plasma was generated in argon, nitrogen, synthetic dry/humid air with frequency up to 10 kHz and plasma power density in the range of 1,2-2,9 W/cm3 (according to the process gas). The influence of process gas, plasma power density, plasma exposition time, type of microorganism and material of the substrate on the sterilization effect of dielectric barrier discharge was evaluated. Furthermore the contribution of each single mechanism (UV radiation, temperature and reactive species) to the sterilization effect of plasma and influence of gas humidity was evaluated. The DBD was analysed by means of optical emission spectroscopy, thermocouple was used to measure temperature during a sterilization process. In order to verify the mechanical damage of the microbial cell or the substrates during the plasma process the samples were studied by scanning electron microscopy. Generally, on the basis of experimental results, at increasing treatment times, the remaining number of spores (CFU) decreased. Similarly at increasing the plasma power input, the sterilization rate increased. When sterilising the spores of A. niger in plasma using different process gasses, the efficiency of plasma sterilization decreased as follows: argon, humid synthetic air, nitrogen and dry synthetic air. The results observed in argon plasma using different microorganism demonstrated that the sensitivity of vegetative cells resp. spores to DBD decreased as follows: A. niger spores, B. subtilis vegetative cells, E. coli vegetative cells and B. subtilis spores. Simultaneously results observed for sterilization of spores and vegetative cells of B. subtilis and A. niger demonstrated that the spores are generally more resistant to plasma than are the corresponding vegetative cells. Combining the results of contribution of each single mechanism, optical emission spectroscopy and inactivation characteristic it was found out that the reactive species significantly contribute to the plasma sterilization in all process gasses. Furthermore the inactivation process can be partly assisted by UV radiation and also the temperature can contribute in limited extent to inactivation process in some gasses. The contribution of UV radiation to the plasma sterilization decreased as follows: nitrogen, argon, dry syntetic air and humid syntetic air. Moreover it was found out that the contribution of each single mechanism can be species dependent, this is due to the different response of microorganism to the unfavorable external conditions. SEM analysis of the substrates prooved the etching actions of the plasma generated in all process gasses on the surface of the PET foil. The several minute plasma exposition of the PET foil resulted in the occurence of the „hole corrosion“ on the PET surface. Contrary to these there were no visible changes observed in the paper structure.
|
|
| |
|
|
Experimental Investigation of the Anode Area in the Hybrid Water-Gas DC Arc Plasma Torch
Ondáč, Peter ; Hrabovský, Milan (advisor) ; Pekárek, Stanislav (referee) ; Bartlová, Milada (referee)
This thesis focuses on an experimental study of the anode area of the hybrid water- gas DC arc plasma torch that is used in many industrial applications, including plasma spraying, hydrocarbon reforming, pyrolysis, and organic waste gasification. The effects of ambient pressure and plasma generation conditions on the torch's plasma jet were studied, with particular focus on the torch's anode area. Movement of the anode arc attachment is described in detail, including its speed, range of its motion on the anode surface, restrike periods, and the frequency of its many sudden decelerations and re-accelerations. It was found that the anode erosion can be compared relatively simply by quick processing of high-speed camera videos. The anode erosion was also measured directly. Many electric probe measurements were made in the anode area of this plasma torch for the first time. By using these electric probes, shock waves, turbulent vortices, and plasma potential fluctuations were studied directly. It was found that a mean plasma electric field and a mean plasma electrical conductivity in the anode area can be satisfactorily estimated also non-intrusively by quick processing of high-speed camera videos. Moreover, schlieren videos of the plasma jet in the anode area were created. 1
|
|
|
Hybridly stabilized arc as a tool for biomass gasification and the degradation of water-soluble organic compounds
Hlína, Michal ; Pacáková, Věra (advisor) ; Jelínek, Ivan (referee) ; Pekárek, Stanislav (referee)
(EN) A plasma torch (the source of plasma) with Gerdien arc was utilized as the source of energy in a reactor for gasification of biomass and for the degradation of organic compounds dissolved in water circling around the arc where the dissolved compounds are exposed to an intensive ultraviolet radiation. Thermal plasmas have electrons, ions and neutrals in thermal equilibrium and are quite often characterized by higher pressures and temperatures than nonthermal plasmas. Therefore, thermal plasmas generally carry a huge amount of energy which can be employed for heating and subsequent gasification of various types of materials. Thermal plasma gasification reactors are operated at higher temperatures than conventional reactors which results in a very good composition with a high percentage of hydrogen and carbon monoxide in produced synthetic gas. Spruce sawdust and spruce pellets were gasified at feeding rates up to 60 kg/h. Oxidizing media such as water, carbon dioxide, oxygen or their mixtures had to be added to the reactor during experiments to avoid the formation of solid carbon. The compositions of produced gas significantly corresponded to calculated compositions and the produced gas was of high quality - hydrogen content approximately 45 % vol., carbon monoxide approximately 48 % vol., a...
|
|
| |
|
| |
|
|
Study of Sterilization Effects Initiated by Dielectric Barriere Discharge
Slámová, Jitka ; Pekárek, Stanislav (referee) ; doc. RNDr. Karol Hensel, Ph.D., oponent (referee) ; Krčma, František (advisor)
The overall goal of the presented dissertation thesis was to study the sterilization efficiency of dielectric barrier discharge operated at atmospheric pressure. The fungi Aspergillus niger, gram-positive bacteria Bacillus subtilis and in some experiments also gram-negative bacteria Escherichia coli were used as a bio-indicator enabling to evaluate the effect of plasma assisted microbial inactivation. The samples of microorganism were placed on paper Whatman 1 or PET foil and exposed to plasma. The plasma was generated in argon, nitrogen, synthetic dry/humid air with frequency up to 10 kHz and plasma power density in the range of 1,2-2,9 W/cm3 (according to the process gas). The influence of process gas, plasma power density, plasma exposition time, type of microorganism and material of the substrate on the sterilization effect of dielectric barrier discharge was evaluated. Furthermore the contribution of each single mechanism (UV radiation, temperature and reactive species) to the sterilization effect of plasma and influence of gas humidity was evaluated. The DBD was analysed by means of optical emission spectroscopy, thermocouple was used to measure temperature during a sterilization process. In order to verify the mechanical damage of the microbial cell or the substrates during the plasma process the samples were studied by scanning electron microscopy. Generally, on the basis of experimental results, at increasing treatment times, the remaining number of spores (CFU) decreased. Similarly at increasing the plasma power input, the sterilization rate increased. When sterilising the spores of A. niger in plasma using different process gasses, the efficiency of plasma sterilization decreased as follows: argon, humid synthetic air, nitrogen and dry synthetic air. The results observed in argon plasma using different microorganism demonstrated that the sensitivity of vegetative cells resp. spores to DBD decreased as follows: A. niger spores, B. subtilis vegetative cells, E. coli vegetative cells and B. subtilis spores. Simultaneously results observed for sterilization of spores and vegetative cells of B. subtilis and A. niger demonstrated that the spores are generally more resistant to plasma than are the corresponding vegetative cells. Combining the results of contribution of each single mechanism, optical emission spectroscopy and inactivation characteristic it was found out that the reactive species significantly contribute to the plasma sterilization in all process gasses. Furthermore the inactivation process can be partly assisted by UV radiation and also the temperature can contribute in limited extent to inactivation process in some gasses. The contribution of UV radiation to the plasma sterilization decreased as follows: nitrogen, argon, dry syntetic air and humid syntetic air. Moreover it was found out that the contribution of each single mechanism can be species dependent, this is due to the different response of microorganism to the unfavorable external conditions. SEM analysis of the substrates prooved the etching actions of the plasma generated in all process gasses on the surface of the PET foil. The several minute plasma exposition of the PET foil resulted in the occurence of the „hole corrosion“ on the PET surface. Contrary to these there were no visible changes observed in the paper structure.
|
|
|
Atmosférický DC koronový výboj v N2-NO směsích: energetická účinnost a cena odstranění NO
Pekárek, S. ; Šimek, Milan
This paper focuses on de-NOX efficiency of the DC atmospheric pressure positive corona discharge enhanced by the flow of the mixture of nitrogen with traces of NO. The experimental findings indicate that the transformation of nitric oxide is controlled by the production of atomic nitrogen. For a particular energy density the NO decomposition increases with flow rate and higher NO removal is obtained for lower initial NO concentrations. Production of NO2 increases with increasing NO removal and NO removal energy cost for energy densities exceeding 2 kJ/m3 converges to about 100 eV/molecule. Providing that the removal of NO is predominantly driven by N atoms this would imply that the specific energy cost for the dissociation of N2 is approximately 200 eV/molecule.
|
|
| |
guest ::
RSS feed.