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Diagnostics of diaphragm discharge in liquids
Dřímalková, Lucie ; Krčma, František (referee) ; Kozáková, Zdenka (advisor)
The main goal of this thesis is the diagnostics of the diaphragm discharge generated in liquids. Although many applications of electric discharge in liquids have been developed during the last years, the exact mechanism of the discharge ignition is not sufficiently known up to now. Based on this reason, this work focused on the investigation of processes before the discharge ignition, breakdown parameters and the discharge itself both in the irregular and stable regime. Using two kinds of inorganic salt solutions the work studied the influence of conductivity and electrolyte kind on the diaphragm discharge and its static current-voltage characteristics. The last task of the work investigated the emission spectra produced by the discharge. The theoretical part of the work presents mechanisms of the discharge generation in gases including the description of particular kinds of known discharges. The base theories of the discharge ignition in liquids are mentioned as well. Experiments were carried out in the reactor divided by the dielectric barrier (diaphragm) with a central pin-hole into two electrode spaces. Diaphragm was made of PET and the pin-hole initial diameter was 0.4 mm. Stainless steel electrodes were installed in the same distance of 2 cm from the barrier and symmetrically with respect to the diaphragm. Time resolved characteristics of current and voltage were recorded using two-channel oscilloscope which detected their output values. Parameters were measured by the constantly increasing DC voltage with a step of 50 V. When the regular discharge was ignited voltage had been gradually decreased. Used solutions contained sodium sulphate or sodium phosphate electrolyte at six different conductivities. Radiation emitted by the discharge was recorded by the spectrometer Jobin Yvon TRIAX 550. Emission spectra were investigated for one electrolyte at two different conductivities. The part with results presents all dependencies that were achieved during the measurements and all obtained data are compared. Recorded time resolved characteristics determine breakdown moment and describe current and voltage in particular parts within the static current-voltage curve. The work compares the influence of conductivity change on current-voltage characteristics as well as the effect of inorganic salt kind. By the conductivity enhancement the measured curve moves towards lower voltage which means that the breakdown voltage is decreased. Changing the inorganic salt the change of voltage related to the creation of bubbles in the diaphragm surroundings is observed. However, the change of electrolyte does not induce any significant change of the breakdown voltage. The last part of the work was focused on the optical emission spectroscopy of the discharge. Typical line system of OH radicals was identified in measured spectra which intensity was not dependent on the salt concentration. The work show particular processes taking place in the diaphragm surroundings when DC voltage is applied on the electrodes in electrolyte up to the diaphragm discharge ignition. Further, results describing the influence of conductivity and electrolyte changes on the processes are presented. The breakdown moment of the discharge and its dependence on the solution conductivity was determined. Optical emission spectroscopy revealed the contents of radiation emitted by the discharge.
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Electric characteristics of the diaphragm discharge in electrolyte solutions
Dřímalková, Lucie ; Slavíček, Pavel (referee) ; Kozáková, Zdenka (advisor)
The main object of this thesis is the diagnostics of the diaphragm discharge generated in water solutions containing supporting electrolytes (mostly NaCl), and description of particular processes before and after discharge breakdown by DC non-pulsed voltage up to 2 kV. Although many applications of electric discharge in liquids have been developed during the last years, the exact mechanism of the discharge ignition is not sufficiently known up to now. Based on this reason, this work is focused on the investigation of processes before the discharge ignition, breakdown parameters and the discharge itself both in the irregular and stable regime. The theoretical part of the work presents proposed mechanisms of the discharge generation in water solutions including the description of particular kinds of known discharges. Diaphragm discharge is one of many possible configurations of electrical discharges in liquids. In fact, electrical discharge in water forms non-thermal plasma, which is generated by high voltage, and many physical and chemical processes are started in plasma channels (so-called streamers). Among physical processes, high electrical field, shock waves and last but not least emission of electromagnetic radiation in visible and ultra-violet radiation belongs. The most important chemical processes are generation of various active species as hydrogen peroxide, and OH radical. Three batch plasma reactors using a diaphragm configuration with different total volume (4 l, 100 ml and 50 ml) are employed in the presented work. The discharge is created in an orifice (a pin-hole) in the dielectric barrier separating two electrode parts of the reactor. DC non-pulsed high voltage up to 4 kV is used for the discharge generation. Electrodes are made of stainless steel or platinum, and they are installed in parallel to the diaphragm in a variable distance from the dielectric barrier in each reactor part. The dielectric barrier is made of PET or Shapal-MTM ceramics with the variable thickness (0.2?2 mm). One pin hole st the diaphragm center with diameter of 0.2?1.5 mm are used in contemporary experiments. Time resolved characteristics of current and voltage are recorded using four-channel oscilloscope which detected their output values. Parameters are measured by the constantly increasing DC voltage with a step of 100 V. The solutions containing sodium chloride electrolyte are used at five different conductivities. Recorded time resolved characteristics determine breakdown moment, and describe current and voltage in particular parts within the static current-voltage curve. The breakdown appeared at lower applied voltage when the electrode distance is enhanced. However, the electrode distances higher than 4 cm does not induce any significant change of the breakdown voltage. The influence of pin-hole diameter is less obvious in the studied range, but a slight enhancement of breakdown voltage is observed with the increasing pin-hole diameter. Current-voltage characteristic curve moves towards lower voltage with the diaphragm thickness enhancement. The work compares the influence of conductivity change on current-voltage characteristics as well as the effect of inorganic salt kind. By the conductivity enhancement, the measured current-voltage curve moves towards lower voltage which means that the breakdown voltage is decreased. Sizes of the reactors do not have any effect on the processes before and after discharge breakdown.
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Diagnostics of Diaphragm Discharge in Water Solutions and its Application for the Nanomaterials Surface Treatment
Dřímalková, Lucie ; Brablec, Antonín (referee) ; Janda,, Mário (referee) ; Krčma, František (advisor)
The exact mechanism of the discharge in liquids ignition is not sufficiently known up to now. Although during the last years was achieved the great progress and overloading which some of them are written in this theoretical part of thesis. This thesis is divided into two experimental parts. When the first part deals with diagnostics of diaphragm discharge in electrolyte solutions and the second part is focused on its use for uncoiling (higher homogenization) of carbon nanotubes in solutions. In experiment 1, three different sized (4 l, 100 ml, 50 ml) diaphragm discharge configurations were used to diagnose diaphragm discharge in electrolyte solutions. Diagnostics is done through current and voltage waveforms with the addition of synchronized ICCD camera images that have been connected to a four-channel oscilloscope. The V-A characteristic can be described by three events occurring in the electrolyte solution with a gradual increase in voltage. Slowly increasing of the voltage in the solution leads first to electrolysis. The next phase is the formation of microbubbles or bubbles, which is characteristic of the curve by a slight decrease in the increase of the current passing between electrodes. The sudden increase in the current flow is characteristic of the last phase, namely the discharge phase. The distance of the electrodes from the diaphragm does not significantly affect the V-A characteristic. The higher diameter of the pin hole, therefore, has a higher voltage, but this does not affect the origin of bubble generation or breakdown. The higher thickness of diaphragm, the higher voltage is needed to the beginning of the bubbles generation, and consequently the discharge breakdown. Comparison of the voltage of the start generation of the bubbles and breakdown for PET diaphragms and diaphragms from the ceramic there was no mark able difference. One of the most important parameters is the conductivity of the electrolyte solution. The lower voltage is needed for the start generation of the bubbles at the higher solution conductivity, and also the discharge generation is observed at a lower breakdown voltage. The second experimental part is focused on the study of the diaphragm discharge effect on carbon nanotubes. A specially designed U-shaped reactor is used to modify carbon nanoparticles. Tap water and aqueous solutions of organic compounds are used as the electrolytic solutions. The discharge is generated by a non-pulsed DC high source with a voltage in the range of 0-2.8 kV supplied to platinum electrodes located in the electrolyte solution. The experimental results have shown that the diaphragm discharge has positive effects on the disintegration of clusters and agglomerates of carbon nanotubes. The primary effect on disintegration is probably the shock waves generated by the discharge. It turned out that it depends on the electrode configuration, where the treatment in anode space has far greater effects than the treatment in cathode half of the reactor. Effects of carbon nanotubes disintegration in solution are long-lasting and the treatment effect is not loosed after several months. There were detected no significant changes in the structure of plasma-treated nanotubes by Infra-red spectroscopy.
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Diagnostics of Diaphragm Discharge in Water Solutions and its Application for the Nanomaterials Surface Treatment
Dřímalková, Lucie ; Brablec, Antonín (referee) ; Janda,, Mário (referee) ; Krčma, František (advisor)
The exact mechanism of the discharge in liquids ignition is not sufficiently known up to now. Although during the last years was achieved the great progress and overloading which some of them are written in this theoretical part of thesis. This thesis is divided into two experimental parts. When the first part deals with diagnostics of diaphragm discharge in electrolyte solutions and the second part is focused on its use for uncoiling (higher homogenization) of carbon nanotubes in solutions. In experiment 1, three different sized (4 l, 100 ml, 50 ml) diaphragm discharge configurations were used to diagnose diaphragm discharge in electrolyte solutions. Diagnostics is done through current and voltage waveforms with the addition of synchronized ICCD camera images that have been connected to a four-channel oscilloscope. The V-A characteristic can be described by three events occurring in the electrolyte solution with a gradual increase in voltage. Slowly increasing of the voltage in the solution leads first to electrolysis. The next phase is the formation of microbubbles or bubbles, which is characteristic of the curve by a slight decrease in the increase of the current passing between electrodes. The sudden increase in the current flow is characteristic of the last phase, namely the discharge phase. The distance of the electrodes from the diaphragm does not significantly affect the V-A characteristic. The higher diameter of the pin hole, therefore, has a higher voltage, but this does not affect the origin of bubble generation or breakdown. The higher thickness of diaphragm, the higher voltage is needed to the beginning of the bubbles generation, and consequently the discharge breakdown. Comparison of the voltage of the start generation of the bubbles and breakdown for PET diaphragms and diaphragms from the ceramic there was no mark able difference. One of the most important parameters is the conductivity of the electrolyte solution. The lower voltage is needed for the start generation of the bubbles at the higher solution conductivity, and also the discharge generation is observed at a lower breakdown voltage. The second experimental part is focused on the study of the diaphragm discharge effect on carbon nanotubes. A specially designed U-shaped reactor is used to modify carbon nanoparticles. Tap water and aqueous solutions of organic compounds are used as the electrolytic solutions. The discharge is generated by a non-pulsed DC high source with a voltage in the range of 0-2.8 kV supplied to platinum electrodes located in the electrolyte solution. The experimental results have shown that the diaphragm discharge has positive effects on the disintegration of clusters and agglomerates of carbon nanotubes. The primary effect on disintegration is probably the shock waves generated by the discharge. It turned out that it depends on the electrode configuration, where the treatment in anode space has far greater effects than the treatment in cathode half of the reactor. Effects of carbon nanotubes disintegration in solution are long-lasting and the treatment effect is not loosed after several months. There were detected no significant changes in the structure of plasma-treated nanotubes by Infra-red spectroscopy.
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Electric characteristics of the diaphragm discharge in electrolyte solutions
Dřímalková, Lucie ; Slavíček, Pavel (referee) ; Kozáková, Zdenka (advisor)
The main object of this thesis is the diagnostics of the diaphragm discharge generated in water solutions containing supporting electrolytes (mostly NaCl), and description of particular processes before and after discharge breakdown by DC non-pulsed voltage up to 2 kV. Although many applications of electric discharge in liquids have been developed during the last years, the exact mechanism of the discharge ignition is not sufficiently known up to now. Based on this reason, this work is focused on the investigation of processes before the discharge ignition, breakdown parameters and the discharge itself both in the irregular and stable regime. The theoretical part of the work presents proposed mechanisms of the discharge generation in water solutions including the description of particular kinds of known discharges. Diaphragm discharge is one of many possible configurations of electrical discharges in liquids. In fact, electrical discharge in water forms non-thermal plasma, which is generated by high voltage, and many physical and chemical processes are started in plasma channels (so-called streamers). Among physical processes, high electrical field, shock waves and last but not least emission of electromagnetic radiation in visible and ultra-violet radiation belongs. The most important chemical processes are generation of various active species as hydrogen peroxide, and OH radical. Three batch plasma reactors using a diaphragm configuration with different total volume (4 l, 100 ml and 50 ml) are employed in the presented work. The discharge is created in an orifice (a pin-hole) in the dielectric barrier separating two electrode parts of the reactor. DC non-pulsed high voltage up to 4 kV is used for the discharge generation. Electrodes are made of stainless steel or platinum, and they are installed in parallel to the diaphragm in a variable distance from the dielectric barrier in each reactor part. The dielectric barrier is made of PET or Shapal-MTM ceramics with the variable thickness (0.2?2 mm). One pin hole st the diaphragm center with diameter of 0.2?1.5 mm are used in contemporary experiments. Time resolved characteristics of current and voltage are recorded using four-channel oscilloscope which detected their output values. Parameters are measured by the constantly increasing DC voltage with a step of 100 V. The solutions containing sodium chloride electrolyte are used at five different conductivities. Recorded time resolved characteristics determine breakdown moment, and describe current and voltage in particular parts within the static current-voltage curve. The breakdown appeared at lower applied voltage when the electrode distance is enhanced. However, the electrode distances higher than 4 cm does not induce any significant change of the breakdown voltage. The influence of pin-hole diameter is less obvious in the studied range, but a slight enhancement of breakdown voltage is observed with the increasing pin-hole diameter. Current-voltage characteristic curve moves towards lower voltage with the diaphragm thickness enhancement. The work compares the influence of conductivity change on current-voltage characteristics as well as the effect of inorganic salt kind. By the conductivity enhancement, the measured current-voltage curve moves towards lower voltage which means that the breakdown voltage is decreased. Sizes of the reactors do not have any effect on the processes before and after discharge breakdown.
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Diagnostics of diaphragm discharge in liquids
Dřímalková, Lucie ; Krčma, František (referee) ; Kozáková, Zdenka (advisor)
The main goal of this thesis is the diagnostics of the diaphragm discharge generated in liquids. Although many applications of electric discharge in liquids have been developed during the last years, the exact mechanism of the discharge ignition is not sufficiently known up to now. Based on this reason, this work focused on the investigation of processes before the discharge ignition, breakdown parameters and the discharge itself both in the irregular and stable regime. Using two kinds of inorganic salt solutions the work studied the influence of conductivity and electrolyte kind on the diaphragm discharge and its static current-voltage characteristics. The last task of the work investigated the emission spectra produced by the discharge. The theoretical part of the work presents mechanisms of the discharge generation in gases including the description of particular kinds of known discharges. The base theories of the discharge ignition in liquids are mentioned as well. Experiments were carried out in the reactor divided by the dielectric barrier (diaphragm) with a central pin-hole into two electrode spaces. Diaphragm was made of PET and the pin-hole initial diameter was 0.4 mm. Stainless steel electrodes were installed in the same distance of 2 cm from the barrier and symmetrically with respect to the diaphragm. Time resolved characteristics of current and voltage were recorded using two-channel oscilloscope which detected their output values. Parameters were measured by the constantly increasing DC voltage with a step of 50 V. When the regular discharge was ignited voltage had been gradually decreased. Used solutions contained sodium sulphate or sodium phosphate electrolyte at six different conductivities. Radiation emitted by the discharge was recorded by the spectrometer Jobin Yvon TRIAX 550. Emission spectra were investigated for one electrolyte at two different conductivities. The part with results presents all dependencies that were achieved during the measurements and all obtained data are compared. Recorded time resolved characteristics determine breakdown moment and describe current and voltage in particular parts within the static current-voltage curve. The work compares the influence of conductivity change on current-voltage characteristics as well as the effect of inorganic salt kind. By the conductivity enhancement the measured curve moves towards lower voltage which means that the breakdown voltage is decreased. Changing the inorganic salt the change of voltage related to the creation of bubbles in the diaphragm surroundings is observed. However, the change of electrolyte does not induce any significant change of the breakdown voltage. The last part of the work was focused on the optical emission spectroscopy of the discharge. Typical line system of OH radicals was identified in measured spectra which intensity was not dependent on the salt concentration. The work show particular processes taking place in the diaphragm surroundings when DC voltage is applied on the electrodes in electrolyte up to the diaphragm discharge ignition. Further, results describing the influence of conductivity and electrolyte changes on the processes are presented. The breakdown moment of the discharge and its dependence on the solution conductivity was determined. Optical emission spectroscopy revealed the contents of radiation emitted by the discharge.
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