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.
| Identifer | oai:union.ndltd.org:nusl.cz/oai:invenio.nusl.cz:216707 |
| Date | January 2011 |
| Creators | Dřímalková, Lucie |
| Contributors | Slavíček, Pavel, Kozáková, Zdenka |
| Publisher | Vysoké učení technické v Brně. Fakulta chemická |
| Source Sets | Czech ETDs |
| Language | Czech |
| Detected Language | English |
| Type | info:eu-repo/semantics/masterThesis |
| Rights | info:eu-repo/semantics/restrictedAccess |
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