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Numerical and Experimental Investigations of the Flow Field of Ionised Gases with Applications to High-Performance Electronics and Oil Shale Gasification
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Numerical and Experimental Investigations of the Flow Field of Ionised Gases with Applications to High-Performance Electronics and Oil Shale Gasification
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Dissertation
Numerical and Experimental Investigations of the Flow Field of Ionised Gases with Applications to High-Performance Electronics and Oil Shale Gasification
2013
Overview
This thesis investigates two new applications of flow field ionised gases. The first application involves coupled electromagnetic and aerothermodynamic phenomena in an electrical contactor chamber. I studied a new blowout technique to control the speed of the flow. With this new blowout technique, the ionised gases can be generated between the electrodes to feed the coils with current. I observed that the recovery time for the case of higher current is less than that of the following low current at the same voltage. This is contrary to expected behavior. The speed of the ionised gases increases with increasing current. Hence, both the burning time and thermal stress of the hot ionised gases on the materials of the electrodes decrease. I discuss a simplified equivalent circuit of the contactor to explain the influence of the circuit components on the arc voltage and current; and observe that the inductance of the coils enhances the arc current as the arc current commutates in the coils. Moreover, the energy balance shows that about 11% of the total energy dissipates in this blowout technique.The movement of arc plasma is analysed experientially by using two optical methods, namely an optical imaging method and a high-speed camera. I developed the optical imaging software to generate dynamic images of the high-speed ionised gases. This allows me to compare the results of this method with those obtained by using a high-speed camera. In addition to these experimental studies, I researched the flow field of the ionised gas, applying the finite volume method to develop a transient numerical model of the ionised gas flow field inside the electrode runner for the case of a DC current. For the purpose of this thesis the properties of the air plasma are considered to be a function of temperature and pressure. The numerical calculations show that the arc plasma accelerates during the arc plasma duration. The dynamic pressure and magnetic pressure values are calculated for the arc plasma pumping in the contactor chamber. The magnetic pressure is higher than the dynamic pressure during the recovery time. The application of a dimensionless analysis reveals the insignificant influences of natural convection, flow compressibility and turbulence on the arc plasma pumping in the range of 100-750 A. Finally, I investigate the thermal boundary layer around the arc plasma shape by calculating the values of the Prandtl numbers in the midplane of the electrode runner. These results show that the cross-section area of the arc plasma changes with time due to the modification of the arc plasma current and speed.In the second application I consider the impact of the ionised gas flow field on the gasification of oil shale. Samples of oil shale were gasified using a low-temperature plasma at atmospheric pressure in the absence of water. A plasma jet was generated at temperatures between 200–550 C, defining a pulsating frequency of 20 kHz and an energy consumption of less than 300 W. I determined the composition of the treated oil shale by using thermogravimetric analysis and found that raw samples contain on average 1.5 wt% of moisture, 17.5 wt% of volatiles, 24 wt% of fixed carbon and 57 wt% of ash.
