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Signal Modulation in a High Voltage Plasma

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A high voltage plasma arc can be created and sustained in air by subjecting the gases to an electric field with high voltage potential, causing ionization. The internal energy of the ionized gases can be transferred to corresponding pressure waves

A high voltage plasma arc can be created and sustained in air by subjecting the gases to an electric field with high voltage potential, causing ionization. The internal energy of the ionized gases can be transferred to corresponding pressure waves when the matter involved switches between the gaseous and plasma states. By pulse-width modulating a transformer driving signal, the transfer of internal electrical energy to resonating pressure waves may be controlled. Audio wave input to the driver signal can then be modulated into the carrier wave and be used to determine the width of each pulse in the plasma, thus reconstructing the audio signal as pressure, or sound waves, as the plasma arc switches on and off. The result will be the audio waveform resonating out of the plasma arc as audible sound, and thus creating a plasma loudspeaker. Theory of operation was tested through construction of a plasma arc speaker, and resultant audio playback was analyzed. This analysis confirmed accurate reproduction of audio signal in audible sound.

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2014-05

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Direct Solar–powered Membrane Distillation for Small–scale Desalination Applications

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Water desalination has become one of the viable solutions to provide drinking water in regions with limited natural resources. This is particularly true in small communities in arid regions, which suffer from low rainfall, declining surface water and increasing salinity

Water desalination has become one of the viable solutions to provide drinking water in regions with limited natural resources. This is particularly true in small communities in arid regions, which suffer from low rainfall, declining surface water and increasing salinity of groundwater. Yet, current desalination methods are difficult to be implemented in these areas due to their centralized large-scale design. In addition, these methods require intensive maintenance, and sometimes do not operate in high salinity feedwater. Membrane distillation (MD) is one technology that can potentially overcome these challenges and has received increasing attention in the last 15 years. The driving force of MD is the difference in vapor pressure across a microporous hydrophobic membrane. Compared to conventional membrane-based technologies, MD can treat high concentration feedwater, does not need intensive pretreatment, and has better fouling resistance. More importantly, MD operates at low feed temperatures and so it can utilize low–grade heat sources such as solar energy for its operation. While the integration of solar energy and MD was conventionally indirect (i.e. by having two separate systems: a solar collector and an MD module), recent efforts were focused on direct integration where the membrane itself is integrated within a solar collector aiming to have a more compact, standalone design suitable for small-scale applications. In this dissertation, a comprehensive review of these efforts is discussed in Chapter 2. Two novel direct solar-powered MD systems were proposed and investigated experimentally: firstly, a direct contact MD (DCMD) system was designed by placing capillary membranes within an evacuated tube solar collector (ETC) (Chapter 3), and secondly, a submerged vacuum MD (S-VMD) system that uses circulation and aeration as agitation techniques was investigated (Chapter 4). A maximum water production per absorbing area of 0.96 kg·m–2·h–1 and a thermal efficiency of 0.51 were achieved. A final study was conducted to investigate the effect of ultrasound in an S-VMD unit (Chapter 5), which significantly enhanced the permeate flux (up to 24%) and reduced the specific energy consumption (up to 14%). The results add substantially to the understanding of integrating ultrasound with different MD processes.

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2020