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Item Design and development of a high frequency Mosfet driver(2004-11) Swart, Arthur James; Pienaar, H. C. van ZA high-power Mosfet was incorporated as a switching device into the efficient Class E configuration, where the switching device switches current through itself either completely on or completely off at high frequencies. The first objective of this project was to demonstrate the effectiveness of a phase-lock loop circuit in generating stable high frequencies when connected in an indirect frequency synthesizer configuration. The indirect frequency synthesizer has established itself as a versatile frequency generator capable of generating high frequencies based on a lower stable reference frequency. The frequency generation stage incorporates a phaselock loop circuit, a frequency divider and a stable reference frequency section. The phase-lock loop section incorporates the TTL based 74HC 4046 that is based upon the common CMOS 4046 integrated circuit. The frequency divider section is built around the CMOS-based 4526 whilst the reference frequency section incorporates the CMOS-based 4060. The frequency synthesizer produced a range of frequencies from 50 kHz to 8 MHz in 50 kHz steps. The output voltage was constant at 5,5 V. The second objective was to show that the complementary emitter follower is indeed a worthy Mosfet gate drive circuit at high frequencies. The Mosfet driver stage produced a voltage signal of at least 11 V, being able to source and sink relatively high peaks of current, especially at high frequencies. Voltage amplification occurred through the use of multiple CMOS-based 40106 inverters. The complementary emitter follower, known for its low output impedance and its ability to source and sink large amounts of current, was an important component in the final Mosfet gate section.Item Design and development of a 100 W Proton exchange membrane fuel cell uninterruptible power supply(2006-01) Du Toit, Johannes Paulus; Pienaar, H. C. v Z.This study presents the design of a proton exchange membrane fuel cell stack that can be used to replace conventional sources of electrical energy in an uninterruptible power supply system, specifically for use in the telecommunications industry. One of the major concerns regarding the widespread commercialization of fuel cells is the high cost associated with fuel cell components and their manufacturing. A fuel cell design is presented in which existing, low-cost, technologies are used in the manufacture of cell components. For example, printed circuit boards are used in the manufacturing of bipolar flow plates to significantly reduce the cost of fuel cells. The first objective was to design, construct and test a single fuel cell and small fuel cell stack in order to evaluate the use of printed circuit boards in bipolar plate manufacturing. Since the use of copper in a fuel cell environment was found to reduce the lifetime of the cells, the bipolar plates were coated with a protective layer of nickel and chrome. These coatings proved to increase the lifetime of the cells significantly. Power outputs of more than 4 W per cell were achieved. The second objective was to analyze a small fuel cell stack in order to obtain a model for predicting the performance of larger stacks. A mathematical model was developed which was then used to design an electronic circuit equivalent of a fuel cell stack. Both models were adapted to predict the performance of a fuel cell stack containing any number of cells. The models were proven to be able to accurately predict the performance of a fuel cell stack by comparing simulated results with practical performance data. Finally, the circuit equivalent of a fuel cell stack was used to evaluate the capability of a switch mode boost converter to maintain a constant voltage when driven by a fuel cell stack, even under varying load conditions. Simulation results showed the ability of the boost converter to maintain a constant output voltage. The use of supercapacitors as a replacement for batteries as a secondary energy source was also evaluated.Item Design and development of a high performance zinc air fuel cell(2006-06) Lourens, Dewald; Pienaar, H. C. v Z.The demand for efficient and environmentally friendly power sources has become a major topic around the world. This research explores the capability of the zinc-air fuel cell to replace conventional power sources for various applications, more specifically telecommunication systems. The research consisted of a theoretical study of the zinc-air fuel cell and its components, as well as their performance characteristics. A zinc-air fuel ce.ll and test rig were built, and the system was tested under various conditions. It was found that the zinc-air fuel cell has an advantage over other fuel cells in that it does not require any expensive materials or noble metals, reducing the overall cost of such a system. The fuel cell showed the potential to power various applications, but problems persisted in the fueling process as well as constant leaking of the aqueous electrolyte.Item Design and development of a remote monitoring system for fuel cells(2006-07) Komweru, Laetitia; Pienaar, H. C. v Z.This dissertation presents the design and development of a remote monitoring system (RMS) for polymer electrolyte membrane fuel cells (PEMFC) to facilitate their efficient operation. The RMS consists of a data acquisition system built around the PIC 16F874 microcontroller that communicates with a personal computer (PC) by use of the RS232 serial communication standard, using a simple wired connection between the two. The design also consists of a human machine interface (HMI) developed in Visual Basic 6.0 to provide a platform for display of the monitored parameters in real time. The first objective was to establish performance variables and past studies on PEM fuel cells revealed that variables that affect the system's performance include: fuel and oxidant input pressure and mass flow rates as well as operation temperature and stack hydration. The next objective was to design and develop a data acquisition system (DAS) that could accurately measure the performance variables and convey the data to a PC. This consisted of sensors whose outputs were input into two microcontrollers that were programmed to process the data received and transfer it to the PC. A HMI was developed that provided graphical display of the data as well as options for storage and reviewing the data. The developed system was then tested on a 150Watt PEM fuel cell stack and the data acquisition system was found to reliably capture the fuel cell variables. The HMI provided a real-time display of the data, with alarms indicating when set minimums were exceeded and all data acquired was saved as a Microsoft Excel file. Some recommendations for improved system performance are suggested.Item Design and development of a methanol concentration controller for fuel cells(2010-09-09T13:41:34Z) Viljoen, MariusThe demand for higher efficiency, sustainability and cleaner power sources increases daily. A Direct Methanol Fuel Cell is a power source that can be applied for small to medium household appliances and office equipment. It can ideally be used for operating appliances like notebook computers on remote sites where no electrical power is available. One of the problems in methanol fuel cells is methanol crossover. Methanol crossover occurs when methanol is not completely used in the process of generating electrons, and a certain percentage of the methanol is wasted. Crossover may damage the proton exchange membrane of the fuel cell and reduce the efficiency of a DMFC. Literature reviews were done and suggestions from other writers are discussed on how to reduce methanol crossover. This research focuses primarily on the fact that crossover can be controlled by controlling the methanol / water concentration. A prototype methanol controller was built with an ultrasonic sensor for detecting the density of the methanol/water mixture and a sensor for the temperature of the mixture; this was done because the density of the mixture is dependant on the temperature and the concentration. The controller was calibrated to determine the amount per volume of water and methanol which enables the controller to control the percentage of methanol in the water. The prototype also had the feature built in to adjust the mixture in order to enable the study on the effects of crossover. A data logger function was added to store collected data on a personal computer for the study on methanol and water. It was observed that the sensor was sensitive enough and was able to produce 1% increments of the level of methanol concentration in the water provided the temperature was stable. A methanol controller was successfully built to ensure the correct volume of methanol.Item Evaluating the effects of radio-frequency treatment of rocks: textural changes and implications for rock comminution(2010-12) Swart, Arthur James; Pienaar, H. C. v Z.; Mendonidis, P.Ore, from a mining operation, goes through a process that separates the valuable minerals from the gangue (waste material). This process usually involves crushing, milling, separation and extraction where the gangue is usually discarded in tailings piles. Current physical methods used for crushing of rocks in the mineral processing industry result in erratic breakages that do not efficiently liberate the economically valuable minerals. Research studies have found that the rock comminution and mineral liberation can be enhanced through various electrical treatment techniques, including pulsed power, ultrasound and microwave. These electrical treatment techniques each have their own advantages and disadvantages which are discussed in this dissertation. However, this research proposes a new technique in an attempt to improve the rock comminution process. The main purpose of this research is to evaluate the effect that RF power exerts on rock samples, with particular focus on textural changes. Four valuable scientific contributions to the fields of metallurgical and electrical engineering were made in this regard. Firstly, a new technique for the treatment of rock samples using RF heating is substantiated. The effect of RF power on textural changes of the rocks is evident in their surface temperature rise, where the RF heating of dole-rite (JSA) and marble (JSB, JS 1 and JS2) resulted in surface temperatures of approximately 100 °C within two minutes of treatment. A particle screening analysis of particles obtained form a swing-pot mill of both the untreated (not exposed to RF power) and treated (exposed to RF power) rock samples were performed to ascertain if the treated samples' size had changed. Two samples (JSA and JSD) revealed a notable change in their particle size distribution. The fact that the percentage of larger sized particles increased (from 38 J..Lm to 90 J..Lffi as seen in Chapter 6) suggests that the rock was strengthened rather than weakened. Secondly, an innovative coupling technique (using a parallel-plate capacitor with dimensions of 28 x 47 mm) to connect rock samples to high powered RF electronic equipment is described. The feasibility of this technique is confirmed by repeated correlated measurements taken on a vector voltmeter and network analyser. Low SWR readings obtained from an inline RF Wattmeter in a practical setup also proves the viability of the matching network used in the coupling technique. Thirdly, anoriginal coupling coefficient (81.58 x 10-3) for the parallel-plate capacitor is presented. This value may be used in similar sized capacitors to determine the specific heat capacity of dielectric materials. However, the value of the coupling coefficient was only verified for seven (relatively dark in surface colour) out of the ten rock samples. Therefore, this coupling coefficient may hold true for all dark coloured rock samples, as it represents the coupling of energy between the parallel-plate capacitor and the rock sample. Finally,this research defines the mathematical models for 10 rock samples for the VHF range of frequencies (30 - 300 MHz), providing unique phase angle to resonance equations for each sample. These equations can be used with each specific rock to determine the resonating frequency where the maximum current flows and the minimum resistance is present. Evaluating the effects of RF power treatment on rocks has brought to light that mineral grain boundaries within specified rock samples are not significantly weakened by RF treatment. This was firstly confirmed by the similar electrical properties of the untreated and treated samples, where consistent values for the resonating frequency were obtained from the network analyser. Secondly, the SEM analysis of the untreated and treated rock samples revealed no significant changes in the form of fractures or breakages along the mineral grain boundaries. Photomicrographs of the thin sections of all ten rock samples were used in this analysis. The particle size distribution of both samples further revealed no weakening or softening of the rock, as the percentage of smaller sized particles did not increase in the treated samples. It may therefore be stated that treating rock samples with RF power within the VHF range will not significantly improve rock comminution and mineral liberation.Item Optimisation of water, temperature and voltage management on a regenerative fuel cell(2012-05-31) Van Tonder, Petrus Jacobus Malan; Pienaar, HCvZâNever before in peacetime have we faced such serious and widespread shortage of energyâ according to John Emerson, an economist and power expert for Chase Manhattan Bank. Many analysts believe that the problem will be temporary, but others believe the energy gap will limit economic growth for years to come. A possible solution to this problem can be fuel cell technology. Fuel cells (FCs) are energy conversion devices that generate electricity from a fuel like hydrogen. The FC however, could also be used in the reverse or regenerative mode to produce hydrogen. The reversible fuel cell (RFC) can produce hydrogen and oxygen by introducing water to the anode electrode chamber, and applying a potential across the anode and cathode. This will cause the decomposition of the water to produce oxygen at the anode side and hydrogen at the cathode side. In order to make this process as efficient as possible several aspects need to be optimised, for example, the operation temperature of the RFC, water management inside the RFC and supply voltage to the RFC. A three cell RFC and its components were constructed. The three cell RFC was chosen owing to technical reasons. The design factors that were taken into consideration were the different types of membranes, electrocatalysts, bipolar plates and flow topologies. A water trap was also designed and constructed to eliminate the water from the hydrogen water mixture due to water crossover within the MEA. In order to optimise the operation of the RFC a number of experiments were done on the RFC. These experiments included the optimal operating voltage, the effect that the temperature has on the production rate of hydrogen, and the effect that the water flow through the RFC has on the production rate of hydrogen. It was found that there is no need to control the water flow through the RFC because it had no effect on the production rate of hydrogen. The results also showed that if the operating temperature of the RFC were increased, the energy it consumes to warm the RFC significantly decreases the efficiency of the whole system. Thus the RFC need not be heated because it consumes significantly more energy to heat the RFC compared to the energy available from the hydrogen produced for later use. The optimised operating voltage for the three cell RFC was found to be 5.05 V. If the voltage were to be increased or decreased the RFC efficiency would decrease.Item Design and development of an automated temperature controller for curing ovens(2012-08-30) Schoeman, Ruaan MornĂš; Janse van Rensburg, J. F.Curing of materials in order to obtain different properties has been a practice for many years. New developments in composite materials increase the need to control certain variables during the curing process. One very significant variable is temperature. Temperature control by itself is an old practice, however when the need for repeatedly controlling the process accurately over long periods of time arises, a system is required that outperforms normal manual control. One of the aspects within such a system that needs to be considered is the ability to replicate the temperatures within an oven which were originally used for a specific materialâs curing profile. This means that a curing profile would need to be defined, saved for later and finally be interpreted correctly by the controlling system. Different control methods were simulated to enable the system to control the temperature which has been defined by literature. This dissertation introduces a variation on the standard control methods and shows improved results. Switching the oven on and off in order to increase or decrease internal oven temperature seems simple, but can cause switching devices to decrease their operational life span, if not designed carefully. A combination switch was introduced which harnesses the advantages of two very common switching devices to form an improved combination switch. Software for the personal computer environment, as well as software for the embedded environment were developed and formed a control system that produced acceptable results for temperature control. Accuracies of 98% and more were achieved and found to be acceptable according to standard engineering control practices. An accurate temperature profile controller was designed, simulated and built in order to control the temperature inside a specific curing oven which, in turn, determined the curing properties of specific materials. The overall results were satisfactory which lead to achieving the objectives outlined in this dissertation.Item Optimisation of the hydrogen pressure control in a regenerative proton exchange membrane fuel cell(2012-10-24) Burger, Melanie; Pienaar, H. C. v Z.Industrial countries, such as South Africa, rely heavily on energy sources to function profitably in todayâs economy. Based on the 2008 fossil fuel CO2 emissions South Africa was rated the 13th largest emitting country and also the largest emitting country on the continent of Africa, and is still increasing. It was found that fuel cells can be used to generate electricity and that hydrogen is a promising fuel source. A fuel cell is an energy generation device that uses pure hydrogen (99.999%) and oxygen as a fuel to produce electric power. A regenerative fuel cell is a fuel cell that runs in reverse mode, which consumes electricity and water to produce hydrogen. This research was aimed at designing and constructing an optimised control system to control the hydrogen pressure in a proton exchange membrane regenerative fuel cell. The hydrogen generated by the fuel cell must be stored in order to be used at a later stage to produce electricity. A control system has been designed and constructed to optimise the hydrogen pressure control in a regenerative proton exchange membrane fuel cell. An experiment that was done to optimise the hydrogen system included the effects that the cathode chamber pressure has on the production of hydrogen and the most effective method of supplying hydrogen to a storage tank. The experiment also included the effects of a hydrogen buffer tank on the output hydrogen pressure and if the system can accommodate different output pressures. It was found that the cathode chamber pressure doesnât need to be controlled because it has no effect on the rate of hydrogen produced. The results also showed that the flow of hydrogen need not to be controlled to be stored in a hydrogen storage tank, the best method is to let the produced hydrogen flow freely into the tank. The hydrogen produced was also confirmed to be 99.999% pure. The system was also tested at different output pressures; the control system successfully regulated these different output pressures.Item Solar driven hydrogen generation for a fuel cell power plant(2012-11-01) Amoo, Akinlawon Olubukunmi; Bekker, W. J.; Pienaar, H. C. v Z.There are a number of ways to produce hydrogen using solar energy as the primary source. Water electrolysis, which uses solar electrical energy, is the rapidly available process. Hydrogen can be produced by using solar electric energy from photovoltaic (PV) modules for the electrolysis of water without emitting carbon dioxide or requiring fossil fuels. Solar hydrogen energy systems are considered one of the cleanest hydrogen production technologies, where the hydrogen is obtained from sunlight by directly connecting the photovoltaic modules to the hydrogen generator. This dissertation presents a designed solar photovoltaic electrolyser hydrogen production and storage system for various applications such as in the power generation and telecommunications industries. Various experiments were performed on the designed system to ensure its reliability and conformity with theoretical findings. The purity of the generated hydrogen was determined. The relationship between the amount of solar irradiance reaching the surface of the PV panel, the PV panel surface temperature, the PV panel tilt angle and the maximum power point voltage and current of the PV panel array were also considered. The effect of dust on the panel voltage and current outputs was also determined. Finally, the factors to consider when designing a solar photovoltaic electrolyser hydrogen system (based on this study) were enumerated.Item A flight data recorder for radio-controlled model aircraft(2013-02) Du Plooy, Andre Fred; Swart, James; Pienaar, ChristoIn the ever growing sport of model aircraft, pilots are challenged with many obstacles. In the division of gliders, one of the biggest problems is the loss of model aircraft. Pilots launch their aircraft off mountain tops and if the aircraft crashes below, the pilot must make use of his best estimates in order to locate the aircraft. This either takes several hours, or the aircraft is never recovered. Pilots are also at a loss with regard to real time data, such as, but not limited to, battery levels, fuel levels, altitude and speed. Model aircraft competitions are also limited to the best estimate of officials. In this work an attempt has been made to design and develop a remote tracking device for model aircraft. This device will retrieve Global Positioning System (GPS) co-ordinates from the aircraft and relay them to the pilot on the ground. In the event of a crash, the pilot will retrieve the last GPS co-ordinates and then proceed to the location to collect the aircraft. An attempt will also be made to design add-on telemetry components that will allow for measurement and transmission of battery levels, fuel levels, altitude, G-Force, orientation, acceleration, wind and ground speed. Some of the data retrieved from the Flight Data Recorder (FDR) in trial 1 are: maximum altitude above sea level of 2139.20 m, maximum speed over ground which was 57.34 m/s and the average battery voltage for transceiver and servos was 15.2 v.Item Design and development of a 200 W converter for phosphoric acid fuel cells(2013-03) Kuyula, Christian Kinsala; Janse van Rensburg, J. F.âIf we think oil is a problem now, just wait 20 years. Itâll be a nightmare.â â Jeremy Rifkin, Foundation of Economic Trends, Washington, D.C., August 2003. This statement harmonises with the reality that human civilisation faces today. As a result, humankind has been forced to look for alternatives to fossil fuels. Among possible solutions, fuel cell (FC) technology has received a lot of attention because of its potential to generate clean energy. Fuel cells have the advantage that they can be used in remote telecommunication sites with no grid connectivity as the majority of telecommunication equipment operates from a DC voltage supply. Power plants based on phosphoric acid fuel cell (PAFC) have been installed worldwide supplying urban areas, shopping centres and medical facilities with electricity, heat and hot water. Although these are facts regarding large scale power plants for on-site use, portable units have been explored as well. Like any other fuel cell, the PAFC output power is highly unregulated leading to a drastic drop in the output voltage with changing load value. Therefore, various DCâDC converter topologies with a wide range of input voltages can be used to regulate the fuel cell voltage to a required DC load. An interleaved synchronous buck converter intended for efficiently stepping down the energy generated by a PAFC was designed and developed. The design is based on the National Semiconductor LM5119 IC. A LM5119 evaluation board was redesigned to meet the requirements for the application. The measurements were performed and it was found that the converter achieved the expectations. The results showed that the converter efficiently stepped down a wide range of input voltages (22 to 46 V) to a regulated 13.8 V while achieving a 93 percent efficiency. The conclusions reached and recommendations for future research are presented.Item Development of a universal bidirectional galvanic isolated switch module for power converter applications(2013-06) Mokhalodi, Kopano; Janse van Rensburg, J. F.The global trends towards energy efficiency have facilitated the need for technological advancements in the design and control of power electronic converters for energy processing. The proposed design is intended to make the practical implementation of converters easier. The development of a universal bidirectional galvanic isolated switch module will be used to drive any MOSFET or IGBT in any position in any topology whether the load is AC or DC. Semiconductor switches are required and are also integrated for fast switching times in power converter applications The structure of the power switch module consists of an opto-coupler which will provide an isolation barrier for maximum galvanic isolation between the control circuitry and power stage. It also consists of a high performance gate drive circuit for high speed switching applications with a floating supply.Item Design of a practical voice over internet protocol network for the multi user enterprise(2013-07-18) Loubser, Jacob Bester; Pienaar, HCvZThis dissertation discusses the design and implementation of a voice over internet protocol system for the multi-user enterprise. It is limited to small to medium enterprises of which the Vaal University of Technology is an example. Voice communications over existing Internet protocol networks are governed by standards, and to develop such a system it is necessary to have a thorough understanding of these standards. Two such standards namely the International Telecommunications Unions H.323 and the Internet Engineering Task Force's SIP were evaluated and compared to each other in terms of their complexity, extensibility and scalability as well as the services they offer. Based on these criteria it was decided to implement a SIP system. A SIP network consists of application software that act as clients and servers, as well as hardware components such as a proxy and redirect and registrar or location servers that allow users of this network to call each other on the data network. Gateways enable users of the network to call regular public switched telephone network numbers. A test network was set up in the laboratory that contained all the hardware and software components. This was done to understand the installation and configuration options of the different software components and to determine the suitability and interoperability of the software components. This network was then migrated to the network of the Vaal University of Technology which allowed selected users to test and use it. Bandwidth use is a major point of contention, and calculations and measurements showed that the codec being used during the voice call is the determining factor. This SIP system is being used on a daily basis and the users report excellent audio quality between soft phones and soft phones, soft phones and normal telephones and even cellular phones.Item Design and development of a phosphoric acid fuel cell(2013-08-21) Pholo, Thapelo; Pienaar, H. C. v ZFuel cells are electrochemical devices that convert chemical energy of a fuel cell into electricity at high efficiency without combustion. They are viewed as viable power sources for many applications including automobiles, distributed power generation and portable electronics. This dissertation presents the design and development of a phosphoric acid fuel cell. It deals with the experimental studies on phosphoric acid fuel cells and possible integration in replacing the conventional sources of electrical energy in stand-by power supply systems, particularly for use in the telecommunications industry. The design of a DC-DC converter system is also incorporated into the system. The first objective was to establish performance parameters and past studies on phosphoric acid fuel cells and this research revealed that parameters that affect the system's performance include: reactant gas pressures, mass flow rates as well as the operating temperature. Mathematical models in the literature were studied and verified against the simulation models acquired. The second objective was to design and assemble a single cell in order to analyze the cell's performances as well as the operating parameters in order to obtain a model for predicting and simulating the performance of larger fuel cell stacks. The next objective was to analyse from a set of design equations and construct a small DC-DC converter. The converter was used to boost a small fuel cell voltage and regulate it at a higher voltage level. Finally, the performance characteristics of the developed fuel cell, mathematical and simulation models were evaluated and compared. Simulation results for the models and the converter showing a regulated output voltage are presented. Some recommendations for improved system performance and for further studies are suggested.Item Non-conventional methods for energy extraction from high voltage transmission lines(2013-08-22) Nicolae, Dan Valentin; Case, M. J.A comprehensive study upon "Non-conventional methods for energy extraction from the high voltage transmission lines" was addressed in this thesis. As defined in this study, a non-conventional method to extract energy is one that does not touch the conductors of the line. The theoretical framework which originated in the Maxwell's equations was presented as a base for discussion of all the methods and the conditions for the extraction to be possible. This study presents various methods such as capacitive and inductive to extract energy from high voltage alternating current transmission lines (HVAC). Although in theory, for high voltage direct current transmission lines (HVDC), the conditions for extraction are not matched, there remain some methods that could still attract interest. The centre point of this thesis is the new power application of the Rogowski coil. This method is analysed in full extent starting from theoretical modelling, computer simulations, design of the actual Rogowski coil and power electronics associated with it, and experimental results on a reduced scale model. In doing this, strong mathematical tools and computer software such as Matlab 6, Quick Field and MathCAD were used. At the end of this thesis, some conclusions are presented together with new ideas for further research in the field.Item The design of a system for evaluating glare from small lighting sources(2013-08-22) Joubert, Theresa; Dicks, D. A.; Case, M. J.Discomfort glare is a topic that has been investigated for many years without any reasonable explanation regarding its effect on the human visual system. Results of previous research concluded that established methods have a lot of similarities in implementation; but a number of differences when comparing the results of observer's evaluations with the mathematically calculated glare ratings. Therefore, an alternative method of evaluating the influence of exposure to an unshielded light source was investigated to establish a more reliable and realistic response from observers. In order to address the discrepancies of previous evaluation systems concerning observer's varying opinions regarding the level of discomfort experienced, it was decided to investigate the feasibility of evaluating the brain activity of the observers exposed to an unshielded incandescent lamp. This was done in order to facilitate the differences in each individual observer's sensitivity to bright light sources and the influence of personal taste therefore, eliminating the effect of personal interpretation. The main purpose of this study was to determine whether it would be possible to get any response regarding brain functions when an observer is exposed to a bare light source. In order to determine the pathway of visual stimuli it was necessary to investigate the operating principles of the human eye in detail. Because the eye is only an instrument that makes seeing possible; it was also important to investigate the brain and all its different functions. The part of the brain where visual interpretation takes place was indicated as the occipital lobe. This is the part of the brain monitored for any change of functional status by taking measurements with an electroencephalogram (EEG). Measurements were indeed possible; it was presented as a suppression of the alpha brain activity. During the testing procedure it was observed that the observers were not equally photosensitive. There was also a difference in the amount of alpha suppression with the observer's eyes open and closed respectively. Because the alpha rhythm has a tendency to increase with closed eyes it was much easier to notice the suppression.Item Analysis of the environmental impact on the design of fuel cells(2013-08-22) Sibiya, Petros Mandla; Pienaar, H. C. v ZThe air-breathing Direct Methanol Fuel Cell (DMFC) and Zinc Air Fuel Cell (ZAFC)were experimentally studied in a climate chamber in order to investigate the impact of climatic environmental parameters such as varying temperature and relative humidity conditions on their performance. The experimental results presented in the form of polarization curves and discharge characteristic curves indicated that these parameters have a significant effect on the performance of these fuel cells. The results showed that temperature levels below 0Âșc are not suitable for the operation of these fuel cells. Instead, it was found that air-breathing DMFC is favored by high temperature conditions while both positive and negative effects were noticed for the air-breathing ZAFC. The results of the varying humidity conditions showed a negative impact on the air-breathing DMFC at a lower temperature level but a performance increase was noticed at a higher temperature level. For air-breathing ZAFC, the effect of humidity on the performance was also found to be influence by the operating temperature. Furthermore, common atmospheric air pollutants such as N20, S02, CO and N02 were experimentally investigated on the air-breathing DMFC and ZAFC. At the concentration of 20 ppm, these air contaminants showed to have a negative effect on the performance of both air-breathing DMFC and ZAFC. For both air-breathing DMFC and ZAFC, performance degradations were found to be irreversible. It is therefore evident from this research that the performance of the air-breathing fuel cell will be affected in an application situated in a highly air-polluted area such as Vaal Triangle or Southern Durban. It is recommended the air-breathing fuel cell design include air filters to counter the day-to-day variations in concentration of air pollutants.Item Current source converters for extraction of power from HVAC lines(2013-08-22) Janse van Rensburg, Johannes Frederik; Case, M. J.Two methods to convert an AC current source to an AC voltage source are presented. Both methods make use of a current transformer to provide energy extraction from the main system while maintaining galvanic isolation between the main system and the output system. Control is via a pulse width modulation scheme in both instances. The ftrst method uses a storage element to provide a DC voltage, which feeds an inverter that supplies the AC load with a voltage source. The second method does not use a storage element but is a direct AC current source to AC voltage source converter employing a current transformer. This has not been done before. A possible application of this study is in the extraction of power from high voltage transmission lines without the conventional substation and rural grid to supply small users such as the telecommunication industry.Item Design and development of a direct methanol fuel cell for telecommunications(2013-08-28) Joubert, Hardus; Pienaar, H. C. v Z;The demand for higher efficiency and cleaner power sources increases daily. The Direct Methanol Fuel Cells (DMFC) is one of those power sources that produces reliable electrical energy at high efficiencies and very low pollution levels. Remote telecommunication sites need power sources that can deliver reliable power. This dissertation informs the reader about the working principles of the DMFC and the materials it consists of. A good amount of theoretical background is also given on the DMFC, especially on the Membrane Electrode Assembly (MEA). Different membranes as well as their properties are discussed. Results from other researchers on DMFCs are also captured. A DMFC stack including a test rig, was built. The DMFC stack consisted of five single DMFC cells. Each cell contained an MEA, Gas Diffusion Layers (GDLS), highly corrosive resistant metal support grids, bipolar flow field plates and end plates. The DMFC stack was operated and tested in a test rig. The test rig held the air blower which supplied the cathode with the required oxidant (air), and the methanol solution tank plus its liquid pump. The liquid pump circulated the methanol solution through the anode side of the stack. It was observed that the DMFC is very susceptible to corrosion, especially if the methanol solution becomes conductive owing to solubility of C02 in it. Methanol itself is a corrosive substance. However the results obtained from the experiments clearly indicate that the DMFC can be implemented as an electrical power source for telecommunications.