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Thesis (Ph. D.)--University of Wisconsin--Madison, 1981. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 220-227).

The induced potential difference across a standing shock front can be used to drive electric current through external loads. Such a "standing shock generator" presents an alternative scheme to the MHD generator for direct conversion of energy from high temperature supersonic flows. We make use of the supersonic flow behind a free running shock in a shock tube and let the flow impinge onto a conical obstacle mounted in the middle of the tube to create a standing shock. This cone has a conducting surface which acts as the anode. The cathode is mounted flush with the shock tube wall at a position upstream of the standing shock. By varying the load resistance, we have obtained current-voltage characteristics for the standing shock generator. These characteristics are families of parallel straight lines similar to the characteristics of a battery. The open-circuit voltage is found to depend on the standing shock potential and the work functions of the electrodes. The internal resistance (equivalent to the slope of the characteristic) is found to be dominated by the plasma-wall interaction at the surface boundary layers. The maximum current collected by the electrode is therefore limited to its ion saturation current. A typical result of the standing shock generator in our experiment gives 1 volt with 0.5.amp for the. 30X10⁻⁶ sec test time duration. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (Ph. D.)--University of Illinois, 1967. / Includes bibliographical references (leaves 161-164).

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During operation of the solid polymer fuel cell (SPFC). its performance is limited by the concentrations of hydrogen and oxygen at the reaction interfaces and in most SPFC designs, the hydration state of the membrane. Since in general, the concentrations of water and the gaseous species vary along the flow channel, the performance is also likely to change along the flow channel. In order to study this phenomenon, a measurement system was developed to map the current distribution across the electrode surface. The current distribution has been measured by dividing one of the current collectors into a number of electrically isolated segments. The current flowing through each of the segments was measured while maintaining a constant potential across the surface of the gas diffusion layer. Two separate segmented current collectors were developed. The first was used to measure the current distribution for an 80 cm2 single cell, and the second was used to investigate the local current densities around a single flow channel. The effects of the feed gas humidities on the spatial current density in the 80 cm2 fuel cell were investigated for two different membrane-electrode configurations. With Nafion 117 as electrolyte and at a cell temperature of 80°C. the membrane was found to dehydrate in the initial portion of the gas flow channel when the relative humidity of both the hydrogen and oxygen feed gases was less than 50%. With a Gore-Select membrane electrode assembly (hydrogen and air. temperature- 60°C). the membrane was sufficiently hydrated at all feed gas humidification conditions. The performance of the cell was found to deteriorate at higher feed gas humidities as a result of the lower partial pressures of the reactant gases. Measurements of the effects of gas pressures, stoichiometries and humidities on the length-wise and width-wise perfonnance around a single flow channel (Gore-Select membrane electrode assembly) are discussed in relation to a gas flow model.

Since only little is known in the field of Solid Oxide Fuel Cell (SOFC) operation about internal reforming of methane at present, the aim of this thesis study is to conduct a detailed investigation delivering the basis for further experimental and theoretical work. Also information is required if the concept of internal reforming has technical development potential. The thesis is arranged into two major parts being a thermodynamic investigation and an application of a suitable kinetic model. Pure methane tends to decompose at the high operation temperatures of the SOFC (about 950°C) thus forming solid carbon. Therefore it is necessary to include a fuel preparation process delivering H2 and CO that can be utilized by the SOFC. The fuel processing can either be carried out by steam reforming or partial oxidation. It is shown by a thermodynamic investigation that fuel processing by partial oxidation yields a fuel gas of inferior quality than fuel processing by steam reforming. The kinetic part contains the application of a model describing the chemical and electrochemical conversion occuring in the SOFC as detailed as possible at present. This model is used to investigate the thermal behaviour of an SOFC process referring to technical operation parameters. It is shown that internal reforming has technical development potential although a lot of care must be paid to the heat management. Particular operation conditions might exist where the highly endothermic steam reforming process could cause a breakdown of the complete fuel cell process due to its enormous local cooling effect.

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