The Effect of Various Electrode Microstructure Parameters on the Effective Conductivity and Three-Phase Boundary Density of Infiltrated SOFC Electrodes

Solid oxide fuel cell (SOFC) technology has the potential to be a significant player in our future energy technology repertoire based on its ability to convert chemical energy into electrical energy. Infiltrated SOFCs, in particular, have demonstrated improved performance and at lower cost than traditional SOFCs. An infiltrated electrode comprises porous ceramic scaffolding (typically constructed from the oxygen ion conducting material) that is infiltrated with electron conducting and catalytic particles. Two important SOFC electrode properties are effective conductivity and three phase boundary density (TPB). Researchers study these electrode properties separately, and fail to recognize them as competing properties. This thesis aims to (1) develop a method to model the TPB density and use it to determine the effect of porosity, scaffolding particle size, and pore former size on TPB density as well as to (2) compare the effect of porosity, scaffolding particle size, and pore former size on TPB density and effective conductivity to determine a desired set of parameters for infiltrated SOFC electrode performance. A computational model was used to study the effect of microstructure parameters on the effective conductivity and TPB density of the infiltrated SOFC electrode. From this study, effective conductivity and TPB density are determined to be competing properties of SOFC electrodes. Increased porosity, scaffolding particle size, and pore former particle size increase the effective conductivity for a given infiltrate loading above percolation threshold. Increased scaffolding particle size and pore former size ratio, however, decreases the TPB density. The maximum TPB density is achievable between porosities of 45% and 60%. The effect of microstructure parameters are more prominent at low loading with scaffolding particle size being the most significant factor and pore former size ratio being the least significant factor.

Assessment Of Dynamic Properties Of A Crowd Model For Human-Structure Interaction Modeling

As lightweight and slender structural elements are more frequently used in the design, large scale structures become more flexible and susceptible to excessive vibrations. To ensure the functionality of the structure, dynamic properties of the occupied structure need to be estimated during the design phase. Traditional analysis method models occupants simply as an additional mass; however, research has shown that human occupants could be better modeled as an additional degree-of- freedom. In the United Kingdom, active and passive crowd models are proposed by the Joint Working Group as a result of a series of analytical and experimental research. It is expected that the crowd models would yield a more accurate estimation to the dynamic response of the occupied structure. However, experimental testing recently conducted through a graduate student project at Bucknell University indicated that the proposed passive crowd model might be inaccurate in representing the impact on the structure from the occupants. The objective of this study is to provide an assessment of the validity of the crowd models proposed by JWG through comparing the dynamic properties obtained from experimental testing data and analytical modeling results. The experimental data used in this study was collected by Firman in 2010. The analytical results were obtained by performing a time-history analysis on a finite element model of the occupied structure. The crowd models were created based on the recommendations from the JWG combined with the physical properties of the occupants during the experimental study. During this study, SAP2000 was used to create the finite element models and to implement the analysis; Matlab and ME¿scope were used to obtain the dynamic properties of the structure through processing the time-history analysis results from SAP2000. The result of this study indicates that the active crowd model could quite accurately represent the impact on the structure from occupants standing with bent knees while the passive crowd model could not properly simulate the dynamic response of the structure when occupants were standing straight or sitting on the structure. Future work related to this study involves improving the passive crowd model and evaluating the crowd models with full-scale structure models and operating data.

Hydrologic and Water Quality Assessment of Miller Run: A Study of Bucknell University’s Impact

Human development causes degradation of stream ecosystems due to impacts on channel morphology, hydrology, and water quality. Urbanization, the second leading cause of stream impairment, increases the amount of impervious surface cover, thus reducing infiltration and increasing surface runoff of precipitation, which ultimately affects stream hydrologic process and aquatic biodiversity. The main objective of this study was to assess the overall health of Miller Run, a small tributary of the Bull Run and Susquehanna River watersheds, through an integrative hydrologic and water quality approach in order to determine the degree of Bucknell University’s impact on the stream. Hydrologic conditions, including stage and discharge, and water quality conditions, including total suspended solids, ion, nutrient, and dissolved metal concentrations, specific conductivity, pH, and temperature, were measured and evaluated at two sampling sites (upstream and downstream of Bucknell’s main campus) during various rain events from September 2007 to March 2008. The primary focus of the stream analysis was based on one main rain event on 26 February 2008. The results provided evidence that Miller Run is impacted by Bucknell’s campus. From a hydrologic perspective, the stream’s hydrograph showed the exact opposite pattern of what would be expected from a ‘normal’ stream. Miller run had a flashier downstream hydrograph and a broader upstream hydrograph, which was more than likely due to the increased amount of impervious surface cover throughout the downstream half of the watershed. From a water quality perspective, sediment loads increased at a faster rate and were significantly higher downstream compared to upstream. These elevated sediment concentrations were probably the combined result of sediment runoff from upstream and downstream construction sites that were being developed over the course of the study. Sodium, chloride, and potassium concentrations, in addition to specific conductivity, also significantly increased downstream of Bucknell’s campus due to the runoff of road salts. Calcium and magnesium concentrations did not appear to be impacted by urbanization, although they did demonstrate a significant dilution effect downstream. The downstream site was not directly affected by elevated nitrate concentrations; however, soluble reactive phosphorus concentrations tended to increase downstream and ammonium concentrations significantly peaked partway through the rain event downstream. These patterns suggest that Miller Run may be impacted by nutrient runoff from the golf course, athletic fields, and/or fertilizers applications on the main campus. Dissolved manganese and iron concentrations also appeared to slightly increase downstream, demonstrating the affect of urban runoff from roads and parking lots. pH and temperature both decreased farther downstream, but neither showed a significant impact of urbanization. More studies are necessary to determine how Miller Run responds to changes in season, climate, precipitation intensity, and land-use. This study represents the base-line analysis of Miller Run’s current hydrologic and water quality conditions; based on these initial findings, Bucknell should strongly consider modifications to improve storm water management practices and to reduce the campus’s overall impact on the stream in order to enhance and preserve the integrity of its natural water resources.