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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Multi-dimensional modeling of transient transport phenomena in molten carbonate fuel cells

Yousef Ramandi, Masoud 01 June 2012 (has links)
Molten carbonate fuel cells (MCFCs) have become an attractive emerging technology for stationary co-generation of heat and power. From a technical perspective, dynamic operation has a significant effect on the fuel cell life cycle and, hence, economic viability of the device. The scope of this thesis is to present an improved understanding of the system behaviour at transient operation that can be used to design a more robust control system in order to overcome the cost and the operating lifetime issues. Hence, a comprehensive multi-component multidimensional transient mathematical model is developed based on the conservation laws of mass, momentum, species, energy and electric charges coupled through the reaction kinetics. In essence, this model is a set of partial differential equations that are discretized and solved using the finite-volume based commercial software, ANSYS FLUENT 12.0.1. The model is validated with two sets of experimental results, available in open literature, and good agreements are obtained. The validated model is further engaged in an extensive study. First, the MCFC behaviour at high current densities or oxidant utilization, when the mass transfer becomes dominant, is investigated using peroxide and superoxide reaction mechanisms. In brief, both mechanisms predicted the linear region of the polarization curve accurately. However, none of these mechanisms showed a downward bent in the polarization curve. A positive exponent for the carbon-dioxide mole fraction is probably essential in obtaining the downward bent (“knee”) at high current densities which is in contrast to what has been reported in the literature to date. Next, a sinusoidal impedance approach is used to examine the dynamic response of the unit cell to inlet perturbations at various impedance frequencies. This analysis is further used to determine the phase shifts and time scales of the major dynamic processes within the fuel cell. Furthermore, numerical simulation is utilized in order to investigate the underlying electrochemical and transport phenomena without performing costly experiments. Results showed that the electrochemical reactions and the charge transport process occur under a millisecond. The mass transport process showed a comparatively larger time scale. The energy transport process is the slowest process in the cell and takes about an hour to reach its steady state condition. Furthermore, the developed mathematical model is utilized as a predictive tool to provide a three-dimensional demonstration of the transient physical and chemical processes at system startiv up. The local distribution of field variables and quantities are presented. The results show that increasing the electrode thickness provides a higher reaction rate, but may lead to larger ohmic loss which is not desirable. The reversible heat generation and consumption mechanisms of the cathode and anode are dominant in the first 10 s while the heat conduction from the solid materials to the gas phase is not considerable. The activation and ohmic heating have the same impact within the anode and cathode because of their similar electric conductivity and voltage loss. Increasing the thermal conductivity of the cathode material will facilitate the process of heat transport throughout the cell. This can also be accomplished by lowering the effects of heat conduction by means of a cathode material with a smaller thickness. In addition, a thermodynamic model is utilized to examine energy efficiency, exergy efficiency and entropy generation of a MCFC. By changing the operating temperature from 883 K to 963 K, the energy efficiency of the unit cell varies from 42.8 % to 50.5 % while the exergy efficiency remains in the range of 26.8% to 36.3%. Both efficiencies initially rise at lower current densities up to the point that they attain their maximum values and ultimately decrease with the increase of current density. With the increase of pressure, both energy and exergy efficiencies of the cell increase. An increase in this anode/cathode flow ratio lessens the energy and exergy efficiencies of the unit cell. Higher operating pressure and temperature decrease the unit cell entropy generation. / UOIT
2

The New Venture Creation Process in Cooperation with Science Park Jönköping

Brettl, Eva, Kleinert, Vinia, Karamatova, Liliya January 2010 (has links)
Purpose The purpose of this thesis is to explore how students at Jönköping University can establish a new business and to what extent Science Park Jönköping is involved throughout the business creation process. Background Numerous researches have been done on new venture creation and business incubation. However, these two areas of research are rarely combined. When it comes to venture creation, most theories focus either solely on the start-up process or on the entrepreneur and the environment. The novelty of this thesis lies in combining those two different fields of research and at the same time focusing on the entrepreneur, the environment and the start-up process. The authors aim at investigating the start-up process in connection with the business incubator Science Park Jönköping. This paper is opposing new venture creation process theory with empirical findings and further examining the influence of the business incubator Science Park Jönköping. Method The authors of this paper followed a qualitative approach which was implemented in the form of personal interviews. The participants of this study are entrepreneurs who created their venture in cooperation with Science Park Jönköping as well as one representative from Science Park Jönköping. Conclusion Contrary to previous research, the participants of this study do not perceive the business creation process and its stages as linear. Moreover, influential factors like the attributes of the entrepreneur and the environment have to be taken into account when speaking about the start-up of a company. Science Park Jönköping offers services at all stages of the process whereas the most intense contact between the business incubator and the entrepreneur takes place in the very beginning.
3

The New Venture Creation Process in Cooperation with Science Park Jönköping

Brettl, Eva, Kleinert, Vinia, Karamatova, Liliya January 2010 (has links)
<p><strong>Purpose</strong></p><p>The purpose of this thesis is to explore how students at Jönköping University can establish a new business and to what extent Science Park Jönköping is involved throughout the business creation process.</p><p><strong>Background</strong></p><p>Numerous researches have been done on new venture creation and business incubation. However, these two areas of research are rarely combined. When it comes to venture creation, most theories focus either solely on the start-up process or on the entrepreneur and the environment. The novelty of this thesis lies in combining those two different fields of research and at the same time focusing on the entrepreneur, the environment and the start-up process. The authors aim at investigating the start-up process in connection with the business incubator Science Park Jönköping. This paper is opposing new venture creation process theory with empirical findings and further examining the influence of the business incubator Science Park Jönköping.</p><p><strong>Method </strong></p><p>The authors of this paper followed a qualitative approach which was implemented in the form of personal interviews. The participants of this study are entrepreneurs who created their venture in cooperation with Science Park Jönköping as well as one representative from Science Park Jönköping.</p><p><strong>Conclusion</strong></p><p>Contrary to previous research, the participants of this study do not perceive the business creation process and its stages as linear. Moreover, influential factors like the attributes of the entrepreneur and the environment have to be taken into account when speaking about the start-up of a company. Science Park Jönköping offers services at all stages of the process whereas the most intense contact between the business incubator and the entrepreneur takes place in the very beginning.</p>

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