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Made available in DSpace on 2014-10-09T12:24:53Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:49Z (GMT). No. of bitstreams: 1 00954.pdf: 5956396 bytes, checksum: 00e5961b8c5182b04c272a41f666c5de (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

The purpose of this research is to investigate human comfort criteria under steady-state conditions as a function of ambient air temperature, mean radiant temperature, relative humidity, air velocity, level of activity, and clothing insulation. Since the current ASHRAE Standard 55-1994 is for sedentary activity, this study will consider relative humidity (20% to 65%), dry bulb temperature (73 oF to 82 oF), air velocity (30 fpm and 50 fpm), and sedentary-to-moderate activity. The mean radiant temperature will be taken to be the same as the ambient air temperature. The experimental results collected at the Kansas State University Environmental Test Chamber are compared with the Fanger (1982) thermal comfort model and with ASHRAE Standard 55-1994. The experimental study results agreed well with ASHARE Standard 55-1994 for 1-met activity level (sedentary), and the thermal comfort for 1-met activity level was predicted with reasonable accuracy by Fanger?s (1982) Model. For 2.3 met activity level, the experimental results did not agree with ASHRAE Standard 55-1994 or the Fanger Model predictions.

Solid oxide fuel cell (SOFC) systems have the potential to provide highly efficient power generation systems capable of utilizing readily available hydrocarbons. It is hoped that these systems will be capable of replacing some of the conventional power systems and act to reduce overall emissions and increase energy efficiency. SOFC technology faces many challenges such as high cost, lifetime uncertainties, and long startup times; and these challenges have prevented SOFC technology from being widely adopted. Established methods for providing SOFC stack thermal management are either very costly, work against system design goals, or are unreliable. If SOFC thermal management needs could be reduced, it is possible that SOFC cost and lifetime could be improved. It is thought that promotion of thermal radiation within a SOFC stack may add thermal control which will reduce the need for stack thermal management. Radiation may be promoted by decreasing the length: hydraulic diameter ratio of cathode flow channels and by increasing the manifold size to create a larger stack radiation enclosure. Full thermal tests of a SOFC stack are difficult and expensive, and due to this simulations of a SOFC are widely used to analyze stack thermal behavior. In this work, a model of a SOFC “unit cell” is adjusted to represent modern SOFC stacks. The proposed methods for radiation promotion are tested with simulations using this model, and conclusions of radiation promotion in SOFC stacks are provided. Additionally, radiative properties of commonly used materials are obtained through experiments, and future work for reducing stack reliance on active thermal management is proposed.

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Safety is a paramount concern in the operation of training and test reactors. A major component of a reactor is the maintenance of safe thermal hydraulic operating conditions. If the temperature of the water coolant exceeds the boiling point, the heat transfer out of the fuel rods into the coolant will greatly decrease and will need to rely upon other safety feedbacks and systems to avoid an accident condition. TRIGA thermal hydraulic systems are currently modeled using a finite differencing code, TRACE/SNAP, developed by the Nuclear Regulatory Commission. While the code is currently certified, it has shortcomings that this work improves upon, notably the simplification of the more complex flow geometries by using circular pipes and a heat transfer correlation that is valid across all flow regimes observed during operation of the TRIGA. A computational fluid dynamics code, FLUENT, along with real-time thermocouple probe measurements of the channel were used to solve both of these major issues. A high resolution model of four adjacent flow channels was created to provide a numerical experimental data set for enhancing the correlations used in the TRACE model. The hot flow channel is connected to three surrounding channels where crossflow occurs causing a more complex flow pattern than the isolated single channel system used in TRACE/SNAP. To calibrate the FLUENT model, a thermocouple probe was designed and placed in the TRIGA core in the center of the flow channel. The reactor was operated over the full range of licensed power levels to obtain a fully encompassing data set of coolant temperatures. The FLUENT model was then adjusted so that the temperatures at the location of the probe in the model matched those from the experimental measurements. Based on the results from the FLUENT testing, data was extracted to develop a new heat transfer coefficient correlation and loss factor coefficient correlation due to the non-circular geometry and fuel rod end fittings for use in the TRACE/SNAP code. These adjustments were then implemented into TRACE/SNAP to improve the code for future users performing safety analysis on TRIGA reactors. / text

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