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Browsing by Subject "FLUENT"

Now showing 1 - 2 of 2
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    Fluid modeling and design of gas channels of solar non-stoichiometric redox reactor
    (2014-02) Kedlaya, Aditya
    The present numerical study in FLUENT analyzes the fluid flow field within a solar powered reactor designed for syngas production. The thermochemical reactor is based on continuous cycling of cerium oxide (ceria) in a non-stoichiometric reduction/oxidation cycle. The reactor uses a hollow cylinder of porous ceria which rotates through a high-temperature zone, by exposure to concentrated sunlight and partially reduced in an inert atmosphere due to flow of the sweep gas (N2), and then through a lower temperature zone where the reduced ceria is re-oxidized with a flow of CO2 and/or H2O, to produce CO and/or H2. In terms of fluid flow modeling, the issue of crossover of species (leakage) within the reactor is critical for proper functioning of the reactor. The first part of the work relates to the geometry and placement of the inlet/outlet gas channels for the reactor optimized to minimize crossover of the species. This is done by conducting a parametric study of geometric variables associated with the inlet/outlet geometry. A simplified 2D fluid flow reactor model which incorporates multi-species flow is used for this study. Further, 2D and 3D reactor models which capture the internal structure more accurately are used to refine the inlet/outlet design. The optimized reactor model is found to have an O2 crossover of 2%-6% and oxidizer crossover of 8%-21% at different flow rates of the sweep gas and the oxidizer studied.In the second part of the work, the reactor model is simulated under varying test conditions. Different working conditions include morphologies of the reactive material, rotational speed of the ceria ring and the recuperator, flow rates of sweep gas and the oxidizer, types of oxidizer (CO2, H2O). The 3D reactor model is also tested using one, two and three discrete inlet/outlet ports and compared with slot configuration
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    Thermodynamic and heat transfer models of an open accumulator.
    (2009-12) Hafvenstein, David James
    A conventional accumulator stores energy for hydraulic systems by compressing an enclosed mass of air, but this air takes up too much volume at low pressure to be practical in applications such as a hydraulic hybrid passenger vehicle. An open accumulator compresses air from the atmosphere to store energy, eliminating the need to store low-pressure air but creating large temperature swings if the heat transfer during compression and expansion is poor. This thesis investigates thermodynamic and heat transfer aspects of an open accumulator to assist in its design. A thermodynamic model was created to determine the efficiency and required heat transfer for open accumulator designs with a volume 1/5th that of a comparable conventional, or “closed,” accumulator. A heat transfer parameter, Z = hA/V, describes how easy it would be to implement the required heat transfer, with low required values of Z being desirable. A design with only one stage of compression and high wall temperature had a lower required value for Z than the high pressure stages in multi-stage designs. For an open accumulator that provides 20 kW of power in expansion and 840 kJ of energy storage at a pressure of 350 times atmospheric conditions, the volume target was 15.7 ℓ and the required Z values for compression and expansion were approximately 6.2×104 W/m3K. A computational fluid dynamics model using the program FLUENT was created to investigate whether the required Z could be achieved in a more practical, three-stage open accumulator design. The expansion case of the lowest-pressure stage was simulated, with a required Z value from the thermodynamic model of 3.83×104 W/m3K. The iv computational domain was a symmetrical, 3-D, diaphragm-bounded chamber of approximately 0.5 ℓ displaced volume, and a realizable k-ε model was used to model the effects of turbulence. The flow pattern generated during the air intake period dominated the flow during expansion, and peak local heat fluxes occurred where the intake flow patterns drew cold fluid next to the walls. The peak heat transfer for the simulation was 386 W. The mean Z value calculated was 9.79×103 W/m3K, around 1/4th of the required value.