Examinando por Materia "REACTORES NUCLEARES"
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- Tesis de maestríaLarge eddy and rans simulations of V-RIB structured cooling channels of the first wall of future fusion reactors(2020) Winzig, Manuel; Klein, ChristineThis work contributes to the development of the future fusion reactor DEMO. It investigates the cooling of the first wall blankets by rib structured cooling channels. For this purpose, RANS simulations using the 𝑘 − 𝜔 − 𝑆𝑆𝑇 model and the Reynolds Stress Model as well as Large Eddy Simulation were carried out on a channel with V-shaped ribs on one side at a Reynolds number of 𝑅𝑒 = 1.56 ⋅ 10 As a working fluid helium was used at an operating pressure of 𝑝 = 8 𝑀𝑃𝑎. The relative roughness of the channel was 𝑒⁄𝐷ℎ = 0.0461 and the rib pitch was 𝑝⁄𝑒 = 10. The focus of the analysis of the results has been on heat transfer quantities, pressure loss and flow patterns. It was shown that the rib induced vortical structures that were associated with a large increase in heat transfer downstream of the rib but also caused a heat transfer deterioration directly behind it. The comparison between the simulations has shown that the 𝑘 − 𝜔 − 𝑆𝑆𝑇 model resolves well the magnitude of the averaged heat transfer but fails to reproduce the flow patterns and friction factor accurately when compared to the Large Eddy Simulation. On the other side, the Reynolds Stress Model showed better accuracy resolving the flow patterns and friction factor but strongly underpredicts the heat transfer for the given case. Additionally, the results of the Large Eddy simulation have been compared to previous simulation results that have been conducted on a smooth and a rib structured channel with 𝑒 = 0.9 𝑚𝑚. It was shown that reducing the rib height led to a slight decrease in heat transfer on the rib structured side but also reduced the pressure loss significantly.
- Tesis de maestríaSynthesis of nickel-based catalysts and their application in pyrolysis oil upgrading in a batch reactor(2018) Gagliardi Reolon, María Belén; Carriel Schmitt, Caroline"The thermochemical decomposition of beech wood biomass results in a poor quality bio-oil, which cannot be directly used in diesel engines. In order to make this oil resemble liquid fossil fuels, an upgrading technique should be applied. Among the available possibilities, hydrodeoxygenation (the removal of oxygen and saturation of double bonds through high pressure hydrogen) appears to be the most auspicious route to produce biofuels. Besides, this method requires a catalyst to increase the activity, which could be reused in further upgrading reactions so as to minimize the generation of waste material. In this work, four nickel-based catalysts were evaluated for the hydrodeoxygenation of beech wood bio-oil. After being synthesized, their superficial and compositional characteristics were assessed. Once the upgrading reaction was performed for the pyrolysis oil, the resulting products (upgraded bio-oil, aqueous phase and gas fraction) were separately analyzed. Considering the obtained results, the catalyst with the best upgrading performance was selected in order to regenerate and use it in further hydrodeoxygenation reactions. The catalyst selection was based on upgraded bio-oil, catalyst and reaction factors. Parameters such as carbon, oxygen and water content, HHV, pH value, poisoning and overall hydrogen consumption were taken into account. With the obtained results, Ni/SiO2 was chosen and therefore regenerated, which included the calcination and reduction of the spent catalyst before it was reused in a new hydrodeoxygenation reaction. Its performance was tested along three consecutive reactions and the quality of upgraded bio-oils corresponding to these cycles were evaluated. It could be concluded that Ni/SiO2 showed an improvement in the upgraded bio-oil quality next to a satisfactory performance after the three regeneration cycles, which points out that this particular catalyst can be regenerated and reused for a minimum of three times without significantly affecting the resulting upgraded bio-oil quality. Further characterization techniques should be performed in order to achieve a bigger understanding of the functioning of nickel-based catalysts and their reutilization in a larger number of consecutive upgrading reactions."
- Tesis de maestríaThermohydraulic investigation on the use of carbon dioxide as coolant for a solid breeding blanket for DEMO(2017) Caspari, Felix; Boccaccini, Lorenzo V.; Hernández González, Francisco A.; Smoglie, Cecilia"The Helium Cooled Pebble Bed (HCPB) Breeding Blanket (BB) is one of the 4 BB concepts being investigated in the EU for their possible implementation in a demonstration nuclear fusion reactor (DEMO). The choice of He as fuid coolant for the BB is motivated by a virtually complete transparency to neutrons, leaving unafected the T production capabilities of the blanket, as well as chemical inertness, molecular stability under high temperatures and neutron irradiation and a superior heat conductivity and capacity, leading to the best cooling performance in terms of heat transfer capabilities among other gas cooling choices. However, this cooling performance figure is hindered by the very low density of the gas, which leads to large pressure drops and high pumping power, thus afecting the overall plant efficiency, as well as to chronic leakages and large coolant inventories. These disadvantages, together with the still immature technology readiness of the respective turbomachinery, the price of this coolant, as well as its recognized limited resources pose concerns about the use of He as coolant for a BB in DEMO. On the other side, carbon dioxide has been the fuid coolant choice since the 50's in the nuclear fission industry for gas cooled reactors (MAGNOX, AGR). Despite its lower heat capacity and thermal conductivity (about 22% and 17% of that of helium respectively), its larger density (11 times larger molecular weight for CO2) can lead to an advantageous performance on heat dissipation rate per unit of pumping power. This feature, coupled with its relative transparency to neutrons, the molecular stability at the operating temperatures of the BB and the industrial scale ready turbomachinery makes CO2 an attractive alternative to He. The feasibility of a CO2-cooled breeding blanket is assessed in this work from the point of view of the thermohydraulic performance."