https://repositorio.ufu.br/handle/123456789/19021 2026-08-07T01:00:14Z 2026-08-07T01:00:14Z https://repositorio.ufu.br/handle/123456789/49147 2026-07-30T06:26:15Z 2025-07-29T00:00:00Z

Title: Investigação numérica e experimental de sistemas de concentração solar com lentes de Fresnel para desinfecção de água Abstract: Universal access to water is one of the United Nation’s 17 sustainable development goals and a fundamental human right. However, factors such as extreme poverty, geographical isolation, and climate change pose challenges to ensuring access to safe water for populations located mainly in rural communities in underdeveloped and developing countries. Among the existing technologies for water treatment in remote regions, solar water disinfection (SODIS) stands out, which can be intensified by solar concentrators that increase the intensity of sunlight, shortening the time required for exposure and increasing the rate of microorganism inactivation. This study evaluated the potential of alternative solar concentrators, such as point and linear Fresnel lenses, in photoactivated processes such as SODIS using computational fluid dynamics to solve the equations of momentum, radiation, and species transport. To this end, two experimental units and their respective computational models were developed and validated experimentally through actinometry with potassium ferrioxalate, and a simulation design was conducted to evaluate the effect of operational variables on the main responses that characterize the performance of these concentrators. A mechanistic model of E. coli disinfection based on the generation of reactive oxygen species (ROS) and inactivation of cell protection enzymes available in the literature was implemented in the computational models to enable the numerical evaluation of the performance of these Fresnel lens concentrator systems. The results obtained indicate that the computational models developed reproduced the radiation and velocity fields properly, and a high potential for radiation intensification in the reactors was observed using the lenses. In the linear Fresnel concentrator system, it was found that the recirculation flow rate has a small effect on the reaction rate within the range of 0.4 L·min-1 to 3.95 L·min-1, and the conversion depends mainly on the position of the reactor and solar irradiation. Disinfection kinetics results showed that for the point lens it is important to ensure adequate radiation distribution, while in the unit with a linear lens it is necessary to seek a balance between increasing the fluid’s residence time in the reactor and the fluid dynamics inside the tubular reactor. Both solar concentrator systems were able to substantially reduce the treatment time of conventional SODIS to just a few minutes of operation, based on the dimensions of the development of the experimental rigs.

2025-07-29T00:00:00Z https://repositorio.ufu.br/handle/123456789/48941 2026-07-22T06:28:28Z 2026-02-09T00:00:00Z

Title: Investigação da produção de Biohidrogênio por Fotofermentação utilizando Bactérias Púrpuras não Sulfurosas na presença de Barita e Basalto Abstract: Hydrogen stands out as a clean and promising fuel, especially when produced from biomass. The current study aimed to evaluate the biological production of hydrogen using rock (Basalt) and ore (Barite) in a fermentation medium, with the intention of favoring microbial activity or promoting cell stabilization and employing in the medium non-sulfur purple bacteria associated in a 1:1:1 ratio: Rhodobacter capsulatus, Rhodospirillum rubrum, and Rhodopseudomonas palustris. As carbon sources, lactose from whey permeate powder, a co-product of the agro-industry, and glucose P.A., both at a concentration of 20 g/L, were used. The control test with lactose resulted in a productivity of 16.67 ± 0.361 mmol H₂/(L·day)], higher than that of glucose [11.35 ± 0.363 mmol H₂/(L·day)]. The presence of Barite in the culture medium increased hydrogen productivity by 12-fold compared to the control [215.32 ± 3.22 mmol H₂/(L·day)], while Basalt resulted in a 6-fold increase [109.28 ± 4.53 mmol H₂/(L·day)]. The most efficient condition in terms of hydrogen productivity, among the lactose concentrations tested (15, 20, 25 and 30 g/L), using Barite and culture medium with molybdate, was 20 g/L. Next, a factorial design was carried out in which the inoculum density and Barite concentration were evaluated and validated. The central point (0.2 gvs/L of inoculum and 0.27 g/L of Barite) was considered operationally optimal, resulting in 213.40 ± 3.80 [mmol H₂/(L·day)]. The Basalt was also subjected to chemical treatments using NaOH, HCl, and H₂SO₄ to hydrogen productivity increases. Among the treatments evaluated, the treatment with NaOH showed the highest performance, resulting in a productivity of 185.23 ± 4.25 [mmol H₂/(L·day)], higher than the value observed in the control condition 124.95 ± 4.37 [mmol H₂/(L·day)]. Among the chemical treatments with NaOH evaluated (15, 20, 25 and 30%), using Basalt, the treatment with 20% NaOH presented the highest hydrogen productivity. Finally, after carrying out a factorial design in which the inoculum density and the concentration of the treated rock were evaluated and validated, the point corresponding to 0.230 gSV/L of inoculum and 0.365 g/L of treated rock was considered operationally optimal, resulting in a production of 193.89 ± 4.37 [mmol H₂/(L·day)].

2026-02-09T00:00:00Z https://repositorio.ufu.br/handle/123456789/48071 2026-01-27T06:19:50Z 2025-07-24T00:00:00Z

Title: Estudo da sedimentação e acomodação de partículas em sistemas submetidos a gradientes de temperaturas Abstract: Sedimentation is a widely used process in industry, encompassing various sectors. Among the factors that influence its efficiency, temperature plays a decisive role in solid-liquid separation. A notable example occurs in oil well drilling, where the drilling fluid is subjected to heating due to geothermal conditions, with a temperature increase as the well depth increases. During interruptions in drilling fluid circulation, suspended particles tend to settle, which can compromise well integrity. In this context, this work investigated the behavior of sedimentation and particle arrangement in systems subjected to different thermal conditions, with emphasis on the formation and structure of the sediment bed. The main objective was to evaluate the behavior of the sediment bed as a function of the sedimentation temperature, considering both isothermal conditions and scenarios with thermal gradients, in systems containing only water as well as more complex fluids, such as drilling fluids. For this purpose, systems containing calcium carbonate suspensions in water and drilling fluids with different solid concentrations were prepared. The analyses included sedimentation tests under isothermal conditions and with horizontal and vertical temperature gradients. The solid concentration profile was determined using the gamma-ray attenuation technique, a non-destructive method that allows the assessment of the solids concentration distribution in the sediment bed. The results indicate that increasing the temperature accelerates the sedimentation process, reduces fluid viscosity, and alters the structure of the sediment bed by promoting sediment expansion. In systems with thermal gradients, particle migration towards heated regions and the formation of asymmetric beds with concentration variations along the horizontal axis were observed. In drilling fluids, temperature directly influenced rheology and resistance to sedimentation, with significant differences observed between the samples analyzed. This research contributes to the understanding of thermal effects on sedimentation, providing insights for the design and operation of industrial systems where temperature variations are relevant, such as in oil well drilling.

2025-07-24T00:00:00Z https://repositorio.ufu.br/handle/123456789/47787 2025-12-03T06:20:44Z 2025-04-29T00:00:00Z

Title: Estudo de catalisadores de cobalto suportados em nióbia mesoporosa aplicados na síntese Fischer-Tropsch Abstract: Fischer-Tropsch synthesis (FTS) is a promising process for converting synthesis gas into high- value fuels and chemicals, typically catalyzed by metals such as iron and cobalt supported on high-surface-area materials. This thesis proposes the use of mesoporous niobia as an alternative support for cobalt catalysts applied in FTS, focusing on the preparation of supports with high surface area and good porosity through the hydrothermal method. The catalytic performance of different cobalt loadings (10, 15, 20, and 30 wt%) supported on Nb2O5-m was evaluated, as well as the effects of the catalyst synthesis method on their activity and selectivity. The results showed that high-surface-area niobia promotes good dispersion of the active phase and high selectivity for liquid hydrocarbons (C5–C19), presenting performance comparable to commercial catalysts, even without the use of noble metal promoters. These findings highlight the feasibility of mesoporous niobia as a catalytic support for hydrocarbon conversion applications, and this research contributes to the advancement of catalytic technologies aligned with global demands for emission reduction and energy transition.

2025-04-29T00:00:00Z