The chemical percolation devolatilization model applied to the devolatilization of coal in high intensity acoustic fields

Neste trabalho, um modelo de percolação química (CPD), desenvolvido para o cálculo da evolução dos produtos de pirólise de partículas de carvão, foi estendido de forma a ser empregado em regimes de degradação térmica sobre a influência de campos acústicos de alta intensidade, típicos de combustores do tipo tubo de Rijke. As oscilações acústicas incrementam os processos de transferência de calor e massa no leito de combustível, bem como na região livre acima do mesmo. Os resultados obtidos em simulações com um combustor do tipo Rijke mostraram um aumento nas taxas de evaporação de água e de degradação térmica das partículas. O modelo de percolação química empregado, no regime pulsante, permitiu o cálculo da evolução dinâmica de CO, CO2, CH4, H2O, outros gases leves e alcatrão, importantes no processo de ignição e estabilização de chamas. O modelo também forneceu a quantidade e forma dos compostos nitrogenados liberados no processo de pirólise que são indispensáveis nas estratégias para abatimento da emissão de poluentes (NOx) em regimes de queima excitados por oscilações acústicas. O bioma Pantanal é caracterizado pela inundação sazonal que determina processos ecossistêmicos específicos, com a ocorrência de plantas e animais adaptados à mudança anual de encolhimento e expansão de hábitats em virtude do regime hidrológico sazonal. A biodiversidade do Pantanal é um componente fundamental dos serviços ecossistêmicos prestados à sociedade humana, que inclui reciclagem de nutrientes, produção pesqueira, ecoturismo, resgate de carbono, controle de enchentes, entre outros, que são importantes consequências ambientais em nível regional e global. O bioma tem sido afetado pelo impacto da conversão de sua vegetação natural em campos agrícolas e pasto para a pecuária, com alteração e perda de hábitats e biodiversidade. O impacto maior tem ocorrido nas terras altas do planalto do entorno da planície, com desmatamento do Cerrado nas áreas onde nascem os rios que alimentam o Pantanal. Este artigo discute as necessidades e prioridades futuras de pesquisa ecológica para melhor entender o ecossistema e, assim, atingir sua conservação e uso sustentável. _______________________________________________________________________________ ABSTRACTThe chemical percolation devolatilization model (CPD) was extended for the prediction of drying and devolatilization of coal particles in high intensity acoustic fields found in Rijke tube reactors. The acoustic oscillations enhance the heat and mass transfer processes in the fuel bed as well as in the freeboard, above the grate. The results from simulations in a Rijke tube combustor have shown an increase in the rate of water evaporation and thermal degradation of the particles. The devolatilization model, based on chemical percolation, applied in pulsating regime allowed the dynamic prediction on the yields of CO, CO2, CH4, H2O, other light gases as well as tar which are important on ignition and stabilization of flames. The model predicted the quantity and form of nitrogen containing species generated during devolatilization, for which knowledge is strategically indispensable for reducing pollutant emissions (NOx) in flames under acoustic excitation

Effects of wet CO oxidation on the operation of engines and power generators

A simplified method is used to determine the optimum water content in the flue gases of charcoal gasifiers to be utilized as alternative fuels in the operation of engines and gas turbines for power generation. Computational models of plug flow reactors and well stirred reactors are employed to simulate the reaction and post-flame zones, adopting different chemical mechanisms. In the simulations reactants enter the reactors at 1000 K, 1 atm and equivalence ratio 0.25. It was observed that mixtures about 3% to 4% in volume of water vapor allow to obtain optimal operation characteristics, including high blowout limit, low ignition delay, maximum reaction zone temperature, high CO2 prodution and low thermal NO formation. It was observed that increasing water contents reduce significantly ignition times up to 3% in volume, while blowout mass flow rates increase continuously up to 6 % in volume, the maximum value considered. Formation of NO decreases continuously with humidity after the flame zone, while there are peaks of NO formation within the flame zone below 1% in volume. Higher water vapor content decreases the final temperatures below 1700 K, leading to a lower thermal efficiency. The method can be used to estimate optimum operational conditions with other input parameters

Aproveitamento de resíduos: um estudo da estimativa da energia de ativação do caroço de pequi para análise de viabilidade como fonte de energia limpa / Utilization of waste: a study of the estimated activation energy of pequi seeds for feasibility analysis as a source of clean energy

A pirólise constitui uma tecnologia de conversão termoquímica utilizada para produção de carvão, bio-óleo e gás. A biomassa lignocelulósica é um importante insumo na conversão termoquímica via pirólise, comprovado pelo grande número de trabalhos de pesquisa publicados de diversos tipos de biomassa. O objetivo deste trabalho é estimar a energia de ativação do caroço de pequi para se modelar o processo de pirólise que permita, em termos práticos, aumentar a produção de alguns subprodutos de interesse. A árvore do pequi tem a sua frutificação de outubro a fevereiro tendo sido extraídas 17150 toneladas da fruta no Brasil, em 2017 (IBGE), tornando-o uma importante fonte de energia renovável para o país. Os resultados da análise termogravimétrica foram utilizados para se estimar a energia de ativação da pirólise do caroço de pequi com taxas de aquecimento de 5, 10 e 20°C/min. As energias de ativação calculadas para os picos referentes a holocelulose pelos métodos de Osawa, k-A-S e Starink, foram, respectivamente, 89032,12, 84984,48 e 85249,73 kJ/mol

A low-cost filament winding technology for university laboratories and startups

This paper systematically explains the methodology and results of empirical work on the development of a low-cost filament winding technology for manufacturing axisymmetric polymer composite structures with a high length-to-diameter ratio, such as tubes, motor casings, and pressure vessels. The principal objective was to examine the experiences and most optimal practices in the development of computer-controlled equipment and auxiliary tooling for the wet filament-winding process. To preclude expensive commercial software for the automated control of a winding machine, analytical equations were derived for the winding trajectory of a four-axis filament-winding machine. The feasibility of the proposed equations was successfully validated by laying the fiber along the geodesic path marked on the surface of a cylindrical mandrel with hemispherical ends. Moreover, the carbon/epoxy cylindrical casings with hemispherical ends and port openings of the same diameter were wound to determine the thickness distribution in the hemispherical dome. The fiber volume ratio in the wound composite parts was evaluated using an optical technique

Implantando um Escritório de Gerenciamento de Projetos Estratégico: um estudo de caso em uma instituição federal de ensino

O presente estudo tem como objetivo geral compreender o processo de implantação de um EGP estratégico. A pesquisa se torna relevante, na medida em que se observa o crescimento em relação à adoção e implantação de EGPs estratégicos, encarregados de exercerem funções de apoio estratégico. Também percebe-se que muitas dessas estruturas estão sendo implantadas sob diferentes formatos, sendo, portanto, um objeto de estudo que precisa ser melhor investigado. O estudo adotou uma abordagem qualitativa, por meio de um estudo de caso em uma instituição pública de ensino, tendo como procedimentos técnicos de coleta uma narrativa, assim como documentos institucionais obtidos, e como procedimento de análise as técnicas de análise de conteúdo e codificação. Os resultados demonstram que há diferenças em relação ao processo de implantação do EGP estratégico, comparado o caso estudado com a literatura existente. Além disso, observou-se que o EGP estratégico foi implantado de forma gradativa e com processos contínuos de melhoria de suas práticas. Contudo, o estudo apresenta como implicações gerenciais a necessidade de se refletir sobre as funções desempenhadas pelo escritório, bem como a possibilidade de ampliar seu escopo de participação, utilizando uma estrutura descentralizada que permita uma maior organização e divisão de suas funções

An optimized hybrid rocket motor for the SARA platform reentry system

This paper has described a system design process, based on a multidisciplinary optimization technique, of a conceptual optimized hybrid propellant rocket motor. The proposed engine could be a technological option for the reentry maneuvering system of the Brazilian recoverable satellite (SARA), which was designed by the Brazilian Institute of Aeronautics and Space. The resulting optimized propulsion system must be viewed as a proof of concept allowing comparison to more conventional technologies, i.e., liquid and solid motors. Design effort was conducted for hybrid propellants engines based on a liquefying fuel (solid paraffin) and two different oxidizers, H2O2 (90% high-testperoxide) and self-pressurizing N2O. The multidisciplinary configuration optimization technique was supported on geometrical operating parameters of the motor, rather than on performance, in order to facilitate subsequent design and fabrication. Results from the code presented a hybrid motor, which was considered a competitive alternative for the deboost engine when compared to the traditional chemical systems, solid and liquid bipropellant, and monopropellant. The estimated mass of the reentry system, for the cases addressed in this study, varied from 22 to 29 kg, which is lower than either liquid bipropellant or solid engines formerly proposed

The tropical forest and fire emissions experiment: Trace gases emitted by smoldering logs and dung from deforestation and pasture fires in Brazil

Earlier work showed that Amazonian biomass burning produces both lofted and initially unlofted emissions in large amounts. A mobile, Fourier transform infrared spectrometer (FTIR) measured the unlofted emissions of 17 trace gases from residual smoldering combustion (RSC) of logs as part of the Tropical Forest and Fire Emissions Experiment (TROFFEE) during the 2004 Amazonian dry season. The RSC emissions were highly variable and the few earlier RSC measurements lay near the high end of combustion efficiency observed in this study. Fuel consumption by RSC was ∼5% of total for a planned deforestation fire. Much regional RSC probably occurs in the residual woody debris burned during pasture maintenance fires. RSC could increase estimated total fire emissions for the Amazon region by 20–50% for several important VOC. FTIR emissions measurements of burning dung (in a pasture) showed high emission ratios for acetic acid and ammonia to CO (6.6 ± 3.4% and 8.9 ± 2.1%). Large emissions of nitrogen containing trace gases from burning dung and crop waste could mean that biomass burning in India produces more particle mass than previously assumed. Measurements of late-stage kiln emissions suggested that VOC/CO may increase as carbonization is extended. A cook stove emitted many VOC and NH3 far outside the range observed for open wood cooking fires. Enclosed/vented cooking stoves may change the chemistry of the smoke that is emitted

Transcranial direct current stimulation influences the cardiac autonomic nervous control

AbstractTo investigate whether the manipulation of brain excitability by transcranial direct current stimulation (tDCS) modulates the heart rate variability (HRV), the effect of tDCS applied at rest on the left temporal lobe in athletes (AG) and non-athletes (NAG) was evaluated. The HRV parameters (natural logarithms of LF, HF, and LF/HF) was assessed in 20 healthy men before, and immediately after tDCS and sham stimulation. After anodal tDCS in AG the parasympathetic activity (HFlog) increased (P<0.01) and the sympathetic activity (LFlog) and sympatho-vagal balance (LF/HFlog) decreased (P<0.01), whereas no significant effects were detected in NAG (P>0.05). No significant changes in HRV indexes were provoked by sham stimulation in both AG and NAG (P>0.05). In conclusion, tDCS applied on the left temporal lobe significantly increased the overall HRV in AG, enhancing the parasympathetic and decreasing the sympathetic modulation of heart rate. Consequently the sympatho-vagal balance decreased at rest in AG but not in NAG. Releasing a weak electric current to stimulate selected brain areas may induce favorable effects on the autonomic control to the heart in highly fit subjects

A STUDY OF THE ATOMIZATION PROCESS USING NUMERICAL SIMULATION

The liquid droplets atomization process plays an important role in several&nbsp;industrial processes and in many aspects of the combustion engines performance, gas&nbsp;turbines, diesel engines and rocket motors. The use of Computational Fluid Dynamics (CFD)&nbsp;to study the atomization process is relatively new and this work studies the atomization spray&nbsp;field using pressure swirl atomizers and the computation simulations was done by the using of the commercial software CFX 15. The parameter analyzed was the semi-angle of the spray.&nbsp;Particles were placed at the entrance and different settings for the primary and secondary&nbsp;breakup were studied. Two models for the primary breakup (BLOB and LISA models) were tested and two other for the secondary breakup (Reitz and Diwakar model and TAB model). The numerical results were compared with experimental data and showed acceptable compatibility.&nbsp

Bowel symptoms associated with coronavirus disease 19 in hospitalized patients with moderate to severe illness

Bowel symptoms, such as diarrhea, have higher prevalence during coronavirus disease 2019 (COVID-19). The correlation between the severity of these symptoms and their prognosis has not been defined yet. Furthermore, higher prevalence of gastrointestinal symptoms after recovery from COVID-19 has been reported. This study aimed to analyze the correlation of potential factors with the severity of diarrhea during COVID-19 and to assess the progression of post-COVID-19 bowel symptoms. This prospective longitudinal cohort included 109 patients with moderate to severe COVID-19 symptoms who were hospitalized from May to July 2021. Patients were interviewed to assess the presence and intensity of bowel symptoms during COVID-19 and 3–6 months after hospital discharge using the Gastrointestinal Symptom Rating Scale questionnaire. Demographic and clinical data were obtained and their correlations with the intensity of bowel symptoms were examined. The presence of severe diarrhea was correlated with the need for ventilatory support and the use of anticoagulants but not with the use of antibiotics. In addition, bowel symptoms, such as loose stools and incomplete evacuation but not diarrhea, constipation, or abdominal pain, persisted for at least 3–6 months after hospital discharge. These results suggest that the severity of diarrhea during COVID-19 may be associated with worsening of the disease and that only loose stools and incomplete evacuation are present after COVID-19. The chronicity of these bowel symptoms should be evaluated to improve the treatment of patients with COVID-19