Propagación de llamas premezcladas

El estudio del fenómeno de la combustión es de gran relevancia científica y tecnológica para la sociedad. La crisis climática que enfrenta la sociedad ha llevado a los científicos a proponer diferentes estrategias para mitigar el impacto en el medio ambiente. Una de las estrategias propuestas es ampliar el uso de combustibles alternativos y de biocombustibles, aprovechando sus características menos contaminantes. Algunos combustibles alternativos, que son considerados como opciones promisoras, son el gas de síntesis, biogas, etanol, hidrogeno y farnesano, entre otros. Sin embargo, el desarrollo de tecnologías que permitan tal uso depende del conocimiento fundamental de los procesos de combustión (Law, 2006). Históricamente, el uso de los combustibles tradicionales ha promovido el desarrollo teórico y experimental de la ciencia de la combustión, con investigaciones que datan de finales del siglo XIX hasta la actualidad. El estudio de la combustión implica el acoplamiento de reacciones químicas (Sarathy et al., 2014) con procesos de transferencia de calor en fluidos compresibles. Además, en el caso de las detonaciones (Ciccarelli & Dorofeev, 2008), y en muchas aplicaciones prácticas, la combustión es turbulenta, adicionando otros aspectos interesantes a su estudio (Swaminathan & Bray, 2011). En términos generales, la combustión se divide en el estudio de llamas premezcladas y no-premezcladas. En esta conferencia abordaré algunos fenómenos relevantes para el estudio de las llamas premezcladas, como son la velocidad de llama laminar, los límites de inflamabilidad, las deflagraciones y las detonaciones

CO2 emission factors and carbon losses for off-road mining trucks

There are myriad questions that remain to be answered in greenhouse gas (GHG) emissions trading. This article addresses carbon dioxide (CO2 ) emission factors and carbon losses from heavy equipment that is used to transport ores. Differences occurred between the Intergovernmental Panel for Climate Change (IPCC) emission factor and those that were obtained by considering incomplete combustion and on-site exhaust concentration measurements. Emissions from four off-road vehicles were analyzed. They operated at idle (loading, unloading, and queuing) and in motion (front and rear, loaded and unloaded). The results show that the average CO2 emission factors can be as low as 64.8% of the IPCC standard value for diesel fuel. On the other hand, carbon losses can be up to 33.5% and energy losses up to 25.5%. To the best of the authors’ knowledge, the method that was developed here is innovative, simple, useful, and easily applicable in determining CO2 emission factors and fuel losses for heavy machinery

Experimental assessment and modeling of solar air heater with V shape roughness on absorber plate

A roughness of the absorber plate can improve the efficiency of a solar air heater. To boost the efficiency of triangle solar air heaters, this research presents the results of a comparison study between with and without rib roughness on absorber plates. Both use black paint with graphene nanoparticles infused into it, coating an absorber plate. Both numerical and experimental methods have been used to examine the impact of surface roughness on friction factors and heat transport properties. ANSYS 14.5 software module and RNG turbulence, k-€ model is used to conduct a three-dimensional simulation and solve the governing equations in the turbulent situation. Based on experimental data, it has been established that smooth plates are more efficient in converting heat into useful work than rough ones, on average, by a factor of 4.82 and 4.46, respectively. The length of the duct in the solar air heater mitigates the temperature gradient seen in the simulation result. The roughness of V-shaped ribs has a far larger effect on the heat transfer and friction factor properties than do variations in relative roughness pitch (P/e) and Reynolds number (Re). Experimental observations supported by modeling and simulation confirms that triangular duct absorber surface roughness provides improved outcome

Simulação da produção e combustão de gás de síntese oriundo de gaseificadores de leite fixo

O objetivo do presente trabalho é desenvolver e comparar quatro modelos, baseados em conceitos de equilíbrio termoquímico, para predizer a composição do gás de síntese de biomassa obtido de gaseificadores de corrente descendente e de corrente ascendente. Assim, também é objetivo do presente trabalho o desenvolvimento de um modelo para determinar a temperatura e a composição do gás produto da combustão de gás de síntese, à pressão e volume constantes. Um dos modelos desenvolvidos para determinar a composição do gás de síntese (M4) leva em conta o carbono não convertido em estado sólido. Os modelos M2 e M3 foram desenvolvidos considerando diferentes reações de equilíbrio, que envolvem o metano. Como uma tentativa para melhorar a aproximação com dados experimentais, a equação de conservação da energia foi corrigida para os modelos M2, M3 e M4, considerando um método diferente para determinar o valor da entalpia de formação da biomassa. Para o modelo M1, a entalpia de formação da biomassa foi determinada aplicando a definição do PCS. Todos os modelos de equilíbrio para a gaseificação foram testados com dados experimentais de gaseificação de biomassa em gaseificadores de corrente descendente tomados de quatro trabalho diferentes, e com dados de gaseificadores de corrente ascendente de dois trabalhos diferentes. Foram considerados diferentes tipos de biomassa, como madeira, pó de serragem, madeira de seringueira, madeira peletizada e lodo de esgoto peletizadoThe goal of the present work is to develop and compare four models, based on thermochemical equilibrium concepts, to predict the composition of synthesis gas obtained from biomass downdraft and updraft gasifiers. Also was a goal of the present work to develop a model to determine the temperature and composition of the product gas originated from the synthesis gas combustion, at constant pressure and at constant volume. One of the models developed to determine the synthesis gas composition (M4) takes into account unconverted carbon in solid state. Models M2 and M3 were created considering different equilibrium reactions, involving methane. In order to improve model accuracy, the energy balance equation was corrected, for models M2, M3 and M4, by considering a different method to calculate the formation enthalpy of biomass. For model M1 the formation enthalpy of biomass was evaluated applying the definition of HHV. All equilibrium gasification models were tested against experimental data of biomass downdraft gasifiers reported in four different works, and experimental data of biomass updraft gasifiers reported in two different works. Different biomass materials, like wood, sawdust, rubber wood, pelletized softwood and pelletized sewage sludge were consideredCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Analytical solution for transient one-dimensional couette flow considering constant and time-dependent pressure gradients

This paperaims to determine the velocity profile, in transient state, for a parallel incompressible flow known as Couette flow. The Navier-Stokes equations were applied upon this flow. Analytical solutions, based in Fourier series and integral transforms, were obtained for the one-dimensional transient Couette flow, taking into account constant and time-dependent pressure gradients acting on the fluid since the same instant when the plate starts it´s movement. Taking advantage of the orthogonality and superposition properties solutions were foundfor both considered cases. Considering a time-dependent pressure gradient, it was found a general solution for the Couette flow for a particular time function. It was found that the solution for a time-dependent pressure gradient includes the solutions for a zero pressure gradient and for a constant pressure gradient

Modeling of syngas composition obtained from fixed bed gasifiers using Kuhn–Tucker multipliers

This work consists of developing a predictive model (PM) for syngas composition obtained from biomass gasification in fixed bed gasifiers. The PM is composed of three correlations which are made for carbon conversion efficiency, gasification temperature and the correction factor for the equilibrium constant of the water-gas homogeneous reaction. Such correlations were established using results obtained from the application of an optimization method (AOM) that uses Kuhn–Tucker multipliers. Syngas compositions determined through AOM were compared with experimental compositions and those estimated by other models, resulting that the AOM always determines the best estimates with respect to the root mean square error (RMSE). For syngas compositions estimated by AOM, the RMSE interval is [0.21, 4.11]. The PM was validated with six experimental compositions. From the predicted syngas compositions it was found that the ranges for LHV, cold gas efficiency, carbon conversion efficiency and gasification temperature were [4.594, 5.116 MJ/Nm3], [55.74, 68.18%], [74.20, 88.40%] and [749, 918 °C], respectively. Additionally, for the predicted syngas compositions the RMSE interval was determined as [0.68, 2.25]. Therefore, the PM was considered to be effective in estimating syngas compositions