Hot surface ignition dynamics in premixed hydrogen–air near the lean flammability limit

The dynamics of ignition of premixed hydrogen–air from a hot glow plug were investigated in a combined experimental and numerical study. Surface temperatures during heating and at ignition were obtained from 2-color pyrometry, gas temperatures were measured by high-speed Mach–Zehnder interferometry, and far-field effects were captured by high-speed schlieren imaging. Numerical simulations considered detailed chemical kinetics and differential diffusion effects. In addition to the known cyclic (puffing) combustion phenomenon, singular ignition events (single puff) were observed near the lean flammability limit. Detailed analysis of the results of our numerical simulations reveal the existence of multiple combustion transients within the thermal boundary layer following the initial ignition event and, at late times, sustained chemical reaction within a thermal plume above the glow plug. The results have significant implications for ignition from hot surfaces within near-flammability limit mixtures, at the edge of plumes resulting from accidental release of hydrogen, or within the containments of nuclear power plants during severe accidents

Dynamics of ignition of stoichiometric hydrogen-air mixtures by moving heated particles

Studying thermal ignition mechanisms is a key step for evaluating many ignition hazards. In the present work, two-dimensional simulations with detailed chemistry are used to study the reaction pathways of the transient flow and ignition of a stoichiometric hydrogen/air mixture by moving hot spheres. For temperatures above the ignition threshold, ignition takes place after a short time between the front stagnation point and separation location depending upon the sphere's surface temperature. Closer to the threshold, the volume of gas adjacent to the separation region ignites homogeneously after a longer time. These results demonstrate the importance of boundary layer development and flow separation in the ignition process

Effects of differential diffusion on ignition of stoichiometric hydrogen-air by moving hot spheres

Studying thermal ignition mechanisms is a key step for evaluating many ignition hazards. In the present work, two-dimensional simulations with detailed chemistry are used to study the effect of differential diffusion on the prediction of ignition thresholds of a stoichiometric hydrogen-air mixture by moving hot spheres. Numerical experiments showed an increase of 40 K in the minimum ignition temperature required for ignition when diffusion of species at different rates is taken into account. Detailed analysis of the species profiles at the ignition location and a sensitivity study of the system to the diffusivity of H_2 and H revealed the key role played by the diffusion of H atoms in preventing ignition to take place at temperatures below 1000 K

Controle emocional por judo na educação primária

Resumen: Introducción: El Judo está concebido por varios pedagogos como un deporte peligroso por implicar un contacto físico, pero realmente no es tan peligroso como se piensa si el profesor de educación física domina el contenido. Este deporte ofrece un gran número de factores educativos y sociales que ayudan a la sociedad a crear personas inteligentes desde un punto de vista social y emocional. Objetivos: El propósito principal del presente artículo es llevar a cabo el desarrollo de una sesión de Judo orientada al control emocional de los alumnos. Métodos: El aprendizaje de Judo se hará mediante juegos, ya que estos son la forma más efectiva y amena de que los niños lleven a cabo aprendizajes lúdicos y fructíferos para su futuro en una sociedad donde lo emocional se demanda cada vez más. Conclusiones: Se considera que tener un control emocional pleno, favorece otros aspectos esenciales para el desarrollo pleno de los alumnos y alumnas tal y como demanda el sistema educativo actual.Abstract: Introduction: Judo is conceived by various pedagogues as a dangerous sport because it involves physical contact, but it really is not as dangerous as it is thought if the physical education teacher dominates the content. Judo offers a large number of educational and social factors that help society to create smart people from a social and emotional point of view. Aim: The main purpose of this article is to carry out the development of a Judo session aimed at emotional control of students. Methods: Judo learning will be done through games, since these are the most effective and enjoyable way for children to carry out playful and fruitful learning for their future in a society where the emotional is increasingly demanded. Conclusions: It’s thought that having full emotional control is considered to favor other essential aspects for the full development of students, as required by the current educational system.Resumo: Introdução: O judô é concebido por vários pedagogos como um esporte perigoso porque envolve contato físico, mas na verdade não é tão perigoso quanto se pensa se o professor de educação física domina o conteúdo. Esse esporte oferece um grande número de fatores educacionais e sociais que ajudam a sociedade a criar pessoas inteligentes do ponto de vista social e emocional. Objectivos: O principal objetivo deste artigo é realizar o desenvolvimento de uma sessão de judô orientada para o controle emocional dos alunos. Métodos: O aprendizado do judô será realizado por meio de jogos, uma vez que essa é a maneira mais eficaz e agradável de as crianças realizarem um aprendizado lúdico e proveitoso para o futuro em uma sociedade em que a emoção é cada vez mais exigida. Conclusões: Considerar que o controle emocional total favorece outros aspectos essenciais para o pleno desenvolvimento dos alunos, conforme exigido pelo sistema educacional atual

Effects of differential diffusion on ignition of stoichiometric hydrogen-air by moving hot spheres

Studying thermal ignition mechanisms is a key step for evaluating many ignition hazards. In the present work, two-dimensional simulations with detailed chemistry are used to study the effect of differential diffusion on the prediction of ignition thresholds of a stoichiometric hydrogen-air mixture by moving hot spheres. Numerical experiments showed an increase of 40 K in the minimum ignition temperature required for ignition when diffusion of species at different rates is taken into account. Detailed analysis of the species profiles at the ignition location and a sensitivity study of the system to the diffusivity of H_2 and H revealed the key role played by the diffusion of H atoms in preventing ignition to take place at temperatures below 1000 K

Dynamics of ignition of stoichiometric hydrogen-air mixtures by moving heated particles

Studying thermal ignition mechanisms is a key step for evaluating many ignition hazards. In the present work, two-dimensional simulations with detailed chemistry are used to study the reaction pathways of the transient flow and ignition of a stoichiometric hydrogen/air mixture by moving hot spheres. For temperatures above the ignition threshold, ignition takes place after a short time between the front stagnation point and separation location depending upon the sphere's surface temperature. Closer to the threshold, the volume of gas adjacent to the separation region ignites homogeneously after a longer time. These results demonstrate the importance of boundary layer development and flow separation in the ignition process

Hot surface ignition of stoichiometric hydrogen-air mixtures

Hot surface ignition is relevant in the context of industrial safety. In the present work, two-dimensional simulations with detailed chemistry, and study of the reaction pathways of the buoyancy-driven flow and ignition of a stoichiometric hydrogen-air mixture by a rapidly heated surface (glowplug) are reported. Experimentally, ignition is observed to occur regularly at the top of the glowplug; numerical results for hydrogen-air reproduce this trend, and shed light on this behavior. The simulations show the importance of flow separation in creating zones where convective losses are minimized and heat diffusion is maximized, resulting in the critical conditions for ignition to take place

Experimental and numerical study of the ignition of hydrogen-air mixtures by a localized stationary hot surface

The ignition of hydrogen-air mixtures by a stationary hot glow plug has been experimentally investigated using two-color pyrometry and interferometry. The ignition process was characterized by the surface temperature at ignition, as well as by the location where the initial flame kernel was formed. The experimental results indicate that: (i) the ignition temperature threshold is a function of equivalence ratio; (ii) the ignition location is a function of the rate at which the glow plug is heated because high heating rates favor non-uniform heating. As a result, ignition occurs on the side rather than near the top face of the glow plug. Comparison with two-dimensional numerical simulations exhibits discrepancies in terms of the temperature threshold value and dependence on equivalence ratio. Simulations performed imposing a non-uniform surface temperature show that a temperature difference between the side and the top of the glow plug as low as 12.5 to 25 K resulted in side ignition for hydrogen-air mixtures. The effect of surface chemistry was estimated numerically by imposing a boundary condition of zero species concentration for intermediate species, H and HO_2, at the hot surface, which increased the ignition threshold by up to 50 K for an initial H_2 concentration of 70%. The present study shows that surface temperature non-uniformity, heterogeneous chemistry and reaction model used, could influence the experimentally reported and numerically predicted ignition threshold as well as the location of ignition

Bonecos, bonecos e teatro de sombras: os grandes esquecidos da Educação Física

Resumen: Introducción: Generalmente la sociedad suele asociar el concepto escuela a la enseñanza de la lectura, la escritura o el conteo de cantidades lo cual se asocia a una función tradicionalista de esta, pero actualmente desde las edades preescolares de los alumnos se deben potenciar la imaginación de los alumnos y el pensamiento lógico y racional junto a actos argumentales coherentes y adecuados. La importancia de la expresión oral, el teatro de títeres y marionetas tienen un gran nivel de importancia en estas edades ya que “los títeres son muy valiosos, pues a través de ellos se pueden expresar ideas y sentimientos, así como representar hechos de la vida diaria.Abstract: Introduction: Generally, society usually associates the concept of school with the teaching of reading, writing or counting quantities, which is associated with a traditionalist function of this, but currently, from the preschool ages of the students, the imagination of the students must be promoted and logical and rational thinking together with coherent and adequate plot acts. The importance of oral expression, the theater of puppets and puppets have a great level of importance in these ages since "puppets are very valuable, because through them ideas and feelings can be expressed, as well as representing facts of life daily.Resumo: Introdução: Geralmente, a sociedade geralmente associa o conceito de escola ao ensino de leitura, escrita ou contagem de quantidades, o que está associado a uma função tradicionalista disso, mas atualmente, desde a idade pré-escolar dos alunos, a imaginação dos alunos deve ser promovida. e pensamento lógico e racional, juntamente com atos de enredo coerentes e adequados. A importância da expressão oral, o teatro de fantoches e fantoches têm um grande nível de importância nessas idades, já que "os fantoches são muito valiosos, porque através deles idéias e sentimentos podem ser expressos, além de representar fatos da vida. diariamente