Simulação numérica de trocadores de calor multitubulares equipados com fitas helicoidais externamente aos tubos

Classical shell-and-tube heat exchangers are usually equipped with segmental baffles. These baffles serve two basic functions: (a) they provide tube supports, thereby preventing or reducing mechanical problems, such as sagging or vibration; (b) they direct the fluid flow over the tubes so as to introduce a cross-flow component, thereby increasing the heat transfer. Segmented baffles have several sources of performance loss, some due to various leakage flows and others caused by stagnation zones. A new concept of longitudinal flow heat exchanger - based on placing twisted tapes along the tube bundle subchannels - was developed to mitigate drawbacks of other types of tubular heat exchangers. In this paper, a numerical model has been implemented in order to simulate the thermal-hydraulic feature of tubular heat exchangers equipped either with segmental baffles or with subchannel twisted tapes. The tube bundle has been described by means of an equivalent porous medium type model, allowing a macroscopic description of the shell-side flow. The basic equations - continuity, momentum and energy - have been solved by using the finite volume method. Typical numerical results have been compared with experimental data, reaching a very good agreement. A comparative analysis of different types of heat exchangers has been carried out, revealing the satisfactory thermal-hydraulic efficiency level of the twisted tapes heat exchangers.

Avaliação da distribuição da densidade em MDF a partir da técnica da onda de ultra-som

The goal of this research was to determine the density distribution in medium density fiberboard (MDF), manufactured with polyurethane derived from castor oil using, ultrasonic wave technique. The equipment used in this test is Steinkamp BP7 with plan and exponential transducers, both with 45 kHz frequencies, located in several zones on the plate in order to determine wave ultrasonic velocity. The Pinus caribaea and Eucalyptus grandis fiberboard were manufactured in the quality control and products development laboratory of Duratex with 500 mm long, 500 mm large, 8 and 15 mm of thickness. Three MDF for each fiber specimen and thickness were fabricated, totalizing twelve plates tested. The MDF were produced with 5% polyurethane addition, in temperature of 160°C, tension press of 53 bars and addition of moisture content of 12%. For determination of fiberboard density, samples were extracted from the same zones where the wave ultrasonic velocity was determined. In this case, DAX-Ray equipment was used. Statistical analysis shows good agreement with wave ultrasonic velocity and the density profile, validating the application of non-destructive technique in order to determine the density profile of MDF's.

Estimativa de alguns parâmetros de transporte de contaminantes para solos Brasileiros

This paper introduces an indirect estimate for the coefficients of distribution, hydrodynamic dispersion and retardation for contaminants commonly encountered in sanitary landfills and their liners, such as Cu2+ and K+; this estimate is based on the relationship between concentration and certain physical characteristics of typical Brazilian soils. The results of previous studies investigating the migration of contaminants were used to develop mathematical expressions from multiple non-linear regressions. Using minimal squares regression, this transport was linked to various combinations of contaminant concentration and both structural and textural characteristics of the porous medium. Various combinations of characteristics and concentrations were investigated, with a mathematical expression obtained for each. The relationship between percentage of clay and the contaminant content proved to be the most closely correlated with actual transport parameters, with coefficients close to one.

Prospects for the use of municipal tree pruning wastes in particleboard production

The purpose of this study was to evaluate the physical and mechanical properties of particleboard made with pruning wastes from Ipê (Tabebuia serratifolia) and Chapéu-de-Sol (Terminalia catappa) trees. Particleboards were prepared with both wood species, using all the material produced by grinding the pruning wastes. The particleboards had dimensions of 45×45 cm, a thickness of approximately 11.5 mm and an average density of 664 kg/m3. A urea-formaldehyde adhesive was used in the proportion of 12% of the dry particle mass. The particleboards were pressed at a temperature of 130 C for 10 mins. The physical and mechanical properties analyzed were density, moisture content, thickness swelling, percentage of lignin and cellulose, modulus of resilience, modulus of elasticity and tensile strength parallel to the grain, accordingly to the standards NBR 14810 and CS 236-66 (1968). The particleboards were considered to be of medium density. The particle size significantly affected the static bending strength and tensile strength parallel to the grain. Ipê presented better results, demonstrating a potential for the production and use of particleboard made from this species. © The Author(s) 2013.

Istmo Centroamericano: la regulación de la distribución de energía eléctrica en los países con empresas privadas. Los casos de El Salvador, Guatemala, Nicaragua y Panamá

Incluye Bibliografía

Aplicação da técnica de elementos finitos na estratificação de armazenadores térmicos com barreiras de meios porosos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Escoamentos em meios porosos: uma análise teórica e experimental dos efeitos dos esforços capilares provocados por percolação de água em elementos de alvenaria

Pós-graduação em Engenharia Mecânica - FEG

Avaliação do intervalo hídrico ótimo em latossolo vermelho cultivado com milho

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise morfológica e topográfica das células ganglionares da retina do caititu (Tayassu tajacu)

Na Amazônia habitam diversas espécies de animais silvestres, tornando-a um importante local de investigação sobre fisiologia comparada. Dentre estas espécies, destacamos o caititu Tayassu tajacu, animal distribuído na América Central e Latina. Existem várias publicações acerca da morfologia de órgãos sexuais, carne e sangue do caititu. Porém, no que diz respeito ao estudo sobre a morfofisiologia visual do caititu, as publicações ainda são escassas. Diante dessa realidade, o presente estudo investigou a morfologia e topografia das células ganglionares da retina do Tayassu tajacu. Foram utilizadas seis retinas, provenientes de oito animais de ambos os sexos da espécie Tayassu tacaju. Os caititus, criados e mantidos em cativeiro na Empresa Brasileira de Pesquisa Brasileira - Embrapa/Pará, foram abatidos de acordo com as normas de manejo animal para posterior retirada e fixação dos olhos. As retinas foram dissecadas e coradas utilizando a técnica de Nissl para visualização de células ganglionares, amácrinas deslocadas, hemácias, micróglia e células componentes da vascularização. A contagem de células ganglionares foi realizada ao longo do eixo horizontal e vertical, sendo o número de células ganglionares por campo convertido em valores de densidade. Diferentes regiões da retina foram analisadas quanto à densidade celular, obtendo-se como valor médio de densidade 351,822 ± 31,434 CG/mm². Verificaram-se diferenças de densidade entre as regiões estudadas: a região dorsal teve densidade média e desvio padrão de 894 ± 44 CG/mm²; a região ventral 894 ± 1 CG/mm²; a região nasal 1.403 ± 43; e a região temporal com 1596 ± 251. O pico de densidade a média, localizado a aproximadamente 3,13 mm de distância no sentido dorsal e 6,77 mm no sentido temporal do nervo óptico, foi de 6.767 CG/mm². Verificaram-se duas regiões especializadas, a faixa visual e a area temporalis. A faixa visual, localizada no sentido horizontal da região nasal para temporal, apresentou alta densidade celular, possivelmente proporcionando melhor visão panorâmica do ambiente e detecção de objetos em movimento no horizonte. Já a area temporalis, localizada dentro da faixa visual, proporciona maior acuidade visual e resolução espacial, do meio em que vivem Os resultados deste trabalho permitem iniciar comparações morfofisiológicas da retina dos caititus com a de outras espécies animais.

Caracterização físico-mecânica de painéis aglomerados de Eucalyptus grandis com adição de resíduos industriais madeireiros

Pós-graduação em Ciência Florestal - FCA

Caracterização física de painéis aglomerados de Eucalyptus grandis com adição de resíduos industriais madeireiros

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Análise do comportamento térmico de paredes de madeira

This study consists in the observation and evaluation of the thermal behavior and distribution of wood composite walls, MDF – Medium Density Fiberboard, HDF – High Density Fiberboard, OSB – Oriented Strand Board and EGP – Edge Glued Panel. This study had the objective to present the experimental thermal behavior and to verify which one fit the thermal comfort standards for human labor For this work, was developed a thermal chamber, with one interchangeable side, so the wall prototypes would fit for each experiment. We studied walls made of MDF, HDF, OSB and EGP, which one had its own distinct behavior due to the panel construction. The EGP wall had shown the most reliable material for this usage at high temperatures. With this work, it was demonstrated the importance of choice for the right material and construction method for wooden composite walls, because if they were scaled poorly, the people exposed to them would be uncomfortable by the proportionate environment, and the costs for a resizing would be too high

Estudo comparativo entre MDF e MDP utilizados na indústria moveleira

Increasingly, the furniture market is competitive. The construction industry presents itself in growth, mainly due to the lines of existing incentives and tax credits established by the government, assisting the impulse to purchase real estate, building materials and furniture. Factors that promote and strengthen the sector's growth. With high demand from the furniture market, demand for higher quality and increasing technological advances, research is often undertaken in search of solutions for process improvement and product features, focusing on the production of materials less harmful to the environment, provision of raw press to lower cost, improve the production process and product development of cost-effective. This research focuses on the comparative study between two materials widely used in furniture manufacturing. MDF (Medium Density Fiberboard) and MDP (Medium Density Particleboard). The subject provides the focus in furniture production, presenting and comparing data collected from three companies producing panels between physical and mechanical characteristics of the materials, also presenting some of the main factors of influence on the quality of the panels, their features and applications on mobile. The study shows the high potential of using the MDP (Medium Density Particleboard) in furniture designs, as well as MDF (Medium Density Particleboard), favoring the final terms of the project , resulting in better utilization of each material , avoiding waste and increase unnecessary cost . Currently, several projects are developed in MDP and MDF furniture, where there is no relevance to their characteristics regarding their limitations. Many of these furnishings are designed without a specific study of the best use and positioning of each material, with better utilization , favoring collateral design , especially furniture designed exclusively for each environment . The lack of technical ...

Caracterização físico-mecânica de painel de MDP produzido com madeira de Eucalipto e Bracatinga

This work is the production of particleboard of particles reconstituted from MDP (Medium Density Particleboard) adding particles in the inner layer of Mimosa Scarelli, popularly known as bracatinga, the ratios of 0%, 25%, 50%, 75% and 100%. The panel produced is composed of three layers, two external particles with smaller particle size and an inner layer composed of particles of larger particle sizes. Assays were performed based on physical and mechanical NBR 14.810/2006 for the determination of the board density, thickness swelling, water absorption, moisture content, bending strength, shear strength and residual moisture, and testing of particle size not existing in the standard cited. The results were analyzed and compared the results of the commercial boards made from 100% eucalyptus, based on the limits specified by the ABNT NBR 14.810/2006. The values of the tests were close to the normative specifications indicating positively the production of MDP with wood decay.

Medidores inteligentes: o primeiro passo em direção as redes inteligentes

Smart grids are the focus of major study today because of the necessity of modernization in electrical systems and reduction of greenhouse gas emissions that increases global warming. Reaching the best deployment method, you must first of all know the current electrical system and how to use them for the benefit of this new technology. Preparing the action plan we should be aware of the main points of smart grids in each step of the electricity system - generation, transmission and distribution. Analyzed these topics, this work will focus on the first step in the implementation of the smart grids: the smart meters, tool which is already being implemented in Brazil. The main characteristics and applications of these devices, as well as their communication structure with the core distributors will be showed during the paper. Finally, we present a case study which will be discussed and analyzed based in the results obtained with the implementation of smart meters in the city of Vancouver, Canada, where we have a considerable savings already in the first year, with fully paying the initial investment and still have a profit