Loading...
50 results
Search Results
Now showing 1 - 10 of 50
- Diagnostic evaluation of chronic venous insufficiency cases using thermal imagingPublication . Martins, Marta; Ribeiro, Luís Frölén; Cury, JorgeThe use of infrared thermography in surgery of Varicose Veins on the inferior limbs is presented. The study was executed at Polytechnic Institute of Bragança and at the Regional Hospital of Bragança, Portugal. The most suitable steps to measure with this technology were determined prior to the clinical studies, where a minimum waiting time of 10 minutes was determined for each individual to reach thermal equilibrium. Both inferior limbs were compared for each patient and it was found that in 75% of the cases there was an aggravation of the healthier leg. In one of the cases residual veins appear. It was concluded that regular thermographic exams on post-operatory allow a closer follow up of the recovery of the operated limb, as well as the evolution of the non-operated limb.
- Gaseificador de blocos de madeira em leito fluidizado: uma revisãoPublication . Chaves, Camila Fonseca; Boloy, Ronney Arismel Mancebo; Ribeiro, Luís FrölénO estudo inicia-se a partir do aproveitamento da biomassa em um gaseificador no qual é gerado cinzas e um gás de síntese. Existem três tipos mais comuns de gaseificadores, sendo estes o gaseificador de leito fluidizado, gaseificador de leito fixo e gaseificador de fluxo de arraste. As quatro etapas do processo de gaseificação são descritas como secagem, pirólise, combustão e redução. O gás de síntese gerado a partir do gaseificador passa por um ciclone, ou mais comumente chamado de catalisador, onde são retirados os materiais particulados e suas impurezas, sendo o alcatrão o resíduo que pode ser denominado um grande desafio para a purificação. Posteriormente, o gás de síntese alimentará um sistema chamado de acionadores primários, sendo eles os motores de combustão interna (Otto ou Diesel), motor de combustão externa (Stirling) microturbinas e células combustíveis.
- Convergent-diffuser for small horizontal wind turbinesPublication . Ribeiro, Luís Frölén; Paulo, Jorge Alexandre Rente; Garcia, ValdemarA small horizontal axis wind turbine (HAWT) equipped with an annular Convergent-Diffuser (C-D) is under development. Small to medium wind turbines equipped solely with a diffuser are becoming quite common: the annular structure around the rotor decreases the pressure downstream the rotor, augmenting the air velocity and power output. It also may replace the wind vane. Previous studies for such designs, for instance Ohya, Y. 2010, report a maximum increase in power output up to 150%. We present the preliminary results of an alternative design for a convergent-divergent annular structure that involves the rotor. This structure was optimized in CFD-simulations and 2 models where built for wind tunnel measurements. The maximum power output obtained was 187% higher than the case for a rotor without the C-D structure. Field tests are undergoing at this moment for a C-D adapted in model Rutland 913 Windcharger of 90 W.
- Automation of optimization synthesis for modular technological equipmentPublication . Zaleta, Olha M.; Povstyanoy, Oleksandr; Ribeiro, Luís Frölén; Redko, Rostyslav G.; Bozhko, Tetiana Ye; Chetverzhuk, Taras I.Technological equipment design based on functionally modular methods is widely used in various technical fields. The designed object can be a technological machine, a production line, or a manufacturing complex. Special attention is paid to the optimization of its structure. The sequence of performing all stages of the optimization synthesis problem is presented in the article. To find a solution to this task, the developer should apply the complete or directed search of acceptable structure options and determine the best one using some optimization criteria to evaluate their quality. It can be simple enough if the designed technical system structure consists of no more than several elements. For example, if the number of alternative elements options is several dozen, it takes much time to accomplish the search correctly. Thus, the greater the number of components considered, the more difficult it is to do all the necessary calculations manually. In this case, machine resources should be involved. This scientific work aims to identify procedures of optimization synthesis that can be automated. Also, appropriate software has to be developed. Our computer program is based on the algorithm of a complete search of all options of the technical system structure. It can process an extensive array of input data and produce all possible and logically permissible results in the form the designer can analyze using the Pareto method to choose the best one. This software can be used for any technical system with a modular structure.
- Two-phase bubble flow: experimental and numerical challengesPublication . Matoba, Gláucio Kenji; Ribeiro, Luís Frölén; Garcia, Valdemar; Suguimoto, Fábio KenjiA water and air mixture model is validated via experimental data in a newly rebuild laboratory apparatus where the main variable compared was the pressure gradient along the pipe in a bubble flow pattern. The experimental apparatus presents a constant circular crosssection of 0.032m of diameter and 3.815m of length. The flow set-up was ascendant co-current and 30 pairs of superficial velocities of liquidgas were measured. A numerical solution, using the mixture model, was implemented to predict the pressure gradient and void fraction of the two-phase flow for a one dimensional, steady-state, isothermal, no phase transition, no mass transfer and constant specific mass and viscosity conditions. The pressure gradient numerical results of the mixture model agreed with experimental data within an relative error envelope inferior to 2%.
- Decommissioned wind turbine blades: a pedagogical project on the uses of the raw materialPublication . Ribeiro, Luís Frölén; Ribeiro, J.E.; Costa, Carlos Casimiro da; Savosh, LarysaThe incorporation of new technical challenges created by the increase of the wind power industry in the world and how they were integrated into a MSc Course of Mechanical Engineering is addressed in this article.
- Dimensionamento de uma câmara de liofilização e de uma câmara de secagem por ar seco frio para alimentosPublication . Araújo, Arnaldo; Pereira, Daniel; Amaral, Fábio Francisco Soeiro; Soares, Júlia Cristina Alves; Alves, Júlio; Ferrari, Maria; Ribeiro, Marina Ervedal; Correia, Miguel; Pinheiro, Paulo; Félix, Rui; Cova, Sónia; Sousa, Vítor Manuel Ribeiro; Ribeiro, Luís FrölénO mercado de produtos liofilizados tem crescido nos últimos anos. Os principais alimentos produzidos são sólidos, como frutas e refeições prontas. O presente trabalho tem como principal objetivo a conceção e dimensionamento de uma câmara de liofilização industrial, na qual se utilizou o fluido frigorígeno R-404A., juntamente com uma câmara de secagem por convecção baseado num sistema mecânico de refrigeração. A câmara de liofilização apresenta uma capacidade de 185 kg, uma potência de 5.42 kW, sendo que a perda de calor por evaporação dos alimentos é cerca de 3613.05 W. O produto alimentar que se destacou neste estudo foi a maçã, pois trata-se de um produto com uma grande produção na Região de Carrazeda de Ansiães, sendo que a câmara dimensionada pode ser adaptada a outros tipos de produtos alimentares, consoante a época de colheita. Para tal, foi necessário um correto dimensionamento dos equipamentos que constituem os circuitos frigoríficos, bem como os componentes elétricos associados a este projeto. A secagem por ar seco frio é uma técnica de processamento de alimentos que tem o potencial de aumentar significativamente a vida útil de alimentos e para reduzir o desperdício de produtos alimentares dos setores de produção e retalho dos alimentos. Foi dimensionada uma câmara de secagem por ar seco frio, utilizando-se o mesmo fluído frigorígeno e, o mesmo produto da câmara de liofilização. Esta apresenta uma capacidade de 56kg, uma potência máxima de 39kW, um caudal de ar de secagem 1,35 m3/min e, comprimento dos tubos do trocador de calor de 3,74 m.
- Model for utilizing natural gas associated with hydrogen in pre-salt off-shore explorationsPublication . Sousa, Antonio Carlos Dutra de; Ribeiro, Luís Frölén; Brasil, Thiago Americano doThis article presents the study of a new concept for H2 production based on SMR technology from associated natural gas in offshore production in the Brazilian Pre-Salt region. It highlights the potential of using this gas, combined with CCUS devices, to explore crude oil and control fugitive emissions. Based on the evolution of historical series data of flaring and losses of natural gas in offshore production units, it is concluded, through the statistical regression method, that flaring and losses of natural gas are predicted to be below 3.0% of natural gas production with rates estimated above 1.5% in 2050 and reaching around 1% of production by the end of this century. By 2050, for a scenario involving the implementation and deployment of multiple H2 processing systems in offshore production units, it is estimated that approximately 41.8% of ordinary flaring will be reduced, and approximately 956 MMm3 of H2 will be produced. Doubts and uncertainties persist about achieving carbon neutrality by 2050 and zero routine flaring in offshore production by 2030 to meet the targets set in public policy agendas.
- Development of technical economic analysis for optimal sizing of a hybrid power system: a case study of an industrial site in Tlemcen AlgeriaPublication . Kerboua, Abdelfettah; Hacene, Fouad Boukli; Goosen, Mattheus F.A.; Ribeiro, Luís FrölénThe current study aimed to develop an optimal sizing simulation model for an off-grid photovoltaic-wind hybrid power system of an industrial site in Algeria. The loss of power supply probability algorithm was used for sizing our hybrid system. The technical and economic evaluation for the case study showed that the storage system occupied the most critical part of the total investment cost of the hybrid system. The investment cost analysis indicated a unique optimal configuration for each size of the batteries bank. For one day's autonomy, the best size of the hybrid system corresponded to 61 PV panels and 9 wind turbines. Based on a levelized cost of energy analysis, the cost of the batteries represented for this combination is 52% of the total investment cost. The wind turbines accounted for 42% and the PV panels for only 3%. This combination of the hybrid system resulted in an energy cost that was very competitive with most European countries. However, the public energy grid cost in the case study region was still six times lower due to government subsidies. The findings are very encouraging and can help decision-makers adopt alternative and more sustainable solutions in energy policy. These results will aid in determining future research directions in Algeria's hybrid renewable energy systems.
- Desafios e tendências na avaliação do recurso eólicoPublication . Ribeiro, Luís Frölén; Marques, FilipeCom o desenvolvimento de aerogeradores cada vez maiores aumenta a necessidade em caracterizar os campos médio e turbulento do escoamento cada vez mais afastados do solo (mais de 100 m). Tal começa a exigir uma alteração da metodologia de caracterização do recurso eólico até então aplicada, nomeadamente através do recurso a anemómetros (de copos ou sónicos) instalados em torres, por técnicas remotas de avaliação do recurso. Comparam-se as vantagens e inconvenientes da adopção dos anemómetros de copos e sónicos contra técnicas remotas como os SODARs e LIDARs. Estes últimos começam a ser identificados pela industria eólica como uma nova e possível tecnologia no apoio sistemático à caracterização do recurso eólico, já havendo resultados de campanhas de medição em terrenos planos. A situação em terreno complexo é mais delicada uma vez que o escoamento horizontal poderá não ser linear na área medida pelo LIDAR, sendo essa uma futura linha de investigação. Apresenta-se um local a 1200 m de altitude na Serra da Nogueira, Portugal, para elaboração da confrontação de medições convencionais entre anemómetros de copos e sónicos instalados em torre contra medições efectuadas com LIDARs.