Browsing by Issue Date, starting with "2010-11"
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- Trigeração numa estufa agrícola: produção de frio e electricidade pelo uso conjunto de microcogeração, bomba de calor e chiller de absorçãoPublication . Figueira, Nelson Miguel Forte; Miranda, Alexandre Borges deEm alguns países, em que as temperaturas durante os meses de Verão são bastante elevadas, são necessários sistemas de climatização nas estufas agrícolas para que a produção de determinadas culturas não seja prejudicada. Com o aquecimento global, as temperaturas estão subir ano após ano e em determinados países a utilização de sistemas de ventilação forçada para o arrefecimento das estufas torna-se insuficiente. A elaboração desta dissertação surgiu com a necessidade de implementar um sistema de arrefecimento de estufas agrícolas alternativo que consiga alcançar as temperaturas ideais de desenvolvimento das culturas e que resulte em benefícios ambientais. Assim, esta dissertação pretende realizar a simulação energética e o estudo de viabilidade da implementação de um sistema de trigeração, constituído por um sistema de microcogeração a funcionar em conjunto com um chiller de absorção, acrescido de uma bomba de calor a funcionar como complemento. Foram realizadas várias simulações energéticas através do software EnergyPlus, que permitiram fazer uma análise pormenorizada do efeito da radiação solar na estufa e das necessidades de arrefecimento. Permitiu também dimensionar o sistema de trigeração necessário e a comparação deste com um sistema constituído apenas por uma bomba de calor. No final foi realizada a respectiva confrontação de resultados entre ambos os sistemas de forma a determinar a viabilidade da implementação do sistema de trigeração numa estufa.
- Intra-operator spectrum sharing concepts for energy efficiency and throughput enhancementPublication . Holland, Oliver; Attar, Alireza; Cabral, Orlando Manuel Brito; Velez, Fernando J.; Aghvami, A. HamidCognitive radio and other dynamic spectrum sharing paradigms have enjoyed the limelight recently for their potential to realize a number of benefits for communications systems. The majority of investigated solutions thus far have looked at primary/secondary access and sharing of spectrum among different spectrum owners. In contrast, this paper investigates solutions for spectrum sharing among different bands owned by the same entity, such as a mobile operator, and demonstrates considerable potential for such solutions to improve power efficiency for the network and to increase throughput. The paper utilizes four means to achieve this potential: spectrum sharing through the opportunistic movement of users between bands allowing radio network equipment in other bands to be switched off when possible, spectrum sharing to opportunistically improve links’ propagation characteristics therefore reducing necessary transmission power, better interference management in spectrum sharing to reduce necessary transmission power, and the opportunistic aggregation of spectrum bands to increase achievable throughput. Power consumption reductions of over 50%, both in terms of mains power draw and in terms of necessary transmission power, are demonstrated. Moreover, throughput enhancements of up to 20% are achieved.
- On the Performance of the Spray Impingement ModelsPublication . Barata, Jorge M M; Silva, AndréThe present paper reports a numerical study of a spray impinging on a surface through a crossflow. This work is aimed at studying the fundamental aspects of the spray impingement phenomena in a three-dimensional configuration, which is relevant to practical engines. A computational study of the flow produced by a spray stream injected through a crossflow is reported and discussed in detail. Different impinging models were used and the results are compared with measurements and predictions of other authors. A new droplet impingement model was developed and tested. The results show a general good agreement with the experiments, and reveal that the splash droplets are very important for the spray development.
- Sacadura Cabral and the Dawn of Portuguese AviationPublication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, AndréSacadura Cabral was one of the two Portuguese navigators that crossed by air the South Atlantic in the beginning of the 20th century. From 1901 to 1915 Sacadura was at Mozambique and Angola where he developed geodetic and geographical missions of the greatest importance for Portuguese interest at Africa. With the Great World War requirements as a Navy Officer with 34 years old he decided to serve Portugal at the Aviation. In 1915 he went to France and obtained its pilot license. In 1916 Sacadura returned to Portugal and begun its instructor pilot career. He developed the “path corrector” which he created to compensate the drift caused by wind. In 1922 Sacadura made the First Air cross from Europe to South Atlantic. In 1923 he proposes himself to make an attempt to the First Air Circumnavigation Journey. He developed all its possible efforts to initiate this journey in March of 1924; however some delays had forced him to postpone the journey. Sacadura received important official medals and prizes, including the PhD Honoris Causa from the Universities of Lisbon and Oporto. In 1924 he died before he could carry out its Circumnavigation Air Journey.