Optimization of flow distribution in flat plate solar thermal collectors with riser and header arrangements

The thermal performance of flat-plate solar collectors with riser and header arrangements is strongly influenced by the flow distribution through the absorber tubes. A more uniform flow distribution leads to a homogenous temperature distribution which gives higher collector efficiency. The Z distribution usually has better performance when compared to P distribution. The design of the manifold influences the observed flow distribution. To optimize the manifold design, a correlation model was developed, based on correlations for minor pressure losses. Furthermore, the flow in this optimized geometry was simulated in 3D using the computational fluid dynamics (CFD) software code in order to confirm the results of the correlation based model. A new experimental low-intrusive technique was used to measure the flow distribution in an existing solar collector, validating the simulation results. The flow inside the absorber tubes is laminar; the major pressure loss inside riser tubes was measured using a high accuracy differential pressure transmitter, which then permits the indirect estimation of the mean velocity inside the tubes. It was the first time that this experimental methodology has been applied to analyse the flow distribution in solar collectors. The influence of the total water flow rate was analysed. For a good flow distribution it was concluded that the outlet header manifold should have a higher diameter compared to the inlet header diameter. Usually commercialised solar collectors have the headers with same diameter

NATUREZA, POESIA, RITMO E MELODIA DA VIDA: O tempo do camponês, do marinheiro e do guerreiro

A luta pela sobrevivência despertou no homem o reconhecimento da Natureza (Phýsis) como forças imortais. Essa experiência foi importante para ampliar o poder de observação, atuação e comunicação entre o mundo divino e humano para (re) organização social, política e pedagógica. Nas obras de Homero e Hesíodo podemos encontrar a reunião da beleza da criação humana que é o resultado desse diálogo inspirado e conturbado com a Natureza. O presente artigo visa apresentar algumas reflexões sobre o processo de desenvolvimento cultural grego através da imagem do camponês, do marinheiro e do guerreiro que encontramos em algumas fontes antigas que serviram como horizonte existencial para encontrar a sua eudaimonia na antiguidade.The struggle for survival awakened in man the recognition of Nature (Phýsis) as immortal forces. This experience was important to expand the power of observation, action and communication between the divine and human world for social, political and pedagogical (re)organization. In the works of Homer and Hesiod we can find the combination of the beauty of human creation that is the result of this inspired and troubled dialogue with Nature. This article aims to present some reflections on the process of Greek cultural development through the image of the peasant, the sailor and the warrior that we find in some ancient sources that served as an existential horizon to find their eudaimonia in antiquity.La lucha por la supervivencia despertó en el hombre el reconocimiento de la Naturaleza (Phýsis) como fuerzas inmortales. Esta experiencia fue importante para ampliar el poder de observación, acción y comunicación entre el mundo divino y humano para la (re)organización social, política y pedagógica. En las obras de Homero y Hesíodo podemos encontrar la combinación de la belleza de la creación humana que es resultado de este inspirado y turbulento diálogo con la Naturaleza. Este artículo tiene como objetivo presentar algunas reflexiones sobre el proceso de desarrollo cultural griego a través de la imagen del campesino, el marinero y el guerrero que encontramos en algunas fuentes antiguas que sirvieron de horizonte existencial para encontrar su eudaimonia en la antigüedad

Quartic solitons of a mode-locked laser distributed model

Dissipative quartic solitons have gained interest in the field of mode-locked lasers for their energy-width scaling which, if identical to the one found in conservative quartic solitons, would allow the generation of ultrashort pulses with high energies. Pursuing the characterization of such solitons, here we found soliton solutions of a distributed model for mode-locked lasers in the presence of group velocity and fourth order dispersions (GVD and 4OD respectively), for two saturable absorber saturation powers. We found that the energy of the pulses follows an inverse relation with the width, with most cases following a different trend than the one found for conservative quartic solitons. Nevertheless, for higher saturation powers and negative 4OD, the pulses showed a behaviour approximate to the one found in the conservative regime, and were the most energetic and the shortest

Caracterização e avaliação de recursos e património geológico do concelho de Mira

Mestrado em Engenharia GeológicaO presente trabalho teve como objectivos caracterizar e avaliar os recursos geológicos do concelho de Mira. Dos recursos geológicos estudados foi dada ênfase especial aos recursos hídricos, em especial às águas subterrâneas, e às argilas. Esta escolha deve-se à importância que as águas subterrâneas têm no abastecimento doméstico deste concelho e ao facto dos recursos geológicos existentes serem essencialmente de constituição arenácea e argilosa. Para o estudo das águas subterrâneas foi realizada uma inventariação dos pontos de água, estabelecida a rede de fluxo local e seleccionados alguns pontos de amostragem nas localidades de Leitões e Lentisqueira para colheita de águas para análises laboratoriais. Dada a importância dos recursos hídricos subterrâneos foram calculados os perímetros de protecção das captações existentes. O cálculo dos perímetros de protecção foi efectuado de acordo com o Decreto de Lei 382/9, a partir dos dados fornecidos pela Câmara Municipal de Mira. De acordo com os resultados das análises físico-químicas foi possível avaliar a qualidade das águas utilizadas no abastecimento público do concelho. De acordo com os dados disponíveis foi possível constatar que algumas amostras de água de poços de grande diâmetro apresentavam teores elevados em nitratos, nitritos e amónio. Os resultados demonstram que o risco de contaminação das águas provenientes dos furos mais superficiais pode ser elevado já que ocorrem situações de poços particulares expostos a todo o tipo de poluição e de mau funcionamento das fossas sépticas resultante de má construção. Neste estudo foram ainda identificados os tipos de matérias-primas mais abundantes no concelho. Estas matérias-primas foram caracterizadas a partir de ensaios físicos químicos e tecnológicos. ABSTRACT: The main objective of this work was to characterize and evaluate the geologic resources of the Mira Municipality. Special emphasis was given to water resources, especially groundwater, and to raw materials. Groundwater is important for the domestic water supply of this municipality. For the groundwater an inventory was carried out, in order to establish a network of local flow. Also some sampling points were selected in Leitões and Lentisqueira localities for water sampling and analysis. Given the importance of groundwater resources the protection perimeters for protection of public watersupply wells were established. The calculation of the perimeters for protection was made in accordance with the Decree Law 382/9, considering the information available in the Mira Municipality. According to the physical-chemical results of water analysis, carried out to assess the water quality used to supply it was possible to see that some samples of water presents high levels of nitrates, nitrites and ammonium. The results show that the high risk of water contamination may occur in private wells exposed to all kinds of pollution and located near septic tanks showing deficient construction. This study also identified the types of raw materials abundant in the county. These raw materials were characterized from testing physical and chemical technology

Manutenção preditiva em centros de conformação na Vista Alegre Atlantis SA

A crescente competitividade do mercado derivada, em grande parte, pela inovação tecnológica, impõe às empresas a necessidade de reformar o modus operandi tradicional e adotar um modelo enquadrado no paradigma da indústria 4.0. A otimização do controlo do processo produtivo através da informatização em tempo real integrada ao longo de todo o chão de fábrica traz benefícios ao nível do custo, da qualidade e da segurança. A análise de dados provenientes da sensorização dos equipamentos em paralelo com algoritmos de Machine Learning constitui o cerne da manutenção preditiva, tema desta dissertação. A manutenção periódica e reativa têm vindo a ser substituídas por intervenções proativas que asseguram a continuidade da produção e a redução de defeitos de fabrico. O trabalho pode ser dividido em três fases: instalação de um equipamento para monitorizar variáveis de funcionamento de máquinas de um centro de conformação plástica da Vista Alegre Atlantis SA; desenvolvimento de um modelo de manutenção preditiva que consiga detetar, antecipadamente, um comportamento irregular de funcionamento; elaboração de uma interface gráfica de visualização. O modelo foi obtido com recurso a algoritmos de aprendizagem supervisionada (árvores de decisão) e algoritmos de clustering (K-Means e DBSCAN), tendo servido como prova de conceito.The increasing market competivity that derives, mostly, from the continuous tecnhological inovation forces companies to retire their traditional modus operandi and to addopt a model of business integrated in the Industry 4.0 paradigm. Production process control optimization by means of real-time informatization of cyber-physical systems scattered along the shop floor brings benefits at the cost, quality and safety levels. Data analysis from equipment sensors in paralel with Machine Learning algorithms constitutes the core of Predictive Maintenance, main subject of this thesis. Periodic and reactive maintenance have lately been replaced with proactive interventions that assure production continuity and reduction of manufacturing defects. The work can be divided in three phases: installation of equipment to monitor operating variables of machines in a plastic forming center at Vista Alegre Atlantis SA; development of a predictive maintenance model that can detect, in advance, an irregular operating behavior; elaboration of a graphical visualization interface. The model was obtained using supervised learning algorithms (decision trees) and clustering algorithms (K-Means and DBSCAN), serving as proof of concept.Mestrado em Engenharia Mecânic

Factory Made Solar Thermal Systems - Dynamic System Testing and development of parameter identification tool and LTPP validation

This paper presents first results of a project that aims at the development of new mathematical models for characterization of Solar Thermal Systems (Factory Made Systems as defined in EN 12976) that can be used in association with dynamic system testing (non intrusive test method defined in the document ISO 9459-5) and which, based on the characteristic parameters defined in the adopted models, allow determination of those parameters by fitting between real test sequences and test sequences produced by the developed models, using fitting techniques independent of the models chosen for system characterization. Another important goal of the project is the validation of results for Long Term (thermal) Performance (LTP) of the solar systems, based on the models developed, by comparison with long term measurement sequences obtained by the monitoring of different system types. Installation of the testing facility for this purpose is also described in the present paper

Estudo de colectores solares incorporando tubos de calor com aplicação em ciclos motores

Tese de mestrado. Faculdade de Engenharia. Universidade do Porto. 199

Thermal behavior of a BIPV combined with water storage: an experimental analysis

ABSTRACT: Buildings play an active role in the global energy consumption and are required to not only minimize their energy use, but also generate energy in a sustainable manner. The integration of renewable energies in building elements can improve their overall performance, as they are able to replace common construction materials, while offering both electrical and thermal energy. The scope of this paper is to present the first results of an experimental study of a Building-Integrated Photovoltaic system combined with a water storage tank (BIPV-WS), a combined integration not extensively studied yet. Both layers are separated by a ventilated air cavity, and the thermal behavior of the system was analyzed experimentally in real functioning conditions. The water tank performs as a thermal storage, maintaining a regular temperature of about 20-30 degrees C during a typical winter day of Lisbon for a period of 11 h. Moreover, through the ventilation of the air cavity, the heat provided by the solar panel was naturally recovered to the indoors of the building, while keeping the temperature high enough to heat up the water. During summer, the ventilated BIPV-WS enabled beneficial nocturnal heat loss while delaying diurnal space heating.info:eu-repo/semantics/publishedVersio

Analysis of long period gratings inscribed by CO2 laser irradiation and estimation of the refractive index modulation

Long period gratings (LPGs) inscribed in single mode fibers (SMFs) using CO2 laser irradiation were modelled numerically using the coupled mode method. The model considers the specifications of the inscription technique, such as the shape of the refractive index modulation that mimics the circularly symmetric point-to-point laser irradiation profile. A simple expression for predicting the resonant wavelength was obtained assuming a two-mode coupling model. However, to explain the spectra of the experimental LPGs, it was necessary to assume a reasonably high refractive index change and a multimode coupling model. Furthermore, using the developed model and a genetic algorithm to fit experimental resonances to simulated ones, we were able to estimate the maximum refractive index change, obtaining a value of 2.2 × 10-3, confirming the high refractive index change. The proposed model also predicts a second order resonance for this high value of refractive index change that was confirmed experimentally. Hence, with this model, we found some significant differences in the LPGs behavior when compared with conventional ones, namely, the emergence of coupling between different cladding modes and the competition of first and second order resonances which change the LPG transmission spectrum.publishe