Composite Heat Sink LED Cooling

Metal coating of 3D printed polymers is an attractive proposition for thermal dissipation of light emitting diodes, due to its high efficiency and markedly lower material costs than conventional aluminum heat sinks. Efficient thermal cooling of light emitting diodes is essential in maintaining electronic and optical performance. The thermal performance of three heat sink designs were experimentally investigated for three applied heat fluxes (0.5-1.5 W cm-2). The results show that metal coating of the polymer heat sinks enables significant heat transfer enhancement of 37% over the uncoated case. The inclusion of an aluminum insert into the base of the composite heat sink design, in tandem with the zinc coating reduced on chip temperatures by 27% over the zinc coated case for the greatest applied heat flux

Optimal Constant-Stress Accelerated Degradation Test Plans Using Nonlinear Generalized Wiener Process

Accelerated degradation test (ADT) has been widely used to assess highly reliable products’ lifetime. To conduct an ADT, an appropriate degradation model and test plan should be determined in advance. Although many historical studies have proposed quite a few models, there is still room for improvement. Hence we propose a Nonlinear Generalized Wiener Process (NGWP) model with consideration of the effects of stress level, product-to-product variability, and measurement errors for a higher estimation accuracy and a wider range of use. Then under the constraints of sample size, test duration, and test cost, the plans of constant-stress ADT (CSADT) with multiple stress levels based on the NGWP are designed by minimizing the asymptotic variance of the reliability estimation of the products under normal operation conditions. An optimization algorithm is developed to determine the optimal stress levels, the number of units allocated to each level, inspection frequency, and measurement times simultaneously. In addition, a comparison based on degradation data of LEDs is made to show better goodness-of-fit of the NGWP than that of other models. Finally, optimal two-level and three-level CSADT plans under various constraints and a detailed sensitivity analysis are demonstrated through examples in this paper

Avaliação da sustentabilidade de estruturas e materiais de pavimentos rodoviários

Tese de Doutoramento em Engenharia CivilA noção de que os recursos que a humanidade tem usado são limitados tem levado à implementação de práticas mais sustentáveis. Dado que os pavimentos rodoviários são infraestruturas cuja construção, utilização e reabilitação provoca impactes ambientais consideráveis, torna-se indispensável a procura de novas técnicas e processos mais sustentáveis, com vista à mitigação das suas consequências. Além disso, importa perceber que os efeitos dos pavimentos rodoviários não se limitam ao período em que são construídos, mas prolongam-se durante toda a sua vida. No entanto, as metodologias de análise do ciclo de vida propostas até agora concentram-se demasiado nas fases de extração, produção, transporte e aplicação dos materiais, o que é insuficiente para estudar todo o período de vida do pavimento. Nesse sentido, pretende-se com este trabalho desenvolver uma metodologia de análise da sustentabilidade dos diferentes materiais e estruturas de pavimentos que inclua também o período de utilização dos pavimentos, considerando para tal, as operações de conservação dos pavimentos ao longo do ciclo de vida e estimativas do consumo de combustível, baseadas na resistência ao rolamento. Para avaliar a resistência ao rolamento, desenvolveu-se um protótipo capaz de determinar as diferenças de consumo de energia provocadas por diferentes superfícies de pavimentos. Os dados obtidos experimentalmente foram depois analisados através de técnicas de Data Mining, e considerados na nova metodologia de análise da sustentabilidade desenvolvida neste trabalho, através de um caso de estudo que incluiu a utilização de diferentes estruturas de pavimentos e cenários/estratégias de conservação. Os resultados obtidos confirmam a preponderância da fase de utilização dos pavimentos, quer em termos de impacte ambiental, quer em termos económicos, na avaliação do seu ciclo de vida, confirmando a importância da sua consideração nesse tipo de análises.The idea that the resources people have used are limited has led to the implementation of more sustainable practices. Being road pavements infrastructures that cause significant environmental impacts during their construction, use and rehabilitation stages, it is essential to search for new techniques and more sustainable processes for the mitigation of their consequences. Furthermore, it is important to realize that the effects of road pavements are not limited to the period in which they are constructed, but extended throughout their lifetime. However, the life cycle methodologies proposed so far are too much focused on resource extraction, production, transportation and material application, which is insufficient to study the entire life cycle of the pavement. Thus, the aim of this work was to develop a methodology for analyzing the sustainability of different materials and pavement structures that also include the pavements’ use phase, taking the conservation operations of the pavements throughout the life cycle and estimates of the fuel consumption, based on the rolling resistance, into consideration. To evaluate the rolling resistance a prototype capable of determining the energy consumption differences caused by different pavement surfaces was developed. The experimental data were then analyzed through Data Mining techniques, and considered in the new sustainability analysis methodology developed in this work through a case study involving the use of different pavement structures and conservation scenarios/strategies. The results confirm the preponderance of the pavements’ use phase, both in terms of economic and environmental impact, in the assessment of their life cycle, confirming the importance of their consideration in this type of analysis

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018