Development of effective thermal management strategies for LED luminaires

The efficacy, reliability and versatility of the light emitting diode (LED) can outcompete most established light source technologies. However, they are particularly sensitive to high temperatures, which compromises their efficacy and reliability, undermining some of the technology s key benefits. Consequently, effective thermal management is essential to exploit the technology to its full potential. Thermal management is a well-established subject but its application in the relatively new LED lighting industry, with its specific constraints, is currently poorly defined. The question this thesis aims to answer is how can LED thermal management be achieved most effectively? This thesis starts with a review of the current state of the art, relevant thermal management technologies and market trends. This establishes current and future thermal management constraints in a commercial context. Methods to test and evaluate the thermal management performance of a luminaire system follow. The defined test methods, simulation benchmarks and operational constraints provide the foundation to develop effective thermal management strategies. Finally this work explores how the findings can be implemented in the development and comparison of multiple thermal management designs. These are optimised to assess the potential performance enhancement available when applied to a typical commercial system. The outcomes of this research showed that thermal management of LEDs can be expected to remain a key requirement but there are hints it is becoming less critical. The impacts of some common operating environments were studied, but appeared to have no significant effect on the thermal behaviour of a typical system. There are some active thermal management devices that warrant further attention, but passive systems are inherently well suited to LED luminaires and are readily adopted so were selected as the focus of this research. Using the techniques discussed in this thesis the performance of a commercially available component was evaluated. By optimising its geometry, a 5 % decrease in absolute thermal resistance or a 20 % increase in average heat transfer coefficient and 10 % reduction in heatsink mass can potentially be achieved . While greater lifecycle energy consumption savings were offered by minimising heatsink thermal resistance the most effective design was considered to be one optimised for maximum average heat transfer coefficient. Some more radical concepts were also considered. While these demonstrate the feasibility of passively manipulating fluid flow they had a detrimental impact on performance. Further analysis would be needed to conclusively dismiss these concepts but this work indicates there is very little potential in pursuing them further

Methods for modeling degradation of electrical engineering components for lifetime prognosis

Reliability of electrical components is an issue studied to improve the quality of products, and to plan maintenance in case of failure. Reliability is measured by studying the causes of failure and the mean time to failure. One of the methods applied in this field is the study of component aging, because failure often occurs after degradation. The objective of this thesis is to model the degradation of components in electrical engineering, in order to estimate their lifetime. More specifically, this thesis will study large area organic white light sources (OLEDs). These sources offer several advantages in the world of lighting thanks to their thinness, their low energy consumption and their ability to adapt to a wide range of applications. The second components studied are electrical insulators applied to pairs of twisted copper wires, which are commonly used in low voltage electrical machines. First, the degradation and failure mechanisms of the various electrical components, including OLEDs and insulators, are studied. This is done to identify the operational stresses for including them in the aging model. After identifying the main causes of aging, general physical models are studied to quantify the effects of operational stresses. Empirical models are also presented when the physics of degradation is unknown or difficult to model. Next, methods for estimating the parameters of these models are presented, such as multilinear and nonlinear regression, as well as stochastic methods. Other methods based on artificial intelli­gence and online diagnosis are also presented, but they will not be studied in this thesis. These methods are applied to degradation data of organic LEDs and twisted pair insulators. For this purpose, accelerated and multifactor aging test benches are designed based on factorial experimental designs and response surface methods, in order to optimize the cost of the experiments. Then, a measurement protocol is described, in order to optimize the inspection time and to collect periodic data. Finally, estimation methods tackle unconstrained deterministic degradation models based on the measured data. The best empirical model of the degradation trajectory is then chosen based on model selection criteria. In a second step, the parameters of the degradation trajectories are modeled based on operational constraints. The parameters of the aging factors and their interactions are estimated by multilinear regression and according to different learning sets. The significance of the parameters is evaluated by statistical methods if possible. Finally, the lifetime of the experiments in the validation sets is predicted based on the parameters estimated by the different learning sets. The training set with the best lifetime prediction rate is considered the best

Sintering

This book is addressed to a large and multidisciplinary audience of researchers and students dealing with or interested in sintering. Though commonly known as a method for production of objects from fines or powders, sintering is a very complex physicochemical phenomenon. It is complex because it involves a number of phenomena exhibiting themselves in various heterogeneous material systems, in a wide temperature range, and in different physical states. It is multidisciplinary research area because understanding of sintering requires a broad knowledge - from solid state physics and fluid dynamics to thermodynamics and kinetics of chemical reactions. Finally, sintering is not only a phenomenon. As a material processing method, sintering embraces the wide group of technologies used to obtain such different products as for example iron ore agglomerate and luminescent powders. As a matter of fact, this publication is a rare opportunity to connect the researchers involved in different domains of sintering in a single book

Carbon-Based Material for Environmental Protection and Remediation

Carbon-Based Material for Environmental Protection and Remediation presents an overview of carbon-based technologies and processes, and examines their usefulness and efficiency for environmental preservation and remediation. Chapters cover topics ranging from pollutants removal to new processes in materials science. Written for interested readers with strong scientific and technological backgrounds, this book will appeal to scientific advisors at private companies, academics, and graduate students

Carbon-Based Material for Environmental Protection and Remediation

Carbon-Based Material for Environmental Protection and Remediation presents an overview of carbon-based technologies and processes, and examines their usefulness and efficiency for environmental preservation and remediation. Chapters cover topics ranging from pollutants removal to new processes in materials science. Written for interested readers with strong scientific and technological backgrounds, this book will appeal to scientific advisors at private companies, academics, and graduate students

Towards the automated synthesis of artemisinin at low temperature

According to the World Health Organisation (WHO) there were an estimated 228 million cases of malaria worldwide in 2018, resulting in 405,000 deaths, the majority of which occur in the most underdeveloped regions in the world.1 Since 2002, Artemisinin-based combination therapies (ACTs) have been designated as the first-line antimalarial treatment by the WHO, and despite the development of the first-generation RTS,S/AS01 vaccine in 2021, ACTs remain the most viable treatment of malaria.2–4 There is, therefore, a great necessity for a substantial and reliable delivery of affordable artemisinin.1 Since industrial production of artemisinin was developed by Sanofi in 2013, investigations have been made to improve the synthesis, with the ultimate aim of reducing the cost of this crucial drug.5 A crucial step in this synthesis is the reaction of the precursor, dihydroartemisinic acid (DHAA), with singlet oxygen (1O2). The reaction can be conducted using photochemically generated 1O2 to produce several hydroperoxide intermediates, of which it is generally accepted that only one can form artemisinin.5–9 The reduction of the photo-oxidative temperature can lead to increased selectivity towards the desired hydroperoxide.8 Herein, this Thesis describes the development of a continuous flow reactor capable of conducting reactions at -80°C, to further exploit increases in selectivity of the photo-oxidation. The reactor was then adapted to perform the continuous synthesis of artemisinin which was simultaneously developed with ‘On-line’ HPLC-UV and -ELSD (evaporative light scattering detector) analysis to produce an automated flow reactor. Chapter 2 details modifications to a prototype photochemical reactor previously built at Nottingham. Ultimately, a minimum interior reactor temperature of -46°C was achieved, resulting in improvements to the selectivity of the photo-oxidation of DHAA. Chapter 3 presents the further development of a second reactor capable of conducting reactions down to -80°C, resulting in further improvements in photo-oxidative selectivity. The reactor was then employed to perform the semi-synthesis of artemisinin using continuous ‘one-pot’ and semi-continuous ‘two-pot’ regimes. Through simultaneous reactor and reaction development, the enhancements at low temperature were found to translate to improved yields of artemisinin at -80°C, achieving a highest yield of 68 %. Chapter 4 explores further adaptations to facilitate automated reactions. This required establishing a method for ‘On-line’ analysis that exhibits high accuracy, precision and sufficient dynamic range. Modifications to the reactor were also needed to implement a reliable sampling of the liquid-gas mixture. HPLC-UV and -ELSD were selected as the methods of analysis. The use of the dual ‘On-line’ detection combined with automatic sampling provided valuable data verification and insights into the formation of artemisinin; showing that the conversion of the hydroperoxide to artemisinin occur slowly and required adaptation to the reactor, including the addition of a Vortex reactor, to improve the formation of artemisinin. The implementation of a low temperature, biphasic, multi-step synthesis into an automated system, provided numerous challenges. However, through iterative reactor development the automated syntheses of artemisinin and rose oxide were performed, showcasing the ability of the system and the self-optimisation framework to conduct computer controlled reactions. These experiments highlighted the potential for further advancements, both in reactor design and the self-optimisation framework, to enable the efficient implementation of fully self-optimised systems. Chapter 5 outlines the experimental work carried out within this Thesis, including HPLC method development for the quantification of photochemically synthesised artemisinin and rose oxide. Many challenges were encountered in the development of the method for artemisinin detection, primarily due to large fluctuations in the sensitivity of the ELSD. Eventually, HPLC-UV was made the primary method for quantitative analysis, while ELSD was used to gather additional information into the composition of the photoproduct. Finally, Chapter 6 summaries the work described in this Thesis and examines the success of the approaches with respect to the initial aims. A summary of future works is also presented

Towards the automated synthesis of artemisinin at low temperature

According to the World Health Organisation (WHO) there were an estimated 228 million cases of malaria worldwide in 2018, resulting in 405,000 deaths, the majority of which occur in the most underdeveloped regions in the world.1 Since 2002, Artemisinin-based combination therapies (ACTs) have been designated as the first-line antimalarial treatment by the WHO, and despite the development of the first-generation RTS,S/AS01 vaccine in 2021, ACTs remain the most viable treatment of malaria.2–4 There is, therefore, a great necessity for a substantial and reliable delivery of affordable artemisinin.1 Since industrial production of artemisinin was developed by Sanofi in 2013, investigations have been made to improve the synthesis, with the ultimate aim of reducing the cost of this crucial drug.5 A crucial step in this synthesis is the reaction of the precursor, dihydroartemisinic acid (DHAA), with singlet oxygen (1O2). The reaction can be conducted using photochemically generated 1O2 to produce several hydroperoxide intermediates, of which it is generally accepted that only one can form artemisinin.5–9 The reduction of the photo-oxidative temperature can lead to increased selectivity towards the desired hydroperoxide.8 Herein, this Thesis describes the development of a continuous flow reactor capable of conducting reactions at -80°C, to further exploit increases in selectivity of the photo-oxidation. The reactor was then adapted to perform the continuous synthesis of artemisinin which was simultaneously developed with ‘On-line’ HPLC-UV and -ELSD (evaporative light scattering detector) analysis to produce an automated flow reactor. Chapter 2 details modifications to a prototype photochemical reactor previously built at Nottingham. Ultimately, a minimum interior reactor temperature of -46°C was achieved, resulting in improvements to the selectivity of the photo-oxidation of DHAA. Chapter 3 presents the further development of a second reactor capable of conducting reactions down to -80°C, resulting in further improvements in photo-oxidative selectivity. The reactor was then employed to perform the semi-synthesis of artemisinin using continuous ‘one-pot’ and semi-continuous ‘two-pot’ regimes. Through simultaneous reactor and reaction development, the enhancements at low temperature were found to translate to improved yields of artemisinin at -80°C, achieving a highest yield of 68 %. Chapter 4 explores further adaptations to facilitate automated reactions. This required establishing a method for ‘On-line’ analysis that exhibits high accuracy, precision and sufficient dynamic range. Modifications to the reactor were also needed to implement a reliable sampling of the liquid-gas mixture. HPLC-UV and -ELSD were selected as the methods of analysis. The use of the dual ‘On-line’ detection combined with automatic sampling provided valuable data verification and insights into the formation of artemisinin; showing that the conversion of the hydroperoxide to artemisinin occur slowly and required adaptation to the reactor, including the addition of a Vortex reactor, to improve the formation of artemisinin. The implementation of a low temperature, biphasic, multi-step synthesis into an automated system, provided numerous challenges. However, through iterative reactor development the automated syntheses of artemisinin and rose oxide were performed, showcasing the ability of the system and the self-optimisation framework to conduct computer controlled reactions. These experiments highlighted the potential for further advancements, both in reactor design and the self-optimisation framework, to enable the efficient implementation of fully self-optimised systems. Chapter 5 outlines the experimental work carried out within this Thesis, including HPLC method development for the quantification of photochemically synthesised artemisinin and rose oxide. Many challenges were encountered in the development of the method for artemisinin detection, primarily due to large fluctuations in the sensitivity of the ELSD. Eventually, HPLC-UV was made the primary method for quantitative analysis, while ELSD was used to gather additional information into the composition of the photoproduct. Finally, Chapter 6 summaries the work described in this Thesis and examines the success of the approaches with respect to the initial aims. A summary of future works is also presented

A systematic approach for integrated product, materials, and design-process design

Designers are challenged to manage customer, technology, and socio-economic uncertainty causing dynamic, unquenchable demands on limited resources. In this context, increased concept flexibility, referring to a designer s ability to generate concepts, is crucial. Concept flexibility can be significantly increased through the integrated design of product and material concepts. Hence, the challenge is to leverage knowledge of material structure-property relations that significantly affect system concepts for function-based, systematic design of product and materials concepts in an integrated fashion. However, having selected an integrated product and material system concept, managing complexity in embodiment design-processes is important. Facing a complex network of decisions and evolving analysis models a designer needs the flexibility to systematically generate and evaluate embodiment design-process alternatives. In order to address these challenges and respond to the primary research question of how to increase a designer s concept and design-process flexibility to enhance product creation in the conceptual and early embodiment design phases, the primary hypothesis in this dissertation is embodied as a systematic approach for integrated product, materials and design-process design. The systematic approach consists of two components i) a function-based, systematic approach to the integrated design of product and material concepts from a systems perspective, and ii) a systematic strategy to design-process generation and selection based on a decision-centric perspective and a value-of-information-based Process Performance Indicator. The systematic approach is validated using the validation-square approach that consists of theoretical and empirical validation. Empirical validation of the framework is carried out using various examples including: i) design of a reactive material containment system, and ii) design of an optoelectronic communication system.Ph.D.Committee Chair: Allen, Janet K.; Committee Member: Aidun, Cyrus K.; Committee Member: Klein, Benjamin; Committee Member: McDowell, David L.; Committee Member: Mistree, Farrokh; Committee Member: Yoder, Douglas P