Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work presents an optimization methodology for lighting systems that employ LED. Initially, this work brings a calculation methodology capable of obtaining a thermal resistance of heat sink from their dimensions of area, besides enable optimization of the system through reducing their volume by through of change in the number of finned, length and consequently the weight of heat sink. Subsequently, the thesis present a new optimization methodology that has the objective of find the optimal point of operation lighting system taking into consideration the parameters of application current in the device, luminous flux, junction temperature, thermal resistance heat sink, number of LED and lifetime. An example of project is shown, confirming the theory, where the obtained results through of routine calculation coincided with the values found in experimental. The work also present the development of electronic topologies to power a public lighting system employing LED. Therefore, a driver to power of LED based in the integrated two-flyback converters was proposed. One prototype this system was implemented, where the luminaire provide a power of 63W. The experimental results proved the project methodology through of system satisfactory operation, presenting power factor near unit, high efficiency and a low input current distortion was obtained. / Este trabalho apresenta uma metodologia de otimização para sistemas de iluminação que empregam LEDs. Inicialmente, traz-se uma metodologia de cálculos capaz de obter a resistência térmica de dissipadores de calor a partir de suas dimensões de área, além de possibilitar a otimização do sistema através da redução do volume do mesmo por meio da variação do número de aletas, do comprimento e consequentemente da massa do dissipador. Posteriormente o trabalho apresenta uma nova metodologia de otimização que tem o objetivo de encontrar o ponto ótimo de operação do sistema de iluminação, levando-se em conta os parâmetros de corrente direta aplicada no dispositivo, fluxo luminoso, temperatura de junção, resistência térmica do dissipador, número de LEDs e vida útil dos mesmos. Um exemplo de projeto é demonstrado confirmando a teoria apresentada, onde os resultados obtidos através da rotina de cálculos coincidiram com os valores encontrados experimentalmente. O trabalho também apresenta o desenvolvimento de uma topologia eletrônica para alimentar um sistema de iluminação pública empregando LEDs. Dessa maneira, um driver para acionamento de LEDs baseado na integração de dois conversores flyback foi proposto. Um protótipo desse sistema foi implementado, onde a luminária apresenta uma potência de 63W. Resultados experimentais comprovam a metodologia de projeto através da operação satisfatória do sistema, apresentando fator de potência próximo ao unitário, elevada eficiência e o conteúdo harmônico da corrente de entrada do sistema de iluminação atendeu a norma.

A pesquisa realizada envolveu a avaliação experimental dos efeitos do fluido e da orientação do escoamento no desempenho de um dissipador de calor baseado na ebulição convectiva em microcanais. Estes dissipadores de calor são usados como uma nova aplicação para a refrigeração dos novos dispositivos eletrônicos que geram altas taxas de calor. Efetuou-se inicialmente uma extensa pesquisa bibliográfica sobre o escoamento monofásico e a ebulição convectiva em microcanais e em multi-microcanais através da qual levantou-se os principais métodos de previsão do coeficiente de transferência de calor e da perda de pressão. Então, utilizando o aparato experimental desenvolvido durante o mestrado de Do Nascimento (2012) avaliou-se a transferência de calor e perda de pressão de um dissipador de calor baseado em multi-microcanais paralelos. O dissipador de calor avaliado possui 50 microcanais retangulares dispostos paralelamente com 15 mm de comprimento, 100 µm de largura, 500 µm de altura e espaçados de 200 µm. Ensaios experimentais foram executados para o R245fa, fluido de baixa pressão utilizado em ciclos frigoríficos de baixa pressão, e R407C, fluido de alta pressão usado para conforto térmico, temperatura de saturação de 25 e 31°C, velocidades mássicas de 400 a 1500 kg/m²s, graus de subresfriamento do líquido de 5, 10 e 15°C, título de vapor máximo de até 0,38, fluxos de calor de até 350 kW/m², e para 3 orientações diferentes do dissipador de calor, horizontal, vertical com os canais alinhados horizontalmente e vertical com escoamento ascendente. Os resultados obtidos foram parametricamente analisados e comparados com métodos da literatura. Coeficientes de transferência de calor médios de até 35 kW/m² °C foram obtidos. Resultados adquiridos para o R245fa e R407C foram inferiores aos levantados por Do Nascimento (2012) para o R134a utilizando o mesmo dissipador. O fluido R407C apresentou frequências e amplitudes de oscilações inferiores aos fluidos R134a e R245fa. Nenhum método para o coeficiente de transferência de calor e perda de pressão proporcionou previsões satisfatórias dos dados experimentais. O modelo Homogêneo com viscosidade da mistura bifásica dada por Cicchitti et al. (1960) apresentou as melhores previsões da perda de pressão, já para o coeficiente de transferência de calor, os métodos de Bertsch et al. (2009) e Liu e Winterton (1991) apresentaram as melhores previsões. O dissipador com sua base posicionada horizontalmente fornece coeficientes de transferência de calor superiores enquanto sua base na vertical e escoamento ascendente verificam-se perdas de pressão inferiores. Imagens do escoamento bifásico foram obtidas com uma câmera de alta velocidade e analisadas. / This study presents an experimental investigation on the effect of the fluid and the footprint orientation on the performance of a heat spreader based on flow boiling inside micro-scale channels. This heat spreader is used in an electronics cooling application with high-power density. Initially an extensive investigation of the literature concerning single-phase and two-phase flow inside a single microchannels and multi-microchannels was performed. In this literature review the leading predictive methods for heat transfer coefficient and pressure drop are described. The experimental study was carried out in the apparatus developed by Do Nascimento (2012). The heat sink evaluated in the present study is comprised of fifty parallel rectangular microchannels with cross-sectional dimensions of 100 µm width and of 500 µm depth, and total length of 15 mm. The fins between consecutive microchannels are 200 µm thick. Experimental tests were performed for R245fa, low-pressure fluid used in low pressure refrigeration cycles, and R407C, high-pressure fluid used for heat comfort, saturation temperature of 25 and 31°C, mass velocities from 400 to 1500 kg/m² s, degrees of subcooling of the liquid of 5, 10 and 15°C, outlet vapor quality up to 0.38, heat fluxes up to 350 kW/m², and for the following footprint heat sink orientations: horizontal, vertical with the microchannels aligned horizontally and vertical with upward flow. The results were parametrically analyzed and compared again the predictive methods from literature. Average heat transfer coefficients up to 35 kW/m² °C were obtained. The results for R134a from Do Nascimento (2012) for the same heat sink presented heat transfer coefficients higher than R245fa and R407C. The fluid R407C presented oscillation of the temperature due to thermal instability effects with lower frequency and amplitude lower than R134a, and R245fa. None predictive method provided satisfactory heat transfer coefficient and pressure drop predictions of the experimental data. The Homogeneous model with the viscosity given by Cicchitti et al. (1960) provided the best pressure drop prediction while the heat transfer coefficient was best predicted by Bertsch et al. (2009) and Liu and Winterton (1991). The horizontal orientation of the footprint provided the highest heat transfer coefficients while the vertical footprint orientation with upward flow the lowest pressure drops. Images of the two-phase flow were obtained with a high-speed camera and analyzed.

In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85°C) is determined. The cooling system is tested for varying values of applied power in the range of 15-40W. The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction. The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results ii compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77°C for a heat source of 40W, which is below the recommended electronic chips temperature of not exceeding 85°C. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.

<p>A battery assembly experiences both mechanical and thermal loadings during its operation. It is critical to perform the thermomechanical analysis to propose a novel design for the highest efficiency.In this study,two main goals include mechanical characterization and deformation responses for a battery cell and assembly, as well as air-cooled concepts design and analysis.Initially, the cell dimensions were measured by cell-sectioning method, and then the mechanical properties were empirically measured by both 3-point flexural, and nanoindentation experiments. Moreover, three pairs of experiments and simulations were conducted to study mechanical behaviors on both a single cell and a battery assembly. They include (1) point-force loading for single, open cell; (2) internal pressurization for single, sealed cell; and (3) internal pressurization for battery assembly.Additionally, both parametric and experimental studies were executed to design, analyze,and validate air-cooled concepts based on the idea of microchannel heatsink. The proposed concepts have the features, which are integrated into the battery cell for generating the cooling channels. A series of thermomechanical simulations and a forced convection testbed were built for computationally and empirically analyzing the performances of the concepts. The results from the mechanical characterization showed a significant difference between the actual and nominal values of both cell dimensions and mechanical properties. Therefore, the effect of the manufacturing process to such values must be considered before inputting for analyzing the deformation responses. From the thermomechanical analyses, it was found that the mechanical loading might negatively influence the thermal performance if there were not enough mechanical supports from the air-cooling structure. The impact was minimal in the tapered-channel battery assembly. This configuration also significantly reduced the temperature difference on the cell compared with other concepts and the reference design.<br></p>

Standardized parts like hydraulic accumulators are used in nearly every hydraulic system, in many cases even several. Therefore, even small changes in size and weight of accumulators can save considerable material costs. In mobile applications, hydraulic accumulators are used among others in hydro-pneumatic suspension systems. There is a strong focus on miniaturization and weight reduction, as the components always have to be transported with the vehicle. Energy density and energy content of conventional hydraulic accumulators cannot be maximized at the same time. This limitation can be overcome by adding a heat capacity with large surface into the gas volume of the accumulator. The heat capacity enlarges the isothermal frequency range and therefore enlarges the energy density of the accumulator at the given frequency and the given size. In this paper an experimental comparison of conventional hydraulic accumulators and accumulators with foam inserts shows, that at a specific frequency band, the stiffness of foam filled accumulators is significantly lower than of conventional accumulators. The energy density is about 11 % higher than in conventional accumulators. Consequently, a space reduction of about 18 % is possible.

No description available.

<p>Advancements in future technologies such as artificial intelligence, electric vehicles, and renewable energy create a consistent need for more powerful and smaller electronic devices and systems. As a result, thermal management components such as heat sinks need to remove higher heat loads from more compact spaces to keep electronics within their operational temperature limits. Constraints imposed by conventional manufacturing processes restrict the design of heat sinks to simple geometries with limited cooling performance. Recent widespread commercialization of metal additive manufacturing (AM) tools offers new potential for leveraging the design freedom of these manufacturing technologies to design and fabricate heat sinks with improved performance. </p> <p>In AM, three dimensional parts are created through layer-by-layer depositing of materials, which allows fabrication of complex geometries that would be impossible or too costly using conventional subtractive methods. Many novel heat sink geometries have been proposed in literature which incorporate features such as manifolds, flow mixers, and curved channels using engineering intuition to reduce pressure drop or enhance heat transfer. Although such designs have been shown to offer improved performance, mathematical design algorithms such as topology optimization (TO) have been shown to outperform engineering intuition. Topology optimization optimizes the material distribution within a given design space, guided by physics-based simulations, to achieve a user-defined objective such as minimization of thermal resistance. Previous TO approaches have used penalization methods to ensure the final designs are composed of macroscopic and non-porous features due to the past precedent of fabrication capabilities. This traditional penalization approach is well-suited to the constraints of conventional manufacturing methods; however, microstructures and porous features are easily fabricable with additive manufacturing. There is a need to develop TO approaches that are better suited for leveraging AM for the design of heat sinks. In this thesis, a homogenization approach to topology optimization is proposed wherein the material distribution is represented as parametrized microstructures. This formulation allows design of thermal management components that have sub-grid features and leverages AM for fabrication. The focus of this thesis is the development of the homogenization approach for TO of heat sinks, as well as the exploration of the design problems it can address, the performance benefits made available, and the two-phase flow physics that it uniquely allows to be incorporated into the topology optimization process.</p> <p>A topology optimization algorithm using the homogenization approach is developed by representing the material distribution as arrays of pin fins with varying gap sizes. To this end, the pin fins are modeled as a porous medium with volume-averaged effective properties. Height-averaged two-dimensional flow and non-equilibrium thermal models for porous media are developed for transport in the pin fin array. Through multi-objective optimization, TO designs are generated for an example case involving a hotspot over a uniform background heat input. The resulting topologies have porous-membrane-like designs where the liquid is transported through a fractal network of open, low-hydraulic-resistance manifold pathways and then forced across tightly spaced arrays of pin fins for effective heat transfer. The TO designs are revealed to offer significant performance improvements relative to the benchmark straight microchannel (SMC) heat sink with features optimized under the same multi-objective cost function. A series of microchannel heat sinks are fabricated using direct metal laser sintering to investigate the printing capabilities and to experimentally demonstrate the performance of topology optimized designs. Advantages of the homogenization approach over the penalization approach can be summarized as follows: (1) reduced computational costs due to its ability to create sub-resolution features, (2) intrinsically fabricable parts using available metal AM tools, and (3) easier to use due to significantly reduced number of hyperparameters (e.g., penalization factors) that are controlled by the user. </p> <p>Topology optimization has been applied to thermal management methods involving single-phase flows such as natural convection, forced air cooling, and pumped liquid cooling. Compared to these conventional heat sink technologies, flow boiling offers very high heat transfer coefficients and effective heat capacities, making it a promising candidate for future cooling electronics applications. The final goal of this thesis is to enable topology optimization of flow boiling heat sinks. However, TO of flow boiling heat sinks has been avoided due to difficulties in modeling the boiling phenomena; of note, there are no examples of TO being applied to the design of heat sink under flow boiling throughout the literature. Multi-dimensional two-phase flow models require prior knowledge of friction factor and heat transfer coefficients. Correlations are available in literature but are not universal and depend significantly on channel/fin geometries, surface roughness, and operating conditions. Given that traditional penalization-based TO approach results in fin and channel geometries with unknown shapes, dimensions, and alignment before the optimization is completed, this prohibits their use for optimization of flow boiling heat sinks. However, the homogenization approach to topology optimization developed in this thesis enables the optimization of flow boiling heat sinks. As it relies on user-defined microstructures with known shapes, alignments, and ranges of geometric dimensions, a universal correlation for flow boiling in microchannels is not needed. Instead, correlations for the user-defined microstructures are sufficient to simulate flow boiling in TO designs generated using the homogenization approach. To this end, a predefined microstructure geometry is chosen for which two-phase flow correlations exist and therefore topology optimization can be performed. Topology optimized heat sink designs under flow-boiling are generated and investigated at various heat inputs, topology optimization grid sizes, and maximum vapor quality constraints. Topology optimized heat sinks designed for single-phase versus two-phase flow are compared.  There are significant differences in hydraulic and thermal responses of the single-phase and two-phase designs due to high effective heat capacity rates and high heat transfer coefficients of flow boiling. The algorithm demonstrated in this work extends the capabilities of topology optimization to two-phase flow physics, and thereby enables the design of various two-phase flow components such as evaporators, condensers, heat sinks, and cold plates.</p> <p>The flow and heat transfer of the TO algorithm for microchannel heat sinks under flow boiling use a two-phase mixture model featuring an effective porous medium formulation. However, closure of the governing equations requires empirical correlations for pressure drop and heat transfer that are specific to the operating conditions, microstructure geometry, and surface finish. Therefore, it must be demonstrated these available correlations can be successfully calibrated over a range of microstructural variations present within the homogenization framework, so as to attain the required prediction generality and accuracy needed to ensure the resulting designs achieve Pareto-optimality. To this end, a set of uniform pin fin calibration samples are additively manufactured and experimentally tested under flow boiling at various flow rates and heat inputs for model calibration. All of the unknown/free coefficients in the adopted correlations are determined by minimizing the error between the model predictions and the experimental measurements using gradient-based optimization. The calibrated topology optimization algorithm is then used to generate a Pareto-optimal set of heat sinks optimized for minimum pressure drop and thermal resistance during flow boiling. Experimental characterization of these additively manufactured heat sinks, unseen during the model coefficient calibration process, reveals that the measured Pareto optimality curve matches that predicted by the topology optimization algorithm. Lastly, a heat sink design is generated for a design space involving multiple hot spots and background heating to showcase the capability of the experimentally calibrated two-phase topology optimization algorithm at handling complex boundary conditions. The optimized heat sink intelligently distributes an adequate amount of coolant flow to each of the heated regions to avoid local dry-out. This work demonstrates a complete framework for two-phase topology optimization of heat sinks through experimental calibration of flow boiling correlations to the porous medium used by the homogenization approach. </p> <p>The major contribution of this thesis is the development of a homogenization approach for TO of additively manufactured microchannel heat sinks under single- and two-phase flows. Not only does the homogenization approach provide several advantages over the traditional penalization approaches such as reduced computational costs, intrinsic fabricability using AM, and ease of use, but it also enables TO of heat sinks under flow boiling and potentially TO of other two-phase thermal management components. The work discussed in this thesis serves a comprehensive end-to-end guide on TO of microchannel heat sinks using the homogenization approach with experimental demonstrations for validation.</p>

Motorcyclists are more often involved in accidents with severe harm or even fatal outcome compared to other road users. An experienced motorcycle driver is well familiar with the problem when the day light is reduced. The visibility is of course highly decreased. Allight International develops a light bulb that through a gyroscopic feature allows the light image to always be projected in the same axi-symmetric plane. The low beam head light usually accompanies the drivers movement when cornering, creating a black void ahead that leads to decreased vision. The light bulb has not yet been tested in a headlight and the LED is assumed to have high working temperature, which can lead to a shortened service life and technical errors due to the heat. By comparing empirical tests such as infrared camera and thermocouples on the prototype with theoretical tests such as computer aided design, finite element method, and computational fluid dynamics, a better understanding of how the model can be adapted to counteract the high temperature has achieved. Empirical analysis show that at a lower current of where the light bulb produces a brightness around the lower region of an automotive low beam headlight, the existing solution seems to work with the help of the fan creating forced convection. The improved and evaluated prototype, makes it possible to increase the current for the light bulb when more of the generated heat dissipates from the heat source. / Motorcyklister är mer involverade i olyckor med allvarlig eller dödlig utgång jämfört med generella trafikanter. En erfaren motorcykelförare är väl bekant med problemen som uppstår vid mörkerkörning. Givetvis blir sikten kraftigt försämrad. Allight International utvecklar en typ av lampa som med hjälp av ett gyroskop tillåter ljusbilden att alltid projiceras i samma axialsymmetriska plan. Vanligtvis följer lampan med förarens rörelse när denne svänger vilket skapar ett svart tomrum frammåt som leder till skymd sikt. Lampan har inte testas än i strålkastare och värmen antas ge en för hög arbetstemperatur, vilket kan leda till en forkortad livslängd samt tekniska fel på grund av värmen. Genom att utföra empiriska tester på prototypen som infraröd kamera och thermoelement tillsammans med teoretiska verktyg som computer aided design, finita elementmetoden och computational fluid dynamics fås en bättre förståelse för hur modellen kan anpassas för att motverka den höga temperaturen. Empiriska analyser visar att vid en lägre strömstyrka som motsvarar den ljusstyrka som är kravet för fordonsändamålsenliga halvljus, fungerar den nuvarande prototypen tillsammans med en fläkt som ger forcerad konvektion. Den förbättrade och utvärderade geometrin gör det möjligt att öka strömstyrkan då mer värme kan föras bort från värmekällan.

In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85℃) is determined. The cooling system is tested for varying values of applied power in the range of 15−40𝑊. The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction. The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results ii compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77℃ for a heat source of 40𝑊, which is below the recommended electronic chips temperature of not exceeding 85℃. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.

В данной магистерской диссертации представлены разработки и результаты исследования влияния конструктивных решений на теплоотвод при точении резцом с внутренним воздушным охлаждением. Разработана конструкция резца с увеличенным теплоотводом. Она позволяет существенно расширить область использования резцов с внутренним воздушным охлаждением вместо традиционных резцов с охлаждением СОЖ. Результаты диссертационной работы опубликованы в V номере инженерного журнала «Справочник». Также по результатам проведенного исследования был получен патент на полезную модель №209971 «Металлообрабатывающий инструмент с внутренним охлаждением». Магистерская диссертация состоит из введения, 5 глав, заключения. Объем диссертационной работы – 72 страниц, в том числе 33 рисунка, 6 таблиц. Библиографический список содержит 25 источников. / This master's thesis presents the developments and results of a study of the influence of design solutions on heat removal when turning with a cutter with internal air cooling. A cutter design with increased heat sink has been developed. It allows you to significantly expand the scope of use of cutters with internal air cooling instead of traditional cutters with coolant. The results of the dissertation work were published in the 5th issue of the engineering journal Spravochnik. Also, based on the results of the study, a patent for utility model No. 209971 "Metalworking tool with internal cooling" was obtained. Master's thesis consists of introduction, 5 chapters, conclusion. The volume of the dissertation work is 72 pages, including 33 figures, 6 tables. The bibliographic list contains 25 sources.