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

Development and thermal performance of a vapor chamber with multi-artery reentrant microchannels for high-power LED

Abstract(#br)This study developed a vapor chamber (VC) with radial multi-artery reentrant microchannels for thermal management of high-power light emitting diodes (LEDs). It featured Ω-shaped reentrant microchannels inside porous wicks to provide separated flow passages for vapor and liquid flow. It was integrated with a high-power LED module for fast heat dissipation and efficient thermal management. Experiments are systematically conducted to evaluate thermal performance of the VC for a wide range of input power of LEDs, air flow rates and inclination angles of LED module. The VC is compared to a copper plate heat sink in the same operation conditions. Results show that compared to the copper plate, the VC presented a faster temperature rise, and was earlier to reach equilibrium state. The VC reduced the substrate surface temperature of LED module for 7% to 27%, and introduced a reduction in the thermal resistance for 19% to 48%, indicating that the VC enhanced cooling capacity remarkably and yield a notable favorable performance for the heat dissipations of LEDs. The thermal performance of the VC was significantly dependent on the input power of LEDs and air flow rates, whereas the inclination angle of LED module showed negligible effects on thermal performance

Simulation and optimization of high-power LED with flat heat pipe heat spreader

为解决大功率LED的散热问题,设计了平板热管散热器来实现LED芯片的高效散热。通过Flotherm模拟软件,对大功率LED在自然对流条件下的散热; 情况进行了三维数值模拟。通过平板热管与常规铜、铝散热基板对比,发现平板热管有效降低了大功率功率LED的结温和热阻,使得LED温度分布更为均匀。此; 外,还研究了平板热管LED散热系统在不同芯片功率下的热性能,并对四种不同排布方式的LED平板热管散热系统进行了优化,发现阵列分布其温度分布最为均; 匀,结温最低,是较优的排布方式。Flat heat pipe heat spreader was designed for the heat dissipation of; high-power LED. The thermal performance of high-power LED in natural; convection conditions was simulated by the Flotherm simulation software.; It is found that the flat heat pipe reduces the junction temperature and; thermal resistance compared to the conventional copper and alumina heat; spreader. The thermal performance of LED with flat heat pipe heat; spreader under different heat power conditions was also explored.; Furthermore, four types of arrangement of the LED chips were also; designed and compared for the optimization. The results indicate that; the uniform array configuration induces the best uniform temperature; distribution and the lowest junction temperature, and seems to be the; optimum choice for high-power LED.广东省惠州市产学研结合项

Diode laser modules based on laser-machined, multi-layer ceramic substrates with integrated water cooling and micro-optics

This thesis presents a study on the use of low temperature co-fired ceramic (LTCC) material as a new platform for the packaging of multiple broad area single emitter diode lasers. This will address the recent trend in the laser industry of combining multiple laser diodes in a common package to reach the beam brightness and power required for pumping fibre lasers and for direct-diode industrial applications, such as welding, cutting, and etching. Packages based on multiple single emitters offer advantages over those derived from monolithic diode bars such as higher brightness, negligible thermal crosstalk between neighbouring emitters and protection against cascading failed emitters. In addition, insulated sub-mounted laser diodes based on telecommunication standards are preferred to diode bars and stacks because of the degree of assembly automation, and improved lifetime. At present, lasers are packaged on Cu or CuW platforms, whose high thermal conductivities allow an efficient passive cooling. However, as the number of emitters per package increases and improvements in the laser technology enable higher output power, the passive cooling will become insufficient. To overcome this problem, a LTCC platform capable of actively removing the heat generated by the lasers through impingement jet cooling was developed. It was provided with an internal water manifold capable to impinge water at 0.15 lmin-1 flow rate on the back surface of each laser with a variation of less than 2 °C in the temperature between the diodes. The thermal impedance of 2.7°C/W obtained allows the LTCC structure to cool the latest commercial broad area single emitter diode lasers which deliver up to 13 W of optical power. Commonly, the emitters are placed in a “staircase” formation to stack the emitters in the fast-axis, maintaining the brightness of the diode lasers. However, due to technical difficulties of machining the LTCC structure with a staircase-shaped face, a novel out-plane beam shaping method was proposed to obtain an elegant and compact free space combination of the laser beam on board using inexpensive optics. A compact arrangement was obtained using aligned folding mirrors, which stacked the beams on top of each other in the fast direction with the minimum dead space

Thermal And Flow Analysis Of Piezoelectric Fans For Cooling LEDS Packages

Computers, LED packages and portable electronic devices, such as minilaptops, tablets, and cellular phones, are rapidly emerging in lighter, slimmer, and more compact forms with high functionalities to meet consumer demands. This tremendous growth in advance electronics necessitates modern solutions to be adapted with the new challenges of thermal management. One of the recent thermal solutions is piezoelectric fans, which recently considered as a very strong candidate for cooling the next generation in general microelectronic devices. Komputer, pakej LED dan alatan elektronik mudah-alih, seperti komputer riba mini, tablet, telefon sel, meningkat dengan ketara dari segi bentuk, ringan, nipis, dan lebih padat dengan fungsi yang tinggi bagi memenuhi permintaan pelangan. Pertumbuhan yang ketara ini dalam elektronik termaju memerlukan penyelesaian moden bagi menyesuaikan dengan cabaran baru pengurusan terma. Salah satu daripada penyelesaian terma terbaru adalah kipas piezoelektrik, yang mana baru-baru ini dianggap sebagai alat yang amat sesuai bagi penyejukan generasi hadapan dalam alatan mikroelektronik umum

Enhancing Electrical and Heat Transfer Performance of High-Concentrating Photovoltaic Receivers

In a world that is constantly in need of a continuous, reliable and sustainable energy supply, concentrating photovoltaic technologies have the potential to become a cost effective solution for large scale power generation. In this light, important progresses have been made in terms of cell’s design and efficiency, but the concentrating photovoltaic industry sector still struggles to gain market share and to achieve adequate economic returns. The work presented in this thesis is focused on the development of innovative solutions for high concentrating photovoltaics receivers. The design, the fabrication and the characterization of a large cell assembly for high concentrations are described. The assembly is designed to accommodate 144 multijunction cells and is rated to supply energy up to 2.6kWe at 500 suns. The original outline of the conductive copper layer limits the Joule losses to the 0.7% of the global power output, by reducing the number of interconnections. All the challenges and the issues faced in the manufacturing stage are accounted for and the reliability of the fabrication has been proven by quality tests and experimental investigations conducted on the prototype. An indoor characterization shows the receiver’s potential to supply a short-circuit current of 5.77A and an open circuit voltage per cell of 3.08V at 500×, under standard test conditions, only 4.80% and 2.06% respectively lower than those obtained by a commercial single-cell assembly. An electrical efficiency of 29.4% is expected at 500 suns, under standard conditions. A prototype’s cost of $0.91/Wp, in line with the actual price of CPV systems, has been recorded: a cost breakdown is reported and the way to further reduce the cost have been identified and is accounted. In a second approach, the design of a natural convective micro-finned array to be integrated in a single cell receiver has been successfully attempted. Passive cooling systems are usually cheaper, simpler and considered more reliable than active ones. After a detailed review of micro-cooling solutions, an experimental investigation on the thermal behaviour of micro-fins has been conducted and has been combined with a multiphysics software model. A micro-finned heat sink shows the potential to keep the CPV temperature below 100°C under standard conditions and the ability to handle the heat flux when the cell’s efficiency drops to zero. Moreover, a micro-finned heat sink demonstrates the potential to introduce significant benefits in terms of material usage and weight reduction: compared to those commercially available, a micro-finned heat sink has a power-to-weight ratio between 6 and 8 times higher, which results in lower costs and reduced loads for the CPV tracker.EPSRC-funded BioCPV projec

Technical Design Report for PANDA Electromagnetic Calorimeter (EMC)

This document presents the technical layout and the envisaged performance of the Electromagnetic Calorimeter (EMC) for the PANDA target spectrometer. The EMC has been designed to meet the physics goals of the PANDA experiment. The performance figures are based on extensive prototype tests and radiation hardness studies. The document shows that the EMC is ready for construction up to the front-end electronics interface

Advanced Thermoelectric Materials for Energy Harvesting Applications

Electrical energy consumption is negatively affecting our environment and contributing to climate change. Therefore the research and industrial communities are working hard to minimize energy consumption using promising energy-efficient and renewable energy technologies. We know that it is possible to convert heat energy into electrical energy using thermoelectric devices; this heat energy can be from the sun or from an electro-mechanical device. However, thermoelectric devices traditionally suffer from lower efficiencies of energy conversion. This book, Advanced Thermoelectric Materials for Energy Harvesting Applications, is a researchintensive textbook consisting of eight chapters organized into three sections. Section 1 consists of Chapters 2, 3, and 4, which cover advanced thermoelectric materials and the topics of organic/inorganic thermoelectric materials, quantum theory of the Seebeck coefficient for the advancement of thermoelectric superconducting material, and the limits of Bismuth Telluride-based thermoelectric materials. Section 2, containing Chapters 5 and 6, evaluates behaviors and performance of thermoelectric devices. Section 3, containing Chapters 7 and 8, focuses on energy harvesting applications of thermoelectric devices. This book will be of interest to a wide range of individuals, such as scientists, engineers, researchers, and undergraduate and postgraduate students in the field of advanced thermoelectric materials

Index to 1985 NASA Tech Briefs, volume 10, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1985 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences