Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards general illumination. The increased electrical currents used to drive the LEDs have focused more attention on the thermal paths in the developments of LED power packaging. The luminous efficiency of LEDs is soon expected to reach over 80 lumens/W, this is approximately 6 times the efficiency of a conventional incandescent tungsten bulb. Thermal management for the solid-state lighting applications is a key design parameter for both package and system level. Package and system level thermal management is discussed in separate sections. Effect of chip packages on junction to board thermal resistance was compared for both SiC and Sapphire chips. The higher thermal conductivity of the SiC chip provided about 2 times better thermal performance than the latter, while the under-filled Sapphire chip package can only catch the SiC chip performance. Later, system level thermal management was studied based on established numerical models for a conceptual solid-state lighting system. A conceptual LED illumination system was chosen and CFD models were created to determine the availability and limitations of passive air-cooling.

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Piezoelectric fans have emerged as a viable cooling technology for the thermal management of electronic devices, owing to their low power consumption, minimal noise emission, and small and configurable dimensions.Piezoelectric fans are investigated for application in the cooling of low-power electronics. Different experimental configurations are considered, and the effect of varying the fan amplitude, the distance between the fan and the heat source, the fan length, its frequency offset from resonance, and the fan offset from the center of the heat source are studied to assess the cooling potential of the fans. A Design-Of-Experiments (DOE) analysis revealed the fan frequency offset from resonance and the fan amplitude as the critical parameters. Transfer functions are obtained from the DOE analysis for the implementation of these fans in electronics cooling. For the best case, an enhancement in convective heat transfer coefficient exceeding 375% relative to natural convection was observed, resulting in a temperature drop at the heat source of more than 36.4°C. A computational model for the flow field and heat transfer induced by the piezoelectric fan is also developed. Effects of the flow on convection heat transfer for different fan-to-heat source distances and boundary conditions are analyzed. Transition between distinct convection patterns is observed with changes in the parameters. The computational results are validated against experimental measurements, with good agreement.

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Light emitting diodes (LEDs) historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors has allowed them to penetrate specialty and general illumination applications. The increased electrical currents used to drive the LEDs have resulted in higher heat fluxes than those for average silicon integrated circuits (i.e., ICs). This has created a need to focus more attention on the thermal management engineering of LED power packages. The output of a typical commercial high brightness, 1mm2, LED has exceeded 100lm at drive levels approaching 3W. This corresponds to a heat flux of up to 300W∕cm2. Novel thermal solutions need to address system architectures, packaging, phosphors for light color conversion, and encapsulants and fillers for optical extraction. In this paper, the effect of thermal management on packaging architectures, phosphors, encapsulants, and system design are discussed. Additionally, discussions of microscopic defects due to packaging problems as well as chip active layer defects are presented through experimental and computational findings.

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With increasing attention to the energy efficiency of consumer and commercial products, thermal engineering and science community is devoting greater effort and attention to the design and implementation of energy-efficient cooling solutions. This study focuses on the cooling potential and Coefficient of Performance, (COP), achievable with three distinct meso-scale cooling technologies, applicable to a wide range of electronics cooling challenges. The thermo-fluid and thermodynamic characteristics of synthetic jets, piezo-driven vibrating blades, and compact muffin fans will be addressed. We are dedicating this paper to Prof. Kakac for his contributions to heat transfer science and technology, developing young scientists, writing highly valuable heat transfer textbooks, and most importantly for his kindness and friendship.