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Single phase forced convection cooling of high power leds


These file attachments have been under embargo and were made available to the public after the embargo was lifted on 4 June 2012.

Author: Ozdemir, M.Z. · Chestakov, D. · Frijns, A.J.H. (Univ. Eindhoven)
Embargo lifted:2012-06-04
Publisher: Philips Research
Institution: Philips Research
Identifier: TN-2011-00348
Keywords: cooling · heat exchange · led · micro-channel · thermal
Rights: (c) Koninklijke Philips Electronics N.V.


LEDs are strong candidates for future illumination applications dueto their much lower consumption of energy compared to conventional lighting options. One of key problems in development of LEDs is successful thermal management during illumination. Therefore, current research ongoing related to high power LEDs is focusing on improvementof cooling performance of them to enhance light output efficiency, durability and reliability of these devices.The goal of current studyis a first characterization of the LEDs arrays cooling with microchanneled flows. The flow and heat transfer characterization of a 5 LED array on top of water driven microchannels are performed and the junction temperature change with flow rate and thermal resistance isstudied. Experimental results show that the microchannel cooler reduces the junction temperature of LED array and improves the heat dissipation capability of the LEDs themselves.X At very low Reynolds numbers, there are discrepancies found between literature data and ourexperimental results. These discrepancies are explained by uncertainty in general measurements at microscale, including geometrical dimensions and operating parameters. It is demonstrated that the uncertainty in f*Re is dominated by the microchannel width and height measurements. Even a very accurate pressure drop measurements are oftenovershadowed by the geometry measurement uncertainties. In addition,the channel geometry is often not exactly the desired geometry dueto manufacturing difficulties associated withsmall scales. Therefore, the flow behavior is different from the expectations based on theory. Nusselt number variation with Reynolds number is investigated. Nusselt number is almost linearly increasing with Reynolds number inthe low Reynolds number range as also observed in literature. In fact, Nusselt number is expected to be constant in fully developed laminarflow according to the classical laminar flow theory. This does not hold for several reasons such as entrance region effects, unclearboundary conditions in microchannel cross section, multi directional heat transfer, flow configuration as also explained in details previously.

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