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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.

The off-axis motion of particles actuated by axial magnetic or gravitational forces is studied in fluidic channels. Single actuated superparamagnetic micro-particles starting from channel walls travel towards the channel center and show unforeseen reversionary rotation phenomena. Different stages of co- and counter-rotation are observed in both micro- and macro-scale experiments and are analyzed by meansof numerical fluid-dynamics models. The related microfluidic near-surface mixing performance of the rotating actuated particles is discussed.