Convective heat transfer coefficient and friction factor of a nanofluid in rectangular microchannel were measured. An integrated microsystem consisting of a single microchannel on one side and two localized heaters and five polysilicon temperature sensors along the channel on the other side were fabricated. Aluminum dioxide (Al2O3) nanofluids with various particle volume fractions were used in experiment to investigate the effect of the volume fraction of the nanoparticles to the convective heat transfer and fluid flow in microchannels. The convective heat transfer coefficient of the Al2O3 nanofluid in laminar flow regime was measured to be increased up to 15% compared to the distilled water at a volume fraction of 1.8 volume percent without major friction loss. The Nusselt number measured increases with increasing the Reynolds number in laminar flow regime. A new type of convective heat transfer correlation was proposed to correlate experimental data of heat transfer coefficient for nanofluids in microchannels.
Microparticles or biological cells mixed in water were separated using the combination of an electrical force due to dielectrophoresis and a mechanical one generated in an evaporating droplet. Micropatterned electrodes of Au were fabricated on the silicon dioxide layer and were used to generate dielectrophoresis. Polystyrene particles, red blood cells. and E. coli were used as separating objects. Microparticles and biological cells were separated by adjusting the amplitude and frequency of the applied voltage. Although the mechanical force was enough to transport the particles to the boundary of the droplet, nevertheless, it could not detach the particles trapped at the electrode. Based on this work, the microparticles and biological cells can be separated, controlled, and sensed without using a liquid pumping unit.
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