The convection performance of nanofluids in microchannels has received relatively little attention. This work reports convective heat transfer experiments of deionized water/Al2O3 nanofluids using 200μm hydraulic diameter MEMs fabricated microchannel structures and a stainless steel tube with 250μm inside diameter. The tube wall is heated electrically producing a constant heat flux boundary condition and an infrared camera is used to measure the outside tube wall temperature. A full numerical conjugate analysis of the apparatus is used to infer the fluid thermal conductivity from the temperature measurements. The effective thermal conductivity of nanofluids increased only by 4% for 4% volume concentration nanofluids in the MEMs fabricated microchannel and 5% for 3% volume concentration in the stainless steel tube under laminar flow conditions. The effective viscosity of the nanofluids increased 12% for 2% volume concentration. A dynamic light scattering system was used to measure the effective particle diameter and particle size distributions of nanoparticles with various pH values and surfactants. The measured mean diameter of Al2O3 nanoparticle is 170 nm, which is larger than the 40–50 nm nominal size.

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