| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 101 === Nanofluid is a liquid suspended with nano particles. According to the literature, the heat conductivity of nanofluid is increased significantly in comparing with their
base fluid. Forced convection is also enhanced for most of the reports, but there is a considerable amount of literature indicates that the heat transfer cannot be enhanced by using nanofluids in natural convection. It is general reported that the heat transfer enhancement is increased as the concentration of the particle increases and as the size of the particles decreases when the volume fraction of the particles is within certain range. The present study aims to study experimentally the convective heat transfer of nanofluids in micro channels.
Micro channels with length 17.5 mm and cross sections 50 um x 50 um, 100 um x 100 um and 100 um x 1000 um were fabricated on silicon substrate using MEMS techniques. The top and the side walls were moulded with PDMS with two cylindrical reservoirs on both ends of the channels. Two heating electrodes were fabricated on the bottom walls of the channel for temperature measurement. The inlet and outlet fluid temperature were also measured using thermocouples.
According to the experiment, the thermal boundary condition for the present micro device can be approximated as constant temperature for the bottom wall with the rest walls insulated. De-ionized water (the base fluid) and nanofluids (de-ionized water suspended with 0.6%, 1.2% and 1.8% nano sized TiO2 particles) were employed for the experiments. It was found that the heat transfer coefficient of the system
increases linearly with Reynolds number for all the cases, but the heat transfer IV enhancement associated with nanofluids was not clearly observed. The heat transfer
coefficient is essentially independent of the power input.
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