| Summary: | 碩士 === 元智大學 === 機械工程學系 === 95 === Due to its excellent thermal conductivity, carbon nanotubes (CNTs) are considered as candidates for heat management materials. In the present works, the epoxy resin is used as the matrix, and the multi-walled carbon nanotubes (MWCNTs) with different diameters are as the reinforcement. The objectives of this study are to understand the effects of MWCNT weight percent (0.1 – 5 wt. %), MWCNT diameter (20 – 40 or 40 – 60 nm), and the thickness of the specimens (1 or 3 mm) on the effective thermal conductivities of the composite. The results show that under 50 and the specimen with thickness = 1 mm, the thermal conductivity of the pure epoxy is 0.204 W/m K. The thermal conductivity of the composite increases with the increase in the MWCNTs weight percent. By adding of the MWCNTs under 0.9 wt. %, the thermal conductivity of the MWCNT/epoxy composite increases linearly, but the increasing rate decreases once the MWCNTs weight percent is over 0.9 wt. %. The thermal conductivities of 0.9 wt. % MWCNT/epoxy composites with a MWCNT diameter D = 20 - 40 nm or D = 40 - 60 nm are 0.289 or 0.281 W/m K, respectively. Compare with the pure epoxy, the thermal conductivities increase 42 or 38 %, respectively. The thermal conductivities of 5 wt. % MWCNT/epoxy composites with a MWCNT diameter D = 20 - 40 nm or D = 40 - 60 nm are 0.404 or 0.423 W/m K, respectively, with the increments of 98 or 107 %. The experimental results of the composite specimens with thickness = 3 mm is lower than that with thickness = 1 mm. This is attributed to the fact that there is a larger lateral area exposing to the external environment in the specimens with thickness = 3 mm, which results in a large heat loss. The micromechanics model, Eshelby, is developed to predict the thermal conductivity of MWCNT-reinforced composites. Compared with the experimental data, the predictions are fitted well with the experimental data of the composite specimens with thickness = 1 mm by adding MWCNTs under 0.9 wt. %, no matter the diameters of the MWCNTs are between 20 - 40 nm or 40 - 60 nm. However, at high wt. % of MWCNTs (> 0.9 wt. %), there are large discrepancies between the predictions and the experimental data because the trend of the increase by adding high wt. % MWCNTs are nonlinear.
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