Development of a Heat Conduction Model and Investigation on Thermal Conductivity Enhancement of AlN/Epoxy Composites

This work explores on the possibility of enhancement of heat conduction capability of a typical particulate filled polymer composite. A theoretical model for one dimensional heat conduction through such a composite has been developed using the law of minimal thermal resistance and equal law of the specific equivalent thermal conductivity. Based on this model, a mathematical correlation between the effective thermal conductivity of the composite and the filler content is proposed. The proposed model is then validated through experimentation conducted in controlled laboratory conditions. Different samples of aluminum nitride filled epoxy composites are prepared by simple hand layup technique. The content of the conductive filler (AlN) in the composites is varied in the range 0% to 15% by volume. Thermal conductivities of these composite samples are measured according to the ASTM standard E-1530 by using the UnithermTM Model 2022 tester, which operates on the double guarded heat flow principle. Gradual increase in thermal conductivity has been observed, with increase in conductive filler percentage in composite samples. Values obtained using the proposed mathematical correlation are then compared with the measured experimental results and also with values estimated with other established correlations such as Rule-of-Mixture (ROM), Maxwell's model, Bruggeman model and Nielson-Lewis model. This comparison reveals that while none of the above models are correctly predicting the effective thermal conductivity of the composites, the results obtained from the proposed model by incorporating a correction factor are in good agreement with the experimental data.