Study on the effective thermal conductivity of fiber reinforced epoxy composites

Abstract

The present paper deals with the effect of volume fraction of fibers on the effective thermal conductivity (keff) for polymer composites. This work sees an opportunity of enhancement on insulation capability of a typical fiber reinforced polymer composite. A mathematical correlation for the effective thermal conductivity of polymer composites reinforced with fiber is developed using the law of minimal thermal resistance and equal law of the specific equivalent thermal conductivity. To validate this mathematical model, two sets of epoxy based composites, with fiber content ranging from 0 to 15.7 vol % have been prepared by simple hand lay-up technique. For one set of composite, natural fiber i.e. banana fibers are incorporated in epoxy matrix and for another set a well-known synthetic fiber i.e. glass fiber is taken as a filler material whereas matrix material remains the same. Thermal conductivities of these composite samples are measured as per ASTM standard E-1530 by using the Unitherm™ Model 2022 tester, which operates on the double guarded heat flow principle. Further, finite element method (FEM) is implemented to determine the keff of such composites numerically using a commercially available finite element package ANSYS. Experimentally measured values are then compared with the values obtained from the proposed mathematical model, the numerical values and also with models established earlier, such as Rule-of-Mixture (ROM), Maxwell’s model, Nielson-Lewis model and Bruggeman model. From the experimental and numerical output, it can be seen that with an increase in fiber content, there is gradual decrease in effective thermal conductivity value for both sets of composites.