Quantifying Nano-Enhancement by Graphite Nanofibers in organic Phase Change Materials
Aaron P. Wemhoff
A multi-scale modeling framework is provided that enables predictions of the effective bulk thermal conductivity of organic phase change materials (PCMs) enhanced through the addition of graphite nanofibers (GNFs). The framework connects GNF molecular structure, GNF percolation, and GNF agglomeration to the nano-enhanced PCM thermal conductivity. The axial and radial thermal conductivities for various styles of GNFs are provided, and updates are given to the percolated cylindrical inclusions (PCI) theory. Experimental data is used to calibrate the thermal boundary resistance values of GNFs in PCMs. The results suggest that ribbon GNFs provide the best enhancement and the most additional benefit from inclusion agglomeration. The results also suggest the possibility of predicting if and when negative enhancement could occur, and a discussion is provided on how experimental measurements featuring agglomerated inclusions may enable a means to improve the accuracy of predicted thermal boundary resistance values.
Keywords: Graphite nanofibers, phase change material, thermal conductivity, negative enhancement.