Manipulation and Characterization of Geometry-dependent Nanoscale Thermophysics in Nanoparticle Enhanced Phase Change Thermal Energy Storage Materials

摘要

Reductions in the size of materials down to the nanoscale have led to the discovery of nanoparticles with exceptionally unique optical, mechanical, electrical and thermal properties. As a result of their extraordinarily high thermal conductivities, carbon-based nanoparticles are projected to become integral components in a wide variety of thermal management systems and devices in the future, including their incorporation into thermal interface materials, microchannel heat sinks and waste heat recovery devices. Despite nearly two decades of intense research in this area, however, carbon-based nanoparticles have not yet been widely adopted in these systems. One major impediment to their integration in these applications is the high degree of phonon boundary scattering that occurs across individual nanoparticle interfaces, particularly when they come into contact with an amorphous material. The physical phenomena responsible for this include: 1) mismatches in the vibrational spectra of the nanoparticle and the surrounding amorphous material, 2) a low adhesion energy (or bonding strength) at the interface and 3) differently sized constrictions that are formed at contacting junctions. Of interest in this work is the last of these, whose magnitude effect on thermal transport in bulk materials is not well known. To this end, the effect of nanoparticle contact area on thermal transport within a bulk paraffin phase change material is quantified and reported for a variety of nanoparticle types. Paraffins are amorphous in nature and are common materials used for the storage of thermal energy. The effect of nanoparticle inclusions on both the micro-scale and macro-scale heat conduction phenomena within paraffin are quantified as a function of nanofillers geometry and type. The results are expected to aid in the analysis and design of next-generation nanocomposites and thermal energy storage materials.