Thermal transmittance of carbon nanotube networks: Guidelines for novel thermal storage systems and polymeric material of thermal interest

Among other applications, the study of thermal properties of large networks of carbon nanoparticles may have a critical impact in loss-free, more compact and efficient thermal storage systems, as well as thermally conducting polymeric materials for innovative low-cost heat exchangers. In this respect, here, we both review and numerically investigate the impact that nanotechnology (and in particular carbon-based nanostructures) may have in the near future. In particular, we focus on the role played by some geometrical and chemical parameters on the overall thermal transmittance of large complex networks made up of carbon nanotubes (CNTs), that can be potentially added as fillers to (thermally) low-conductive materials for enhancing the transport properties. Several configurations consisting of sole and pairs of single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs), characterized by different dimensions and number of C-O-C interlinks, are considered. Based on the results found in the literature and using focused simulations using standard approaches in Non-Equilibrium Molecular Dynamics (NEMD), we highlight the dependence on the particle diameter, length, overlap and functionalizations of both thermal conductivity and boundary resistance across CNTs, which are indeed the relevant quantities for obtaining composite materials with desired unusual thermal properties. We observe that CNTs with short overlap length and a few interlinks already show a remarkable enhancement in the overall transmittance, whereas further increase in the number of C-O-C connections only carries marginal benefits. We believe that much understanding has been gained so far in this field thanks to the work of chemists and material scientists, thus it is time to draw the attention of engineers active in the energy sector and thermal scientists on such findings. Our effort, therefore, is to gather in this article some guidelines towards innovative thermal systems that may be manufactured and employed in the near future for addressing a great challenge of our society: Storage and use of thermal energy.