1 Copyright © 2013 by ASME Proceedings of the ASME 2013 Summer Heat Transfer Conference HT2013 July 14-19, 2013, Minneapolis, MN, USA HT2013-17478 MOLECULAR DYNAMICS STUDY OF THE INTERFACIAL THERMAL CONDUCTANCE AT THE GRAPHENE/PARAFFIN INTERFACE IN SOLID AND LIQUID PHASES Hasan Babaei Mechanical Engineering Department, Auburn University, Auburn, AL 36849-5341, USA Pawel Keblinski Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA J. M. Khodadadi Mechanical Engineering Department, Auburn University, Auburn, AL 36849-5341, USA ABSTRACT By utilizing molecular dynamics (MD) simulations, we study the interfacial thermal conductance at the interface of graphene and paraffin. In doing so, we conduct non-equilibrium heat source and sink simulations on systems of parallel and perpendicular configurations in which the heat flow is parallel and perpendicular to the surface of graphene, respectively. For the perpendicular configuration, graphene with different number of layers are considered. The results show that the interfacial thermal conductance decreases with the number of layers and converges to a value which is equal to the obtained conductance by using the parallel configuration. We also study the conductance for the solid phase paraffin. The results indicate that solid paraffin-graphene interfaces have higher conductance values with respect to the corresponding liquid phase systems. INTRODUCTION Paraffin with their desirable thermophysical properties for energy storage applications has been extensively considered as an appropriate candidate for phase change materials (PCM). However, one of the drawbacks of paraffin is its low thermal conductivity which hinders the fast charge/discharge of thermal energy. Despite spherical nanoparticles (1-5), it has been recently shown that high aspect-ratio carbon-based nanofillers such as carbon nanotube and graphene can be used as additives to enhance thermal transport in paraffin (6-16). In the search for finding the key mechanisms in thermal transport of such mixtures/composites for optimization, thermal conductance at the interface plays an important role in thermal conductivity of graphene-paraffin mixtures/composites. Interfacial thermal conductance can limit thermal transport when its value is small. In this article, we study the thermal conductance at the interface of the paraffin-graphene mixtures in both solid and liquid phases by utilizing atomic-level simulations. Molecular dynamics (MD) simulations have been frequently used in studying interfacial thermal conductance (17-20). Here, we use two configurations in determining the interfacial thermal conductance. The effects of the number of graphene layers and the phase of paraffin on the value thermal conductance are investigated. METHODOLOGY AND MODEL STRUCTURES In this paper we have used two different configurations for obtaining the thermal conductivity. In the first model structure, we have considered thermal transport in a system in which the heat flux is parallel to the graphene plane. In the parallel configuration, the interfacial thermal conductance is predicted by utilizing the Nan’s model (21). In the second model configuration, we use the direct method in which the heat flux is perpendicular to the graphene plane. In this method, the interfacial thermal conductance is obtained by using its definition which is the ratio of heat flux to the average temperature difference between paraffin and graphene sheet at the interface. The relation reads as T q G ∆ = (1) where quantity G is the interfacial thermal conductance, q is the heat flux crossing the interface and T ∆ is the temperature difference at the interface. In this study, since there are multiple interfaces, we take the average of quantity T ∆ over all interfaces. To study the effect of the number of layers of graphene on the value of the interfacial thermal conductance, we consider graphenes containing one and three layers and thicker graphite