Research Paper Enhanced thermal conductivity of phase change nanocomposite in solid and liquid state with various carbon nano inclusions Sivasankaran Harish a , Daniel Orejon a,b , Yasuyuki Takata a,b , Masamichi Kohno a,b,⇑ a International Institute for Carbon-Neutral Energy Research (WPI – I 2 CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan b Department of Mechanical Engineering, Thermofluid Physics Laboratory, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan highlights  Thermal conductivity of lauric acid with various carbon additives are measured.  Contrasting thermal conductivity enhancement in solid and liquid state is noticed.  For 1 vol% CNTs, enhancement in solid and liquid state is 171% and 20%.  For 1 vol% graphene, enhancement in solid and liquid state is 223% and 37%.  Thermal interface resistance is an order of magnitude higher in liquid state. article info Article history: Received 23 March 2016 Revised 27 September 2016 Accepted 18 October 2016 Available online xxxx Keywords: Phase change material Thermal conductivity Carbon nanohorns Carbon nanotube Graphene abstract We report contrasting enhancement in the solid state and liquid state thermal conductivity of phase change nanocomposite seeded with various carbon nano inclusions. Phase change nanocomposites were prepared using n-Dodecanoic acid as the host matrix. Single-walled carbon nanohorns, multi- walled carbon nanotubes and few-layer graphene nanosheets were considered as the nano inclusions. Thermal conductivity measurements were carried out using a custom built transient hotwire technique. The thermal conductivity enhancement significantly depends on the shape and aspect ratio of the nano inclusions. Maximum thermal conductivity enhancement was obtained in the presence of graphene nanosheets as the nanofiller candidate followed by carbon nanotubes and carbon nanohorns. The ther- mal conductivity enhancement was significantly higher in the solid state than the liquid state of the material for all the nano composites. Thermal conductivity enhancement results were compared with the effective medium theory calculations and Yamada-Ota model calculations considering the role of interfacial thermal resistance between the nanomaterial and the surrounding host matrix. The model calculations show that that the interfacial thermal resistance significantly limits the thermal conductiv- ity enhancement in the liquid state compared to the solid state. The model calculations also show that interfacial thermal resistance is an order of magnitude higher at the solid-liquid interface compared to that of solid-solid interface which leads to a contrasting thermal conductivity enhancement in liquid and solid state of the nanocomposites. Ó 2016 Published by Elsevier Ltd. 1. Introduction Solid-liquid phase change materials (PCM) due to its excellent energy storage capabilities, low cost, abundance in natural resources are frequently used for thermal energy storage applica- tions in concentrated solar power plants [1,2], passive electronics cooling [3] and waste heat recovery systems [4]. Among numerous PCMs, organic PCMs, have proved to be desirable for latent heat storage purposes due to its high stability, negligible super cooling and low cost. Especially organic fatty acid based PCMs possess many favourable properties such as high phase change enthalpy, low vapour pressure and wide range of melting point which makes it ideal for several applications [5,6]. Unfortunately, organic PCMs suffer from inherently low thermal conductivity which limits its application in energy storage systems and passive electronic http://dx.doi.org/10.1016/j.applthermaleng.2016.10.109 1359-4311/Ó 2016 Published by Elsevier Ltd. ⇑ Corresponding author at: International Institute for Carbon-Neutral Energy Research (WPI – I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819- 0395, Japan. E-mail address: kohno@mech.kyushu-u.ac.jp (M. Kohno). Applied Thermal Engineering xxx (2016) xxx–xxx Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng Please cite this article in press as: S. Harish et al., Enhanced thermal conductivity of phase change nanocomposite in solid and liquid state with various carbon nano inclusions, Appl. Therm. Eng. (2016), http://dx.doi.org/10.1016/j.applthermaleng.2016.10.109