Thermal conductivity enhancement of lauric acid phase change nanocomposite in solid and liquid state with single-walled carbon nanohorn inclusions Sivasankaran Harish a, *, Daniel Orejon a, b , Yasuyuki Takata a, b , Masamichi Kohno a, b a Department of Mechanical Engineering, Thermofluid Physics Laboratory, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan b International Institute for Carbon-Neutral Energy Research (WPI – I 2 CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan A R T I C L E I N F O Article history: Received 16 September 2014 Received in revised form 25 November 2014 Accepted 6 December 2014 Available online 10 December 2014 Keywords: Phase change material Thermal conductivity Carbon nanohorns Calorimetry A B S T R A C T We prepared lauric acid based phase change nanocomposite embedded with chemically functionalized single-walled carbon nanohorns and measured its thermal properties. We report contrasting enhancements in thermal conductivity of such nanocomposites in the solid and liquid phase for the same loading of nanohorn inclusions. Maximum thermal conductivity enhancement in solid and liquid phase at 2 vol% is found to be 37 and 11%, respectively. The nanocomposites’ thermal conductivity enhancement is compared with calculations of effective medium theory considering the role of interfacial thermal transport. Model calculations show that Kapitza resistance is an order of magnitude lower at the solid–solid interface compared to the solid–liquid interface. Differential scanning calorimetry study of the nanocomposites shows that the phase change temperature and enthalpy marginally increases to that of pristine material. Such a nanocomposite with enhanced thermal transport and phase change enthalpy makes it a promising candidate for thermal energy storage applications. ã 2014 Elsevier B.V. All rights reserved. 1. Introduction Nanomaterials offer a facile way to enhance the thermophysical properties of heat transfer fluids, latent heat storage and thermal interface materials [1–3]. Manipulating the thermal transport properties of conventional materials using nano inclusions has several practical applications of technological importance in the field of thermal energy storage and thermal management of microelectronic devices [4–6]. Organic phase change materials, often employed in thermal energy storage applications possess low thermal conductivity which limits the energy storage and release rate [7]. This has resulted in intense efforts to increase the thermal conductivity of phase-change materials (PCM) through the addition of high thermal conductivity nanomaterials [8–13]. High conductive metallic and metallic oxide nanoparticles and carbon allotropes have been used for enhancing the thermal conductivity of PCMs as reviewed by Khodadadi et al. [14]. However, most of the thermal conductivity results reported in the literature correspond to the solid phase of the PCM. Recently, Zheng et al. [15] reported that the thermal and electrical conductivity of n-hexadecane based phase change nanocompo- sites can be manipulated by solid–liquid phase transition process using graphite nanoparticles. Schifferes et al. [16] with 1 vol% of n-hexadecane/graphene nanocomposites showed that by varying the cooling rate of the phase change material from 10 3  C/min to 10 2  C/min, the aspect ratio of crystal can vary from micrometers to several millimeters. For such nanocomposites, they reported that the electrical and thermal conductivity contrast ratio (solid state conductivity to the liquid state conductivity) can vary by a factor of 5 and 2 respectively. Harish et al. [17] reported that for n-octadecane/single walled carbon nanotube nanocomposite the thermal conductivity enhancement in liquid state is nominal and in good agreement with the predictions of classical theoretical models, while in solid state, the thermal conductivity enhance- ment is anomalous and beyond the predictions of classical theories. Recently, Angayarkanni and Philip [18] reported that the thermal conductivity of n-hexadecane can be significantly enhanced using inexpensive cationic and anionic surfactants. They reported that the linear chain surfactant micelle entrapped within the grain boundaries upon solidification enhance the thermal conductivity of phase change material significantly. However, surfactant micelles possess lower thermal conductivity than many * Corresponding author. Tel.: +81 80 3279 1605. E-mail address: s.harish.341@m.kyushu-u.ac.jp (S. Harish). http://dx.doi.org/10.1016/j.tca.2014.12.004 0040-6031/ ã 2014 Elsevier B.V. All rights reserved. Thermochimica Acta 600 (2015) 1–6 Contents lists available at ScienceDirect Thermochimica Acta journa l home page : www.e lsevier.com/loca te/tca