Preparation, thermal properties and thermal reliability of eutectic mixtures of fatty acids/expanded vermiculite as novel form-stable composites for energy storage Ali Karaipekli, Ahmet Sarı * Department of Chemistry, Gaziosmanpas ¸ a University, 60150, Tokat, Turkey 1. Introduction Thermal energy storage becomes an important aspect engi- neering applications. Especially, storage of thermal energy is one of promising methods for the improvement of the energy efficiency and conservation in buildings. Latent heat storage using phase change material (PCM) is the most attractive thermal energy storage method due to high storage density and small temperature variation from storage to retrieval. PCMs have the ability to change their state with a certain temperature range and can store and release large amounts of energy during phase change process. Therefore, they have been potentially used for thermal energy storage in many applications such as solar energy storage, waste heat recovery, building heating or cooling, indoor temperature controlling and insulation clothing [1–4]. In recent years, the use of PCMs to enhance the thermal energy storage capacity of building materials has become one of the best interesting topics in the fields of thermal energy engineering and building industry [5]. The PCMs can be used adding in building components such as porous gypsum board, porous filler, plaster or other wall-covering material. Building material with PCM permits the storage of high amounts of energy without changing the temperature of the indoor and helps to moderate temperature swings and improve thermal comfort in buildings. But, there are some difficulties in the development of building materials containing PCMs. One of these difficulties is incorporation of PCMs in construction materials. PCMs in building materials are usually enclosed in metallic or polymeric capsules. In such cases, it takes longer to storage or release heat because of thermal resistance of solid phase and capsule material. Therefore, it is needed to direct heat exchange between PCM and heating medium to provide higher heat exchange. Composite PCMs made of porous building materials and PCMs are promising materials since they enables no corrosion, quick heat transfer and offers a large heat storage density if building materials with high porosity are selected. To prepare composite PCMs, there are two general methods: impregnation of molten PCMs and direct incorporation of PCMs into porous material [6–9]. The impregnation method is obviously the simplest and cheapest for fabrication. Impregnation Journal of Industrial and Engineering Chemistry 16 (2010) 767–773 ARTICLE INFO Article history: Received 26 November 2009 Accepted 6 April 2010 Keywords: Fatty acid Expanded vermiculite Composite PCM Thermal properties Thermal reliability Energy storage ABSTRACT This paper deals with the preparation, characterization, thermal properties and thermal reliability of novel form-stable composite phase change materials (PCMs) composed of eutectic mixtures of fatty acids and expanded vermiculite for thermal energy storage. The form-stable composite PCMs were prepared by incorporation of eutectic mixtures of fatty acids (capric–lauric, capric–palmitic and capric– stearic acids) within the expanded vermiculite by vacuum impregnation method. The composite PCMs were characterized by SEM and FTIR techniques. Thermal properties of the composite PCMs were determined by differential scanning calorimeter (DSC) method. DSC results showed that the melting temperatures and latent heats of the prepared composite PCMs are in the range of 19.09–25.64 8C and 61.03–72.05 J/g, respectively. The thermal cycling test including 5000 heating and cooling process was conducted to determine the thermal reliability of the composite PCMs. The test results showed that the composite PCMs have good thermal reliability and chemical stability. Furthermore, thermal conductivities of the composite PCMs were increased by adding 10 wt% expanded graphite. Based on all results, the prepared form-stable composites can be considered as promising PCMs for low temperature thermal energy storage applications due to their satisfactory thermal properties, good thermal reliability, chemical stability and thermal conductivities. ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +90 356 2521616; fax: +90 356 2521585. E-mail addresses: akaraipekli@gop.edu.tr (A. Karaipekli), asari@gop.edu.tr (A. Sarı). Contents lists available at ScienceDirect Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec 1226-086X/$ – see front matter ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2010.07.003