Preparation and thermal properties of capric acid/palmitic acid eutectic mixture as a phase change energy storage material Ahmet Sarı ⁎ , Ali Karaipekli Gaziosmanpaşa University, Department of Chemistry, 60240, Tokat, Turkey Received 10 April 2007; accepted 5 July 2007 Available online 20 July 2007 Abstract This study focuses on the preparation, thermal properties and thermal reliability of capric acid (CA)/palmitic acid (PA) mixture as phase change material (PCM) for low temperature latent heat thermal energy storage (LHTES). The differential scanning calorimetry (DSC) results indicated that the CA/PA mixture with eutectic composition (76.5/23.5 wt.%) was suitable PCM for low temperature LHTES applications in terms of melting and freezing temperatures (T m = 21.85 °C; T f = 22.15 °C) and latent heats of melting and freezing (ΔH m = 171.22 J/g; ΔH f = 173.16 J/g). The thermal properties make it potential PCM for LHTES systems used in heating, ventilation, and air conditioning applications. Accelerated thermal cycling tests showed that the eutectic mixture as a PCM has good long-term thermal reliability. The probable reasons of the changes occurred in thermal properties of the PCM during accelerated thermal cycling were also investigated using Fourier Transform Infrared (FT-IR) spectroscopy method. © 2007 Elsevier B.V. All rights reserved. Keywords: Capric acid; Palmitic acid; Eutectic mixture; PCM; LHTES; Thermal property; Thermal reliability 1. Introduction The magnitude of the energy recovered from latent heat thermal energy storage (LHTES) system basically depends on the heat storage capacity of a phase change material (PCM) during solid–liquid phase change at a constant temperature [1]. The selection of suitable heat storage material plays an important role in terms of thermal efficiency, economic feasi- bility and utility life of LHTES system. Therefore, developing PCMs with respect to the energy storage requirements has been gained significant interest. A large number of inorganic, organic compounds and their mixtures have been studied as PCM for different LHTES purposes [2–4]. Among the evaluated PCMs, fatty acids are promising ones because of the following advan- tages: suitable phase change temperature, high latent heat ca- pacity, no or less volume change during phase change, and easy manufacturing from common vegetable and animal oils [5–7]. By taking into account of predominant characteristics above, binary mixtures of fatty acids can be tailored as new PCMs, with almost any suitable phase change temperature for LHTES sys- tems used for heating and cooling purposes [8–10]. The deter- mination of thermal properties and thermal reliability of new developed PCM is essential to predict not only its energy storage life but also LHTES performance in practical applica- tions. There are a few studies on assessment of thermal pro- perties and thermal reliability of different PCMs [6,11]. Previous investigations showed that the capric acid (CA; m.p: 32.14 °C) and the palmitic acid (PA, m.p: 59.40 °C) have desirable thermal and heat transfer characteristics, but their melting points are quite high for low temperature LHTES re- quirements [7,10]. The phase change temperature of PA can be modified to a lower value by addition of CA in eutectic ratio and therefore, a eutectic CA/PA mixture can be formed as suitable PCM for low temperature LHTES applications. The objective of this study is to prepare CA/PA eutectic mixture as PCM for low temperature LHTES and determine its thermal properties and thermal reliability using DSC analysis technique. The cause of the changes in thermal properties of the PCM with accelerated thermal cycling was also investigated using FT-IR spectroscopy technique. Since there is no compre- hensive data on this PCM in literature, the present paper is an Available online at www.sciencedirect.com Materials Letters 62 (2008) 903 – 906 www.elsevier.com/locate/matlet ⁎ Corresponding author. Tel.: +90 3562521616; fax: +90 3562521285. E-mail address: asari@gop.edu.tr (A. Sarı). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.07.025