Dodecanoic acid as a promising phase-change material for thermal energy storage

The melting transition of dodecanoic acid (CH3(CH2)(10)COOH, also known as lauric acid) has been examined with a view to use for latent heat energy storage in solar thermal applications. The influence of purity (reagent grade [98% pure] compared with practical grade [<80% pure]) on the melting transition was found to be insignificant. The long-term stability of the melting transition of practical-grade dodecanoic acid was investigated by thermal cycling of samples from completely solid through complete melting and back to the solid phase, nearly 500 times. It was found that the transition enthalpy and the melting onset temperature remain within experimental uncertainty of their values, 184 J g(-1) and 43.3 degrees C, respectively. Neither data set showed significant trends with number of thermal cycles. The freezing temperature of 41 degrees C for practical-grade dodecanoic acid also was stable with respect to thermal cycling, showing almost negligible hysteresis, without addition of nucleating agents. The specific heat in the region of the phase transition was determined, along with the thermal conductivity in the solid state (0.150 +/- 0.004 W m(-1) K-1 at 30 degrees C) and the volume change associated with melting (6%). Although the thermal conductivity of dodecanoic acid is low in both the solid phase and liquid phase, and thermal energy storage devices would need to be designed accordingly, dodecanoic acid is inexpensive, readily available (used as a foodstuff), has a low volume change on melting, and is stable over hundreds of thermal cycles even in practical grade, making it a promising phase-change material for thermal energy storage. (C) 2013 Elsevier Ltd. All rights reserved.