Improving the thermal performance of novel low-temperature phase change materials through the configuration of 1-dodecanol-tetradecane nanofluids/expanded graphite composites

To improve the thermal conductivity (λ) of organic phase change materials (PCMs) in air-conditioning systems, a series of novel organic PCMs were prepared via a two-step method, including high-speed emulsification and natural physical adsorption. The effect of the mass ratio of the 1-dodecanol-tetradecane nanofluids to the expanded graphite (EG) onmass loss percentage and thermal stability of 1-dodecanol-tetradecane/EG composite PCMs was investigated. Differential scanning calorimetry, Hot Disk thermal constants analyser, and thermogravimetric analysis, as well as scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction were employed to analyse the thermal performance, surface topography, surface functional groups, and crystal structure of 1-dodecanol-tetradecane nanofluids/EG composite PCMs. The molar ratio of the 1-dodecanol and tetradecane with in the nanofluids was determined to be 26.3:73.7, while the optimal EG additional amount was 7 wt%. The results show that the melting and solidification temperatures (Tm and Ts) of the nanofluids are 3.43 °C and 4.17 °C, respectively, whereas the corresponding latent heats of melting and solidification (Hm and Hs) are 212.96 J/g and 213.00 J/g, respectively. After the natural adsorption process, the Tm and Ts of the 1-dodecanol-tetradecane/EG composite PCM with an optimal mass ratio of 93:7 are 3.63 °C and 7.71 °C, respectively, while the corresponding Hm and Hs decrease to 197.95 J/g and 198.81 J/g, respectively. Notably, the λ values of the nanofluids and the 1-dodecanol-tetradecane/EG composite PCM are 0.2186 W/(m∙K) and 2.4070 W/(m∙K), respectively, thereby indicating a tenfold increase in λ. The present study confirms that the 1-dodecanol-tetradecane/EG composite PCM is a potential candidate for cold energy storage in air-conditioning system and cold chain logistics.