Preparation, characterization and thermal properties of fatty acid eutectics/bentonite/expanded graphite composites as novel form–stable thermal energy storage materials

• Published in: Solar energy materials and solar cells Vol. 166; pp. 157 - 166
• Main Authors: Huang, Xiang, Alva, Guruprasad, Liu, Lingkun, Fang, Guiyin
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2017; Elsevier BV
• Subjects: Bentonite; Calorimetry; Clay; Composite materials; Composite phase change materials; Conductivity; Differential scanning calorimetry; Energy storage; Eutectics; Fatty acids; Form–stable; Fourier transforms; Graphite; Gravimetric analysis; Heat measurement; Heat transfer; Iridium; Latent heat; Leakage; Palmitic acid; Phase change materials; Specific heat; Stearic acid; Temperature; Thermal analysis; Thermal conductivity; Thermal energy; Thermal energy storage materials; Thermal properties; Thermal stability; Thermal storage; Thermodynamic properties; Thermal properties; Form–stable; Eutectics; Composite phase change materials; Thermal energy storage materials
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2017.03.026

In this work, bentonite–based composite phase change materials (CPCMs) were fabricated by the impregnation of fatty acid eutectics into bentonite clay. In the composites, the palmitic acid (PA)–stearic acid (SA) eutectics mixtures were undertook as phase change materials (PCMs) for thermal energy storage, and the bentonite were performed as the supporting material. Expanded graphite (EG) was employed for helping restrain the eutectic mixtures from leakage as well as improving thermal conductivity of the CPCMs. The differential scanning calorimetry (DSC) was adopted to assess the thermal properties of the composites, the results showed that the CPCMs have suitable melting temperature of around 54°C with latent heat capacity of 89.12–163.72kJ/kg. Fourier transformation infrared (FT–IR) and X–ray diffractometer (XRD) were utilized to test the chemical structure and crystalline phase of the CPCMs. The scanning electron microscope (SEM) images revealed that the organic PCMs homogenously spread to the surface and interior of the bentonite. The thermal gravimetric analyzer (TGA) detected that the CPCMs were provided with good thermal stability. As the content of the EG increased, the leakage of the PA–SA eutectics reduced considerably. The results from the thermal conductivity meter (TCM) showed that the thermal conductivity of the CPCM with content of 5% EG reached to 1.51W/(mK) in liquid state and 1.66W/(mK) in solid state, which was nearly 5.6 times and 4.9 times higher than that of the CPCM without the EG. Experiments displayed that the thermal storage and release rates were noticeably enhanced by combining the EG into original CPCMs. The CPCMs maintained thermal properties after 50 heating–cooling cycling. It is envisioned that the satisfactory CPCMs maintain considerable prospects in thermal energy storage. The temperature curves of the CPCM3 and CPCM6 in melting and solidifying processes are shown. The heat storage time initiates from the same temperature (23°C) and ends at the same melting temperature (72.5°C). The interval starts from 70°C and finishes at the same solidifying temperature (26.5°C) in solidification period. The heat storage time of the CPCM3 and CPCM6 were 11min and 8.7min respectively. The heat release time of the CPCM3 and CPCM6 were respectively 68min and 42min [Display omitted] •The fatty acid eutectics/bentonite/expanded graphite composites were synthesized for improving thermal properties.•Microstructure and chemical structure analysis of the CPCMs were displayed and analyzed.•Thermal properties and thermal reliability of the CPCMs were investigated and discussed.•Thermal conductivity of the CPCMs in liquid state by adding EG is 5.6 times higher than that of the pure CPCMs.