Abstract
A novel composite phase change material (CPCM), capric–myristic acid/expanded graphite (CA–MA/EG) CPCM, was prepared by absorbing liquid CA–MA (as the phase change material (PCM)) into EG (as the substrate material) for heat storage in the backfill materials of soil-source heat pump systems. The thermal characteristics and microstructure of the novel CPCM were analyzed using differential scanning calorimetry (DSC) and scanning electronic microscopy (SEM). The thermal conductivities of CA–MA/EG CPCM were surveyed. The thermal stability of the CA–MA/EG was analyzed using thermogravimetric analysis (TGA) and thermal cycle tests. The results showed that the optimal mass content of CA–MA in CPCM was approximately 92.4% and the CA–MA was uniformly distributed in the vesicular structure of EG; the CA–MA/EG CPCM had an appropriate phase change temperature (Tm: 19.78 °C, Tf: 18.85 °C), high latent heat (Hm: 137.3 J/g, Hf: 139.9 J/g), and excellent thermostability and thermal reliability. The thermal conductivity of the CPCM was remarkably enhanced after adding EG. Therefore, the CPCMs demonstrated outstanding thermal performance and can be utilized in low-temperature latent heat thermal energy storage (LHTES) systems, such as soil-source heat pump systems.
Highlights
The results show that the stearic acid/diatomite composite phase change materials (CPCMs) melt and freeze at 52.3 ◦ C and 48.4 ◦ C, respectively, with a latent heat of 57.1 J/g, which has the potential for practical applications with good thermal stability
The form-stable capric–myristic acid ternary eutectic mixture (CA–MA)/EG CPCMs with the largest CA–MA quality content of 92.4% is suitable for latent heat thermal energy storage (LHTES) systems, such as backfill materials of soil-source heat pump systems
The differential scanning calorimetry (DSC) effects indicated that the CPCMs had appropriate phase change temperatures (Tm : 19.78 ◦ C, Tf : 18.85 ◦ C) and high latent heat (Hm : 137.3 J/g, Hf : 139.9 J/g)
Summary
Phase change materials (PCMs) can be utilized to store thermal energy temporarily and release it when necessary, which can alleviate the contradiction of energy supply–demand and energy saving.Thermal energy storage by virtue of latent heat is a powerful method to enhance energy efficiency [1].To date, PCMs for thermal energy storage have been widely employed for solar energy utilization [2], building energy savings [3], industrial waste heat recovery [4], and air conditioning condensation heat recovery systems [5].In accordance with the chemical composition, PCMs can be classified as organic phase change materials [6], inorganic phase change materials [7], and composite phase change materials [8]. Phase change materials (PCMs) can be utilized to store thermal energy temporarily and release it when necessary, which can alleviate the contradiction of energy supply–demand and energy saving. PCMs for thermal energy storage have been widely employed for solar energy utilization [2], building energy savings [3], industrial waste heat recovery [4], and air conditioning condensation heat recovery systems [5]. Fatty acid PCMs have been generally utilized for their positive characteristics, including large latent heat of phase change, no supercooling, non-toxicity, and their low price [11]. When aliphatic acids are utilized as PCMs, the choice of the phase transition temperature is very flexible; can Energies 2020, 13, 2462; doi:10.3390/en13102462 www.mdpi.com/journal/energies
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