Preparation and characterization of lauric–myristic–palmitic acid ternary eutectic mixtures/expanded graphite composite phase change material for thermal energy storage

• The ternary eutectic mixture of lauric–myristic–palmitic acid (LA–MA–PA) was prepared.
• The form-stable composites PCM of LA–MA–PA/EG (expanded graphite) were fabricated.
• The maximum absorption of LA–MA–PA in the LA–MA–PA/EG is 94.7 wt%.
• The thermal conductivity of LA–MA–PA/EG is 1.67 W/m K, a sharp increase than that of LA–MA–PA.

Based on the theoretically calculated mass ratio and the melting temperature of ternary eutectic mixtures, the ternary eutectic mixture of lauric acid (LA), myristic acid (MA) and palmitic acid (PA) was prepared firstly. The differential scanning calorimetry (DSC) results indicated that the eutectic mixture was composed by LA, MA and PA in the ratio of 55.24:29.74:15.02 (by mass). Then the LA–MA–PA was absorbed in expanded graphite (EG), which acts as a supporting material, to prepare six kinds of composite phase change material (PCM). The optimal mass ratio of LA–MA–PA to EG is found. The SEM, FT-IR and DSC comprehensive characterization results show that EG interacted with the capillary tubes and surface tension of LA–MA–PA via its porous structure, instead of any chemical action. At the maximum mass ratio of LA–MA–PA to EG of 18:1 (by mass), the phase change temperature and latent heat of LA–MA–PA ternary eutectic mixture were 31.41 °C and 145.8 J/g respectively; and the LA–MA–PA/EG composite PCM had a phase change temperature of 30.94 °C and a latent heat of 135.9 J/g, and the thermal conductivity of the LA–MA–PA/EG was measured as 1.67 W/m K, a sharp increase than that of LA–MA–PA. Thermal cycling test showed that the LA–MA–PA/EG composite had a good thermal reliability. Based on all results, it was concluded the prepared LA–MA–PA/EG composite PCM has a proper melting temperature and latent heat for low temperature thermal storage.