Supercooling Suppression and Thermal Conductivity Enhancement of Na₂HPO₄·12H₂O/Expanded Vermiculite Form-Stable Composite Phase Change Materials with Alumina for Heat Storage

Abstract

In the heat storage applications, Na2HPO4·12H2O phase change materials (PCM) show significant defects including form instability, high supercooling degree and low thermal conductivity. Aiming at these drawbacks, the Na2HPO4·12H2O-alumina/expanded vermiculite (EVM) form-stable composite phase change materials (NEA fs-CPCMs) with supercooling suppression and heat transfer enhancement were prepared. The favorable wettability of NEA fs-CPCMs was beneficial to their form-stabilization (encapsulation mass fractions above 59.7 wt %). The supercooling degree of NE5.3 was reduced to 1.4 °C after adding 5.3 wt % alumina as the nucleating agent (decreased by 90%). The surface effects of EVM and alumina and high wettability of PCM-alumina were responsible for the supercooling suppression of PCM. Large specific surface area of EVM could provide nucleation sites for crystallization of PCM. The surface electronegativity of alumina increased the affinity ability and diffusion rate of ions, thus effectively increasing the probability of nucleation. The heat transfer of NEA fs-CPCMs was significantly enhanced by the alumina as the thermal conductivity enhancement filler. The thermal conductivity of NE5.3 reached 0.418 W/(m K). Thermal energy storage behavior analysis indicated that the NEA fs-CPCMs showed large heat storage capacity (melting process: 97–151 J/g; solidification process: 60–89 J/g). The thermal reliability of NEA fs-CPCMs was effectively improved by coated paraffin.

Shape‐Stabilized PCMs@Foam‐Based Porous Polymers for Thermal Energy Storage

“…The key of this technology is to prepare high‐performance phase change materials (PCMs).However, most pure organic solid–liquid PCMs have poor shape‐stability during a phase change process and low thermal conductivity, which limits their application in solar or electric energy storage, cooling of power electronic devices, and thermal insulation of buildings . To overcome these disadvantages, porous materials were used as matrix to prepare shape‐stabilized PCMs, included carbon materials, diatomite, porous silica, expanded vermiculite, metal organic framework (MOFs) and microporous organic polymers (MOPs)…”

Smart Utilization of Multifunctional Metal Oxides in Phase Change Materials

“…67 In particular, porous Al 2 O 3 ceramic foams are conducive to not only improving thermal storage capacity but also enhancing thermal conductivity due to their unique 3D interpenetrated network structure. 68 To integrate the advantages of porous Al 2 O 3 ceramic foams and graphite, Gong 66 Copyright 2018, American Chemical Society. ll et al 69 prepared hierarchical Al 2 O 3 ceramic foam@expanded graphite (EG) composite to encapsulate 1-octadecanol.…”

“…(C) Thermal conductivities of Na2HPO4$12H2O-alumina/expandedvermiculite composite PCMs (D) Scheme of the nucleation mechanism of PCMs on the surface of Al 2 O 3 . Adapted with permission from Deng et al66 Copyright 2018, American Chemical Society.…”

Highly Stable and Nonflammable Hydrated Salt-Paraffin Shape-Memory Gels for Sustainable Building Technology

“…Unfortunately, the application of paraffin in buildings is limited by its high flammability and high cost. On the other hand, hydrated salts, due to their high latent heat of fusion, nonflammability, high thermal conductivity, low volume changes, and low cost, − make these materials highly interesting candidates for building thermal management. For example, Zhang and co-workers impregnated eutectic hydrated salts (Na 2 SO 4 ·10H 2 O–Na 2 CO 3 ·10H 2 O with a 1:1 mass ratio) into expanded vermiculite used for building energy storage.…”

“…Once the water from the crystallizable phase separates or vaporizes during the phase change process, the hydrated salt transforms into a dehydrated form that melts at much higher temperatures. Immobilization of PCMs is an excellent way to solve the problem of leakage and thus to prevent water escape, by using porous materials as the support, or encapsulation of the PCMs within microscaled or nanoscaled shells. , For example, eutectic hydrated salts (Na 2 SO 4 ·10H 2 O–Na 2 CO 3 ·10H 2 O) were fixed in poly­(acrylamide- co -acrylic acid) copolymer hydrogels by Liu and co-workers to slow down water loss of the hydrated salts. The latent heat of PCM hydrogels remained unchanged following 300 cycles in a thermocycling test chamber in the reported experiments.…”