Freeze-cast form-stable phase change materials for thermal energy storage

Abstract Form-stable phase change materials (PCMs) can provide containerless thermal energy storage with enhanced thermal conductivity relative to the pure PCMs. In the present work, the use of many different freeze-cast matrices (alumina, titania, carbon black, alumina/carbon black, chitosan, carbonized chitosan) is explored with many different PCMs (fatty acids, PEG, paraffin, esters, sugar alcohols, salt hydrates), to prepare a wide variety of form-stable phase change materials, using commodity materials. Materials were characterized by density, PCM fill, phase transition characteristics (melting point, enthalpy of fusion) including after melt-freeze cycling up to 1000 times, morphology (SEM), thermal conductivity and Vicker's hardness. The matrix did not substantially influence the PCM melting points, but did control the fill, thermal conductivity and mechanical properties of the form-stable PCMs. Alumina at a 38 mass% loading of PCM gave the best thermal conductivity, up to 3.2 W m−1 K−1, significantly enhanced compared with 0.15 W m−1 K−1 for the pure PCM, and with excellent hardness and mechanical stability after 1000 cycles. Chitosan and carbonized chitosan scaffolds gave form-stable PCMs with the highest PCM loading, up to 95 mass%.