Influence of Nucleation Techniques on the Degree of Supercooling and Duration of Crystallization for Sugar Alcohol as Phase Change Material : Investigation on erythritol-based additiveenhanced Composites

University essay from KTH/Energiteknik; KTH/Energiteknik

Abstract: Utilizing Phase Change Materials (PCM) for Latent Thermal Energy Storage (LTES) applications have previously been extensively researched as a measure to reduce greenhouse gas emissions from energy consumption. In order to make use of the waste heat from industrial processes for LTES purposes, a new demand emerged for PCMs capable of phase change in mid-temperature ranges of 100 °C - 200 °C. This higher temperature requirement made most of the previously studied material inapplicable as they had much lower melting and solidification temperatures. With this in mind, a new generation of PCMs consisting of Sugar Alcohols (SA) has been proposed. Erythritol is seen as an especially promising SA with good thermophysical properties for LTES purposes. However, it has been shown to suffer from severe supercooling, which makes it unreliable in real applications. To eradicate this issue, two additives, Graphene Oxide (GO) and Polyvinylpyrrolidone (PVP) at varying mass fractions were mixed with pure erythritol to form a composite which was studied using the Temperature-history (T-history) method to determine its effectiveness in reducing supercooling. Results show that at its most effective mass fraction, GO reduces supercooling by 28 o C and a 31 o C reduction is seen by the addition of PVP. The impacts on the duration of crystallization was also documented and analyzed using the same method. It was observed that the duration of crystallization was increased with increasing mass fractions of the additives. Other important properties of the composites were also studied in order to determine the overall feasibility for industrial applications. It includes analysis of the storage capacity through latent heat, changes in viscosity along with impacts on thermal diffusivity of the composites.

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