Thermal History Characterization and　Controlled Nucleation of Supercooled Gallium

摘要

Paraffin phase change materials are often used for thermal energy storage due to their high gravimetric latent heat values and low cost. However, they are not well suited for high heat transfer rate applications where their low thermal conductivities limit use. Additionally, applications in which there are volume restrictions may drive material selection toward metallic phase change materials, where the volumetric latent heat can be higher than those of paraffins with comparable melting points. Gallium, for example, has over twice the volumetric latent heat and a thermal conductivity that is two orders of magnitude greater than that of paraffins (for example, octadecane). The use of gallium is not without issue. Gallium is known to experience supercooling, which is often viewed as a detrimental property. Thus, an improved understanding of supercooled gallium nucleation is useful. The purpose of this study is to explore the effects of the thermal history and mass on the supercooling of gallium. In this work, differential scanning calorimetry and a thermal cycling chamber were used to characterize these effects. Material overheating was found to have the largest impact. Additionally, an active control methodology was created to successfully activate solidification without significantly affecting the bulk material temperature.