Experimental Characterization of Inward Freezing and Melting of Additive-Enhanced Phase-Change Materials Within Millimeter-Scale Cylindrical Enclosures

Abstract

The inward melting and solidification of phase-change materials (PCM) within millimeter-scale cylindrical enclosures have been experimentally characterized in this work. The effects of cylinder size, thermal loading, and concentration of high-conductivity additives were investigated under constant temperature boundary conditions. Using a custom-built apparatus with fast response, freezing and melting have been measured for time periods as short as 15 s and 33 s, respectively. The enhancement of PCM thermal conductivity using exfoliated graphene nanoplatelets (xGnPs) has also been measured, showing a greater than 3× increase for a concentration of 6 wt.%. Reductions in the total melting and freezing times of up to 66% and 55%, respectively, have been achieved using xGnP concentrations of only 4.5 wt.%. It is shown that the phase-change dynamics of pure and enhanced PCM are well predicted using a simple conduction-only model, demonstrating the validity of approximating enhanced PCM with low additive loadings as homogenous materials with isotropic properties. While general consistency between the measurements and model is seen, the effect of additives on heat transfer rate during the initial stages of freezing and melting is lower than expected, particularly for the smaller cylinder sizes of 6 mm. These results suggest that the thermal resistance of the PCM is not the limiting factor dictating the speed of the solid–liquid interface during these initial stages.

Solidification of additive-enhanced phase change materials in spherical enclosures with convective cooling

“…The size effect can also be attributed to the dendrite growth as the effect of dendrites can be more pronounced for smaller enclosure size. This trend of increasing sol Fo with increasing enclosure size is consistent with the observation of solidification of PCM in cylindrical enclosure [28].…”

“…As one of the most popular PCMs, eicosane has been used in many experimental studies on PCM thermal properties and phase change behavior [21,[28][29][30][31]. In the present study, n-eicosane (99%, Sigma Aldrich) is used as the PCM, with a melting point of 36.4 °C, heat of fusion of 247.3 kJ/kg, solid density of 815 kg/m 3 , liquid density of 780 kg/m 3 , solid specific heat of 1.92 kJ/(kgK), and liquid specific heat of 2.46 kJ/(kgK) [32].…”

Performance evaluation of a novel concentric metal hydride reactor assisted with phase change material

“…The duration between approaching the maximum hydrogen storage capacity and reaching the steady melting fraction significantly decreases as the thermal conductivity of PCM increases. As described in [52], thermal conductivity plays an important role in the loading and discharging rates in case of 100% phase change thermal cycles.…”

Phase-Change Process Inside a Small-Radii Cylinder Subjected to Cyclic Convective Boundary Conditions: A Numerical Study

“…Many experimental, analytical, and numerical studies on the melting and solidification of the PCM in encapsulated geometries have been reported in the literature by imposing constant temperature or heat flux at the encapsulation boundary and for a variety of encapsulation geometries such as spheres [24][25][26], rectangular containers [27][28][29][30], and horizontal [31][32][33] and vertical cylinders [34][35][36][37][38][39][40][41][42][43]. These studies provide a good understanding of the heat transfer and thermal storage characteristics of the encapsulated PCMs (EPCMs) under fixed temperature or heat flux boundary conditions.…”