The present study explores numerically the processes of melting and solidification of a phase change material (PCM). The material used was a commercially available paraffin wax, which is non-toxic, recyclable, chemically inert, non-corrosive and can withstand an unlimited number of cycles. The phase-change material was stored in a rectangular box, open at the top. The bottom of the box could be heated or cooled. The inner space of the box was partitioned by vertical conducting plates attached to the bottom. Thus, heat was transferred to and from the PCM both through its melted/solidified layer and by conduction through the vertical plates. Transient two-dimensional numerical simulations were performed using the Fluent 6.0 software. The melting temperature of the wax, 23–25°C was incorporated in the simulations along with its other properties, including the latent and sensible specific heat, thermal conductivity and density in solid and liquid states. The simulations provided detailed temperature and phase fields inside the system as functions of time, showing evolution of the heat transfer in the system as the phase change material melts/solidifies. The dependence of the heat transfer rate on the properties of the system and on the PCM phase composition at various time instants is presented and discussed.
The present study explores numerically the transient performance of a heat sink based on a phase change material (PCM), during the process of melting. Heat is transferred to the sink through its horizontal base, to which vertical fins made of aluminum are attached. The phase change material is stored between the fins. Its properties, including the melting temperature, latent and sensible specific heat, thermal conductivity and density in solid and liquid states, are based on a commercially available paraffin wax. A parametric investigation is performed for melting in a relatively small system, 10mm high, where the fin thickness is 1.2mm, and the distance between the fins varies from 2mm to 8mm. The temperature of the base varies from 12°C to 24°C above the mean melting temperature of the PCM. Transient numerical simulations are performed, yielding temperature evolution in the fins and the PCM. The computational results show how the transient phase-change process, expressed in terms of the volume melt fraction of the PCM, depends on the thermal and geometrical parameters of the system, which relate to the temperature difference between the base and the mean melting temperature, and to the thickness of the PCM layer. This paper was also originally published as part of the Proceedings of the ASME 2005 Heat Transfer Summer Conference.
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