Phase-change materials (PCMs) are able to store large amounts of heat but have low thermal conductivity. In order to enhance the rate of heat transfer into PCMs, one of the most common methods is the use of fins which increase the heat transfer area that is in contact with the PCM. However, when the PCM melts during the storage unit charging, a layer of liquid is growing at the fins creating an increasing thermal resistance that impedes the process. On the other hand, during a so-called close-contact melting (CCM), which occurs when the solid phase is approaching a heated solid surface, a thin liquid layer formed beneath the solid phase remains thin. Although CCM was extensively studied in the past, its possible role in finned storage units has not been explored.
The present work presents a further proof of the special role that close-contact melting can play in thermal energy storage units and finned systems in general. It is also shown that the fins should be considered not only as extended surfaces, which contribute to heat transfer via an increase in the area, but also as the surfaces that, when properly designed and oriented, cause the material to melt in their proximity throughout the entire melting process. As demonstrated, a very significant increase in the melting rate is achieved in this case.
