Market-Orientated Solutions to Increase Thermal Conductivity in Latent Thermal Energy Storage Systems

Abstract

It is well-known that the thermal conductivity of PCMs (phase change materials) is low hence a major limitation for their commercial application. This work proposes alternative, inexpensive, but nevertheless effective solutions to increase the thermal conductivity of a PCM (a commercial paraffin wax) used for thermal energy storage. The PCM fills an annulus wrapping an inner tube used to either charge or discharge heat to the PCM. The effect of the flow rate and temperature of the water used as heat transfer fluid was experimentally analysed. We tested three different aluminum-based thermal enhancers: a commercially available metal foam sample, a wire mesh, and irregular flakes (chips) obtained as waste product of machining operations. A performance indicator, in terms of cost per phase change rate, is proposed to compare different enhancers. It was observed that both the economical solutions can reduce the phase change time compared with the only PCM. Then, the addition of chips seems to be the most cost-effective solution to increase the average thermal conductivity of the system while keeping costs down.

Keywords: PCM, metallic foam, metallic chip, economic solution, thermal conductivity, latent thermal energy storage