Corrosion of Fe-based containers by molten Al-12.5 wt% Si and its effects on heat transfer for a thermal storage

Kurzfassung

Certain metals and metallic alloys are idoneous for their use in high temperature thermal storages due to their high latent heat of fusion and volumetric energy density. Besides, metallic Phase Change Materials (mPCMs) often present a high thermal conductivity that allows for fast energy charge and discharge of thermal storage systems. On the other hand, reactivity between molten metals and their containers can be a handicap for their performance and durability [2]. Completely avoiding a reaction between a mPCM and its container can drastically increase the cost of the storage due to the price of the materials or the complexity of their manufacture (e.g. coatings). A compromise can be reached if the extent of the reaction does not become critical during the product lifetime. That entails not only that the integrity of the housing will persist, but also that the performance of the thermal storage is still at an acceptable level. One of the points that needs to be considered is how the growth of a reaction layer affects the thermal contact resistance, potentially hindering heat transfer and slowing down the energy charge and discharge in the storage. In this work, the viability of using Fe and stainless steel S304 as container materials for an Al-12.5 wt.%Si based thermal storage is assessed. The evolution of the reaction extent was determined by performing high temperature holds in a furnace and then analyzing the samples by means of X-Ray tomography. The impact on the thermal contact resistance between the mPCM and the container was measured using Light Flash Analysis and used to quantify the detrimental effects on heat transfer. As a result, the estimated product life and performance loss of each of the combinations could be assessed.