Thermal analysis of evacuated honeycomb structures: Experimental validation and optimisation of non-uniform structures

Today, energy storage is a key vector to achieve a full decarbonisation of the energy sector in order to limit the impact of climate change. In particular, ultra-high temperature (C) thermal storage is of high importance and has recently received significant attention with multiple technologies being investigated. However, uneconomical thermal losses are a barrier to their development, and currently available high-temperature insulation technologies suffer from decreased efficiency at high temperature, and lack the structural strength to support the storage vessel whose support structure therefore acts as thermal bridging, further degrading the system’s overall efficiency. As a complement to previous work, this paper provides an analysis to investigate the thermal efficiency of non-uniform rectangular honeycomb structures without mechanical constraints, with an application to ultra-high temperature thermal insulation. First, an experimental procedure is presented to validate the numerical model used in previous work. The results show that the model can accurately predict thermal transfers through three-dimensional cuboid evacuated honeycombs. A thermal optimisation of honeycombs with a non-uniform cell size distribution is then conducted to complement the findings of previous work on uniform honeycombs. A statistical condition on the cell size distribution for optimal thermal performance is derived and numerically validated, and non-uniform structures are shown to be more thermally-efficient than uniform ones. These results provide further motivation for research into the development of manufacturing processes for such structures.