Thermo-mechanical analysis of evacuated honeycomb structures. Application to ultra-high temperature thermal insulation and structural elements

Abstract

Thermal energy storage is one of the key vectors to achieve a full decarbonisation of the energy sector in order to mitigate the effects of climate change. Specifically, ultra-high temperature (>900 K) thermal storage is of particular importance as it unlocks greater energy densities and round-trip efficiencies, among other benefits. However, increased thermal losses and reduced structural strength of insulation materials constitute significant challenges in that temperature range, and insulating structures are required which retain thermal efficiency and mechanical robustness at elevated temperatures. In this paper, a thermo-mechanical analysis of evacuated honeycomb structures at ultra-high temperature is proposed, and the impact of mechanical stresses on their structural integrity and thermal efficiency is investigated. In particular, plastic yield, brittle fracture, buckling, sagging and creep are considered for mechanical failure modes. The structures are then optimised for thermal insulation efficiency whilst avoiding mechanical failure.It is found that mechanical stresses must be considered even in the absence of external loads as such structures may collapse under their own weight over time. However it is also shown that, in the absence of external loads, structurally-sound honeycomb structures at elevated temperatures (>1200 K) remain 3-14 times more thermally efficient than other non load-bearing and structurally-ideal market-available technologies, while the presence of an external load inevitably reduces their thermal efficiency. But wall thicknesses as low as 1μm may be required, which is below today’s manufacturing capacities and highlights the importance of further research into manufacturing processes beyond what is achievable today.