Dr. Bjørn Petter Jelle, Professor, Department of Civil and Environmental Engineering, Norwegian University of Science and Technology (NTNU), Norway

Bjørn Petter Jelle is a professor at the Norwegian University of Science and Technology (NTNU) and a chief scientist at SINTEF Building and Infrastructure. Jelle's background is as a physicist, chemist and material scientist, and examples of current work fields include building physics, materials science, solar radiation, thermal radiation, climate exposure, accelerated climate ageing, solar cells, building integrated photovoltaics, high performance thermal insulation materials, nano materials, and electrochromic materials for energy-efficient windows.

Speech Title: Nano Insulation Materials Exploiting the Knudsen Effect

Aims: The aim of this study is to develop an understanding for the governing thermal transport mechanisms and utilize the Knudsen effect in nano-porous high-performance insulation materials through theoretical concepts and experimental laboratory explorations, thus being able to synthesize nano insulation materials (NIM) with very low thermal conductivity values as a major final goal.

Methods: Nano insulation materials based on hollow silica nanospheres (HSNS) are synthesized by a sacrificial template method, where the idea is that the heat transport by gas conductance and gas/solid state interactions decreases with decreasing pore diameters in the nano range as predicted by the Knudsen effect. Moreover, steps are also taken to ensure as low solid state and radiation contributions as possible to the overall thermal transport.

Results: Hollow silica nanospheres with reduced thermal conductivity compared to their solid counterparts have been manufactured where the hollow sphere cavities and voids between the spheres are filled with air at atmospheric pressure, i.e. eliminating the need for various measures like e.g. protecting metallized foils to maintain a vacuum or expensive low-conducting gase in the cavities and voids. Furthermore, measures to avoid condensation of moisture in the air-filled pores have been investigated.

Conclusions: As a potential and promising stepping-stone toward the future high-performance insulation materials, hollow silica nanospheres with reduced thermal conductivities have been fabricated.