Impact of aeration and deaeration of switchable vacuum insulations on the overall heat conductivity using different core
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ORIGINAL RESEARCH
Impact of aeration and deaeration of switchable vacuum insulations on the overall heat conductivity using different core materials and filling gases Lars Erlbeck1 · S. Sonnick1 · D. Wössner1 · H. Nirschl2 · M. Rädle1 Received: 5 June 2020 / Accepted: 31 August 2020 © The Author(s) 2020
Abstract Investigating switchable vacuum insulation panels might lead to a new type of insulation, which can be switched on to enable a low heat flow when a good insulation effect is desired and switched off when exchange with the environment is requested, during a cold summer night, for example. For this reason, different core materials for vacuum insulations as typical silica powder were investigated as well as silica agglomerates and silica gel. These materials were checked for the necessary time of aeration and evacuation and the corresponding change of heat conductivity along with the change of gas-pressure. Silica gel in combination with helium as filling gas showed best results corresponding to a high difference of the heat conductivities evacuated and aerated. Beside the solid backbone structure of the silica gel, this is caused by the high heat conductivity and small kinetic atomic diameter of the helium gas. Silica agglomerates decreased the aeration time as well as the deaeration time, but the improvement was neglected because of a lower change of heat conductivity during pressure drop or rise. Nevertheless, a good switchable vacuum insulation can be produced using silica gel and helium, for example. Keyword Aerated vacuum insulation · deaerated vacuum insulation · switchable vacuum insulation · thermal superinsulation · vacuum insulation · vacuum insulation panels List of Symbols a Parameter [−] b Parameter [−] c Parameter [−] d Parameter [−] kn Knudsen number [−] k Constant [−] L Mean free path of molecules [m] p Pressure [Pa] T Temperature [°C] t Time [s] x Pore size [m] δ Diameter [m
* Lars Erlbeck l.erlbeck@hs‑mannheim.de 1
Center for Mass Spectrometry and Optical Spectroscopy, Mannheim University of Applied Sciences, Paul‑Wittsack‑Str. 10, 68163 Mannheim, Germany
Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology, Kaiserstrasse 12, 76131 Karlsruhe, Germany
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Greek α Accommodation coefficient [−] β Factor [−] κ Adiabatic coefficient [−] λ Heat transfer coefficient [Wm−1 K−1] λ Time-dependent heat conductivity [Wm−1 K−1 s−1] λ Pressure-dependent heat conductivity [Wm−1 K−1 Pa−1] Φ Porosity Subscripts Ae Aeration B Boltzmann De Deaeration end Ending point g Gas IP Inflection point M Molecule 0 Starting point 10 Logarithm to base ten ∞ Ambient condition
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International Journal of Energy and Environmental Engineering
Introduction Insulation materials are quite important to reduce the heating and cooling demand of, for example, residential or office buildings and, therefore, to prevent a high-energy demand and thus a high carbon dioxide emission caused by the power generation based on fossi
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