I found conference proceedings about VIP (vacuum insulation panels) and I made an upload because these methods are really interesting. The introduction lecture by U. Heinemann, Bavarian Center for Applied Energy Research, Germany is maybe the most important one for this post, I make two citations:
- Despite relatively high thermal conductivity in the non-evacuated state the lowest thermal conductivity when evacuated is achieved for glass fibers, 0.002 W m-1K-1. For fibers oriented perpendicular to the overall temperature gradient dot like contacts between single fibers yield a high thermal resistance. In the non-evacuated state these contacts are shortcut by the gas.
- For a typical panel sized 0.5 to 1 m², 2 cm thick, with a volume of 10 l, this rate corresponds to a tolerable 3 E-7 mbar l s-1, the leak rate of one single sealing ring used in high and ultra-high vacuum technique. Only metallic layers or an envelope made of glass fulfill the high requirements on low permeation rates.
The first citation shows again that the thermal conductivity from glass wool lowers from 0.038 W/mK to 0.002 W/mK by removing the air or an improvement of 0.036 W/mK. We all know that the thermal conductivity of still air is only 0.026 W/mK or we conclude that the air is not still in low density glass wool. It seems that natural convection is much more important than simulations suggest, which means that forced convection is also much more important in low density glass wool beyond the protection of a laboratory.
The second citation states that the envelope of a VIP is the weak point for the life time of VIP unless the envelope is made from metal or glass. But these materials have a large thermal conductivity. On the other hand, cellular glass is gastight AND has a low thermal conductivity. Probably, there is an opportunity for cellular glass as the envelope. The VIP becomes somewhat thicker but we combine the unique properties of cellular glass (non combustible, vapour tight, gas tight, rigid, …) with a very good thermal conductivity down to 0.018 W/mK for the total panel.
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