The level of vacuum (rough, high, etc) in a vacuum insulating panel determines its insulating value (typically measured in U or R value). Does the VOLUME matter? That is, for the same level of vacuum in an vacuum insulating panel with a thickness of 1 inch, would the performance be altered by being 2 inches thick?
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$\begingroup$ Thickness of insulation always matters for conduction (and convection) in terms of energy; the vacuum is not perfect and so thickness will matter en.wikipedia.org/wiki/R-value_(insulation)#Thickness. Volume is a different matter because more area tends to have the opposite effect of more thickness- bigger houses have more surface area. $\endgroup$– AbelCommented Nov 15, 2023 at 13:39
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$\begingroup$ How hard is the vacuum? If the vacuum is hard enough that the mean free path of the residual gas molecules is large compared with the layer thickness, then the effective thermal conductivity of the vacuum is proportional to thickness, which makes the U or R value thickness-independent. OTOH, if the vacuum is not so hard, so the mean free path of the residual gas molecules is small compared with the layer thickness, the thermal conductivity is thickness-independent and the U value is inversely proportional to thickness (R value proportional to thickness). $\endgroup$– user28774Commented Aug 11 at 16:40
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$\begingroup$ But in the latter case, the thermal conductivity will be the same as that of normal air, i.e. it will have been a waste of time and effort evacuating the layer in the first place. $\endgroup$– user28774Commented Aug 11 at 16:41
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No, the goal is remove any conduction between the wall of the panel and any fluid within. This way the only means of transmission is radiation. I would like to argue however that having a greater volume in an imperfect vacuum would make things worse as there is more stuff in the gap to transmit heat, but I think it would be negligible.
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$\begingroup$ Maybe, but there's a domain in which the vacuum is hard enough to reduce conduction considerably, but not hard enough to render conduction entirely negligible compared with radiation. $\endgroup$– user28774Commented Aug 11 at 16:49