Thermal isolation
Maximizing for thermal isolation in products of advanced gemstone metamaterial technology is not as trivial
as maximizing for good mechanical properties with which the gemstone like base materials already come with (See: High performance of gem-gum technology).
In general the for mechanical reasons desired dense and stiff gemstone metamaterials have in their solid bulk
form low to record level low thermal isolation performance (that is record level high thermal conduction properties).
By:
- choosing a base material that is perhaps not one of the best thermally conducting ones
- picking crystal structures with lower symmetries (pseudo-amorphous)
- and most importantly smartly structuring the material into a thermal metamaterial
- integrating voids and means for IR reflection
Exceptionally high thermal isolation levels should be achievable.
Contents
Basics
Because of the scaling laws for surface-to-volume-ratio single isolated nanoscale parts would cool of / heat up very fast to average environment temperature. Thus thermal isolation layers makes only sense between macroscopic spaces.
For thermal isolation one has to suppress:
- convection (this is easy in advanced APM systems "filled" with practically perfect vacuum)
- phononic and electronic heat transport
- radiative heat transport
Material influence on phononic and electronic heat transport
The stiff high density structures usually desirable for advanced AP systems somewhat contradict low thermal conductance since these materials usually lead to a high phononic (lattice vibration) contribution to thermal conductance. Electronic contributions can be kept low more easily.
Carbon based
When one restricts oneself to pure hydrocarbon systems it gets even worse. The common allotropes of carbon (diamond, lonsdaleite, graphene, nanotubes, fullerenes?) are all pretty bad thermal isolators. Diamond is one of the worst possible thermal isolators in existence. Structuring carbon in novel ways (parse and non-stiff) may yield acceptable results.
With silicon and other elements
If advanced APM will be reached through the incremental path it's likely that silicates will be mechanosynthesizable to an atomically precise break resistant aerogel like substance. Usually one can increase thermal isolation by making the structure more sparse introducing vacuum chambers. For very sparse structures:
- the lack of material stiffness may pose problems in assembly.
- high forces e.g. by external air pressure and mass loads could temporarily squish the material thereby drastically reducing the thermal isolation level.
Radiative heat transport
Regular gaps between electrically conductive surfaces can have influence on the allowed modes of electromagnetic (heat) radiation transport.
(TODO: check whether macroscopic structures can be electro-statically levitated in multiple shells whith nano-scale distances in between)
Semi concrete implementation proposals
Thermal conduction adjustment µ-components
A metamaterial for practically instant adjustment of thermal conduction can be made from components that are optimized for thermal isolation but can be actuated such that a stiff diamond bridge is made that creates a thermal short circuit. Such materials would be perfect for advanced atomically precise produced clothing.
The diamond thermal bridge coupling needs to be stiffly clamped in all three dimensions for maximal thermal conductance thus it may be better to make the individual bridges bridge binary in action (either off or on) instead of continuously sliding together (which may leave one dimension less stiff coupled. The global thermal conductance can still be adjusted by the number and location of activated thermal bridges.
A sliding design would only be necessary for keeping nano-scale thermal differences. Such differences are very short lived even with the best possible thermal isolation since the surface to volume ratio of nano scale heat spots is so big and thus their little heat capacity is quickly depleted.
Isotopic enrichment of the carbon atoms in the thermal bridges can further increase thermal conductance. The shape of the thermal bridges can be optimized (smooth?) to not disturb the phonons. Or they can be made in wedge shape adding a thermal diode effect - an anisotropic heat conductance like presented here: [Todo: add link]
[Todo: include illustrating image]
A slightly different method would be the use of highly heat conductive coplanar sheets that can be separated or brought in (interlocking) contact with some kind of barely heat conducting scissoring mechanism. This Metamaterial would change its volume when it changes its heat conductivity. Also if it increases it's volume in an atmosphere its pulling up a vacuum thus quite a bit of energy needs to be put in. When the volume gets decreased the energy can get recuperated. Although it works with air pressure nothing of the energy that is put in will be converted to a temperature difference like in entropomechanical converters since the outer pressure stays constant.
Notes
(TODO: Check out which effect the use of tensegrity structures has on thermal isolation.)
Related
- Thermal metamaterials
- Diamondoid metamaterials
- Diamondoid heat pump systems – to charge or discharge a temperature difference across a thermal isolation layer
- Gem-gum solid state heat pipes – the opposite – maximizing heat condition rather than thermal isolation
