Thermal Insulating Plastic

Well said.
it would be possible to construct all sorts of clever heat exchangers or mechanisms, maybe bimetalic levers that force contact with conductive sufaces if the temperature gradient is one way but not the other....or loads of control electronics....
But not a homeneous material.

Del

Can you imagine the efficiencies that could be obtained with a true "heat diode" material? It would be more revolutionary than the microchip!

I don't think there are any materials that could do this, but heat pipes sort of do what you want.

We all know of the "Greenhouse Effect". Shorter wavelengths of visible light, which are relatively "hot" (energy = hν), pass through glass or transparent polycarbonate, and enter the greenhouse. The hot light energy then hits plants or dirt or the floor, and is adsorbed, warming the inside of the greenhouse. These warm internal elements then start to radiate this internal longer wavelength (lower temperature) heat back out, at a much lower frequency (ν low). At this lower frequency, glass or polycarbonate is not transparent, so the heat inside the greenhouse does not easily pass back out. So glass is a radiative heat diode, in this special situation of radiative frequency shifting.

At a fixed frequency or wavelength, there is no such effect.

What you want is a heat diode.

As said before by others: When you invent this you are up the row for Nobel price and Euro-millions.

In fact it does exists: the Peltier element does transport heat from the cold side to the hot side. Or when in balance, blocks the passage of heat.

But as you might know: it consumes energy. Which is exactly what you don't want.

In Solar Collectors they play with the wavelengths to receive energy from the sun (short wavelengths) and prevent cool down (long wavelengths). the reflective coating on the inner wall of the glass tubing is wavelength selective: wavelengths longer than a certain value are reflected and the shorter pass by. Modern solar heat reflecting glazing do work the same way, you don't see it reflecting but if you look through a thermal imager the picture is completely different.

A possible solution might be a sheet of metal (copper) or glass with one side painted black and the other side painted white or silver.

A possible solution .

Indeed, you have hit the nail on the head...
We don't know the actual problem, therefore we can't be sure of giving appropriate answers.

I'm feeling a bit foolish at the moment

Immediately after I dispatched my response I realized that the request was for a plastic material which I completely disregarded.

I suppose one could subsitute some type of plastic material for the metal or glass but of course it then would not be as effective a conductor in the desired direction.

Perhaps a powdered metal filled plastic.

All plastics are in principle thermal insulators, and I am not aware of the existence of a thermally selected material.

The radiation shield with a black side and the other polished may not work, in my opinion, according to your desire. Radiation heat transfer is very weak for small temperature differences (it requires large areas for heat exchange).

The first thing that springs to my mind is that you could use a heat pipe as a heat diode, provided that your system is in gravity conditions (e.g. not orbiting in space): when you place a linear heat pipe in vertical conditions, with the hot source connected with the bottom end, the heat is easily transferred to the upper cold end. The reflux of the heat fluid vector is guaranteed by gravity. On the contrary, when the hot side is on top of the heat pipe, the reflux should guaranteed by capillary forces (inside the grooves of the heat pipe), but in this case the gravity force on the fluid vector is generally of a much higher order. In this condition, therefore, gravity acts in such to prevent the reflux, and no heat transfer occurs in steady state conditions (or a very little heat transfer, as a limit case).

I experienced such a condition during a test on-ground for a space equipment. I had a heat pipe rotating around an inclined axis (simulating the rotation of a satellite), in such that the reflux condition due to gravity occurred for only half a complete rotation. It was actually observed that the efficiency was close to nominal expected values when reflux was induced by gravity, and it fell down to negligible figures in the worst opposite conditions.

I don't have any other hints for such a problem, sorry!

Hi, Harold.goldbaum!

I noticed your various blog entries over the last two months, and am trying to determine what it all means.

Are you developing an interstellar sailing ship?

Mark

I wouold guess he is working with CSP

I was reading th March 2008 issue of Physics World and this article reminded me of this thread.

Called phononics, thermal diodes and transistors do exist, but are not quite a plastic material, yet. They are using emerging nanotech products like nanotubes and quantum dots to do so, it is bond to evolve steadily.

And the phenomenon has been observed since the 1930's.

We'll see for the Nobel prize...

Good reading.