you said “sea ice” so, there’s a good amount of seawater on the outside? In that case you have to consider the plant and other life that will accumulate on the outer layer. It’ll break apart and destroy any unprotected porous material like concrete (and even steel would still accumulate material), but until it does, it will affect the insulative properties.
No, it doesn’t matter how reflective the inner surface is – the photons don’t have anywhere else to go, so they will eventually get absorbed on the surface whether is an almost-perfect mirror or flat black.
For a flat wall, the order of insulators doesn’t matter. For a sphere, with a thick layer compared to the size of the sphere, I haven’t thought it through, but it’s possible there might be some very small theoretical difference whether the more insulative material is inside or outside, but it’s certainly not enough to outweigh any other engineering considerations.
Practically speaking: 1. LED’s don’t give off much energy, either as heat or light. If they are giving off much energy, they’re probably going to have a very short lifespan.
You’d probably need some dedicated heating elements, which are designed to deal with thermal stress etc. 2. If you need insulation, as mixdenny said, concrete isn’t great, and some foam/fiberglass/etc insulation is likely going to be necessary (again, shiny doesn’t matter since it’s in closed container), and even a thin layer of insulation will provide more heat retention than lots of concrete.
Air absorbs in the IR spectrum.
I was thinking about 80w/square meter. Although LEDs radiate less thermal energy, they are still very hot. Keeping them below 65 centigrade is of crucial importance.
As I recall from my heat transfer classes, covering a smallish cylinder with insulation with a low R value can actually increase the heat loss. The surface area grows faster then the increased thickness can compensate for. The term is “critical radius” or some such that relates the R value to the increase in thickness.
Don’t ask me to come up with it, try and locate Professor Poulos. He was a great guy with lots of stories. He escaped ahead of the Nazis and came to the states in a submarine. I forget why. We told him he should write a book of his adventures and call it “View Factor: America”. (That’s a heat transfer joke).
Dennis
What if we forgot insulation (I prefer concrete outside), but if the design were like a vacuum flask - shining steel on the inside and thick acrylic coated outside of concrete. Is it not easy have a vacuum in between? In the long run…
Normally when you put steel and concrete in sea water, you put the concrete on the outside and the steel on the inside. Lacking any really convincing argument otherwise, I’d go with standard engineering practice:
The problem will not be that growths on the concrete will break it up: the problem will be that corrosion on the steel will break up the concrete. The concrete is alkali and will protect the steel, but that won’t be enough long term. Long term you probably want a stainless steel and a waterproof concrete.
How hard would it be to maintain two cylinders apart from each other by permanent magnets? I’m still thinking of the two separate spaces and a vacuum in between.
Impossible.
With a little assistance of electromagnets and sensors?
Can you give us a general idea of the size and shape of the object and how deep it will be? For a vacuum jacketed tank they generally use thin struts or rings to maintain the distance. And fill the space with insulating beads.
Dennis
… but it cave you not any better startpoints. I’m awaiting…
You trilobite - I will!