Having trouble imagining an implimentable use case that will provide a net benifit.
The biggest nix on this idea, is that nothing in nature has tried a similar approach, and artic animals have a whole bunch of optical light adaptations , as do sea creatures, many of them are startlingly efficient and complex.
See polar bears, with optical fiber white hair that chanels light to black skin and riendeer who can see them by ulra violet light in cold snowy night, when.they are otherwise, invisible.
Likely will have industrial uses however.
Smart fabric heats up under the sun
21–30 of 45 posts
Re: Smart fabric heats up under the sun
#22Earlier quoted context omitted.
I take "external power" to mean power that is not "free" as in humans paid for it. Otherwise the phrase "External power" is meaningless, as all energy comes from somewhere else eventually. (unless you're at some point in time extremely close to the birth of the universe, then we might accept that it's actually internal or at least locally sourced)
You bring up an interesting point about the birth of the universe. Doesn’t that violate the principle that energy cannot be created?
That depends on what you believe was there the instant before the universe was created.
Answering that with "nothing" would indeed violate all kinds of conservation laws. The currently most popular theory is that time and space also started at the big bang. If that's true there is no "before the big bang", and thus the energy was always there.
Other possible answers:
- the energy was there but kind of dormant, then something triggered the big bang
- we live in a cyclical universe: after the big bang the universe expands until it reaches some maximum, then it contracts, collapses in to itself and triggers a new big bang (this seems unlikely given current experimental evidence)
- The multiverse sometimes creates "bubbles" like our universe. This is similar to spacetime starting at the big bang, but tries to explain why that happened
- Same idea, but in regular 4d spacetime: we are a kind of bubble, possibly expanding bubble, in a void filled with bubbles
- We are the inside of a rotating black hole
I'd have to go back and check how the last three reason about energy.
As you can imagine, testing any of those theories is incredibly difficult. Not impossible, but really really hard. They are more like fan theories that can be tested for internal consistency without any good hope of showing which one is true.
Re: Smart fabric heats up under the sun
#23Isn't that like, the default? I would find it more impressive if it didn't.
Yes, I am confident that all materials get warmer when exposed to sunlight. Evaporative cooling might be argued as an exception, however I do not consider it so. There might be some materials that do not absorb solar radiation, I'm not aware of them. https://en.wikipedia.org/wiki/Evaporative_cooler
What about a mirror?
Re: Smart fabric heats up under the sun
#24Isn't that like, the default? I would find it more impressive if it didn't.
Yes, I am confident that all materials get warmer when exposed to sunlight. Evaporative cooling might be argued as an exception, however I do not consider it so. There might be some materials that do not absorb solar radiation, I'm not aware of them. https://en.wikipedia.org/wiki/Evaporative_cooler
There is radiative cooling paint that in addition to reflecting most light radiates heat in wavelengths that don't get absorbed by the atmosphere. That makes them cooler than ambient temperature when they are under the open sky.
They still get heated by the sun, just less so than everything else. But very similar sounding sentences about them would be true (because on a sunny day, in the shadow, they would be cooler than indoors at the same ambient temperature)
Re: Smart fabric heats up under the sun
#25Earlier quoted context omitted.
You bring up an interesting point about the birth of the universe. Doesn’t that violate the principle that energy cannot be created?
That depends on what you believe was there the instant before the universe was created. Answering that with "nothing" would indeed violate all kinds of conservation laws. The currently most popular theory is that time and space also started at the big bang. If that's true there is no "before the big bang", and thus the energy was always there. Other possible answers: - the energy was there but kind of dormant, then s…
Or, you know, an higher and/or omnipotent entity. At some point along the causal chain, there is no "testing" - you are forced to resort to metaphysical reasoning.
Re: Smart fabric heats up under the sun
#26> Notably, when exposed to 600 W m−2 irradiation for 600 s, the equilibrium temperature of the photo-thermochromic elastic fiber rises impressively from the ambient 20.0 °C to 53.5 °C. Does anyone know what's the expected raise from that much energy in basic cotton for comparison?
I naively tried to calculate in a closed system consisting of cotton canvas but I got a temperature rise of 600K. Oh well, I guess heat loss from the system is important.
600 W/m2 / (1.34 kJ/(kg K) * 390 g/m2) * 600s
Re: Smart fabric heats up under the sun
#27[dead]
Re: Smart fabric heats up under the sun
#28Earlier quoted context omitted.
Yes, I am confident that all materials get warmer when exposed to sunlight. Evaporative cooling might be argued as an exception, however I do not consider it so. There might be some materials that do not absorb solar radiation, I'm not aware of them. https://en.wikipedia.org/wiki/Evaporative_cooler
What about a mirror?
Mirrors are nowhere near perfect with their reflections. You'll get some of the light/heat absorbed.
Re: Smart fabric heats up under the sun
#29> Notably, when exposed to 600 W m−2 irradiation for 600 s, the equilibrium temperature of the photo-thermochromic elastic fiber rises impressively from the ambient 20.0 °C to 53.5 °C. Does anyone know what's the expected raise from that much energy in basic cotton for comparison?
If we assume a clothes dryer is 3000W, how long does it take a cotton shirt to get heated from 20c to 53c? A few minutes? So perhaps this fabric heats up 3-5x faster
Re: Smart fabric heats up under the sun
#30Isn't that like, the default? I would find it more impressive if it didn't.
It does it better than the default.
HTH.