Smart fabric heats up under the sun | Hacker News Reader

Smart fabric heats up under the sun

uwaterloo.ca

37 pointsgnabgib40 comments

After the recent "save 30% power in datacenters" thing¹, I've grown a bit weary of the university of waterloo, and "things get warm in the sun"² isn't helping.

¹ it was a IRQ polling change in the Linux kernel that only helps network-heavy applications under high load with good NIC offload capabilities. I'll accept it might save 30% in the "best degenerate" case, but it'll be nowhere close in general. https://news.ycombinator.com/item?id=42841981

² yes I'm exaggerating. The problem is I have no clue about this heat thing, but I do have an understanding Linux NAPI/IRQ behavior, and that made me with good reason call massive exaggeration there. So what am I to do when I see something from this same source that I don't know about?

> So what am I to do when I see something from this same source that I don't know about?

Well there's always <https://en.m.wikipedia.org/wiki/Gell-Mann_amnesia_effect>. Sounds like your not as vulnerable though.

> 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

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

Different kind of heat transfer. Clothes in the dryer match the temperature of the heated air around them. This paper is about radiated heat captured by the cloth.

Ok stick your shirtsleeve in a toaster. 1000W? How many minutes until it’s 125F. Same answer?

If I understand the quote from the paper, it's not quite the same. They're putting a controlled amount of irritation over a long time on the cloth. It seems like the change is a higher temperature than other fabrics, not necessarily faster (maybe, but not noted)

"... enabling the fabric to absorb heat and convert it into warmth" is a fun sentence

"The design requires no external power"

Umm, so sunlight is not external power?

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?

At the very large scale, the universe does not appear to conserve energy. The whole "lambda" in "lambda cold dark matter" is a description of how energy is being added to the universe.

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.

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.

This doesn't actually solve the original problem. Either something was always there or something can come from nothing, and both of those seem to violate causality as we understand it. Saying "God was always there" isn't really that different from "The universe was always there" when it comes to resolving the violation of causality.

Obviously, something was always there. "Always" refers to the run time of our simulation.

An omnipotent being would presumably have invented causality and time, and therefore not be bound by the axioms thereof.

Sure, you can invent any explanation that you like. It just isn't more convincing than "the universe (or an outer universe giving birth to this one) was always there", since they solve exactly the same problem.

Converting heat into warmth is like converting meat into a burger. An abstract resource vs a directly consumable thing.

Isn'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?

Mirrors are nowhere near perfect with their reflections. You'll get some of the light/heat absorbed.

I'm pretty sure the cheapest mirrors still manage 80% with good quality ones in the 95-99% and 99.999% achievable if you're prepared to get fancy. So I'd say they're pretty dang close to perfect. Definitely well down the asymptote.

I don't get what point you're trying to make... They reflect some radiation depending on quality. Regardless how close to perfect they get, the answer to the original question is - no, they don't break the "everything heats up" rule.

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)

It does it better than the default.

HTH.

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.

Gosh, it's almost as if ALL things heat-up under the sun. ;)

Given their (cough) publication history, one would hope UW would've learned by now avoid the terms "smart" and "nano particles".

In actuality, this is the university's PR department completely dropping the ball on how to describe a non-phase-change passive heater https://link.springer.com/article/10.1007/s42114-024-00994-4 .

It's not going to replace good 'ole phase-change pocket warmers or, god forbid, lighter-fluid burners (check out the W/m^2/s), and there's going to be some serious manufacturing R&D to make these fibers into wearable fabrics (hint, substituting phase-change for length-change (color is micro-length adjustment) does not bode well for durable stitching), but it's neither an outright outlandish engineering proposition nor as remotely as "sci-fi" as the article claims.

FWIW, the 600 W/m^2 is often used as a stand-in source for nominal solar irradiance though I can't find the specific spectra of the source. If you're changing color (length), spectra really matters.

I have little doubt the authors of the paper cringed when they saw that headline, but I'm also likewise as sure they're happy to get any press.

Wear black non-glossy skin tight stuff all over and I can tell you it heats up darn fast to unbearable levels. Great for mountains and cold times though. This must be a smidge better and uses different colors so some evolution it seems.

Depends on price and tons of other aspects like long term durability and resistance to frequent washing to make it interesting for masses, I expect some major issues there

Stupid fabric also heats up under the sun, as does braindead fabric.

Yeah, but this one will do your taxes /s

Stupid fabric can only grab a few degrees, while the smart fabric acquires full 30. A genius fabric could likely boil water in the wintertime with sunlight alone!

A wet black sock around a beverage can in direct sunlight will cool down the can as it dries.

Don’t all fabrics already absorb IR and heat up?

This new fabric would need to be the outer layer of a garment to receive light, so no insulation and no layering. Most of the heat would not be warming you up. Seems kinda useless?

I would be more interested in a fabric that cools down under the sun.

Do I have a treat for you https://youtu.be/G8YBV7GoF_s?feature=shared

  Don’t all fabrics already absorb IR and heat up?

Yes, but the paper's abstract says this fabric heats up faster:

  Through the incorporation of a modest amount (as little as 0.5%) of photothermally active polyaniline (PANI) and polydopamine (PDA) nanoparticles, this fiber exhibits exceptional photothermal conversion performance compared to pure thermoplastic polyurethane (TPU) fiber. 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.

So basically useless in winter above 60 degrees latitude, when and where it would be most needed: sun is up only a few hours per day, and only one or two of those hours get 100W per square meter on a clear day.

50-90 latitude it might be useful plus mountains.

Might be good for daytime heating of a tent?

Reply on news.ycombinator.com