Smart fabric heats up under the sun • Hacker News Board

Re: Smart fabric heats up under the sun

#41

Post by DangitBobby » Sun, Feb 02, 2025, 2:38 AM UTC

10000truths wrote: post #40

DangitBobby wrote: post #38

Earlier quoted context omitted.

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.

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.

Re: Smart fabric heats up under the sun

#42

Post by nejsjsjsbsb » Sun, Feb 02, 2025, 3:21 AM UTC

cluckindan wrote: post #9

rahimnathwani wrote: post #7

Earlier quoted context omitted.

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…

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?

Re: Smart fabric heats up under the sun

#43

Post by MadnessASAP » Sun, Feb 02, 2025, 4:26 AM UTC

viraptor wrote: post #28

xhkkffbf wrote: post #23

Earlier quoted context omitted.

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.

Re: Smart fabric heats up under the sun

#44

Post by calmbonsai » Sun, Feb 02, 2025, 4:55 AM UTC

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.

Re: Smart fabric heats up under the sun

#45

Post by viraptor » Sun, Feb 02, 2025, 6:18 AM UTC

MadnessASAP wrote: post #43

viraptor wrote: post #28

Earlier quoted context omitted.

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.