Your Future iPhone May Be Stuffed With Wax | Hacker News Reader

Your Future iPhone May Be Stuffed With Wax

wired.com

59 pointsLibertatea26 comments

The point is taking advantage of matter phase transitions: a lot of energy goes into converting a solid into a liquid, without changing the temperature. Ergo, you can dump a lot of heat into something without then having to move the something away fast to keep the heat source cool. Only works insofar as it only takes so much energy to melt the solid (wax, ice, whatever), after which you need to either resume a classic moving-coolant process or otherwise stop generating so much heat and let the now-melted substance cool via ambient surroundings and re-solidify.

An interesting variant on this is Coffee Joulies http://www.joulies.com which are metal balls you drop in your too-hot coffee to rapidly cool it to a desirable temperature, then keep it at that temperature much longer than it normally would stay. The initial heat is absorbed to melt the ball's contents, then is re-released back during the reversed phase transition. Kinda neat.

A limited solution, but easily quantified and quite applicable to a narrow but popular range of use.

I first thought the title's point was Apple would be stuffing the phone's interior with wax to either make it waterproof or further frustrate reverse-engeineering attempts.

Joulies do not in fact work:

http://en.wikipedia.org/wiki/Coffee_Joulies

Basically, if your vessel isn't insulated, you lose the same amount of heat to the walls and air. The part where they cool your beverage to a certain temperature and then stop cooling it works fine. The part where they retain heat is thermodynamically senseless.

Fortunately, when you replace "beverage" with "chip", you have something that cools the chip for awhile and then stops. Hence the article.

Why is it senseless? You lose the same amount of heat in joules/sec, but the total heat stored in the system is higher, since there's a buffer in it with a higher volumetric heat capacity than coffee. So unless I'm missing something, it would indeed cool slower in degrees/sec, but the effect is likely very small.

(Note however that the extra volume of the ball would slightly increase surface of the coffee, losing slightly more joules/sec)

I agree with you.

Most coffee vessels ARE insulated, or at least have low thermal conductivity.

u/computer explained the buffer effect nicely. You're right that the keeping it hot part might be insignificant.

In a 30c room a cup of 80C coffee loses heat energy a lot faster than 60C coffee so there is a faire amount of free energy when the coffie is to hot to drink. Phase changes store and release identical amounts of energy. So, while the increased drinking time may not be significant it is there assuming that increasing the liquids volume does not overly increase the heat loss.

Edit: look at the graph on page 2 of this PDF. http://web.eecs.umich.edu/~martinjs/math115/coffee_expl.pdf

The former point is correct as far as it goes. The latter is not. A cup of coffee loses heat around the perimeter, not the middle, and the rate of heat loss is entirely determined by that perimeter. The only thing the Joulies can keep warmer than that equilibrium is themselves.

If they start warmer than the coffee, they may contribute to slowing the rate of heat loss. If they do not, they cannot.

I have come to think of this as the Monty Hall problem of thermodynamics. People with degrees similar to my own disagree with me all the time.

To forestall the most common objection:

Yes, the joulies store more heat than water/coffee, by virtue of being denser. The phase change is irrelevant except as a trick; think of it as extra density you don't have to carry. You also don't get to drink it; it's more heat, but less coffee.

Water/coffee stores more heat per gramme than either the phase change or the joulies, so unless you're short of volume, just insulate your coffee.

If they start warmer than the coffee, they may contribute to slowing the rate of heat loss. If they do not, they cannot. Except people don't drink 80C coffie so the absolute time it takes to reach 30C is less important than how long it spends in the drinkable range.

Now I don't know what wax there using or how much, but Paraffin wax for example has about 1/2 the heat of fusion of water. So it would store enough energy to keep ~35 times as much water at a constant temperature rather than failing one degree c at which point the was would freeze and provide negligible benifit. On the other hand if the wax water ratio was 1:5 then the temperature would stabilize though 7 degrees worth of cooling when the coffie was 80C and then 7C of warming when the coffie was 37C which would be noticeable. Granted, 37C is a little to cold for coffie, other waxes have a higher melting point.

PS: I still don't think this would be all that useful in practice. I am just pointing out it's not physically impossible.

That's why this is a Monty Hall problem. If you put the phase change material between the coffee and the insulation, it works. If you don't, it does not, because we are forgetting that the definition of heat is of a system, and heat exchange is on the interface. Coffee exchanges with a certain efficiency that is unaffected by the presence of a more efficient heat transfer material holding a reservoir of heat, unless that reservoir begins at a higher temperature.

You may need to go all the way back to definitions on this one, but it works out, and it predicts, correctly, that the effect is insignificant, per volume of coffee.

Yes, you can keep less coffee warmer longer by putting a volume inside it. That's not impressive. Can you keep the same amount of coffee warmer longer? You cannot.

The reason is that that Joulies, or anything else you put inside the system, displaces coffee out to a larger surface of interaction with the outside system. All other things being equal (basically, with a lid), it cancels out.

Without a lid, convection is primary over any other factor, and the entire system will tend to reach equilibrium at about the same rate.

Unless you a) add heat or b) reduce the rate of heat transfer at a surface, you cannot slow thermodynamic equlibrium.

If the heat transfer material is inside the coffee then the heat transfer is not just with the outside material but also with the phase change material. Also, even if the phase change material is the same temperature at the start, it becomes warmer at the point the phase change occurs. Now, increasing heat loss to the outside world is possible as the coffee surface area increases. However, that's vary much a question of cup design as a matalic vacuum thermos generally heats up the internal metallic part reasonobly evenly almost regardless of fluid level.

PS: And if you don't believe me actually model the equations it works out after you realize drinking time only starts below an acceptable temperature.

Interesting - one of the few links where the article delivers more than the title promises. How about "dissipating short bursts of heat in mobile CPUs"? Just for HN, of course, where people are genuinely interested in such topics. /2cents

I'm slightly disappointed by the article. It's a novel and interesting topic but wired fails to explain the details of how this works and doesn't even try to explain the physics behind it. IMO it wouldn't be too difficult, since the idea is actually quite simple and can probably explained to a non-technical reader in a few sentences.

In my opinion the Figure A in this PDF really explains it well:

http://acg.cis.upenn.edu/papers/ieeemicro13_responsiveness.p...

(page 3 of pdf)

A similar idea is used in practice in a building I'm frequently in. Beads of wax in the concrete floor keep it cool in summer by melting when the temperature rises, and recover overnight when the windows are open and resolidify.

Some of the larger skyscrapers in my city are cooled using a phase-change material as well: water.

A local facility makes ice overnight when energy is cheaper and then pumps the melting cold water into the buildings to assist the air conditioning units.

My first thought at the title was that this would result in the ability for them not to be damaged by water. But it also makes sense as a coolant system.

Same here. Fill every empty space inside the thing with wax, and you have a waterproof phone! Wonder if that would really work.

Not the way you'd hope. Without some way to seal it off, you'd have wax dripping out of your phone every time you use it... or charge it. If you do have some way to seal it in, then you've probably solved the waterproofing problem anyway.

If you do want a waterproofed iPhone, there are cases out there that claim to be waterproof, e.g. LifeProof. I've not used or tested one yet, though...

I love approaches like this: instead of butting your head against the same limits, look at the whole problem, find a re-frame the problem with a new trade-off that actually the whole problem.

Arguably, this is what Clayton Christensen is talking about with "over-shooting": making your product better than it needs to be in some particular dimension, just because that's the way you've always been making it better. But like doing your shopping in a Ferrari, maybe increased horsepower isn't what's really needed.

Here, they'll saying that bursty usage (they call it "sprinting") is what is actually needed. I noted this with word-processors - most of the time the PC is idle - and wondered how those cycles could be harnessed. Instead, they say, turn it off.

This might be an alternative to many-core - just boost it x100 faster. It can also go the other way, having a much less powerful processor, just super-boosted for when needed. Cheetah would be a good code name for this project.

It doesn't solve "the whole problem". It won't help with any sort of batch processing, nor with the latest game trying to squeeze every bit of performance out of the hardware.

Worse, it may actually encourage bad behavior by applications. We already have problems with applications draining batteries unreasonably fast on mobile devices because they implement features in ways that look "fast enough" interactively, but under the hood are an unnecessary power drain. Now such inefficiencies can be even less obvious!

There's a lot more to practical application of this than tossing some wax on a chip.

The "whole problem" doesn't mean "every problem". It means taking a step back and seeing what the user is really trying to accomplish, and everything that is needed for that problem to be solved - as opposed to myopically seeing just one aspect of that problem. Some extreme examples of whole solutions: Edison establishing a power generator and power line infrastructure, not just a light bulb (Musk's Tesla is doing similar now); Birdseye establishing freezers in supermarkets, not just selling frozen fish. Sometimes, you'll focus on one specific user problem, which can even mean removing features. BTW: I'm taking the term from Crossing the Chasm (Geoffrey Moore).

Of course, what you say is true about continuous loads, and also battery drainage for bursty loads. It's not a solution to every usage pattern, and as the article mentions, it's around 10 years away.

I love changing problems to see unexpected ways of solving them - even if it does take years to realise the vision.

I'm curious how this works long-term. Old computers already have coolant systems that degrade - thermoconductive paste gets brittle and cracks, fans get gummed up. How will this wax work long-term?

http://www.youtube.com/watch?v=OpCJzdWxEbQ

I believe paste and fans work longer than the average useful lifetime of a PC, I guess planned obsolesence is at work here too...

Lots of devices have been using wax motors for a long time, like dishwashers and automotive thermostats. It seems the mechanical parts wear out long before the phase-change material breaks down.

And I was so hopeful from the headline that Apple was adopting the Lua Wax SDK as an official API.

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