Ask HN: Any Chemistry hackers here? | Hacker News Reader

Ask HN: Any Chemistry hackers here?

There's a project I want to undertake. I want to do it out in the open. I've been inspired by a few Maker projects as of late. I keep hearing "you should file a patent right now" when I have shared this idea with close friends. Which is why I want to do the opposite.

I don't know enough about the specific domain for the crux move of the solution. I think the solution lies in Chemistry or Chemical Engineering, but I am not certain that the problem is solvable in a cost effective way. My gut tells me that it is.

The first step is for me to be able to ask some very specific questions about phase change temperatures and latent heat of fusion of different chemical compounds. Any takers? The background info is too much for an Ask HN post, but I ABSOLUTELY promise that as soon as this enters the realm of "yeah, that's probably solvable" I will start posting the whole project and living it the Maker way.

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You can give me a try. I am an amateur chemist. Edit: Email in my profile.

I am looking to identify a material or compound that can dissipate heat generated by the human body. I want to use this for an athletic textile application. Specifically a cooling element that is to be placed against the skin along the forearm, or on the head.

Principle characteristics I need are light weight, self contained reaction, non-toxic, and can remain cool/cold for as long as possible while dissipating this heat. Reusable is ideal, but one time use is also OK.

Biotechnologist here....As I see it there are three options: 1. Uptake of the thermic energy by an endothermic chemical reaction (like http://en.wikipedia.org/wiki/Instant_cold_pack) 2. Passive removal of the heat with a heat conducting material (you have to get rid of the heat somewhere else) 3. Active removal of the heat (see http://en.wikipedia.org/wiki/Cooling_vest)

I think thermoelectric cooling (http://en.wikipedia.org/wiki/Thermoelectric_cooling) would be suitable for your application. It is also compatible with Arduino technology I think.

Yes, in doing my research the cooling vest was one of the first items I looked at. The biggest problem for my target customer (triathletes and runners) is the weight (>4 lbs), the lack of mass security (vests tend to move around a bit), and the heat blocking nature of the vest when cooling is depleted.

I have been experimenting with saline based solutions to test my theory of perception of heat reduction. They have worked for the most part, the challenge has been that they last about :30. I need longer. I have not experimented with any of the break+mix solutions from the wikipedia article, though am aware of them.

My preference for an endothermic reaction with a PCM is that in theory the mechanism is reusable, or easily replaceable, the weight penalty is low, and the complication of the solution (no pun intended) is also low).

There are some of these "cool materials" on the market right now, and they are somewhat interesting, though they are not operating as a heat dissipation level of the endorthermic reactions.

My vision for this product (at this point in time) is a sleeve that houses chambers with the endothermic reaction solution, and those chambers are either in an arm sleveve, or inside of a hat (think of the head band of a runner's hat).

Whether that solution is a one time use, and thus replaceable in the chamber, or multi use, and thus more permanent, is not really my challenge right now. A marathoner going to secure their Boston spot would pay $50-$100 for a hat that is guaranteed to keep them cool on a 90 degree day when their alternative is to keep throwing ice on themselves at aid stations, or stuffing cold sponges down their shirts. This is how it is handled today. Same for the age grouper triathlete who is getting ready for a sprint or Ironman. These folks are pretty obsessive about gear and kit, and aren't very price discriminating.

The trouble with most endothermic reactions is they involve far less energy absorbed per kg than exothermic reactions tend to emit (and their reaction rates much slower than you'd like). As a runner I'd not be too enthused about lugging around a 500g brick of goo that has the best possible endothermic heat absorption. You'd lose far more in heat dissipation potential than that brick could ever absorb, at least if it started at ambient. (Imagine how less popular ice would be if it never melted but stopped cooling).

A peltier cooler would be right out; they only work when they have an active cooling mechanism (heat sink and fan usually).

If you wanted to ditch the cooler and put together a hat or other appliance with a 3V case fan and ultrathin solar cells (CIGS probably), you'd get an excellent improvement in heat dissipation, and it would work indefinitely as long as it was daytime (probably a safe bet).

Correct me if I'm wrong, but from a thermodynamic point of view the major problem is the entropy. You can't just convert heat into any other form of energy (light) without also caring of the entropy. In the case of solving some salt in water, the entropy is going into the chaos of the solved ions (versus the low-entropy crystal). With all the other methods you need to get rid of the heat. With peltier coolers I could imaging "watercooling" the hot side.

On the other hand sweat (evaporation) is already a pretty good cooler and covering the skin with something else stops that effect. Additionally you enrich sweat inbetween which does not feel well. Completely absorbing the sweat also kills the cooling effect..

So maybe, as mchannon suggested, all you have to do is design a nice, flexible and good-looking sweatband with an integrated fan ;)

You might find this paper worth a read as it covers garments and water absorbtion/heat disapation effect. Quick read to me a material that will absorb as much sweat as possible will carry on disapating heat better due to captured moisture post sweating. But different sports/enviroments will need be needed, something that retains moisture in a cold enviroment would potentualy overcool them post sporting.

"A Study of Heat and Mass Transfer in Porous Material under Equilibrium Conditions" : http://www.bckiln.ir/Wood_Dryer/download_files/enteghal%20ha...

I also know that the cooling of the feet is a overlooked area as shoes will allow a heat buildup and the blood will happily cicle that heat around. With that if you also cool the feet it will mentaly make you feel colder than you are, same effect wwitht he hands.

So maybe look at cooling gloves as you will have less sweat to deal with and in most sporting/athletic events the hands will always be moving, so air cooling of the gloves will help.

Chemist here, just musing @ breakfast, so I am not backing any of that stuff with literature research.

I understand you would like to have a permanent cooling effect. Unfortunatly, materials that undergo conformational/phase transition processes do not require a permanent feed of thermal energy e.g.

  A + dT --> A'  conversion with heating
  A' -> A + dT   fall back to original state with cooldown

  with dT temperature difference (thermal energy)
  and A and A' the respective states of the material.

As such you would need a material that uses the thermal energy for some other effect e.g. radiation of light, permanent conformational movement creation of electric potential etc. The trouble I see here is that the effiency of energy conversion is fairly low with the current polymers. And the price tag.

Ok, here is a crazy idea, but not sure if it is not impractical or even stupid (; . Maybe use of superadsorbing polymers with a specific thermoresponsive behaviour somewhere around the working temperature of the athlete would give you a higher cooling effect. Once the athlete heats up, the polymer becomes more hydrophilic, allowing for more sweat to enter the fabric. Hopefully, the wet fabric would have a better thermal energy flow than the dry fabric. Basically, you make a supersoaking sweatshirt. But then again, maybe you just use a hydrophilic fabric?

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