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What is the best wire for generating heat?

I am making an Instructable for some contests. The basic concept is below:
-Put two peltier modules on each bloodline on the neck
-Put small heat sinks that takes advantage of wind on the other sides of the peltier modules
-Use the electricity generated by the peltier modules (While skiing in ~20F) on a heat-generating device located near the hands
-Cover the parts that I can with some fabric and possibly build it into a neck warmer or face mask

So my question here is: What kind of wire should I use to generate the heat on my hands? I'm looking for high-efficiency and fast to generate the heat

Also, do you see any flaws in my concept that I should change?

Lastly, the most important question I feel I should ask here is: Will the peltier modules generate enough electricity to make a significant difference on the heat of my hands? My hands get cold enough to hurt when I go back into room temperature if that helps.

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Well a pair of peltiers with only the difference of a person's neck and the outside air isn't going to generate enough power to get any kind of Nicrome wire to heat up. The problem being the outside air will be affect the hot side of the peatier as much if not more so than a person's neck will. All you'll end up with is a cold neck from having a cold plate pressed against it. Interesting concept and all just not viable.

knexpert1700 (author)  mpilchfamily2 years ago

I could sew or glue the peltier modules into a wind-proof neck warmer that fits snug around my neck. My neck would be insulated and protected from contact with wind. The blood pumping in my neck will generate more heat in the neck warmer.

For best possible heat you want them along the small of your back. But still not going to be enough to power any kind of heating element. Be better off using a battery pack.

BTW, The secret to keeping you hands warm is to keep your chest and head warm. Your body restricts blood flow to the extremities to help keep the blood and heat going to the vital organs. A simple wool scarf will go a long way to keeping you warm overall. Not to mention a pair of gloves. Mittens are better as your fingers stay together helping to increase the amount of heat to stay warm.

knexpert1700 (author)  mpilchfamily2 years ago

This idea does seem to be too convoluted for a simple solution.

dot7242 years ago

nichrome wire

You asked if there are any flaws in your concept.

There are flaws. You seem to have some misunderstandings concerning electricity and heat. I am hopeful my comment will bring you closer to enlightenment.

Converting electrical energy to heat is easy. Any resistor converts electrical energy to heat at 100 percent efficiency. That's an ideal resistor, but real practical resistors can get arbitrarily close to this, e.g. 95, 99 percent, etc.

For this reason it is kind of a silly question to ask which kind of wire is best for converting electricity to heat. All that is required of your wire is resistance greater than those in the other parts of the circuit, e.g. batteries, wires, so that most of the heat is dissipated by the resistor that is your heating element, and much smaller amounts of heat dissipated in the batteries and connecting wires

In contrast, converting heat into electrical energy is difficult, and the maximum efficiency is limited by the temperatures of the hot reservoir, TH, providing heat, and the cold reservoir, TC, sinking the heat. Specifically the Carnot limit:

(See:

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

)

eff(Carnot) = (TH-TC)/TH

Note, for that formula, TH and TC must be measured on an absolute temperature scale, such as the Kelvin scale.

As an example, for a hot reservoir, like your neck, at temperature (98F,37C,310K), and a cold reservoir at (20F,-8C,265K)
So in Kelvin, TH = 310K, TC= 265K, and

eff(Carnot) = (TH-TC)/TH = (310-265)/310 = 0.145 = 14.5%

which is an upper limit for a perfect heat engine.

The efficiency for a real Peltier device is necessarily much less than this. If you'd like to know how much less, there's a more complicated formula for this, here
http://en.wikipedia.org/wiki/Thermoelectric_materi...
Using that formula, and a value of 2.4 for ZTavg, gives an overall efficiency of only about 4.5 percent.

Anyway, I think the lesson to take away from all this is it's easy to turn electricity into heat, but very difficult to turn heat into electricity.

If you need to move heat from one place to another, often the best way to do that, is to move it as heat, e.g. with hot fluid moving through pipes. That's the way the heater in a car works. There is some plumbing and a valve, to re-route some of the engine coolant, which is hot, into a small radiator in the passenger compartment. This small radiator is, essentially, just a small version of the big radiator on the front of the engine compartment, which dumps heat into the air outside the car.

As others responding to your question have pointed out, your existing circulatory system; i.e. blood vessels, should be very capable of moving heat around your body.

Just bundle up, and your hands will hands will stay warm.

Or perhaps, like Iceng suggested, there is a way to gain motor control over your own blood vessels (usually thought to be autonomic). The technique he suggested, of visualizing fingers getting heavy, that might work for you too.

knexpert1700 (author)  Jack A Lopez2 years ago

Thanks for the helpful explanation. I was looking for these explanations and efficiency rates, however, I couldn't find them in the time that I had to research. I will search for a more practical Instructable idea that still has as much of an interesting concept.

+2

iceng2 years ago

Your using neck blood heat to warm your hands as you ski, Cool idea.

I learned to warm my hands by visualizing my fingers getting heavy which causes capillaries in finger tips to dilate and allow more body warm blood to flow where you want it.