Also note, calling the device a Peltier is a misnomer, her flashlight is a thermoelectric device utilizing the Seebeck Effect, similar but opposite to the Peltier Effect. Peltier has just become the connotation for thermoelectric devices.
The Seebeck effect only works with a temperature gradient, the flashlight will begin to heat up when held and the Peltier will produce less power. The next step is to add a heat sink and fan to maintain a temperature gradient for operation longer than 20mins.
I ended up not doing this because the Seebeck effect isn't really a useful power-plant (in the broad sense of the word) when you have a small temperature gradient because it is really inefficient, although it is useful for thermometers and other low power items, and for some exotic things like Radioisotope Thermoelectric Generators, which is what powers Voyager and other long distance spacecraft. It becomes worth using when you have a large, consistent energy source, which is usually geothermal energy. But the small temperature difference between the human body and the flashlight and the low efficiency of thermocouples means that this project won't seriously compete with battery powered flashlights. However, it is a cool idea and could have some niche uses.
Good on your for using peltiers back in HS. In HS I made a sweet exoskeleton using peltiers for active cooling while outside in the summer heat.
Yep, I was going to try to use that (peltier) in conjunction with a small array of solar panels to cool my car because summer afternoons can get incredibly hot - outside temperature reaches 45C, so I'm reasonably sure the car's interior would reach 55-60 easy. Alas! running some back of the envelope calculations (before jumping into the whole thing) I quickly discovered that I'm better off trying to find an efficient and tiny compressor, and large secondary battery to charge off the solar panels.
This problem still remains unsolved and no, remote start is not an option. I'm trying to craft something that is completely independent of the gas in the tank and preferably self sufficient.
A simple reflective car cover would do far more than all of that tech.
Smetimes it is really easy to over-engineer solutions to problems. I am reminded (and I am guilty) of this frequently.
I do realize that the problem needs to be approached two fold - expelling hot air outside to reach ambient + cooling air that's being taken in some manner.
So, if your willing to go all out and spend a few thousand on modding your car. Automatic shades for every window, a fair sized solar array on the roof and an independent AC system designed for continuous operation.
Speaking of phase-change materials, why not fill the flashlight with them? It still wouldn't be steady-state of course, but I envision the fan eating up all the power. Heat pipes might help, but they still leave the problem of heat rejection. Evaporative cooling pad?
Idea: using PCM you could make a flashlight that you recharge in the oven.
Combining ideas may make sense here. A flashlight with PCM and a black handle that you can leave in the sun, and optionally wrap in a soaked cloth. Perhaps PV makes more sense, but I haven't run the math.
Of course, you'd also want a thermos to carry it in. ;)
Basically, the heat was stored in the wax, which melted. Then, radiators would pull the heat from the wax out into space when the Rover was resting, which would solidify the wax again ready for the next run.
Think of sink/source temperature, cost/mass/performance/reliability tradeoffs, air vs. vacuum, power requirements, etc.
What about a series of smaller copper tubes that then stick out the bottom of the handle to transfer heat from inside to outer air?
I guess it also depends on the relative importance of mass vs. volume optimization.
Maybe there's some way to lower the melting point of paraffin?
Evaporative cooling could work, but if you are planning on even including 20ml of cooling liquid, you could just as well put a CR2032 battery in there, which'll power the thing just fine.
It doesn't suddenly become imitation if you came up with it on your own.
ThermalForce says price is available upon request -- so it may be available for sale as a custom order. There are some other interesting products at that first link as well.
More women should see example like these, it is a great example of woman in engineering kicking ass.
I'll state for the purposes of prior art that, if you can get enough power to add a little fan or other air-moving mechanism to the circuit to pull air through the tube/heatsink, it will operate in still air for as long as a human can keep it warm.
This opens the mind to a realm of interesting body-powered devices, especially in environments where heat sinking is easy, like for divers, motorcycle riders, and sailors. Want a wetsuit or jacket that lights up or operates sensors on its own? Easy peasy.
Why not just put the candles where the flashlight was in the first place? (or just put a reliable battery powered flashlight there.)
It sounds like it's saying "this flashlight should last long enough for you to find your better flashlight".
The interesting question for a science fair would be to see what she had learned of the science. Did she evaluate the efficiency of the Peltier device? (typically single digit percentages) Did she compute the amount of work you could do with different energy differentials? Coming up with the total joules available, versus the joules harvested? Did she look at the efficiency of the LED to convert energy into light. What is its lumens per joule rating, and given the choices did she look at single color light (say red) versus broad spectrum light via a 'white' LED (which is a UV led exciting phosphors to get different colors). Did she go over the various enhancement strategies (drop an ice cube in a hollow tube inside the light?).
And most importantly, given what she has learned about how one can convert a temperature differential into work, what other problems might she solve with that principle?
It is unfortunate that ExtremeTech goes for the link baitey angle "ooh a flashlight that works off body heat" and less on the "Hey if we teach kids real science, they can do stuff!" (which in my opinion is a better angle on the story).
I don't care about the use case or whether it works well. I care that it exists.
I found it a bit disappointing that they mentioned one use case as finding candles when the power is out, shortly after mentioning that it works only marginally at 50 degrees F. It takes quite a while for a normally-heated house to drop to that temperature.
It's a neat invention, no doubt, but the practical use cases for this particular version are going to be outdoors.
I'd have to work through numbers to guess, and do the experiment to be sure...
The consensus of the camping community seems to be that it's not worth it. Batteries + camping stove is easier/cheaper.
It usually isn't a good idea.
> I usually do not buy sexism in tech
So I guess you don't "buy" it because you don't usually see it, if only on account of not being on the receiving end of it?
Well you're the one who just had to note you don't buy sexism in tech.
However it's not difficult to find sexists pricks in tech.
Or online, or in public.
My objective in my project was to create a flashlight that runs solely on the heat of the human hand. Using four Peltier tiles and the temperature difference between the palm of the hand and ambient air, I designed a flashlight that provides bright light without batteries or moving parts. My design is ergonomic, thermodynamically efficient, and only needs a five degree temperature difference to work and produce up to 5.4 mW at 5 foot candles of brightness.
5 foot candles is about 54 lux.
30 to 50 lux is minimal illuminance for reading.
Practically speaking, however, I'm not sure that it would have any advantages over the flashlights that you crank for a while. Though perhaps those crank flashlights use a rechargeable battery that degrades over time, and this new flashlight would have a longer shelf-life? Though I should think a good capacitor instead of a battery would solve that potential problem with the crank flashlights.
will make quite a lot of light using a single NIMH AA that has been out of a charger for weeks (pushing ~ 1 volt...). It doesn't get you to 0 batteries, but it does a nice job of making light when you happen to realize you need it (without thinking about it in the interim).
Just from the headline, I said to myself, "sounds like some kid discovered peltier junctions and LEDs and the media decided to act like she's invented something," which was exactly right. Good for her, she's learning and experimenting, and that's a great thing, but let's not get carried away with our portrayal of how amazing it is.
Think back a month or so to the girl who "invented" a new way of charging cellphones in 30 seconds using capacitors. The sensationalism of that story was so over the top, I had non-technical people sharing the story with me on Facebook with breathless comments about what a genius this kid was and looking forward to this fantastic tech being available in all of our cell phones. Was it anything like that? No. It was a kid experimenting with well-understood technology and learning how things work, and there was no discovery or invention of anything non-obvious to any actual engineer. I don't want to detract from her industriousness or enthusiasm for learning, but when half the world is convinced she's done something notable enough to get her on the talk show circuit, something is wrong with the reporting.
I'm cool with A or C. B seems lame.
It might, however, be awfully useful in a stiatuion where there is no ambient light available at all, or where equipment needs to be light and very simply constructed. Perhaps something like in an emergency kit in case of a mine or cave collapse. Or in a situation with very adverse operating conditions, like a desert. Moving parts (as for a hand crank torch) would be a liability in an environment with omnipresent particulate contamination.
Could a 15 year old child invent safety equipment for the trillion $ mining corps. Of course not.
People with 4 year degrees in engineering have as much commitment and inventiveness as children and money to boot. Plus a fully developed brain.
As is always the case child age x invents new way to do blah, invents object blah they of course haven't.
As a tired cliche does it have a place on HN. Is this site aimed in part at children is the question?
We've know for years washing your hands in hospitals saves lives.
And we've know for years people are not doing it. Even just putting up signs helps an amazing amount, but even this isn't done.
Cause it's a really hard problem.
How does one improve the issue? Some hospitals are trying cameras, ranking deaths in hospitals, rfid tags tracking people making sure they wash.
I'm willing to bet even though the checklist above is pretty close to proven most hospitals don't use it.
The hypothesis was approached from both the theoretical and experimental side.
I'm thinking backup light source for camping, spelunking, power outages at home... just enough light to find a path when there is no other light.
Scientific measure of luminosity : 1 glimmer = 100,000 bleans. Usherettes' torches are designed to produce between 2.5 and 4 bleans, enabling them to assist you in falling downstairs, treading on people or putting your hand into a Neapolitan tub when reaching for change.
~ Douglas Adams and John Lloyd
All in all, very good invention! And also inspiring. I hope more teens will be involve in inventing things. I hope she wins. Also, (totally unrelated) I think she's cute. :)
1) a cool room at temperature T
2) enough light, L, to see by
3) a happy human at temperature H
Assuming that T,H, and L are fixed, you're going to use more energy with a less-efficient process. So, you'll 'spend' more energy to get there.
If you're trying to run the process at fixed energy, you're going to wind up accepting a slightly higher T. If that's the case, you'd be able to use even less energy by powering the LED directly and moving the setpoint for T up to that same temperature.
So to keep the temperature where you want it, you'd need to cool the room even more.
due to the temperature reliance of Peltier tiles, the flashlights worked better in colder temperatures (tested at 41 degrees Fahrenheit). The flashlight still worked in warmer temperatures (50 degrees, for instance), but the colder the surrounding temperature, the more the hand’s body heat can help the Peltier generate electricity.
It could be like a Fremen suit so they can pump the water coolant around and potentially and power electronics.
1. If it were not the case, then assuming ideal peltiers, you should be able to simply stack one peltier after another and get more energy than just one from the same temperature differential. And that's clearly crazy talk. If peltiers do not impede heat conduction, they must have some other limitation that prevents this from being the case.
2. Peltiers are reversible; a thermoelectric generator also acts as a thermoelectric cooler if you put current through it. So when you heat one side of the peltier and cool the other, generating a current, then that current should cause it to simultaneously act as a TEC (analogously to how counter-EMF causes an electromagnetic generator to resist as you turn it, essentially by turning it into a motor trying to turn in the opposite direction). That is, the very current you are generating will cause the peltier to transfer heat from the cold side to the hot side, with the end result that it would act as an insulator.
Edit: However, if I'm right about this, then assuming you can have efficient and flexible peltiers, it should work quite well for winter clothing.
So the current running through a peltier acting as a generator should actually transfer heat from the cold side to the hot side, making it act as a better conductor of heat. I don't know how to reconcile this with argument 1, but as far as my knowledge of thermodynamics is concerned, 2 has to trump 1.
So I figure I must be wrong, and peltier generators must conduct heat quite well. In which case I guess it would be good for summer wear - but then, in the summer, the differential between the human body and the surrounding air isn't all that great.
But even without pre-chilling (i.e. in the steady-state case), while you may be right that a TE device necessarily slows down the conduction of heat across a gradient, I don't think it follows that any such 'suit' would result in overheating rather than hypothermia.
Consider 2 people in a 70-degree (F) room. One wearing light clothing, and the other sitting in a tub of water. The water in the tub will equilibrate at somewhere warmer than 70 degrees, and the person will become hypothermic, since the capacity of their 'suit' to conduct heat to the environment is greater than the ability of their body to generate heat to compensate. You could have a TE device that extracted power from the gradient between the warm water and the room without saving the person from hypothermia.
That is to say, I think we're both wrong :): a well-designed suit could keep the amount of heat transferred within the range of the needs and capabilities of the human body.
(Fun trivia: according to Murray Hamlet, a US Army cold weather injury researcher, the leading cause of 'morgue wakeups' in the US is drug users who pass out in the bath, become severely hypothermic, and are wrongly declared dead).
Its a really nice idea though. Its stories like this that make me wish i paid a bit more attention in science when i was younger.
It would be trivial to put some circuitry in there to rectify the voltage so it works in either direction. No separate version required.
(changing ambient temperature is the obvious answer to my joke, btw)
Yes, I realize this was meant as a joke, but I'm still curious if current can be reversed by just changing the gradient. Does it still work but maybe it is less efficient? Is there no difference at all?
Sorry, could not resist. Great to see our youth being creative.