6 ms·

Wow, her dad is my coworker and I heard this casually mentioned at work the other day that his daughter was working with Peltiers and I should consult with her

Wow, her dad is my coworker and I heard this casually mentioned at work the other day that his daughter was working with Peltiers and I should consult with her because I am also working with Peltiers for characterization of phase change materials. 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.

deleted 13y ago
[deleted]
schiffern 13y ago
Wow, an encouraging comment on HN? Not assuming they're a moron?!?! You give me hope for this place. 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?
- ChuckMcM 13y ago
  Paraffin would be a good choice, although just putting a slug of copper into it and storing it in the freezer would probably work just as well. Of course you have to be able to find your freezer in the dark ...
  - schiffern 13y ago
    Heck, ice would be pretty good, and would maintain a large ∆T until it melted. Copper's a great conductor, but the specific heat is pretty poor: http://hyperphysics.phy-astr.gsu.edu/hbase/tables/sphtt.html http://hyperphysics.phy-astr.gsu.edu/hbase/tables/sphtt.html I guess it also depends on the relative importance of mass vs. volume optimization.
  - eksith 13y ago
    Paraffin would be excellent. In fact, wax + copper was such an excellent combination to pull away thermal energy, this was the same mechanism used on the NASA Lunar Rover : http://en.wikipedia.org/wiki/Lunar_Roving_Vehicle#Wheels_and_power http://en.wikipedia.org/wiki/Lunar_Roving_Vehicle#Wheels_and... 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.
    - samstave 13y ago
      Wouk the wax be in a copper tube, or would you have a copper tube/rod in the center of a pool of wax? 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?
    - schiffern 13y ago
      Careful now. The space-rover-cooling regime is substantially different from the handheld-Seebeck-flashlight regime. What makes sense in one place doesn't necessarily make sense in the other. Think of sink/source temperature, cost/mass/performance/reliability tradeoffs, air vs. vacuum, power requirements, etc.
    - tekromancr 13y ago
      That's how coffee joulies work! http://en.wikipedia.org/wiki/Coffee_Joulies http://en.wikipedia.org/wiki/Coffee_Joulies
      - Samuel_Michon 13y ago
        Except that, you know, they don’t actually work. Even the creators admitted to as much. http://boingboing.net/2011/10/26/coffee-joulies-review-the-effect-is-barely-noticeable.html http://boingboing.net/2011/10/26/coffee-joulies-review-the-e...
        tekromancr 13y ago
        T.T But the idea was so neat!
  - Ives 13y ago
    Does paraffin melt at body temperature? Not even core body temperature, hand temperature at a time when the air temperature is substantially lower. Maybe there's some way to lower the melting point of paraffin?
- pocketstar 13y ago
  Thanks, No doubt the fan would eat most of the power, thats just another engineering challenge to overcome. There doesnt seem like a better way without making the flashlight huge, then again the scale of power I am used to is an several orders of magnitude greater than what she uses, I probably have a scale bias. Im sure she could design an innovative passive and small heatsink. Idea: using PCM you could make a flashlight that you recharge in the oven.
  - schiffern 13y ago
    True, or by leaving it in the sun. 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. ;)
- solistice 13y ago
  I also don't quite think incorporating a fan into the design would increase it's efficiency. A quick google trip for PC Fan power usage gives me 1-2 watts for a 80mm fan. Small 5mm LEDs at 20mA and 3V should, calculated via rule of thumb, be at roughly 60 something mW. It just doesn't quite add up. 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.
LowKarmaAccount 13y ago
When I was in high school I looked into making a micro-power plant using the Seebeck effect for the Intel Science Talent Search. I thought about using liquid sodium as a heat sink, which is what some heliostats use. Solar power towers use the captured energy to power turbines, but this isn't very efficient, so I thought I would add thermoelectric generators to capture some of the energy that is lost as heat. 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.
- pocketstar 13y ago
  Yup, Seebeck is incredibly inefficient, as for RTG's in space I think they would rather use a Rankine cycle but that would be prohibitively too heavy to launch. 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.
  - sigkill 13y ago
    >Seebeck is incredibly inefficient 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.
dclowd9901 13y ago
Is it accurate to say the device would perform better in cold environments than warm environments, then?
- notdrunkatall 13y ago
  I believe that would be an accurate statement, yes, and it also would seem that the performance of the device would increase non-linearly.
notdrunkatall 13y ago
A heat sink yes, but a fan? The electrical output is already very low.
theshadow 13y ago
Shocked that the top comment is not just another one criticizing or trying to diminish something about the article/story.
temac 13y ago
A fan might be counterproductive, drowning too much current.
seabrookmx 13y ago
Greetings fellow Victorian.
- pocketstar 13y ago
  Victoria HN meetup? :D

deleted 13y ago

[deleted]

schiffern 13y ago

Wow, an encouraging comment on HN? Not assuming they're a moron?!?! You give me hope for this place. 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?

ChuckMcM 13y ago
Paraffin would be a good choice, although just putting a slug of copper into it and storing it in the freezer would probably work just as well. Of course you have to be able to find your freezer in the dark ...
- schiffern 13y ago
  Heck, ice would be pretty good, and would maintain a large ∆T until it melted. Copper's a great conductor, but the specific heat is pretty poor: http://hyperphysics.phy-astr.gsu.edu/hbase/tables/sphtt.html http://hyperphysics.phy-astr.gsu.edu/hbase/tables/sphtt.html I guess it also depends on the relative importance of mass vs. volume optimization.
- eksith 13y ago
  Paraffin would be excellent. In fact, wax + copper was such an excellent combination to pull away thermal energy, this was the same mechanism used on the NASA Lunar Rover : http://en.wikipedia.org/wiki/Lunar_Roving_Vehicle#Wheels_and_power http://en.wikipedia.org/wiki/Lunar_Roving_Vehicle#Wheels_and... 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.
  - samstave 13y ago
    Wouk the wax be in a copper tube, or would you have a copper tube/rod in the center of a pool of wax? 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?
  - schiffern 13y ago
    Careful now. The space-rover-cooling regime is substantially different from the handheld-Seebeck-flashlight regime. What makes sense in one place doesn't necessarily make sense in the other. Think of sink/source temperature, cost/mass/performance/reliability tradeoffs, air vs. vacuum, power requirements, etc.
  - tekromancr 13y ago
    That's how coffee joulies work! http://en.wikipedia.org/wiki/Coffee_Joulies http://en.wikipedia.org/wiki/Coffee_Joulies
    - Samuel_Michon 13y ago
      Except that, you know, they don’t actually work. Even the creators admitted to as much. http://boingboing.net/2011/10/26/coffee-joulies-review-the-effect-is-barely-noticeable.html http://boingboing.net/2011/10/26/coffee-joulies-review-the-e...
      - tekromancr 13y ago
        T.T But the idea was so neat!
- Ives 13y ago
  Does paraffin melt at body temperature? Not even core body temperature, hand temperature at a time when the air temperature is substantially lower. Maybe there's some way to lower the melting point of paraffin?
pocketstar 13y ago
Thanks, No doubt the fan would eat most of the power, thats just another engineering challenge to overcome. There doesnt seem like a better way without making the flashlight huge, then again the scale of power I am used to is an several orders of magnitude greater than what she uses, I probably have a scale bias. Im sure she could design an innovative passive and small heatsink. Idea: using PCM you could make a flashlight that you recharge in the oven.
- schiffern 13y ago
  True, or by leaving it in the sun. 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. ;)
solistice 13y ago
I also don't quite think incorporating a fan into the design would increase it's efficiency. A quick google trip for PC Fan power usage gives me 1-2 watts for a 80mm fan. Small 5mm LEDs at 20mA and 3V should, calculated via rule of thumb, be at roughly 60 something mW. It just doesn't quite add up. 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.

LowKarmaAccount 13y ago

When I was in high school I looked into making a micro-power plant using the Seebeck effect for the Intel Science Talent Search. I thought about using liquid sodium as a heat sink, which is what some heliostats use. Solar power towers use the captured energy to power turbines, but this isn't very efficient, so I thought I would add thermoelectric generators to capture some of the energy that is lost as heat. 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.

pocketstar 13y ago
Yup, Seebeck is incredibly inefficient, as for RTG's in space I think they would rather use a Rankine cycle but that would be prohibitively too heavy to launch. 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.
- sigkill 13y ago
  >Seebeck is incredibly inefficient 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.

dclowd9901 13y ago

Is it accurate to say the device would perform better in cold environments than warm environments, then?

notdrunkatall 13y ago
I believe that would be an accurate statement, yes, and it also would seem that the performance of the device would increase non-linearly.

notdrunkatall 13y ago

A heat sink yes, but a fan? The electrical output is already very low.

theshadow 13y ago

Shocked that the top comment is not just another one criticizing or trying to diminish something about the article/story.

temac 13y ago

A fan might be counterproductive, drowning too much current.

seabrookmx 13y ago

Greetings fellow Victorian.

pocketstar 13y ago
Victoria HN meetup? :D