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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 flash

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.

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.