DOES FINNING DISSIPATE HEAT?

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william lafferty

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Can someone comment on the issue of whether finning on flashlight heads and bodies actually helps the dissipation of heat?

FM put out a feeler for a finned body, but apparently nothing came of it. The thread is here http://candlepowerforums.com/vb/showthread.php?t=204829.

Also, Mac has a feeler out for custom heatsinks for C and D Mags. http://www.candlepowerforums.com/vb/showthread.php?t=239032.

If heat is really an issue with some of the new led's does finning the whole body/head really help, or would it be better to have a thicker body/head with no fins, in effect, using more metal to absorb more heat?

bill
 
Finning helps to dissipate heat because it increases the surface area of the body and therefore allows more heat to flow from it to the outside world.

Of course the heat needs to be effectively conducted from the heat-sink to the body in the first place.

Therefore the closer the contact between the heat-sink and the body and the larger the surface area between the heat-sink and the body, the better.
 
It does help. Any time you increase the surface area that's exposed to air it's going to improve heat transfer. The question then becomes does it help enough to be worthwhile? I'm interested to see what people have to say about this also.

Edit: easilyled beat me to it.
 
sure it does, that is why all air cooled bike engine cylinders are finned
 
easilyled said:
Finning helps to dissipate heat because it increases the surface area of the body and therefore allows more heat to flow from it to the outside world.
Click to expand...


But isnt it the case that more heat is dissipated by holding the light than by setting it on a table? If so, doesnt that suggest that static air circulating among the fins isnt very efficient?

Of course, if air is forced between the fins, as in a motorcycle engine running down the highway, then cooling seems likely to be more efficient. But if the engine is running down the highway, it is exposed to more air with or without fins.
 
william lafferty said:
But isnt it the case that more heat is dissipated by holding the light than by setting it on a table? If so, doesnt that suggest that static air circulating among the fins isnt very efficient?

Of course, if air is forced between the fins, as in a motorcycle engine running down the highway, then cooling seems likely to be more efficient. But if the engine is running down the highway, it is exposed to more air with or without fins.
Click to expand...

If you set a finned light on the table and compare it to a non-finned light on the table where all other conditions are the same, the finned light will lose heat more quickly.

If you hold a finned light in your hand and compare it to a non-finned light held in the hand, the finned light will lose heat more quickly.

However if you compare a light held in the hand to one on the the table then you are not comparing like with like.
 
william lafferty said:
Cnjl3 posted this interesting thread. http://www.candlepowerforums.com/vb/showthread.php?p=1378650#post1378650


Maybe I am reading it wrong, but doesnt the model in this thread suggest the opposite? That a finned head is less efficient at conducting heat, all other things being equal?
Click to expand...

Yes, its seems to be opposite to conventional wisdom in that particular example which seems to compare a grooved and non-grooved flashlight left to stand in a situation where there is no circulating air.

However I'm not sure how the test conditions were set up.

Were those real-life measurements or just predictions based on some sort of computer model?

Certainly its interesting and maybe its not as clear-cut as I thought and probably many others too.

However when a flashlight is taken outside (and not left on the table), presumably there is often a wind cooling the fins.

In addition, the flashlight will be held at the handle which may be some distance away from the fins.

The majority of the heat is still at the fins though, so I would presume that outside, finning can still be effective.
 
I hope modamag (Jonathan) pipes in here, he has definately done some research on thermal profiles. There was also some threads on this by NewBie (Jarhead), I'll have to find them.
 
socom1970 said:
I don't mean to be difficult, but this thread does not belong in BST. Nothing is being bought, sold or traded in it.
Click to expand...


The reason I initiated the thread in BST was that two items concerning heat dissipation were being offered for sale and were the subjects of this thread. I did not want to raise this issue in either of those threads because I thought that would hijack those threads. If the thread belongs somewhere else, so be it.
 
A finned object held in the hand, where the hand covers the fins, would get hotter.

Fins rely on air exposure to work.

Trap a pocket of air in them, underneath a hand, and you've just created an insulator rather than a dissipator.
 
No one holds a mag at the fins on the head.
It is always held at the handle which is quite some distance away in real life.
The area around the fins becomes hotter much sooner though than the handle.
It seems logical therefore that if the mag is being carried by the handle at night outdoors where there is some air circulating, for example wind, that the movement of the mag through the air will help to dissipate the heat better than if the head wasn't finned.
The linked thread seemed to be for a light where there was no air circulating and presumably indoors.
Unfortunately, I found it a bit vague in describing the exact conditions it was tested in.
 
I'm surprised this thread hasn't been closed or moved yet. It belongs in the General Flashlight Discussion or Homemade And Modified Lights
 
maxspeeds said:
I'm surprised this thread hasn't been closed or moved yet. It belongs in the General Flashlight Discussion or Homemade And Modified Lights
Click to expand...

+1

However on the topic at hand (whereever it ends up), when I think about all the various finned objects such as computer CPU & chip cooling blocks (with or without a fan), hot oil/water radiators, auto radiators, etc. they are finned.

There is not enough information in Modamag's thread to verify objective controls in his testing. I would not draw any conclusion between the two images in his post #10. It is interesting, but only to look at testing methods used.

Assuming no movement of finned head, and no ambient airflow, I can imagine there may not be significant improvement as the stagnant air acts like a pocket of insulation. However, that is not a realistic scenario for flashlights. There will always be some movement while a person is using them, and that should be the scenario being addressed.

If ambient air temp is cooler, the increased finned metal surface area will have more heat transferring contact with air.
 
Yes, in theory finning enhanced heat dissipation. But whether its effects are practically significant or not is another story.

With as much fins as the one in the 2nd link, I'd say it has a VERY GOOD chance to be able to noticeably improve heat dissipating.
william lafferty said:
Can someone comment on the issue of whether finning on flashlight heads and bodies actually helps the dissipation of heat?

FM put out a feeler for a finned body, but apparently nothing came of it. The thread is here http://candlepowerforums.com/vb/showthread.php?t=204829.

Also, Mac has a feeler out for custom heatsinks for C and D Mags. http://www.candlepowerforums.com/vb/showthread.php?t=239032.

If heat is really an issue with some of the new led's does finning the whole body/head really help, or would it be better to have a thicker body/head with no fins, in effect, using more metal to absorb more heat?

bill
Click to expand...
 
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