trout
Enlightened
Which type of groove is the most effiecient for the use in a light heatsink
a Question about grooves
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Th232
Flashlight Enthusiast
All other things like orientation being equal, I'd expect the far left one due to the greater surface area created.
Edit: Brain fart, right, not left! Circular would mean less surface area. *bangs head on desk*
Edit: Brain fart, right, not left! Circular would mean less surface area. *bangs head on desk*
Last edited:
gadget_lover
Flashaholic
If this is a heat-sink that goes INSIDE a light, any grooves at all are detrimental. You want metal to metal contact to convey the heat through conduction. There is little to no air circulation inside the light.
If this is the outside of a light, then the squared off grooves allow more surface area, assuming that there will be enough air flow to remove heat. There are formulas that will let you determine high a fin of a certain thickness should be to maximize the heat transfer to air. I do NOT know the formula.
Daniel
If this is the outside of a light, then the squared off grooves allow more surface area, assuming that there will be enough air flow to remove heat. There are formulas that will let you determine high a fin of a certain thickness should be to maximize the heat transfer to air. I do NOT know the formula.
Daniel
HarryN
Flashlight Enthusiast
I would like to expand on gadget_lover's explanation if I might.
I am assuming that your flashlight is an LED version and you are trying to remove heat via thermal conduction to the outside of the body, where it is carried away by either conduction, radiation, or convection.
A surprising amount of the heat is actually removed from the light by conduction into your hand - up to about 10 watts. Your hand can be considered a sort of forced flow water cooling setup, which dissipates heat to the rest of the body. People think I am kidding when I say they should hold a cold drink in one hand if they are trying to remove more than 10 watts this way - actually, I am not. Somewhere around 15 watts going into your hand, the light will "feel" hot.
In terms of using the fins to enhance convection cooling, several things are important:
- Fin surface area
- Surface "smoothness" (contributes to flow stability)
- Design which helps get the heat out to the fin ends
- Design to avoid "dead flow areas"
The designs you have with curved bases are going to be better at moving heat from the body of the light out to the end of the fins (less thermal resistance). If your goal is to maximize heat movement, then this is better. If you goal is to have a fin design which has relatively poor conduction to the end of the fin "cooler to hold" then the flat bottom groove with longer fins will be better.
The flat bottom grooves will tend to form "dead" convection channels in those corners, which frankly, will further decrease heat transfer.
There are also radiative effects from the surface finish that are quite significant in some cases.
I am assuming that your flashlight is an LED version and you are trying to remove heat via thermal conduction to the outside of the body, where it is carried away by either conduction, radiation, or convection.
A surprising amount of the heat is actually removed from the light by conduction into your hand - up to about 10 watts. Your hand can be considered a sort of forced flow water cooling setup, which dissipates heat to the rest of the body. People think I am kidding when I say they should hold a cold drink in one hand if they are trying to remove more than 10 watts this way - actually, I am not. Somewhere around 15 watts going into your hand, the light will "feel" hot.
In terms of using the fins to enhance convection cooling, several things are important:
- Fin surface area
- Surface "smoothness" (contributes to flow stability)
- Design which helps get the heat out to the fin ends
- Design to avoid "dead flow areas"
The designs you have with curved bases are going to be better at moving heat from the body of the light out to the end of the fins (less thermal resistance). If your goal is to maximize heat movement, then this is better. If you goal is to have a fin design which has relatively poor conduction to the end of the fin "cooler to hold" then the flat bottom groove with longer fins will be better.
The flat bottom grooves will tend to form "dead" convection channels in those corners, which frankly, will further decrease heat transfer.
There are also radiative effects from the surface finish that are quite significant in some cases.
trout
Enlightened
Thanks Guys
it is for a bike light so forced air when moving and convection when stopped .
Cheers Harry you have made a lot of sense it is like the handle of a poker for the fire would have the square bottomed fins to slow the heat getting to your hands .
it seemed to me the curved fins looked right but the square fins looked to have the most area
so on that theme is the curved better for the forced air cooling also
it is for a bike light so forced air when moving and convection when stopped .
Cheers Harry you have made a lot of sense it is like the handle of a poker for the fire would have the square bottomed fins to slow the heat getting to your hands .
it seemed to me the curved fins looked right but the square fins looked to have the most area
so on that theme is the curved better for the forced air cooling also
greenlight
Flashlight Enthusiast
Tough to play with your flashlight with a drink in EACH hand.
HarryN
Flashlight Enthusiast
The difference in cooling rate for forced convection vs natural convection is so dramatic that it will wipe out any shape differences.
On a bike, of course the bike frame becomes part of the cooling system as well.
Technically, the best cooling is for the fins to be parallel to the flow, so when the bike is in motion - the fins front to back, but when it is still, the warm air rises, so fins up and down. I would design for natural convection.
I guess that goes along with some porcupine shaped cooling fin approaches.
How much power are you trying to move ?
