# Thermal management optimization.



## Barbarin (Oct 27, 2004)

This is part of a post I have written on another thread, but I think you could find it interesting, and I will find to share your ideas.

"Thermal management: 

I have been always very concerned about the thermal management of the heat generated by the diodes as it can result on output loose if not designed properly. Most of the people won't use a flashlight more than 30 hours, and at that point won't be noticeable, but from just 100 hours you can detect even a 30% lumen if heat is not managed properly. The cooler the diode runs, the better, and the initial moment, when you switch it on is a critical moment on thermal stress. Heat is generated instantaneously on the die so you have to take it out as soon as possible. 
That is why I have designed a intercooler sandwich based on a thick pure copper disc, as copper is near double than pure aluminium, and double than alloys: 

Ag (silver) 420 W/(m K) 
Cu 400 W/(m K) 
Al 240 W/(m K) 
(Al, Si, Mg) Alloys 200 W/(m K) average. 

Of course a very important point is the joint between that copper disc and the diodes, but even using the best thermal epoxi (arctic) the conductivity of this compounds is 30 times worse than copper itself, arround 8 W/(m K), so we need to get this epoxi layer as thin as possible. In my case I have designed a simple tool wich press the diode against the disc with no less than 15Kg/cm2 during the curing process to make that heat barrier as thin as possible. 

Once the heat is on the copper disc it needs to be redirected to the flashlight body itself which in my opinion should be always made of aluminum alloys on diode based flashlights as thermal conductivity of other materials is quite poor when compared: 

Steel 45 W/(m K) 
Brass 85 W/(m K) 
Titanium 22 W/(m K) 

To get that trasnference as good as possible teh best way to do it to have the larger area, polished, with a interface material (micronized copper grease in my case) and to press it firmly to minimize the heat barrier. 

So once we have that heat on the head of the flashlight a good design to get it redirected to the hole body, and finally to surrounding air or water, is the key the have our porr diodes running as cool as possible. In my case I have done a large threaded area between head and flashlight body, with no o-rings at all, but thin compound, and thsi area is 125cm2. 

As a result the hole flashlight becomes warm quickly, and the temperature of the tailcap is similar to the head"

Javier Lopez


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## Doug S (Oct 27, 2004)

*Re: Thermal managemet optimization.*

Good advice here /ubbthreads/images/graemlins/thumbsup.gif


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## McGizmo (Oct 27, 2004)

*Re: Thermal managemet optimization.*

I agree that thermal consideratins are very important at the design level and assembly level. They are also very significant at the user level! Some designs are not intended for constant on operation. To use these lights in long runs is not friendly to the LED to be sure!

On comment you didn't hit on is that one sure way of dealing with thermal output is to minimize its creation in the first place! Efficient drivers and moderate drive levels are significant at the design stage, IMHO.


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## Doug S (Oct 27, 2004)

*Re: Thermal managemet optimization.*

More good advice. /ubbthreads/images/graemlins/thumbsup.gif


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## Barbarin (Oct 27, 2004)

*Re: Thermal managemet optimization.*

[ QUOTE ]
*McGizmo said:*
I agree that thermal consideratins are very important at the design level and assembly level. They are also very significant at the user level! Some designs are not intended for constant on operation. To use these lights in long runs is not friendly to the LED to be sure!

On comment you didn't hit on is that one sure way of dealing with thermal output is to minimize its creation in the first place! Efficient drivers and moderate drive levels are significant at the design stage, IMHO. 

[/ QUOTE ]

You are right 100%. Better optics, clear lenses, efficient driving and improved thermal management are more noticeable than a 20% overdriving. I'm sure a Lux III driven at 900mAh with a good optic and lens is brighter than same diode with a NX05 at 1200 mAh, consuming less battery and generating less heat.


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## greg_in_canada (Oct 27, 2004)

*Re: Thermal managemet optimization.*

How thick are your copper discs?

I've heard that a rule of thumb is to have a heatsink
thickness equal to the width of the contact area so
that the spreading resistance of the heat sink isn't
the limiting factor.

Greg


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## Barbarin (Oct 27, 2004)

*Re: Thermal managememt optimization.*

They are 46mm diameter, 2mm thick. 
On this case that rule is not exact as long as the disc is in contact with the flashlight body, laying on a wall 2 mm thick too. It's purpose is to take away heat as soon as possible to minimize thermal stress during firts moments. Once the body temperature is stabilized it does not mind if it is copper or alloy, then is more important the form factor and the capability to transmit heat to surrounding air or water.


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## greg_in_canada (Oct 28, 2004)

*Re: Thermal managememt optimization.*

Interesting. If you have a temperature probe it would
be interesting to compare the temp at the center of
the disk (on the back behind the LED) versus right at
the outside edge. A significant temperature difference would
indicate a high spreading resistance which would be
improved by using a thicker disk.

I'm not sure I understand your statement "It's purpose is 
to take away heat as soon as possible to minimize thermal 
stress during first moments." It will be a benefit for
any length of run time (after the 20ms time constant of
the Luxeon).

Here's the best article I managed to find on heatsink
spreading resistance (in a few minutes of searching):
web page. It even has a calculator.

Using the default number for the top parameter in the
calculator and your numbers of 400 for copper, 2 mm thick
and 46 mm diameter (and a guess of 5mm for the heat
source diameter), the optimum thickness comes out at
about 7.5 mm thick. Now this is for a finned heatsink
so after a while making the base thicker just reduces the
heat that can get to the fins.

For your case thicker will be better since it allows
more copper for the heat to pass through to get to the
flashlight walls. Once the thickness gets to be close to
or larger than the radius of the disk increasing the
thickness won't be of much help since the path to the
bottom outside edge of the disk is much further away
from the heatsource than the top outside edge.

Interesting discussion. I don't disagree with your approach.
But I do think thicker (up to 10 or 15 mm) would still
make a significant improvement.

Cheers - Greg


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## NewBie (Oct 28, 2004)

*Re: Thermal managememt optimization.*

Or you can evolve on to heatpipes, instead of using the technologies of the 1900's, and go with thermal transfer's which can easily reach 2,000 times better than even copper..... Yes, I know heatpipes became reality back in 1945, and saw wide adoption and use in the 1970's when they figured out how to make them highly reliable.


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## Barbarin (Oct 28, 2004)

Greg,

Of course the thicker is the better, but besides thermal considerations I can't forget that I'm designing a hand held light. 7,5 mm thick copper would increase too much the weight of the unit.
I like to imagine the paths as roads, and heat (excited atoms) as cars. We have a number of cars, if we don't want them too cloose one to each other we need a lot of road (mass of flashlight), better highway (copper or alloy) and ways as wide as possible. As long as I'm designing a flashlight I can not create the perfect intercooling desing, but I try to make that "roads" as fast as possible, always under main consideration which is in fact a hand held flashlight.

Take a look at this picture







What we can see is a overdimensionated threading on the body part next to the head. The purpose of this is the larger contact area to get heat transfered to body quickly to avoid "hot points". That threaded wall is 2mm thick, and if you add 2mm of the the body we have 4mm wide and enormous lenght (almost to tailcap). It happens that diodes are just over this cooling circle.

I have tried to make the best "cooling" flashlight, but first of all is a flashlight, not a cooling device. so some guidelines are fixed by other considerations other than thermal management.

Please don't be offended when I use this kind of language for kids when describing things, beacuse I try to write thsi for everypeople and modder... and pleae excuse my poor english when I translate my technical thoughts to english.


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## Barbarin (Oct 28, 2004)

*Re: Thermal managememt optimization.*

[ QUOTE ]
*NewBie said:*
Or you can evolve on to heatpipes, instead of using the technologies of the 1900's, and go with thermal transfer's which can easily reach 2,000 times better than even copper..... Yes, I know heatpipes became reality back in 1945, and saw wide adoption and use in the 1970's when they figured out how to make them highly reliable. 

[/ QUOTE ]

Heat pipes are a very interesting concept to add on a flashlight, but if I want to make flashlights and to keep them under the 1000 bucks barrier.... Of course there is a possibility of adding this interesting feature without costing a leg or an arm per unit, but it is not for me by now, as I'm making a few hundreds flashlight series, and it would mean at less a few thousands.

I still like that idea, and I'm sure it could find its place on a overpowered or multiLED compact lighting device, but not on a "conventional" flashlight. I think it would allow 2 Amps or higher on a LUXIII with propper design.


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## greg_in_canada (Oct 28, 2004)

[ QUOTE ]
*barbarin said:*
Greg,

I have tried to make the best "cooling" flashlight, but first of all is a flashlight, not a cooling device. so some guidelines are fixed by other considerations other than thermal management.

Please don't be offended when I use this kind of language for kids when describing things, beacuse I try to write thsi for everypeople and modder... and pleae excuse my poor english when I translate my technical thoughts to english.


[/ QUOTE ]

I understand. 

That looks like a very nice light you have 
created.

Greg


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## cy (Nov 18, 2004)

just revisited this excellent thread on thermal management and Barbolight U-09. 

Got an U-09 en route, looking forward to results. Going to be interesting! should produce 200+ lumens if thermo management stays under control.


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## NewBie (Nov 18, 2004)

*Re: Thermal managememt optimization.*



> *barbarin said:*
> 
> 
> > *NewBie said:*
> ...



Actually, you can get the heatpipes in the 2-3 dollar range.


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## aosty (Apr 4, 2006)

*bump* to re-index thread


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## gadget_lover (Apr 4, 2006)

I'm afraid the "re-index" does not seem to work. A search for "heat pipes" had no matches.

You might be able to do it by listing all the keywords. Let's see if "heat pipes" matches now?

- -- 

EDIT:


Yes, it matches. This leads me to believe the new posts will be indexed, but the old ones are not. SHEESH! What a bummer.

I suggest that as we bump posts to the top we list all the keywords that make the thread valuable.

I gotta do that to the 'silly newbie tricks' thread? Groan.

Daniel


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## aosty (Apr 4, 2006)

Good point... I mistakenly assumed it was smart enough. :sigh: 

heat
thermal management
copper
aluminum
silver
heat pipes
conductivity
transfer

:touche:


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## NewBie (Apr 7, 2006)

Thanks for digging it out!

There are some older posts I made about heatpipes that go into more detail and depth, but alas, they are lost in the halls of the CPF vault.


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## Ken_McE (Apr 16, 2006)

Barbarin said:


> "Thermal management:
> 
> I have been always very concerned about the thermal management of the heat generated by the diodes as it can result in output loss if not designed properly.... The cooler the diode runs, the better, and the initial moment, when you switch it on is a critical moment on thermal stress. Heat is generated instantaneously on the die so you have to take it out as soon as possible.



If you want to reduce the thermal shock associated with starting up the LEDs, how about if you ramp up the power gradually, rather than going directly from zero to full on?


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## cy (Apr 16, 2006)

an excellent old thread worth revisiting..


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## amanichen (May 2, 2006)

I don't know if this thread is still open for discussion but...

I see talk about heatpipes as some miracle of cooling: heatpipes work best when vertical, because the force that drives the flow inside is mostly gravity. Capillary fibers/structures are incorporated into many heatpipes, but this doesn't mean they'll work when horizontal. Motion of the fluid within the tube isn't a good thing either: carrying a flashlight would most likely disrupt the flow of mass and heat within the tube.

Integrating a heatpipe of practical length into a flashlight would be difficult. Another consideration is that for them to work properly, you must get the hot surface up to the boiling point of the fluid within it. One must *carefully* select the fluid and pressure to be used to match the expected heat load, and ambient temperature. A heatpipe designed for use in one ambient temperature might not work at all in others, because conduction and convection to the surroundings might keep the fluid beneath its boiling point. You can also have the opposite problem, where the fluid never gets cold enough to condense (i.e. ambient temperature is above the fluid boiling point.)

I'm not saying it's impossible, just extremely difficult without placing certain constraints on how the light is used.


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## gmeyer4 (May 3, 2006)

Just to be clear about the use of heat pipes and their function. Heat pipes are made of three parts, the housing which is generally copper, the working fluid which is generally water and a wick structure that lines the inside of the tubing. A water heat pipe will work at temperatures as low as 10 or 20 degrees C. This is due to the fact that the water is under a vacuum and will vaporize when heated at very low tempertures. Once the change of state occures there is a change in volume causing a positive presure at the evaporation point. This positive pressure causes the vapor to move away from the area of evaporation taking with it it's latent heat. This vapor will condense on any surface that is cooler than the temperture of the vapor. Here is where the wick comes in. Now you have condensate that needs to be moved back to the area wher the heat is being applied. The wicks are designed to use cappilary action as a pump to move the liquid. Most wicks will work a few inches against gravity and other will work 6, 8 or 10" against gravity. The operating window for this type of heat pipe is wide enough for almost any electronics application. Take a look in your laptop, your xbox.

The question is not if a heat pipe will work in this application but do you need it.

By the way, heat pipes are manufactured today in huge volumes for the computer market and the price the OEMs pay for production volume is on the order of $0.75 each for 6mm diameter and 150 to 250mm lengths.

More info you you would like.

George


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## amanichen (May 3, 2006)

gmeyer4 said:


> The question is not if a heat pipe will work in this application but do you need it.


I'll have to disagree with you here. Yes, it is first a question of will it work.

Heatpipes act as energy-mass transporters and are not necessarily good heat exchangers to air. Remember, any energy transported by a heatpipe still needs to be convected away. Any heat load above a couple of watts on a heatpipe means you need cooling fins on the end of it -- the copper tube alone doesn't have enough area. In a flashlight, using a big heatsink on it would be silly, because you generally already have a large metal body of sufficient mass and surface area to act as a heatsink.

Again, heatpipes work best when vertical, and when motionless. If you don't believe me, take a look at "Results and Discussion" on Page 2 of this experiment, where it talks about dryout: http://www.dodsbir.net/Sitis/view_pdf.asp?id=AF05-184Ref3.pdf

Capillary action can only provide so much performance when they're horizontal, and any motion of the heatpipe itself can disrupt the delicate flow pattern that's created, further reducing performance. A certain amount of sloshing can slightly increase performance, but only if it's done in a very specific manner. Most flashlights experience erratic motions and accelerations when in use. Heatpipes are great for stationary applications where you have a constant heat load and a small range of expected ambient temperatures.

Again, not impossible, you'd just have to place certain limitations on the flashlight use, and design the light from the ground up to use heatpipes. Both of which would be impractical for any lighting source that you would want to be able to carry in your hands.


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## gmeyer4 (May 3, 2006)

[font=&quot]Yes, absolutely correct, heat pipes primarily act as a transport mechanism and added heat exchange mechanism is required to get rid of the heat either by added surface area or air flow or even the exchange of heat to the person’s hand. [/font]

[font=&quot]There are many types of heat pipes and most of them will exhibit large performance variations with changes in position. The key point is that the heat pipe needs to be designed for the application. The wick structure needs to be designed to work within the requirements of the application. For many, many years heat pipes have been used in military electronics applications where there are wide temperature extremes, shock and vibration and orientation insensitivity demands. Properly designed these heat pipes performed to specification for 10s of thousands of hours with no change in performance. [/font]

[font=&quot]Please, I am not trying to be a smart_ss. I have worked in the heat pipe industry for over 30 years. I have designed, built and tested heat pipes for all types of applications, military, consumer, solar etc.. I have just applied for my 10th patent in this field. I have designed, built and run heat pipe production facilities in Taiwan, Korea and Mexico. Heat pipes and heat pipe applications are my forte’. I also am very much involved in the thermal management of LED’s for general illumination, automotive, backlighting and even headlamps for bikes.[/font]

[font=&quot]We agree, the limit for this application is the heat exchange portion of the design and that getting rid of the heat is the challenge.

Before you ask, the heat pipes used in the consumer electronics market today are a direct result of many years of SBIR funding and military applications. The design you may find in your Dell notebook is almost identical to the design used in Martin Marietta's night vision system and target acquisition system that hung in pods under the winks of F15 and 16 aircraft. Yet today they are selling for under $1.
[/font] 
[font=&quot]George[/font]


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## amanichen (May 3, 2006)

As a mechanical engineer, I also have an interest in heatpipes. I'd be more than happy to look at your patents, especially those which apply to heatpipes that will work effectively on erattically moving objects. By this, I don't mean harmonic motion or regular vibration with an occasional shock. I mean something like a flashlight, which will be randomly dropped, shaken, and oriented in a way that the fluid goes away from the hot end, effectively stopping the phase change, and disrupting the fluid and vapor flow patterns.

Again, I'm not saying it's impossible, just that there's too many limitations for it to be practical.


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## McGizmo (May 4, 2006)

Cool you thermal gurus! Keep it coming!! :thumbsup:


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## NewBie (May 4, 2006)

Humm...where to start, there is so much dis-information.

Getting the heat to the body of the flashlight, and spread across the length of the flashlight body with a heatpipe, which can have up to 2000x the thermal conductivity of copper, will go a long way towards removing heat. (takes better advantage of the surface area of the flashlight)


Most modern heatpipes are not just some liquid in a simple copper pipe. They contain capilary structures which will actually "pump" the liquid back to the hotspot, even upside down. Sometimes this takes the form of very fine grooves in the internal walls, a copper wick that is fused to the walls, and a few other methods. Each has it's advantages for a particular application.


I have a number of heatpipes that work nearly as good upside down as they do rightside up, and I can hardly tell the difference at all when they are sideways. 


This being said, not all heatpipes are created equal.


Some heatpipe designs work pretty good when bent on a radius, some not so well. Though, most modern heatpipes are designed to be bent, so the issue then becomes how tight of a radius and how much do I loose.


Keep also in mind that the dryout condition was with +137Watts input...

And they are using a heatpipe with an evaporator wick and condenser setup, which is a whole different ball of wax...as compared to what you typically find in consumer goods these days...things have evolved rather rapidly...

And, "dryout was not encountered for 35C"

And can you imagine trying to maintain a 9.8G loading continously??? Do you plan on operating your flashlight while you are on a centrifuge operating your flashlight at 9.8G, then shaking it vigrously at the sub 1Hz frequencies at the same time, and at the same time, using an LED that makes 137 Watts of heat?

Conversely, notice with the heatpipe type they had, with a specific condenser and evaporator assembly, as the frequencies increased, they actually found better performance.

But still, they note, with no acceleration, the heatpipe dealt with 150W just fine. Okay, so with a very specific single controlled frequency input (not a condition that is typically found in the real world), you could see a slight decrease in performance due to dryout if you also had several other conditions at the same time, and put in over 137W. Swell, keep the heat source down below 100W...

Sometimes the obvious solutions escape the blind.

Unfortunately, portion of the final analysis is cut off...


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## amanichen (May 4, 2006)

NewBie said:


> Most modern heatpipes are not just some liquid in a simple copper pipe. They contain capilary structures which will actually "pump" the liquid back to the hotspot, even upside down. Sometimes this takes the form of very fine grooves in the internal walls, a copper wick that is fused to the walls, and a few other methods. Each has it's advantages for a particular application.


Are there any which completely avoid fluid sloshing and dry-out, and maintain their ability to cool?



> I have a number of heatpipes that work nearly as good upside down as they do rightside up, and I can hardly tell the difference at all when they are sideways.


What applications are they installed in? Are these stationary, or moving errattically? I'm interested in your test results for said heatpipes. You even say "not all heatpipes are created equal," which seems to contradict your implication that just because your small selection of heatpipes pipes works in multiple orientations, all heatpipes in general, work equally as well when horizontal as when vertical. Which statement are you trying to make?



> And they are using a heatpipe with an evaporator wick and condenser setup, which is a whole different ball of wax...as compared to what you typically find in consumer goods these days...things have evolved rather rapidly...


I'm just asking for someone to show me a heatpipe, a patent for a heatpipe, or ANY BIT of experimental evidence on a heatpipe that prevents sloshing and dryout under errattic movement.



> And can you imagine trying to maintain a 9.8G loading continously??? Do you plan on operating your flashlight while you are on a centrifuge operating your flashlight at 9.8G, then shaking it vigrously at the sub 1Hz frequencies at the same time, and at the same time, using an LED that makes 137 Watts of heat?


My point was to prove that dry-out and sloshing were problems. I linked to this document in case nobody believed me that they were, and it seems that everybody here is still missing the point.

*Once again, the big picture I'm trying to paint here is that they're impractical for use on flashlights. I'm not saying it's physically impossible. I'm saying the mainly horizontal orientation, combined with errattic motion causing sloshing and dry-out will make them impractical.*



> Sometimes the obvious solutions escape the blind.


Sir, there's no need to talk in a condescending manner. Lets keep the discussion on heatpipes.


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## NewBie (May 4, 2006)

amanichen said:


> My point was to prove that dry-out and sloshing were problems. I linked to this document in case nobody believed me that they were, and it seems that everybody here is still missing the point.



I think the point you are completely missing is that heatpipes come in many forms and construction methods. Just because one contruction method has issues under a certain environment, does *NOT* mean that all construction methods will have the same problem.


You will find that the heatpipes used in laptops, which are used on the go (vibration etc.), and are actually employed in a sideways (horizontal) fashion, bent usually several ways, deformed from round, don't have a condenser on one end and an evaporator on the other.

With the capillary structure from one end to the other, and all along it's length, you can even put the heatsource (or the cooling area/fins/plate) in the middle, or along a whole portion of it.

If you buy some of the ones you find in laptops, when you shake it, you will even find there is no sloshing liquid. The capilary structure is saturated, but no additional liquid is inside. In fact, the evaporator and condensor structure are one the same in these heatpipes. It is the capilary structure itself that serves as the evaporator, where the water boils off under the vacuum, in the hot area. Now, this hot vapor, carrying the heat with it, goes to the cooler area in the heatpipe and condenses on that area. The structure it actually condenses on, is that the same capillary structure, which- in this type of heatpipe, runs from end to end. The nifty thing is, that capillary structure that it evaporates from and condenses on, is one and the same, and so it is automatically captured by nature. 

This prevents this sloshing issue you are talking about in these types of heatpipes. 

These heatpipes which are used in laptops/heatsinks have *extremely* thin walls, a very fine capillary structure, and are very low mass. And do get into the under one dollar range, mine cost me 2-3 dollars, depending on which size (diameter and length), due to the fact I only purchased a few. 

You will find that in laptops, the heatpipe orientation is horizontal...

Did you know the Space Shuttle uses thousands of heatpipes? They are found in a wide variety of areas, and not only in the electronics. 


In reality, heatpipes are definitely suitable for use on flashlights and work *great* in a horizontal application. I do have a prototype flashlight I built three years ago which has heatpipes in it, and they do a very awesome job, sideways, upside down, when shaken, and especially work great for transporting the heat from the LED to a human hand. They also do a great job of spreading the heat down the length of the flashlight, even when I orient it horizontal or upside down.

Thats why I have recommended them several times since I showed up here in 2003 (I used to have a different account, search for Jarhead).


Some specs on heatpipes can be found by going here and clicking on the text below the heatpipes of different diameters:
http://www.avc.com.tw/products/oem/nb thermal-products/index--b.html

Another manufacturer and specs:
http://www.acktechnology.com/Heat Pipe.htm

Places to learn more:
http://www.cheresources.com/htpipes.shtml
http://www.lanl.gov/orgs/esa/epe/Heat_Pipe_Site/ancient4.html#Cott_65
http://www.transterm.ro/overview.htm


Other interesting cooling technologies:
http://www.stanford.edu/group/microheat/hex.html


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## Seth (May 4, 2006)

What a great thread!

Now, besides the heatpipe- /no heatpipe-discussion, there is another interesting trend.

As usual, the guys who overclock CPU´s created it 

Judged by the reviews at several computer-magazines, thermal interface materials like arctic silver will become obsolete.

The new "trendy" TIM seems to be liquid metal, like this one: Coollaboratory TIM 

Seth


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## NewBie (May 4, 2006)

Seth said:


> What a great thread!
> 
> Now, besides the heatpipe- /no heatpipe-discussion, there is another interesting trend.
> 
> ...




Unfortunately, this material only shows a 4C difference verses artic silver, when you have ~100W (the delta would be much less, with a 5W LED, you'd only be looking at an improvement of less than 0.2 Celcius verses artic silver):
http://www.frozencpu.com/images/products/detail_secondary_hires/thr-26_5.jpg


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## HarryN (May 5, 2006)

That is an interesting material - possibly a Ga alloy. I noticed it is not recommended for use with Al, which is a bit of a pain for this market.


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## xiorcal (Jun 16, 2007)

*Re: Thermal management*

Seeing as this thread has resided on the exact topic of my question, I hope I will be forgiven for digging up an oldie...

Has anyone gotten around to using heat pipes in the body of an (LED) flashlight to spread heat to the grip/body, from the head? (I am guessing this would be completely futile in an incan.)
I am interested in their use for spreading heat, and would be grateful if anyone (* newbie*) could suggest a general cost, or retail supplier for acquiring them.

I am also interested to know if anyone has had experience with http://www.novelconceptsinc.com/heat-spreaders.htm
Particularly of interest are their "Die Level Heat Spreaders", apparently able to spread 3W per square mm of heat evenly over the entire surface of the spreader.

I'm thinking thermal-epoxy an emitter onto them, then thermal epoxy them onto a piece of copper just thick enough to drill some holes to insert the round-type heat pipes in far enough to reach their effective point, and run those cylindrical pipes down the length of the flashlight.
Then again, this is going past the point of normal heat-synching which could possibly be surpassed simply by epoxying the emitters on the DLHSs instead of onto copper. Perhaps the spreader could be epoxied in turn onto a copper sink, although I'm not sure how many junctions epoxy is good for before you start losing the benefit.

I wonder if there is a way to lay hands on these "Novel concepts"..

It would be good if someone with some thermal/fluid engineering expertise could check these out, as they look good to me, but I've got no clue if my thoughts are correct.


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