How much heat can a heat pipe move btw?, can those small ones move say 30W away from the source?, so with 4 of those a full power 100W XHP70 can be cooled?
And can they handle the heat of being soldered into a copper block?
Other than active cooling with a fan, probably the best way to manage heat in a flashlight is unibody construction. That’s how Zebralight does it.
Most of our lights have a separate head and body. Heat conducts fine through the head, but gets to the transition between head and body and conduction is drastically reduced. The solution is to remove that transition. Use a single piece of aluminum for the head, body tube and LED shelf.
With unibody construction, the entire flashlight heats up at a much more uniform rate. Result is much more heat gets synced to your hand and the light can sustain higher outputs for its size.
Enderman, the way I read that equation above is different. I may be wrong, but I’m pretty sure.
First, the terms.
Q is the rate of heat transfer.
Qt is probably the theoretical heat transfer rate of the pipe.
Leff is Effective Length.
Le is Length of pipe in hot thingy
Lc is Length of pipe in colder thingy
Anyway. In the first equation in your post. Leff is in the denominator on the right hand side of the equeation. So, as Leff gets larger, it would make Qmax smaller. This means shorter heat pipes are more efficient. This is born out if you’ve ever looked under the hood of a PC and seen a strange octopus looking thing under the heat sink for the CPU. The heat pipes are very short in relation to the distance they are inserted in the heat source and sink.
This does not mean that longer heat pipes are bad. Or, won’t do the job. They are just less efficient.
I’ve mentioned this idea before, somewhere here
Q is just heat transfer.
Heat conductivity is W/mK, not just W.
If you have a short heatpipe then there is very little Le and Lc which defeats the purpose of having a heatpipe because your W/mK goes down and you might as well just use solid copper.
The advantage of heatpipes is several thousand W/mK, which is much higher than copper.
To get these numbers you need large Le and Lc, which means that the heatpipe is going to be long.
You cannot just put one or two centimeters of the end of a heatpipe inside your flashlight pill and expect it to do anything significant.
Many flashlights have quite a bit of space between reflector and head. It would be costly but the reflector could be integral to the head - cast as one piece then turned and machined. Then cooling fins could be either part of the mold or machined in afterwards.
The $39 Ray-O-Vac spotlight at the big box stores has a reflector with cooling fins and it looks pretty darn cool. Of course it’s done this way because the entire housing is plastic, and unfortunately the LED is potted in the reflector assembly.
I understand what you are saying. A longer heat pipe will have higher thermal conductivity than a short one. But, heat transfer is what I am interested in, not the thermal conductivity value of the pipe. I am constrained by the physical dimensions and temperatures that are common for this problem. So, Le and Lc are pretty much dictated to me. There is some wiggle room, since I will be making the components. I will experiment with values as I can.
I have seen claims for water/copper heat pipe thermal conductivity ranging from 40,000 W/mK - 200,000 W/mK. If I don’t use a heat pipe optimally, maybe its Conductivity will be 10,000 W/mK instead of 40,000W/mK. Everything has tradeoffs. 10,000W/mK is still way better than what solid copper gives at around 400 W/mK if I can move 50 watts of heat from under the LED die to the outside of the light.
Here is a water/copper heat pipe calculater provided by ACT, a company that makes them.
https://hpc.1-act.com/heatpipes/performance_form Here is their heatpipe design guide. https://hpc.1-act.com/resources/heat-pipe-design-guide.php
Give it a try. (The height against gravity box is finicky. If you keep clicking on it, it will eventually give in and let you put in a number.)
I plugged in L=2.36 and Le = Lc=0.5 with 0 for Height against gravity. (The length value is from the heatpipe I was looking at buying on ebay)
That yeilds pretty impressive results. A 6mm heatpipe moves almost 118 watts at 80C. If I can get half of that I will be thrilled!
Anyway, I’m going to give it a shot with some cheap ebay heatpipes. I enjoy the attempt and always learn something when trying out new things. Who knows. Maybe I’ll be shipping a new copper monstrosity down to the DBC compound that might let him keep one of those monsters on turbo a little longer.
If you just care about the watts then you might as well use solid copper because then there is basically no limit.
Heatpipes are for carrying heat far away, not an inch and a half from a flashlight shelf to the head.
You don’t need to explain how heatpipes work. I already own many.
Even with the flat ones which are easy to work with it’s not anywhere in the hundreds of thousands of W/mk.
Here is a simple example of a body that I could cast, then machine. The biggest problem with this type is the heatpipe has to be inserted after the light is assembled. Thus, it would not have a very tight fit with either the heat sink or the tail cap…crappy conduction at both ends.
Thanks for posting these examples. Looking at all that surface area for heat transfer, and not even finned like some other lights. Just imagine all that heat losing potential. Now seat a reflector to allow extra heat to be brought up to the bezel for more bleed. Maybe heat pipes looping between the head and reflector up to the bezel is too complicated.
Very interesting concepts here,can’t wait to see where the road turns and gets fast. 
I’m using the Ham’r mounted on a light stand bouncing out of a reflective umbrella (36”) for portrait lighting. Like with most lights used in this manner there is some heat but so far the big aluminum head is handling it quite well.
More is better, of course! 