Electronics > Projects, Designs, and Technical Stuff
Thermal Management : How to go fanless in a small space?
IDEngineer:
Your photos look like FatSharks, complete with the RF module and dual SMA's. My son and I have thought a lot about actively cooling the interior of that enclosure. There's an existing fan for keeping the optics defogged but you're correct, the interior gets quite warm. On really hot days my son is aggressive about keeping them unplugged when he's not actively using them (most people just plug them in and leave it, since they don't have a power switch).
My suggestion is an externally mounted fan (just like the defogger on top) on one end with vent slots on the other end, to draw fresh air across the entire interior length of the volume. You could add some baffles if you want to favor cooling one area over another. But beyond this, I don't think there's enough volume internally to embed a fan inside the existing-sized enclosure.
I suppose you could reinvent the entire enclosure as some sort of futuristic heat sink with fins everywhere, but 1) the additional weight will anger customers, and 2) you still have the challenge of coupling the internal heat sources to the heat sink. Remember, your goal isn't to chill the AIR inside, it's to chill the COMPONENTS. If you don't thermally couple the latter to the former, the dead air inside will act as an insulator and you won't get much benefit for all the extra weight on your face.
Here's a wild concept: Do the fluid cooling that others have recommended, but make it a pocket or belt module to keep the additional weight out of the goggles themselves. Then combine the fluid coupling with the battery connection so users still only have a single connector to mess with. Many professional-level pilots (including my son) are already doing something like this, they ditch the headband battery for a standard LiPo pack in their pocket and use a "rabbit in the python" SMPS cable with an XT60 on one end to drop the battery voltage down to what the goggles expect. The result is a cable running from their pocket to the goggles.
EDIT: My son has discussed internal heat dissipation with the head honchos at FatShark, so they are definitely aware that their customers are sensitive to it. One of my son's goggles lost one eye's LCD due to what we believe was excessive heat, and the leadership of FatShark agreed it's a challenge. So you're in good company.
3roomlab:
--- Quote from: ebastler on April 27, 2019, 08:35:41 pm ---
I am truly curious about good (i.e. quantitative and simple) ways to estimate radiation and convection. If you have experience with such methods, could you please eleborate?
--- End quote ---
edit
I have updated the convection/radiation transfer method below
Marco:
--- Quote from: IDEngineer on April 28, 2019, 03:39:41 pm ---Here's a wild concept: Do the fluid cooling that others have recommended, but make it a pocket or belt module to keep the additional weight out of the goggles themselves. Then combine the fluid coupling with the battery connection so users still only have a single connector to mess with. Many professional-level pilots (including my son)
--- End quote ---
A pretty much dead silent slim 80mm PC fan will also move more air than anything you can put on the helmet. Presumably you'd just attach the heatsink and pump fixed with the headset and then connect the battery to the heatsink.
3roomlab:
(edit)
after several messy LTspice approaches to estimating the heat dissipation
here is the nearly scientific way
convective dissipation added to radiative
excitedbox:
Trying to think outside the box here. Could you stuff it full of a copper sponge type material (I had a copper foam type air filter once that I think would be perfect for this) and add vents at the top and bottom? The theory is that the heat rises out the top vents causing air current to move through the copper mesh which acts as a heat dissipation surface.
Experiment with different sized vents and amount of copper mesh to optimize the results. A very slow moving small fan should be possible with minor vibration though. If you have use the sponge idea you have a huge surface area and could blow a little bit of air from the side across the front of the PCB and out the other side.
https://image.ec21.com/image/changshalyrun/oimg_GC04161679_CA04161891/Copper-Foam-As-Filter-Element.jpg
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