Looking for some guidance here. I've a project with a number of different elements inside a case. One of these elements is a HD video capture card which has a few chips which generate a fair amount of heat.
The project is going to be contained in an aluminium enclosure so I'm looking to use that to sink the heat. The target environment is going to be dusty so vents and/or active cooling aren't really going to work.
The distance from the chips to the enclosure is currently about 9mm. I've options to reduce that to about 4 - 5 mm by raising the card but that's the closest.
Could you attach a piece of U shaped aluminium channel to the enclosure so that it touches the chips? - assuming the fact that aluminium is conductive is not a problem.
Since you are trying to transfer the heat by conduction to the enclosure you are probably better off using a solid piece of copper rather than the aluminum heat sink. The fins on the heat sink are designed to increase free and forced convective heat transfer by increasing surface area for contact with air. For your application the fins simply reduce the amount of conductive material available to transfer energy to the enclosure. I would use copper because at the temps you are working with it has a significantly higher thermal conductivity.
It is a fairly easy exercise to calculate the rate of heat transfer and final temp of your chip based on the type of heat sink you use. Depending on how much heat you are dealing with, the finned heat sinks might be a good idea on the outside of the Al enclosure directly above the Cu sink.
If dust is a real problem then seal the box. You can circulate the air inside the box to transfer the heat to the box skin, which may have conventional finned heatsinks on the outside. The only problem with this is the fan motor probably puts out more heat than you started with.
If you can attach a heatsink directly to the chips and have that heatsink extend out through a portal in the box that's best. To get a good heat transfer by conduction, you have to have it really well-attached to the heatsink. Just a 0.1mm gap will greatly reduce the heat transfer. You can't really have the box be the heatsink unless you have a spring or something pushing the chips up against the heat transfer pads.
If you can get your hands on a high-powered laptop, then look for the heat pipes that transfer heat from the CPU and graphics chips to the heatsink. That kind of thing can be well-attached to a chip and to an output heatsink. Obviously you can buy heat pipes but they're usually a custom item for each individual device.
Maybe there's some kind of gel pad that will give you good contact between the chips and the box but still allow for some misalignment during final assembly. It's a common-enough problem that there must be commercial solutions available.
How big is this box? Can you adapt a PC watercooling system?