My "fans" want to know: what's the thermal impedance of dust?

6/4/2010 12:00 PM EDT

Some web searching among the vendor and independent forums revealed that this PC family, and many others, suffer from a marginal cooling design: the fan, airflow duct, and heat-sink assembly were working pretty hard to keep that small-ish CPU cool (there is another fan for the power supply, but it seemed to be much quieter).

There were plenty of suggestions on what to do:

• Get a "better" fan, one with double ball bearings; but since the high noise level seemed to be due to air-flow volume and speed, and not the fan's bearings, this didn’t seem to me like a worthwhile choice
• Get a quieter fan, with a better blade design and thus a quieter airflow vortex; this might be a good idea–except that the vendor used a non-standard connector and pin-out, so some rewiring and splicing would be needed
• Get a bigger, better heatsink; or a heat sink that uses liquid cooling; or install a heat sink that has a heat pipe to pull the heat away more effectively; while a good suggestion, there would be mechanical and mounting challenges here
• Put the entire PC in another room (!) or in a noise-tight box (um, what about the airflow and likely overheating then)?
• Add a quiet fan on the outside to assist the internal one; while perhaps a little counterintuitive, the second fan might allow the internal one to run slower and thus quieter
• Put sound-damping foam pads inside the PC (sound at auto-supply stores, among other places); this seemed to me to offer only marginal improvement and would impede whatever radiational cooling there was
• Clean the existing heat sink and air-flow paths of any dust buildup.
• Learn to live with it

But the more I thought about it, the more I wondered if the design weakness is not just a poor cooling strategy which relies on a substantial airflow volume. If the design also requires the average user to open the case every few months to vacuum out the interior, that's not good. Maybe an external, removable air filter would be better (yes, it adds cost, and may reduce nominal airflow)? Or perhaps the design should rely less on forced air, and more on unforced convection cooling, plus better conduction and radiation cooling?

It's a difficult set of design and cost tradeoffs, for sure, but the one that this major PC vendor choose seems to me to have been the weakest one for a low-end PC and CPU: loud, maintenance-intensive, and marginal performance.

But the entire situation is a dramatic demonstration of the thermal impedance and subsequent impact of common household dust, and I won’t forget it. Next up: clean the coils on the air conditioner and refrigerator–it's the same problem in a different guise! ♦