Now that i've been running my new Mac Mini for a week or so I have been testing it and stressing it to see what its capable of. It seems pretty happy transcoding 3 1080p H.265 streams at once but it does spin up the fan to full speed and maxes out at about 95c CPU core temp. I want to remedy this, one way would be to move the Mini to somewhere else in the house where it would get cooler air or just more airflow. However i can't do that at the moment.
I'm going to try make a cooling plinth for the Mac to sit on, I have a couple of new 120mm fans i can cannibalise to come up with something.
First step was to modify a fan to see if it was likely to work properly. The fan spec states 12V @ 300mA however i intend to run it from a standard 5V USB socket. Ohms law states that voltage is proportional to current. So with a bit of math: 0.3A/12 gives us 0.025A per volt, times that by 5V = 125mA. 5V*0.125A = 0.625W, so well within the power spec of USB. I soldered a USB lead directly to the fan and it works. Its turns slow enough to be silent but is big enough to produce decent airflow.
After that i cut the fan from its frame, i used a stanley knife, coping and jewellers saw to cut and shave the tough glass reinforced plastic shell.
To my surprise a 120mm computer fan is more like 110mm (blade diameter). This is a stroke of good fortune as i happen to own a 114mm hole-saw that i bought for running some extractor fan ducting some time ago.
I cut a hole in a piece of chipboard for the base, this will be sufficient to test my idea. The Mini will sit directly on top of it, having air pushed into its intake. I spaced it off the floor with some felt spacers to allow the fan to suck air from underneath.
I'll test the idea over the next few days.