Saturday, 4 October 2014

The benefits of fan cooling on a CPU-cooler / TEC

I've been playing with my Peltier TEC cooler mounted on my ZWO ASI120MC astro-camera: http://julianh72.blogspot.com.au/2014/10/peltier-tec-cooler-for-zwo-asi120mc.html

Even though my CPU cooler came with a fan, I was hoping to get away with running it without a fan to avoid vibrations etc. However, even though I've been running the TEC at only 6 volts, I've noticed that sometimes the camera sensor temperature will stabilize at a Delta-T of about 12 degrees Celsius below ambient, but will sometimes then climb back again almost to ambient after a while, especially in warmer ambient air.

What I suspect is happening is this:

As long as the top radiator stays cool enough to re-condense the fluid in the Heat Tubes, it can pump heat away from the hot side of the TEC, and everything works nicely. However, if the top radiator gets too hot to allow the fluid to condense effectively, the Heat Tubes lose their ability to pump the heat efficiently, and the whole CPU Cooler assembly gets quite hot, and the TEC starts to heat up again, including the cold side.

It looks like my CPU cooler without a fan can pump the heat from the TEC running at 6 volts effectively as a passive device (no fan), with ambient temperatures of up to about 24 Celsius or so, maintaining a Delta-T on the camera sensor of around 10 to 12 degrees. However, at a certain critical heat load and / or critical ambient temperature, the fan-less CPU cooler can no longer shift the heat without the cold side of the TEC warming up again.

Since we are quickly approaching summer in Brisbane, and evening temperatures can stay at 24 degrees or more, I need to do something to maintain effective cooling - so I thought I'd put the fan on and see what happens:


The fan is rated at 12 volts, but since I'm running my TEC at only 6 volts, I thought I'd run the fan at 6 volts as well.

And the results?

Wow!

The fan runs more slowly than it does at 12 volts (no surprise there!), but importantly, it runs silently, and apparently free of vibrations (which is good!)

Secondly, the top radiator and copper heat pipes go from feeling warm-to-hot without a fan, to feeling quite cool to the touch - barely warmer than ambient -so the fan forcing is REALLY helping!

And with ambient temperature of 28 degrees, the camera temperature sensor dropped quickly from around 15 degrees (which was about the best I could do without a fan) down to just 2 degrees Celsius - and it stays there! That's a Delta-T of 24 degrees Celsius, compared to a (sometimes-unstable) 10 to 12 degrees that I was getting before!

I'll definitely be trying the fan-forced cooler outside next chance I get!