For my work on computer vision I needed an upgrade from my veteran netbook, so I don't have to spend most of the time watching the compilation for every little change in the code. I got myself an Asus U24E, and upgraded it with an i7-2720qm processor, 8Gb ram, and a ssd hard drive (thanks the guys at this thread for the tips on the upgrade).
Because the new processor dissipates more heat (45w instead of 35w), I was afraid of high core temperatures during the spanish summer.
With the original cooling, at a room temperature of about 18ºC, the cores quickly reach 85ºC at 100% load (junction Tmax is 100º).
I first tried to put some thermal paste and a fanless chipset-heatsink on top of the heatpipe, over the processor. This resulted in instantly lowering the temperature about 10ºC, but as soon as the sink got hot, it couldn't handle the dissipation of the heat just by natural convection.
|Test attaching a heatsink over the processor.|
So, adding any mass there wouldn't help.
Then I thought about adding a new heatpipe, as seen in many gamer laptops that have several pipes in parallel. I was lucky to savage two small heatpipes from an old laptop, that would fit perfectly in the space left at both sides of the actual heatpipe.
|Two small heatpipes savaged from an old laptop, next to the Asus u24e|
Of course, I would need to flatten and re-bend the pipes in the proper shape. I did it slowly, by gently applying some heat to them in the kitchen fire and with the help of a custom wood mold.
|Custom wood mold to help bending the pipes|
|Flattening the pipes|
I also made an extra support out of a cooper plate, to increase the heat transfer at the end of the pipes opposite from the processor; and a fitting to fill the gap on one side of the original heatsink (which wasn't properly soldered in the middle, but displaced about 2mm).
|Making the cooper support|
|Piece of cooper to fill the gap, just on one side.|
After reading this article about efficient cooling with heatpipes, that shows the poor result of a bad cooling configuration, I was afraid of getting an opposite result from my mod. So I did a preliminary test attaching the pieces with some nylon cord and putting a nice amount of thermal paste.
|New heatsinks held on place with nylon cord (I)|
|New heatsinks held on place with nylon cord (II)|
|New heatsinks held on place with nylon cord (III)|
The results were very satisfactory: with prime 95 the temperature took about twice as much time to reach a peak and it never went above 84ºC (without the mod it reached 85º after a few seconds).
So I got some thermal adhesive to make the thing permanent. Soldering would probably improve the performance a lot, but I didn't dare to do it, as the lowest melting point solder alloy (179ºC, alloy: SnPb 2%Ag), is almost the maximum recommended temperature of the heatpipes (180ºC).
|Mixing the thermal adhesive|
|Some pressure to keep the bond as thin as possible.|
|Detail of the fixture.|
Some lapping of the cooper plate in contact with the processor would also help, as there were some irregularities in it's surface. I noticed the thermal paste made an excellent polishing paste, used together with some regular kitchen paper.
|Irregular surface of the cooper face. There was a longitudinal line-dent in the middle.|
|The plate almost mirror-finished|
|The thermal paste ended up shiny as well.|
In my excitement I forgot to make pictures of the finished piece. But you can see how it looked like when installed. I had to flatten one of the pipes at the tightest point, to be able to put the board in place.
|The cooling mod finished and in place.|
|Detail of the tightest point between the memory banks and one screw's place.|
After the mod the temperature playing some very demanding games went down from 85ºC to about 73ºC. Not as cool as some gamer laptops, but lower than before anyway. We'll see how well it performs in the summer !