Ducted Zalman 7000CU w/Countercurrent Flow Cooling

Do-It-Yourself Systems
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Once you have captured the heat from the CPU, it would be foolish to let it escape in the case, so it’s dumped to the outside. The photos below show how the cooler and ducted fan are integrated in the case.

Before the duct is fitted into the heatsink, the two big gaps between the left and right banks of the heatsink fins are blocked with foam. This is to force the airflow to go only through the fins rather than taking the shortcut that the gaps represent.

Note that there is a foam insert at the back of the case. This helps to minize the transfer of vibrations from the fan into the case. The foam block was also a way to make it all fit.

  1. First I built the duct, then mounted the heat-sink / duct
  2. Then I measured the gap between the exhaust end of the duct and the back panel.
  3. I then cut the foam-block to a thickness that would fill the gap.
  4. The foam-block was mounted using 2" long wood-screws inserted from the back (note: the foam-block still doesn't have the large hole in it).
  5. Then I marked on the foam where the Panaflo meets the foam block. (marks are visible in the picture)
  6. The case exhaust fan-grill and the fan in the duct did not line-up perfectly. Using the markings on the foam and the case's fan-grill as a guide, I cut out a slightly odd-shaped hole in the foam which compensated for the small differences.

The wires around the duct are for a sensor to read the CPU-exhaust temperature. You can see the three suspended hard drives, and the Nexus 120mm fan that replaced the stock 120mm Yate Loon fan in this case. The front bezel was Dremeled out at the sides to provide extra air-intakes.

On the outside, I installed a chimney with another Panaflo L1A on top to make a push/pull fan system for the CPU cooling; see below.

Although back panel was fitted with a 120mm fan, I used 80mm fans instead because "suction power" is closely related to RPM. Too low a fan speed means not enough suction. It takes some suction power to pull enough air through this ducted heatsink because there is a fair amount of impedance. I would rather have an 80mm fan @ 900 RPM than a 120mm fan at the same speed. An undervolted Panaflo 80L1A couldn't provide enough suction power, hence the second fan. Two fans working in tandem are preferable to a single more powerful fan; I believe it is as effective in moving air and quieter. [Editor's Note: Two fans in push-pull in-line mode provide more pressure than one fan; pressure in this case is akin to torque.]

Initially, the second fan was mounted directly on the back panel, but with only ~5cm between the fans, it seemed to result in very turbulent airflow and too much noise. This is why the additional elbow duct was added and the second fan mounted at the its end.

The whole rig has 4 fans:

  • Front case fan 'Nexus real silent' 120mm @ 6V
  • PSU modded with a 'Nexus real silent' 120mm fan, probably @ 5V
  • Two Panaflo L1A fans, working in tandem, @ 6V to suck air through the Zalman cooler

AMD's Cool'n'Quiet feature was disabled as the CPU could be undervolted at full speed. This CPU runs stable at 1.3V when it normally is supposed to run at 1.5V.

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