ZEN Radiator Cooler

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A promising technology but a flawed implementation. — Joe

SUMMARY: A promising technology badly implemented.


Dimensions: Top 85mm square, 70 mm high; base about 73 mm square; weight about 310 grams.

The good guys at Inflow Direct were nice enough to send a sample of the ZEN heatsink. As the cooling challenge increases, newer approaches are making their way to the market, and the ZEN is one of the more interesting.

The ZEN comes unassembled:


After you open the box, this is what you find; Heatpipe Radiator, two 60mm fans, mounting clips, screws and heatsink case. You also get instructions in Japanese, although the pictures are fine. I won’t say you need an engineering degree, but some mechanical ability won’t hurt.


The “radiator” is made from a heatpipe. It is a long vertical unit that is folded to make it compact. Cooling fins, such as you would see on a radiator, are interspersed among the folds to increase surface area for maximal cooling. The fluid inside the heatpipe is identified as “HFC-134a”, a fluorocarbon alternative. All told, an interesting design!


The bottom plate is nickel coated copper, 32 mm square – very shiny and lapped smooth.


The Radiator, fans and plastic socket clips are assembled into and onto the ZEN’s case.


The two brass bolts embedded into the case’s side are to attach the plastic socket clips.


The 60 x 15mm fans bolt onto both ends inside the case, one blowing in, one blowing out. The arrow points to a metal clip that pushes the radiator down onto the CPU. The fans are NMB 2406KL-04W-B59; this model is not listed by NMB, but the closest spec is 4600 rpm, about 18 cfm.


Looking down into the case, circled is the metal clip’s high point. The radiator’s base must be situated over this point, ensuring the pressure is exerted onto the CPU core.


This shows the whole thing assembled. Note the arrows on the fan casings are pointing in the same direction – one blowing in, one out. The radiator is not firmly held by the clips and case – it moves such that each time you mount the ZEN, the radiator will most likely be in a different position.


The clips are easy to assemble – just follow the pictures. The socket arm is articulated and you squeeze them onto the socket’s lugs. NOT EASY! I found this one of the most difficult heatsinks to mount. After the Simulated Die Test, I mounted it on an Iwill BD133u as I did not want to drill a hole into the side of the bottom plate until I had some pre-testing done.


After some difficulty, I mounted the Zen, only to find that I killed the CPU – I found a chip on one edge that did it in. There is a video on Inflow Direct’s site that shows mounting the ZEN by engaging one clip and rocking it to engage the other clip. I pushed down evenly on the ZEN to avoid rocking and tried to engage both clips, but it looks like the pressure I used was too much for the CPU.

I definitely do not recommend rocking the ZEN to mount it. The bottom plate is not large enough to contact the pads on an AMD CPU, and experience with other heatsinks demonstrated that rocking is a NO-NO. This is not an isolated incident – Overclockers Australia and this thread over at AMD MB Forum also speaks to this problem.

Some may ask why not use a shim? If a shim is necessary, it should be included with the ZEN. I tested it as it’s shipped, as purchasers would receive it.


I first tested the ZEN on the Simulated CPU Die. I ran the ZEN from 70 to 122 watts. I estimated what the ZEN would show with a thermocouple embedded in the base based on the average ratio observed during numerous heatsink tests between the Die and Heatsink Thermocouple – 0.7. I then mounted the Zen on an Iwill BD133u with some difficulty. After finally succeeding, the CPU died due to a chip on one side.

The two fans are not particularly noisy – I measured the noise level 8″ above the heatsink at 63 dBA – about the same level as one YS Tech 26 cfm fan. It is noiser if you measure sound directly in front of the fans – about 65 dBA.

Simulated CPU Die

Die Temp

Ambient Temp



Est. Heatsink C/W

Die @ 70 Watts

45.9 C

21.5 C




Die @ 100 Watts

57.4 C

22.8 C




Die @ 122 Watts

65.4 C

22.9 C




Delta = CPU temp – Ambient Temp
C/W = Delta / CPU Watts

Interpreting C/W: For every watt the CPU radiates, the heatsink will cool the core by the (C/W x watts) plus ambient temp. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that the CPU temp will be 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

Performance on the Simulator shows the ZEN to be very competitive; although lacking motherboard tests, the ZEN should fall into the top ranks of performance heatsinks.


Based on the CPU Die Simulator, the ZEN comes in at the low end of current heatsink tests. Not having tested it on a motherboard, this is only an estimate.

The mounting system is a terrible design and can lead to CPU damage. The radiator is “free floating” and will not consistently locate on the CPU at exactly the same point.

Spring pressure, combined with the bulky plastic clips, makes the ZEN very difficult to mount on a socket; mounting with a motherboard inside a case might be a daunting challenge.

Overall, the ZEN may hold some real promise IF costs come down significantly (retail is over $100) and mounting issues are overcome.

Thanks again to Inflow Direct for sending this our way.

Manufacturer’s website (Japanese)

Email Joe


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