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Performance of cape cora HF 642 ?


New member
I'm looking to put my PC inside my desk (unused drawer) and I'm considering using cape cora HF 642 passive radiators.
Since I have a relatively powerful PC (CPU : 140W, GPU : 250W considering to upgrade to a 3090 witch has an announced tdp of 320), I want to check the dissipation heat of this radiator (could daisy chain 3 or 6 of them) is sufficient for that or not and couldn't find any info.
Room temperature ranges from 18°C to 24°C in the summer.
Is that something realistic to consider?


Staff member
3090 has 350W TDP and one of the passive tubes can cool about 40-50W. So you can calculate yourself how much you need.


New member
I imagine that such a solution requires a high flow rate pump. Any recommendation on that? (I have a dual EK D5 pump rated for 1500L/h at max)
Would making 2 separate loops, 1 CPU, 1 GPU be better ?


Staff member
Makes no real sense to make two loops. Only if you have 3-4 GPUs, than it would make sense but not with one CPU and GPU.


Staff member
Each rip of the cape cora can move 10W heat. This is not much compared to the TDP of the new graphics cards.


New member
Not quite sure what you call a rip. (And now, also what you call a tube in your first post) EDIT: didn't see that it was someone else posting. As I understand,, the cape cora 642 is composed of 6 tubes and the 142 is just one tube. Did I understand it correctly?
If that's the case, then it's ok since I can install two 642 and four 142 on the side of my desk, for a total of 16*40=640W heat dissipation.
EDIT: Or is finally one tube only dissipating 10W?
Last edited:


New member
10W seems like a quite low number considering the amount of aluminium in each module...

I have 10w Raspberry Pi's colled with quite small heatsinks...

Are you guys sure each module dissipates just 10w?

I have 30 modules at the moment sitting around, and was considering building a custom case "made" out of them. My biggest concern is the plastic water links and endcaps.

BTW, LtZeouk, I would advise against mouting the 642 Cape Coras with a dual EK D5 setup. I did mount 24 of them like that, and the endcaps poped off due to water preassure, almost cooking my system.

AlphaCool, do you guys plan to have threaded mounts for these rads?



New member
Found my post from 10 years ago on silentpcreview:

I just wanted to share my newest build - happens to be my first custom watercooling rig.

However, my quest was to get high end performance, but silent.

I already have enough fans in several SuperMicrO server cases that would cause OSHA to demand hearing protection if I left them on all the time!
I've already been down the big heatsink/quiet fan routes and that just wasn't enough ... or maybe is was just a challenge to see if I could make a silent performance rig.

So watercooling looked to be in my future, but not with traditional rads that require fans to push/pull and get back to the noise factor.
This led me to researching Zalman external solutions and finally to come across the AlphaCool Cape Cora passive radiators. There are only a few reviews of them online, but each reviewer was amazed at their totally silent, convective performance.

But what case to start with? Most cases still had and needed some airflow through them - resulting in still having fans. Ultimately, any case I got would just be a standing block for the AlphaCools so I decided to make the Cape Cora components rigid which would become my case!

After a couple of months tinkering with drawings, both OO-Draw and then Google Sketchup, I think I had a design that would house my components and yet provide enough convective flow for the radiator cooling.

Then I came to an impass... originally I wanted no moving parts in the box: SSD, fanless coolers on the video card and CPU... but with water, that meant a pump! Pumps have moving parts, moving parts make noise. grrrr
On top of that, I realized that with the EVGA Hydro Copper2 GTX580, I would theoretically be over the 460W limit of a Seasonic fanless PSU!

CRAP! it's gonna have moving parts after all!

With really no design modifications, I chose the Seasonic 850W that is fanless at low power (idle) and then only spins the fan as needed under load. And when it is used, its position draws additional air over the memory and mosfets around the CPU. Also, I wanted redundancy in my pumps, so I have two 655's in series to push the water through the CPU, video card and then 24ft of radiator. Normally, the water would run through the AlphaCool radiators in parallel, but I had plugs made to fit in every other T-connector so that every bit of the water actually passes through ALL of the radiators before hitting the reservoir. From the pump, it splits into two paths, one for the CPU and the other for the GPU, then they come back together to feed into the radiator.

Finally, upon realizing that I had two pumps, and a fan in the PSU, I decided to go ahead and place a couple of Noctua 140mm fans at the bottom to assist with the convective effort. They are silent at 600rpm and offer enough air bleeding off the sides to fill the channels of the radiators from the bottom of the case to out the top. And to keep the rest of it quiet and fast, I chose an OCZ Vertex3 240Gb SSD.

The two things missing from a standard case would be:
- optical drive, for which I use an external DVD in the rare instance I need one
- more storage space/options, no worries - as I have a 30TB NAS server in the next room.

Ok, so it has performance with the components I've chosen...
- MSI P67A-GD65
- 16Gb GSkill DDR1600
- i7-2600k @ 4.6Ghz (1.385v)
- OCZ 240Gb Vertex3 on 6Gbps channel
- EVGA GTX580 Hydro @ 1.005Ghz (1.38v)
- 2x MCP655 pumps at level 3 (out of 5)
- Seasonic 850W PSU
- 18 channels of AlphaCool Cape Cora passive radiator
- 250ml Balancer reservoir
- EK Supreme waterblock
- EK dual pump top block
- lots of Koolance fittings (including QDs) and tubing and a couple Bitspower fittings
- AC Ryan mesh for top and bottom, heavy duty speaker grill for corners (front corners hold the 'cover' in place, back corners purely aesthetic)
- serveral aluminum channels (legs), angle (corners) and panels (rigidity)
- Also, alot of rubber washers, rivets, felt, sweat and ad-lib design changes

So how quiet is it? With the fans at their default of 1200rpm, there is a steady slight hiss of alot of air moving - not desired.
At 600rpm, well, lets say that I'm glad for the network activity light, otherwise I don't know it's on. I am seriously talking silent. I have to put my ear to the case (<2in from the top) and know what to listen for to hear a very slight hum of pumps and fans. Imperceptible is how I would quantify it. Only if I ramp up both Prime95 AND Furmark can I get the PSU fan to an audible level (but way less hiss than fans at 1200). Normal operations or even running MilkyWay (multiCPU and GPU) folding do not raise the noise level.
But... what if I had no fans - as originally designed? Then it sounds like a silkworm under a 3 ton boulder in the middle of the Australian outback at night.

Ok...You throw enough money at the situation and you can make it fast and quiet... but what about thermals?
1200RPM fans
- CPU idles @ 34°C (avg), load settles @ 52°C (avg) (Prime95)
- GPU idles @ 28°C, load settles @ 39°C (Furmark)
- Prime95 + Furmark gets the CPU up to 62°C and GPU to 43°C
- CPU idles @ 35°C (avg), load settles @ 54°C (avg) (Prime95)
- GPU idles @ 29°C, load settles @ 41°C (Furmark)
- Prime95 + Furmark gets the CPU up to 63°C and GPU to 44°C
- CPU idles @ 37°C (avg), load settles @ 65°C (avg) (Prime95)
- GPU idles @ 30°C, load settles @ 46°C (Furmark)
- Prime95 + Furmark gets the CPU up to 70°C and GPU to 48°C

So, other than the PSU fan coming on with Prime and Furmark running, the system with no 'case' fans is functional. However, since I've already got the Noctuas and they fit so well, I've left them in there at 600RPM for a silent running, but performance oriented solution. Anyway, like many of you here, I wanted to share my results of what happens when you think outside the box!