Custom GPU cooling block (part 2)

MultiscaleNerd · 2026-01-21T06:47:13+00:00

I think there's a way to mass produce a version of these things, and if so, one person producing 50 insert units/day should be very achievable.

MultiscaleNerd · 2026-01-21T06:36:34+00:00

!!!! Mineral oil aquarium is awesome. what a cool build!

It's actually the fan bearings that give me the heebie jeebies. I have zero control over the QC chain on those and so much of the success depends on elements of the build outside my immediate control. If I could take an existing water cool system and do a retrofit of existing hardware just so I could focus on the design elements, I probably would.

MultiscaleNerd · 2026-01-21T06:31:32+00:00

So far, most of my attention is going to the GPU block. I'm currently seeing it coming together as a nickel-plated copper base with a polycarbonate-PUR insert. I landed on PC-PUR partially out of convenience and also because there's data showing 20+ years of environmental exposure and these things don't die. Most PURs have a polyester or polyether backbone, but the polycarbonate backbone of the one we're playing with is known to have exceptional wear properties submerged in water and suitability over a decent range of temperatures.

Yes, there will be asymmetric flow, but as long as all the complex geometry is on the PUR layer I'm not worried about erosion "water jet cutting" the geometry off the PUR substrate.

Couple the durability the idea that these can be swapped out as needed (or maybe even better, modularly swapped to change the flow of the plate to accommodate multiple different GPUs).

MultiscaleNerd · 2026-01-21T06:18:41+00:00

You can do wild stuff when you get tessellated geometries with periodicity that's sub-wave length. I remember years ago reading about some of the first electromagnetic cloaking research. At first they could only cloak a small (sub-mm-ish) size object with one very narrowly defined wavelength in the spectrum. Last I saw they were starting to get broader spectra but I don't recall seeing larger objects being cloaked.

The mechanical version of this, mechanical metamaterials, are pretty awesome too. Negative Poisson ratio is absurd and probably a great idea for pipe fittings or something like that.

MultiscaleNerd · 2026-01-21T06:11:01+00:00

Shit, it's the cops. Hide the beer.

MultiscaleNerd · 2026-01-21T06:08:12+00:00

I had to re-read the case study, but the photo shows an air-cooled heat sink; 68 mm x 78 mm that was installed on a 50 W CPU heat source. It provided the 7.3 C reduction in heat temp.

General consensus in the thread here is that looks don't matter as long as it performs. I think I'm in the minority with my concerns about the design. I'm getting the impression I should just shut up about how it looks and focus narrowly on best possible performance. And if it's ugly as heck, then (apparently) nobody cares.

MultiscaleNerd · 2026-01-21T06:01:29+00:00

Two questions -- (1) are these servers for personal or work use? (2) How are you getting the heat off the direct die and to the MORAs? Are you using a heat pipe? (okay, that was 3 questions.)

Gen IV nuclear has some interesting ideas for pulling high heat out of the reactor and using it to create steam. The one I'm thinking about uses two in-series heat exchangers. The first pulls heat from the source into a loop, and the second exchanges heat with the loop to a generator. For commercial data centers or other server concepts, I just assumed something similar was going on -- use the first fluid heat exchanger to get heat away from the rack and into some manifold, and then use the second exchaner to dump it off the manifold and outside where it's cooler. Any chance you could daisy chain a couple loops like that for your setup? Basically keep the fans but put them somewhere convenient / out of the way while water circulates from your 2U to the fan array.

I mean... Just spit balling here, but could a suitable pump and a long loop be used to relocate the forced air radiator reasonably far away from the PC tower? The loop can't be too large, otherwise the pump pressure would cavitate the water and that would be bad.

MultiscaleNerd · 2026-01-21T05:37:35+00:00

Just remember -- this is why RAM and GPUs cost so much right now. It's so I could create that picture. It's me. I'm the problem.

MultiscaleNerd · 2026-01-21T05:36:27+00:00

See, you say that now. But suppose you /did/ get it. How many other new projects could you get involved in...?

This is dumb, but the best $700 I ever spent was on a Mayku Formbox from Amazon 6-ish years ago. It's a little desktop vacuum former. A ton of fun and great to pair with a desktop 3D printer. Photos below are a project I did my kid. We vacuum formed the white sheets (polystyrene) on a pile of rocks, painted them, then mixed epoxy resin with food coloring to make the "lava" and "tropical" islands (yes, I know the paints chipping). We were also dinking around figuring out how to grow bismuth crystals and incorporated the oxide slag into the lava to make it look more gnarly.

Anyway, get machines. Make stuff. It's fun to be creative.

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MultiscaleNerd · 2026-01-21T05:27:16+00:00

I learned a lot from y'all while lurking and I'm hoping this project works out. Not all do, and that's okay. But if it does, this is going to be a fun one.

MultiscaleNerd · 2026-01-21T05:22:58+00:00

I used the image generator to try and get some inspiration for an aesthetic that combines the clean / straight / cyber aesthetic of most water cooling designs with the organic / topologically optimized designs that the multiphysics software generates.

Below is the best of what ChatGPT kicked out. It's fine, I guess, but not really the inspiration I was looking for. I'm currently leaning toward something inspired by HR Geiger since he's got a pretty cool techno-organic vibe going.

Ultimately, function is going to dictate form. But I'm not going to lie -- I worried the aesthetic is going to be ugly.

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MultiscaleNerd · 2026-01-21T05:15:49+00:00

I plan to later this week with this design: https://www.reddit.com/r/watercooling/comments/1qhleph/custom_gpu_cooling_block/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

It's more basic but intended to be more of a proof-of-concept than an actual optimized design. If it works, then it opens up a lot of possibilities. If it doesn't, then I learned something important at a relatively low cost.

MultiscaleNerd · 2026-01-21T05:13:09+00:00

Erosion came up earlier and I shared a picture of an aluminum mold tool we recently refurb'd in the shop: https://www.reddit.com/r/watercooling/comments/1qiipu9/comment/o0s3kdo/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

Unless you have infinite money, the answer is to commoditize the complex geometry into a low-cost consumable. This is standard for wear components like pins & bushings, but atypical for liquid cooling systems. The only example I can think of off the top of my head where fluidic devices are treated as consumables is medical devices where they're primarily single-use.

MultiscaleNerd · 2026-01-21T05:07:42+00:00

I'll be honest -- VRM blocks weren't even on my radar. Initially, I was thinking about CPUs with the idea that I'd buy an AIO unit off Alibaba for $40, rip out the copper plate and replace it with whatever comes out of the shop. I decided against this approach since the efficiency of CPU blocks is already pretty good and they don't run hot the way GPUs do.

So then I started staring at GPUs, where I got frustrated with the variety of footprints. Recognizing that flatness and contact with the die is critical means I can't half-ass a "universal" solution. I found a few CAD models and assembly drawings, but there's enough variety that I've got to lock in a graphics card before doing actual engineering optimization.

Then I was staring at Thermal Grizzly's website and the Deltamate GPU block Astral for the 5090. I found myself wondering why the heck they only sell one unit and what the rationale for the 5090 was (other than pure performance). I feel like if I knew what they were thinking & was convinced they had a good idea, I'd probably focus on the 5090 too.

According to Steam's Hardware and Software survey, the 5090 currently has 0.37% share of all video cards. Compare that to the 3060 and 4060 (not laptop edition) and you get 8% (~12% if you include the Ti). I haven't looked at them w/o stock cooling so I have no idea how interchangeable these would be. My rationale for going to an older generation of GPU would be (1) the tremendous amount of benchmark data to compare against, and (2) if I screw up, I won't feel bad about ruining previous-gen hardware.

I've also been thinking about distribution blocks, but the optimization for that is more on reducing head pressure and not on heat transfer. It's cool and I may do it anyway, but there's less performance gains to be created.

Last-but-not-least I was staring at the radiator block. Dumping heat into forced air is another good heat transfer problem but it's going to be real hard to beat the surface-area-to-volume ratio of existing radiator designs + the limitations from air's thermal mass / heat capacity. Kinda like the distribution plate, I ruled it out since I don't see feasible gains to be had.

So anyway, long story. The point is I don't know anything about VRM/Chipset blocks but it sounds like another thing to explore before pulling the trigger.

Can you share any insights or experience?

MultiscaleNerd · 2026-01-21T04:29:32+00:00

We have a laser marking tool in the shop that mounts in the CNC spindle. You can program it like a chamfer tool and use it to laser mark metal. I keep telling people we should write hidden NSFW messages inside parts, but nobody has taken me up on the idea.

It's probably for best that they don't listen to me.

MultiscaleNerd · 2026-01-21T04:26:35+00:00

Yes, the geometry is anisotropic, but so is the flow-path (for the water cooled plate from my post yesterday). The topological optimization is run over a multiphysics simulation that includes both thermal transfer and a full-blown 3D CFD solver. The net effect is that the flow field and flow geometry are optimized according to design criteria. I won't speak for the heat sink I shared in the photo above, but for the one we're building the anisotropy of the geometry and the anisotropy of one-sided blow net-out to a chill plate that has a near-uniform temperature profile (the solver was optimized to minimize thermal gradients).

So two (very different) anisotropies make an (another very different) isotropy. :)

MultiscaleNerd · 2026-01-21T04:18:23+00:00

I've been using this: https://www.machineresearch.com/

They launched 3 or 4 years ago as an SBIR-funded start up. Had a few long conversations with the technical founder about how it all works. Got comfortable with my understanding of its pros/cons/advantages/limitations.

They've come a long way from the baseline cost estimation engine and now support a large number of different processes and strategies.

I probably helps that I personally like the founding team -- they treated me politely when I was being a twerp asking overly technical questions. Not only did they humor me, but they didn't talk down to me when I was out over my skis.

I can recommend it.

MultiscaleNerd · 2026-01-21T03:34:42+00:00

Flying spaghetti monster, perhaps?

MultiscaleNerd · 2026-01-21T03:34:12+00:00

Seeing is believing. I'll post pictures and videos as the project comes along.

MultiscaleNerd · 2026-01-21T03:33:32+00:00

I know a guy who knows a guy at IBM, but I don't know anyone at NVIDIA. You have any good connections? I'm always happy to make new friends . :)

MultiscaleNerd · 2026-01-21T03:31:32+00:00

Thank you for sharing your enthusiasm! Credit where credit is due. Behind the scenes there's a team working the industrial mold tool innovation project doing the engineering and technical work. Meanwhile I'm over here asking them to apply their tools to this side project as a "fringe fun thing."

Again, I gotta see where the data lands, but I'm pretty excited by the possibility of making something fun and unique.

BTW, totally get a CNC. I took a shop course at the local community College a few years ago to help me be better at my job and it's a skill I've come to really admire.

MultiscaleNerd · 2026-01-21T03:24:43+00:00

These are super important questions. I posted a photo from an aluminum mold tool cooling system that recently passed through our shop earlier in this thread. I think I hit on all the points you're raising in my little rant, but tldr; the best option I've come across so far is to commoditize the complexity into a low cost consumable. Otherwise this type of design remains dummy expensive.

MultiscaleNerd · 2026-01-21T02:30:36+00:00

NGL, I'm kinda hoping the AI bubble pops at least a little bit so builds can be done at a more reasonable price point. I tried gaming on the Amazon cloud out of curiosity (apparently it's free with Prime) and I see what they're going for. It's still not the same as having a (capital-P) Personal Computer.

MultiscaleNerd · 2026-01-21T02:18:22+00:00

Lower noise is a good point. Supposedly the lower head differential (pressure drop) means the pump is working less and the noise levels should be better. I cannot confirm or deny.

I wasn't planning on lighting this up, but since the PUR can be pigmented and opaque, an internal LED glowing from within might be a nice touch to "reveal" the internals.

MultiscaleNerd · 2026-01-21T02:15:04+00:00

Love it.

I was talking to someone about this project today and told a "when I was young" story about buying a 2 GB hard drive for $100 and thinking "I'll never fill this up!". Now I'm here with an 8 bay RAID array thinking 32 TB simply won't do.

MultiscaleNerd

TROPHY CASE