Lah Kara

October 2021

Pitch

A RISC-V mini-ITX immersion-cooled Linux workstation.

Compute

SiFive Unmatched: 4+1 RISC-V cores at 1.5GHz, 16GB RAM, in Mini-ITX form factor.
Intel AX-200 Wifi 6 / Bluetooth 5 adapter.
1TB NVMe M.2 SSD. I’ve got a double-sided high performance one from a previous build, and if it’s not compatible I’ll get something like a Samsung 970 Evo.
RX 570 4GB graphics. The goal here is not high perfomance (not a gaming rig), but something that can handle a few screens and only need a PCIe Gen 3 interface.

Cooling

Wide-gap slant-fin heat sinks to replace the OEM fin array (PCIe chip) and fan (CPU).
Extension cabling for USB and Ethernet.
I’m undecided whether I’ll strip the fans off the graphics card and attempt to immerse it, or if I’ll get a riser/extension to bring it outside.

Immersion fluid (oil)

Requirements:

Boiling and smoke points above 120C
Liquid at room temperature
Long shelf life (doesn’t go rancid quickly)

Nice to haves:

Fairly clear or transparent (for aesthetics)
Edible / non-toxic
Doesn’t stink!

The “long shelf life” requirement basically reduces the possibility set to:

Mineral oil (petroleum, colorless, odorless, non-edible, but not touch-toxic, quite cheap)
Ben oil (golden, edible, fairly soft smell, 200C smoke point, very expensive)

So as much as I’d love having a veggie oil computer I’ll probably go with mineral.

I’m thinking of making a custom acrylic/copper/solid wood box that would be roughly the size of a classic mini-ITX case. A copper side would be the thermal interface, and it could be sealed to make it portable and safe from spills (not permanently glued, with a rubber seal or something), so it can sit on the topside of the desk looking all cool!

Base: solid wood (Macrocarpa)
Glass: 3mm acrylic. This puts a further thermal restriction as it will melt at 80°C
Haven’t decided for the back. If I can find a large extruded alu heat sink like plate, that would be ideal, but otherwise will probably reuse and machine some existing computer case steel

Power

NJ450-SXL from Silverstone. This is a small form factor fanless modular 450W. Selecting factors:

450W is more than enough, I could do with 300. But a detailed review of this one shows it’s most efficient at 50% load, which should be my average load on this system. That works out nicely.
It’s fanless, but not only that, it’s the only PSU I found which was completely enclosed without a grate. It’s not waterproof or anything, I’m not gonna go stick it in oil, but it looks really good, certainly good enough to sit outside the case
It’s modular, which will help integrate it into the case design, and will certainly make for a clean look given I only need the 24-pin and one 6+2 pci feed.

Naming

I name all my devices in a Star Wars theme. Workstations (desktop, laptops) after minor characters, phones and tablets after vehicles, and IoT / utility devices (vacuum, printer, routers, various SBC things, etc) after droids. My wifi network is named after a star system. I’m a nerd, sue me.

Lah Kara is from the new Visions series.