Liquid Cooling
Notes on cooling computers.
Wet Rocks is a single phase liquid immersion cooled computer.
Air
Air cooling with fans is the method used to cool the vast majority of workstations and servers in the world.
Pros:
Widely used
Readily available components for a wide variety of setups.
Easy.
Cheap.
Many manufacturers and suppliers.
Cons:
LOUD.
Inefficient cooling capacity.
Inefficient power usage.
Requires lots of physical space for fans, plus airflow area.
High failure rate relative to other components in computers.
Direct to Chip
While rare compared to fan cooling, direct to chip (DTC) is by far the most common way to cool computers with liquid cooling.
The tinyrocs-01 node uses direct to chip cooling.
With this setup, a custom mount block is sourced for each component that needs cooling. Most commonly this is the CPU, then the GPU. Parts of the motherboard, the RAM, hard drives, can also be cooled. Most commonly, the water-based cooling liquid is pumped from a small reservoir through hoses which connect to each device that needs to be cooled. In the case of tinyrocs-01 there is a “water block” on the CPU, and each of the GPUs has in and out hoses that pump the liquid across the device.
Pros:
Not uncommon.
Decent availablility of components.
Widely available documentation on a wide variety of setups.
Not so expensive.
Coolants are widely available and not particularly unsafe.
Cons:
In general, each device needs a custom block designed for it.
Only cools some of the components, not the whole system.
Somewhat of a maintanence issue if hardware configuration needs changing (e.g. more steps to swap out a video card than fan cooling).
Single Phase Immersion Cooling
Wet Rocks uses single phase liquid immersion cooling.
Single phase immersion cooling is relatively rare, but there are various publicly documented setups from homebrew to large industrial uses.
Cooling liquids can be well over 1,000 times more efficient in heat transfer than air.
A variety of coolants can be used, such as:
Specialized dielectric coolant.
Mineral oil.
“Pure” water.
Of these, using the specialized ElectroCool coolant from Engineered Fluids, Inc. may be the best.
Mineral oil is carcinogenic.
Example mineral oil cooled computer from Puget Systems:
ElectroCool
ElectroCool is a dielectric coolant from Engineered Fluids, Inc.
Wet Rocks uses ElectroCool for the dielectric coolant.
Pros:
Relatively efficient.
Can cool entire system.
Specialized dielectric coolants can be “environmentally friendly” (relatively).
May require fewer components.
Cons:
Relatively little documentation about deployments.
Fewer known systems.
Fewer COTS (commodity of the shelf) parts.
More custom built parts required.
More expensive.
Few specialized dielectric coolant manufacturers.
No readily available systems for single motherboard size (large industrial custom tanks are available).
Still need to dump the heat somewhere, so it still generally uses fans.
Engineered Fluids, Inc. has docs on retrofitting a Koolance unit for immersion cooling.
Click the tabs to go to “Upgrading a Koolance ERM-3K3UA”
ElectroCool is 80% the weight of water. The smallest container ElectroCool comes in is 20L (~5 gal).
Two Phase Immersion Cooling
Two phase immersion cooling is the most efficient, but least common, of the options presented here. It works great, but is toxic and expensive. It is pretty much “never” done homebrew.
In two phase, the coolant used has a boiling point at low temperature, such as 50C. When a component such as a CPU gets this hot, the liquid next to it boils off. This process of converting from a liquid to a gas uses energy which then keeps the component cool. So the CPU will look like it is boiling water just as if boiling water on a stove top. The gases rise to the top of the sealed container. There the gases hit a condenser, where they cool off, become a liquid, and drop back down into the tank.
Pros:
Most efficient.
Majickly fantastic.
Cons:
Coolants are toxic to humans.
Coolants are the most expensive relative to all other options.
Not environmentally friendly.
Only one manufacturer? 3M.
Complex chassis requires sealed setup to prevent evaporation.
Requires sealed setup so gases don’t escape and be inhaled by humans.
Process causes cavitation in components (e.g. eats your chip).
Process causes solder whiskers.
In general, not very good for hardware.
High maintenance.
Liquids need to be frequently replaced.
Example two phase cooling system:
Other
A few other ways to cool a computer:
Dry ice.
Liquid nitrogen.
Liquid helium.
These allow the components to be pushed to their extremes (e.g. overclocking), but aren’t suitable for long term usage.
TEC (thermo electric cooling, aka Peltier).
This is neat, but very inefficient, and still requires other methods on top.
Thermosiphon
Many thermosiphons use the same chemicals as two phase immersion cooling (e.g. Novec), therefore have the same environmental and health drawbacks.
Heatsinks
The vast majority of heatsinks are designed for air (fan) cooling. There are a wide variety of heat pump, thermosiphon, vapour chamber, and other heatsinks that can out perform air heatsinks, especially if they are optimized for liquid immersion.