Also known as liquid submersion cooling, it is the practice of submerging computer components (or full servers) in a thermally, but not electrically, conductive liquid (dielectric coolant). Liquid submersion is a routine method of cooling large power distribution components such as transformers. Still rarely used for the cooling of IT Hardware, this method is slowly becoming popular with innovative datacenters the world over. IT Hardware or servers cooled in this manner don't require fans and the heat exchange between the warm coolant and cool water circuit usually occurs through a heat exchanger (i.e. heater core or radiator). Some extreme density supercomputers such as the Cray-2 and Cray T90 use large liquid-to-chilled liquid heat exchangers for heat removal.
The liquid used must have sufficiently low electrical conductivity not to interfere with the normal operation of the computer. If the liquid is somewhat electrically conductive, it may be necessary to insulate certain parts of components susceptible to electromagnetic interference, such as the CPU. For these reasons, it is preferred that the liquid be dielectric.
With Immersion Cooling the heat is transferred directly from the heat source to the working fluid. In "watercooling" the working fluid is potentially harmful to electronics and thus flows through a sealed loop isolated from the heat source. A watertight waterblock is used to indirectly transfer the heat from the heat source to the working fluid. With Immersion Cooling the working fluid must be non-conductive and that generally limits us to four families of fluids:
Immersion Cooling systems used to have a higher fluid cost than water cooling, but this is already changing.
A wide variety of liquids exist for this purpose, the most suitable being transformer oils and other specialty electrical cooling oils (such as 3M Novec, Dupont or Galden). Non-purpose oils, including cooking, motor and silicone oils, have been successfully used for cooling personal computers.
Depending on the properties of the coolant, we can classify the Immersion Cooling techniques in:
1. Single-Phase Immersion Cooling
Single-Phase coolant never changes state, it never boils or freezes and always remains in a liquid form. The coolant gets pumped to a heat-exchanger where heat is transferred to a cooler water-circuit. This technique uses "open baths", as there's little (or no) risk of the coolant evaporating:
2. Two-Phase Immersion Cooling (also known as evaporative cooling or flow boiling)
In two phase cooling the working fluid boils and thus exists in both a liquid and gas phase. The system takes advantage of a concept known as "latent heat" which is the heat (thermal energy) required to change the phase of a fluid. The working fluid is only cooled by boiling and thus remains at the boiling point ("saturation temperature"). Energy is transferred from the heat source into the working fluid will cause a portion of it to boil off into a gas. The gas rises above the fluid pool where it contacts a condenser which is cooler than the saturation temperature. This causes the fluid to condense back into a liquid and fall (rain) back into the pool.
This Immersion Cooling method required "semi-open baths". This means that when the system operates its sealed to avoid the evaporation or the coolant.
With two-phase or even some single-phase Immersion Cooling liquids, evaporation can pose a problem, and the liquid may require either to be regularly refilled or sealed inside the "bath's enclosure". On top of that, two-phase coolants are extremely expensive and it's not very clear how their vapours can affect people operating the baths.
At Submer, we use either a special vegetable-based dielectric coolant, or a synthetic dielectric coolant, both specifically crafted for Immersion Cooling. One of the biggest advantages about our coolant is that its not mineral-based and is naturally bio-degradable if accidentally freed into the environment. We're very proud of using a green and totally hazardous-free biodegradable coolant in comparison to our competitors.
The Submer solution uses a single-phase immersion coolant and so we provide a 22U and a 45U open-bath system designed for easy day-to-day operation in the datacenter.
Submers' target customers are the worlds datacenters that can't move their infrastructure to cold climates (mainly because of end-customer proximity and local security policies) and still need to compete with the Big Boys of the market.
It is also the perfect solution for high density applications like cryptocurrency mining (Bitcoin, Etherium, Ripple, Litecoin...) using any ASIC or GPU hardware.
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