Immersion cooling
Server Immersion Cooling[1] is a the practice of submerging computer components (or full servers) in a thermally but not electrically conductive liquid. This coolant liquid is commonly a mineral-based oil with dielectric properties.
Server Immersion Cooling has the potential of becoming a popular server cooling solution green for data centers[2], as it allows to drastically reduce Power Usage Effectiveness.
IT hardware or servers cooled by immersion cooling don’t require fans, thus these are removed together with any thermal paste to avoid it from melting in the oil. The oils in immersion cooling usually operate at temperates between 35-50ºC (95-122ºF), this allows data centers to use much more efficient evaporative or adiabatic cooling towers[3] instead of chiller-based air cooling.
Current commercial applications for immersion cooling range from data center orientated solutions for commodity server cooling, server clusters, HPCC applications and Bitcoin Mining.
History
Although still rarely used for cooling of IT hardware, the usage of mineral or vegetable-based oil for cooling large power distribution components such as transformers and industrial machinery is a common practice since beginning of the 1900's[4].
Some extreme density supercomputers such as the Cray-2 (release in 1985) and Cray T90 used large liquid-to-chilled liquid heat exchangers for heat removal.
Server Immersion Cooling techniques
Open or Semi-Open Bath Immersion Cooling
Open or semi-open bath immersion cooling is a data center cooling technique that implies fully submerging servers in dielectric coolant fluid. Its called open or semi-open bath because servers are placed side-by-side in large tanks that assimilate bath tubs. These baths operate at atmospheric pressure and allow the coolant fluid to be pumped through the hardware components or servers submerged in it.
Open Bath Immersion Cooling
Open Bath Immersion Cooling uses single-phase oils. These oils always remain in liquid state while operating. They never boil or freeze. The oil is usually pumped to a heat exchanger where the oil is cooled thanks heat exchange with a cooler water-circuit. This technique uses “open baths“, as there’s little (or no) risk of the coolant evaporating:
Semi-Open Bath Immersion Cooling
In semi-open bath Immersion Cooling, two-phase oil is the working fluid. It literally boils thanks to its low boiling point[5] 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 (in this case two-phase dielectric mineral oil). The oil is only cooled by boiling and thus remains at the boiling point (“saturation temperature”). Energy transferred from the servers into the two-phase oil will cause a portion of it to boil off into a gas (this is the second phase of the oil). The gas rises above the liquid oil level where it contacts a condenser which is cooler than the saturation temperature. This causes the vapoured oil to condense back into a liquid form and fall (rain) back into the bath.
The term "semi-open bath" means, that when the system operates, its sealed to avoid the evaporation or the coolant:
Sealed Server Immersion Cooling
A different approach to open or semi-open bath immersion cooling are sealed server immersion cooling solutions, where servers are specially built in an oil-tight casing. Dielectric oil is pumped inside each server to collect heat from the components. The heat is then taken to a backplane in the rack which is cooled by a water circuit.
The main advantage of this approach is that servers don't require to be placed in horizontal baths. The main disadvantage is that not any hardware can be used as the vendor defines the hardware specs of the sealed servers.
References
- ^ "What is Immersion Cooling? | Immersion Cooling Solution for Data Centers". Submer Technologies. September 25, 2015.
- ^ "Eight emerging data center trends to follow in 2016". Robert Gates. December 15, 2015.
- ^ "Data center liquid immersion cooling with adiabatic cooling towers". Submer Technologies. January 2, 2016.
- ^ "The original transformers were replaced with Stanley oil filled transformers in 1904". The Folsom Power Plant 1895. Edison Tech Center.
- ^ "3M™ Novec™ 7100 Engineered Fluid". © 3M.
External links
- Liquid immersion cooling relief for ultra-dense data centers
- 3M - Two-Phase Immersion Cooling
- Mineral Oil Cooled PC
- Data center cooling methods
Commercial Immersion Cooling Solution Providers:
- Green Revolution Cooling (Open-bath)
- Allied Control (Semi-Open bath)
- Iceotope (Sealed Server)
- Submer Technologies (Open-bath)
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