Immersion liquid cooling has been proposed in the era of computer DIY or mainstream,but more is still in the concept stage.
Until the Tianhe No. 2 and Taihu Lake Light Supercomputer,liquid cooling technology has been applied on a large scale. In
the past two years, the "Earth Numerical Simulation Device Prototype System" of the Institute of Atmospheric Sciences of the
Chinese Academy of Sciences and the Supercomputing System of the Simulation Center of the State Grid Electric Power Research
Institute have deployed nearly one thousand nodes of liquid cooling servers. Liquid cooled servers will also be deployed in
the weather station project of HPC Asia's largest singles, including the previous time.In addition, Alibaba Cloud, Shuguang, etc.
have specific research and application. There are also many mining machines distributed throughout the country that have applied
this technology.
The early liquid cooling was soaked in a large pool (pool immersion), more of a symbolic concept,only considering good heat dissipation,
without worrying about the evaporation of the coolant.
In general, the immersion cooling system requires a special sealed cooling box. The server and other equipment can be placed in a high-density
cooling tank, immersing the main heat-dissipating components of the server with insulating coolant, and equipped with a coolant internal
circulation system to accelerate heat transfer.
When the equipment is running, a large amount of heat is generated, so that the coolant part is converted from a liquid state to a gas state,
so that the heat is carried away with the steam, and the steam is condensed on the upper condenser and returned to the liquid backflow to the
immersion liquid, and the cycle is repeated, thereby making the server cooling system Constant in a certain temperature range.
Compared with air, the insulating coolant has a thermal conductivity of 6 times that of air and a specific heat capacity of 1000 times that of air.
Therefore, for the same volume of heat transfer medium, the liquid cooling system coolant transfer heat rate is 6 times that of air, and the heat
storage capacity is 1000 times that of air.
different insulating coolants.For standardized or commercial applications, the biggest problem with immersion liquid cooling is how to achieve
coolant circulation, including control of pressure changes and leaks in the chamber, which is also more difficult in a closed environment.
Only when the CPU load is constant, it is impossible to ensure that the pressure of the sealing system is constantand thus zero pressure is
eliminated to eliminate the leakage problem. The load on the server is always changing as the task changes, resulting in a positive pressure
and sometimes a negative pressure in the sealed chamber,which in turn leads to the possibility of leakage.
There have been two types of immersed liquid cooling methods in closed environments - phase change immersion and no phase change immersion.
"Phase change" is a concept of thermodynamics, that is, the change of matter from one "phase"to another. In short, whether the liquid will
generate bubbles during operation.
The inert insulating coolant is combined with a dedicated sealed cooling box to achieve a veritable green room.
Efficient and energy efficient: efficient and rapid heat transfer, greatly reducing power consumption in the equipment room.
PUE (power usage efficiency) reaches 1.1 or less, which is more than 85% energy saving compared with traditional air conditioning.
Simple equipment: Compatible with the server running power of 2000kW or 300kW.
No noise: only the fan on the dry cooler works.
No loss: Loop within the system.
Space saving: High-density integration of servers can be realized, and space utilization can be increased by more than three times.
Cost savings: The location of the equipment room is no longer demanding and critical, no need for precision air conditioning,
small distribution and infrastructure, from hardware investment to post-operation, saving costs in all aspects.
At present, the high-performance field is the main direction of liquid cooling applications, because this part of the application has
an inexhaustible demand for performance, and the appearance of liquid cooling can help the system achieve better heat dissipation and
lower temperature, on the other hand. Can promote further improvement in performance. In an immersive environment, the CPU can be overclocked, which allows for faster operation and greater stability.