The liquid cooling technology revolution in data centers
With the innovative development of technologies such as AI, cloud computing, and big data, data centers and communication equipment, as information infrastructure, are undertaking an increasing amount of computation. With the rapid increase of computing power in data centers, the power density of single cabinets has increased, which puts higher demands on heat dissipation efficiency. On the other hand, under the "dual carbon" policy, data centers, as "major energy consumers", are required to continuously reduce their PUE indicators in order to lower the electricity consumption of the refrigeration system. However, traditional air cooling can no longer meet the above heat dissipation requirements, and liquid cooling technology has emerged.
The top of the line data center GPU available on the market 10 years ago was the NVIDIA K40, with a thermal design power (TDP) of 235W. When NVIDIA released the A100 in 2020, the TDP was close to 400W, and with the latest H100 chip, the TDP skyrocketed to 700W. The thermal design power consumption of a single high-performance AI chip has reached 1000W. It is understood that Intel is developing a chip that may reach 1.5kW. The competition in artificial intelligence ultimately boils down to competition in computing power, and a major bottleneck for high computing chips is their heat dissipation capability. When the chip's TDP exceeds 1000W, liquid cooling technology must be adopted.
Liquid cooling technology can effectively solve the problems of high-density deployment and local overheating in computer rooms, among which immersion liquid cooling has outstanding advantages in heat dissipation and energy saving. Immersion liquid cooling is a typical direct contact liquid cooling method, in which electronic devices are immersed in a cooling liquid, and the heat generated is directly transferred to the cooling liquid and conducted through the circulation of the liquid. Immersion liquid cooling can be classified into two types: single-phase immersion liquid cooling and phase change immersion liquid cooling, depending on whether the cooling liquid used will undergo a state change during the cooling of electronic devices. The advantage of single-phase is that the deployment cost and cooling medium cost are lower, and there is no risk of coolant overflow; The advantage of phase change lies in its higher heat dissipation capacity and limit, but it still lags behind single-phase in terms of cost and technological maturity.
Single phase immersion cooling provides a compelling solution for data centers seeking efficient and reliable thermal management. In this method, the IT components are completely immersed in a specially formulated insulating liquid. This liquid directly absorbs heat from the server, similar to two-phase immersion cooling. Unlike two-phase systems, single-phase coolant does not boil or undergo phase transitions. It remains liquid throughout the entire cooling process. The heated insulating liquid circulates through the heat exchanger inside the cooling distribution unit (CDU). This heat exchanger transfers thermal energy to an independent cooling medium, typically a closed-loop water system. The cooled insulating liquid is then pumped back into the immersion tank to complete the cooling cycle.
In a two-phase immersion cooling system, electronic components are immersed in an insulated heat conducting liquid bath, which has much better thermal conductivity than air, water, or oil. The difference between two-phase immersion liquid cooling is that the coolant undergoes a phase transition. The heat transfer path of two-phase immersion liquid cooling is basically the same as that of single-phase immersion liquid cooling, with the main difference being that the secondary side coolant only circulates in the internal area of the immersion chamber, with the top of the immersion chamber being the gaseous zone and the bottom being the liquid zone; The IT equipment is completely immersed in a low boiling point liquid coolant, which absorbs heat from the equipment and boils. The high-temperature gaseous coolant produced by vaporization, due to its low density, gradually gathers at the top of the immersion chamber and exchanges heat with the condenser installed at the top, condensing into a low-temperature liquid coolant. It then flows back to the bottom of the chamber under the action of gravity, achieving heat dissipation for the IT equipment.
In the process of innovative development of heat dissipation technology, whether it is chips or electronic devices, the volume, design cost, reliability, and other aspects of products are thresholds that enterprises cannot avoid. These are also problems that heat dissipation technology must balance and solve. Different combination technologies can be used to develop products for various heat dissipation materials, technologies, and application scenarios, in order to find the optimal solution for the current pattern.
