According to the cooling principle, cold plate type, immersion type and spray type are the three main deployment methods of liquid cooling at present.Among them, immersion and spray liquid cooling are contact liquid cooling, and the cooling liquid is in direct contact with the heating element.(1) Immersion liquid cooling: Immersion liquid cooling immerses all the heating elements of IT equipment in the cooling liquid to achieve heat dissipation. According to whether the working fluid undergoes phase change, it is divided into single-phase liquid cooling and phase change liquid cooling. The cooling liquid after absorbing heat is cooled or condensed by means of air cooling or water cooling.(2) Spray-type liquid cooling: Spray-type liquid cooling relies on pump pressure or gravity drive, and precisely sprays cooling liquid from top to bottom to the circuit board of IT equipment according to the demand of heating elements. The heat-absorbing cooling liquid is air-cooled or water-cooled Equal circulation cooling. (3) Cold plate liquid cooling: The cold plate liquid cooling is a non-contact liquid cooling, and the cooling liquid does not directly contact the heating device. The cold plate liquid cooling passes the cooling liquid to the cold plate that is in contact with the heating element of the IT equipment through the flow channel to export the heat, and the cooling liquid after absorbing heat is circulated and cooled by air cooling or water cooling.

Contact liquid cooling has a better cooling effect than indirect liquid cooling. Contact liquid cooling is completely different from indirect liquid cooling. The liquid refrigerant is in direct contact with the electronic device, and the insulating liquid medium can ensure the insulation of the electronic device. Contact liquid cooling technology has the following advantages: 1) The specific heat capacity of liquid is much higher than that of air, with large heat transfer and high efficiency.2) Energy saving and consumption reduction. As mentioned earlier, the use of contact liquid cooling technology greatly reduces cooling energy consumption. The PUE can reach 1.04, which is infinitely close to the theoretical limit. 3) Improve the performance and reliability of computing equipment. A sudden increase in chip power consumption will not cause a large instantaneous change in temperature. In addition to the power consumption of servers and cooling equipment, in fact, hardware repair and maintenance costs are not a small cost for data centers.Server repair and maintenance costs are estimated to account for half of server and cooling electricity bills. According to practice, in the data center, the replacement frequency of the hard disk is the highest.In addition, the reliability and lifetime of electronic devices decreases by 50% for every 10 oC increase in temperature. Therefore, immersion (contact) liquid cooling technology can control the temperature uniformity of the server to the greatest extent, and greatly improve the performance and reliability of computing equipment.4) Reduce fan vibration, noise and energy consumption. Immersion (contact) liquid cooling technology does not require fans at all, minimizing noise pollution sources. 5) Improve the power density of the data center and reduce the floor space of the computer room. According to the 42U capacity configuration of a single cabinet, traditional 19-inch standard servers are placed, and the power density range of a single cabinet can be increased from 20kW to 200kW.

Contact liquid cooling has higher requirements on the purity of fluorinated liquid and the control of fluid boiling process.1) First of all, the fluorinated liquid in the liquid seal module must be very pure, and the residues generated during the welding process of the continuous pad between the chip and the substrate must also be cleaned (the actual operation is more difficult). Otherwise, after prolonged soaking and phase change cycles, these residues would dissolve and deposit on the pad during boiling. Long-term use will corrode the pads and cause them to fail.2) Second, in the fluid boiling cooling test, temperature fluctuations appear on the chip surface when the boiling of the chip surface just starts. In some experiments, if the chip had reached the desired temperature level before the boiling started, a significant hyperthermia (overheating) would occur at the beginning of the boiling and before a large number of bubbles appeared on the chip surface, raising the junction temperature of the chip.3) Finally, in the non-boiling test, if the chip is cooled by natural convection of fluorinated liquid, there will be unacceptable high temperature of the chip due to low specific heat capacity and insufficient heat dissipation capacity.

The cold plate liquid cooling has the highest maturity, and the immersion liquid cooling and spray liquid cooling have better energy-saving effects.At present, the three different liquid cooling solutions have some application cases in the communication industry. Among them, the cold-plate liquid-cooled heating device does not need to contact the cooling liquid. It has the earliest development time and high technology maturity. The cold-plate liquid cooling adopts micro-channel enhanced heat transfer technology with extremely high heat dissipation performance. It is used in military radar and high-density data centers. , high-performance computers, power batteries, and high-power LED heat dissipation are all applied in the field of heat dissipation. It is an effective application solution to solve the deployment of high-power consumption equipment, improve energy efficiency, reduce cooling operating costs, and reduce TCO; With 100% liquid cooling, it has better energy saving effect.Immersion liquid cooling has obvious advantages in energy saving and heat dissipation, and has been widely used in the fields of supercomputing and high-performance computing; there are relatively few research results and application practices of spray liquid cooling.