New technology for heat dissipation of electronic equipment
The gradual miniaturization and precision of electronic equipment has brought about the problem of heat dissipation. Temperature has a great influence on the working performance of electronic equipment. For a stable and continuous working electronic chip, the maximum temperature cannot exceed 85 ℃ as required. Every time the temperature of a semiconductor component increases by 10 ℃, the reliability of the system will be reduced by 50%. According to statistics, more than 55% of the failures of electronic equipment are caused by excessive temperature. In the traditional electronic chip, the volume used for cooling accounts for 98%, and only 2% is used for computing operation, but it is still difficult to solve the current heat dissipation problem. High temperature will have a harmful effect on the performance of electronic equipment, and those traditional heat dissipation methods have certain limitations. Therefore, in order to ensure the service life and efficient performance of electronic equipment, it is urgent to explore and develop better heat dissipation methods for electronic equipment.
01 Cooling technology The traditional heat dissipation method is often seen in our daily life, because the current development is very mature and the principle is simple, so I will not repeat it here.
1.1 Liquid cooling
Liquid cooling uses the liquid passing through the heat source to take away the heat generated by the chip, without noise, and has a high heat exchange capacity. The following are several methods of liquid cooling that are new technologies that are based on the traditional direct liquid cooling extension.
1.1.1 Microchannel cooling
Micro-channel cooling is to etch multiple micrometer-level fluid channels on the substrate below the chip, so that the heat of the chip is absorbed when the fluid flows through the channel. This method includes single-phase heat exchange and two-phase heat exchange. Among them, the heat capacity of single-phase heat exchange is small, the heat exchange effect is poor, and the temperature after cooling is uneven, resulting in excessive stress. On the contrary, the two-phase heat exchange has a large latent heat, the heat exchange capacity is high, the temperature after cooling is uniform, no great stress is generated, and the working fluid temperature does not rise very high. Two-phase heat transfer in microchannel cooling is a current research hotspot. In two-phase heat transfer using low-pressure refrigerant as a working fluid, the heat dissipation capacity can reach more than 300 W/cm2. Through experiments, Yu Zukang et al. obtained surface hydrophilic properties to effectively improve the heat transfer performance of microchannels. Under low heat flux and low inlet dryness, the average heat transfer coefficient of super-hydrophilic surfaces is the largest, which is 64% higher than that of ordinary smooth surfaces. The average heat transfer coefficient of the hydrophilic surface is up to 27% higher than that of the ordinary smooth surface; under the conditions of high heat flux and high inlet dryness, the average heat transfer coefficient value of the super-hydrophilic surface is up to about 80% higher than that of the ordinary smooth surface. The hydrophilic surface is up to about 50% higher than the normal smooth surface. Figure 1 shows the structure of microchannel cooling.
Critical Heat Flux (CHF) is one of the important parameters that affect the performance of microchannels. Yuan Xudong and others introduced the research progress of CHF in detail, and introduced its influencing mechanism and improvement methods in detail, as well as the CHF existing in academia. Differences in opinions. Due to the small size of the microchannel, the resistance along the way is very large; its structure also has a great influence on cooling, and the use of straight and parallel microchannels will cause a large pressure drop and temperature gradient. It has many advantages. Because the channels are etched and do not occupy more space, the microchannel cooling becomes more efficient and compact, and it is more suitable for small electronic chips. It is generally believed that the double-layer micro radiator can meet the increasing heat load of the next generation of electronic equipment. Xiaogang Liu et al. proposed the double-layer matrix structure (DL-M) and the double-layer interconnect matrix structure (DL-IM) structure of microchannels. And through numerical simulation to study the various performance of the radiator, it is proved that they have better thermal performance.
Although there are certain shortcomings in microchannel cooling, it can solve the problems that have arisen, and the development is more mature. Although the research on CHF has different views, this will not hinder the development of microchannel technology, and the future development direction will be more focused. How to improve CHF to achieve more efficient micro-channel cooling, this kind of heat dissipation method will also become more popular.
1.1.2 Spray cooling Spray cooling is to atomize the liquid through a nozzle to form a gas-liquid two-phase spray to the electronic device. One part of it absorbs heat and vaporizes, and part of the heat is taken away by phase change; the other part forms a liquid film on the surface of the heat source, and the heat follows the liquid. The flow of the membrane is taken away. The non-condensable gas in the liquid film enhances the disturbance to the heat exchange, which can greatly improve the heat dissipation capacity of electronic equipment. The phase-change heat heat flux density of spray cooling can reach more than 1000 W/cm2. Lin et al. used fluorocarbon, methanol, and water as working fluids for phase-change heat. The maximum heat flux density obtained through experiments was 90, 90, and 90, respectively. 490, 500 W/cm2 or more. Figure 2 is a schematic diagram of spray cooling.
This cooling method has certain shortcomings to be solved. The spray cooling method has a complex system, high space requirements, and is difficult to maintain. Because of its small liquid flow rate, uniform chip temperature distribution after cooling, and low stress, spray cooling is regarded as a heat dissipation method for electronic chips with good development potential. At present, because the existing problems have not been solved, it can only be used in military and aviation products. Wang Gaoyuan et al. conducted spray cooling experiments on R134a under low pressure conditions, and found that spray cooling under low pressure conditions gradually reduces heat transfer capacity with the decrease of pressure, and flash evaporation has a great influence on heat transfer capacity, which needs to be considered when arranging nozzles. Adding nanoparticles, surfactants, soluble salts and gases, and alcohol additives to the spray cooling fluid can greatly improve the heat transfer characteristics. Li Yiyi verified through experiments that the addition of surfactants can effectively improve the heat transfer performance of spray cooling, especially the addition of SDS has the best effect. However, the current method of adding additives is still in its infancy, and the existing problems are more complicated.
Spray cooling is restricted by space and cannot be used in small electronic devices, but the effect is very good when used in supercomputers. At present, spray cooling technology is applied to CREY supercomputers and is also used on a large scale in data centers. With the development of this cooling method, it is believed that the application will be more mature.
The above three liquid heat dissipation methods have their own advantages and disadvantages. Spray cooling and jet cooling are similar. Their structures are very complex and not suitable for daily electronic equipment. However, they have strong heat dissipation capabilities. Spray cooling is suitable for supercomputers, In big data heat dissipation; jet cooling is suitable for military-industrial items, such as fighter jets, aircraft, etc. These two heat dissipation methods cannot be replaced in recent years. Micro-channel cooling is the general direction of future development, whether it is in daily electronic equipment or other precision electronic instruments, this method will be adopted.
