With the explosive growth of data volume, a large amount of computing power needs to be supported by massive servers. Limited by the construction area of the data center and environmental protection regulations, increasing the power density of a single cabinet has become a key solution to reconcile the growing computing power demand and limited data center carrying capacity. A large amount of data throughput and computing makes the data center, as the "brain" of emerging technologies such as artificial intelligence and big data, face unprecedented challenges in energy consumption and heat dissipation.

Under this background, the liquid cooling data center, which applies liquid cooling technology and liquid cooling server and other equipment, came into being, providing a new solution for the cooling of the data center.

Liquid cooling refers to the technology that uses liquid to replace air as refrigerant to exchange heat for heating parts and take away heat. The efficient cooling effect of liquid cooling technology effectively improves the service efficiency and stability of the server. At the same time, it enables the data center to arrange more servers in the unit space to improve the operation efficiency of the data center. It has the advantage of noise reduction, and the utilization of waste heat can also create more economic value.

This article will popularize science for you from three aspects: liquid cooling technology classification, liquid coolant (coolant) and outdoor cold source. Today, the theme is liquid coolant.

2、 Liquid coolant

Liquid coolant, also known as coolant, refers to the use of liquid cooling medium, such as antifreeze used in automobile engines. The liquid medium involved in liquid cooling technology, in addition to maintaining the liquid state under the temperature and pressure of the operating environment, also includes the medium that is mainly liquid in use but can be partially or completely transformed into a gas state to take away heat.

Compared with air, liquid coolant also has good fluidity, but the molecular spacing of liquid substances is smaller, and the heat taken away by unit volume of liquid is far more than that of the same volume of gas, thus obtaining better heat transfer effect. In theory, using liquid as the cooling medium can design a smaller and more efficient cooling system.

Liquid cooling technology not only has single-phase application of absorbing heat through temperature rise (or sensible heat), such as single-phase cooling circuit composed of pump, heat exchanger and radiator; There are also phase change systems that use the latent heat of vaporization of low boiling volatile liquids to absorb heat, such as heat pipes, thermosyphons, spray cooling and phase change liquid cooling systems.

In the cooling application of electronic equipment, there are many requirements for liquid coolant, and the requirements will change accordingly according to the specific type of application. The requirements are summarized as follows:

Good thermophysical properties (high thermal conductivity and specific heat, low viscosity; high latent heat of vaporization in phase change applications);

Low freezing point and expansion coefficient (especially for water-based liquids that expand during solidification, it is required to have corresponding expansion protection measures in low temperature environment, such as - 40 ℃ or below, to facilitate transportation and storage);

High boiling point of liquid in single-phase application, or low steam pressure at operating temperature;

Suitable boiling point and narrow boiling range required by phase change system (higher than ambient temperature and lower than maximum operating temperature of heating element);

Good chemical and thermal stability for electronic systems;

High flash point and autoignition temperature (or completely nonflammable);

It is non corrosive to materials (metal, rubber, plastic and other substances) composed of the system;

No or only minimal regulatory restrictions (non-toxic, environment-friendly, biodegradable, etc.) are required;

Economy.

It can be seen from the above that the ideal electronic coolant should be a cheap non-toxic liquid, with excellent thermophysical properties, and compatible with the materials in contact with the system. It has the characteristics of flame-retardant or nonflammable in order to meet the safety needs, and needs to have high stability to achieve a longer service life, as well as the degradability after emission or waste.