What Is Free Cooling?

Natural cooling is the process of exhausting heat from the object to the environmental medium through heat transfer, such as heat exchange, convection, and heat radiation, reducing the temperature of the object, and finally reaching the same spontaneous process as the ambient temperature.

Free cooling is utilized

The principle of the natural cooling unit we introduced is as follows:

1. The entire air conditioning system uses

1) Most small electronic components are best cooled by natural cooling.

2) Maximize the use of simple and reliable cooling technologies such as heat conduction, natural convection and radiation.

3) Shorten the heat transfer path as much as possible and increase the heat transfer or heat transfer area.

4) Try to dissipate the heat generated in the module through the module chassis and mounting frame.

5) Reduce the contact thermal resistance during installation, and the arrangement of components is conducive to the convective heat transfer of the fluid.

6) Adopting heat dissipation circuit board, edge guide with small thermal resistance.

7) The installation direction and installation method of components should ensure that the heat can be transferred by convection to the maximum extent. The installation of components should fully consider the effects of heat radiation from surrounding components, etc., to ensure that the temperature of each component does not exceed its maximum operating temperature, and avoid excessive hot spots.

8) The distance between circuit board components is controlled between 19 and 21mm, and there should be no interference between components on adjacent boards, sockets, and heads in a vibrating environment.

9) For heat-sensitive components near the heat source, thermal isolation measures should be taken; increase the blackness of the surface of the chassis and enhance radiant heat transfer.

10) The key of transformer natural cooling design is how to reduce the thermal resistance of the heat transfer path. Thicker wires should be used and have good thermal contact with the mounting structure. The mounting surface should be flat and smooth. Metal foil can be added at the contact interface to reduce its interface thermal resistance. If the transformer has a shield, make sure that the shield and the base have a good thermal connection as far as possible. Installing copper tape between the shell or core and the base helps to enhance the guidance ability. ^[3]

If the climatic conditions are cold and the humidity is low, natural cooling is the only way to improve the cooling system, otherwise, the consequences will not prove that the investment in natural cooling is correct. For example, if the outside air is relatively cold but humid, it will require a necessary investment in equipment to reduce the humidity to an extreme limit, so this will offset the cost savings from natural cooling.

For relatively high temperature environmental conditions, the use of air is desirable. The main reason behind this principle is that the installation of water economizers is relatively expensive. Therefore, in relatively hot areas, the installation of water economizers may not be completely reasonable.

Another indirect way to supplement free cooling is to reduce the cooling load by increasing the temperature in the data center to some extent. It has been observed that most data centers are too cold. If the temperature is a bit higher, it is still OK. There is no doubt that this will lead to more efficient use of natural cooling.

Free cooling antenna

The natural cooling method relies on the surface of the antenna for heat radiation and convection. It is used for occasions where the power consumption of the antenna is low, the heat flux is low, or the working time is short.

The natural radiation cooling method is widely used for thermal control of spaceborne active phased array antennas. Considering the complexity and reliability, when the heat dissipation and heat flux density of the antenna is low, the antenna thermal control system generally does not use a liquid cooling or two-phase flow system. At this time, conduction and radiation are the most important thermal control methods.

Traditional thermal control systems are divided into two basic types: passive thermal control technology without automatic adjustment capability and active thermal control technology that can actively change heat transfer characteristic parameters according to temperature requirements. For a SAR antenna with relatively stable orbit and attitude, the thermal environment and working mode are relatively fixed, and there is no need to consider the adverse factors from human interference. However, most spacecraft adopt passive-active and active-assisted thermal control modes, and the change of periodic external heat flow can also be achieved by simple passive thermal control technologies such as coatings and multilayer insulation materials. A typical spaceborne SAR antenna thermal control solution is shown in the figure. Its heating unit includes T / R components, power modules, wave control units, etc., and the antenna dissipates heat through surface radiation to deep space.

Implementation scheme of spaceborne SAR antenna thermal control

In recent years, with the development and practical requirements of SAR antenna technology, especially the increase in antenna power and resolution has caused the array power consumption and heat flux density to increase rapidly, the existing thermal control technology has become increasingly unsatisfactory. Claim. The design concept of "autonomous thermal control technology" has become one of the research hotspots at home and abroad. Autonomous thermal control draws on the idea of autonomous operation of the spacecraft, meaning that the thermal control system does not rely on external information injection or external intervention as little as possible, and combines intelligent control actions with its own state to complete thermal control tasks. ^[4]