Views: 113 Author: Site Editor Publish Time: 2019-10-15 Origin: Site
Vapor chamber is a vacuum cavity with fine structure on its vapor chamber wall, which is usually made of copper. When heat is conducted from the heat source to the evaporation area, the cooling liquid in the cavity starts to generate the gasification phenomenon of the cooling liquid after being heated in the environment with low vacuum degree. At this time, the heat energy is absorbed and the volume expands rapidly. The cooling medium in the gas phase rapidly fills the whole cavity. When the working medium in the gas phase contacts a relatively cold area, the condensation phenomenon will occur. The condensation phenomenon releases the heat accumulated during evaporation, and the condensed cooling liquid will return to the evaporation heat source through the micro-structure capillary tube, and this operation will be repeated in the cavity.
Vapor chamber is usually used for electronic products requiring small volume or rapid dissipation of high heat. At present, it is mainly used in servers, high-grade graphics cards and other products. It is a strong competitor to the heat dissipation method of heatpipe solutions.
The vapor chamber is a flat plate-like object in appearance, and the upper and lower covers are closely connected with each other, and copper columns are supported in the covers. The upper and lower copper sheets on the vapor chamber are made of oxygen-free copper, usually pure water is used as the working fluid, and the capillary structure is made by copper powder sintering or copper net process. As long as the vapor chamber maintains its flat plate characteristics, the shape profile is relatively unrestricted depending on the environment of the applied heat dissipation module, and there is no restriction on the placement angle during use. In practical application, the temperature difference measured at any two points on the flat plate can be less than 10℃, which is more uniform than the conduction effect of the heat pipe to the heat source, hence the name of vapor chamber. The thermal resistance of the common vapor chamber is 0.25℃/W, which is applied to 0℃ ~ 100℃.
The working principle of the vapor chamber cooling system is the same as that of the heat pipe, including four main steps of conduction, evaporation, convection and solidification. The vapor chamber is a two-phase fluid device formed by injecting pure water into a container full of microstructures. Heat enters the plate through heat conduction from the external high-temperature area, and water around the heat source near the point quickly absorbs heat and vaporizes into vapor, taking away a large amount of heat energy. Using the latent heat of water vapor, when the vapor in the plate diffuses from the high-pressure region to the low-pressure region (i.e. the low-temperature region) and the vapor contacts the lower-temperature inner wall, the water vapor quickly condenses into liquid and emits heat energy. Condensed water flows back to the heat source point by capillary action of microstructure to complete a heat transfer cycle, forming a two-phase circulation system in which water and water vapor coexist. Gasification of water in the vapor chamber continues, and the pressure in the chamber will keep balance with the change of temperature. The heat conduction coefficient of water is relatively low when it operates at low temperature, but because the viscosity of water varies with temperature, the vapor chamber can also operate at 5℃ or 10℃. Since the liquid backflow is effected by capillary force, the vapor chamber is less affected by gravity, and the design space of the application system can be used at any angle. The vapor chamber has no power supply and no moving components, and is a completely sealed passive device.
The principle and theoretical framework of the combination of vapor chamber, VC heatsink, cast heatsink and extrusion heatsink are basically the same, with the difference in dimensions, manufacturing method, vacuum pumping and water injection procedures, etc. The vapor chamber technologyhas the advantages of low expansion thermal resistance, uniform heat flux, rapid heat diffusion, light weight, etc.
