What liquid is in the heat pipe radiator and what is its function?

It is pure water. The heat pipe of the heat pipe radiator is not a hollow pipe structure, but has many flocculent or needle-like capillaries on the inner wall. When the water in the heat pipe that comes into contact with the CPU is heated and evaporated, it will rise to the top of the heat pipe, then be cooled by the cooling fan, and return to the CPU base as liquid. Because it is fully enclosed and has a capillary structure, all the effects of gravity on the internal liquid can be ignored. However, due to the different design and materials of heat pipes, the heat dissipation of CPU is slightly different in different installation directions. Some products will have a sudden decrease in heat dissipation effect at a certain angle, but this situation is relatively rare.