Overview of heat pipes and equalizing plates
The manufacture of heat pipes and temperature equalizing plates is achieved by making grooves or sintering powder in a copper tube or a flat cavity. Grooves and sintered powder form a capillary structure.
Then add a small amount of working fluid to the device, and then vacuum seal. The core structure (sintered powder, mesh, groove) and liquid (water, ammonia, nitrogen) can be changed to achieve the purpose of changing the heat transfer characteristics of the equipment. A complete two-phase cooling module includes one or more heat pipes and/or steam chambers, a heat sink set for dissipating heat into the surrounding air, and a mechanical method of connecting the radiator to the heat source.
When heat acts on a two-phase device (evaporator), as shown in the figure, the liquid near the heat source will vaporize, increasing the vapor pressure. This local pressure increase causes steam to flow to the low pressure area of the equipment (to the condenser).
The steam will condense on all colder surfaces to form an isothermal device. Next, the condensate transfers the latent heat of the steam through the condenser wall to the fins and is discharged into the air. The condensate is absorbed by the wick and capillary, and then the water is moved back to the evaporator.
This process is like immersing a corner of a sponge in water to completely absorb water. Although gravity plays a role in this cycle, the natural capillary action of the core (sintered metal, grid or groove) is the main cause of liquid movement. Heat pipe and steam chamber wick type
The most common heat pipe core material structure is sintered core material, because it has the highest versatility in terms of power handling capacity and anti-gravity work ability. Mesh screen cores are less expensive to manufacture, but allow the heat pipe or steam chamber to be thinner relative to the sintered core. However, since the capillary force of the screen is significantly smaller than that of the sintered core, its ability to resist gravity or handle higher thermal loads is reduced. The groove core has the lowest cost and performance. Only when the evaporator is located below the condenser should gravity assist applications be considered. The groove serves as an internal fin structure to help evaporation and condensation.
The most common uniform temperature plate structure is as follows:
Choice of heat pipe and uniform temperature plate
1. The heat pipe transfers heat, and the uniform temperature plate emits heat.
For many reasons, thermal design may require the heat source to be located at different positions of the radiator, the heat pipe can be formed in any shape along all the axial directions, and even the heat pipe can extend from the substrate to the fin. This is impossible to achieve with a uniform temperature plate.
When the thermal power of the chip is very large, the speed of heat diffusion is required. And temperature gradient. At this time, the uniform temperature plate has an advantage, because the uniform temperature plate is two-dimensional, and the heat pipe is one-dimensional.
The use of heat pipes for low power or low power density is cost-effective. If multiple heat pipes are used, an even temperature plate can be considered.
2. If the power is small and the density is very high, the effect of using a uniform temperature plate will be much better. Because the surface of the uniform temperature plate is large and flat, the heat source and the uniform temperature plate are in direct contact. The heat pipe needs the support of the substrate to realize the heat transfer. The uniform temperature plate does not need an intermediate medium, the cooling effect will increase by 3-4 degrees, and the thermal resistance of the condensation zone is two-dimensional, which can be reduced by 1-2 degrees. Therefore, it is recommended to use a temperature equalizing plate in low-power and high-density occasions.
Finally, it is recommended that if the temperature difference at the bottom of the chip exceeds 10 degrees, it is recommended to use an equalizing plate or heat pipe to quickly transfer heat. To achieve the optimization of semiconductor electrical performance.
