high power loop heatpipe cooling technology

     Loop heat pipe is a new type of heat pipe, which has the advantages of rapid start-up, good temperature uniformity and high heat transfer performance. It has been widely used in the field of thermal solution. 

 However, when applying loop heat pipe to solve the thermal problem of high-power chips, it faces the problems of high manufacturing cost and difficult processing technology. Therefore, It is necessary to explore the low-cost loop heat pipe heat dissipation module. Based on the manufacturing of single loop heat pipe and the combined application of multiple loop heat pipes, this paper meets the needs of high-power heat dissipation module, reduces the manufacturing process difficulty of loop heat pipe and the manufacturing cost of heat dissipation module, and has positive practical significance for the R & D and industrial application of high-power heat dissipation module.

Working Principle:

     First ,Sinter the capillary layer inside the "evaporation pipeline" of a single loop heat pipe, and then weld it with the "steam and liquid return pipeline and liquid injection pipe". Vacuum the entire pipeline through the "liquid injection pipe", and then inject an appropriate amount of refrigerant to form an independent loop heat pipe.

    Then, the four loop heat pipes and heat sink devices such as heat sink fins, aluminum blocks and copper blocks are welded into a whole to form a heat dissipation module; After the heat dissipation module is installed in the application scenario, the heat generated by the heat source causes the working medium in the capillary structure to change phase and generate steam. Driven by the pressure difference, the steam flows along the pipeline to the condenser end, releases the latent heat, cools into liquid, and returns to the evaporation end, so as to re circulate.

Material:

     The sintered tube is made of oxygen free copper c1020, with a diameter of 9mm and a wall thickness of 0.5mm.

Capillary layer design:

     The powder layer structure inside the sintering tube is designed to be conical, with one end as a small hole and the other end as an opening. Its purpose is to make the steam in the tube flow in the design direction, prevent the steam in the tube from diffusing equally to both ends at the same time, and form a steam balance in the tube, so as to block the steam in the tube and cause failure.

Loop Heatpipe Soldering:

     The loop heat pipe adopts high-frequency welding method, and the sintered pipe, copper pipe and liquid injection pipe are welded into a whole loop heat pipe. Considering that the heat pipe needs high-temperature reduction before liquid injection, therefore, the solder used for welding is high-temperature solder: 15ag, and the welding temperature is about 780 ℃ ~820 ℃.

Vacuum pumping of loop heat pipe:

     High temperature reduction shall be carried out for the loop heat pipe of the processed liquid injection port, and vacuum pumping shall be carried out as soon as possible after cooling. The vacuum degree shall be 3e-4torr.

Filling refrigerant:

       Fill refrigerant R134a into the loop heat pipe that has completed the vacuum pumping process through the liquid injection port. Since the boiling point of refrigerant R134a is low, the heat pipe needs to be injected in 5 ℃ ice water; The valve core and bonnet shall be tightened to prevent micro leakage of the needle valve.

Benefits And Advantages:

      The structure design of loop heat pipe heat dissipation module is flexible. According to different application scenarios and power consumption requirements, loop heat pipes with different structures, different quantities and different pipe diameters can be designed to be used in the same heat dissipation module to meet the heat dissipation requirements of various high-power chips;

      Loop heat pipe and other components are relatively independent components. A single loop heat pipe is made independently, which is easy to scale and mass manufacture; As an independent individual, the quality of a single loop heat pipe is easier to control to ensure that the heat pipe with qualified performance can flow into the next process and reduce the quality risk of the finished product. 

     The manufacturing process of a single loop heat pipe is easy to realize, and can basically be shared with common heat pipe manufacturing equipment, which can save the initial equipment investment cost.