**3.4 Loop heat pipe assembly**

The connection between evaporator and condenser in heat pipe is vapor pipeline and liquid pipeline. In order to reduce the flow resistance of the medium, the more smooth the inner, the better. In this paper, stainless steel tube is selected and the inner polishing is done. The vapor liquid phase change process is involved in the operation of the loop heat pipe, and the sealing property is very high. Therefore, stainless steel is used in all parts of the loop heat pipe, and the connection between each part is argon arc welding. All stainless steel components (including liquid accumulators and evaporators) should be cleaned according to the stainless steel cleaning method before final use to improve the performance of the loop heat pipe. The loop heat pipe also needs to be equipped with a new belt valve. The working fluid filling mouth of the door is filled and sealed with heat pipe working fluid. After welding the loop heat pipe, it is necessary to pick up the leakage of the system, inflate the system with air compressor from the filling port, and place the system

**Figure 16.** *Condenser structure (including two heat dissipation modes).*

in water. If there is no bubble, the system is sealed completely, and if there is air bubble, the leakage point of welding should be rewelded. In order to reduce the difficulty of welding and to facilitate the performance experiment in the future, the loop heat pipe is made into a rectangle, 1000 mm in length and 300 mm in width, in order to match the heat transfer test bed designed later.

The structure and dimensions of the heat pipe are described in **Figure 17** and **Table 1**.

### **3.5 Vacuum and perfusion of loop heat pipes**

In addition to the capillary core properties, the internal working fluid perfusion of the loop heat pipe has the greatest influence on the performance of the loop heat pipe. There are two factors that influence the perfusion effect: one is the quality of perfusion, the other is the degree of vacuum during perfusion, that is, the purity of the injected working fluid. First of all, the heat pipe is filled with flux, when the charge is too small, it will cause the heat pipe to be burned out in the liquid storage device of the heat pipe evaporator, and the heat pipe will fail. When the charge is too much, there will be a lot of liquid working fluid in the condenser, which will cause excessive resistance along the path and hinder the forward operation of the heat pipe. It is inevitable to mix air and other non-condensable gases when pouring working fluid into the loop heat pipe. The research of Beihang [84DIAN85] finds Danghuan when there are non-condensable gases such as nitrogen in the heat pipe, it will lead to the difficulty of starting the loop heat pipe, the high temperature of the evaporator and

#### **Figure 17.**

*Loop heat pipe structure diagram.*


**39**

**Figure 18.**

*Perfusion pipeline diagram.*

*The Recent Research of Loop Heat Pipe*

**3.6 Vacuum infusion**

shown in **Figure 18** above.

*DOI: http://dx.doi.org/10.5772/intechopen.85408*

the decrease of the heat transfer efficiency. It is also found that the non-condensable gas will greatly reduce the service life of the loop heat pipe. Therefore, it is necessary to maintain a vacuum environment during perfusion. We should pay attention to the leakage of the loop heat pipe and the leakage of the working fluid during the simula-

Loop heat pipe perfusion is divided into two important steps: first, vacuum, and secondly, perfusion. Therefore, a loop heat pipe perfusion platform integrating vacuum pumping and perfusion is established in this paper. Based on dual functions, the pipeline must have two routes. The first is the perfusion pipeline, which is used to introduce liquid ammonia into the loop heat pipe. The perfusion line is

The pipeline is designed from top to bottom, the top is a liquid ammonia bottle, and the bottom is connected with a loop heat pipe. The loop heat pipe outlet is a pressure reducing valve to monitor the liquid ammonia outlet and the pressure in the pipeline. Then there are two condensing units to try to prevent liquid ammonia from liquefaction. Ensure the accuracy of subsequent flowmeter measurements and prevent too much gas in the pipeline from fluctuating the flow rate. The flowmeter is used to detect the amount of heat in the heat pipe. Continue after a one-way valve to prevent working fluid backflow. One-way valve is a flow valve. The pressure reducing valve can control the flow velocity of the working fluid in the pipeline to control the filling speed. The flow valve is followed by the valve and the loop heat pipe.

The exhaust line also consists of two parts, one is the air in the perfusion line and the other is the air in the heat pipe of the loop, as shown in **Figure 19**. The design scheme of the main line of the heat pipe pumping vacuum perfusion test rig is shown in **Figure 22**. The valve which combines the pouring pipe and the vacuum pumping pipe to control the pipe passage condition is designed as shown in **Figure 20**.

The designed pipe is placed vertically, the aluminum alloy frame is arranged, and the flowmeter display device is designed to monitor the quality of the working fluid that has been poured in the heat pipe. During perfusion, the heat pipe accumulator should be placed in a lower temperature environment than the perfusion tube condenser. This is because it is difficult for liquid ammonia to flow into a loop heat pipe simply because of the gravity effect, so that the temperature in the heat pipe is lowered so that the pressure inside the loop heat pipe remains relatively low all the time. The flow of liquid ammonia in the pipeline is promoted by the pressure of different positions in the pipeline. The vacuum pumping system designed

tion of the perfusion according to the way mentioned in this paper.
