5.1.1. Mechanical part of heat pipe manufacture

In the mechanical part of the production, the individual components of the heat pipe are first prepared: the body, the filling pipe, the wick structure, and the end caps. All components are then joined together by welding or soldering. In the case of wick heat pipe production, a wick structure is placed in the internal space of the body before to heat pipe closure. The closure of the heat pipe is the connection of the body with the end caps. In Figure 20, the standard types of the heat pipe closure by end caps are shown. The filling pipe is connected to one of the end caps due to the inner space vacuuming. After vacuuming, the heat pipe is filled with the working fluid,

Figure 20. Types of the heat pipe closure by end caps.

filling pipe is pressed, and after disconnection from the vacuuming pump, filling pipe is sealed by soldering.

5.2. Heat pipe manufacture

ture are shown.

Figure 21. Copper powders (35, 63, and 100 μm).

Although the production of the porous wick structure is most difficult from all types of wick structures, it is one of the three most used wick structures in the heat pipe, because it is able to create a large capillary pressure that allows the heat pipe to transfer a high heat flux in the antigravity position. One method of making a porous wick structure is to sinter a copper powder uniformly poured around a coaxially centered steel mandrel located inside the copper pipe at a temperature close to melting the powder material in a high temperature electric furnace. By sintering copper powders is possible made wick structure with the high thermal conductivity, high wick porosity, small capillary radius, and high wick permeability what are the main which the wick structure have to ensure supplies evaporator with the condensed liquid. The high thermal conductivity of copper ensures that the wick structure will not have high thermal resistance, which is one of the expecting properties of wick structure too. The formation of a suitable porous structure by sintering the metallic powder depends, in addition to the sintering temperature, both on the time of sintering and the grain size of the powder. Copper powders with a particle size of 30–100 μm or copper fibbers of 2–3 mm in length and a

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diameter of 20–100 μm are used for the production of porous sintering structure.

various pore size. The overall length of the heat pipes is 0.5 m.

The most important part of the heat pipe is wick structure. This expersiment deal with heat pipes with sintered wick structure made from copper powder with granularity of 100, 63 and 35 μm by sintering in the high thermal electric oven using powder metallurgy. By sintering the copper powder on the inner wall of the heat pipe container, 1.5 mm thick wick structures were created. The sintering process of the wick structure was approx. at temperature of 1000C and time of 30 min. Seeing that the pore size of the wick structure depends on the grain size of the copper powder, sintering the copper powder of various grain size creates the wick structure of

In Figure 21, copper powders are shown, and in Figure 22, manufactured porous wick struc-

The other important part of the heat pipe design depends on factors related to the properties of the working fluid. The working fluid must have good thermal stability in relation to the specific working temperature and pressure. The most important requirements that the working fluid must have are the following: compatibility with the capillary system and with the material of the pipe, high thermal stability, high state of heat, high thermal conductivity, low
