Vacuum Brazing Process of Heat Pipe Type Vacuum Collector
Source：http://mu263.comRelease Time：2018-05-31
The heat pipe is usually composed of a condensation section, an evaporation section, and a working medium. The inside of the heat pipe maintains a high degree of vacuum. When the heat is transferred from the high temperature heat source to the evaporation section of the heat pipe, the liquid medium in the pipe rapidly evaporates and vaporizes, absorbing a large amount of latent heat of vaporization during the heat transfer; the vapor of the working fluid gradually rises to the condensation section of the heat pipe, condenses on the cooler inner surface, and is released during the period. There is a lot of latent heat of vaporization; the condensed liquid fluid flows back to the evaporation section of the heat pipe by its own gravity; this cycle is endless and the heat is continuously transmitted from one end of the heat pipe to the other. At present, the heat pipe is commonly used, its metal shell is copper, and the internal working medium is water.
With the successful development, promotion and application of solar water heaters for civilian use, the heat collection efficiency of solar water heaters is required to be higher and higher. Therefore, heat pipes are applied as a high-efficiency heat transfer tool to the field of solar water heaters. The most typical application is the heat pipe type vacuum collector tube. . The heat pipe type vacuum heat collecting pipe is obtained by sealing a heat pipe welded with a metal heat absorbing plate in a vacuum glass pipe ( FIG. 2 ). In the work of the heat pipe type vacuum collector tube, solar radiation passes through the glass tube and is projected on the metal heat sink. The metal heat absorption plate absorbs solar radiation and converts it into heat energy. It is then conducted to the evaporation section of the heat pipe to quickly vaporize the liquid medium in the evaporation section of the heat pipe. After the vapor of the working fluid rises to the condensation section of the heat pipe, heat is released and the heat is transferred to the heat transfer medium of the solar collector. One end of the glass tube has a metal end cap and the glass tube is evacuated to a vacuum, so that air conduction and convection heat losses are reduced to negligible levels. In the heat pipe type vacuum heat collection tube, an evaporative getter and a non-evaporation getter are generally placed at the same time to maintain the high vacuum in the glass tube. Due to the adoption of heat pipe technology, the heat pipe type vacuum heat collection tube has the advantages of quick startup, no backflow of heat, strong antifreeze capability, good heat transfer performance, thermal shock resistance, and high heat collection efficiency, and is an inevitable choice for efficient use of solar energy.
For the heat pipe type vacuum collector tube, the performance of the heat pipe directly determines the heat transfer and collection efficiency, and the most critical factor affecting the performance and service life of the heat pipe is whether the negative pressure in the heat pipe can be maintained for a long time. Therefore, welding between the evaporation section and the condensation section of the heat pipe is particularly important. In order to avoid oxidation of copper tubes and solder during welding, vacuum brazing technology is used. In this paper, we examine the influence of parameters such as brazing vacuum degree, solder, vacuum welding power, and weld size on vacuum brazing performance. Then, the best vacuum brazing process was used to fabricate heat pipes and heat pipe vacuum collector pipes, and the performance of the samples was compared and tested.
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