How heat pipes work The heat pipe is a vacuum sealed container filled with a proper amount of working medium, and is a high-efficiency heat transfer element mainly composed of a die, a shell and a working medium. The heat pipe is made by sealing the pipe first and pumping it into a negative pressure. In this state, a small amount of liquid working medium is charged. The inner wall of the heat pipe has a concentric cylindrical wire mesh (or other porous medium), which is called a wick. The wick is filled with liquid working medium. When heat is transferred into the evaporation section of the heat pipe, the working medium absorbs heat and evaporates. Condensation section, where the medium vapor is cooled, releasing the latent heat of vaporization, condensing into a liquid, and then returning to the evaporation section under the action of the capillary force or gravity of the porous wick, thus repeating the cycle, passing the phase change and transmission of the working fluid The quality achieves efficient transfer of heat. The die and working fluid are the two most important parts of the heat pipe. On one hand, the die distributes the working fluid to the entire evaporation section and the condensation section, and on the other hand provides the means and power for the condensate to return. Traditional heat pipe research often studies gravity heat pipes based on the principle of thermosiphons, and there is no special die, just some cleaning or oxidation treatment of the inside of the pipe. More and more research institutions are now working on the study of die structures, especially capillary structures, such as wire mesh uniform dies, channel dies, and combined dies. The choice of working fluid in the heat pipe should take into account the temperature range of steam operation [2], and the compatibility of the working medium with the material of the die and the shell. Under the precondition of suitable temperature range and compatibility, the type and filling amount of the working fluid should be selected according to various thermodynamic constraints received by the heat flux in the heat pipe. These limits include viscosity limits, sound speed limits, capillary limits, carry limits, and boiling limits. Heat pipe characteristics (1) Excellent thermal conductivity. Since the heat pipe transfers heat in the form of latent heat, the heat pipe per unit weight can transfer several orders of magnitude of heat compared to metals such as silver, copper, and aluminum. (2) Isotherm with low thermal resistance. When the heat pipe is running, the temperature of the surface of the condensation section tends to be constant. If the heat load is locally applied, more steam is condensed there to maintain the temperature at the original level; likewise, the evaporation section is also isothermal. When the heat pipe is working, the steam in the pipe is in a saturated state, the temperature difference between the steam flow and the phase change is small, and the pipe wall and the capillary core are relatively thin, so the surface temperature gradient of the heat pipe is small, that is, the isothermality of the surface is good. (3) It has the ability to convert heat flux density. The space for evaporation and condensation in the heat pipe is separate, so that the heat flux density can be changed, the high heat flux density can be input in the evaporation section, and the low heat flux density can be output in the condensation section. vice versa. (4) Excellent thermal responsiveness. The internal pressure of the heat pipe is small, and when the evaporation end is heated, the steam advances at a speed of sound similar to that temperature. (5) The heat pipe has a simple structure, light weight, small volume and convenient maintenance. (6) The heat pipe has no moving parts, reliable operation and long service life. Working principle and characteristics of casing heat pipe heat exchanger The casing type heat pipe heat exchanger structure is a concentric phase sleeve of two unequal diameter pipes, which is also called a radial heat pipe because its heat transfer direction is radial. When the outer side of the outer tube is the high temperature side and the inner side of the inner tube is the low temperature side, the hot side working medium in the vacuum gap is heated to vaporize and expand, forming a high-speed convection with the cold side working medium and condensing on the cold side, that is, when the heat is introduced. When the outer tube of the heat pipe is used, the working medium absorbs heat and evaporates, and flows to the cold side, where the medium vapor is cooled, releasing the latent heat of vaporization, condensing into a liquid, and then returning to the hot side, thus repeating the cycle, passing the phase change and transmission of the working medium. The quality achieves efficient transfer of heat. In addition to the characteristics of a conventional gravity heat pipe heat exchanger, the casing type heat pipe heat exchanger has the following features. (1) The heat transfer direction can be carried out in both directions, either from the outside to the inside or from the inside to the outside; while the conventional gravity heat pipe can only be transmitted from the evaporation section to the condensation section and cannot be reversely transmitted. (2) The direction of the relative gravity field can be arbitrarily placed during operation, from vertical to parallel angle; while the conventional gravity heat pipe cannot work perpendicular to the direction of the gravity field. (3) Because the heat transfer between the hot and cold sides of the tube-type heat pipe heat exchanger is greatly shortened compared with the conventional gravity heat pipe, the heat transfer coefficient is increased, so the thermal resistance on both sides is small, and the temperature difference is correspondingly small. . (4) Since the cross-sectional area of ​​heat transfer between the hot and cold sides of the casing-type heat pipe heat exchanger is greatly increased compared with the conventional gravity heat pipe, the heat load per unit area on both sides can be large; the sound speed of the conventional gravity heat pipe is not available. Limits, carrying limits, no capillary limits and boiling limits. 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