JPH03156293A - Liquid metal heat pipe structure operated in bottom heating mode - Google Patents

Abstract

PURPOSE:To prevent dryup of the heat transfer surface of an evaporator by engraving cutouts at both upper and lower ends of a cylindrical laminated wick, opening a radial through hole at a position suitably separated from both ends, and concentrically disposing a columnar article with the wick in the evaporator of the vapor passage. CONSTITUTION:Heat is applied externally to the evaporator E of a heat pipe having a wick 11, work fluid is evaporated, vapor is fed to a condenser C, and condensed by heat radiating. The fluid is heated to generate bubbles in an air gap 12 of the evaporator E at the time of starting to heat to rise in two phases flow in the air gap 12. As the bubble rises, a cold work fluid flows from a cutout 11a, a through hole 11c to the gap 12. A part of the rising fluid is discharged through a cutout 11b and a through hole 11d to a vapor passage 13, condensed and fed down along the wick 11. As input heat is increased, the temperature of the fluid in the evaporator becomes uniform to be evaporated and boiled. The wick 11 is so extended as to slightly increase the interval of the air gap 12, a condensed liquid is always circulated, and local dryout is avoided due to sealing fluid quantity reducing effect by a columnar article 14.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for generating capillary pressure in the evaporator section in a liquid metal heat pipe that operates in a bottom heat mode.
This invention relates to a wick and a cylindrical object provided in the evaporator to uniformly wet the inner wall surface of the evaporation section, promote heat transfer, and reduce the amount of enclosed working fluid.

[Conventional technology]

As is well known, liquid metal thermosiphon heat pipes are
The working fluid sealed inside the sealed tube evaporates and condenses and circulates between the evaporating section and the condensing section to transport heat, and the working fluid that radiates heat in the condensing section is transferred to the evaporating section. To achieve reflux, gravity is used, and the capillary pressure generated by the wick is not used, so there is no wick.

[Purpose of the invention]

As mentioned above, in the thermosiphon type heat vibrator,
Normally wicks are not used. When a liquid metal working fluid is filled in 10 to 30% of the internal volume of the evaporator section, as is adopted in a normal thermosiphon heat pipe, in the case of bottom heat mode, the working fluid accumulates at the bottom of the sealed tube. ,
At the start of heating, 70 to 90% of the inner wall area of the evaporator section is heated without coming into contact with the working fluid. In addition, liquid metal has a higher density than water, etc., and therefore has a large heat capacity and a high boiling point, so it takes a long time for the liquid metal working fluid to start evaporating. Heat transfer surfaces that are not in contact may reach abnormally high temperatures. Furthermore, even if some evaporation occurs, the amount of evaporation is small and the reflux liquid does not flow down the inner wall surface uniformly, so that a portion of the inner wall of the evaporation heat transfer surface remains unwetted. For example, the surface temperature of the heat pipe evaporator part that is in contact with the working fluid is 400°C, but the surface temperature of the heat pipe evaporator part that is not in contact with the working fluid is 8°C.
There are places where the temperature reaches 00°C or higher. In such a situation,
Problems arise in the heat resistance strength of sealed pipe materials. Therefore, there is a risk of damage to the sealed tube at the start of heating, and operation at the start of heating may be extremely difficult. Further, when bumping occurs, a large amount of heavy working fluid falls from the condensing section to the evaporating section, and an impact force is applied to the end plate on the evaporating section side.

In order to remove as much as possible the damage caused by overheating of the sealed tube at the start of heating and the impact force on the end plate of the evaporator section due to bumping, 1) Attach a wick to the evaporator section and wet the heat transfer area of the evaporator section as much as possible. You must do so. or,
2) In order to alleviate the impact force, it is necessary to reduce the amount of working fluid and satisfy the condition (2). This invention was made in view of the above circumstances, and it cleverly utilizes the air bubbles generated in the gap between the inner wall of the sealed tube and the wire mesh wick, and also by providing a cylindrical object in the steam passage of the evaporation section. The purpose is to prevent the notch on the evaporator side from drying out, reduce the amount of working fluid, and alleviate the impact force, thereby improving the performance of liquid metal heat pipes that operate in bottom heat mode.

[Structure of the invention]

In order to achieve the above object, this invention provides notches and through holes in the wick to prevent the working fluid from drying out and allows it to flow in and out, and also provides a cylindrical object in the steam passage of the evaporation section to reduce the amount of working fluid. is arranged. More specifically, a laminated wick mainly consisting of a plurality of laminated wire meshes formed into a cylindrical shape is stretched over the inner wall surface of a sealed tube, and notches are carved at both upper and lower ends of the cylindrical laminated wick. At the same time, radial through holes are bored in the cylindrical laminated wick at positions appropriately spaced from both ends in the axial direction, respectively,
A cylindrical object is arranged concentrically with the cylindrical laminate wick in an evaporation section of a steam passage formed on the inner peripheral side of the cylindrical laminate wick.

[Effect]

In a heat pipe with a wick configured as described above, when external heat input starts in bottom heat mode, the working fluid in the gap first boils. Since it is difficult for the bubbles generated at this time to escape to the steam passage through the mesh of the wick, they rise through the gap along the pipe wall. As the bubbles rise, the working fluid passes through the notch or through hole on the evaporator side and is sucked in from the steam passage side. A portion of the working fluid that rises along the pipe wall travels in vapor form and the rest in liquid form. That is, a two-phase flow is formed.

At this time, the vapor is cooled in the condensing section, becomes a liquid, and flows back through the gap, and some passes through a notch or through hole on the condensing section and flows back through the steam passage. Due to the liquid that has returned to the narrow gap, the working fluid in the narrow gap passes through the mesh, the notches or through holes on the evaporator side, and is pushed out to the steam passage side. As a result, the temperature of the working fluid on the steam passage side rises quickly. When the heat input is small, the evaporation of the working fluid in the narrow gap, the generation and rise of bubbles produces a large pumping effect, and plays an extremely important role in heating and circulating the working fluid.

As the heat input increases, evaporation and boiling begin to occur not only in the narrow voids but also outside the wick layer.

Therefore, the occurrence of extremely large boiling that would occur if no wick is provided is suppressed, and good heat exchange with the working fluid is always performed. As a result, the heat flux is increased, and damage caused by the temperature rise of the sealed tube at the start of heating is eliminated, ensuring extremely stable operation.

〔Example〕

Next, an example of this invention will be explained with reference to the drawings.

The sealed tube IO, which is a heat pipe container, has a structure in which both ends of a metal tube are sealed by end plates 10a and 10b, and the inner wall surface 10c is laminated and formed in a cylindrical shape to generate capillary pressure. The cylindrical laminated wick 11, which is equipped with a cylindrical laminated wick 11 mainly made of a plurality of pieces of wire mesh, is stretched over the hermetic tube 10 with a very narrow gap 12 between it and the inner wall surface 10c of the hermetic tube 10. There is. In addition, the cylindrical laminated wick 11 has notches lla at both ends.
, llb are engraved. Further, a plurality of radial through holes 11 are provided at positions appropriately spaced from both ends in the axial direction so as to communicate the gap 12 and the steam passage 13.
C111d is bored in the cylindrical laminated wick 11.

The evaporator end plate 1 is designed so that the working fluid exists over the entire heat transfer surface of the evaporator and to reduce the amount of liquid required for this purpose as much as possible.
A cylindrical object 14 with one end deflected is placed at 0a. The cylindrical object 14 is concentric with the cylindrical laminated wick 11, and its length and diameter are determined by the inner diameter of the sealed tube 10, the amount of working fluid enclosed, the length of the evaporation section, and the like.

In the heat pipe having the wick 11 having the structure shown in FIG. 1, the working fluid is evaporated by applying heat from the outside to the evaporation section E in the bottom heat mode, and the vapor is transferred to the condensation section. After flowing into C, it radiates heat and condenses. In that case, at the start of heating, the evaporation section E
In the cavity 12 , the working fluid is heated to form bubbles that rise through the narrow cavity 12 in a generally two-phase flow. As the bubbles rise, the notch lla or the through hole 11c
The surrounding cold working fluid flows into the cavity 12 from the air. On the other hand, a part of the rising two-phase flow flows through the notch llb and the through hole 11d.
is discharged into the steam passage 13, condenses and becomes the wick 11.
flowing down along the As the heat input increases, the occurrence of two-phase flow in the gap 12 decreases, and the temperature of the working fluid in the evaporator becomes uniform, causing evaporation and boiling to occur on average.

The wick 11 is stretched so that the gap in the cavity 12 is slightly larger than that of a heat pipe having a normal wick. In this way, since the condensed liquid is constantly refluxed, local dryout is less likely to occur.

〔Effect of the invention〕

As is clear from the above description, according to the cylindrical laminated wick 11 and the internal structure of the evaporator section of the present invention, the gap 12 formed between the inner wall surface 10c of the sealed tube 10 and the wick 11
and a notch lla that communicates with the steam passage 13.

11b or through holes 11c and lld, it is possible to utilize the pumping of air bubbles generated in the cavity 12. As a result, due to the effect of reducing the amount of sealed working fluid due to the cylindrical object 14 placed in the evaporation part of the steam passage 13, damage to the sealed tube is caused by localized dryout that occurs at the start of operation of the liquid metal heat vibrator operated in the bottom heat mode. 11a, llb notch, llc, llb through hole, which can avoid damage to the end plate due to bumping, increase heat flux, and improve heat transport ability.

[Brief explanation of the drawing]

FIG. 1 is a partially omitted schematic exploded sectional view showing an embodiment of the present invention, and FIG. 2 is a schematic exploded perspective view of a wick. Both figures show the posture in bottom heat mode, with the bottom direction being downward. 10 Sealed tube, 11 Cylindrical laminated wick, Fig. 1 Y2 Fig.

Claims (1)

[Claims] A laminated wick mainly consisting of a plurality of laminated wire meshes formed into a cylindrical shape is stretched over the inner wall of the sealed tube, and notches are carved at both the upper and lower ends of the cylindrical laminated wick, and from both ends Radial through holes are formed in the cylindrical laminated wick at positions appropriately spaced apart from each other in the axial direction, and a cylindrical object is inserted into the evaporation section of the steam passage formed on the inner peripheral side of the cylindrical laminated wick. The structure of a liquid metal heat pipe operating in bottom heat mode is characterized by its concentric arrangement with a laminated wick.