JPH0547964Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a heat pipe used in a heat exchanger, and in particular to a heat pipe with a double tube structure.

BACKGROUND TECHNOLOGY A double-tube heat pipe has a condensable fluid sealed as a working fluid inside an evacuated sealed tube.
The working fluid undergoes heating evaporation, heat dissipation and condensation, and then circulates and flows inside the sealed tube, thereby transporting heat as latent heat of the working fluid, which has the characteristics of a heat pipe with excellent thermal conductivity. When exchanging heat between different types of fluids,
Because it has a double-tube structure in which a heat pipe is installed in a jacket shape on the outer circumference of one pipe that flows through the fluid, even if a defect such as a pinhole occurs in the pipe that flows through the fluid, the leaked fluid will be removed. A heat exchanger that exchanges heat between fluids that must avoid contact or mixing, such as sodium and water, because they only mix with the working fluid in the heat pipe and do not mix directly with the other fluid. etc. is also used.

FIGS. 6 and 7 show conventional double-tube heat pipes, and the double-tube heat pipe 1 is
It has an outer tube 2 which is disposed vertically with both ends sealed and an inner tube 3 which passes through the outer tube 2 vertically along the axis in an airtight manner. A condensable fluid such as mercury or Freon (trade name) is sealed as a working fluid 4 in the airtight space between the outer tube 2 and the inner tube 3 after being vacuum degassed. The space between the outer peripheral surface and the outer circumferential surface has a heat pipe structure.

The double-tube heat pipe 1 is, for example, disposed vertically in a high-temperature tank 5a so that the outside of the outer tube 2 serves as a high-temperature heat medium 5, and the inside of the inner tube 3 is provided with a low-temperature heat medium. (see Fig. 7), and when the inner circumferential surface of the outer tube 2 is used as the evaporating section and the outer circumferential surface of the inner tube 3 is used as the condensing section, the working fluid 4 flows through the outer tube 2. It receives heat from the outside on the inner circumferential surface of the tube and evaporates, and the steam flows toward the center and is heated to the inner tube 3.
As a result, the working fluid 4 transports the heat possessed by the high-temperature heat medium as its latent heat toward the low-temperature heat medium flowing inside the inner tube 3, and the heat medium of both Heat exchange takes place between them.

Problems to be Solved by the Invention However, the conventional double-tube heat pipe 1 described above is arranged vertically, and the heat pipe is disposed vertically so that the outside of the outer tube 2 is high temperature and the inside of the inner tube 3 is low temperature. When the exchange is performed, the working fluid 4 forms a liquid pool in the lower part of the outer pipe 2 of the double-pipe heat pipe 1, and becomes less dense and dilute as it goes to the upper part of the outer pipe 2. There is a tendency that this upper part is thin,
When heat is input over the entire length of the outer tube 2, uniform evaporation may not occur, and an abnormally high temperature area may occur in the upper part due to dryout. However, there was a problem in that the effective area of the evaporation section was reduced and the function of the heat pipe was degraded, resulting in a significant decrease in performance as a heat exchanger.

This idea was created in view of the above problems.
The purpose is to provide a double-pipe heat pipe for heat exchangers with excellent heat exchange efficiency.

Means for Solving the Problems As a means for solving the above problems, the double-tube heat pipe for heat exchangers of this invention has an outer pipe that is sealed at both ends, and an inner pipe that is airtight along the axial direction of the outer pipe. In a double-tube heat pipe for a heat exchanger, the working fluid is sealed in a sealed space between the outer circumferential surface of the inner tube and the inner circumferential surface of the outer tube in a vacuum deaerated state. is divided into multiple chambers in the axial direction by a partition plate, and a ventilation hole with a diameter less than the Taylor coefficient λ defined by the formula λ = 2π√( _-V ) is formed in this partition plate. This is a characteristic feature. Here, σ is the surface tension of the liquid-phase working fluid, g is the gravitational acceleration, ρ is the density of the liquid-phase working fluid, and ρ _V is the density of the gas-phase working fluid.

Operation With the above configuration, the working fluid in the outer tube evaporates when it receives heat from the high-temperature heat medium, and the vapor flows upward through the ventilation holes in the partition plates that partition each chamber. Move into each chamber. In each chamber, the steam radiates heat on the outer circumferential surface of the inner tube through which the low-temperature heat medium flows.
Condenses and liquefies. The liquefied working fluid travels down the outer circumferential surface of the inner tube due to gravity, reaches the partition plates that partition each chamber, and attempts to flow down through the ventilation holes formed in the partition plates. The diameter of the vent hole formed in the partition plate is λ=2π√( _-V ) (where σ is the surface tension of the liquid phase working fluid, g is the gravitational acceleration, ρ is the density of the liquid phase working fluid, and ρ _(V is the density of the gas-phase working fluid.) Since the working fluid in the liquid state forms a liquid film on the vent hole and blocks the flow, The working fluid that is prevented from flowing down to the lower chambers accumulates on the partition plate, forming a working fluid reservoir for each chamber. Therefore, the working fluid is distributed uniformly to each chamber, and subsequent heat exchange is carried out in each chamber divided in the height direction within the double-pipe heat pipe. Since the isothermal surface temperature distribution of the tube is maintained, the occurrence of abnormally high temperature areas such as dryout caused by the low density of the working fluid is prevented, and a sufficient effective area of the evaporation section is secured, maintaining high heat exchange efficiency. be done.

Embodiment Hereinafter, an embodiment of this invention will be shown in Figures 1 to 5.
This will be explained based on the diagram.

A double-tube heat pipe 11 for a heat exchanger includes a cylindrical outer tube 12 whose both ends are sealed by end plates 12a, and a tube having a smaller diameter than the outer tube 12 and coaxially passing through the outer tube 12 in an airtight manner. Inner pipe 13
and four partitions provided at approximately equal intervals so as to equally and airtightly divide the sealed space formed between the outer circumferential surface of the inner tube 13 and the inner circumferential surface of the outer tube 12 in the axial direction. The inside of the sealed space is divided into five chambers C 1 to C 5 in the axial direction by four partition plates 14, and adjacent chambers C ₁ to _{C 5} are formed in each partition plate 14. The chambers are in communication with each other, and the sealed space between the outer tube 12 and the inner tube 13 is filled with a condensable fluid such as mercury, fluorocarbon, or molten sodium after being vacuum degassed to perform a heat exchange action. A working fluid 16 having a boiling point within a temperature range is enclosed.

A plurality of ventilation holes 1 are formed in each of the partition plates 14 and communicate between adjacent chambers.
The diameter D of 5 is a dimension that allows the working fluid 16 to pass through when it is in a vapor state (gas phase), and allows the working fluid to form a liquid film and close the vent hole when the working fluid 16 is in a liquid state (liquid phase). When molten sodium is sealed as the working fluid 16, a hole with a diameter that matches the surface tension and physical properties of molten sodium such as viscosity is formed, and λ=2π√( − _V ) (where σ is the surface tension of the liquid-phase working fluid, g is the gravitational acceleration, ρ is the density of the liquid-phase working fluid, and ρ _V is the density of the gas-phase working fluid.) The holes are formed with dimensions smaller than the value of λ.

Next, when the double tube heat pipe 11 of this embodiment configured as described above is used in an intermediate heat exchanger of a fast breeder reactor that exchanges heat between both heat media of molten sodium and water. Explain the effect of

The intermediate heat exchanger of a fast breeder reactor is designed to prevent the two heat carriers from mixing in the event of an accident.
Molten sodium serving as a heating source is disposed outside the outer tube 12 of the double tube type heat pipe 11, and the outer tube 1
Both heat carriers are completely separated so that water flows through the inner tube 13 separated by a chamber in which the working fluid 16 is sealed inside the outer tube 12 or the inner tube 13.
When a defect such as a pinhole occurs in the chamber, the leaked heat medium flows into the chamber and is prevented from mixing with the other heat medium.

The double tube type heat pipe 11 has an outer tube 1
2 is placed in the high temperature heat medium tank 17a so that its outer circumference is in contact with the high temperature heat medium 17 serving as the heating source, and its axis is vertical. be distributed.

The double-tube heat pipe 11 disposed in the high-temperature heat medium tank 17a is heated by the outer tube 12, thereby enclosing a working fluid that forms a liquid reservoir in the lowest chamber _C1 . 16 evaporates. Then, the vapor of the evaporated working fluid 16 rises and flows into the upper chamber via a plurality of ventilation holes 15 formed in each of the partition plates 14 that partition the chambers C ₁ to _{C 5} .

Working fluid 1 flowing into each chamber C ₁ to _{C 5}
The steam in No. 6 is cooled by water, which is a low-temperature heat medium, flowing through the inner tube 13 that vertically passes through the center of each chamber C ₁ to _{C 5} . It comes into contact with the inner tube 13 and condenses, condenses on the outer peripheral surface of the inner tube 13, and descends due to gravity.
(See Figure 3).

The working fluid 16 descending along the outer circumferential surface of the inner tube 13 is prevented from descending by the partition plates 14 that partition the lower portions of each of the chambers C ₂ to C ₅ , and flows downward through the ventilation holes 15 of each partition plate 14 . However, the diameter _D of the ventilation holes 15 formed in each partition plate ₁₄
is adjusted to a size such that the liquid phase working fluid 16 forms a liquid film so as to close the vent hole 15.
The vent hole 15 of each partition plate 14 is closed with a liquid film 16a of the working fluid 16, thereby preventing the liquid phase working fluid 16 from flowing down. (See Figure 5). Therefore, the working fluid 16 evaporates and flows into the upper chamber and is distributed approximately evenly within each chamber, and the working fluid in the gas phase flows into each chamber.
In C ₁ to _{C 5} , heat is taken away by the low-temperature heat medium flowing in the inner tube 13 on the center side, and the fluid condenses, becoming a liquid-phase working fluid 16 and flowing into the lower part of each chamber C ₁ to C ₅ . This results in the formation of a liquid pool (see Figure 4).

Therefore, from now on, the inner circumferential surface of the outer tube 12 facing into each chamber becomes the evaporation section, and the outer circumferential surface of the inner tube 13 facing into each chamber becomes _the heat radiating _section . In order to configure an independent heat pipe structure and repeatedly change from liquid phase to gas phase or from gas phase to liquid phase independently for each chamber C ₁ to C ₅ , each divided chamber
By preventing insufficient reflux of the working fluid 16 to the inner circumferential surface of the outer tube 11, which is the evaporation section of _C1 to _C5 , the generation of abnormally high temperatures due to dryout etc. is effectively prevented,
Efficient heat exchange will be achieved.

Effects of the invention As explained above, the double-tube heat pipe for heat exchangers of this invention divides the sealed space between the outer circumferential surface of the inner tube and the inner circumferential surface of the outer tube into multiple chambers in the axial direction using a partition plate. At _{the same} time, this partition plate is divided into Since the vent hole is formed with a diameter less than the Taylor coefficient λ defined by the equation (the density of the fluid), the working fluid can be distributed evenly over the entire length, resulting in a simple structure and heat reduction. A device with excellent exchange efficiency can be obtained.

[Brief explanation of the drawing]

Figures 1 to 5 show one embodiment of this invention, in which Figure 1 is a partially cutaway perspective view of a double tube heat pipe, Figure 2 is a plan view of the partition plate, and Figure 3 is a partially cutaway perspective view of a double tube heat pipe.
The figure is an explanatory diagram showing the flow of working fluid vapor at the beginning of heat exchange, FIG. A cross-sectional view of the ventilation hole portion of the partition plate, and FIGS. 6 and 7 show conventional examples. FIG. 6 is a longitudinal cross-sectional view of a double-pipe heat pipe, and FIG. 7 is an explanatory diagram showing the state of use. It is. 11...Double tube heat pipe, 12...Outer tube, 12a...End plate, 13...Inner tube,
14...Partition plate, 15...Vent hole, 16 _{...Working fluid, 16a...Liquid film, 17...High temperature heat medium, C1-C5 ...} Chamber.

Claims (1)

[Claims for Utility Model Registration] A sealed space between the outer circumferential surface of the inner tube and the inner circumferential surface of the outer tube, in which an inner tube is passed through an outer tube that is sealed at both ends in an airtight manner along the axial direction of the outer tube. In a double-tube heat pipe for a heat exchanger in which a working fluid is sealed in a vacuum-degassed state, this sealed space is divided into multiple chambers in the axial direction by a partition plate, and the partition plate is defined by the following formula. 1. A double-pipe heat pipe for a heat exchanger, characterized in that a vent hole is formed with a diameter less than or equal to a Taylor coefficient λ. λ=2π√( _-V ) Where, σ is the surface tension of the liquid-phase working fluid, g is the gravitational acceleration, ρ is the density of the liquid-phase working fluid, and _ρ is the density of the gas-phase working fluid.