US20080283233A1

US20080283233A1 - Coolant tube

Info

Publication number: US20080283233A1
Application number: US12/118,800
Authority: US
Inventors: Guenter Heidrich
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2007-05-14
Filing date: 2008-05-12
Publication date: 2008-11-20
Also published as: DE102007022520A1

Abstract

A coolant tube with a tube has with a tube jacket formed of a plastic material that exhibits a high diffusion coefficient for gas and that contains at least one electrically conductive additive.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention concerns a coolant tube with a tube jacket.
2. Description of the Prior Art
For explosion or rupture protection it is known to make coolant tubes of metal. In such a known coolant tube, a cooling medium (for example a high-voltage insulation oil) is transported by means of a pump into a cooling circuit between a cooling unit and a heat-emitting apparatus, for example a high-power x-ray radiator.
Depending on the maximum heat quantity to be dissipated, the possible cooling capacity must be deigned correspondingly. High flow speeds of the cooling medium occur at maximum cooling capacity, which leads to a corresponding friction of the cooling medium on the inside of the tube jacket, causing the tube jacket to become electrostatically charged. This electrostatic charging can lead to a blow-out of the tube jacket and therefore to a leakage of the coolant tube. Often only a creeping coolant loss that is not promptly noticed occurs given a small leak.
If a decomposition in which gas is released occurs in the coolant during its operation time, this can lead to a saturation of the cooling medium. If the coolant also serves as insulation, the insulation properties of the coolant corresponding degrade due to the decomposition reactions.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a coolant tube of the aforementioned type that ensures optimal cooling by the employed coolant during its entire operation time.
This object is achieved by a coolant tube according to the invention that has a tube jacket formed of a plastic (synthetic) material that has a high diffusion coefficient for gas and contains at least one electrically conductive additive.
In the present invention the term “plastic material” is not limited to a material that consists only of a single plastic. Rather, this term also encompass a plastic matrix composed of multiple different plastics or a compound material that does not necessarily have to consist exclusively of plastics, for example.
In the coolant tube according to the invention, gases that are released given a decomposition of the coolant can escape the coolant tube due to the possibility to diffuse through the tube jacket. A saturation of the cooling medium with gases (which cooling medium is directed in the coolant tube according to the invention) is thereby reliably prevented. The insulation properties of the cooling medium are thus not negatively affected.
In the inventive coolant tube, an electrically conductive connection is produced between the tube jacket (which contains at least one electrically conductive additive) and a connection armature (likewise electrically conductive) arranged on the outside of the coolant tube or tube jacket, this electrically conductive connection leads to a potential compensation or equilibration between the inside of the tube jacket (which electrostatically charges due to the friction of the cooling medium) and the connection armature.
A leak of the coolant tube with the unwanted after-effects is thereby reliably avoided.
The plastic material advantageously has a diffusion coefficient (diffusion constant) of at least approximately 3 m²for the gas escaping from the cooling medium. Compared to a tube jacket made from metal (the difference coefficient of hydrogen in iron is 124·10⁻¹³m²/s), the gases that are released given a decomposition of the coolant can therefore immediately leave the coolant tube after their formation. A saturation of the cooling medium (which cooling medium is directed in the coolant tube) with gas thus does not arise, so the insulation properties of the cooling medium are not negatively affected.
If the coolant tube is part of a cooling circuit in a high-power x-ray radiator, the generated x-ray radiation decomposes the high-voltage insulation oil in the cooling circuit and hydrogen (H₂) thereby arises. This can lead to a saturation of the high-voltage insulation oil with hydrogen. If the cooling medium also serves for insulation with regard to the high voltage applied at the x-ray radiator, the insulation properties of the high-voltage insulation oil are then correspondingly worsened by the decomposition reactions.
A diffusion coefficient of approximately 14.7 m²/s has proven to be entirely sufficient for hydrogen gas (H₂). A plastic material that exhibits a diffusion coefficient of approximately 14.7 m²/s is, for example, polytetrafluorethylene (PTFE), which is also known under the trade name Teflon®.
Depending on the geometric dimensions of the coolant tube and/or depending on the manufacturing method of the tube jacket, the following electrically conductive additives are suitable for an embedding in the plastic material, for example: graphite powder, metal powder, graphite particles and metal particles. Further suitable, electrically conductive additives are graphite fibers and metal fibers as well as electrically conductive wire cloth. In the framework of the invention the electrically conductive additives cited as examples can be introduced into the plastic material either alternatively or in an arbitrary combination. An adaptation of the tube jacket to the respective application case with regard to its electrical conductivity is thereby possible in a simple manner in the coolant tube according to the invention.
In the event that the plastic material is exposed to particularly high mechanical loads, according to an embodiment of the inventive coolant tube an intermediate layer can be at least partially arranged between the tube jacket and the protective jacket. If gas escape is anticipated, for a metallic protective jacket this intermediate layer must be a woven-type of layer (for example steel mesh) in order to not prevent the diffusion of the gas escaping from the cooling medium.
In particular given a protective jacket made from a metallic weave, for mechanical protection of the tube jacket it is advantageous to arrange an intermediate layer at least partially between the tube jacket and the protective jacket, which intermediate layer is fashioned as a plastic weave, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

A schematically presented exemplary embodiment of a coolant tube according to the invention is subsequently explained in detail in the drawing without, however, being limited to this. The single FIGURE shows the coolant tube in a longitudinal section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A coolant tube 1 that has a tube jacket 2 is shown in the FIGURE. According to the invention, the tube jacket 2 is formed of a plastic material that has a high diffusion coefficient D for gas and contains at least one electrically conductive additive.
The coolant tube 1 shown in the FIGURE is part of a cooling circuit between a cooling unit and a high-power x-ray radiator. In this case high-voltage insulation oil that is transported in the cooling circuit by means of a pump serves as a cooling medium 3. The cooling unit, the high-power x-ray radiator and the pump are known and therefore not shown in the FIGURE.
The generated x-ray radiation can interact with the high-voltage insulation oil 3 in the cooling circuit and hydrogen (H₂) thereby arises. This can lead to a saturation of the high-voltage insulation oil 3 with hydrogen. The cooling medium 3, which also serves for insulation with regard to the high voltage present at the x-ray radiator, correspondingly worsens in terms of its insulation properties due to decomposition reactions that occur. Since the decomposition reactions in the cooling medium 3 cannot be prevented, the hydrogen must be removed from the cooling medium 3. According to the invention, this is achieved by the use of a plastic material for the tube jacket 2 that exhibits a sufficiently high diffusion coefficient for hydrogen. A plastic material with a sufficiently high diffusion coefficient for hydrogen is polytetrafluorethylene (PTFE). This material has a difference coefficient of approximately 14.7 m²/s for hydrogen.
Depending on the geometric dimensions of the coolant tube 1 and/or depending on the manufacturing method of the tube jacket 2, graphite powder, metal powder, graphite particles and metal particles are possible, for example. Further suitable, electrically conductive additives are graphite fibers and metal fibers as well as electrically conductive wire cloth. In the framework of the invention, the electrically conductive additives cited as examples can be introduced either alternatively or in an arbitrary combination into the plastic material of the tube jacket 2. An adaptation of the tube jacket 2 to the respective application case with regard to its electrical conductivity is thereby possible in a simple manner given the coolant tube 1 according to the invention.
The coolant tube 1 is connected in an electrically conductive manner with its tube jacket 2 with a connection armature 4 via an electrically conductive compression, so potential equilibrium occurs between the inside of the tube jacket 2 (which electrostatically charges due to the friction of the cooling medium 3) and the connection armature 4.
A leak of the coolant tube 1 with the unwanted after-effects is reliably avoided via this potential compensation or equilibration.
In the coolant tube according to the invention an electrically conductive connection arises between the tube jacket (which contains at least one electrically conductive additive) and a connection armature (likewise electrically conductive) arranged on the outside of the coolant tube or tube jacket. This electrically conductive connection produces a potential equilibration between the inside of the tube jacket (which electrostatically charges due to the friction of the coolant) and the connection armature.
In the shown exemplary embodiment the tube jacket 2 has on its outer surface a protective jacket 6 made of a metallic weave, for example a steel mesh. Insensitivity to mechanical damage is increased while the electrical conductivity of the compression 5 with the connection armature 4 is improved by the protective jacket 6.
Furthermore, an intermediate layer (not shown in the drawing) that, for example, is formed of a plastic weave can be arranged between the tube jacket 2 (made from a plastic material) and the protective jacket 4 (made from a metallic weave).
Due to the weave structure in the (possibly present) protective jacket 5 and given the (possibly present) intermediate layer, the hydrogen diffusing through the tube jacket 2 is not hindered from escaping from the tube jacket 2, such that the diffusion properties of the tube jacket 2 for hydrogen are not impaired.
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.

Claims

1. A coolant tube comprising:

a tube jacket having an interior channel therein configured to conduct an insulating oil therethrough; and

said tube jacket being comprised of a plastic material having a high diffusion coefficient for gas and containing at least one electrically conductive additive.

2. A coolant tube as claimed in claim 1 wherein said plastic material has a diffusion coefficient of at least approximately 3 m²/s for gas.

3. A coolant tube as claimed in claim 2 wherein said plastic material has a diffusion coefficient of approximately 14.37 m²/s for hydrogen.

4. A coolant tube as claimed in claim 1 wherein said plastic material is polytetrafluoroethylene.

5. A coolant tube as claimed in claim 1 wherein said plastic material is a composite material.

6. A coolant tube as claimed in claim 1 wherein said electrically conductive additive is at least one material selected from the group consisting of graphic powder and metal powder.

7. A coolant tube as claimed in claim 1 wherein said electrically conductive material is at least one material selected from the group consisting of graphite particles and metal particles.

8. A coolant tube as claimed in claim 1 wherein said electrically conductive material is at least one material selected from the group consisting of graphite fibers and metal fibers.

9. A coolant tube as claimed in claim 1 wherein said electrically conductive additive is formed as an electrically conductive wire woven material embedded in the plastic material.

10. A coolant tube as claimed in claim 1 comprising a protective jacket that covers at least a portion of an exterior of said tube jacket.

11. A coolant tube as claimed in claim 10 wherein said protective jacket is formed of a metallic woven material.

12. A coolant tube as claimed in claim 10 comprising an intermediate layer disposed between said exterior of said tube jacket and said protective jacket.

13. A coolant tube as claimed in claim 12 wherein said intermediate layer is comprised of a plastic woven material.

14. A coolant tube as claimed in claim 1 wherein said tube jacket has a channel diameter between approximately 4 mm and 50 mm.

15. A coolant tube as claimed in claim 1 wherein said tube jacket has a wall thickness between said channel and an exterior of said tube jacket in a range between approximately 0.2 mm and approximately 0.5 mm.