JPH02192595A - Ehd heat pipe - Google Patents

Abstract

PURPOSE:To lengthen the life of a heat pipe, prevent the generation of dry-out and permit efficient heat transportation, far larger in the amount of heat transportation and smaller in a temperature difference, by covering an electrode and the inner surface of a tubular body, opposed to the electrode, with an insulation film. CONSTITUTION:The whole surface of an electrode 2 and the inner surface of a metallic seal tube 1, opposed to the electrode 2, are covered by an insulating film 4 or a polyeth ylene film, for example. When a DC voltage E is impressed on the electrode 2, an electric field 5 is generated and an electric force 6 is generated in a direction orthogo nal to the surface of operating liquid 3 by the electric field 5. The operating liquid situated on one part between the electrodes initially bridges the electrodes 2, 1 by the electric force 6. In this case, the electric field in the liquid 3 in the bridge part is weak and no force is exerted but when a part, in which there is no operating liquid, exists between the electrodes, an extracting electric force 7 is generated toward a part, in which the operating liquid 3 is not existing, whereby the operating liquid 3 is moved into the axial direction of the metallic seal tube 1 and reflux from a condensing section to an evaporating section is generated, whereby heat transportation may be effected.

Description

Detailed Description of the Invention (Industrial Field of Application)
This relates to extending the life of the HD heat vibrator and increasing the amount of heat transport.

(Prior art) Heat pipes, which are conventionally used for heat exchangers, waste heat recovery, heat transport in heat storage devices, or cooling of electronic equipment and cables, have concentric capillary linings on the inner surface, and operate in an internal vacuum. It consists of a metal sealed tube containing working liquid. By heating one end and cooling the other,
The enclosed working liquid is evaporated to absorb the heat to be transported, and this vapor is condensed on the other surface to release the absorbed heat and transport the heat. The idea is to transport a large amount of heat without using any power by performing reflux using capillary action.

Incidentally, in this case, the amount of heat transported per unit time and the transport speed are approximately determined by the properties of the working liquid and the reflux rate, but as mentioned above, the method of using capillary action for refluxing the working liquid has its own limitations.

Therefore, a so-called EHD heat pipe that uses electric power to circulate the working liquid has been proposed and is attracting attention. As shown in the cross-sectional view shown in Figure 1, this heat pipe has a sealed tube (1) inside a metal sealed tube (1).
multiple electrodes (2) concentrically and spaced apart at appropriate intervals.
For example, four ribbon-shaped electrodes are provided at equal intervals, and
A working liquid (3) with low electrical conductivity, such as fluorocarbon, is sealed therein. Then, by applying a DC voltage E between each ribbon-shaped electrode (2) and the metal sealed tube (1) (the voltage application to the three electrodes is omitted in the figure), the following is achieved. It operates to transport heat.

When a DC voltage is applied to the ribbon-shaped electrodes (2), the working liquid (3) is moved between each electrode (2) and the metal sealed tube (1 ) are collected between the inner surfaces of the When the working liquid (3) bridges the electrodes (2) and (1), an outward drawing electric force acts on the liquid surface (3a). Therefore, when one end of the metal sealed tube (1) is heated H as shown in the cross-sectional view of Fig. 2(a) and the other end is cooled as shown in Fig. 2(b), a As shown in Figure 2 (a) and Φ), the shape of the liquid surface (3a) changes, and the outward pulling force T acts on the liquid surface in the evaporation section.
evaO is stronger than the outward drawing force Tcon of the condensing part (Tova > Tcon), so the working liquid moves in the axial direction of the metal sealed tube (1), reflux occurs, and heat is transported. be exposed.

(Problems to be Solved) As described above, since the EHD heat pipe uses electric power to force the working liquid to flow back, it is possible to increase the amount of heat transport compared to the conventional capillary tube method.

On the other hand, however, in this EHD heat vibrator, (1) If the working liquid has high electrical conductivity, power loss due to leakage current increases and deterioration becomes significant, so the usable working fluid is limited to one with low electrical conductivity.

■Many working liquids with low electrical conductivity have low thermal conductivity, resulting in inferior heat transfer effects. ■Unable to withstand long-term use because deterioration of the working fluid and generation of discharge cannot be prevented. (2) There are various problems that must be solved, such as dry-out, that is, interruption of the reflux of the working liquid, which tends to impede stable heat transport.

(Purpose of the invention) The present invention extends the lifespan and prevents dryout.
EHD has a much larger amount of heat transport than conventional heat pipes and is capable of efficient heat transport with small temperature differences.
It was created for the purpose of providing heat vibes.

(Means of the Invention to Solve the Problems) The present invention is characterized in that the electrode explained in FIG. 1 and the inner surface of the tube facing the electrode are coated with an insulating coating. This makes it possible to suppress the current flowing between the electrode (2) and the tube (1), thereby preventing the deterioration of the working fluid (3) and the occurrence of discharge, and at the same time making it possible to prevent the current from flowing between the electrode (2) and the tube (1). This makes it possible to use not only working fluids with low electrical conductivity, such as Freon, which is commonly used, but also working fluids with high electrical conductivity. This allows the use of working fluids with excellent heat transfer properties, such as water, and provides a long-life E
We aimed to realize an HD heat pipe. Next, the present invention will be explained with reference to examples.

(Example) Figure 3 is a cross-sectional view showing an example of the present invention, and Figure 4 (a
)(b) is the third example to explain the reflux effect according to the present invention.
1 is a vertical cross-sectional view taken along the dashed-dotted line in the figure (the same reference numerals as in FIG. 1 indicate the same parts); In Fig. 3, (1) is a metal sealed tube, (2) is an electrode, and (3) is a working liquid. The inner surface of (1) is coated with an insulating coating (4), for example, a polyethylene film, and the EHD heat vibe of the present invention configured in this manner transports heat in the following manner. When a DC voltage E is applied to the electrode (2) as in the conventional case, an electric field (5) as shown by the dotted line in Fig. 4(a) is generated.
, thereby generating an electric force (6) shown by a solid line in the figure in a direction perpendicular to the surface of the working liquid (3). For this reason, the working liquid (3) that was initially located between the electrodes, as shown in Figure 4 (
As in b), bridge the electrodes (2) and (1). However, in the bridged part, the electric field in the liquid (3) is weak and no force is exerted, but if there is a part where there is no working liquid (3) between the electrodes, this is shown by the solid line in Figure 4(b). The working liquid (3
) to generate an electric force (7) in the direction of the part without the part to move the working liquid (3) in the axial direction of the metal sealed tube (1), causing reflux from the condensing section to the evaporating section. Heat transport takes place.

(Effects of the Invention) In conventional EHD heat pipes, electric conduction is used as the working liquid (3) in order to prevent deterioration of the working liquid (3) and suppress loss due to leakage current between the electrode (2) and the tube (1). The use of low-strength fluorocarbons is being considered, but as in the present invention, an insulating coating (
If 4) is provided, there is no need to consider the electrical conductivity of the working liquid.

Table 1 Therefore, as shown in Table 1, it is possible to use liquids that have a much higher electrical conductivity than the fluorocarbons that have been considered for use in the past, such as water, which has a much higher latent heat of vaporization than fluorocarbons and has a higher thermal conductivity. As a result, it is possible to obtain a much higher amount of heat transport than with fluorocarbons, and it is also efficient because it can transport heat with a small temperature difference.

Next, the EHD performance index N, □, which is used as an index representing the heat transport performance of the EHD heat pipe, for the case where Freon is used as the working liquid and the case where water is used as the working liquid. Show value. NEM is the figure of merit for conventional EHD heat pipes. =(ε3−1)ε. E/
/”δ1/μ is used, but in the case of the field according to the present invention, the direction of the electric field at the liquid surface is different, so N.D = (
1-1/ε, )ε.・It is expressed as E・ρ・i,/μ. Here, ρ: density of liquid, l: latent heat of vaporization, μ: viscosity coefficient of liquid, ε,; dielectric constant of liquid, ε. :Vacuum permittivity 8
．． 854 X 10-' “F/m, Ett. E:
These are electric fields parallel and perpendicular to the liquid surface.

So now E// = EA = 10 (KV/cm)
Assuming that, and calculating NtHD from the values in Table 1, Freon 1
In the conventional method using 13, NEHD = 4.7X10'
(w/1ffl), whereas in the present invention using water as the working liquid, NEHD = 2.5X10' (W/1ffl).
cffl), indicating that the present invention can provide a heat pipe with high heat transport performance.

In addition to the above, in the present invention, water, which has a significantly higher surface tension than Freon as shown in Table 1, can be used as the working fluid. Therefore, the working fluid is less likely to be interrupted, and dryout can be prevented from occurring.

Furthermore, in the present invention, since the electrodes are insulated, there is no deterioration of the working fluid or occurrence of discharge, and a longer life can be expected.

(1)...metal sealed tube, (2)...electrode, (3a)
...Liquid level, H...Heating, (4)...Insulating coating,
(5)...Electric field, (7)...Extraction electric force.

(3)... working liquid, C...Cooling, (6)...Electric force,

Claims (1)

[Claims] In an EHD heat pipe, a DC voltage is applied between a plurality of electrodes provided concentrically at intervals within the tube and the tube, and the electric force generated thereby causes the internal working liquid to flow back, An EHD characterized in that the electrode and the inner surface of the tube facing the electrode are coated with an insulating film.
heat pipe.