Self-regenerating bridge-type heat pipe

Abstract

In order to provide a self-regenerating bridge-type heat pipe capable of effectively transporting heat while keeping a filling ratio of a working fluid low, in an aluminum self-regenerating bridge-type heat pipe according to the present invention, in which flow passages that are alternately folded back are filled with the working fluid, inner surfaces of the flow passages are treated so as to be water-repellent, and the filling ratio of the working fluid is at most equal to 30 vol.%.

Description

[Technical Field]

[0001] The present invention relates to a self-regenerating bridge-type heat pipe. [Background technology]

[0002] In recent years, the heat density of electronic components has been rapidly increasing as electronic devices have become smaller and more powerful. Various types of heat pipes, which transfer heat by changing the gas-liquid phase of the refrigerant filled inside, have been widely used as cooling and thermal control devices for electronic devices. Recently, the use of heat pipes has also been considered as heat exchange devices for the purpose of recovering waste heat to curb global warming. Furthermore, the use of various types of heat pipes as heat transport devices for thermal control of batteries for electric vehicles (EVs) is being investigated.

[0003] A wide variety of heat pipe devices have been proposed, including conventional wick heat pipes and loop heat pipes. Among these, the Pulsating Heat Pipe (PHP) or Oscillating Heat Pipe (OHP), hereafter referred to as PHP, is a type of heat pipe in which a thin flow path is formed by multiple bends between a heating section HS and a cooling section CS, as shown in Figure 1. The PHP achieves high passive heat transfer by forming a liquid slug LS between vapor plugs VP, which are held by the surface tension of the working fluid and move due to self-excited oscillations.

[0004] The features of PHP include high heat transport performance compared to conventional heat pipes, as it can utilize the sensible heat transfer of the liquid slug LS caused by self-excited vibration; it is suitable for miniaturization as it does not require internal structures such as a wick; and its heat transport performance is less affected by gravity.

[0005] Furthermore, unlike conventional heat pipes, PHPs have no liquid reflux limitations due to capillary forces or flooding, and as such, they have attracted attention for their high heat transport performance, and various studies have been conducted on them. Generally, parameters that affect the heat transport performance of PHPs include the flow path shape and number of turns (number of channels), the physical properties and filling rate of the working fluid, the installation conditions, and various dimensional ratios.

[0006] However, due to the complexity of the self-excited vibration mechanism and heat transport pattern of PHP, it has not yet been possible to obtain design guidelines for a practical device, and a large amount of basic research and applied research aimed at improving heat transport performance is currently being conducted.

[0007] Based on the above background, research has been conducted into the performance improvement effect of PHP when a self-rewetting solution (also called a self-wetting liquid) is used as the working fluid (see Non-Patent Document 1). Self-rewetting solutions refer to dilute aqueous solutions of alcohols with four or more carbon atoms (such as butanol and pentanol). These aqueous solutions are known to differ from general liquids in that there is a temperature range in which the surface tension increases with increasing temperature. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Koji Fumoto and 1 other, "Study on performance improvement of self-oscillating heat pipe using self-rewetting solution (in the case of butanol and pentanol)," Thermal Science & Engineering Vol.19 No.1 (2011) Summary of the Invention [Problem to be solved by the invention]

[0009] Several researchers, including the inventors, have reported that the self-wetting effect associated with this unique surface tension property improves the heat transport performance of PHP and is also expected to have a dryout suppression effect.

[0010] Previous research on PHP has revealed that the optimum working fluid filling rate is in the range of 40 to 60 vol.%. Outside this range, sufficient self-excited oscillation cannot be obtained, and heat transport performance is known to decrease, which has been an obstacle to practical application. Specifically, when the working fluid filling rate is 30 vol.% or less, less working fluid is supplied to the evaporator, resulting in a dryout state and reaching the operating limit of the heat pipe. This makes it difficult to ensure a long flow path length for the heat pipe.

[0011] However, the inventors have taken a different approach from conventional methods and succeeded in creating a heat pipe that can effectively transport heat over long distances even when the working fluid filling rate is 30 vol.% or less.

[0012] SUMMARY OF THE INVENTION An object of the present invention is to provide a self-regenerative bridge-type heat pipe that can effectively transport heat while keeping the filling rate of the working fluid low. [Means for solving the problem]

[0013] In order to solve the above problems, one of the representative self-regenerative bridge-type heat pipes of the present invention is an aluminum self-regenerative bridge-type heat pipe in which a working fluid is filled in alternately folded flow passages, The inner surface of the flow path is subjected to a water-repellent treatment, Inside the flow path formed in The working fluid bridge is movable along the flow path in response to the internal pressure difference in the flow path before and after the bridge, and the filling rate of the working fluid is 5 to 10 vol.%. This is achieved by: [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a self-regenerative bridge-type heat pipe that can effectively transport heat while keeping the filling rate of the working fluid low. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0015] [Figure 1] Figure 1 is a schematic diagram of traditional PHP. [Figure 2] FIG. 2(a) is a side view of the self-regenerative bridge-type heat pipe of this embodiment, and FIG. 2(b) is a cross-sectional view of the configuration of FIG. 2(a) taken along line AA and viewed in the direction of the arrow. [Figure 3] FIG. 3 is a schematic diagram of the experimental apparatus used by the present inventors. [Figure 4] FIG. 4 is a diagram showing the temperature measurement positions and the area ratio of the evaporation section to the condensation section of a self-regenerative bridge-type heat pipe. [Figure 5] Figure 5 shows a microscopic image of the cross section of the flow path of a self-regenerative bridge-type heat pipe. [Figure 6] FIG. 6 is a diagram showing the relationship between the input power to the cartridge heater and the net amount of heat supplied. [Figure 7] Figure 7 shows the net heat supply and temperature history of the evaporator, insulator, and condenser sections when a self-regenerating bridge-type heat pipe with a water-repellent treatment applied to the flow path surface is filled with a typical amount of working fluid (50 vol.%) as Comparative Example 1. [Figure 8] Figure 8 shows the net heat supply and the temperature history of the evaporator, heat insulating, and condenser sections when a heat pipe without a water-repellent treatment on the flow path surface is filled with a working fluid at a filling amount (30 vol.%) as Comparative Example 2. [Figure 9] Figure 9 shows the temperature history of the evaporator, insulator, and condenser sections in the heat transfer state of the self-regenerative bridge-type heat pipe of Comparative Example 1 when the working fluid filling rate is 5 vol.% (Example 1). [Figure 10]Figure 10 shows the temperature history of the evaporator, heat insulator, and condenser sections in the heat transfer state of the self-regenerative bridge-type heat pipe of Comparative Example 1 when the working fluid filling rate is 10 vol.% (Example 2). [Figure 11] FIG. 11 is a diagram showing the relationship between the net heat supply amount and the thermal resistance. [Figure 12] FIG. 12 is a diagram showing the relationship between the net heat supply amount and the effective thermal conductivity. [Figure 13] FIG. 13 is a diagram showing a schematic view of the inside of a heat pipe. DETAILED DESCRIPTION OF THE INVENTION

[0016] Inspired by the improvement of heat transport performance by improving the wettability of the flow channel using a conventional self-rewetting solution, the inventors have further improved the heat transport performance of PHP by directly modifying the flow channel surface. Specifically, after applying a water-repellent treatment to the flow channel surface of the heat pipe, in order to further effectively utilize the water-repellent effect, the working fluid filling rate was deliberately set to 30 vol.% or less, for example, around 10 vol.%, and they succeeded in achieving ultra-efficient heat transport without changing the shape of the conventional PHP.

[0017] It has been confirmed that this type of heat pipe exhibits a heat transfer phenomenon that is clearly different from that of conventional PHPs, and so to distinguish it from conventional PHPs, it is called a self-regenerative bridge-type heat pipe. In a self-regenerative bridge-type heat pipe, a thin liquid slug-like film (bridge) formed in the flow channel by extremely low filling rate of the working fluid moves at a high vibration frequency, thereby achieving heat transfer performance that is unattainable with conventional PHPs. The details of the self-regenerative bridge-type heat pipe are explained below.

[0018] (Self-regenerative bridge-type heat pipe) FIG. 2(a) is a side view of the self-regenerative bridge-type heat pipe SV of this embodiment, and FIG. 2(b) is a cross-sectional view of the configuration of FIG. 2(a) taken along line AA and viewed in the direction of the arrow. The self-regenerative bridge-type heat pipe SV consists of an aluminum flat multi-hole tube (also called an aluminum flat multi-hole PHP), the schematic of which is shown in Figure 2(a). The main component of the material of the flat multi-hole tube is aluminum (A1297), and in this case, the shape is 400 mm in length, 48 mm in width, and 2 mm in thickness, although there are no particular restrictions on the dimensions. The internal flow channels PS are arranged in parallel in the length direction, with adjacent flow channels PS separated by partitions, but the number of channels is not particularly limited.

[0019] As shown in Figure 2(a), the end faces of the flow paths are machined in a staggered pattern. Specifically, the upper end of the (N+1)th flow path in the direction of the parallel flow paths is connected to the upper end of the (N)th flow path and sealed from the atmosphere, and the lower end of the (N+1)th flow path is connected to the lower end of the (N+2)th flow path and sealed from the atmosphere. This results in a continuous flow path PS that alternates between the two paths. Both ends, except for one injection section, are pressure-clamped and then sealed with a resin adhesive (heat-resistant up to 200°C). The shape of the self-regenerative bridge-type heat pipe SV is not limited to the above. For example, the distance from one return end to the other return end of the flow path is preferably 50 mm or more, and even more preferably 300 mm or more.

[0020] The cross section of the flow passage of the self-regenerative bridge-type heat pipe SV is square as shown in Fig. 2(b), with one side of the cross section being 1.26 mm and the cross-sectional area being 1.59 mm. 2 However, the cross-sectional area is 0.25 mm 2 Over 9.0mm 2 Less than or equal to 1.0 mm, more preferably 2 Over 5.0mm 2 The cross-sectional shape is not limited to a square, but may be, for example, a circle.

[0021] The self-regenerative bridge-type heat pipe SV can be formed by repeatedly bending an aluminum pipe with a continuous flow path multiple times.

[0022] (experiment) The following describes an experiment conducted by the inventors on the self-regenerative bridge-type heat pipe SV. Figure 3 is a schematic diagram of the experimental equipment used by the inventors. The experimental equipment comprises a heating system HS, an injection system IS, and a measurement system MS. The heating system HS comprises a copper block CB that holds the lower end of the self-regenerative bridge-type heat pipe SV, a cartridge heater CH that serves as a heater and is located within the copper block CB, and thermally conductive grease (not shown) that contacts the self-regenerative bridge-type heat pipe SV and the cartridge heater CH. The cartridge heater CH generates heat by the current input from the transformer TF, and the current value can be confirmed by a power meter PM.

[0023] As will be described later with reference to Figure 4, the area within the copper block CB where the self-regenerative bridge-type heat pipe SV faces the cartridge heater CH is called the evaporation section EA, the area of ​​the self-regenerative bridge-type heat pipe SV within the copper block CB other than the evaporation section is called the insulating section AA, and the self-regenerative bridge-type heat pipe SV exposed outside the copper block CB and in contact with the outside air is called the condensation section CA.

[0024] The injection system IS consists of a vacuum pump PP equipped with a digital vacuum gauge and a syringe SR for filling the working fluid, either of which can be selectively connected to the injection part of the self-regenerative bridge-type heat pipe SV by switching the valve VV.

[0025] The measurement system MS includes multiple thermocouples TC (K type: φ0.3 mm) attached to the self-regenerating bridge-type heat pipe SV. The thermocouples TC are connected to the data logger DL, and the temperature data measured through the thermocouples TC is processed at high speed.

[0026] The self-regenerative bridge-type heat pipe SV is maintained in a bottom-heat state by the heating system HS, and the upper end is cooled naturally.

[0027] Figure 4 shows the temperature measurement position of the self-regenerative bridge-type heat pipe SV, and the area ratio of the evaporator section EA and the condenser section CA. The unit of the values ​​in Figure 4 is mm. At the evaporator section EA, the measured value T e1 , T e2 , T e3 Three thermocouples TC are placed (three points at 10 mm from the bottom end) and the measured value T ad A thermocouple TC is placed (at the center of the heat insulating section AA) and a measurement value T is obtained in the condensing section CA. c1 ~T c5 Five thermocouples were placed (three points 10 mm from the top end and two points at the center in the flow direction) to output the signal. Each thermocouple TC was fixed to the surface of the self-regenerative bridge-type heat pipe SV, and the outside air side was covered with insulating material to eliminate the influence of the outside air temperature.

[0028] In this experiment, the area ratios of the evaporator section EA, the adiabatic section AA, and the condenser section CA were fixed at 20%, 30%, and 50%, respectively, based on the total length of the self-regenerative bridge-type heat pipe SV. Distilled water was used as the working fluid. All surfaces of the self-regenerative bridge-type heat pipe SV used in this experiment, except for the condenser section EA (one side of the natural air-cooling section), and the heating system HS, were covered with insulation (insulating foam, 10 mm thick). In this experiment, the flow channel surfaces of the self-regenerative bridge-type heat pipe SV were treated with hard anodizing to improve their water repellency.

[0029] Figure 5 is a microscopic image of the cross section of the flow passage of the self-regenerative bridge-type heat pipe SV. As shown in Figure 5, a hard anodized aluminum layer of approximately 5 μm is formed on the inner surface of the flow passage PS.

[0030] The following describes the experiments conducted by the inventors. In preparation for the experiment, the inside of the self-regenerative bridge-type heat pipe SV was evacuated using a vacuum pump PP until the gauge pressure reached -0.099 MPa or less. Then, the valve VV was switched and the working fluid was filled using a filling microsyringe SR, ensuring that no non-condensable gas (air) was introduced. Considering that the working fluid also contains dissolved air, the working fluid itself was degassed in advance. The filling ratio (FR) of the working fluid is defined by the following equation (1):

[0031]

number

[0032] where V fluid [mm 3 ] is the volume of the filled working fluid, and V PHP [mm 3 ] is the total flow channel volume of the self-regenerative bridge-type heat pipe SV confirmed in advance (= 1.75 × 10 -5 m 3 ) The filling rates in this experiment were 0 (no working fluid), 5, 10, and 50 vol.%. The measurement error of the working fluid filling amount can be estimated to be within ±0.2% based on the measurement accuracy of the electronic precision weighing scale.

[0033] The experiment began by confirming that the temperature of each part of the self-regenerative bridge-type heat pipe SV had stabilized, and then the procedure of increasing the power applied to the cartridge heater was repeated. For safety reasons, the experiment was terminated when it was confirmed that dryout had occurred and when the temperature of the evaporator reached approximately 120°C.

[0034] As a preliminary test prior to the actual experiment, a heat flux sensor was inserted between the self-regenerative bridge-type heat pipe SV and the cartridge heater CH for an empty self-regenerative bridge-type heat pipe SV (filling rate 0 [vol.%]) that was not filled with working fluid, and the power supplied to the cartridge heater CH and the net amount of heat transferred to the self-regenerative bridge-type heat pipe SV were measured.

[0035] Figure 6 shows the relationship between the input power to the cartridge heater CH and the net heat supply. Figure 6 also shows the net heat supply, the temperature difference in the heat-insulating section, and the effective thermal conductivity of the empty self-regenerative bridge-type heat pipe SV, calculated from the cross-sectional area of ​​the heat pipe.

[0036] Figure 6 shows that the net heat supply transferred from the cartridge heater CH to the self-regenerative bridge-type heat pipe SV increases linearly with increasing input power. Furthermore, the effective thermal conductivity of the empty self-regenerative bridge-type heat pipe SV was found to be 206.8 [W / (m·K)] on average, regardless of input power. This is within 6% of the thermal conductivity of the aluminum alloy (A1297), the material used for the self-regenerative bridge-type heat pipe SV, which is 220-230 [W / (m·K)], confirming the accuracy of this experimental apparatus and measurement system. Hereafter, all heat supply values ​​will be evaluated using the net heat supply value.

[0037] The overall performance evaluation was carried out using the thermal resistance (R) and effective thermal conductivity (K eff The thermal resistance is calculated using equation (2).

[0038]

number

[0039] where T e , T c [°C] are the measured values ​​(T e1 , T e2 , T e3 ) and the measured value at the condensation part CA (thermocouple T c1 , T c2 , T c3 ) Q [W] is the net heat supply. Effective thermal conductivity (K eff ) is calculated using equation (3).

[0040]

number

[0041] where L eff [m] means the temperature measurement distance (0.38 [m]) between the evaporator section EA and the condenser section CA. cr is the cross-sectional area of ​​the self-regenerative bridge-type heat pipe SV (0.002 × 0.048 [m 2 ]).

[0042] Next, we will discuss the experimental accuracy. The accuracy of thermal resistance (R) is defined by equation (4).

number

[0043] The data accuracy of thermal resistance R is ±1.6%. Next, the effective thermal conductivity K eff The accuracy of is defined by equation (5).

[0044]

number

[0045] Distance L in the tube axis direction between the evaporator section EA and the condenser section CA eff The measurement error is ±3.0%, so the effective thermal conductivity K eff The data accuracy is ±3.3%.

[0046] (Experimental results and discussion) (1) Comparative Example 1 Figure 7 shows the net heat supply and evaporation area EA (T e2 ), insulation part AA(T ad ), and condensation CA(T c2 ) temperature history. Distilled water is used as the working fluid.

[0047] The vertical axis of Figure 7 represents the temperature, and the horizontal axis represents the experimental time. The figure also shows the value of the net heat supply, which was gradually increased in intervals of 10.0W, 15.2W, 20.3W, 25.4W, and 30.6W. Figure 7 shows that when the heat supply was 15.2W, the measured value of the condenser EA (T c2 ) and it is clear that self-excited oscillation occurs simply within the self-regenerative bridge-type heat pipe SV. However, the temperature difference (T e2 -T c2 ) is relatively large, it cannot be inferred that continuous and intense vibrations are occurring.

[0048] On the other hand, when the heat supply is 20.3 W or more, the temperature difference between the evaporator EA and the condenser CA (T e2 -T c2 ) was maintained at around 7.3 K (heat supply of 25.4 W), and it was found that heat was being transported from the evaporator EA to the condenser CA due to intense self-excited oscillations. These trends are similar to those reported in previous research when the working fluid filling amount was 50 vol.%. In addition, when the heat supply amount was 30.6 W, the temperature of the condenser CA decreased after 16,500 seconds, and the temperature difference with the evaporator EA tended to increase, confirming that dryout occurred after that.

[0049] (2) Comparative Example 2 Figure 8 shows the relationship between the net heat supply and the evaporation area EA (T e2 ), insulation part AA(T ad ), and condensation CA(T c2 Distilled water was used as the working fluid. The shape of the heat pipe and the temperature measurement position were the same as those in Comparative Example 1.

[0050] In Figure 8, the vertical axis represents temperature and the horizontal axis represents experimental time. The figure also includes the value of the net heat supply, which was gradually increased over the following intervals: 10.0W, 12.0W, 13.8W, 15.0W, and 16.0W.

[0051] In Figure 8, the temperature (T e2 , T ad , T c2 ) rises, but the evaporation section (heating section: T e2 ) compared to the condensation section (cooling section: T c2 ) temperature does not rise much. This means that heat transfer from the evaporation section is not efficient. Also, after 20250 seconds (16 W), the condensation section (cooling section: T c2 ) temperature decreases, while the evaporation section (heating section: T e2 ) temperature rose sharply, which shows a typical temperature history caused by dryout (operating limit = phenomenon in which the inside of the evaporator part of the heat pipe becomes dry).

[0052] Example 1 Figure 9 shows the heat transfer performance of the comparative example of the self-regenerative bridge-type heat pipe SV when the working fluid filling rate is set to 5 vol.%. e2 ), insulation part AA(T ad ), and condensation CA(T c2 ) temperature history. Distilled water is used as the working fluid. The vertical and horizontal axes and the net heat supply are shown in the same way as in Figures 7 and 8.

[0053] From Figure 9, when the heat supply amount is 15.2W or more, the temperature of the evaporation section EA (T e2 ) and the temperature of the condensation area CA (T c2 ) rapidly approach each other and become almost the same temperature, which indicates that intense heat transfer is occurring inside the self-regenerative bridge-type heat pipe SV from the evaporator section EA to the condenser section CA. If we consider this amount of heat as the start of heat transfer in the self-regenerative bridge-type heat pipe SV, we can see that it starts when the evaporator section EA is about 60°C (a difference of 40°C from the room temperature of 20°C). Furthermore, as the amount of heat supplied increases, we can see that the temperatures of the evaporator section EA, the adiabatic section AA, and the condenser section CA remain consistent.

[0054] In particular, it was found that the temperature difference between the evaporator section EA and the condenser section CA was less than 1.0 K around 8000 seconds when a heat amount of 20.3 W was being supplied, and furthermore, it was found to be 0.69 K around 10000 seconds when a heat amount of 25.4 W was being supplied.

[0055] Example 2 Figure 10 shows the heat transfer performance of the comparative example of the self-regenerative bridge-type heat pipe SV when the working fluid filling rate is 10 vol.%. e2 ), insulation part AA(T ad ), and condensation CA(T c2 ) temperature history. Distilled water is used as the working fluid. The vertical and horizontal axes of the figure, and the display of the net heat supply are the same as in Figure 9.

[0056] From Figure 10, when the amount of heat supplied is 10.0 W or more, the temperature of the evaporator EA (T e2 ) and the temperature of the condensation area CA (T c2 ) rapidly approach each other, indicating that heat transfer is occurring from the evaporator section EA to the condenser section CA inside the self-regenerative bridge-type heat pipe SV. Considering this amount of heat as the start of heat transfer in the self-regenerative bridge-type heat pipe SV, it can be seen that the lower evaporator section EA starts at approximately 50°C (a difference of 30°C from the room temperature of 20°C) compared to Example 1. Furthermore, it can be seen that as the amount of heat supplied increases, the temperatures of the evaporator section EA, the adiabatic section AA, and the condenser section CA remain consistent.

[0057] In particular, it was found that the temperature difference between the evaporator section EA and the condenser section CA was 0.77 K or less at around 12,300 seconds when a heat amount of 20.3 W was being supplied, and furthermore, it was 0.63 K at around 15,000 seconds when a heat amount of 30.6 W was being supplied. For safety reasons, the experiment ended at a maximum temperature of 120°C, but at the end of the experiment, no dryout or other problems were observed when the working fluid filling rate was between 5 and 10 vol.%, suggesting the possibility of further heat transport.

[0058] (Comparison between Comparative Examples and Examples) As is clear from the experimental results in Figure 8 (Comparative Example 2), when the filling rate of the working fluid is 30 vol% (or less), the heat pipe without water-repellent treatment does not operate normally. Also, as is clear from comparing the graph in Figure 8 with the graphs in Figures 9 and 10, the amount of heat supplied (W in the figure) and the temperature rise are completely different. Specifically, in Figure 8, at 15.0 W, the evaporator (heater: T e2 ) temperature reaches around 120℃, and the condensation part (low temperature part: T c2 ), which indicates that there is a temperature difference of about 20°C with respect to the evaporator (heating unit: T e2 ) is around 70°C. The reason why the temperature is slightly lower in Comparative Example 1 than in Comparative Example 2 under almost the same conditions is that heat is transported from the evaporation section (heating section) to the condensation section (low temperature section) due to the self-excited vibration phenomenon of the heat pipe. In other words, in the case of a heat pipe with a filling rate of 50 vol% and a water-repellent treatment, it can be said that it has a certain degree of heat transport function but is not sufficient. In contrast, in the self-regenerative bridge-type heat pipes of Examples 1 and 2, which have a lower filling efficiency, the evaporation section (heating section: T) is heated at 15.2 W, as shown in Figures 9 and 10. e2 ) is slightly lower than 70°C and is almost the same temperature as the condensation section temperature, so it is clear that a large amount of heat is being transported.

[0059] (thermal resistance and effective thermal conductivity) Figure 11 shows the relationship between net heat supply and thermal resistance. The vertical axis shows the thermal resistance value in logarithmic scale. The horizontal axis shows net heat supply. The parameters are the working fluid filling ratios, including 0 vol.% (empty self-regenerative bridge-type heat pipe SV). In the comparative example, where the self-regenerative bridge-type heat pipe SV is filled with working fluid at a typical filling ratio of 50 vol.%, the thermal resistance is 2.1 K / W when the heat supply is 10 W. After that, the thermal resistance decreases as the heat supply increases, reaching a minimum of 0.19 K / W. Thereafter, the thermal resistance tends to increase at a heat supply of 30.6 W, where a tendency for dryout is observed.

[0060] On the other hand, in Example 1, in which the self-regenerative bridge-type heat pipe SV was filled with working fluid at 5 vol.%, the thermal resistance was 0.86 K / W when the heat supply amount was 10 W, and then the thermal resistance decreased significantly as the heat supply amount increased, and the thermal resistance was 0.022 K / W when the heat supply amount was 30.6 W.

[0061] In addition, in Example 2, in which the self-regenerative bridge-type heat pipe SV was filled with working fluid at 10 vol.%, the thermal resistance was 0.36 K / W when the heat supply amount was 10 W, and then the thermal resistance decreased significantly as the heat supply amount increased, and the thermal resistance was 0.021 K / W when the heat supply amount was 30.6 W. From the above, it can be seen that when the working fluid is filled at filling rates of 5 and 10 [vol.%], a value of 1 / 10 or less of the filling rate (for example, 50 [vol.%]) is obtained.

[0062] Figure 12 shows the relationship between net heat supply and effective thermal conductivity. The parameter is the working fluid filling rate. When the self-regenerative bridge-type heat pipe SV is filled with working fluid at a typical filling rate of 50 vol.%, the effective thermal conductivity reaches a maximum of 21,498.6 W / (m K) at a heat supply rate of 25 W, and then begins to decrease. In contrast, when the working fluid is filled at 5 vol.%, the effective thermal conductivity is 176,171.8 W / (m K) at a heat supply rate of 30.6 W. When the working fluid is filled at 10 vol.%, the effective thermal conductivity is 191,068.1 W / (m K) at a heat supply rate of 30.6 W.

[0063] FIG. 13 is a diagram showing a schematic view of the inside of a heat pipe. In various experiments, including visualization of PHP, the optimal filling rate of the working fluid has been considered to be approximately 50 vol.%. In this case, when the PHP is brought into contact with the high-temperature and low-temperature sections, vapor plugs VP and liquid slugs LS are randomly formed at a volume ratio of approximately half the flow path, as shown in Figure 12 at 50 vol.% (Figure 13(b)).

[0064] On the other hand, in the case of a self-regenerative bridge-type heat pipe SV with a low filling rate, when the high-temperature section corresponding to the evaporation section and the low-temperature section corresponding to the condensation section are brought into contact, the liquid slug LS in the flow path is short and exists in an extremely small proportion within the flow path, as shown at 5 to 10 [vol.%] in Figure 12 (Figure 13(c)).

[0065] Furthermore, this short liquid slug LS is thought to occur mainly in the condensation section, where the liquid becomes a drop-like condensation state DP (Figure 13(d)) due to the water-repellent treatment effect on the flow path surface, and as it grows, a thin-film bridge BG is formed that acts as a lid inside the flow path (Figures 13(e) and (f)).In other words, unless the filling rate of the working fluid is sufficiently low, for example, 30 [vol.%] or less, the liquid slug LS will become a relatively large mass, preventing the formation of a bridge BG.

[0066] The bridge BG is defined as a film thickness of less than half the maximum length of the surface facing the vapor plug VP. To effectively form the bridge BG, the cross-sectional area of ​​the water-repellent treated flow passage of the self-regenerative bridge-type heat pipe SV must be less than 0.25 mm2, taking into account the surface tension of the working fluid. 2 Over 9.0mm 2 It is preferable that:

[0067] In conventional PHPs, a relatively large liquid slug LS exists within the flow channel. Heat transport is achieved by flowing and vibrating the liquid slug LS, requiring a large pressure difference across both ends of the liquid slug LS. In contrast, in the self-regenerative bridge-type heat pipe SV with a low filling factor like the present embodiment, an extremely short and extremely small liquid slug (a thin-film bridge BG that shields the flow channel cross section) is formed within the flow channel. Therefore, the inertia of the liquid slug LS is smaller than in conventional PHPs, allowing it to flow and vibrate easily due to the relatively small pressure difference between its front and rear. This allows the bridge BG to move even in flow channels with lengths of 400 mm or more from one return end to the other. Furthermore, the bridge BG can oscillate and flow while maintaining its shape in the condensation section, but it is thought to collapse quickly upon reaching the evaporation section due to evaporation, thereby creating and transmitting pressure that moves another bridge BG.

[0068] The thermal performance of the self-regenerating bridge-type heat pipe SV, which is made by anodizing the flow passages of an aluminum flat multi-hole PHP to make it water-repellent, and further sealing distilled water as the working fluid at an ultra-low filling rate, was experimentally investigated, and the following conclusions were drawn. (1) It was revealed that by making the surface of the flow channel of an aluminum flat multi-hole PHP water-repellent, self-excited vibration occurs even at an extremely low filling rate of the working fluid, and high heat transfer efficiency is demonstrated. (2) It was confirmed that the temperature difference between the evaporator and condenser sections of a 400mm long self-regenerative bridge-type heat pipe SV was less than 1K when the working fluid filling rate was 5vol.%. (3) The heat transport performance was evaluated using thermal resistance and effective thermal conductivity, and the maximum thermal resistance was 0.019 [K / W], which is less than 1 / 10 of the thermal resistance of a conventional PHP with a working fluid filling rate of 50 [vol.%].

[0069] In the above embodiment, the inner surface of the flow path of the aluminum flat multi-hole PHP is treated with anodizing to make it water-repellent. However, it has been confirmed that similar results can be obtained with a PHP that has been treated with boehmite by immersing an untreated aluminum flat multi-hole plate in warm water (90°C) for 30 minutes to make it water-repellent. [Explanation of symbols]

[0070] HS: Heating system, IS: Injection system, MS: Measurement system, BG: Bridge, CB: Copper block, CH: Cartridge heater, DL: Data logger, PM: Power meter, PP: Vacuum pump, PS: Flow path, SR: Syringe for filling working fluid, SV: Self-regenerating bridge-type heat pipe, TC: Thermocouple, TF: Transformer, VV: Valve

Claims

1. In a self-regenerative bridge-type heat pipe made of aluminum, the working fluid is filled into alternately folded flow passages, The inner surface of the flow path is subjected to a water-repellent treatment, A self-regenerative bridge-type heat pipe characterized in that the bridge of working fluid formed within the flow path is movable along the flow path depending on the internal pressure difference of the flow path before and after the bridge, and the filling rate of the working fluid is 5 to 10 vol.%.

2. The cross-sectional area of ​​the flow path is 0.25 mm ２ More than 9.0 mm ２ 2. The self-regenerative bridge-type heat pipe according to claim 1, wherein:

3. 2. The self-regenerative bridge-type heat pipe according to claim 1, wherein a bridge of the working fluid is formed within the flow path when the self-regenerative bridge-type heat pipe is brought into contact with the high-temperature portion and the low-temperature portion.

4. 2. The self-regenerating bridge-type heat pipe according to claim 1, wherein the distance from one folded end of the flow path to the other folded end is 50 mm or more.

5. 2. The self-regenerating bridge-type heat pipe according to claim 1, wherein the water-repellent treatment is anodizing or boehmite treatment.

6. The self-regenerative bridge-type heat pipe according to any one of claims 1 to 5, wherein the working fluid is water.

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