Cooling structure

Abstract

To reduce the time needed for cooling an object to be cooled (a cooled object) to a cryogenic temperature by using a liquid refrigerant such as liquid nitrogen.SOLUTION: A device which circulates liquid nitrogen serving as a refrigerant through a circulation system 10 and a pipe 11 to cool a cooled object 20 is formed. A resin layer 23 is formed on a surface of the cooled object 20. Slit parts 22 are formed at the resin layer 23. The liquid nitrogen serving as the refrigerant contacts with the resin layer 23 of a cooling structure at a refrigerant layer 12 to cool the cooled object 20. Forming a cooling structure in which the resin layer 23 having the slit parts 22 is formed on the surface of the cooled object 20 can inhibit Leidenfrost phenomenon or film boiling of the liquid refrigerant. Consequently, the time needed for cooling the cooled object 20 to a cryogenic temperature can be reduced.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technique for promoting cooling when an object to be cooled is cooled to an extremely low temperature with a liquid refrigerant such as liquid nitrogen. [Background technology]

[0002] It is known that when cooling to extremely low temperatures with a liquid refrigerant such as liquid nitrogen, if the temperature difference between the object to be cooled and the refrigerant is large, a phenomenon called the Leidenfrost phenomenon or film boiling occurs at the contact surface between the two, preventing contact between the refrigerant and the object to be cooled, and thus lengthening the time required for cooling. Patent Document 1 discloses a technique for shortening the time required for cooling by providing a porous layer of poor thermal conductor such as glass wool, carbon fiber, or ceramics on the surface of the metal object to be cooled. A technique for forming a resin layer instead of a porous layer is also known. The principle of these techniques is that a temperature gradient is generated in the porous layer or resin layer from the surface in contact with the object to be cooled to the surface in contact with the refrigerant, thereby reducing the temperature difference with the refrigerant at the surface in contact with the refrigerant and suppressing the occurrence of the Leidenfrost phenomenon. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-307791 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional techniques, in order to obtain a sufficient effect, it is necessary to form a layer exceeding 50 μm, and there is a problem in that forming the layer is difficult. An object of the present application is to provide a technique for solving such problems and shortening the time required for cooling to extremely low temperatures using a liquid refrigerant. [Means for solving the problem]

[0005] The present invention relates to A cooling structure that promotes cooling of a liquid refrigerant of an object to be cooled, a resin layer formed on a contact surface of the object to be cooled that comes into contact with the refrigerant; The cooling structure may include a notch formed in the resin layer.

[0006] In the present invention, not only is a resin layer formed on the contact surface between the object to be cooled and the refrigerant, but cuts are also formed in the resin layer. As a result of experiments by the inventors, it was confirmed that by providing cuts in this way, cooling can be promoted even with a resin layer that is significantly thinner than in the past. The principle behind the above-mentioned effects has not been fully elucidated, but it is believed that the refrigerant that vaporizes upon contact with the resin layer enters the cutout, thereby maintaining contact between the liquid refrigerant and the resin layer without being impeded by the vaporized refrigerant. In the present invention, any refrigerant may be used, for example, liquid nitrogen. In the present invention, the shape, dimensions, etc. of the cuts can be determined arbitrarily. However, in consideration of the above-mentioned principle, it is considered that a relatively narrow width is preferable. The cuts may be formed in a geometric or regular pattern, or may be irregular. In addition, the width, length, depth, etc. of the cuts do not need to be uniform.

[0007] In the present invention, The resin layer may be made of a fluororesin.

[0008] The inventors' experiments confirmed that fluororesin is effective. In particular, it is preferable to use Fluorosurf (registered trademark), but polytetrafluoroethylene (PTFE) can also be used. Note that this is not intended to exclude materials other than fluororesin, such as epoxy resin.

[0009] In the present invention, The resin layer is preferably formed by solidifying a resin having a viscosity at 25° C. of 40 m·Pa·s or more and 50 m·Pa·s or less.

[0010] It has been found that by using a resin with such a viscosity, it is relatively easy to form a resin layer with an appropriate thickness and cut portions.

[0011] In the present invention, The resin layer preferably has a thickness of 30 μm or less.

[0012] If the resin layer exceeds this thickness, there is a concern that the resin layer may become easily peeled off. Therefore, from the viewpoint of durability of the resin layer, the above range is preferable.

[0013] In the present invention, The resin layer preferably has a thickness of 7 μm or more.

[0014] As a result of experiments, it was confirmed that such a thickness is preferable from the viewpoint of forming effective cuts in the resin layer.

[0015] In the present invention, The resin layer is The cut portion divides the shape into a plurality of closed shapes, The diameter of the smallest encompassing circle of the closed figure is preferably 100 μm or more and 300 μm or less.

[0016] Experimental results confirmed that this range is preferable.

[0017] In the present invention, It is preferable that the cut portion is a crack that occurs in the resin layer by applying the resin that constitutes the resin layer to the object to be cooled and then cooling the resin.

[0018] As a result of the experiment, it was confirmed that cracks can be generated on the surface by cooling the resin layer, and that such cracks are useful for accelerating cooling.

[0019] In the present invention, it is not necessary to have all of the various features described above, and some of them may be omitted or combined as appropriate. Furthermore, the present invention can be configured in various other aspects in addition to the cooling structure described above.

[0020] For example, the present invention provides Any one of the cooling structures described above; The cooling device may be configured to include a refrigerant chamber that holds a liquid refrigerant so as to be in direct contact with the surface of the resin layer on which the cut portions are provided.

[0021] According to this cooling device, the object to be cooled can be cooled effectively. The coolant may be, for example, liquid nitrogen. The refrigerant chamber may be a tank-shaped one for storing the refrigerant, or may be a pipe for circulating the refrigerant, etc. A combination of both may be used, and a mechanism for circulating the refrigerant may be added separately to the tank-shaped refrigerant chamber.

[0022] The present invention also provides a method for manufacturing a cooling structure for promoting cooling of a liquid refrigerant of an object to be cooled, comprising the steps of: (a) preparing the object to be cooled; (b) applying a resin onto a contact surface of the object to be cooled that comes into contact with the refrigerant; (c) forming a cut portion in a surface of the resin layer formed by curing the resin.

[0023] In this way, the cooling structure can be realized relatively easily.

[0024] In addition, in the above method, The step (c) may be a step of forming crack-like cuts in a surface of the resin layer by cooling the resin layer.

[0025] In this way, the cut portion can be formed relatively easily. Moreover, experimental results have confirmed that the crack-like cut portion thus formed acts very effectively.

[0026] Furthermore, in the above method, The cooling temperature in the step (c) is preferably 220K or lower.

[0027] As a result of experiments, it was confirmed that by doing so, it is possible to effectively form a crack-like cut portion. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is an explanatory diagram showing an overall configuration of a cooling device according to an embodiment; [Diagram 2] FIG. 1 is an explanatory diagram showing the principle of promotion of cooling. [Diagram 3] FIG. 4 is a process diagram of a cooling structure manufacturing process. [Figure 4] FIG. 13 is an explanatory diagram showing the influence of cooling temperature. [Diagram 5] 1 is a graph showing the cooling promotion effect in an example. [Figure 6] 1 is a graph showing the effect of crack generation. [Figure 7] FIG. 13 is an explanatory diagram showing the influence of film thickness. [Figure 8] FIG. 13 is an explanatory diagram showing the cooling promotion effect due to the film thickness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Examples of the present invention will now be described. 1 is an explanatory diagram showing the overall configuration of a cooling device according to an embodiment of the present invention, which uses liquid nitrogen to cool an object 20 to be cooled. The object 20 to be cooled is preferably a metal. A resin layer 23 is formed on the surface of the object to be cooled 20. A cut portion 22 is formed in the resin layer 23. The object to be cooled 20, the resin layer 23, and the cut portion 22 correspond to the cooling structure in the present invention. The liquid nitrogen, which is the refrigerant, comes into contact with the resin layer 23 of the cooling structure in the refrigerant layer 12 and cools the object 20 to be cooled. The liquid nitrogen is circulated by a circulation device 10 through a pipe 11 .

[0030] FIG. 2 is an explanatory diagram showing the principle by which cooling is promoted. First, as a comparative example, FIG. 2(a) shows a state where the resin layer is not formed. In this state, the refrigerant is in direct contact with the object to be cooled 20. The temperature of the object to be cooled 20 and the refrigerant are shown in the figure. Since the object to be cooled 20 is a metal and has a very high thermal conductivity, no temperature gradient occurs in the thickness direction (vertical direction in the figure), and the temperature is almost uniform T1. On the other hand, the temperature of the refrigerant is T0. At the contact surface between the refrigerant and the object to be cooled 20, the temperature difference between them is DT1. If this temperature difference is large, a phenomenon called the Leidenfrost phenomenon or film boiling occurs at the contact surface between the two, and the refrigerant will suddenly vaporize. When this phenomenon occurs, the vaporized refrigerant will be present at the contact surface, preventing the liquid refrigerant from contacting the object to be cooled 20, and effective cooling will not be performed.

[0031] FIG. 2(b) shows the cooling structure in the embodiment. In the cooling structure, a resin layer 23 having a cut portion 22 is formed on the surface of the object to be cooled 20. Inside the object to be cooled 20, the temperature T1 is almost uniform, and the temperature of the refrigerant is T0, as in the case of FIG. 2(a). However, in this cooling structure, the surface of the resin layer 23 is cooled by the refrigerant, and as a result, a temperature gradient occurs in the resin layer 23, in which the temperature gradually decreases from the temperature T1 of the object to be cooled in the thickness direction. If the temperature of the surface of the resin layer 23 is T2, the temperature difference DT2 with the refrigerant is the difference between the temperature T2 and the temperature T0, which is smaller than the temperature difference DT1 shown in FIG. 2(a). In this way, by interposing the resin layer 23, the temperature difference with the surface in contact with the refrigerant can be reduced, so that the Leidenfrost phenomenon can be suppressed and cooling can be promoted. In the cooling structure of this embodiment, the resin layer 23 is formed with the cut portions 22. The effect of the cut portions 22 will be described later based on the results of experiments.

[0032] 3 is a process diagram of the cooling structure manufacturing process. First, an object to be cooled is prepared, and its surface is resin-coated (step S10). The resin coating can be performed by applying it with a spray or brush, or by immersing the object to be cooled in a container that contains the resin. Various fluororesins such as PTFE can be used as the resin. In this example, Fluorosurf (registered trademark) FG-3650C was used. The resin coating can be applied to any thickness, but is preferably in the range of 7 μm to 30 μm, as described below.

[0033] After the resin coating is performed, the cooled object is cooled until cracks appear in the resin coating (step S11). These cracks become the cuts 22. As described below, experiments have confirmed that cracks appear at 220K or less, so it is preferable to cool to this temperature. Once it is confirmed that cracks have occurred in the resin coating, the manufacture of the cooling structure is complete.

[0034] 3 is merely one example of a method for manufacturing the cooling structure, and other methods may be used. For example, the cutouts 22 may be formed in the resin coating by embossing or cutting.

[0035] Figure 4 is an explanatory diagram showing the effect of cooling temperature. A photograph of the surface of the resin coating is shown. The resin used is Fluorosurf (registered trademark), and the thickness of the resin coating is 15 μm. Cooling was performed by pouring liquid nitrogen onto the surface. Figure 4(a) shows the state after resin coating and before cooling. It can be seen that there are no cracks on the surface. Figure 4(b) shows the state after cooling to 250 K. Even at this point, it can be confirmed that no cracks have occurred. Figure 4(c) shows the state after cooling to 220K. At this point, it can be confirmed that cracks have appeared. Figure 4(d) shows the state after cooling to 200K, and Figure 4(e) shows the state after cooling to 170K. It can be clearly confirmed that cracks have appeared in each case. Figure 4(f) is a micrograph of the resin coating after cooling to 77 K. It can be clearly seen that the surface of the resin coating was divided into several irregular closed shapes due to the cracks. The diameter of the smallest inclusive circle of the closed shapes was between 100 μm and 300 μm.

[0036] Fig. 5 is a graph showing the cooling promotion effect in the example. A square copper plate measuring 30 mm in length and width and 2 mm in thickness was used as the object to be cooled, a resin layer was formed using Fluorosurf (registered trademark) FG-3650C, and the back and sides where the resin layer was not formed were covered with a heat insulating material. The object was then dropped into a bath of liquid nitrogen at 77 K, and the temperature change of the object to be cooled was measured. Curve C1 shows the temperature change of the object to be cooled without a resin coating, i.e., without a resin layer, and curve C2 shows the temperature change when a 15 μm-thick resin coating is applied. As shown in the figure, the time required to cool from 290 K to 90 K was 130 seconds when no resin layer was formed, whereas it was 26 seconds when a resin layer was formed. From this result, it is understood that the resin layer in this embodiment is effective in shortening the time required for cooling.

[0037] Figure 6 is a graph showing the effect of crack generation. It shows temperature changes in an experiment similar to that of Figure 5. The results are for a test piece with a 15 μm-thick resin layer, where cooling was repeated five times. Curves C11 to C15 show the results for the first to fifth times, respectively. As explained above in the process diagram (Fig. 3), cracks on the surface of the resin layer occur due to cooling, so there are no cracks on the surface of the resin layer during the first cooling. After cracks appear in the resin layer due to the first cooling, the second and subsequent cooling steps are carried out. As shown in the figure, in the first cooling (curve C11), it took 26 seconds to cool from 290 K to 90 K, whereas in the second to fifth coolings (curves C12 to C15), the time was reduced to less than 20 seconds. From these results, it was confirmed that the cooling time can be shortened by generating cracks on the surface of the resin layer. Although the principle by which cracks promote cooling has not been elucidated, it is believed that the refrigerant vaporized during cooling of the resin layer is sucked into the cracks, making it difficult for the resin layer to contact the refrigerant. Based on this principle, it is believed that the cuts on the surface of the resin layer do not necessarily have to be cracks generated by cooling, and may be formed mechanically by embossing or cutting. However, the method of this embodiment has the advantage of being simple, since effective cracks can be produced by cooling.

[0038] Fig. 7 is an explanatory diagram showing the effect of film thickness. It shows the state of cracks when a resin coating was applied using Fluorosurf (registered trademark) and then cooled to 77 K. Fig. 7(a) to Fig. 7(e) show the results for film thicknesses of 5, 7, 12, 15, and 21 μm, respectively. As shown in Figure 7(a), when the film thickness is 5 μm, no cracks appear even after cooling. As shown in Figures 7(b) to 7(e), when the film thickness is 7 μm or more, cracks appear. From these results, it was confirmed that in order to promote cooling, including the effect of cracks, a film thickness of 7 μm or more is preferable.

[0039] Fig. 8 is an explanatory diagram showing the cooling promotion effect due to film thickness. Cooling was repeated five times for the test pieces with each film thickness shown in Fig. 7, and the time required for cooling from 290K to 90K was plotted. However, as explained in Fig. 6, the first cooling was performed in a state where no cracks had occurred, so Fig. 8 shows the results for the second to fifth coolings. As shown in the figure, the time required for the results when the film thickness was 5 μm (point group P1) was clearly longer than the results when the film thickness was 7 μm or more (point groups P2 to P5). This is thought to be because no cracks occurred at a film thickness of 5 μm, as explained in FIG. 7. In other words, this result confirmed that the occurrence of cracks in the resin layer promoted cooling.

[0040] Furthermore, according to the results of point groups P2 to P5, there is no significant difference between the results of film thicknesses of 15 μm (point group P4) and 21 μm (point group P5). On the other hand, it is confirmed that the results of point groups P4 and P5 promote cooling significantly more than film thicknesses of 7 μm (point group P2) and 12 μm (point group P3). From these results, it can be said that it is more preferable to set the film thickness to 15 μm or more. On the other hand, experimental results showed that when the film thickness was 30 μm or more, the resin layer peeled off from the object to be cooled. From this point of view, it is preferable to set the film thickness to 30 μm or less. Considering all of the above, it is believed that a film thickness of 15 μm to 20 μm would be optimal in order to achieve both the cooling promotion effect and the durability of the resin layer.

[0041] Here, the resin used in this example will be described. As already explained, Fluorosurf (registered trademark) FG-3650 was used as the resin in this example. Its physical properties are as shown in Table 1. Any resin may be used to form the resin layer, but if one with a viscosity of 40 to 50 mPa·s at 25°C is used, the film thickness will be 10 to 20 μm in one application, and the above-mentioned optimal film thickness can be realized. From this perspective, it can be said that it is preferable to use Fluorosurf (registered trademark) FG-3650 with this viscosity. [Table 1]

[0042] According to the cooling structure and the cooling device of the embodiment described above, it is possible to cool an object to be cooled to an extremely low temperature in a short period of time. It is not necessary to provide all of the various features described in the above embodiments, and some of them may be omitted or combined as appropriate. In the experiments of the embodiment, Fluorosurf (registered trademark) was used as the resin, but other resins can also be used. In addition, although a copper plate was used as an example of the object to be cooled in the experiment, other metals may be used as well. Furthermore, the object to be cooled is not limited to metals, and any object that can cause the Leidenfrost phenomenon may be used as the object to be cooled. The cooling device of the embodiment may be configured as a device for pre-cooling facilities for transferring and storing liquid refrigerants, pre-cooling piping of liquid fuel rockets, quick-freezing biological cells, and the like. [Industrial Applicability]

[0043] The present invention can be utilized to cool an object to a cryogenic temperature with a liquid refrigerant such as liquid nitrogen. [Explanation of symbols]

[0044] 10 Circulation device 11 Piping 12 Refrigerant layer 20 Object to be cooled 22 Cutting section 23 Resin layer

Claims

1. A cooling structure that promotes cooling of a liquid refrigerant of an object to be cooled, a resin layer having a thickness of 7 μm or more and 30 μm or less formed on a contact surface of the object to be cooled that comes into contact with the refrigerant; A cooling structure comprising: a crack-like cut portion formed in the resin layer.

2. The cooling structure according to claim 1 , The resin layer is a cooling structure formed of a fluororesin.

3. The cooling structure according to claim 1 , The resin layer is The cut portion divides the shape into a plurality of closed shapes, A cooling structure in which the diameter of the smallest encompassing circle of the closed figure is 100 μm or more and 300 μm or less.

4. The cooling structure according to claim 1 , The cooling structure is such that the notch is a crack that occurs in the resin layer by applying the resin that constitutes the resin layer to the object to be cooled and then cooling the resin.

5. A cooling structure according to any one of claims 1 to 4, a refrigerant chamber that holds a liquid refrigerant so as to be in direct contact with the surface of the resin layer on which the cut portion is provided.

6. A method for manufacturing a cooling structure that promotes cooling of a liquid refrigerant of an object to be cooled, comprising the steps of: (a) preparing the object to be cooled; (b) applying a resin onto a contact surface of the object to be cooled that comes into contact with the refrigerant; (c) forming crack-like cuts in the surface of a resin layer having a thickness of 7 μm or more and 30 μm or less formed by curing the resin.

7. The method of claim 6, The step (c) is a step of forming crack-like cuts in a surface of the resin layer by cooling the resin layer.

8. The method of claim 7, The manufacturing method, wherein the cooling temperature in the step (c) is 220K or less.

9. The method of claim 6, The resin has a viscosity of 40 m·Pa·s or more and 50 m·Pa·s or less at 25° C.

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