Dry ice jet device

Abstract

To provide a dry ice jet device capable of generating hard dry ice particles each having a small particle size.SOLUTION: A dry ice jet device 1 has: a liquefied carbon dioxide supply path 2 to which liquefied carbon dioxide is supplied; a jet hole 7A which jets liquefied carbon dioxide supplied from the liquefied carbon dioxide supply path 2; and a dry ice generation pipe 4 which causes the liquefied carbon dioxide jetted from the jet hole 7A to expand in an expansion space 8 which gradually expands to generate dry ice particles.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a dry ice spraying device that sprays dry ice particles produced from liquefied carbon dioxide. [Background technology]

[0002] Dry ice cleaning technology has long been known, in which dry ice particles are generated using liquefied carbon dioxide, mixed with compressed gas, and sprayed onto an object to remove contaminants from the surface of the object. A typical method of generating dry ice particles using liquefied carbon dioxide involves spraying the liquefied carbon dioxide from a pressure vessel into a dry ice generation tube using an orifice nozzle or throttle valve. When the liquefied carbon dioxide is released into the dry ice generation tube, it changes from a liquid to a gas, and expands in volume by 550 times. The gas is rapidly cooled by the Joule-Thomson effect, changing into carbon dioxide gas and a solid (dry ice).

[0003] A typical dry ice spraying device is structured to spray carbon dioxide gas and dry ice particles mixed with an acceleration gas inside or outside the nozzle (see, for example, Patent Documents 1 to 4). In the above structure, the dry ice generation tube that sprays liquefied carbon dioxide using an orifice nozzle, throttle valve, etc., is a pipe-like expansion space, and is sized according to the rate at which dry ice particles are generated. For example, Non-Patent Document 1 describes that it has been measured that the dry ice particles have a median diameter of about 1 μm in the sprayed gas, and that when a cylindrical chamber is attached, the particles aggregate and the median diameter becomes 100 μm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-122805 [Patent Document 2] JP 2019-72813 A [Patent Document 3] JP 2016-87745 A [Patent Document 4] JP 2003-145429 A [Non-patent literature]

[0005] [Non-Patent Document 1] Liu Yihong, Matsuzaka Shuji, Formation of dry ice particles and their application to surface cleaning, Aerosol Research, Japanese Society of Aerosol Science, 2013, Vol. 28, No. 2, pp. 155-162 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, when removing contaminants from the surface of an object, it is effective to use the conventional dry ice jetting device to accelerate dry ice particles with gas and collide them to remove fine particles that adhere due to van der Waals forces. However, in the case of more stubborn adhesions (such as dried stains on glass or resins adhering to precision molds), it is difficult to remove them unless the dry ice particles are strongly aggregated and hard.

[0007] Therefore, in order to peel off and remove stubborn adhesions, it is necessary to use gas to spray pellets / dry ice particles with a particle size of 100 μm or more, which are generated through a pressing process. In this case, however, it is impossible to clean narrow gaps with a particle size smaller than the large pellets / dry ice particles of 100 μm or more.

[0008] Therefore, an object of the present invention is to provide a dry ice spraying device capable of generating hard dry ice particles with a small particle size. [Means for solving the problem]

[0009] The dry ice spraying device of the present invention has a liquefied carbon dioxide supply passage through which liquefied carbon dioxide is supplied, a spray hole for spraying the liquefied carbon dioxide supplied from the liquefied carbon dioxide supply passage, and a dry ice generation tube for expanding the liquefied carbon dioxide sprayed from the spray hole in an expansion space that gradually expands to generate dry ice particles.

[0010] According to the dry ice spraying device of the present invention, the liquefied carbon dioxide sprayed from the spray hole into the expansion space is decompressed in a short time and changes from liquid to gas, and the gas is rapidly cooled by the Joule-Thomson effect and changes into gas (carbon dioxide gas) and solid (dry ice particles with an average particle diameter of about 1 μm). At this time, turbulence is generated by the first step in the expansion space, and the dry ice particles with an average particle diameter of about 1 μm are aggregated by the force of the vortex. Then, turbulence is similarly generated in the second and subsequent steps in the expansion space, and the dry ice particles are grown stepwise by the force of the vortex, thereby generating hard dry ice particles with an average particle diameter of 10 to 20 μm. In other words, in a smooth expansion space without steps, the dry ice particles softly aggregate in the wall boundary layer of several μm thickness formed on the inner wall surface of the expansion space, so in order to prevent this, a certain step is provided to create a high-speed turbulence on the wall surface, destroying the wall boundary layer and strongly aggregating the dry ice particles with the vortex force.

[0011] Here, the total length of the expansion space is preferably 10 to 30 mm. If the total length of the expansion space is shorter than 10 mm, the average particle diameter of the dry ice particles will be smaller than 10 μm, and the hardness will be low. If the total length of the expansion space is longer than 30 mm, the average particle diameter of the dry ice particles will be too large, and the hardness will be low.

[0012] Furthermore, in the dry ice sprayer of the present invention, it is desirable that the surface that the dry ice particles come into contact with or the entire device is made of a resin with a thermal conductivity of 0.5 W / m K or less. This ensures that the surface that the dry ice particles come into contact with or the entire device is insulated from the outside, reducing the sublimation of the dry ice particles. Effect of the Invention

[0013] (1) By having a liquefied carbon dioxide supply passage through which liquefied carbon dioxide is supplied, a nozzle for spraying the liquefied carbon dioxide supplied from the liquefied carbon dioxide supply passage, and a dry ice generation tube for generating dry ice particles by expanding the liquefied carbon dioxide sprayed from the nozzle in an expansion space that gradually expands, it is possible to generate hard dry ice particles with an average particle diameter of 10 to 20 μm and remove stubborn adhesions.

[0014] (2) If the surface or the entire surface that comes into contact with the dry ice particles is made of resin with a thermal conductivity of 0.5 W / m K or less, the surface or the entire surface that the dry ice particles come into contact with is insulated from the outside, reducing the sublimation of the dry ice particles and improving the efficiency of dry ice production from liquefied carbon dioxide. [Brief description of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing a main part of a dry ice spraying device according to an embodiment of the present invention. [Diagram 2] 2 is an enlarged cross-sectional view of a main part of the dry ice production pipe of FIG. 1. [Diagram 3] 1 is a graph showing the particle size distribution of dry ice particles at the nozzle outlet. [Figure 4] 1 is a photograph showing the state of the aluminum plate surface after a peel test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Fig. 1 is a cross-sectional view showing the main part of a dry ice jetting device in an embodiment of the present invention, and Fig. 2 is an enlarged cross-sectional view of the main part of the dry ice production pipe in Fig. 1. In addition, in this specification, a numerical range expressed by "to" means a numerical range including the numerical values ​​before and after "to" as the lower limit and upper limit.

[0017] As shown in FIG. 1, the dry ice spraying device 1 includes a liquefied carbon dioxide supply pipe 2 that supplies liquefied carbon dioxide, an acceleration gas supply pipe 3 that supplies an acceleration gas, a dry ice generation pipe 4 that generates dry ice particles, a junction member 5 having a junction section 5A therein where the acceleration gas supplied through the acceleration gas supply pipe 3 and the dry ice particles flowing out from the dry ice generation pipe 4 join, and a nozzle 6 that accelerates the dry ice particles that have joined with the acceleration gas at the junction section 5A and sprays them at supersonic speed.

[0018] The liquefied carbon dioxide supply pipe 2 is connected to a base end of the junction member 5. The liquefied carbon dioxide supply pipe 2 has a liquefied carbon dioxide supply path 2A through which liquefied carbon dioxide is supplied. The tip of the liquefied carbon dioxide supply pipe 2 protrudes into the junction portion 5A of the junction member 5. The dry ice production pipe 4 is provided at the tip of the liquefied carbon dioxide supply pipe 2 protruding into this junction portion 5A.

[0019] The dry ice production pipe 4 has an expansion space 8 that gradually expands the liquefied carbon dioxide sprayed from the spray hole 7A. The expansion space 8 is composed of first to third expansion spaces 8A, 8B, and 8C. The dry ice production pipe 4 is provided with an orifice section 7. The orifice section 7 has one spray hole 7A and a first expansion space 8A formed therein.

[0020] In this embodiment, the inner diameter of the ejection hole 7A is 0.2 to 0.3 mm. The orifice portion 7 is provided at the boundary between the downstream end of the liquefied carbon dioxide supply path 2A and the dry ice production pipe 4. The ejection hole 7A ejects the liquefied carbon dioxide supplied from the liquefied carbon dioxide supply path 2A into the first expansion space 8A. In this embodiment, the temperature and pressure of the liquefied carbon dioxide ejected into the first expansion space 8A are set to -20°C (2.5 MPa) to 25°C (6 MPa).

[0021] The dry ice production pipe 4 expands the liquefied carbon dioxide ejected from the ejection hole 7A in the stepwise expanding expansion space 8, i.e., the first to third expansion spaces 8A to 8C, to generate dry ice particles. The first expansion space 8A is the first stage of the stepwise expanding expansion space 8, i.e., the first stage. The inner diameter a of the first expansion space 8A is 2.4 to 4 mm, and the length e is a × (0.2 to 1.0). The first expansion space 8A is connected to the outlet of the ejection hole 7A by a groove 7B of 120 to 180°, as shown in FIG. 2.

[0022] The second expansion space 8B is the second stage of the expansion space 8 which expands stepwise. The inner diameter b of the second expansion space 8B is a×(1.2-2.2), and the length f is b×(0.2-1.0). In this embodiment, the second expansion space 8B does not have a groove at the connection portion with the first expansion space 8A, but a groove of 120° to 180° may be provided. In addition, when a groove is provided at the connection portion between the first expansion space 8A and the second expansion space 8B, this groove is included in the length e of the first expansion space 8A.

[0023] The third expansion space 8C is the third stage of the expansion space 8 which expands stepwise, that is, the final stage. The inner diameter c of the third expansion space 8C is b×(1.1-2.0), and the length g is c×(0.5-5.2). In this embodiment, the third expansion space 8C does not have a groove at the connection portion with the second expansion space 8B, but a groove of 120° to 180° may be provided. In addition, when a groove is provided at the connection portion between the second expansion space 8B and the third expansion space 8C, this groove is included in the length f of the second expansion space 8B.

[0024] The inner diameter a of the first expansion space 8A is set so that the average flow rate of the carbon dioxide gas passing through this first expansion space 8A is 70 to 100 m / sec. The inner diameter b of the second expansion space 8B is set so that the average flow rate of the carbon dioxide gas passing through this second expansion space 8B is 20 to 40 m / sec. The inner diameter c of the third expansion space 8C is set so that the average flow rate of the carbon dioxide gas passing through this third expansion space 8C is 6 to 20 m / sec. The total length d of the expansion space 8 is 10 to 30 mm.

[0025] In the dry ice production pipe 4 configured as above, the liquefied carbon dioxide ejected from the ejection hole 7A into the expansion space 8 is decompressed in a short time, changing from liquid to gas, and the gas is rapidly cooled by the Joule-Thomson effect, changing into gas (carbon dioxide gas) and solid (fine dry ice particles with an average particle diameter of about 1 μm). At this time, turbulence is generated by the first step in the expansion space 8, that is, the step between the inner diameter of the ejection hole 7A and the inner diameter a of the first expansion space 8A, and the force of the vortex causes the dry ice particles with an average particle diameter of about 1 μm to aggregate.

[0026] Then, turbulence is also generated in the second and subsequent steps of the expansion space 8, that is, the step between the inner diameter a of the first expansion space 8A and the inner diameter b of the second expansion space 8B, and the step between the inner diameter b of the second expansion space 8B and the inner diameter c of the third expansion space 8c, and the dry ice particles grow due to the force of the vortex. As a result, hard dry ice particles with an average particle diameter of 10 to 20 μm are generated in the dry ice generating pipe 4.

[0027] The acceleration gas supply pipe 3 is connected to the side of the base end of the junction member 5. The acceleration gas supply pipe 3 has an acceleration gas supply path 3A to which acceleration gas is supplied. In this embodiment, dry air of 0.4 to 0.6 MPa is used as the acceleration gas. The acceleration gas supplied from the acceleration gas supply path 3A to the junction 5A flows from the periphery of the dry ice production pipe 4 toward the nozzle 6 and merges with the dry ice particles produced in the dry ice production pipe 4. Note that a gas with a low dew point temperature can be used as the acceleration gas, and in addition to dry air, nitrogen gas, carbon dioxide gas, etc. may also be used.

[0028] The nozzle 6 is connected to the tip of the confluence member 5. The nozzle 6 has a contraction section 6A where the flow path cross-sectional area contracts in the flow direction, a throat section 6B where the flow path cross-sectional area is the smallest, and a Laval-shaped expansion section 6C. The contraction section 6A is a cone-shaped flow path that contracts at a contraction angle f. The contraction angle α is set to 10 to 30°. The cross-sectional area of ​​the upstream end of the contraction section 6A is the same as the cross-sectional area of ​​the downstream end of the confluence section 5A.

[0029] The throat section 6B is a narrowed portion between the contraction section 6A and the expansion section 6C. The inner diameter of the throat section 6B is 3 mm. The distance L from the nozzle hole 7A to the throat section 6B is 40 to 120 mm. The expansion section 6C is a Laval shape calculated using, for example, the Foelsch method. The inner diameter M of the nozzle 6D is 4.5 mm. The dry ice particles that merge with the acceleration gas at the confluence section 5A ride the flow of the acceleration gas and are accelerated to supersonic speed by passing through the contraction section 6A, throat section 6B, and expansion section 6C in the nozzle 6 in that order, and reach the nozzle 6D.

[0030] In the dry ice spraying device 1 configured as described above, liquefied carbon dioxide supplied from the liquefied carbon dioxide supply line 2A is sprayed through the spray hole 7A into the expansion space 8 of the dry ice generation pipe 4, and hard dry ice particles having an average particle diameter of 10 to 20 μm are formed by adiabatic expansion in this gradually expanding expansion space 8, which are then sprayed from the dry ice generation pipe 4 to the confluence 5A.

[0031] The dry ice particles ejected from the dry ice generating tube 4 merge with the acceleration gas supplied from the acceleration gas supply passage 3A at the junction 5A and ride the flow of the acceleration gas. At this time, in the dry ice ejection device 1 in this embodiment, since the distance from the ejection hole 7A to the throat portion 6B is 40 to 120 mm, the dry ice particles are mixed without touching the inner wall surfaces of the junction portion 5A and the contraction portion 6A, so that the dry ice particles reach the throat portion 6B while being mixed with the acceleration gas without growing agglomerates and without losing heat to the wall surface, and reach the throat portion 6B while being mixed with the acceleration gas, and become supersonic in the Laval-shaped expansion portion 6C, and are ejected at a uniform particle density from the ejection port 6D to the outside. Therefore, in this dry ice ejection device 1, it is possible to prevent the throat portion 6B from being blocked without heating the piping, and the dry ice particles can be ejected at a uniform particle density at a supersonic speed.

[0032] Fig. 3 is a graph showing the distribution of particle diameters D of dry ice particles at the injection port 6D of the nozzle 6. As shown in Fig. 3, the particle diameters D of the dry ice particles were mostly 40 µm or less, with most being in the range of 10 to 20 µm.

[0033] It is desirable to make the surfaces of the nozzle hole 7A, groove 7B, expansion space 8, junction 5A, contraction 6A, throat 6B, and expansion 6C that come into contact with the dry ice particles, or the entire orifice 7, dry ice generation pipe 4, junction member 5, and nozzle 6 out of a resin with a smooth surface and low thermal conductivity, such as a fluororesin or PPS (polyphenylene sulfide) resin with a thermal conductivity of 0.5 W / m·K or less. This provides insulation from the outside and reduces the sublimation of the dry ice particles, improving the efficiency of dry ice generation from liquefied carbon dioxide.

[0034] In addition, by making these resins conductive, the generation of static electricity is prevented and the effects of static electricity on dry ice particles can be prevented, thereby improving the efficiency of producing dry ice from liquefied carbon dioxide.

[0035] In this embodiment, the expansion space 8 that expands stepwise is configured in three stages, the first to third expansion spaces 8A to 8C, but it is also possible to configure it in two stages or four or more stages. Also, in this embodiment, the first expansion space 8A is configured to be provided in the orifice portion 7, but it is also possible to configure it separately from the orifice portion 7. EXAMPLES

[0036] A peeling test of adhesions due to dry ice particles was carried out using the dry ice jetting device 1 in the above embodiment. The peeling test was carried out by applying ALP-KZ α Clozome Spray (TRUSCO NAKAYAMA) to an aluminum plate and changing the shape of the dry ice generation tube.

[0037] The temperature of the liquefied carbon dioxide injected into the first expansion space 8A was 19.3°C, and the pressure was 5.6MPa. The acceleration gas pressure was 0.6MPa, and the flow rate was 650L / min (pressure dew point -62°C). The distance from the injection port 6D to the aluminum plate was 5mm, and the feed speed was 5mm / sec.

[0038] Table 1 shows the dimensions a, b, c, e, f, and g of the dry ice generating tube and the test results. The inner diameter of the nozzle 7A is all φ0.25mm. The dry ice generating tube number (2) does not have the first expansion space 8A. Figure 4 is a photograph showing the condition of the aluminum plate surface after the peeling test.

[0039] [Table 1]

[0040] As shown in Figure 4, for numbers (1), (3), and (5), the underlying aluminum plate was clearly exposed, and it was confirmed that the deposits could be peeled off. The ALP-KZ α Clozomes Spray (TRUSCO NAKAYAMA) applied to the aluminum plate contains synthetic resin and graphite, so the coating film was hard, and the difference in hardness of the dry ice particles was clearly visible. Even with the same liquefied carbon dioxide consumption and air injection flow rate, if the dry ice particles were softer, the coating film would not have been peeled off. For numbers (4), (6), and (7), it was possible to remove the coating film formed using Magic Ink (Teranishi Chemical Industry Co., Ltd.). [Industrial Applicability]

[0041] The dry ice spraying device of the present invention is useful as a dry ice cleaning device that mixes dry ice particles generated from liquefied carbon dioxide with compressed gas and sprays the mixture onto an object to remove contaminants from the surface of the object, and is particularly suitable as a dry ice spraying device that generates hard dry ice particles with an average particle diameter of 10 to 20 μm and is capable of removing stubborn adhesions. [Explanation of symbols]

[0042] 1. Dry ice blower 2. Liquefied carbon dioxide supply pipe 2A Liquefied carbon dioxide supply line 3 Acceleration gas supply pipe 3A Acceleration gas supply line 4 Dry ice generating tube 5 Joint members 5A Confluence 6 Nozzles 6A Reduced section 6B Throat 6C Extension 6D injection port 7 Orifice 7A spout hole 7B Bevel 8,8A,8B,8C expansion space

Claims

1. a liquefied carbon dioxide supply path through which liquefied carbon dioxide is supplied; a jet hole for jetting the liquefied carbon dioxide supplied from the liquefied carbon dioxide supply path; a dry ice generating tube for expanding the liquefied carbon dioxide ejected from the ejection hole in an expansion space which gradually expands to generate dry ice particles; A dry ice injection device having a

2. 2. The dry ice spraying device according to claim 1, wherein the total length of the expansion space is 10 to 30 mm.

3. The expansion space is The inner diameter a of the first stage is 2.4 to 4 mm, and the length is a×(0.2 to 1.0), The inner diameter b of the second stage is a×(1.2 to 2.2), and the length is b×(0.2 to 1.0), The inner diameter c of the final stage is b x (1.1 to 2.0), and the length is c x (0.5 to 5.2).

3. The dry ice jetting device according to claim 2.

4. 2. The dry ice spraying device according to claim 1, wherein the average flow velocity of the carbon dioxide gas passing through the first stage of the expansion space is 70 to 100 m / sec.

5. 5. The dry ice spraying device according to claim 4, wherein the average flow velocity of the carbon dioxide gas passing through the second stage of the expansion space is 20 to 40 m / sec.

6. 6. The dry ice spraying device according to claim 5, wherein the average flow velocity of the carbon dioxide gas passing through the final stage of the expansion space is 6 to 20 m / sec.

7. 7. The dry ice spraying device according to claim 1, wherein the surface or the entire surface that comes into contact with the dry ice particles is formed from a resin having a thermal conductivity of 0.5 W / m·K or less.

Images