Nozzle atomization performance evaluation method and evaluation system

Abstract

To provide an evaluation method for easily evaluating the quality of a spraying pattern in a nozzle at high accuracy.SOLUTION: An evaluation method of evaluating spraying performance of a nozzle for spraying a liquid includes: a spraying step in which a hydrophilic liquid is sprayed from the nozzle toward a non-hydrophilic plate, fusing sprayed droplets on the non-hydrophilic plate, and forming a group of fused droplets consisting of the obtained fused droplets on the non-hydrophilic plate; and an evaluation step in which spraying performance of the nozzle is evaluated by evaluating uniformity of a distribution state in the group of fused droplets.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an evaluation method and evaluation system for evaluating the quality of a spray pattern in a nozzle for spraying a fluid. [Background technology]

[0002] In spray research, a device that uses a laser to measure the concentration of droplet particles has been used to evaluate the state of a liquid sprayed from a nozzle. In particular, when spraying a liquid, tiny droplets ranging in diameter from a few microns to a few tens of microns are generated, resulting in extremely high concentrations of droplets. Therefore, droplet distribution is measured using methods that utilize the diffraction phenomenon caused by laser irradiation. However, because this device uses a laser, safety precautions and measurement preparation are complicated. Furthermore, the use of a laser results in significant energy loss and high equipment costs, making it inefficient as an inspection device.

[0003] Furthermore, spray nozzles are used for spraying fuel (fuel oil), such as in burners for oil-fired water heaters and burners for drying grains. These spray nozzles are required to have atomization performance to improve combustion efficiency. For example, in the case of spraying from oil-fired water heater burners, a hollow cone-shaped spray pattern is used, which is advantageous for atomization performance.

[0004] A commonly used method for inspecting the spray quality of hollow cone nozzles that spray fuel oil involves inspecting the spray pattern using water at spray rates of 0.3 to 300 ml / min. When spraying fuel oil, ensuring uniformity of the spray pattern without being affected by changes in flow rate is important to control combustion at different flow rates. Poor spray pattern characteristics include (1) defects where the droplet spray density is low or dense in the smallest spray area on the circumference of the pattern, and (2) defects where the droplet density differs between the top, bottom, left, and right of the pattern. Therefore, efficient inspections to detect such defects are necessary, but conventional methods have limitations.

[0005] As a method for inspecting injection devices used in injectors for internal combustion engines, Japanese Patent No. 4013236 (Patent Document 1) discloses a method for inspecting the concentration distribution of spray by irradiating light from the side of the spray's direction of travel, photoelectrically converting the reflected or transmitted light in an imaging unit, and then parameterizing the output obtained for each pixel in multiple stages and performing image processing.

[0006] Meanwhile, Japanese Patent No. 6157933 (Patent Document 2) discloses a method for inspecting the spray pattern of a liquid repellent agent sprayed onto a mounting substrate during the manufacturing process of a light-emitting diode (LED) light source light-emitting module. This method involves reading the spray pattern of a functional film formed by spraying a functional liquid onto a substrate to be sprayed, and from the resulting image, determining the bias of the spray pattern and the droplet density of the entire spray pattern, and judging whether the droplet density is appropriate. A specific example of the functional liquid is spraying the liquid repellent agent by supplying compressed air to it. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4013236 [Patent Document 2] Patent No. 6157933 Summary of the Invention [Problem to be solved by the invention]

[0008] However, with the method of Patent Document 1, it was difficult to accurately evaluate the distribution on the pattern perpendicular to the spray direction. Furthermore, with the method of Patent Document 2, only the density of the entire pattern was evaluated, and it was not possible to evaluate the distribution state of the spray pattern, for example, the distribution state in the circumferential direction of a circular pattern. Furthermore, Patent Document 2 does not disclose details of the image processing method.

[0009] Furthermore, various factors are involved in the uniformity of the spray pattern. For example, in a nozzle obtained by assembling multiple parts, factors such as the part shapes and assembly method are intricately related. Therefore, the uniformity of the spray pattern must be evaluated by actually spraying with the nozzle, and a simple and accurate evaluation method is required.

[0010] Therefore, an object of the present invention is to provide an evaluation method and evaluation system that can easily evaluate the uniformity of a spray pattern with high accuracy. [Means for solving the problem]

[0011] As a result of intensive research into achieving the above-mentioned object, the inventors have discovered that a method for evaluating the spraying performance of a nozzle for spraying a fluid can be achieved by combining a spraying step in which a hydrophilic liquid is sprayed from the nozzle toward a non-hydrophilic plate, the sprayed droplets are caused to fuse on the non-hydrophilic plate, and a group of fused droplets composed of the resulting fused droplets is formed on the non-hydrophilic plate, with an evaluation step in which the spraying performance of the nozzle is evaluated based on the uniformity of the distribution state of the group of fused droplets, thereby easily evaluating the uniformity of the spray pattern and completing the present invention.

[0012] That is, the evaluation method of the present disclosure is a method for evaluating the spraying ability (uniform spraying ability) of a nozzle for spraying a fluid, a spraying step of spraying a hydrophilic liquid from the nozzle toward a non-hydrophilic plate, fusing the sprayed droplets on the non-hydrophilic plate, and forming a group of fused droplets on the non-hydrophilic plate; and evaluating the spray performance of the nozzle based on the uniformity of the distribution of the fused droplets.

[0013] In the evaluation step, the non-hydrophilic plate may be irradiated with light, the distribution state may be photographed with a camera, and the photographed image may be analyzed with an image analyzer.

[0014] In the spraying step, the average diameter of the fused droplets may be 300 to 5000 μm. In the evaluation step, the quality of the spray pattern may be determined by setting a threshold based on the diameter of the fused droplets, and in particular, the area of ​​a region where the diameter of the fused droplets is smaller than a predetermined diameter may be set as the threshold. In the spraying step, the hydrophilic liquid may be sprayed at a spray rate of 0.3 to 300 ml / min for 0.1 to 10 seconds. The average diameter of the sprayed droplets may be 5 to 100 μm. The average diameter of the fused droplets may be 3 to 1000 times the average diameter of the sprayed droplets. The hydrophilic liquid may be water. The non-hydrophilic plate may be a transparent or translucent plate (e.g., a resin plate or a water-repellent glass plate). The nozzle may be a one-fluid nozzle for spraying a liquid. The nozzle may be a hollow cone nozzle. The nozzle may be a burner nozzle. The evaluation method may further include, as a pre-step of the spraying step, an adjustment step of adjusting the spray amount, spray pressure, spray distance, and spray time of the hydrophilic liquid in the nozzle to determine conditions under which fused droplets having an average diameter of 300 to 5000 μm can be obtained. In the spraying step, the spraying time may be controlled by using a shielding means capable of shielding the sprayed liquid between the nozzle and the non-hydrophilic plate.

[0015] The present disclosure provides a system for evaluating the atomization capability of a nozzle for atomizing a fluid, the system comprising: a non-hydrophilic plate for forming a group of fused droplets made up of fused droplets obtained by fusing spray droplets of the hydrophilic liquid sprayed from the nozzle; and an evaluation means for evaluating the spray performance of the nozzle by evaluating the uniformity of the distribution state of the coalesced droplet group.

[0016] The evaluation means may include a light source for irradiating light onto the non-hydrophilic plate on which the fused droplet group is formed, a camera for photographing the distribution state, and an image analysis device for analyzing the image photographed by the camera. [Effects of the Invention]

[0017] The present disclosure provides a method for evaluating the spray performance of a nozzle for spraying a fluid, which combines a spraying step of spraying a hydrophilic liquid from the nozzle toward a non-hydrophilic plate, fusing the sprayed droplets on the non-hydrophilic plate, and forming a group of fused droplets on the non-hydrophilic plate, with an evaluation step of evaluating the spray performance of the nozzle by evaluating the uniformity of the distribution of the fused droplets. This method allows for easy evaluation of the uniformity of the spray pattern with high accuracy. Furthermore, by analyzing an image of the distribution of the fused droplets taken with a camera using an image analyzer, the quality of the spray pattern can be determined with high inspection efficiency. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a flowchart for determining nozzle spray performance in one example of the evaluation method of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram for explaining the method for evaluating nozzle spraying performance in the examples. [Figure 3] FIG. 3 is an image showing the distribution of fused droplets in Sample 2 in the example. [Figure 4] Figure 4 is an image of the image in Figure 3 in which fused droplets with a droplet diameter of 1.3 mm or more have been colored using image processing software. [Figure 5] FIG. 5 is an image showing the distribution of fused droplets in Sample 5 of the example. [Figure 6] FIG. 6 is an image in which fused droplets with a droplet diameter of 1.3 mm or more in the image of FIG. 5 have been colored using image processing software. [Figure 7] Figure 7 shows an image of Sample 1 in the example, in which fused droplets with a droplet diameter of 1.3 mm or more have been colored using image processing software, and the evaluation area and the angle of the area where fused droplets with a droplet diameter of 1.3 mm or more do not exist are indicated. [Figure 8]Figure 8 shows an image of Sample 2 in the example, in which fused droplets with a droplet diameter of 1.3 mm or more have been colored using image processing software, and the evaluation area and the angle of the area where fused droplets with a droplet diameter of 1.3 mm or more do not exist are indicated. [Figure 9] Figure 9 shows an image of Sample 3 in the example, in which fused droplets with a droplet diameter of 1.3 mm or more have been colored using image processing software, and the evaluation area and the angle of the area where fused droplets with a droplet diameter of 1.3 mm or more do not exist are indicated. [Figure 10] Figure 10 shows an image of Sample 4 in the example, in which fused droplets with a droplet diameter of 1.3 mm or more have been colored using image processing software, and the evaluation area and the angle of the area where fused droplets with a droplet diameter of 1.3 mm or more do not exist are indicated. [Figure 11] Figure 11 is an image of Sample 5 in the example, in which fused droplets with a droplet diameter of 1.3 mm or more have been colored using image processing software, and the evaluation area and the angle of the area where fused droplets with a droplet diameter of 1.3 mm or more do not exist are indicated. [Figure 12] Figure 12 is an image of Sample 6 in the example, in which fused droplets with a droplet diameter of 1.3 mm or more have been colored using image processing software, and the evaluation area and the angle of the area where fused droplets with a droplet diameter of 1.3 mm or more do not exist are indicated. DETAILED DESCRIPTION OF THE INVENTION

[0019] The method for evaluating nozzle sprayability according to the present disclosure is a method for evaluating nozzle sprayability by determining whether a uniform spray pattern can be sprayed, and includes the spraying step and the evaluation step.

[0020] [Spraying process] In the spraying process, a hydrophilic liquid is sprayed from a nozzle (spray nozzle) whose spraying ability is to be evaluated toward a non-hydrophilic plate, and the sprayed droplets are fused on the non-hydrophilic plate to form a group of fused droplets on the non-hydrophilic plate.

[0021] (nozzle) The nozzle is not particularly limited as long as it is a nozzle for spraying a fluid, but a nozzle for spraying a fluid containing a liquid is preferred.

[0022] The nozzle may be a single-fluid nozzle that sprays a liquid, or a two-fluid nozzle that sprays a liquid and a gas (air). Of these, a single-fluid nozzle that sprays a liquid is preferred because it allows for highly accurate evaluation of the uniformity of the spray pattern. If the air pressure (air pressure) of a two-fluid nozzle is high or the flow rate is high, the droplets on the plate are likely to be blown away or the droplet shape is likely to be deformed or merged by the air flow, making it difficult to project the spray pattern onto the plate. In contrast, a single-fluid nozzle for spraying a liquid makes it easy to project the spray pattern onto the plate.

[0023] The liquid may be, for example, water, a solvent, an oil, etc., depending on the application. Among the liquids, oil such as fuel oil (fossil fuel) is preferred because it is sprayed in the form of minute droplets and the evaluation method of the present disclosure is highly effective.

[0024] Examples of the nozzle include burner nozzles, nozzles for inkjet printers, humidifying or cooling nozzles, nozzles for disinfecting, sterilizing, or spraying chemicals, oiling nozzles, and nozzles used in the electronics field (e.g., spray nozzles for etching substrates and spray nozzles for coating substrates). Of these, burner nozzles are preferred because they spray fine droplets and are highly effective in the evaluation method of the present disclosure, and burner nozzles for spraying fuel oil (fossil fuel) in burners for oil-fired water heaters, burners for grain drying, etc. are particularly preferred.

[0025] The nozzle is not limited in the spray mode, and may be any of a full cone nozzle, a hollow cone nozzle, and a flat (fan-shaped) nozzle. Among these, a hollow cone nozzle is preferred because the droplet diameter is small, making it difficult to evaluate uniformity, and the effect of the evaluation method of the present disclosure is significant.

[0026] The shape (extension shape) of the spray pattern of the nozzle may be, for example, a circle, an ellipse, a flat pattern, etc. Among these, a circle is preferred because it can be easily evaluated with high accuracy.

[0027] (hydrophilic liquid) In the evaluation method disclosed herein, a hydrophilic liquid is used as the fluid (evaluation fluid) for evaluating the uniformity of the spray pattern in the nozzle, instead of the liquid (fuel oil, etc.) sprayed from the burner nozzle in actual use.

[0028] Examples of hydrophilic liquids include water and hydrophilic organic solvents (lower alcohols such as ethanol and isopropanol, and ketones such as acetone). The hydrophilic liquid may contain chemicals such as hydrochloric acid, sulfuric acid, and sodium hydroxide. Among these, from the standpoint of simplicity, water, a mixed solvent (aqueous solvent) containing water as the main component and a hydrophilic organic solvent, or an aqueous solution containing the chemicals is preferred, with water being particularly preferred. Even when evaluating the spray of a hydrophobic liquid such as fuel oil, a hydrophilic liquid can be used instead to evaluate the uniformity of the spray.

[0029] (non-hydrophilic plate) The non-hydrophilic plate may be any plate having a non-hydrophilic surface that allows droplets of the hydrophilic liquid sprayed from the nozzle to fuse on the plate and form fused droplets. A non-hydrophilic plate with a moderately non-hydrophilic surface can prevent droplets colliding with the plate from forming a continuous film on the plate, promoting the generation of fused droplets by moderately fusing with surrounding droplets. The generated fused droplets have a larger droplet diameter than the original droplets, making image processing using light irradiation easier. Therefore, the uniformity of the spray pattern can be evaluated with high accuracy using a non-hydrophilic plate on which a group of fused droplets has been formed.

[0030] The non-hydrophilic plate may have at least a non-hydrophilic surface, may be a hydrophobic plate having at least a hydrophobic surface, or may be a water-repellent plate having at least a water-repellent surface.

[0031] The water contact angle of the non-hydrophilic plate surface (temperature 26.5°C, humidity 25% RH) may be greater than 30°, and is preferably 35° or greater (e.g., 35 to 170°), more preferably 40° or greater, even more preferably 50° or greater, and most preferably 60° or greater. In the case of a hydrophobic plate, the water contact angle may be, for example, 40 to 70°, preferably 50 to 70°, and even more preferably 60 to 70°. If the water contact angle is too small, it may be difficult to form droplets on the non-hydrophilic plate.

[0032] In this specification and claims, the water contact angle can be measured by a conventional method, for example, the contact angle sessile drop method.

[0033] The non-hydrophilic plate may be made of an organic material or an inorganic material.

[0034] Conventional plastics can be used as the organic material. Examples of conventional plastics include olefin resins (polyethylene, polypropylene, etc.), styrene resins (polystyrene, etc.), (meth)acrylic resins (polymethyl methacrylate, polyacrylonitrile, etc.), vinyl chloride resins (polyvinyl chloride, etc.), polyester resins (polyethylene terephthalate, etc.), polycarbonate resins (bisphenol A polycarbonate, etc.), polyamide resins (polyamide 6, etc.), polyurethane, and fluororesins. Of these, olefin resins, (meth)acrylic resins, and polyester resins are preferred, with (meth)acrylic resins being particularly preferred.

[0035] Examples of inorganic materials include glass, ceramics, and metals. Among these, glass is preferred from the viewpoint of transparency. The glass may be glass whose surface has been treated to be hydrophobic or water-repellent, and water-repellent glass is particularly preferred.

[0036] The non-hydrophilic plate is not limited to glass, and the hydrophobicity and water repellency may be adjusted by subjecting the surface to hydrophobic or water repellent treatment (for example, coating with a water repellent agent).

[0037] The non-hydrophilic plate is preferably transparent or semi-transparent, and particularly preferably transparent, from the viewpoint of facilitating the capture of an image that clearly shows the distribution of the fused droplet group by irradiating light thereon in the evaluation step described below.

[0038] The total light transmittance of the non-hydrophilic plate may be, for example, 50% or more, for example, 50 to 100%, preferably 60 to 100%, and more preferably 70 to 100%. If the total light transmittance of the non-hydrophilic plate is too low, it may be difficult to process images of the fused droplets in the evaluation step.

[0039] In this specification and claims, the total light transmittance can be measured in accordance with JIS K7361.

[0040] The surface of the non-hydrophilic plate is preferably smooth, for example, with an arithmetic mean surface roughness Ra of 10 μm or less, preferably 5 μm or less (e.g., 0.001 to 5 μm), more preferably 1 μm or less (e.g., 0.005 to 1 μm), more preferably 0.5 μm or less (e.g., 0.01 to 0.5 μm), and most preferably 0.2 μm or less (e.g., 0.013 to 0.2 μm). In this specification and claims, the mean roughness can be measured by a method in accordance with JIS B0601 (2001).

[0041] The average thickness of the non-hydrophilic plate is, for example, 0.5 to 10 mm, preferably 1.0 to 8.0 mm, and more preferably 1.5 to 6.0 mm.

[0042] (Spraying conditions) In the evaluation method of the present disclosure, a hydrophilic liquid is sprayed from the nozzle toward a non-hydrophilic plate in order to evaluate the uniformity of the spray pattern of the nozzle.

[0043] The average diameter of the sprayed droplets can be selected from a range of about 1 to 1000 μm, but from the viewpoint that it is difficult to evaluate the uniformity of the spray pattern and the effect of the method of the present disclosure is large, it is, for example, 3 to 300 μm, preferably 5 to 100 μm, further preferably 10 to 80 μm, and even more preferably 30 to 70 μm. If the average diameter of the sprayed droplets is too small, the droplet diameter of the fused droplet group will also be small, which may make it difficult to evaluate the uniformity, and if it is too large, it may be difficult to prepare the fused droplet group, which may make it difficult to evaluate the uniformity.

[0044] In this specification and claims, the mean diameter of the spray droplets [Sauter mean particle size (D32)] can be measured using a phase Doppler laser particle analyzer (PDPA).

[0045] In the spraying process, the sprayed liquid collides with the non-hydrophilic plate, and multiple sprayed droplets fuse to generate fused droplets having a droplet diameter larger than the droplet diameter of the sprayed liquid. Therefore, the average diameter of the fused droplets is larger than the droplet diameter of the sprayed liquid. In the method disclosed herein, by adjusting the average diameter of the fused droplets to a predetermined range larger than the droplet diameter of the sprayed liquid, it becomes easier to analyze the droplet distribution state, and the uniformity of the spray pattern can be accurately and simply evaluated.

[0046] The average diameter of the fused droplets (droplets reaching the non-hydrophilic plate) can be selected from a range of about 100 μm to 10 mm, for example, 300 to 5000 μm, preferably 500 to 4000 μm, further preferably 700 to 3500 μm, more preferably 800 to 3300 μm, and most preferably 1000 to 3000 μm. If the average diameter of the fused droplets is too small, it may be difficult to easily evaluate the uniformity of the spray pattern. Conversely, if it is too large, it may be difficult to determine the uniformity of the distribution state of the fused droplets, and the spray time may be longer, which may reduce the efficiency of the inspection.

[0047] The average diameter of the fused droplets may be at least three times the average diameter of the sprayed droplets, for example, 3 to 1000 times, preferably 5 to 500 times, further preferably 10 to 300 times, more preferably 20 to 100 times, and most preferably 30 to 50 times. If the ratio of the diameter of the fused droplets to the diameter of the sprayed droplets is too small, it may be difficult to easily evaluate the uniformity of the spray pattern.

[0048] In this specification and claims, the average diameter of fused droplets can be measured based on images taken with a camera, specifically, by the method described in the Examples below. When image processing software is used, the average diameter may be the projected circle equivalent diameter (Heywood diameter).

[0049] The spray direction from the nozzle is preferably the gravity direction, since this makes it easier to form a stable group of fused droplets on the non-hydrophilic plate.

[0050] In the spraying step, the spray pressure, spray amount, spray distance and spray time of the hydrophilic liquid are not particularly limited as long as they can produce fused droplets having an average diameter in the above range.

[0051] The spray pressure can be selected from the range of about 0.01 to 10 MPa, for example, 0.05 to 8 MPa, preferably 0.1 to 4 MPa, further preferably 0.2 to 3 MPa, and even more preferably 0.3 to 2 MPa.

[0052] The spray amount can be selected from the range of about 0.1 to 500 ml / min, for example, 0.3 to 300 ml / min, preferably 0.5 to 250 ml / min, further preferably 1 to 200 ml / min, even more preferably 3 to 150 ml / min, and most preferably 5 to 100 ml / min.

[0053] The spray distance (the shortest distance between the nozzle outlet and the non-hydrophilic plate) can be selected from the range of about 10 to 500 mm, for example, 20 to 200 mm, preferably 30 to 150 mm, further preferably 40 to 120 mm, and even more preferably 50 to 100 mm.

[0054] The spray time can be selected from the range of about 0.05 seconds to 1 minute depending on the spray amount, for example, 0.1 to 20 seconds, preferably 0.2 to 10 seconds, further preferably 0.2 to 7 seconds, and even more preferably 0.3 to 5 seconds.

[0055] The spray angle of the spray pattern [in the case of a hollow cone nozzle, the taper angle (apex angle) of the hollow cone-shaped pattern (cone)] can be selected from a range of approximately 30 to 150° depending on the pressure, application, etc., and is, for example, 35 to 135°, preferably 40 to 120°, even more preferably 45 to 110°, and even more preferably 50 to 100°.

[0056] The evaluation method of the present disclosure preferably further includes an adjustment step, prior to the spraying step, of adjusting the spray amount, spray pressure, spray distance, spray time, etc. of the hydrophilic liquid in order to determine the conditions (the spray pressure, spray amount, spray distance, and spray time) for obtaining a predetermined fused droplet diameter.

[0057] In the adjusting step and the spraying step, the spray time may be adjusted by stopping the introduction of the hydrophilic liquid into the nozzle. However, in order to precisely adjust the short spray time, it is preferable to use a shielding means capable of shielding the spray liquid between the nozzle and the non-hydrophilic plate. Such a shielding means is not particularly limited as long as it can move horizontally instantaneously to block the flow path of the spray liquid. For example, an air cylinder equipped with a timer, a shutter (shielding block) driven by a solenoid, or the like can be used. Specifically, a shutter that physically blocks the spray liquid by moving a shielding device to block the spray flow by operating a driving source such as a cylinder using a timer can be used. The shielding device may be plate-shaped or cup-shaped. The shielding device may have the function of absorbing and draining water to prevent the spray liquid from scattering.

[0058] The use of the shielding means allows for precise adjustment of the spray time not only for short spray times but also for long spray times, and is therefore particularly effective when the spray time is changed in the adjustment process. Furthermore, by shortening the spray time in the adjustment and spray processes, adjustment and evaluation can be performed in a short time, thereby improving inspection efficiency.

[0059] [Evaluation process] In the evaluation step, the spray performance of the nozzle is evaluated by evaluating the uniformity of the distribution of the fused droplets. That is, the method disclosed herein allows for accurate and simple evaluation of the spray performance of the nozzle based on the distribution of the fused droplets obtained using a hydrophilic liquid as the evaluation fluid, regardless of the type of fluid actually used in the nozzle.

[0060] (camera) The uniformity of the distribution state of the fused droplet group may be evaluated by the naked eye, but is preferably evaluated based on images captured by a camera, as this allows for accurate and simple evaluation. Examples of cameras include CCD (solid-state imaging device) cameras, CMOS (complementary metal-oxide semiconductor) cameras, laser cameras, thermal imaging cameras, and stereo vision cameras. Among these, digital cameras such as CCD cameras and CMOS cameras are preferred because of their high image processing speed and accuracy and low cost, with CMOS cameras being particularly preferred.

[0061] When photographing a non-hydrophilic plate having a group of fused droplets on its surface with a camera, the non-hydrophilic plate may be moved to a position for photographing with the camera after the hydrophilic liquid has been sprayed in the spraying step.

[0062] (light source) When photographing with a camera, it is preferable to irradiate light from a light source onto a non-hydrophilic plate having a group of fused droplets on its surface. When a hydrophilic liquid is sprayed onto the non-hydrophilic plate in the spraying step, a group of fused droplets is formed on the upper surface of the non-hydrophilic plate. When the non-hydrophilic plate is translucent or transparent, the group of fused droplets may be photographed with a camera from either the bottom or top of the non-hydrophilic plate. However, photographing from the top is preferable because of the high image discernibility. When photographing with a camera from the top, it is preferable to install a projector below the non-hydrophilic plate and irradiate light from the bottom of the non-hydrophilic plate. Furthermore, to improve the clarity of the image of the group of droplets, a light diffuser may be interposed between the light source and the non-hydrophilic plate. It is preferable to photograph with a camera simultaneously with or immediately after spraying in order to prevent the droplets from drying or deforming.

[0063] Examples of light sources include a strobe light source, a tungsten light source, a fluorescent light source, an LED light source, etc. Among these, an LED light source is preferred because of its high energy efficiency and long life.

[0064] (Judgment method) When an image of the fused droplet group is captured with a camera, the atomization performance of the nozzle can be evaluated by identifying an evaluation area of ​​the fused droplet group, quantifying the number of droplets, density, droplet diameter, etc., and combining the obtained values. Furthermore, when the spray pattern is circular, the nozzle atomization performance can be determined by quantifying the distance (angle) between droplets on the circumference and combining it with the above-mentioned value. Whether the distribution of the fused droplet group is uniform or not can also be analyzed as an indicator of atomization performance using a conventional image analyzer equipped with commercially available image processing software.

[0065] A specific method of judgment is, for example, to divide a group of fused droplets (a spray pattern of a hydrophilic liquid) into multiple equal regions, compare the droplet size distribution, the area occupied by the droplet size, and the distance between droplets for each region, determine the threshold value for each setting, and judge whether the spray pattern is uniform or not.

[0066] Another method for determining the uniformity of the spray pattern is to set a threshold value based on the diameter of the fused droplets. In this method, the diameter of the fused droplets tends to be larger in regions of high spray concentration in the target spray region (in the case of a hollow cone nozzle, a hollow cone-shaped spray pattern). Therefore, by comparing the diameters of the fused droplets, the distribution of the fused droplets (the spray pattern of the hydrophilic liquid) can be grasped, and the uniformity of the spray pattern can be easily evaluated.

[0067] The method for determining the threshold value based on the diameter of fused droplets may be a method for determining the longest distance between droplets of a certain diameter or more. In particular, in the case of a hollow cone nozzle with a circular spray pattern, the method for determining the threshold value based on the diameter of fused droplets may be a method based on the algorithm shown in the following steps (procedure) (1) to (5).

[0068] (1) A step of detecting a circular region (a circular region formed by all the fused droplets) in the fused droplet group in the image and identifying the central circumference of the fused droplet group. (2) A step of identifying an evaluation region (concentric circumference) having a predetermined width from the central circumference. (3) A step of setting a reference droplet diameter that can identify poor distribution within the evaluation area. (4) identifying a region where droplets having a diameter equal to or larger than the reference droplet diameter are not present; (5) A step of setting a threshold value for the area ratio of the region where the reference droplet diameter does not exist.

[0069] The spray pattern of a hollow cone nozzle (hollow cone pattern) is a circle centered on the intersection with the nozzle axis, with a hollow donut-shaped center, so the image of the fused droplet group formed by the hydrophilic liquid also has a donut shape.

[0070] In step (1) of the algorithm, a circular region centered on the intersection with the nozzle axis is detected in an image of the donut-shaped fused droplet group. The donut-shaped fused droplet group has a distribution structure in which the droplet diameter decreases toward the outer periphery and toward the inner periphery, relative to the central circumference where the spray concentration is highest and the droplet diameter of the fused droplet group is largest. The method for identifying the central circumference may be a method of determining the central circumference based on the droplet diameter and droplet density by observing the captured image with the naked eye, or a method of determining the central circumference based on the radial droplet diameter distribution and droplet density distribution (the proportion of the area occupied by droplets in the image) using image processing software. The center of the circular region may also be directly below the nozzle center.

[0071] In step (2), an evaluation area for evaluating the droplet distribution is identified. That is, an evaluation area (area surrounded by concentric circles) having a predetermined width each on the inner and outer sides of the central circumference is set, and the distribution state of the fused droplets is evaluated based on this evaluation area using the procedure described below. In the evaluation area, the width on the inner side and the width on the outer side relative to the central circumference are usually the same. For example, in a fuel oil burner nozzle, each width may be 10 mm or less (e.g., 1 to 10 mm), preferably 8 mm or less (e.g., 2 to 8 mm), and more preferably 6 mm or less (e.g., 3 to 6 mm). The evaluation area may be identified based on the droplet diameter of the fused droplet group observed with the naked eye, or may be identified based on the radial droplet diameter distribution using image processing software.

[0072] In step (3), a reference droplet diameter is set for the fused droplets within the evaluation region, allowing for the determination of poor distribution. The reference droplet diameter is determined by comparing the droplet diameters of droplets uniformly distributed and included in the large droplet diameter region of the fused droplet group with the droplet diameters of droplets included in the region other than the large droplet diameter region (small droplet diameter region). Specifically, droplets in the large droplet diameter region that do not fall within the small droplet diameter region are selected, and the smallest droplet diameter among the selected droplets is determined as the reference droplet diameter. If a clear reference droplet diameter cannot be determined, return to step (1) and determine using another nozzle. The reference droplet diameter for determination can be selected depending on the type of nozzle. For a fuel oil burner nozzle, it may be, for example, 0.5 to 3 mm (particularly 1 to 2 mm). The region may be identified by visual observation or by using image processing software. From the standpoints of simplicity and accuracy, the method of determination using image processing software is preferred.

[0073] In step (4), a region where droplets having a diameter equal to or larger than the reference droplet diameter do not exist (small droplet diameter region) is identified using image processing software, etc. This small droplet diameter region may be identified by visual observation or by using image processing software.

[0074] In step (5), a threshold value for the area ratio of the small droplet diameter region is set. The area ratio of the small droplet diameter region may be compared using the central angle (the region angle) of the fan shape based on the center of the doughnut shape. That is, a larger region angle means a larger area ratio of the small droplet diameter region and a decrease in uniformity of the spray pattern. Note that, if there are multiple regions, the region angle refers to the largest angle. Therefore, if the region angle is used as the threshold, the larger the region angle, the larger the area of ​​the small droplet diameter region and the decrease in uniformity of the spray pattern. The threshold value may be determined by actually operating and comparing nozzles with different region angles depending on the application, or may be determined based on simulations using image processing software or the like. Of these, a method of determining a threshold value using image processing software is preferred from the viewpoint of simplicity. Examples of methods of determining a threshold value using image processing include a method using deep learning, a method using machine learning, and a method using artificial intelligence (AI). From the viewpoint of accuracy and efficiency, a method using machine learning or AI is preferred, and a method using AI is particularly preferred. The threshold value of the region angle can be selected depending on the type of nozzle, and for a fuel oil burner nozzle, it may be, for example, 30° or less, preferably 20° or less (for example, 5 to 15°).

[0075] A flowchart for evaluating the spray performance of a nozzle using the threshold value obtained by the algorithm as a reference is shown in Figure 1. In the evaluation method of the present disclosure, after acquiring an image of a group of fused droplets, the area percentage of the small droplet diameter region (the region where droplets of the reference droplet diameter do not exist) is identified using the same procedure as in the algorithm, as shown in Figure 1. If the obtained area percentage is within the threshold, the product is judged to be good, but if it is outside the threshold, the product is judged to be defective.

[0076] [Rating System] The evaluation system of the present disclosure may be a combination of a non-hydrophilic plate used in the evaluation method and an evaluation means. That is, the evaluation system of the present disclosure includes a non-hydrophilic plate for forming a group of fused droplets formed by fusing spray droplets of a hydrophilic liquid sprayed from a nozzle, and an evaluation means for evaluating the spray performance of the nozzle by evaluating the uniformity of the distribution state of the fused droplet group. The evaluation means may include a light source for irradiating light onto the non-hydrophilic plate on which the group of fused droplets has been formed, a camera for photographing the distribution state, and an image analyzer for analyzing the image photographed by the camera. [Example]

[0077] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. The method for measuring droplet diameter, details of the equipment used in the examples, camera shooting conditions, and results of evaluation of the nozzle spraying ability are shown below.

[0078] [Average diameter of spray droplets] The average diameter of the spray droplets was measured by irradiating the spray area with two lasers using a phase Doppler laser particle analyzer (TSI "FSA4000 / 4W water-cooled Ar laser").

[0079] [Equipment used] Hydrophobic plate: transparent acrylic plate (commercially available acrylic plate), water contact angle 64° (temperature 26.5°C, humidity 25% RH), length 165 x width 185 mm x thickness 2 mm Light diffusion plate: Milky white resin plate (commercially available acrylic resin), 165mm long x 185mm wide x 2mm thick Shielding block: Air cylinder (SMC CDJ2RKA16-100) equipped with a timer (Omron H3CA) and a shielding device (a shielding device for receiving and shielding the spray flow) Camera: Canon EOS KISS X9, 24.2 megapixels LED floodlight: “10W-LED floodlight DT-11” manufactured by Choki Co., Ltd., 12W, 850 lm Image processing software: "Mac-View Ver.4" manufactured by Mountech Co., Ltd.

[0080] [Photography conditions] Using a camera with the following conditions, the LED floodlight, light diffusion plate, hydrophobic plate, and camera were placed in that order, and the droplet was focused on to capture a rear projection image.

[0081] Camera: SLR camera Lens: EF-S 18-55mm Camera settings: ISO sensitivity ISO400 Shutter speed 1 / 250 Aperture value: F8.0.

[0082] [Nozzle spray performance evaluation] Six hollow cone nozzles were fabricated as described in the examples of JP 2002-306992 A. These six hollow cone nozzles were designated Samples 1 to 6, and the spraying performance of each was evaluated. As shown in Figure 2(a), a transparent acrylic plate was placed 7 cm directly below the nozzle 1 as the hydrophobic plate 3. Water was sprayed at a rate of 88 ml / min at a pressure of 1.0 MPa for 0.5 seconds at a spray angle of 71°, forming a fused droplet group 2 on the hydrophobic plate 3. The spraying time on the acrylic plate was controlled by a shielding block 4 capable of shielding the space between the nozzle 1 and the hydrophobic plate 3. The average droplet diameter measured under the above conditions was approximately 60 μm.

[0083] As shown in Figure 2(b), the hydrophobic plate 3 carrying the fused droplet group 2 was moved horizontally and illuminated with an LED projector 6 from the opposite direction of the spray. The distribution of the fused droplet group 2 was photographed using a camera 5 from the direction of the spray. To improve image clarity, a light diffuser 7 was placed between the hydrophobic plate 3 and the LED projector 6. The light diffuser 7 was positioned 30 mm away from the hydrophobic plate 3. The captured images were then analyzed using image processing software to determine the central circumference of the fused droplet group 2. The evaluation area was then identified as a region within an inner diameter of 60 mm and an outer diameter of 70 mm. The fused droplets within this region could be classified as droplets with a projected circle equivalent diameter (Heywood diameter) of 1.3 to 3 mm, and the reference droplet diameter was determined to be 1.3 mm.

[0084] The photographed image of Sample 2 is shown in Figure 3, and an image of the photographed image in which fused droplets with a droplet diameter of 1.3 mm or more (the reference droplet diameter) were colored using image processing software is shown in Figure 4. As is clear from Figure 4, there is a lightly colored area diagonally downward to the left of the evaluation area, and it can be observed that the fused droplet diameter in this area is small and the distribution of the fused droplet group is uneven.

[0085] Furthermore, the photographed image of Sample 5 is shown in Figure 5, and the image of the photographed image in which fused droplets with a diameter of 1.3 mm or more (the reference droplet diameter) were colored using image processing software is shown in Figure 6. As is clear from Figure 6, it can be observed that the distribution of the fused droplets is more uniform than that of Sample 2.

[0086] For each of Samples 1 to 6, the angle (central angle) of the region where no droplets of 1.3 mm or more were present was measured, and the results are shown in Table 1. Furthermore, for each of the photographed images of Samples 1 to 6, fused droplets with a droplet diameter of 1.3 mm or more were colored using image processing software, and the photographed images showing the evaluation region and the angle of the region where no fused droplets with a droplet diameter of 1.3 mm or more were present are shown in Figures 7 to 12.

[0087] [Table 1]

[0088] A region where there were no droplets of 1.3 mm or more in diameter was selected as a non-defective product if the angle was within 10°, and a region where the angle was greater than 10° was selected as a defective spray. In other words, from the results in Table 1, it was confirmed that for this nozzle, the angle of 10° was the threshold, and that when the angle exceeded 10°, the spray pattern became non-uniform and the spraying ability of the nozzle deteriorated.

[0089] As a result, the quality of the spray pattern could be determined accurately, quickly, and automatically. In the droplet region of 1.3 mm or less, the droplet density of the spray droplets is low, so it is believed that small droplets form on the hydrophobic plate after colliding with it. In this way, the evaluation method disclosed herein allows for automatic, accurate, and efficient quality determination of the spray pattern by appropriately setting the nozzle flow rate, spray distance, time, and droplet diameter to be selected. [Industrial Applicability]

[0090] The evaluation method and evaluation system disclosed herein can be used for various nozzles for spraying fluids, such as burner nozzles, nozzles for inkjet printers, humidification or cooling nozzles, nozzles for disinfection, sterilization, or chemical spraying, oiling nozzles, and nozzles used in the electronics field (e.g., spray nozzles for substrate etching and substrate coating). Of these nozzles, burner nozzles are preferred because they are effective for spraying fine droplets, and burner nozzles for spraying fuel oil in burners for oil-fired water heaters, burners for grain drying, etc. are particularly preferred. [Explanation of symbols]

[0091] 1...Nozzle 2…Fusion droplet group 3...Hydrophobic plate 4...Shielding block 5. Camera 6...LED floodlight 7...Light diffusion plate

Claims

1. An evaluation method for evaluating the atomization performance of a nozzle for atomizing a fluid, a spraying step of spraying a hydrophilic liquid from the nozzle toward a non-hydrophilic plate, fusing the sprayed droplets on the non-hydrophilic plate, and forming a group of fused droplets on the non-hydrophilic plate; an evaluation step of irradiating the non-hydrophilic plate with light, photographing the distribution state of the fused droplet group with a camera, analyzing the photographed image with an image analyzer, and evaluating the spray performance of the nozzle based on the uniformity of the distribution state, In the evaluation step, a threshold value is set based on the diameter of fused droplets to determine whether the spray pattern is good or bad.

2. 2. The evaluation method according to claim 1, wherein in the spraying step, the average diameter of the fused droplets is 300 to 5000 μm.

3. 3. The evaluation method according to claim 1, wherein in the spraying step, the hydrophilic liquid is sprayed at a spray rate of 0.3 to 300 ml / min for 0.1 to 10 seconds.

4. The evaluation method according to any one of claims 1 to 3, wherein the average diameter of the sprayed droplets is 5 to 100 µm, and the average diameter of the fused droplets is 3 to 1000 times the average diameter of the sprayed droplets.

5. 5. The evaluation method according to claim 1, wherein the hydrophilic liquid is water, and the non-hydrophilic plate is a transparent or translucent plate.

6. The evaluation method according to any one of claims 1 to 5, wherein the nozzle is a single-fluid nozzle for spraying a liquid.

7. The evaluation method according to any one of claims 1 to 6, wherein the nozzle is a hollow cone nozzle.

8. The evaluation method according to any one of claims 1 to 7, wherein the nozzle is a burner nozzle.

9. The evaluation method according to any one of claims 1 to 8, further comprising, as a pre-step of the spraying step, an adjusting step of adjusting the spray amount, spray pressure, spray distance, and spray time of the hydrophilic liquid in the nozzle to determine conditions under which fused droplets having an average diameter of 300 to 5000 µm can be obtained.

10. The evaluation method according to any one of claims 1 to 9, wherein in the spraying step, a spraying time is controlled using a shielding means capable of shielding the sprayed liquid between the nozzle and the non-hydrophilic plate.

11. An evaluation system for evaluating the atomization capability of a nozzle for atomizing a fluid, comprising: a non-hydrophilic plate for forming a group of fused droplets made up of fused droplets obtained by fusing spray droplets of the hydrophilic liquid sprayed from the nozzle; and an evaluation means for evaluating the uniformity of the distribution state of the fused droplet group to evaluate the spray performance of the nozzle, The evaluation means a light source for irradiating the non-hydrophilic plate on which the fused droplet group is formed with light; a camera for photographing the distribution state; and an image analyzer for analyzing the images captured by the camera.

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