Efficiency calibration method for particulate matter cutter

Abstract

The invention discloses a particulate matter cutter efficiency calibration method which comprises the following steps: S1, providing a particulate matter cutter efficiency calibration device which comprises a rack, a mounting cavity, an air inlet pipe, an aerosol atomizer and the like; s2, dry dust-containing gas is formed; s3, dry dusty gas enters a gas path shunting joint through a gas inlet pipe and then is uniformly shunted into different shunting connecting screw holes by a shunting cone, one path of shunting gas enters a total dust concentration detection instrument, and the other path of shunting gas enters a particle cutter; other dust-containing gas enters the mounting chamber and is exhausted through the exhaust port; s4, the total dust concentration detection instrument detects one path of split-flow gas to obtain Cup; s5, after the split-flow gas is separated by the particulate matter cutter, particulate matters in a specified particle size range enter a gas outlet pipe; s6, detecting Cdown according to a standard particulate matter concentration detection instrument; and S7, obtaining Ex = Cdown / Cup * 100% according to a formula. The method is accurate in result.

Description

Technical Field

[0001] The present invention relates to the technical field of particle cutter efficiency calibration, and in particular to a particle cutter efficiency calibration method. Background Art

[0002] A particle cutter is a device that separates particles within a specific vertical range. For example, a PM2.5 particle cutter separates particles with a diameter less than or equal to 2.5 microns. The cutter must be calibrated and calibrated before use. According to the calculation formula E of the cutter's cutting efficiency x =C down / C up ×100%, where E x is the cutting efficiency; C down is the particle concentration downstream of the cutter, and C up is the particle concentration upstream of the cutter.

[0003] The application document with patent number CN201210056491.2 discloses a calibration system for a particle cutter, which includes a mixing chamber and a suspension chamber. The particles are directly placed in the mixing chamber, and then two gas sources are used to blow into the mixing chamber to lift and mix the particles. The mixed particles then enter the suspension chamber to mix and form a standard gas, which is then used for the calibration of the cutter through a joint. However, the calibration system has the following technical disadvantages: 1. Particles are stored in the mixing bin, and the particles are raised by the airflow. This results in a large amount of dust and a high concentration of particles when there are more particles in the early stage. When the particles are gradually used, the particle concentration is lower. At this time, the contact surface with the airflow will be small, so the dust volume is low, which leads to a large fluctuation in the particle concentration of the discharged standard gas. 2. After the standard gas is discharged, the cutter needs to be connected, and when the cutter is calibrated, C down and C up There are several ways to detect , the most accurate but the least efficient one is the membrane filter method, which is to pass the standard gas into a detection chamber, and then the detection chamber is connected to the cutter on one side, and the other side is pumped through the filter membrane, the particles will be filtered by the membrane, and finally the membrane is weighed, and the weight of the membrane before and after filtration is obtained, and the total weight of the filtered particles can be obtained, and then divided by the amount of air pumped to get the particle concentration C up Similarly, all the gases downstream of the cutter are filtered through the membrane to obtain the particle concentration C down Although this detection method is accurate, its efficiency is very low.

[0004] The other method is to directly detect the particle concentration through two calibrated standard detection instruments. down and particle concentration C up , which greatly improves the efficiency. However, in the above calibration process, the gas extracted from the detection chamber enters the particle cutter one way and is connected to the main detection instrument one way. It is necessary to ensure the consistency of other flow states of these two routes, so that the data detected by the main detection instrument can correspond to the concentration of particles entering the cutter. However, due to the above connection method, the gas particle concentration at different positions of the detection chamber is not necessarily completely uniform, and the gas will also be turbulent during gas extraction sampling, so it is impossible to determine the consistency of the dust-containing gas entering the main instrument and the cutter. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a particle cutter efficiency calibration method, which uses a diversion method to perform efficiency calibration, ensures the consistency of the state of the dust-containing gas entering the particle cutter and the dust-containing gas entering the total dust concentration detection instrument, ensures the accuracy of the detection results, thereby ensuring the accuracy of the efficiency calibration results, and solves the problems of low efficiency and inaccuracy in the prior art.

[0006] In order to solve the above technical problems, the technical solution of the present invention is: a particle cutter efficiency calibration method, comprising the following steps: S1. Provide a particle cutter efficiency calibration device, including a frame, a mounting chamber is arranged on the frame, an air inlet pipe is arranged at the upper end of the mounting chamber, an aerosol atomizer is arranged at the upper end of the air inlet pipe, a dilution air path and a drying device for drying dust-containing gas are also connected between the air inlet pipe and the aerosol atomizer, an air path diversion joint is connected to the lower end of the air inlet pipe, a particle cutter and a calibrated total dust concentration detection instrument are fixed in the mounting chamber, the air path diversion joint includes a cylindrical connecting pipe section and a diversion cone cylinder arranged at the downstream end of the connecting pipe section in a flared shape, the air inlet pipe is inserted into the connecting pipe section and fixed by a locking structure, the air path diversion joint is located in the mounting chamber, a diversion chamber is arranged inside the diversion cone cylinder, and the bottom of the diversion cone cylinder A diverter cone is provided which extends axially toward the pipe mouth of the connecting pipe section, the upstream tip of the diverter cone corresponds to the center of the connecting pipe section, a plurality of diverter connection screw holes which are evenly distributed around the central circumference of the connecting pipe section are provided at the bottom of the diverter chamber, two of which are respectively threadedly connected to diverter pipe joints, and the other diverter connection screw holes are connected to the inner cavity of the installation chamber, and an exhaust port is provided in the installation chamber; one of the diverter pipe joints is connected to the air inlet of the total dust concentration detection instrument, and the other diverter pipe joint is connected to the air inlet of the particle cutter, the air outlet of the particle cutter is connected to an air outlet pipe, the air outlet pipe is connected to a vacuum power device, a sampling port is further provided on the air outlet pipe, a sampling tube is provided in the sampling port, and the sampling tube is connected to a standard particle concentration detection instrument; S2. The aerosol atomizer continuously and quantitatively generates aerosol, which is first diluted by the clean dilution gas provided by the dilution gas path and then enters the drying device for drying to form dry dust-containing gas; S3. The dry dusty gas enters the gas path diversion joint through the air inlet pipe and is evenly diverted by the diversion cone to different diversion connection screw holes. One diversion gas enters the total dust concentration detection instrument, another diversion gas enters the particle cutter, and the other dusty gas enters the installation chamber and is discharged; S4. The total dust concentration detection instrument detects the particle concentration of the bypass gas and obtains the particle concentration C up ; S5. After the particle cutter separates the split gas, particles within the specified particle size range enter the outlet pipe; S6, the vacuum power device vacuums the outlet pipe to provide auxiliary suction, and the standard particle concentration detection instrument detects the particle concentration in the outlet pipe to obtain C down ; S7. E is obtained according to the calculation formula of the cutting efficiency of the cutter x =C down / Cup ×100%.

[0007] Preferably, the connecting pipes between one shunt pipe joint and the particle cutter and between the other shunt pipe joint and the total dust concentration detection instrument have the same size and are both provided with flow meters. By controlling the power of the vacuum power device, the flow rate of the dust-laden gas entering the particle cutter and the flow rate entering the total dust concentration detection instrument are made the same, thereby ensuring that the flow rate and flow velocity are exactly the same, the flow state of the two shunt dust-laden gases and the particle distribution state remain consistent, and the particle concentration detection results are the same.

[0008] Preferably, the drying device includes a drying chamber in which dry silica gel particles are stored. After the aerosol is dried in the drying chamber, it enters the air intake pipe. An electric heating wire is arranged in the air intake pipe to perform secondary heating and drying on the gas. After the silica gel particles are dried, they enter the air intake pipe for heating and drying. This can avoid adhesion between particles, thereby making the cutting of the cutter more accurate and avoiding adhesion to the tube wall and causing errors in particle concentration detection.

[0009] Preferably, the air inlet pipe and the air outlet pipe are both arranged vertically, and the sampling tube detected by the standard particle concentration detection instrument extends from bottom to top into the air outlet pipe, and the upper end of the sampling tube is higher than the suction port connected between the air outlet pipe and the vacuum power device, so that the dust-containing gas has little resistance when flowing in the air inlet pipe and the air outlet pipe, and at the same time avoids the bending of the flow path causing the particles to hit the pipe wall, which further avoids the particles from adhering to the pipe wall. The upper end of the sampling tube is higher than the suction port, so that the sampling part of the sampling tube is the area of ​​stable flow after separation by the cutter, and the concentration distribution of the particles in this stable flow area is more uniform.

[0010] Preferably, the two branch pipe joints are arranged symmetrically with respect to the center line of the connecting pipe section of the gas path branch joint, so that the symmetrically distributed airflows will have less influence and interference on each other.

[0011] Preferably, a dust concentration detection instrument to be calibrated is also placed in the installation chamber, and a diversion pipe joint is connected to one of the idle diversion connecting screw holes of the gas path diversion joint and connected to the air inlet of the dust concentration detection instrument to be calibrated. The calibration can be carried out by comparing the readings of the dust concentration detection instrument to be calibrated and the total dust concentration detection instrument. Therefore, this method can also calibrate the instrument.

[0012] Preferably, a guide groove is provided on the conical surface of the diversion cone, which is connected to the diversion connecting screw hole in a one-to-one correspondence. The guide groove extends along the conical surface of the diversion cone. The guide groove is an arc-shaped groove. The arc contour of the arc-shaped groove completely coincides with the diversion connecting screw hole. The dust-laden gas entering the air intake pipe is diverted by the diversion cone and then enters the diversion connecting screw hole along the arc-shaped groove. In this way, the state of the dust-laden gas after diversion is consistent and smoother. At the same time, since the dust-laden airflows after diversion are all flowing in the guide groove, mutual interference is also smaller.

[0013] After adopting the above technical scheme, the effect of the present invention is as follows: compared with the current conventional efficiency calibration method, the efficiency calibration method has the following advantages: 1. This method directly uses an aerosol atomizer to generate aerosol, which is diluted by a diluent gas and dried by a drying device before entering the air intake pipe for mixing. Since the diameter of the air intake pipe is relatively small, the particle distribution is more uniform, so there is no need for additional mixing chamber mixing, which saves space; 2. The mixed dust-containing gas is directly evenly diverted through the gas path diversion joint, which can ensure the consistency of the dust-containing gas state after diversion, so that the particle concentration C up The value is more accurate; 3. This efficiency calibration method has higher calibration efficiency than the conventional membrane filter method and better calibration accuracy than the instrument calibration method. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0015] Figure 1 is a stereogram of an embodiment of the present invention; Figure 2 is a front view of an embodiment of the present invention; Figure 3 yes Figure 2 Structural cross-section along AA; Figure 4 is a cross-sectional view of a drying device, an air inlet pipe and an air path flow splitter joint according to an embodiment of the present invention; Figure 5 is a stereoscopic diagram of a gas path flow splitter joint according to an embodiment of the present invention; Figure 6 is a three-dimensional diagram of the gas path flow splitter joint from another angle according to an embodiment of the present invention; Figure 7 2 is a front view of a gas path flow splitter joint according to an embodiment of the present invention; Figure 8 yes Figure 7 Structural cross-section along BB; Fig. 9 yes Figure 7 A cross-sectional perspective view along CC; Fig.10 yes Figure 7 Sectional view along CC; Fig.11 Schematic diagram of the structure of an aerosol nebulizer according to an embodiment of the present invention; In the attached figure: 1. rack; 2. installation chamber; 3. air inlet pipe; 4. aerosol nebulizer; 41. nebulizer body; 42. dust outlet; 43. compressed air pipe outlet; 44. air supply window; 45. sealing plate; 5. drying device; 6. gas path diversion joint; 61. connecting pipe section; 62. diversion cone; 63. diversion chamber; 64. diversion cone; 65. diversion connection screw hole; 651. threaded hole section; 652. straight through section; 653. joint positioning step; 66. guide groove; 7. particle cutter; 8. total dust concentration detection instrument; 9. diversion pipe joint; 10. vacuum power device; 11. standard particle concentration detection instrument; 12. outlet pipe; 13. sampling tube; 14. dilution gas path; 15. suction port; 16. exhaust port; 17. locking structure. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below through specific examples.

[0017] like Figure 1-11 As shown, a particle cutter efficiency calibration method comprises the following steps: S1. Provide a particle cutter efficiency calibration device, comprising a frame 1, wherein the frame 1 is provided with an installation chamber 2, wherein the upper end of the installation chamber 2 is provided with an air intake pipe 3, wherein the upper end of the air intake pipe 3 is provided with an aerosol atomizer 4, wherein a dilution gas path 14 and a drying device 5 for drying dust-containing gas are also connected between the air intake pipe 3 and the aerosol atomizer 4, wherein the lower end of the air intake pipe 3 is connected with an air path diversion joint 6, wherein a particle cutter 7 and a calibrated total dust concentration detection instrument 8 are fixed in the installation chamber 2, wherein the air path diversion joint 6 comprises a cylindrical connecting pipe section 61 and a diversion cone 62 which is arranged at the downstream end of the connecting pipe section 61 in an expanded shape, wherein the air intake pipe 3 is inserted into the connecting pipe section 61 and fixed by a locking structure 17, wherein the air path diversion joint 6 is located in the installation chamber 2, wherein a diversion chamber 63 is arranged inside the diversion cone 62, and wherein the bottom of the diversion cone 62 is provided with a diversion chamber 63. A diverter cone 64 is provided which extends axially toward the pipe mouth of the connecting pipe section 61, and the upstream tip of the diverter cone 64 corresponds to the center of the connecting pipe section 61. A plurality of diverter connection screw holes 65 which are evenly distributed around the central circumference of the connecting pipe section 61 are provided at the bottom of the diverter chamber 63, wherein two of the diverter connection screw holes 65 are respectively threadedly connected to the diverter pipe joints 9, and the other diverter connection screw holes 65 are connected to the inner cavity of the installation chamber 2, and the installation chamber 2 is provided with an exhaust port 16; one of the diverter pipe joints 9 is connected to the air inlet of the total dust concentration detection instrument 8, and the other diverter pipe joint 9 is connected to the air inlet of the particle cutter 7, and the air outlet of the particle cutter 7 is connected to an air outlet pipe 12, and the air outlet pipe 12 is connected to the vacuum power device 10, and a sampling port is also provided on the air outlet pipe 12, and a sampling tube 13 is inserted into the sampling port, and the sampling tube 13 is connected to the sub-standard particle concentration detection instrument 11; The air inlet pipe 3 and the air outlet pipe 12 are both arranged vertically, and the sampling pipe 13 detected by the standard particle concentration detection instrument 11 extends from bottom to top into the air outlet pipe 12, and the upper end of the sampling pipe 13 is higher than the air suction port 15 connected between the air outlet pipe 12 and the vacuum power device 10. A dust concentration detection instrument to be calibrated can also be placed in the installation chamber 2. A shunt pipe joint 9 is connected to one of the idle shunt connection screw holes 65 of the gas path shunt joint 6 and connected to the air inlet of the dust concentration detection instrument to be calibrated. The dust concentration detection instrument to be calibrated can be calibrated by comparing the readings of the dust concentration detection instrument to be calibrated with the total dust concentration detection instrument 8. S2, the aerosol atomizer 4 continuously generates aerosol quantitatively, the aerosol is first diluted by the clean dilution gas provided by the dilution gas circuit 14, and then enters the drying device 5 for drying to form dry dust-containing gas, In this embodiment, the selected aerosol nebulizer 4 is a medical nebulizer, such as a PARI LC SPRINT sprayer. The aerosol nebulizer 4 includes an aerosol body 41, the upper opening of the aerosol body 41 is provided with a container cover, the aerosol body 41 is provided with a dust outlet 42, the aerosol body 41 is provided with a compressed air pipe port 43 connected to the compressed air, the container cover is provided with an air replenishment window 44, and the container cover is also rotatably mounted with a blocking piece 45 for adjusting the size of the air replenishment window 44. Of course, the aerosol nebulizer 4 can also use the aerosol nebulizer 4 in patent number CN201721210278.7 of the applicant, The drying device 5 includes a drying chamber, in which dry silica gel particles are stored. After the aerosol is dried in the drying chamber, it enters the air inlet pipe 3 for full mixing. An electric heating wire is arranged in the air inlet pipe 3 to perform secondary heating and drying on the gas. S3, the dry dusty gas enters the gas path diversion joint 6 through the air inlet pipe 3 and is evenly diverted by the diversion cone 64 to different diversion connection screw holes 65, one diversion gas enters the total dust concentration detection instrument 8, another diversion gas enters the particle cutter 7, and the other dusty gas enters the installation chamber 2 and is discharged through the exhaust port 16. Specifically, a guide groove 66 is provided on the conical surface of the diverter cone 64 and is connected to the diverter connection screw hole 65 in a one-to-one correspondence. The guide groove 66 extends along the conical surface of the diverter cone 64. The guide groove 66 is an arc-shaped groove. The arc profile of the arc-shaped groove completely coincides with the diverter connection screw hole 65. The dust-laden gas entering the air intake pipe 3 is diverted by the diverter cone 64 and enters the diverter connection screw hole 65 along the arc-shaped groove. In this embodiment, the diverter connection screw hole 65 includes a threaded hole section 651 and a through straight section 652 that passes through the diverter cone 62. The diameter of the threaded hole section 651 is larger than the through straight section 652 to form a joint positioning step 653. The locking structure 17 includes a plurality of radial locking screw holes provided on the connecting pipe section 61. The radial locking screw holes are threadedly connected with a tightening bolt that radially tightens the air intake pipe 3. S4, total dust concentration detection instrument 8 detects the particle concentration of the diverted gas and obtains the particle concentration C up ; S5, after the particle cutter 7 separates the split gas, the particles within the specified particle size range enter the outlet pipe 12; S6, the vacuum power device 10 vacuums the air outlet pipe 12 to provide auxiliary suction, and the standard particle concentration detection instrument 11 detects the particle concentration in the air outlet pipe 12 to obtain C down , S7. E is obtained according to the calculation formula of the cutting efficiency of the cutter x =Cdown / C up ×100%.

[0018] In this embodiment, the two branch pipe joints 9 are symmetrically arranged relative to the center line of the connecting pipe section 61 of the gas path branch pipe joint 6. The connecting pipe between one branch pipe joint 9 and the particle cutter 7 and the connecting pipe between the other branch pipe joint 9 and the total dust concentration detection instrument 8 are of the same size and are both provided with flow meters. By controlling the power of the vacuum power device 10, the flow rate of the dust-containing gas entering the particle cutter 7 and the flow rate entering the total dust concentration detection instrument 8 are made the same. The vacuum power device 10 uses a vacuum pump.

[0019] The gas circuit system, actuators such as servo motors, gear transmission mechanisms, and lead screw nut mechanisms mentioned in this embodiment are all current conventional technologies. The specific structures and principles and other designs of cylinders, motors, and other transmission mechanisms are disclosed in detail in the "Mechanical Design Manual, Fifth Edition", the 28th printing of the fifth edition in Beijing in April 2008, which belongs to the prior art and its structure is clear. The SMC training textbook "Modern Practical Pneumatic Technology, 3rd Edition" published by the Machinery Industry Press on August 1, 2008 discloses vacuum components, gas circuits, and program control in detail, indicating that the gas circuit structure in this embodiment is also an existing technology and is clear. The book "Motor Drive and Speed ​​Regulation" published by the Chemical Industry Press on July 1, 2015 also introduces the control of the motor and the travel switch in detail. Therefore, the circuit and gas circuit connections are clear.

[0020] The above-described embodiments are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Various modifications and alterations to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A particle cutter efficiency calibration method, characterized in that: The following steps are involved: S1. Provide a particle cutter efficiency calibration device, including a frame, a mounting chamber is arranged on the frame, an air inlet pipe is arranged at the upper end of the mounting chamber, an aerosol atomizer is arranged at the upper end of the air inlet pipe, a dilution air path and a drying device for drying dust-containing gas are also connected between the air inlet pipe and the aerosol atomizer, an air path diversion joint is connected to the lower end of the air inlet pipe, a particle cutter and a calibrated total dust concentration detection instrument are fixed in the mounting chamber, the air path diversion joint includes a cylindrical connecting pipe section and a diversion cone cylinder arranged at the downstream end of the connecting pipe section in a flared shape, the air inlet pipe is inserted into the connecting pipe section and fixed by a locking structure, the air path diversion joint is located in the mounting chamber, a diversion chamber is arranged inside the diversion cone cylinder, and the bottom of the diversion cone cylinder A diverter cone is provided which extends axially toward the pipe mouth of the connecting pipe section, the upstream tip of the diverter cone corresponds to the center of the connecting pipe section, a plurality of diverter connection screw holes which are evenly distributed around the central circumference of the connecting pipe section are provided at the bottom of the diverter chamber, two of which are respectively threadedly connected to diverter pipe joints, and the other diverter connection screw holes are connected to the inner cavity of the installation chamber, and an exhaust port is provided in the installation chamber; one of the diverter pipe joints is connected to the air inlet of the total dust concentration detection instrument, and the other diverter pipe joint is connected to the air inlet of the particle cutter, the air outlet of the particle cutter is connected to an air outlet pipe, the air outlet pipe is connected to a vacuum power device, a sampling port is further provided on the air outlet pipe, a sampling tube is provided in the sampling port, and the sampling tube is connected to a standard particle concentration detection instrument; S2. The aerosol atomizer continuously and quantitatively generates aerosol, which is first diluted by the clean dilution gas provided by the dilution gas path, and then enters the drying device for drying to form dry dust-containing gas; S3. The dry dusty gas enters the gas path diversion joint through the air inlet pipe and is evenly diverted by the diversion cone to different diversion connection screw holes. One diversion gas enters the total dust concentration detection instrument, the other diversion gas enters the particle cutter, and the other dusty gas enters the installation chamber and is discharged through the exhaust port. S4. The total dust concentration detection instrument detects the particle concentration of the bypass gas and obtains the particle concentration C up ; S5. After the particle cutter separates the split gas, particles within the specified particle size range enter the outlet pipe; S6, the vacuum power device vacuums the outlet pipe to provide auxiliary suction, and the standard particle concentration detection instrument detects the particle concentration in the outlet pipe to obtain C down ; S7. E is obtained according to the calculation formula of the cutting efficiency of the cutter x =C down / C up ×100%.

2. A particle cutter efficiency calibration method as claimed in claim 1, characterized in that: The connecting pipe between one of the shunt pipe joints and the particle cutter and the connecting pipe between the other shunt pipe joint and the total dust concentration detection instrument are of the same size and are both provided with flow meters. By controlling the power of the vacuum power device, the flow rate of the dust-containing gas entering the particle cutter and the flow rate entering the total dust concentration detection instrument are made the same.

3. A particle cutter efficiency calibration method as claimed in claim 2, characterized in that: The drying device comprises a drying chamber, in which dry silica gel particles are stored. After being dried in the drying chamber, the aerosol enters the air intake pipe, and an electric heating wire is arranged in the air intake pipe to perform secondary heating and drying on the gas.

4. A particle cutter efficiency calibration method as claimed in claim 3, characterized in that: The air inlet pipe and the air outlet pipe are both arranged vertically, and the sampling pipe detected by the standard particle concentration detection instrument extends from bottom to top into the air outlet pipe, and the upper end of the sampling pipe is higher than the air suction port connected between the air outlet pipe and the vacuum power device.

5. A particle cutter efficiency calibration method as claimed in claim 1, characterized in that: The two flow-dividing pipe joints are arranged symmetrically with respect to the center line of the connecting pipe section of the gas path flow-dividing joint.

6. A particle cutter efficiency calibration method as claimed in claim 5, characterized in that: A dust concentration detection instrument to be calibrated is also placed in the installation chamber. A diversion pipe joint is connected to one of the idle diversion connection screw holes of the gas path diversion joint and connected to the air inlet of the dust concentration detection instrument to be calibrated. Calibration can be carried out by comparing the readings of the dust concentration detection instrument to be calibrated and the total dust concentration detection instrument.

7. A particle cutter efficiency calibration method as claimed in claim 6, characterized in that: The conical surface of the diverter cone is provided with a guide groove which is connected to the diverter connection screw hole in a one-to-one correspondence. The guide groove extends along the conical surface of the diverter cone. The guide groove is an arc-shaped groove. The arc-shaped contour of the arc-shaped groove completely coincides with the diverter connection screw hole. The dust-containing gas entering the air intake pipe is diverted by the diverter cone and enters the diverter connection screw hole along the arc-shaped groove.

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