A combined muffler

Abstract

The invention relates to a combined muffler, which comprises a shell, a first small-hole muffler, a second small-hole muffler and a sound absorber, wherein the shell is provided with an inlet and an outlet for fluid, the first small-hole muffler is connected to the inlet of the shell, the second small-hole muffler is sleeved on the outside of the first small-hole muffler and forms a cavity with the first small-hole muffler, and the sound absorber is installed in the shell outside the second small-hole muffler to absorb the medium and high frequency noise in the fluid from the second small-hole muffler, characterized in that it further comprises a diffuser outside the shell, the diffuser is provided with an axial through taper hole, the cross section of the outlet end of the taper hole is larger than that of the inlet end, and the outlet end is fixed to the inlet of the shell and connected to the inlet of the shell. The muffler of the invention has the advantages of high sound absorption and low resistance, and can meet the use requirements of the system.

Description

Technical Field

[0001] This invention relates to the technical field of a silencing device, and more specifically to a combined silencing device. Background Technology

[0002] Diffuser silencers are typically used for silencing high-speed fluids, such as boiler exhaust and turbine exhaust. In boiler exhaust pipes, the fluid velocity is very high, often reaching the speed of sound or even supersonic speeds, and the mass flow rate of the fluid is large, resulting in extremely high noise levels (generally, the exhaust noise of medium-pressure boilers exceeds 120 decibels). Therefore, if a diffuser silencer is used alone, it is difficult to reduce the noise to below 85 decibels (environmental noise emission standards). Thus, it is now commonly combined with a resistive silencing structure to create a combined silencer. For example, the patent authorization announcement number CN203858858U discloses "A Throttling and Diffusion Composite Silencer". This composite silencer includes a rain cap, an air outlet, a shell, lifting lugs, a resistive sound absorber, a sound-absorbing layer, a small-hole injection device, a throttling and pressure-reducing device, a drain port, and an air inlet. The shell has a columnar structure, with an air inlet at one end and an air outlet at the other end. A throttling and pressure-reducing device is installed inside the shell near the air inlet. A small-hole injection device is set around the throttling and pressure-reducing device. A sound-absorbing layer is set around the inner wall of the shell. A resistive sound absorber is set inside the shell near the air outlet. A rain cap is installed outside the air outlet. At least two lifting lugs are symmetrically set outside the shell near the air outlet. While such silencers can reduce noise by 50-60dB, they also increase fluid resistance, thus failing to meet the system's fluid resistance requirements. This often puts the design of such silencers in a dilemma between reducing noise and increasing resistance, meaning that they cannot simultaneously achieve both high noise reduction and low resistance.

[0003] Therefore, further improvements are needed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a combined silencer that can improve the sound level and meet the system's requirements for low fluid resistance, in light of the current state of the technology.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a combined silencer, comprising a shell and a primary small-hole silencer, a secondary small-hole silencer, and a sound absorber installed inside the shell, wherein the shell has a fluid inlet and an outlet, the primary small-hole silencer is connected to the inlet of the shell; the secondary small-hole silencer is sleeved on the outside of the primary small-hole silencer and forms a cavity with the primary small-hole silencer; the sound absorber is installed inside the shell outside the secondary small-hole silencer to absorb mid- and high-frequency noise in the fluid coming out of the secondary small-hole silencer, characterized in that: it further comprises a diffuser section located outside the shell, the diffuser section having an axially penetrating conical hole, the cross-section of the outlet end of the conical hole being larger than the cross-section of the inlet end, and the outlet end being fixed at the inlet of the shell and connected to the inlet of the shell.

[0006] In the above scheme, a further improvement is that the first-stage small-hole silencer is a first cylinder that is closed at one end and open at the other end and connected to the inlet of the outer shell. The side wall of the first cylinder is densely covered with multiple first injection holes, which makes the structure relatively simple.

[0007] In the above-mentioned improved scheme, the inner wall of the outlet end of the tapered hole, the inner wall of the inlet of the outer shell, and the inner wall of the opening of the first cylinder are connected by a circular arc in sequence, so that when the fluid flows through the point, the local resistance at that point can be reduced.

[0008] In the above-mentioned improved scheme, the sum of the areas of the plurality of first injection holes is greater than the area of ​​the opening of the first-stage small hole silencer, so that when the fluid flows in the first cylinder, it can achieve the purpose of slowing down and pressurizing, so as to counteract the resistance encountered during flow.

[0009] In the aforementioned improved scheme, the ratio of the total area of ​​the first injection orifice to the outlet area of ​​the diffuser section has a significant impact on fluid resistance. If the ratio is too small, the flow velocity at the first injection orifice will be too high, resulting in high local resistance and additional noise. If the ratio is too large, the spacing between the first injection orifices will be too small, increasing manufacturing difficulty, and the jets (airflow) between adjacent first injection orifices will interfere with each other. Through multiple experiments, it has been found that, preferably, the sum of the areas of the multiple first injection orifices is 2 to 3 times the area of ​​the opening of the primary small-hole silencer. This matching is most reasonable for reducing fluid velocity and increasing pressure.

[0010] In the above-mentioned improved scheme, the secondary small hole silencer is further improved by being a second cylinder with one end closed and the other end open and fixed to the inner wall around the entrance of the outer shell. The side wall of the second cylinder is densely covered with second injection holes to cooperate with the first cylinder, so that the overall structure is simple and easy to install.

[0011] To achieve better sound absorption, the exit edge of each of the first and second injection holes extends outward to form an auxiliary tube. The inner wall of the auxiliary tube, the inner wall of the corresponding injection hole, and the inner wall of the outer shell at the corresponding injection hole are sequentially connected by a rounded arc to form a rounded corner, so as to reduce the local resistance at the inlet end of each injection hole and reduce the regenerated noise generated by eddies at this location.

[0012] Preferably, the radius of the arc angle is 0.2 to 0.3 times the diameter of the outlet end of the corresponding injection hole, so as to optimize the noise reduction effect.

[0013] For reasonable arrangement and considering the noise reduction effect, the inner diameter of the first cylinder is the same as the inner diameter of the outlet end of the conical hole, and the inner diameter of the second cylinder is 1.2 to 1.4 times the inner diameter of the first cylinder.

[0014] In the above embodiments, the sound absorber further comprises a front sound absorber and a rear sound absorber made of sound-absorbing material. The front sound absorber is a sound-absorbing cylinder attached to the inner front wall of the outer shell near the inlet. The rear sound absorber is located between the front sound absorber and the outlet of the outer shell, and has multiple elongated axial channels. Thus, by utilizing the front and rear sound-absorbing structures, the fluid flowing out of the secondary perforated silencer is further effectively noise-reduced, thereby achieving a higher level of noise reduction.

[0015] To extend the service life of the front sound absorber, a protective liner is provided on the inner wall of the sound-absorbing cylinder, and multiple small holes are opened on the wall surface of the liner. Simultaneously, to increase the strength of the liner, a support ring can be provided inside the outer shell, abutting against the inner wall of the liner. Multiple support rings can be provided, and the specific number can be set as needed.

[0016] Similarly, to extend the service life of the rear sound absorber, a liner is provided inside the axial channel to protect it, and multiple through holes are formed on the side wall of the liner. Additionally, a front sealing plate located at the front end of the rear sound absorber and a rear sealing plate located at the rear end of the rear sound absorber can also be provided inside the housing. Both the front and rear sealing plates have through holes corresponding to the axial channel, thus serving the same purpose of protecting the rear sound absorber.

[0017] Compared to existing technologies, this invention cleverly adds a diffuser section to the outer casing. Utilizing the conical orifice within the diffuser section, the high-speed fluid before entering the casing first flows through the conical orifice. The gradually expanding inner diameter of the conical orifice reduces the fluid velocity, simultaneously increasing the fluid pressure (static pressure). This increased pressure offsets most of the resistance encountered by the fluid as it flows through the silencer. After entering the casing, the fluid further passes through primary and secondary small-hole silencers and absorbs mid- and high-frequency noise, resulting in the absorption of most of the noise in the fluid or its conversion into ultrasonic waves outside the audible range. Repeated experiments have proven that the silencer using this invention produces a fluid noise level of only 35–45 dB as it exits the casing, with a resistance of only 0–0.5 kPa. Therefore, this invention significantly improves noise reduction while maintaining the fluid's inherent low resistance, ensuring that the fluid exiting the casing meets the system's operational requirements. Attached Figure Description

[0018] Figure 1 This is a cross-sectional schematic diagram of an embodiment of the present invention;

[0019] Figure 2 for Figure 1 Schematic diagram of the AA section;

[0020] Figure 3 for Figure 1 Enlarged diagram of point B in the middle. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] In the following description of the embodiments, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "axial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Since the embodiments disclosed in the present invention can be arranged in different directions, these terms indicating direction are only for illustration and should not be regarded as limitations. For example, "upper" and "lower" are not necessarily limited to directions opposite to or consistent with the direction of gravity. In addition, features defined as "first" and "second" may explicitly or implicitly include one or more of such features.

[0023] like Figures 1 to 3As shown, the combined silencer includes a housing 1, a diffuser section 2, a primary small-hole silencer, a secondary small-hole silencer, and a sound absorber. The housing 1 has a fluid inlet 1a and an outlet 1b. Specifically, the housing 1 includes a shell 11, a front cover 12, and a rear cover 13. The shell 11 is designed as a cylindrical structure with open ends, and is placed horizontally on the ground or a desired foundation via a support base 14 (it can also be placed upright as needed). The front cover 12 and the rear cover 13 are located at both ends of the shell 11 to cover the front and rear ports. In this embodiment, both the front cover 12 and the rear cover 13 are welded to the shell 11. Of course, other connection methods in the prior art, such as hinges, can also be used to achieve opening and closing as needed. The fluid inlet 1a is located on the front cover 12, and the fluid outlet 1b is located on the rear cover 13. Figure 1 As can be seen from the preferred embodiment, the center of the inlet 1a and the center of the outlet 1b are both located on the axial center line of the housing 11.

[0024] The aforementioned diffuser section 2 is located outside the outer casing 1 and corresponds to the inlet 1a of the outer casing 1. The diffuser section 2 has an axially penetrating tapered hole 21. The cross-section of the outlet end 2b of this tapered hole is larger than the cross-section of the inlet end 2a. Figure 1 The conical hole 21 can be circular, square, or polygonal, and its outlet end 2b is fixed to the inlet 1a of the outer casing. Specifically, it can be welded to the outside of the front cover 12 and connected to the inlet 1a. Figure 1 It is understood that the centerline of the conical hole 21 is preferably on the same straight line as the axial centerline of the housing 11. Furthermore, the diffuser section 2 is formed by rolling a steel plate into a conical shape and then welding it, so that its outer contour is also conical, which facilitates processing and reduces costs. Of course, those skilled in the art will understand that the diffuser section 2 only needs to have a conical hole 21 inside, and the outer contour can adopt other shapes.

[0025] The aforementioned primary orifice silencer is installed inside the outer casing 1 and connected to the inlet 1a of the outer casing 1. Specifically, the primary orifice silencer is designed as a first cylindrical body 3, closed at one end and open at the other. The open end of the first cylindrical body 3 is fixed to the inner side of the front cover 12 and connected to the inlet 1a. To reduce local pressure loss caused by abrupt changes in shape, the inner diameter of the first cylindrical body 3 is the same as the inner diameter of the outlet end of the conical orifice 21, and the inner wall of the outlet end of the conical orifice 21, the inner wall at the inlet 1a, and the inner wall at the opening of the first cylindrical body 3 are sequentially connected by an arc. Simultaneously, to ensure good noise reduction of the fluid entering the first cylindrical body 3, the side wall of the first cylindrical body 3 is densely covered with multiple first injection holes 31. The density of these holes is preferably such that the sum of the areas of the multiple first injection holes 31 is greater than the area of ​​the opening of the primary orifice silencer. Figure 1As shown, the sum of the areas of the multiple first injection holes 31 should be greater than the cross-sectional area of ​​the first cylinder 3 (that is, the area at the inlet). Considering the strength of the first cylinder 3, in this embodiment, the sum of the areas of the multiple first injection holes 31 should be 2 to 3 times the cross-sectional area of ​​the first cylinder 3. Furthermore, in order to reduce the local resistance at the inlet end of each first injection hole 31, an auxiliary tube is added to each first injection hole 31. Specifically, the auxiliary tube extends outward from the edge of the outlet end of each first injection hole 31. To distinguish it from the auxiliary tube at the second injection hole described below, the auxiliary tube at this injection hole 31 is called the first auxiliary tube 32. The inner wall surface of the first auxiliary tube 32, the inner wall surface of the first injection hole 31, and the inner wall surface of the shell 11 at the first injection hole are connected by a circular arc to form a rounded angle. Correspondingly, this rounded angle is called the first rounded angle R1. The radius of the first rounded angle is 0.2 to 0.3 times the diameter of the outlet end of the first injection hole 31.

[0026] The aforementioned secondary small-hole silencer is also fixed inside the outer shell 1 and sleeved on the outside of the primary small-hole silencer, forming a cavity between them. In order to match the shape of the primary small-hole silencer, in this embodiment, the secondary small-hole silencer is also designed as a second cylinder 4 with one end closed and the other end open. In order to obtain a suitable cavity size, the inner diameter and length of the second cylinder 4 are 1.2 to 1.4 times the corresponding inner diameter and length of the first cylinder 3. After they are nested together, the open end of the second cylinder 4 is welded and fixed to the inner wall of the front cover 12 around the inlet 1a. The wall of the second cylinder 4 is also densely covered with second injection holes 41. Similarly, the edge of the outlet end of the second injection hole 41 also extends outward to form an auxiliary tube, which is called the second auxiliary tube 42. The inner wall surface of the second auxiliary tube 42, the inner wall surface of the second injection hole 41, and the inner wall surface of the housing 11 at the second injection hole are connected in a circular arc to form a rounded corner. Correspondingly, the rounded corner is called the second rounded corner R2. The radius of the second rounded corner R2 is preferably 0.2 to 0.3 times the diameter of the outlet end of the second injection hole 41, so as to reduce the resistance of the fluid at the inlet end of each second injection hole 41.

[0027] The aforementioned sound absorber is installed inside the outer casing 1, outside the secondary orifice silencer, to absorb mid- and high-frequency noise in the fluid exiting the secondary orifice silencer. Specifically, the sound absorber includes a front sound absorber and a rear sound absorber 6 made of sound-absorbing material, wherein the front sound absorber is a sound-absorbing cylinder 5 attached to the inner front wall of the outer casing 1 near the inlet 1a. Figure 1As can be seen, the axial length of the sound-absorbing cylinder 5 is approximately half the axial length of the shell 11. To protect the sound-absorbing cylinder 5, a liner 7 is provided on the inner wall of the sound-absorbing cylinder. Multiple small holes are opened on the wall of the liner 7. Generally, the liner 7 is made of a thin porous plate. Therefore, to improve its rigidity, a support ring 71 is provided in the front part of the shell 1, abutting against the inner wall of the liner 7. Multiple support rings can be designed as needed, distributed sequentially from front to back at intervals. The rear sound absorber 6 is located between the front sound absorber and the outlet 1b of the shell 1. The material of the rear sound absorber 6 can be the same as or similar to that of the front sound absorber. Multiple narrow axial channels 61 are opened on the rear sound absorber 6. Please refer to [link to relevant documentation]. Figure 2 To allow fluid to pass through, a liner 8 is provided inside the axial channel to protect the rear sound absorber 6. Multiple through holes are formed on the side wall of the liner 8. The outer casing 1 also includes a front sealing plate 9a located at the front end face of the rear sound absorber 6 and a rear sealing plate 9b located at the rear end face of the rear sound absorber 6. Both the front and rear sealing plates have through holes corresponding to the axial channel.

[0028] To facilitate connection, flanges 10 are designed at the inlet end 2a of the aforementioned diffuser section 2 and the outlet end of the rear cover 13.

[0029] The working principle is as follows: High-noise fluid enters from the inlet end of the diffuser section. Since the outlet cross-section of the diffuser section is larger than the inlet cross-section, the fluid velocity gradually decreases as it moves through the diffuser section. According to the law of conservation of energy, some of the fluid's kinetic energy is converted into pressure energy, causing the fluid's static pressure to rise. Simultaneously, since the local resistance encountered by the fluid is proportional to the square of its velocity, as the fluid velocity decreases, the corresponding local resistance in the diffuser section also decreases. Furthermore, the circular arc transition between the outlet end of the diffuser section and the inlet of the shell and the first cylinder further reduces the local resistance at that point.

[0030] Next, the fluid, after passing through the diffuser section, enters the primary small-hole silencer body, i.e., flows into the first cylinder. Because the first cylinder has numerous first injection holes, and the sum of the cross-sectional areas of all the first injection holes is greater than the area of ​​the opening end of the first cylinder, the fluid velocity within the first cylinder will be further reduced. Simultaneously, the rounded angle at the inlet end of the first injection hole further reduces local resistance and suppresses the generation of secondary noise. This causes a frequency shift in the noise spectrum as it flows through the first injection hole; some high-frequency noise is converted into ultrasonic waves, exceeding the range of human hearing, while low-frequency noise, which is not easily absorbed by the primary small-hole sound absorber, is converted into mid- and high-frequency noise. The fluid exiting the first injection hole enters the cavity and, upon flowing through the secondary small-hole silencer body (i.e., the second cylinder), undergoes another frequency shift. More high-frequency noise is converted into ultrasonic waves, and more low-frequency noise is converted into mid- and high-frequency noise. After entering the second cylinder, most of the noise in the fluid is absorbed by the front sound absorber through the sound-absorbing cylinder.

[0031] Then, the noisy fluid continues to flow towards the rear silencer. Because the rear silencer has multiple narrow axial channels, it has a large length-to-diameter ratio, resulting in high sound absorption efficiency. Most of the remaining noise in the fluid is absorbed by the rear silencer or converted into ultrasonic waves outside the audible range. Therefore, when the fluid exits the casing, its noise reduction value is only 35–45 dB, which is far higher than the noise reduction level of similar silencers.

[0032] Obviously, by adopting this embodiment, the static pressure of the fluid not only does not decrease but increases by utilizing the diffuser section. This increase can almost offset the resistance of the fluid flowing through the silencer, so that the silencer has the characteristics of large noise reduction and low resistance, thereby meeting the system's requirements for these two parameters.

Claims

1. A combined silencer, comprising a housing (1) and a primary perforated silencer, a secondary perforated silencer, and a sound absorber installed within the housing (1), wherein, The outer shell (1) has a fluid inlet (1a) and an outlet (1b). The primary small-hole silencer is connected to the inlet of the outer shell (1). The secondary small-hole silencer is sleeved on the outside of the primary small-hole silencer and forms a cavity with the primary small-hole silencer. The sound absorber is installed inside the outer shell (1) outside the secondary small-hole silencer to absorb medium and high frequency noise in the fluid coming out of the secondary small-hole silencer. It also includes a diffuser section (2) located outside the outer shell (1). The diffuser section (2) has an axially penetrating conical hole (21). The cross-section of the outlet end (2b) of the conical hole (21) is larger than the cross-section of the inlet end (2a). The outlet end (2b) is fixed at the inlet (1a) of the outer shell (1) and is connected to the inlet of the outer shell (1). The first-stage small-hole silencer is a first cylinder (3) that is closed at one end and open at the other end and connected to the inlet (1a) of the outer shell (1). The side wall of the first cylinder is densely covered with a plurality of first injection holes (31). The second-stage small-hole silencer is a second cylinder (4) that is closed at one end and open at the other end and fixed to the inner wall around the inlet of the outer shell (1). The side wall of the second cylinder (4) is densely covered with second injection holes (41). The feature is that the sum of the areas of the plurality of first injection holes (31) is greater than the area of ​​the opening of the first-stage small-hole silencer. Furthermore, each of the first and second injection holes extends outward to form an auxiliary tube. The inner wall of the auxiliary tube, the inner wall of the corresponding injection hole, and the inner wall of the outer shell (1) at the corresponding injection hole are sequentially connected by a circular arc to form a rounded corner. The radius of the rounded corner is 0.2 to 0.3 times the diameter of the corresponding injection hole's outlet end.

2. The combined silencer according to claim 1, characterized in that: The inner wall of the outlet end (2b) of the conical hole (21), the inner wall of the inlet (1a) of the outer shell (1) and the inner wall of the opening of the first cylinder (3) are connected in a circular arc in sequence.

3. The combined silencer according to any one of claims 1 to 2, characterized in that: The sound absorber includes a front sound absorber and a rear sound absorber (6) made of sound-absorbing material. The front sound absorber is a sound-absorbing cylinder (5) attached to the inner wall of the front part of the outer shell (1) near the inlet. The rear sound absorber (6) is located between the front sound absorber and the outlet of the outer shell (1), and a plurality of narrow axial channels (61) are opened on the rear sound absorber.

4. The combined silencer according to claim 3, characterized in that: The inner wall of the sound-absorbing tube (5) is provided with a liner (7) to protect the sound-absorbing tube, and multiple small holes are opened on the wall surface of the liner (7).

5. The combined silencer according to claim 3, characterized in that: The axial channel is provided with a liner (8) to protect the axial channel, and multiple through holes are opened on the side wall of the liner (8).

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