Bionic low-wind-resistance dust removal device

Abstract

The invention discloses a bionic low-wind-resistance dust collection device which comprises a bionic dust collection box, the bionic dust collection box is provided with a dust collection cavity, an air inlet and an air outlet are formed in the side face of the bionic dust collection box, a plurality of imitated cuttlebone unit columns are arranged in the bionic dust collection box at intervals, and the axes of the imitated cuttlebone unit columns are parallel to the plane where the air inlet is located; the cross sections of the imitated cuttlebone unit columns are gradually increased from the head to the tail, and at least one imitated shark intestinal tract spiral flow guide belt spirally surrounds the outer sides of the plurality of imitated cuttlebone unit columns in the first preset direction. According to the invention, the cuttlebone-imitating unit columns imitate the microstructure of cuttlebones, so that the turbulivity of secondary dust-containing airflow is further reduced, the disturbance effect of turbulent air mass is reduced, and the curve of the shark intestinal tract-imitating spiral flow guide belt imitates the characteristic spiral structure of the shark intestinal tract, so that the surface area of the boundary layer of the dust-containing airflow is increased; the kinetic energy of dust haze particles is effectively consumed, so that the dust retention efficiency is effectively improved.

Description

Technical Field

[0001] The present invention discloses a bionic low-wind dust-blocking device, belonging to the technical field of atmospheric environmental protection. Background Art

[0002] In industrial production such as mining, coal and ore stacking, and port loading and unloading, as well as in the process of material storage and transportation, dust is diffused, resulting in serious air pollution, which greatly affects the lives and work of residents. Therefore, in areas with serious air pollution, effective dust-blocking measures are urgently needed, which can not only improve air quality, reduce the potential threat to residents' health, but also help relevant industries meet environmental protection compliance requirements and promote sustainable development.

[0003] In the field of dust-blocking technology, traditional dust-blocking devices have many limitations. They have high construction costs, consume a lot of materials, are relatively bulky, and have poor adaptability to wind direction changes. Most of the existing dust removal devices mainly achieve the sedimentation of particulate matter by slowing down the speed of the dust-containing air flow and increasing the collision frequency between particles, thereby reducing the concentration of suspended particles in the air; some fine particles are difficult to be completely removed and are easily re-suspended when encountering strong air currents, resulting in secondary pollution problems; in the case of high wind speeds, generally heavy materials such as steel are used, resulting in a large amount of material consumption and high costs. In addition, although a few dust suppression nets with adsorption functions can capture a certain amount of dust, they quickly reach a saturated state and lack an effective mechanism to centrally treat the adsorbed pollutants. At the same time, the pore structures of these products are usually designed relatively simply and directly, which limits the effective interception ability of particulate matter of different sizes. In addition, in terms of material selection, the types of products available on the market are relatively single.

[0004] In the shark intestine, there is a spiral network around the internal passage of the intestine. This unique structure promotes the unidirectional flow of liquid in the shark digestive tract. The cuttlefish bone material is found to have a multi-layer continuous corrugated array structure and is a thin-walled hollow structure, which can achieve light weight and high strength, and has a small Reynolds number under natural wind. Imitating the spiral structure of the shark intestine and the microstructure of the cuttlefish bone can provide an important theoretical basis for the design of the bionic low-wind dust-blocking device. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of low adsorption performance of existing traditional dust-blocking devices, and propose a bionic low-wind dust-blocking device.

[0006] The problems to be solved by the present invention are realized by the following technical solutions:

[0007] A bionic low-wind dust-blocking device, comprising: a bionic dust-holding box which has a dust-holding cavity, an air inlet and an air outlet are respectively arranged on the side surface of the bionic dust-holding box, a plurality of bionic cuttlefish bone unit columns are arranged at intervals in the bionic dust-holding box, and the axes of the bionic cuttlefish bone unit columns are respectively parallel to the plane where the air inlet is located. The bionic cuttlefish bone unit columns are arranged such that the cross-section gradually increases from the head to the tail. At least one bionic shark intestinal spiral guide belt is spirally wound around the outside of the plurality of bionic cuttlefish bone unit columns along a first preset direction. The air with haze particles enters the dust-holding cavity through the air inlet, and after being guided and dust-reduced by the plurality of bionic cuttlefish bone unit columns and the bionic shark intestinal spiral guide belt, it exits through the air outlet.

[0008] Further, the bionic cuttlefish bone unit column has a bionic cuttlefish bone cavity, and the cavity contour of the bionic cuttlefish bone cavity gradually increases from the top to the bottom. The ratio range of the wall thickness of the bionic cuttlefish bone unit column to the height of the bionic cuttlefish bone unit column is 1:120 to 1:180.

[0009] Further, the angle between the bionic shark intestinal spiral guide belt and the outer contour surface of the bionic cuttlefish bone unit column is 90°. The width of the bionic shark intestinal spiral guide belt along a second preset direction is K, where the value of K is 1 ≤ K ≤ 2.2, and the measurement unit of K is centimeter.

[0010] Further, the bionic cuttlefish bone unit column fits to obtain a hyperbolic cosine function curve as shown in formula (1):

[0011] f(t) = Acosh(ωt) + B (1)

[0012] Where: the value range of A is -1.3 ≤ A ≤ -0.9; the value range of B is 20 ≤ B ≤ 32; the value range of ω is 0.8 ≤ ω ≤ 1.6; the value range of t is -4.5 ≤ t ≤ 4.5, and the measurement unit of t is centimeter.

[0013] Further, the bionic shark intestinal spiral guide belt fits to obtain a spiral curve equation as shown in formula (2):

[0014]

[0015] Where: r is the distance from the moving point on the spiral curve in the Cartesian coordinate system to the spiral axis, the value range of r is 0 ≤ r ≤ 4.5, the value range of θ is 2.81 ≤ θ ≤ 5, the value range of q is 0 < q ≤ 6.5, the value range of x is -4.5 ≤ x ≤ 4.5; the value range of y is -4.5 ≤ y ≤ 4.5; the value range of z is 0 ≤ z ≤ 31.1, and the measurement units of r, x, y and z are centimeter, and the measurement unit of θ is radian.

[0016] Further, electrostatic adsorption coatings are respectively sprayed on the dust retention cavity, multiple cuttlefish bone unit columns, and the shark intestine spiral flow guide belt.

[0017] Further, it further includes: a dust collection box, which is arranged at the bottom inside the dust retention cavity. The dust collection box is movably connected to the bionic dust retention box, and the dust collection box is used to collect the haze particles after the flow guide and dust reduction.

[0018] Further, the bionic dust retention box includes: a box body, which has a dust retention cavity; a partition board, which is arranged inside the dust retention cavity and divides the dust retention cavity into a sedimentation cavity and a dust collection cavity. The dust collection box can be movably arranged in the dust collection cavity, and multiple cuttlefish bone unit columns are arranged in the sedimentation cavity. A number of through holes are provided on the partition board, and the haze particles pass through the through holes into the dust collection box after being sedimented and adsorbed by the multiple cuttlefish bone unit columns and the shark intestine spiral flow guide belt.

[0019] Further, an opening is arranged on one side of the dust collection cavity. The dust collection box has a dust collection position inside the dust collection cavity, and at least part of the dust collection box has a cleaning position moved outside the dust collection cavity.

[0020] Further, the bionic dust retention box further includes: a first fence, which is a honeycomb grid structure and is arranged at the air inlet; a second fence, which is arranged at the air outlet.

[0021] The beneficial effects of the present invention compared with the prior art are as follows:

[0022] The present invention discloses a bionic low-wind resistance dust retention device. By imitating the microscopic tissue structure of cuttlefish bones with cuttlefish bone unit columns, the secondary dust-containing airflow is further reduced in turbulence intensity, decomposed into finer laminar dust-containing airflows, and the disturbance effect of turbulent air masses is reduced. The curve of the shark intestine spiral flow guide belt imitates the characteristic spiral structure of the intestine of great white sharks, which can achieve the functions of guiding the flow and extending the movement trajectory of the dust-containing airflow, increasing the surface area of the boundary layer of the dust-containing airflow, effectively consuming the kinetic energy of the haze particles, promoting their sedimentation, preventing the occurrence of countercurrent phenomena when the dust-containing airflow spirally flows around the cuttlefish bone unit columns, promoting the sedimentation process of the haze particles in the dust-containing airflow, and further increasing the collision probability between the haze particles and the solid wall surface, thereby effectively improving the dust retention efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is an axonometric view of a bionic low-wind resistance dust retention device of the present invention;

[0024] Figure 2 is an internal structure diagram of a bionic low-wind resistance dust retention device of the present invention;

[0025] Figure 3It is a cross-sectional view of the cuttlefish bone unit column in a bionic low-wind dust-blocking device of the present invention;

[0026] Figure 4 It is a width schematic diagram of the shark intestine spiral diversion belt in a bionic low-wind dust-blocking device of the present invention;

[0027] Figure 5 It is a structural schematic diagram of the middle partition board in a bionic low-wind dust-blocking device of the present invention;

[0028] Wherein:

[0029] 1 - First fence;

[0030] 2 - Second fence;

[0031] 3 - Dust collection box;

[0032] 4 - Bionic dust-blocking box;

[0033] 5 - Cuttlefish bone unit column;

[0034] 6 - Shark intestine spiral diversion belt;

[0035] 41 - Dust-blocking cavity;

[0036] 42 - Box body;

[0037] 43 - Spacer;

[0038] 431 - Through hole. Specific implementation manners

[0039] The following further describes the present invention according to the attached Figures 1-5 :

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0042] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "linkage" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] As Figure 1 and Figure 2 shown, on the basis of the prior art, the first embodiment of the present invention provides a bionic low wind resistance dust collecting device, including: a bionic dust collecting box 4 and a plurality of bionic cuttlefish bone unit columns 5. The bionic dust collecting box 4 has a dust collecting cavity 41, and an air inlet and an air outlet are respectively arranged on the side surface of the bionic dust collecting box 4. The plurality of bionic cuttlefish bone unit columns 5 are arranged in the bionic dust collecting box 4 at intervals. The bionic cuttlefish bone unit columns 5 imitate the microscopic tissue structure of the cuttlefish bone, and the axes of the bionic cuttlefish bone unit columns 5 are respectively parallel to the plane where the air inlet is located. The cross section of the bionic cuttlefish bone unit columns 5 is gradually increased from the head to the tail.

[0044] The hyperbolic cosine function curve fitted by the above bionic cuttlefish bone unit column 5 is as follows:

[0045] f(t) = Acosh(ωt) + B (1)

[0046] Where: the value range of A is -1.3 ≤ A ≤ -0.9; the value range of B is 20 ≤ B ≤ 32; the value range of ω is 0.8 ≤ ω ≤ 1.6; the value range of t is -4.5 ≤ t ≤ 4.5, where the measurement unit of t is centimeter.

[0047] In an exemplary embodiment, the hyperbolic cosine function of this embodiment is f(t) = -cosh(1.2t) + 22, that is: A is -1, B is 22, ω is 1.2, and there are 6 bionic cuttlefish bone unit columns 5. The overall structure of the bionic dust collecting box 4 formed by the 6 bionic cuttlefish bone unit columns 5 arranged in an array is similar to the lattice sandwich structure of the cuttlefish bone, which can realize the lightweight and high strengthening of the device, improve the bending strength of the device when it is impacted by the dust-containing air flow, and further improve the anti-wind vibration performance of the device; and, under natural wind force, the Reynolds number of the bionic cuttlefish bone unit columns 5 in a specific size range is small, and the air flow is mainly viscous force, which promotes the secondary dust-containing air flow to further reduce the turbulence intensity, decompose into finer laminar dust-containing air flow, reduces the disturbance of the turbulent air mass, makes the wind resistance of the device decrease, and further improves the anti-wind vibration performance of the device.

[0048] As Figure 3As shown, the cuttlefish bone-like unit column 5 has a cuttlefish bone-like cavity and is a hollow thin-walled structure. The cavity contour of the cuttlefish bone-like cavity is set to gradually increase from the top to the bottom. The wall thickness of the cuttlefish bone-like unit column 5 is M, and the height of the cuttlefish bone-like unit column 5 is L. The ratio range of the wall thickness M to the height L is 1:120 to 1:180.

[0049] On the outer side of multiple cuttlefish bone-like unit columns 5, at least one shark intestine-like spiral flow guiding band 6 is spirally wound along a first preset direction. In this embodiment, there is one shark intestine-like spiral flow guiding band 6.

[0050] As Figure 4 shown, the included angle between the shark intestine-like spiral flow guiding band 6 and the outer contour surface of the cuttlefish bone-like unit column 5 is 90°. The width of the shark intestine-like spiral flow guiding band 6 along a second preset direction is K, and the value range of K is 1 ≤ K ≤ 2.2, where the measurement unit of K is centimeter. The spiral curve OP of the shark intestine-like spiral flow guiding band 6 imitates the spiral curve characteristics of the great white shark's intestine. The spiral curve equation obtained by fitting the shark intestine-like spiral flow guiding band 6 is as follows:

[0051]

[0052] where: r is the distance from the moving point on the spiral curve in the Cartesian coordinate system to the spiral axis (usually taken as the Z axis). When z is equal to f(t) in formula (1), the numerical value of r is the same as the numerical value of t in formula (1); the value range of r is 0 ≤ r ≤ 4.5, the value range of θ is 2.81 ≤ θ ≤ 5, the value range of q is 0 < q ≤ 6.5, the value range of x is -4.5 ≤ x ≤ 4.5; the value range of y is -4.5 ≤ y ≤ 4.5; the value range of z is 0 ≤ z ≤ 31.1, where the measurement units of r, x, y, and z are centimeter, and the measurement unit of θ is radian.

[0053] The shark intestine-like spiral flow guiding band 6 can achieve the functions of guiding the flow and extending the movement trajectory of the dust-containing air flow, increasing the surface area of the boundary layer of the dust-containing air flow, effectively consuming the kinetic energy of the haze particulate matter, and promoting its sedimentation; and this characteristic structure can also prevent the reverse flow phenomenon from occurring when the dust-containing air flow spirally flows around the cuttlefish bone-like unit column 5. On the one hand, it can promote the sedimentation process of the haze particulate matter in the dust-containing air flow, and on the other hand, it can increase the collision probability between the haze particulate matter and the solid wall surface, thereby effectively improving the dust retention efficiency of this device.

[0054] Thus, the air with haze particulate matter enters the dust retention cavity 41 through the air inlet, and after being guided and dust-removed by multiple cuttlefish bone-like unit columns 5 and shark intestine-like spiral flow guiding bands 6, it exits from the air outlet.

[0055] Further, in this embodiment, the dust retention chamber 41, the plurality of squid bone unit columns 5, and the shark intestine spiral flow guiding belt 6 are respectively sprayed with an electrostatic adsorption coating. The electrostatic adsorption effect can be utilized to assist in adsorbing haze particles; and this coating endows the device with good corrosion resistance and anti-aging characteristics, enabling it to be stably used for a long time under diverse climate conditions, improving the weather resistance of the device. Further, the electrostatic adsorption coating is a mixed coating of micron-scale oxygen anion powder and polyether ether ketone powder.

[0056] Further, as Figure 1 , Figure 2 and Figure 5 shown, this embodiment further includes: a dust collection box 3. The dust collection box 3 is located at the bottom inside the dust retention chamber 41. The dust collection box 3 is movably connected to the bionic dust retention box 4 and is used to collect the haze particles after diversion and dust reduction.

[0057] The specific structure of the bionic dust retention box 4 in this embodiment includes: a box body 42, and the box body 42 has a dust retention chamber 41; a partition plate 43, the partition plate 43 is arranged inside the dust retention chamber 41 and divides the dust retention chamber 41 into a sedimentation chamber and a dust collection chamber. The dust collection box 3 can be movably installed in the dust collection chamber. A plurality of squid bone unit columns 5 are installed in the sedimentation chamber. A plurality of through holes 431 are provided on the partition plate 43. After the haze particles are sedimented and adsorbed by the plurality of squid bone unit columns 5 and the shark intestine spiral flow guiding belt 6, they pass through the through holes 431 and enter the dust collection box 3. An opening is provided on one side of the dust collection chamber. The dust collection box 3 has a dust collection position inside the dust collection chamber, and at least part of the dust collection box 3 has a cleaning position moved outside the dust collection chamber.

[0058] Further, the bionic dust retention box 4 in this embodiment further includes: a first fence 1 and a second fence 2. The first fence 1 has a honeycomb grid structure. The first fence 1 is arranged at the air inlet. Its honeycomb grid has a negative Poisson's ratio effect, which can increase the bending strength of the device in the normal direction of the air flow and assist in improving the mechanical properties of the device. The second fence 2 is arranged at the air outlet.

[0059] Specific working process:

[0060] The present application is installed in the working area. The dust-containing air flow passes through the first fence 1 and enters the interior of the device. First, the honeycomb-shaped first fence 1 can break up the large eddies of the dust-containing air flow and organize them into a secondary air flow in a transitional laminar state. Secondly, after being organized, the dust-containing air flow enters the bionic dust retention box 4. When passing through a number of bionic cuttlefish bone unit columns 5 arranged in an array, due to the small Reynolds number of the bionic cuttlefish bone unit columns 5 within the specific size range in the present invention under natural wind force, the fluid microgroups of the secondary dust-containing air flow are dominated by viscous force, and its turbulence intensity is further reduced and decomposed into finer laminar dust-containing air flows. Thereafter, the laminar dust-containing air flow is guided by the bionic shark intestinal spiral guide belt 6 to flow spirally downward around the bionic cuttlefish bone unit columns 5, thereby extending the movement trajectory of the haze particles and promoting the sedimentation effect of the haze particles. Moreover, when the laminar dust-containing air flow moves along the bionic shark intestinal spiral guide belt 6, a large number of boundary boundary layers are formed, converting the kinetic energy of the dust-containing air flow into the work done to overcome friction, reducing the movement speed of the haze particles, and at the same time increasing the collision probability between the haze particles and the solid wall surface, thereby effectively improving the dust retention efficiency. In addition, the interior of the bionic dust retention box 4 is sprayed with an oxygen anion powder, and an electrostatic adsorption effect is generated by friction when the dust-containing air flow passes through, which can assist in adsorbing the haze particles. Finally, the cleaned and filtered air flow flows out of the device from the second fence 2, and the haze particles settled or attached inside the bionic dust retention box 4 can enter the dust collection box 3 below through the through holes distributed on the spacer 43, and the dust collection box 3 is regularly taken out to clean the accumulated haze particles inside according to the actual situation.

[0061] Although the embodiments of the present invention have been disclosed as above, they are not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrated and described examples here.

Claims

1. A bionic low wind resistance dust retention device, characterized in that: The invention comprises a bionic dust-trapping box (4), wherein the bionic dust-trapping box (4) has a dust-trapping chamber (41), and the sides of the bionic dust-trapping box (4) are respectively provided with an air inlet and an air outlet, and a plurality of imitation cuttlefish bone unit columns (5) are arranged at intervals in the bionic dust-trapping box (4), and the axes of the imitation cuttlefish bone unit columns (5) are respectively parallel to the plane where the air inlet is located, and the imitation cuttlefish bone unit columns (5) are arranged with a cross section gradually increasing from the head to the tail, and at least one imitation shark intestine spiral guide belt (6) is arranged on the outer side of the plurality of imitation cuttlefish bone unit columns (5) in a spiral manner along a first preset direction, and air carrying dust and haze particles enters the dust-trapping chamber (41) through the air inlet, and is guided and dust-reduced by the plurality of imitation cuttlefish bone unit columns (5) and the imitation shark intestine spiral guide belt (6), and then goes out from the air outlet.

2. The bionic low wind resistance dust retention device according to claim 1, characterized in that: The imitation cuttlefish bone unit column (5) has an imitation cuttlefish bone cavity, the cavity contour of the imitation cuttlefish bone cavity is gradually increased from the top end to the bottom end, and the ratio of the wall thickness of the imitation cuttlefish bone unit column (5) to the height of the imitation cuttlefish bone unit column (5) is in the range of 1:120 to 1:

180.

3. The bionic low wind resistance dust retention device according to claim 2, characterized in that: The angle between the shark gut-simulating spiral guide belt (6) and the outer contour surface of the cuttlefish bone-simulating unit column (5) is 90°, and the width of the shark gut-simulating spiral guide belt (6) along the second preset direction is K, wherein the value of K is 1≤K≤2.2, and the unit of measurement of K is centimeters.

4. The bionic low wind resistance dust retention device according to any one of claims 1 to 3, characterized in that: The simulated cuttlefish bone unit column (5) is fitted to obtain a hyperbolic cosine function curve as shown in formula (1): f(t)=Acosh(ωt)+B (1) Among them: the value range of A is -1.3≤A≤-0.9; the value range of B is 20≤B≤32; the value range of ω is 0.8≤ω≤1.6; the value range of t is -4.5≤t≤4.5, where the unit of t is centimeter.

5. The bionic low wind resistance dust retention device according to claim 4, characterized in that: The spiral curve equation obtained by fitting the shark intestine-simulating spiral guide belt (6) is shown in formula (2): Wherein: r is the distance from the moving point of the spiral curve in the Cartesian coordinate system to the spiral axis, the value range of r is 0≤r≤4.5, the value range of θ is 2.81≤θ≤5, the value range of q is 0<q≤6.5, the value range of x is -4.5≤x≤4.5; the value range of y is -4.5≤y≤4.5; the value range of z is 0≤z≤31.1, wherein the measurement units of r, x, y and z are centimeters, and the measurement unit of θ is radians.

6. The bionic low wind resistance dust retention device according to claim 5, characterized in that: The dust-retaining chamber (41), the plurality of cuttlefish bone-like unit columns (5) and the shark intestine-like spiral guide belt (6) are respectively sprayed with electrostatic adsorption paint.

7. The bionic low wind resistance dust retention device according to claim 1, characterized in that: Also includes: A dust collection box (3), the dust collection box (3) being arranged at the bottom of the dust retention chamber (41), the dust collection box (3) being movably connected to the bionic dust retention box (4), and the dust collection box (3) being used to collect dust and haze particles after the dust is diverted and reduced.

8. The bionic low wind resistance dust retention device according to claim 7, characterized in that: The bionic dust-trapping box (4) comprises: A box body (42), wherein the box body (42) has a dust retention chamber (41); A partition plate (43), wherein the partition plate (43) is arranged in the dust retention chamber (41) to divide the dust retention chamber (41) into a sedimentation chamber and a dust collection chamber, the dust collection box (3) is movably arranged in the dust collection chamber, a plurality of the imitation cuttlefish bone unit columns (5) are arranged in the sedimentation chamber, and a plurality of through holes (431) are arranged on the partition plate (43), and the dust haze particles are precipitated and adsorbed by the plurality of the imitation cuttlefish bone unit columns (5) and the imitation shark intestine spiral guide belt (6), and then pass through the through holes (431) into the dust collection box (3).

9. The bionic low wind resistance dust retention device according to claim 8, characterized in that: An opening is provided on one side of the dust collecting chamber, the dust collecting box (3) has a dust collecting position in the dust collecting chamber, and at least a portion of the dust collecting box (3) has a cleaning position that can be moved to the outside of the dust collecting chamber.

10. The bionic low wind resistance dust retention device according to claim 1, characterized in that: The bionic dust-trapping box (4) further comprises: A first fence (1), the first fence (1) being a honeycomb grid structure, and the first fence (1) being arranged at the air inlet; A second fence (2), wherein the second fence (2) is arranged at the air outlet.

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