Piezoelectric fan of ring-shaped jet piston type horizontal air duct

Abstract

The application discloses a piezoelectric fan with a ring-shaped jet flow piston type horizontal air duct, which comprises an outer frame, an inner cavity shell, a piezoelectric driving unit and a piston. The outer frame has an outer cavity, an air inlet and an air outlet. The inner cavity shell has a jet flow cavity, and a jet flow hole is arranged on the inner cavity shell. The piezoelectric driving unit is arranged in the jet flow cavity and can produce expansion and contraction deformation in a first direction to change the volume of the jet flow cavity. The piston is arranged on the piezoelectric driving unit and moves synchronously with the piezoelectric driving unit. When the piezoelectric driving unit expands and contracts in the first direction, gas is sprayed from the ring-shaped gap to form a ring-shaped jet flow, and is directly discharged from the air outlet after completing the entrainment in the horizontal air flow channel. In this way, the jet flow generation and the air flow guidance are both completed in the horizontal direction, and a bending air duct for converting the vertical direction into the horizontal direction is not needed, so that the air volume loss caused by the air duct conversion is avoided.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric fans, and in particular to a piezoelectric fan with an annular jet piston-type horizontal air duct. Background Technology

[0002] As portable electronic devices continue to evolve towards thinner, lighter, and higher-performance designs, the internal space of these devices is becoming increasingly compact, and power consumption density is constantly rising. Heat dissipation has become one of the core bottlenecks restricting the release of product performance.

[0003] Traditional centrifugal mechanical fans are limited by the physical structure of their motors and impellers, making it difficult to further reduce their thickness and meet the integration requirements of ultra-thin devices. Against this backdrop, synthetic jet cooling technology based on piezoelectric materials is considered a highly promising alternative due to its advantages such as simple structure, ease of flattening, and absence of rotating parts.

[0004] The basic principle of synthetic jet piezoelectric fans is to utilize the inverse piezoelectric effect of piezoelectric materials to generate periodic vibrations under alternating current, changing the volume of a sealed cavity and causing gas to be pulsedly ejected from the jet orifice to form a jet. The entrainment effect of the jet drives the surrounding air to participate in the flow, thereby achieving air cooling. However, existing synthetic jet fans generally adopt a vertical air duct design. The purpose is to increase the radial area of ​​the piezoelectric oscillator to obtain a larger amplitude and increase the air volume. The jet direction is generally perpendicular to the working surface of the oscillator. This design is feasible when working alone, but when the fan is installed inside the terminal equipment, it is often necessary to change the air direction from vertical to horizontal. The additional bend in the air duct leads to a significant loss of air volume, reduces the overall heat dissipation efficiency, and also limits the application of the product in thin and light devices.

[0005] Therefore, a new technical solution needs to be researched to address the above problems. Summary of the Invention

[0006] In view of this, the present invention addresses the deficiencies of the prior art, and its main objective is to provide a piezoelectric fan with an annular jet piston-type horizontal air duct. By setting the inner cavity shell and the inner wall of the outer cavity at intervals to form a horizontal airflow channel, and forming an annular gap between the jet hole and the piston, when the piezoelectric drive unit extends and retracts in a first direction, gas is ejected from the annular gap to form an annular jet, which is directly entrained in the horizontal airflow channel and discharged from the air outlet. In this way, the jet generation and airflow guidance are both completed in the horizontal direction, eliminating the need for additional vertical-to-horizontal bend air ducts, avoiding airflow loss caused by air duct turning, and improving the overall heat dissipation efficiency of the machine.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A piezoelectric fan with an annular jet piston-type horizontal air duct includes: The outer frame has an outer cavity, an air inlet and an air outlet connected to the outer cavity; An inner cavity shell is disposed within an outer cavity, with the inner cavity shell and the inner wall of the outer cavity shell spaced apart to form an airflow channel; a jet chamber is formed inside the inner cavity shell, and a jet hole communicating with the jet chamber is provided on the inner cavity shell; A piezoelectric drive unit is disposed in the jet chamber and can expand and contract along a first direction to change the volume of the jet chamber; wherein the first direction is parallel to the axial direction of the jet hole. A piston is mounted on a piezoelectric drive unit and moves synchronously with the piezoelectric drive unit. The piston is at least partially located inside the jet hole, and the circumferential edge of the piston is spaced apart from the circumferential edge of the jet hole to form an annular gap. When the piezoelectric drive unit extends and retracts along a first direction, it compresses the gas in the jet chamber, causing the gas to be ejected from the annular gap to form an annular jet. The annular jet completes entrainment in the airflow channel and is then discharged through the air outlet.

[0008] As a preferred embodiment, the piezoelectric drive unit has two opposing working surfaces. The piezoelectric drive unit generates telescopic deformation along a first direction perpendicular to the working surfaces. By defining the piezoelectric drive unit as having two opposing working surfaces and generating telescopic deformation along a first direction perpendicular to the working surfaces, the thickness direction deformation of the drive unit can directly act on the volume change of the jet chamber. The driving force transmission path is short, which is beneficial to improving the volume change efficiency. Furthermore, it ensures that the piston always maintains coaxial alignment with the jet hole during the movement, preventing interference.

[0009] As a preferred embodiment, the thickness of the piezoelectric drive unit along the first direction is greater than 0.5 mm and less than or equal to 20 mm. This ensures that the piezoelectric drive unit has sufficient driving force output while avoiding an increase in the overall fan size due to excessive thickness, thus balancing heat dissipation performance and compact installation space requirements.

[0010] As a preferred embodiment, the piston is attached to the side of the piezoelectric drive unit facing the jet hole. The connection structure is simple and easy to assemble. It can ensure that the piston and the piezoelectric drive unit move synchronously without relative displacement, avoid energy loss and vibration noise caused by mechanical connection gaps, and reduce the number of parts and manufacturing costs.

[0011] As a preferred embodiment, the outer diameter of the piston is smaller than the inner diameter of the jet orifice, so that an annular gap is formed between the piston and the jet orifice. When the gas is ejected from the annular gap, an annular jet is formed, eliminating the need for additional nozzles or flow guiding structures. The annular jet has a larger shear boundary and entrainment area, which can more fully drive the surrounding air to participate in the flow, thereby improving air volume and heat dissipation efficiency.

[0012] As a preferred embodiment, the jet chamber is a Helmholtz resonant cavity, whose inherent resonant frequency matches the driving frequency of the piezoelectric drive unit. By utilizing the acoustic resonance effect to amplify the gas pressure pulsation within the jet chamber, a higher jet ejection speed is obtained under the same jet chamber compression to achieve stronger entrainment capacity. This increases airflow without increasing power consumption, thereby improving fan cooling efficiency.

[0013] As a preferred embodiment, the piezoelectric drive unit reciprocates along a first direction, and the piston is fixedly connected to the piezoelectric drive unit and reciprocates synchronously. When the piezoelectric drive unit extends, the piston moves toward the jet orifice to compress the gas in the jet chamber and eject it outward through the annular gap; When the piezoelectric drive unit contracts, the piston moves away from the jet orifice to expand the volume of the jet chamber, allowing external gas to be drawn into the jet chamber through the annular gap. By alternating compression and exhaust and expansion and intake within the jet chamber during the drive cycle, a continuous and stable periodic jet can be formed, and a directional and continuous net flow rate is established within the airflow channel, thereby achieving stable heat dissipation.

[0014] As a preferred embodiment, the piezoelectric drive unit includes a plurality of piezoelectric ceramic sheets stacked sequentially along a first direction, and the polarization direction of the plurality of piezoelectric ceramic sheets is parallel to the first direction. By utilizing the longitudinal expansion and contraction mode of the piezoelectric ceramics, a larger cumulative displacement output can be obtained under the same driving voltage, thereby increasing the movement amplitude of the piezoelectric drive unit and the piston and thus improving the jet velocity.

[0015] As a preferred embodiment, the air inlet and air outlet are respectively located on opposite sides of the outer cavity. The air inlet, airflow channel and air outlet form a horizontal air duct, which enables the airflow to flow in a straight line in the horizontal direction, avoiding flow resistance and air volume loss caused by the turning of the air duct, improving the overall heat dissipation efficiency of the fan, and also facilitating the horizontal airflow arrangement inside thin and light electronic devices.

[0016] As a preferred embodiment, a guide wall is provided on the outer side of the air outlet, which is used to block the annular jet ejected from the air outlet and guide it to undergo secondary entrainment.

[0017] Compared with the prior art, the present invention has significant advantages and beneficial effects. Specifically, as can be seen from the above technical solution, The main feature is that a horizontal airflow channel is formed by setting the inner cavity shell and the inner wall of the outer cavity at intervals, and an annular gap is formed between the jet hole and the piston. When the piezoelectric drive unit extends and retracts in the first direction, the gas is ejected from the annular gap to form an annular jet, and is directly entrained in the horizontal airflow channel before being discharged from the air outlet. In this way, the jet generation and airflow guidance are both completed in the horizontal direction, without the need to set up an additional vertical to horizontal bend air duct, avoiding airflow loss caused by air duct turning, and improving the overall heat dissipation efficiency. Secondly, the piezoelectric drive unit extends and retracts along a first direction parallel to the axis of the jet hole, and generates a jet through the annular gap between the piston and the jet hole. It no longer relies on increasing the radial area of ​​the piezoelectric vibrator to obtain the amplitude, effectively reducing the space occupied by the fan in the radial direction, making the overall structure more compact and more conducive to integration into portable electronic devices. Furthermore, an annular gap is formed between the circumferential edge of the piston and the circumferential edge of the jet orifice, forming an annular jet when the gas is ejected. The annular jet has a larger entrainment boundary, which can more fully drive the surrounding air to participate in the flow, thereby obtaining a higher net mass flow rate and heat dissipation capacity under the same driving conditions.

[0018] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0019] Figure 1 This is a perspective view of an embodiment of the present invention; Figure 2 This is an exploded view of an embodiment of the present invention; Figure 3 This is a cross-sectional view of an embodiment of the present invention (piezoelectric drive unit expansion exhaust). Figure 4 This is another cross-sectional view of an embodiment of the present invention (piezoelectric drive unit compression and air intake). Figure 5 This is a partial structural diagram of an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached diagram: 10. Outer frame 11. Outer chamber 12. Air inlet 13. Air outlet 14. Top cover plate 15. Bottom plate 16. Flow guide wall.

[0021] 20. Inner cavity shell 21. Airflow channel 22. Jet chamber 23. Jet orifice 30. Piezoelectric drive unit 40. Piston; 41. Annular clearance. Detailed Implementation

[0022] Please refer to Figures 1 to 5 As shown, it illustrates the specific structure of an embodiment of the present invention.

[0023] In the description of this invention, it should be noted that the terms "upper", "lower", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this 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. Therefore, they should not be construed as limiting this invention.

[0024] A piezoelectric fan with an annular jet piston-type horizontal air duct includes an outer frame 10, an inner cavity housing 20, a piezoelectric drive unit 30, and a piston 40.

[0025] The outer frame 10 has an outer cavity 11, an air inlet 12 and an air outlet 13 communicating with the outer cavity 11; preferably, it also includes an upper cover plate 14 and a bottom plate 15, the bottom plate 15 covering the bottom end face of the outer frame 10, the upper cover plate 14 covering the upper opening of the outer cavity 11, and the bottom plate 15, the upper cover plate 14 and the outer frame 10 together form the outer cavity 11.

[0026] Preferably, the air inlet 12 and the air outlet 13 are respectively located on opposite sides of the outer cavity 11. The air inlet 12, the airflow channel 21 and the air outlet 13 form a horizontal air duct, which enables the airflow to flow in a straight line in the horizontal direction, avoiding the flow resistance and air volume loss caused by the turning of the air duct, improving the overall heat dissipation efficiency of the fan, and also facilitating the horizontal airflow arrangement inside thin and light electronic devices.

[0027] The inner cavity shell 20 is disposed inside the outer cavity 11, and the inner cavity shell 20 and the inner wall of the outer cavity 11 are spaced apart to form an airflow channel 21; a jet chamber 22 is formed inside the inner cavity shell 20, and a jet hole 23 communicating with the jet chamber 22 is provided on the inner cavity shell 20. Preferably, the jet chamber 22 is a Helmholtz resonant cavity, and the inherent resonant frequency of the jet chamber 22 is matched with the driving frequency of the piezoelectric drive unit 30. The acoustic resonance effect is used to amplify the gas pressure pulsation in the jet chamber 22, and a higher jet ejection speed is obtained under the same compression of the jet chamber 22 to achieve a stronger entrainment capacity. The air volume is increased without increasing its power consumption, thereby improving the fan heat dissipation efficiency.

[0028] Specifically, the specific volume of the jet chamber 22 and the aperture or effective cross-sectional area of ​​the jet hole 23 can be matched and designed according to the Helmholtz resonant frequency formula. In actual operation, the inherent resonant frequency of the jet chamber 22 can be adjusted by changing the structural dimensions of the inner cavity shell 20 or the diameter of the jet hole 23, so as to match the driving frequency of the piezoelectric drive unit 30.

[0029] The piezoelectric drive unit 30 is disposed inside the jet chamber 22 and can expand and contract along the first direction to change the volume of the jet chamber 22; wherein, the first direction is parallel to the axial direction of the jet hole 23. Preferably, the piezoelectric drive unit 30 has two opposing working surfaces. The piezoelectric drive unit 30 generates telescopic deformation along a first direction perpendicular to the working surfaces. By limiting the piezoelectric drive unit 30 to have two opposing working surfaces and generating telescopic deformation along a first direction perpendicular to the working surfaces, the thickness direction deformation of the drive unit can directly act on the volume change of the jet chamber 22. The driving force transmission path is short, which is beneficial to improving the volume change efficiency. Furthermore, it ensures that the piston 40 always maintains coaxial alignment with the jet hole 23 during the movement, preventing interference.

[0030] Preferably, the thickness of the piezoelectric drive unit 30 along the first direction is greater than 0.5 mm and less than or equal to 20 mm, which can ensure that the piezoelectric drive unit 30 has sufficient driving force output while avoiding the increase in the overall fan size due to excessive thickness, thereby taking into account both heat dissipation performance and compact installation space requirements.

[0031] like Figures 3 to 4 As shown, it illustrates the expansion and compression states of the piezoelectric drive unit 30; the piezoelectric drive unit 30 reciprocates along the first direction, and the piston 40 is fixedly connected to the piezoelectric drive unit 30 and reciprocates synchronously. When the piezoelectric drive unit 30 extends, the piston 40 moves toward the jet hole 23 to compress the gas in the jet chamber 22 and eject it outward through the annular gap 41. When the piezoelectric drive unit 30 contracts, the piston 40 moves away from the jet orifice 23 to expand the volume of the jet chamber 22, allowing external gas to be drawn into the jet chamber 22 through the annular gap 41. By alternating compression and exhaust and expansion and intake in the jet chamber 22 during the driving cycle, a continuous and stable periodic jet can be formed, establishing a directional and continuous net flow rate in the airflow channel 21, thereby achieving stable heat dissipation.

[0032] Preferably, the piezoelectric drive unit 30 includes a plurality of piezoelectric ceramic sheets stacked sequentially along a first direction, and the polarization direction of the plurality of piezoelectric ceramic sheets is parallel to the first direction. By utilizing the longitudinal expansion and contraction mode of the piezoelectric ceramics, a larger cumulative displacement output can be obtained under the same driving voltage, thereby increasing the movement amplitude of the piezoelectric drive unit 30 and the piston 40 and thus increasing the jet velocity. It should be noted that the plurality of piezoelectric ceramic sheets are made into a whole by co-firing or bonding, and are electrically connected to an external driving power supply through lead wires.

[0033] The piston 40 is disposed on the piezoelectric drive unit 30 and moves synchronously with the piezoelectric drive unit 30; the piston 40 is at least partially located inside the jet hole 23, and the circumferential edge of the piston 40 is spaced apart from the circumferential edge of the jet hole 23 to form an annular gap 41; when the piezoelectric drive unit 30 extends and retracts along the first direction, it compresses the gas in the jet chamber 22, causing the gas to be ejected from the annular gap 41 to form an annular jet, so that the annular jet is entrained in the airflow channel 21 and then discharged through the air outlet 13.

[0034] Preferably, a guide wall 16 is provided on the outer side of the air outlet 13. The guide wall 16 is used to block the annular jet ejected from the air outlet and guide it to undergo secondary entrainment.

[0035] Specifically, during operation, the piezoelectric drive unit 30 reciprocates at high frequency under AC drive, pushing the piston 40 to reciprocate within the jet hole 23. During the compression phase, the gas is forced to be ejected in a ring shape from the annular gap 41. Due to the action of the outer chamber 11, this jet first completes the entrainment effect in the gap between the inner cavity shell 20 and the outer chamber 11, entraining the cold air at the air inlet 12, and then ejecting it from the air outlet 13. Due to the blocking effect of the guide wall 16 on the outside of the air outlet 13, the airflow forms a secondary entrainment on the outside of the air outlet 13, driving the surrounding air. Because the inner cavity is a zero-mass jet with an intake volume equal to the exhaust volume, and the presence of the outer shell allows the gas to form a net flow with a constant direction from the air inlet 12 to the air outlet 13, the airflow always flows in a straight line in the horizontal direction through the air inlet 12, the airflow channel 21 and the air outlet 13 without turning, avoiding bending losses. In addition, the annular jet has two suction surfaces, inner and outer, which, together with the speed amplification effect of Helmholtz resonance, increases the suction volume and the outlet pressure. Through the multi-layer ceramic stacking design, high back pressure output can be achieved under low voltage, effectively overcoming the internal airflow resistance.

[0036] Preferably, the piston 40 is attached to the side of the piezoelectric drive unit 30 facing the jet hole 23. The connection structure is simple and easy to assemble. It can ensure that the piston 40 and the piezoelectric drive unit 30 move synchronously without relative displacement, avoid energy loss and vibration noise caused by mechanical connection gaps, and reduce the number of parts and manufacturing costs.

[0037] Specifically, the piston 40 is a flat disc, one side of which is bonded to the working surface of the piezoelectric drive unit 30 facing the jet hole 23 with epoxy resin. There is no relative displacement at the connection, ensuring that the two move completely synchronously. A part of the piston 40 extends into the interior of the jet hole 23. The outer diameter of the piston 40 is smaller than the inner diameter of the jet hole 23, so that an annular gap 41 of equal width is formed between the circumferential edge of the piston 40 and the circumferential edge of the jet hole 23. When the piezoelectric drive unit 30 extends along the first direction, it drives the piston 40 to move closer to the jet hole 23, compressing the gas in the jet chamber 22. The high-pressure gas is ejected at high speed from the annular gap 41 to form an annular jet. When the piezoelectric drive unit 30 contracts, the piston 40 moves in the opposite direction, the volume of the jet chamber 22 increases, and a negative pressure is formed, which draws in external gas.

[0038] Preferably, the outer diameter of the piston 40 is smaller than the inner diameter of the jet hole 23, so that an annular gap 41 is formed between the piston 40 and the jet hole 23, so that when the gas is ejected from the annular gap 41, an annular jet is formed, without the need for additional nozzles or flow guiding structures; when the gas is ejected through the annular gap 41, an annular jet is formed, and the annular jet has a larger shear boundary and entrainment area, which can more fully drive the surrounding air to participate in the flow, thereby improving the air volume and heat dissipation efficiency.

[0039] The key design feature of this invention is that it forms a horizontal airflow channel by spaced between the inner cavity shell and the inner wall of the outer cavity, and forms an annular gap between the jet hole and the piston. When the piezoelectric drive unit extends and retracts in the first direction, the gas is ejected from the annular gap to form an annular jet, which is directly entrained in the horizontal airflow channel and discharged from the air outlet. In this way, the jet generation and airflow guidance are both completed in the horizontal direction, eliminating the need for additional vertical to horizontal bend air ducts, avoiding airflow loss caused by air duct turning, and improving the overall heat dissipation efficiency. Secondly, the piezoelectric drive unit extends and retracts along a first direction parallel to the axis of the jet hole, and generates a jet through the annular gap between the piston and the jet hole. It no longer relies on increasing the radial area of ​​the piezoelectric vibrator to obtain the amplitude, effectively reducing the space occupied by the fan in the radial direction, making the overall structure more compact and more conducive to integration into portable electronic devices. Furthermore, an annular gap is formed between the circumferential edge of the piston and the circumferential edge of the jet orifice, forming an annular jet when the gas is ejected. The annular jet has a larger entrainment boundary, which can more fully drive the surrounding air to participate in the flow, thereby obtaining a higher net mass flow rate and heat dissipation capacity under the same driving conditions.

[0040] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A piezoelectric fan with an annular jet piston-type horizontal air duct, characterized in that, Including: The outer frame has an outer cavity, an air inlet and an air outlet connected to the outer cavity; An inner cavity shell is disposed within an outer cavity, with the inner cavity shell and the inner wall of the outer cavity shell spaced apart to form an airflow channel; a jet chamber is formed inside the inner cavity shell, and a jet hole communicating with the jet chamber is provided on the inner cavity shell; A piezoelectric drive unit is disposed in the jet chamber and can expand and contract along a first direction to change the volume of the jet chamber; wherein the first direction is parallel to the axial direction of the jet hole. A piston is mounted on a piezoelectric drive unit and moves synchronously with the piezoelectric drive unit. The piston is at least partially located inside the jet hole, and the circumferential edge of the piston is spaced apart from the circumferential edge of the jet hole to form an annular gap. When the piezoelectric drive unit extends and retracts along a first direction, it compresses the gas in the jet chamber, causing the gas to be ejected from the annular gap to form an annular jet. The annular jet completes entrainment in the airflow channel and is then discharged through the air outlet.

2. The piezoelectric fan with an annular jet piston-type horizontal air duct according to claim 1, characterized in that: The piezoelectric drive unit has two opposing working surfaces, and the piezoelectric drive unit generates expansion and contraction deformation along a first direction perpendicular to the working surfaces.

3. The piezoelectric fan with an annular jet piston-type horizontal air duct according to claim 2, characterized in that: The thickness of the piezoelectric drive unit along the first direction is greater than 0.5 mm and less than or equal to 20 mm.

4. The piezoelectric fan with an annular jet piston-type horizontal air duct according to claim 1, characterized in that: The piston is attached to the side of the piezoelectric drive unit facing the jet hole.

5. A piezoelectric fan with an annular jet piston-type horizontal air duct according to claim 1, characterized in that: The outer diameter of the piston is smaller than the inner diameter of the jet orifice, so that an annular gap is formed between the piston and the jet orifice, so that when the gas is ejected from the annular gap, an annular jet is formed.

6. A piezoelectric fan with an annular jet piston-type horizontal air duct according to claim 1, characterized in that: The jet chamber is a Helmholtz resonant cavity, and the driving frequency of the piezoelectric driving unit matches the inherent resonant frequency of the jet chamber.

7. A piezoelectric fan with an annular jet piston-type horizontal air duct according to claim 1, characterized in that: The piezoelectric drive unit reciprocates along a first direction, and the piston is fixedly connected to the piezoelectric drive unit and reciprocates synchronously. When the piezoelectric drive unit extends, the piston moves toward the jet orifice to compress the gas in the jet chamber and eject it outward through the annular gap; When the piezoelectric drive unit contracts, the piston moves away from the jet orifice to expand the volume of the jet chamber, allowing external gas to be drawn into the jet chamber through the annular gap.

8. A piezoelectric fan with an annular jet piston-type horizontal air duct according to claim 1, characterized in that: The piezoelectric drive unit includes a plurality of piezoelectric ceramic sheets stacked sequentially along a first direction, and the polarization direction of the plurality of piezoelectric ceramic sheets is parallel to the first direction.

9. A piezoelectric fan with an annular jet piston-type horizontal air duct according to claim 1, characterized in that: The air inlet and air outlet are respectively located on opposite sides of the outer chamber, and the air inlet, airflow channel and air outlet form a horizontal air duct.

10. A piezoelectric fan with an annular jet piston-type horizontal air duct according to claim 1, characterized in that: The outer side of the air outlet is provided with a guide wall, which is used to block the annular jet ejected from the air outlet and guide it to undergo secondary entrainment.

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