A smoke and ash separating device for an aspirating smoke fire detector

Abstract

The present application relates to the technical field of aspirating smoke detection, and particularly relates to a smoke-sand separation device of an aspirating smoke fire detector, which comprises a main body and an upper cover, the main body is provided with an air inlet and an air outlet at two ends respectively, a flue gas channel is arranged between the air inlet and the air outlet, and a first convex Coanda curve and a second convex Coanda curve are arranged in the flue gas channel. The first convex Coanda curve and the second convex Coanda curve are arranged, so that the smoke dust airflow group flowing through is deflected along the curves, the smoke and the sand dust in the airflow group are deflected at different angles, and the sand dust is collected and deposited in a sand dust bin, so that smoke and sand are separated, the sand dust passes through the airflow channel of the smoke, the problem that the filter in the aspirating smoke fire detector is prone to blockage is fundamentally solved, the air flow resistance is reduced, the sensitivity of smoke detection and alarm is improved, and the adaptability of the aspirating smoke fire detector in sand dust prone areas is improved.

Description

A smoke and sand separation device for an aspirating smoke detector Technical Field

[0001] This invention relates to the field of aspirating smoke detection technology, and more particularly to a smoke and dust separation device for an aspirating smoke fire detector. Background Technology

[0002] Aspirating smoke detectors are an important component of the fire alarm system, primarily used in large spaces, warehouses, cold storage facilities, and data centers. However, due to their high sensitivity to smoke, aspirating detectors are easily susceptible to false alarms caused by dust, sand, and moisture. Furthermore, dust and sand deposits on the inner wall of the detector chamber, turning it from black to grayish-white, increases the amount of scattered light and reduces smoke detection sensitivity. To address the issues of false alarms and reduced sensitivity caused by dust and sand during normal operation of aspirating detectors, the industry solution is to add filters.

[0003] Chinese patent publication number CN110176123A discloses an aspirating smoke detector. Its technical point is that it uses a filter unit with filter cotton to pre-filter the sample air, removing large particles from the airflow and thus improving detection accuracy and speed. It is evident that existing aspirating smoke detectors often use filters to remove large particles such as dust and sand from the airflow. However, adding filters to aspirating smoke detectors increases resistance to the aspirating air sampling pipe, shortening its effective length and reducing the monitoring area. Furthermore, dust and sand accumulate in the filter medium, further increasing airflow resistance and even causing blockages, affecting the normal flow of smoke and air, and leading to smoke detection alarm failure. Summary of the Invention

[0004] To address this issue, the present invention provides a smoke and dust separation device for an aspirating smoke detector, which solves the problem that filters in existing aspirating smoke detectors are prone to clogging, increasing the resistance of the air sampling pipeline and resulting in low sensitivity of smoke detection alarms.

[0005] To achieve the above objectives, the present invention provides a smoke and sand separation device for an aspirating smoke detector, comprising a main body and a top cover;

[0006] The main body has an air inlet and an air outlet at both ends. A flue gas channel is provided between the air inlet and the air outlet to allow smoke to flow. A first Coanda surface and a second Coanda surface are provided on both sides of the flue gas channel. The first Coanda surface is closer to the air inlet, and the second Coanda surface is closer to the air outlet. A gap is left between the first Coanda surface and the second Coanda surface.

[0007] Furthermore, the cavity between the first Coanda curved surface and the opposite flue gas passage sidewall constitutes a primary flue gas separation zone. The second Coanda curved surface is located below the primary flue gas separation zone, and a dust trough is provided at the top of the second Coanda curved surface. The bottom of the dust trough is connected to the first dust chamber located outside the flue gas passage.

[0008] The minimum cross-sectional width of the primary smoke and dust separation zone shall not be less than two-thirds of the inner diameter of the air inlet.

[0009] Furthermore, the bottom of the dust trough is set as a plane and tilted towards the side closer to the first dust chamber. The angle between the bottom plane of the dust trough and the side should be no less than 120°.

[0010] Furthermore, the cavity between the second Coanda curved surface and the opposite flue gas passage sidewall constitutes a secondary smoke and dust separation zone. The first Coanda curved surface is located above the secondary smoke and dust separation zone, and a second dust chamber is provided below the secondary smoke and dust separation zone. The second dust chamber is located outside the flue gas passage and is connected to the flue gas passage.

[0011] The minimum cross-sectional width of the secondary smoke and dust separation zone shall not be less than two-thirds of the inner diameter of the air inlet.

[0012] Furthermore, the air outlet is located below the second Coanda curved surface, and a filter is provided at the upper end of the air outlet.

[0013] Furthermore, the width of the first Coanda surface and the second Coanda surface is not less than two-thirds of the inner diameter of the air inlet.

[0014] Furthermore, the radius of curvature at the point of maximum curvature of the first Coanda surface is not less than twice the surface width; the radius of curvature at the point of maximum curvature of the second Coanda surface is not less than twice the surface width.

[0015] Furthermore, the minimum distance between the first Coanda surface and the second Coanda surface is not less than one-third of the inner diameter of the air inlet and not more than two-thirds of the inner diameter of the air inlet.

[0016] Furthermore, the main body is a cuboid structure with a cavity, and the main body is sealed to the top cover.

[0017] Furthermore, both the first and second sand and dust chambers are connected to the main body via threads.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: by setting a first Coanda surface and a second Coanda surface in the smoke channel of the smoke-dust separation device, the smoke and dust airflow passing through the first and second Coanda surfaces is deflected along the surfaces. The smoke in the airflow has a large deflection angle after passing through the Coanda surface due to its high viscosity, while the dust has a small deflection angle after passing through the Coanda surface due to its low viscosity, high specific gravity, high inertia, and high centrifugal force, or even no deflection. Furthermore, dust chambers are set according to the corresponding positions of the first and second Coanda surfaces to collect the deposited dust, thereby achieving smoke-dust separation. The dust does not pass through the smoke airflow channel, fundamentally solving the problem of easy clogging of filters in aspirating smoke detectors. At the same time, it reduces airflow resistance, improves the sensitivity of smoke detection alarms, and enhances the adaptability of aspirating smoke detectors in dusty areas. Attached Figure Description

[0019] Figure 1 is a schematic diagram of the installation position of the tobacco and sand separation device in this embodiment;

[0020] Figure 2 is a partial cross-sectional structural diagram of the tobacco and sand separation device in this embodiment;

[0021] Figure 3 is a schematic diagram of the forces acting on the airflow at the Coanda surface in this embodiment;

[0022] Figure 4 is a schematic diagram of the velocity gradient force of the airflow at the Coanda surface in this embodiment.

[0023] Reference numerals: 1. Sampling tube; 2. Smoke and dust separation device; 3. Smoke detection chamber labyrinth; 4. Photoelectric detection component; 5. Control alarm circuit board; 6. Intake pump; 7. Exhaust vent; 9. Main body; 10. Top cover; 11. Air inlet; 12. Air outlet; 13. Smoke passage; 14. First Coanda surface; 15. Second Coanda surface; 16. Primary smoke and dust separation zone; 17. Dust trough; 18. First dust chamber; 19. Secondary smoke and dust separation zone; 20. Second dust chamber; 21. Filter plate. Detailed Implementation

[0024] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0025] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0026] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0027] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] Please refer to Figure 1. This embodiment provides a smoke and dust separation device for an aspirating smoke detector. It uses a smoke and dust separation method to replace the traditional filtration method, and is particularly suitable for smoke detection in areas with strong winds and dusty weather. In this embodiment, the aspirating smoke detector includes a sampling tube 1, a smoke and dust separation device 2 (in this embodiment), a smoke detection chamber labyrinth 3, a photoelectric detection component 4, a control alarm circuit board 5, an intake pump 6, and an exhaust port 7. The intake end of the smoke and dust separation device 2 is connected to the sampling tube 1, and the exhaust end of the smoke and dust separation device 2 is connected to the smoke detection chamber labyrinth 3. The function of the smoke and dust separation device 2 in the aspirating smoke detector is to replace the filter in traditional products. The traditional filtration method blocks sand and dust in the filter, which eventually leads to an accumulation of sand and dust in the filter, which can easily block the airflow channel, even to the point that it is difficult for smoke to pass through, resulting in low sensitivity of smoke detection alarm or even failure.

[0029] Please refer to Figure 2. In this embodiment, the smoke and sand separation device is set as a cuboid structure, including a main body 9 and an upper cover 10. The upper cover 10 and the main body 9 are sealed to prevent air leakage.

[0030] The main body 9 has a cavity structure. An air inlet 11 and an air outlet 12 are respectively provided at both ends of the main body 9. A flue gas channel 13 is provided between the air inlet 11 and the air outlet 12 to allow smoke to flow. A first Coanda surface 14 and a second Coanda surface 15 are respectively provided on both sides of the flue gas channel 13. Since the first Coanda surface 14 and the second Coanda surface 15 are respectively provided on both sides of the flue gas channel 13, the protrusion directions of the first Coanda surface 14 and the second Coanda surface 15 are opposite, and the protrusion directions are both facing the flue gas channel 13.

[0031] The first Coanda surface 14 and the second Coanda surface 15 do not contact each other and are provided with a gap distance to ensure sufficient flow in the flue gas passage 13.

[0032] The cavity between the first Coanda curved surface 14 and the side wall of the opposite flue gas passage 13 forms a primary smoke and dust separation zone 16. The second Coanda curved surface 15 is located below the primary smoke and dust separation zone 16, and a dust trough 17 is opened at the top of the second Coanda curved surface 15. The bottom of the dust trough 17 is connected to the first dust chamber 18 located outside the flue gas passage 13.

[0033] The bottom of the dust trough 17 is set as a plane and is inclined towards the side closer to the first dust chamber 18. The angle between the bottom plane of the dust trough 17 and the side should be greater than 120° to ensure that the dust separated from the primary dust separation zone 16 can fall into the dust trough 17 and slide into the first dust chamber 18 through the inclined plane at the bottom of the dust trough 17.

[0034] The cavity between the second Coanda curved surface 15 and the side wall of the opposite flue gas passage 13 forms a secondary dust separation zone 19. The first Coanda curved surface 14 is located above the secondary dust separation zone 19. A second dust chamber 20 is provided below the secondary dust separation zone 19. The second dust chamber 20 is located outside the flue gas passage 13 and is connected to the flue gas passage 13. Since the second dust chamber 20 is directly located below the secondary dust separation zone 19, there is no need to set up a trough for dust to fall. The dust can fall directly into the second dust chamber 20 to collect the dust separated from the secondary dust separation zone 19.

[0035] Below the second Coanda curved surface 15 is the air outlet 12, and the upper end of the air outlet 12 is provided with a filter 21. In this embodiment, the filter 21 is thinner than the filter in the traditional aspirating smoke detector, has better air permeability, and has very little resistance to the airflow channel. Since most of the sand and dust have been separated, only air, smoke, and light dust flow through the filter 21. In addition, the filter 21 is relatively thin, and the replacement cycle due to dust accumulation and blockage is relatively long, which makes the service life of the smoke and sand separation device longer.

[0036] In this embodiment, the first dust chamber 18 and the second dust chamber 20 are both connected to the main body 9 by threads and can be disassembled by rotation to clean the collected dust; the filter 21 can be replaced by removing the top cover 10 of the dust separation device, making the dust separation device easier to maintain.

[0037] In this embodiment, the air inlet 11 and air outlet 12 of the main body 9 are both set as inner conical tube structures, that is, the diameter of the tube at one end near the inner side of the main body 9 is smaller than the diameter of the tube at the other end; so as to facilitate the insertion and installation of external pipes and ensure that the insertion is tight and leak-proof.

[0038] In this embodiment, the surface width of the first Coanda surface 14 is set to W1, the radius of curvature at the maximum curvature of the first Coanda surface 14 is set to R1, the surface width of the second Coanda surface 15 is set to W2, the radius of curvature at the maximum curvature of the second Coanda surface 15 is set to R2, and the inner diameter of the air inlet 11 is set to D; wherein, W1≥2D / 3, W2≥2D / 3. Since the smoke and sand separation device in this embodiment is a cuboid structure, the surface widths of the first Coanda surface 14 and the second Coanda surface 15 are affected by the thickness of the main body 9, and the surface widths of the first Coanda surface 14 and the second Coanda surface 15 are equal, which is the thickness of the flue gas channel 13; the air inlet The inner diameter D of 11 is close to the outer diameter of the sampling tube 1 inserted into the air inlet 11, usually 25mm; R1≥2W1, R2≥2W2, the first Coanda surface 14 or the second Coanda surface 15 needs to be smoothly connected to other parts in the flue gas channel 13 in a streamlined manner. Therefore, the radius of the maximum curvature of the first Coanda surface 14 and the second Coanda surface 15 is limited and cannot be infinitely large. There is no need to give the maximum value of R1 and R2. In actual production, it can be set according to the size or shape of the smoke and sand separation device. If the radius of curvature is too small, the surface becomes a small convexity. Then the surface arc is too short, the viscous force stroke is too short, and the Coanda effect is not obvious.

[0039] The minimum straight-line distance L1 between the first Coanda surface 14 and the sidewall of the opposite flue gas passage 13, i.e. the minimum cross-sectional width L1 of the primary flue gas separation zone 16, should satisfy L1≥2D / 3 to ensure sufficient flow and reduce airflow resistance. Similarly, the minimum straight-line distance L2 between the second Coanda surface 15 and the sidewall of the opposite flue gas passage 13, i.e. the minimum cross-sectional width L2 of the secondary flue gas separation zone 19, should satisfy L2≥2D / 3 to ensure sufficient flow and reduce airflow resistance.

[0040] In this embodiment, taking the flue gas channel 13 at the primary smoke and dust separation zone 16 as an example, the cross-sectional area S of the flue gas channel 13 here is the product of the minimum cross-sectional width L1 and the curved surface width W1. Therefore, the minimum values ​​of L1 and W1 are limited to two-thirds of the inner diameter D of the inlet 11 to avoid large flow velocity fluctuations in the airflow entering through the inlet 11 due to the reduction of the flow cross-section. In this embodiment, the cross-sectional area of ​​the flue gas channel 13 at the primary smoke and dust separation zone 16 is set to be no less than half of the cross-sectional area of ​​the inlet 11. If the minimum cross-sectional width L1 and the curved surface width W1 are equal, a square cross-section is formed. The cross-section of the air inlet 11 is circular. For ease of calculation, the radius of the circular cross-section of the air inlet 11 is set to 1, the area to be π, and the diameter to be 2. The area of ​​the square cross-section of the flue gas passage 13 should be greater than π / 2. With a 10% margin, the square cross-section of the flue gas passage 13 is calculated to be (π+10%π) / 2≈1.7. The side length of the square cross-section is 1.7 square root, which is approximately 1.3. The diameter of the circular cross-section is 2. Therefore, the ratio of the side length of the square cross-section to the diameter of the circular cross-section is 1.3 / 2, which is approximately two-thirds. The side length of the square cross-section is the minimum cross-sectional width L1 and the surface width W1.

[0041] Similarly, the surface width W2 of the second Coanda surface 15, the radius of curvature at the maximum curvature R2, and the minimum cross-sectional width L2 of the secondary smoke and sand separation zone 19 are also set in the same way.

[0042] In this embodiment, the second Coanda surface 15 is located below the first Coanda surface 14, and a gap distance H is provided between the first Coanda surface 14 and the second Coanda surface 15. That is, H is the minimum distance between the first Coanda surface 14 and the second Coanda surface 15, which should satisfy D / 3≤H≤2D / 3. Since the gap between the first Coanda surface 14 and the second Coanda surface 15 is the node where the airflow completes the first deflection and enters the second deflection, in order to ensure that the airflow can smoothly enter the second deflection, a relatively small flow cross section needs to be set to temporarily increase the airflow velocity at this point. Therefore, the gap distance H is not higher than 2D / 3. At the same time, to ensure sufficient flow, the gap distance H is not lower than D / 3.

[0043] Please refer to Figure 2. In this embodiment, the smoke separation process of the smoke separation device is as follows: smoke enters the smoke separation device through the air inlet 11. The smoke that is close to the first Coanda curved surface 14 will deflect to the left, and will also cause the smoke near the right side of the first Coanda curved surface 14 to flow to the left and enter the left area of ​​the second Coanda curved surface 15. Similarly, the smoke that is close to the second Coanda curved surface 15 will deflect to the right along the curved surface, and will also cause the smoke near the left side of the second Coanda curved surface 15 to deflect and flow together, and enter the lower right smoke channel 13 area, reaching the filter 21 and the air outlet 12.

[0044] When the dust reaches the primary dust-smoke separation zone 16 through the air inlet 11, only a small portion of the lighter dust will deflect to the left along the first Coanda surface 14 and the smoke path. Most of the dust will continue to flow downward in the primary dust-smoke separation zone 16, fall into the dust trough 17 and slide into the first dust chamber 18. When the lighter dust that deflects to the left reaches the secondary dust-smoke separation zone 19, only a small amount of extremely light dust can deflect again and flow to the lower right. Most of the lighter dust falls directly downward into the second dust chamber 20 in the secondary dust-smoke separation zone 19, thus achieving dust-smoke separation. The small amount of extremely light dust is filtered by the filter 21, and only smoke reaches the air outlet 12. The smoke that reaches the air outlet 12 enters the smoke detection chamber labyrinth 3 under the negative pressure of the air pump 6 and is monitored.

[0045] This embodiment provides a set of actual product size settings for the smoke and sand separation device. The air inlet 11 is a conical interface with an innermost inner diameter of 24.0 mm, an outermost inner diameter of 25.5 mm, and an interface length of 20 mm to facilitate tight insertion of a standard 25 mm outer diameter plastic sampling tube. The air outlet 12 has the same size settings as the air inlet 11.

[0046] The first Konda surface 14 has a surface width of 20mm and a maximum radius of curvature of 40mm, and the first-level tobacco and sand separation zone 16 has a minimum cross-sectional width of 25mm.

[0047] The second Coanda surface 15 has a surface width of 20mm and a maximum radius of curvature of 40mm, and the secondary tobacco and sand separation zone 19 has a minimum cross-sectional width of 23mm.

[0048] The gap between the first Coanda surface 14 and the second Coanda surface 15 is 10mm.

[0049] In this embodiment, the two raised curved surfaces set in the internal channel of the smoke and dust separation device utilize the Coanda effect to deviate the fluid from its original flow direction and instead flow along the convex object surface. The direction of fluid flow bends with the curved surface. On curved surfaces within the same radius of curvature, the flow direction bending effect of fluids with higher viscosity flowing on the object surface is more pronounced. The viscous force of the fluid is a shear stress generated by the internal friction between molecules. When the fluid flows close to the surface, the fluid layer near the surface experiences surface resistance, resulting in a decrease in flow velocity, while the fluid layer farther from the surface has a higher flow velocity. At the same time, this flow direction bending is the result of the combined action of viscous force, fluid gravity, and fluid inertial force. This embodiment utilizes the significant difference in viscous force, gravity, and inertial force between smoke and dust, resulting in a large difference in flow direction bending, to achieve the separation of smoke and dust.

[0050] Specifically, in this embodiment, since smoke and dust have a certain viscosity, their hydrodynamic properties can be analyzed and described using the Navier-Stokes equations, ignoring the compressibility of the gas. The equations are as follows:

[0051] ρ( V / t+V· V)= - p+μ ²v+f ;(1)

[0052] Where ρ is the fluid density; V is the fluid velocity vector; t is time; p is pressure; μ is the dynamic viscosity coefficient; and f is the external force density.

[0053] Based on the conservation of momentum in fluid mechanics, the left side of equation (1) represents the inertial force of the airflow, where ρ( V / t) represents local acceleration, which in this embodiment is mainly represented by centrifugal force, expressed as FR=ρV² / R, where R is the radius of curvature of the Coanda surface; ρ(V· V) is the convection term, representing convective acceleration. Let be the gradient operator. On the right side of equation (1), we have, in order, the pressure gradient, the viscous force (internal friction), and the external force (gravity); where, - p represents the pressure gradient term, with the negative sign indicating that the force points in the direction of decreasing pressure. In this embodiment, the pressure gradient force comes from the negative pressure generated by the intake pump 6 connected to the outlet 12. It is the main driving force for the airflow to move from the high-pressure area to the low-pressure area, and also the main source of the force that achieves the Coanda deflection effect; μ ²v represents the viscous force term, which manifests as the internal friction force generated by the viscosity of the airflow. ² is the Laplace operator. In this embodiment, the viscous force term is represented by the rate of change of the velocity gradient generated by the viscous force of the airflow in the normal direction of the Coanda surface. It describes the momentum component existing in the normal direction of the surface due to the momentum diffusion caused by viscosity. It is the main force that generates the Coanda effect and one of the main forces that separate sand and dust. f is the external force density, which in this embodiment is mainly represented by gravity and is also the main force that separates large sand and dust particles and causes them to fall into the sand and dust chamber.

[0054] Please refer to Figure 3. According to the analysis and description of equation (1), the force situation of the air mass close to the Coanda surface is shown in Figure 3. p represents the pressure gradient generated by the suction pump 6 connected to the smoke and sand separation device; mg represents the gravity of the air mass; FR represents the inertial force. Since the airflow velocity in this embodiment is not high, the calculated Reynolds number Re is less than 1500, indicating laminar flow. Therefore, the force generated by the convection term is negligible. In this invention, FR is mainly centrifugal force; Fr represents the velocity gradient force generated by the velocity gradient in the normal direction due to viscous force; in the pressure gradient... The combined force of p, inertial force FR, gravity mg, and viscous force Fr causes the incoming airflow to deflect.

[0055] Please refer to Figure 4. Based on the deflection of the airflow, the separation of smoke and dust in the airflow is achieved. This embodiment describes the derivation of the velocity gradient force of the airflow.

[0056] Specifically, in Figure 4, arrow r represents the normal direction of the Coanda surface, and V1, V2, V3, and V4 are the tangential velocities of the Coanda surface as it moves from near to far away from the surface. Due to the viscosity of the airflow, the airflow velocity directly against the Coanda surface is close to 0. The airflow velocity gradually increases from near to far away from the Coanda surface due to the viscous internal friction (but stops changing after a certain point away from the Coanda surface). Therefore, in Figure 4, V1 < V2 < V3 < V4, thus forming a velocity gradient in the normal direction of the Coanda surface, represented as: Vr= V / R; combined with equation (1), the viscous force term μ ²v is typically represented using the internal frictional stress tensor τ generated by viscous forces: τ = µdV / dy, where μ is the gas viscosity coefficient; therefore, in this embodiment, τ = µ V / R;

[0057] in, V / R represents the rate of change of velocity along the normal direction of the Coanda surface, also known as the velocity gradient. Further variations of this equation involve dividing both the numerator and denominator by the change in time. t,

[0058] τ=µ V / R=µ( V / t) / ( R / t);

[0059] Where the partial derivative of velocity V with respect to time is the rate of change with time, which is acceleration; the rate of change of displacement along the normal direction of the Coanda surface with time is velocity, therefore, a = V / t, Vr= R / Substituting t into the above equation: τ = µa / Vr;

[0060] Multiplying the numerator and denominator by the gas mass m, the numerator and denominator become the tangential stress and the normal momentum, respectively:

[0061] τ=µa / Vr = µma / mΔVr = µF / p;

[0062] Where momentum p can also be expressed as impulse of force, FrΔt=Δp or FrΔt=mΔVr=m(Vr2-Vr1), then:

[0063] τ = µF / FrΔt;

[0064] Fr = µF / (τΔt);

[0065] Therefore, the viscous force tensor τ is directly proportional to the tangential internal frictional stress F and inversely proportional to the normal gradient force Fr. Fr is the equivalent force of the velocity gradient along the normal direction, called the velocity gradient force. Fr is proportional to the tangential viscous force (internal frictional resistance of the airflow) and the viscosity coefficient. The greater the airflow viscosity, the greater the normal Fr force. It is precisely because of the existence of the normal velocity gradient force counteracting the centrifugal force of the airflow mass near the Coanda surface that airflow deflection occurs.

[0066] When the airflow leaves the Coanda surface, it continues to move in the direction of deflection due to inertia. In the above formula, Δt represents a small segment of time during which the airflow continues to deflect, which is clearly inversely proportional to the airflow velocity. The higher the velocity, the shorter the time Δt is maintained, and the larger Fr is. However, the higher the airflow velocity, the greater the centrifugal force, and the easier it is for the airflow to deviate from the direction of deflection. Therefore, the maximum angle of airflow deflection along the Coanda surface is related to the velocity, and the Coanda effect is not necessarily more pronounced with higher velocity.

[0067] Based on the above principle, the Coanda effect is caused by the pressure gradient force. The Coanda effect is caused by the combined effects of the air mass's gravity (mg), inertial centrifugal force (FR), and viscous force leading to a velocity gradient force (Fr) in the normal direction. Gravity and centrifugal force have a side effect on the Coanda effect, forcing the airflow away from the Coanda surface, while viscous force keeps the airflow close to the Coanda surface, making it the primary force generating the Coanda effect. The pressure gradient, used to generate airflow velocity, affects both smoke and dust and will not be analyzed.

[0068] Under standard atmospheric pressure, 25°C, and 40% relative humidity, the air density ρ = 1.2 kg / m³, and the density of smoke is close to that of air. However, the density of dust is much greater than that of smoke. Therefore, the gravitational force on dust is much greater than that on smoke. When flowing below the Coanda surface, the dust is difficult to deflect due to the immense gravitational force. Even the relatively low-density dust has a density much greater than that of smoke. Near the lower surface of the Coanda surface, the centrifugal force and gravity of dust are also much greater than those of smoke. When flowing past the lower surface of the Coanda surface, the dust is located on the periphery of the surface. The two-stage Coanda surface structure in this embodiment will separate most of the dust. From a viscous force perspective, smoke is formed by the smoldering of substances, containing a large amount of volatile organic compounds. These substances mixed in the smoke make the viscous force of the smoke greater than that of the dust, making it easier to produce the Coanda effect and thus more easily deflected and flow along the surface of the Coanda surface.

[0069] Ultimately, due to its high viscosity, low specific gravity, low inertia, and low centrifugal force, the smoke undergoes a large deflection angle after passing through the Coanda surface and flows out from the position close to the Coanda surface. On the other hand, due to its low viscosity, high specific gravity, high inertia, and high centrifugal force, the dust undergoes a small deflection angle after passing through the Coanda surface, or even no deflection at all, and is deposited at the dust chamber and collected instead of flowing through the smoke's airflow channel.

[0070] Compared with the traditional air-suction filter, the main advantages of the smoke and sand separation device in this embodiment are:

[0071] Extending the lifespan of the suction pump 6: As a key component of the aspirating smoke detector, the suction pump 6 continuously draws gas from the sampling tube 1 into the smoke detection chamber labyrinth 3 for monitoring. Therefore, the lifespan of the suction pump 6 directly affects the product's lifespan. If large, heavy dust particles enter the suction pump 6, they will impact the high-speed rotating impeller blades, affecting the fan's lifespan. Furthermore, excessive dust deposition on the impeller will affect its balance, consequently impacting the bearing's stress balance, accelerating bearing wear, and shortening the fan's lifespan. By having the airflow pass through a smoke and dust separation device before entering the suction pump 6 to separate the dust, the lifespan of the suction pump 6 will be extended.

[0072] Improving detection sensitivity: Because sand and dust are relatively heavy, they are more likely to deposit on the inner surface of the smoke detection chamber labyrinth 3, causing the originally blackened surface to turn grayish-white, increasing the diffuse scattering level and reducing detection sensitivity; Before the airflow enters the smoke detection chamber labyrinth 3, the sand and dust are separated by the smoke and dust separation device, which greatly reduces the deposition of sand and dust on the inner wall of the detection chamber, delays the contamination of the smoke detection chamber labyrinth 3 by dust, not only extending the life of the smoke detection chamber labyrinth 3, but also improving detection sensitivity.

[0073] Traditional filters are quite thick, which increases airflow resistance and affects the airflow velocity in the sampling tube, thus prolonging the alarm time or shortening the effective tube length. On the other hand, because large, heavy dust particles follow the same path as smoke, as dust accumulates in the filter medium, air permeability decreases, air resistance increases, affecting the smoke detection response time. Severe blockage can prevent smoke from passing through, causing smoke detection to fail. The smoke and dust separation device uses a dust separation method, preventing dust from entering the smoke path, significantly improving the impact of the filter medium on smoke detection and airflow.

[0074] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A smoke and sand separation device for an aspirating smoke detector, characterized in that, The system includes a main body and a top cover. The main body has an air inlet and an air outlet at each end. A smoke passage for smoke flow is provided between the air inlet and the air outlet. A first Coanda surface and a second Coanda surface are respectively provided on both sides of the smoke passage. The first Coanda surface is closer to the air inlet, and the second Coanda surface is closer to the air outlet, with a gap between them. The cavity between the first Coanda surface and the opposite sidewall of the smoke passage forms a primary smoke-dust separation zone. The second Coanda surface is located below the primary smoke-dust separation zone, and a dust groove is formed at the top of the second Coanda surface. The bottom of the dust groove is connected to the smoke passage... The first dust chamber outside the flue is connected; the minimum cross-sectional width of the primary dust separation zone is not less than two-thirds of the inner diameter of the air inlet; the cavity between the second Coanda surface and the opposite sidewall of the flue gas passage constitutes the secondary dust separation zone, the first Coanda surface is located above the secondary dust separation zone, and the second dust chamber is located below the secondary dust separation zone. The second dust chamber is located outside the flue gas passage and is connected to the flue gas passage; the minimum cross-sectional width of the secondary dust separation zone is not less than two-thirds of the inner diameter of the air inlet; the minimum distance between the first Coanda surface and the second Coanda surface is not less than one-third of the inner diameter of the air inlet and not more than two-thirds of the inner diameter of the air inlet.

2. The smoke and sand separation device for an aspirating smoke detector according to claim 1, characterized in that, The bottom of the sand and dust trough is set as a plane and is inclined towards the side closer to the first sand and dust chamber. The angle between the bottom plane of the sand and dust trough and the side should not be less than 120°.

3. The smoke and sand separation device for the aspirating smoke detector according to claim 1, characterized in that, The air outlet is located below the second Coanda curved surface, and a filter is provided at the upper end of the air outlet.

4. The smoke and sand separation device for an aspirating smoke detector according to claim 1, characterized in that, The width of the first Coanda surface and the second Coanda surface is not less than two-thirds of the inner diameter of the air inlet.

5. The smoke and sand separation device for an aspirating smoke detector according to claim 1, characterized in that, The radius of curvature at the point of maximum curvature of the first Coanda surface is not less than twice the surface width; the radius of curvature at the point of maximum curvature of the second Coanda surface is not less than twice the surface width.

6. The smoke and sand separation device for an aspirating smoke detector according to claim 1, characterized in that, The main body is a cuboid structure with a cavity, and the main body is sealed to the upper cover.

7. The smoke and sand separation device for an aspirating smoke detector according to claim 1, characterized in that, Both the first and second sand and dust chambers are connected to the main body via threads.

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