Fire detector

Abstract

To obtain a fire detector equipped with a structure that can suppress the adhesion of dust and other particles to the light-receiving glass surface. [Solution] The fire detector according to this disclosure is a fire detector in which a light-receiving element for fire detection is arranged inside a convex light-receiving glass, wherein dimples are formed on the surface of the convex light-receiving glass, and by forming dimples on the surface of the light-receiving glass 20 and intentionally making the surface shape rough, air resistance can be reduced, and wind containing dust and the like can be easily deflected along the surface of the light-receiving glass.

Description

Technical Field

[0001] The present disclosure relates to a fire detector that detects the occurrence of a fire by detecting radiated light such as ultraviolet rays and infrared rays emitted from a flame with a light-receiving element disposed inside a light-receiving glass.

Background Art

[0002] Conventionally, in cases where a tunnel is set as a fire monitoring area or the like, radiation-type fire detectors have been widely used. In this radiation-type fire detector, a light-receiving element for fire detection is disposed inside a convex light-receiving glass.

[0003] However, as time elapses after the installation of the fire detector, the light-receiving glass that protects the light-receiving element may be contaminated by the influence of dust and the like contained in the outside air, and the light transmittance may gradually decrease.

[0004] As a result, the amount of light received by the light-receiving element decreases, which may lead to the inability to perform accurate fire detection. For this reason, especially when used in a harsh environment such as a tunnel, it is necessary for workers to periodically clean the surface of the light-receiving glass.

[0005] Some advanced fire detectors are designed to allow an operation test to confirm whether the fire detector performs normal detection operation, by turning on a test light-emitting element as a pseudo flame installed on the side of the light-receiving glass, and causing the light of the pseudo flame to act on the light-receiving element through the light-receiving glass.

[0006] Furthermore, regarding the convex light-receiving glass, as a conventional technique for preventing adhesion of dirt due to dust or the like, a design for moderating the rising angle of the light-receiving glass is known (for example, refer to Patent Document 1). Specifically, in the fire detector according to Patent Document 1, the rising angle of the light-receiving glass is changed from the conventional about 70 degrees to 40 degrees to 50 degrees.

[0007] This structure allows airflow to easily follow the light-receiving glass surface, preventing dust and other particles from colliding with it and suppressing the progression of contamination. As a result, it becomes possible to extend the cleaning interval of the light-receiving glass surface. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2000-215362 [Overview of the project] [Problems that the invention aims to solve]

[0009] In environments such as highway tunnels, passing vehicles stir up dust, and the dust carried by the airflow tends to adhere to convex light-receiving glass. In such environments, a structure is required that can suppress dust adhesion to the light-receiving glass surface, regardless of whether the angle of the light-receiving glass is gentle or not.

[0010] This disclosure is made to solve the above-mentioned problems and aims to provide a fire detector equipped with a structure that can suppress the adhesion of dust and other particles to the light-receiving glass surface. [Means for solving the problem]

[0011] The fire detector relating to this disclosure is a fire detector in which a light-receiving element for fire detection is arranged inside a convex light-receiving glass, and the light-receiving glass has dimples formed on its convex surface. [Effects of the Invention]

[0012] According to this disclosure, it is possible to obtain a fire detector equipped with a structure that can suppress the adhesion of dust and other particles to the light-receiving glass surface. [Brief explanation of the drawing]

[0013] [Figure 1] This is an explanatory diagram showing the general configuration of a conventional fire detector. [Figure 2] This is an explanatory diagram showing the detection area by the light-receiving element mounted on the fire detector shown in Figure 1. [Figure 3] This is an explanatory diagram showing the schematic configuration of a fire detector according to Embodiment 1 of the present disclosure. [Figure 4] This diagram illustrates the effects of forming dimples on the surface of the light-receiving glass in the fire detector according to Embodiment 1 of this disclosure. [Figure 5] This is an explanatory diagram relating to the shape of dimples formed on the light-receiving glass of a fire detector according to Embodiment 1 of the present disclosure. [Modes for carrying out the invention]

[0014] Hereinafter, preferred embodiments of the fire detector of this disclosure will be described with reference to the drawings. The fire detector described herein is characterized by its technical features, which include forming dimples on the surface of the light-receiving glass covering the light-receiving element, thereby reducing air resistance by intentionally creating an uneven surface shape and preventing dust and other particles from adhering to the glass surface.

[0015] In particular, when fire detectors are installed in tunnels, forming dimples on the surface of the light-receiving glass can reduce air resistance caused by wind (airflow) that occurs along the direction of vehicle travel. As a result, the adhesion of dust and other particles to the light-receiving glass surface can be suppressed, and the cleaning interval of the light-receiving glass surface can be extended.

[0016] In the following Embodiment 1, we will first describe a typical conventional fire detector in which a light-receiving element for fire detection is arranged inside a convex light-receiving glass, using Figures 1 and 2. Then, we will describe the technical features of the fire detector according to this disclosure using Figures 3 to 5.

[0017] Embodiment 1. Figure 1 is an explanatory diagram showing a schematic configuration of a conventional fire detector. Further, Figure 2 is an explanatory diagram showing a sensing region by a light-receiving element mounted on the fire detector shown in Figure 1.

[0018] As shown in Figure 1, the fire detector is configured to include a left flame detector 10L and a right flame detector 10R. When installed on a tunnel wall surface, as shown in Figure 2, the left flame detector 10L can monitor the left region at its own installation position, and outputs a left flame detection signal when the occurrence of flame is detected in the left region.

[0019] Similarly, the right flame detector 10R can monitor the right region at its own installation position, and outputs a right flame detection signal when the occurrence of flame is detected in the right region.

[0020] The left flame detector 10L and the right flame detector 10R correspond to the fire detection light-receiving element 10. The left flame detector 10L and the right flame detector 10R corresponding to the light-receiving element 10 are covered by a convex light-receiving glass 20.

[0021] For example, the fire detector having such a configuration is installed at a plurality of predetermined different positions in the longitudinal direction of a tunnel that is a fire monitoring target. Each of the plurality of fire detectors monitors the presence or absence of flame occurrence at its own installation position, and when a flame is detected, outputs either one or both of the left flame detection signal and the right flame detection signal according to the detection result.

[0022] Note that Figure 2 shows a form in which the fire detector is installed exposed to the tunnel wall surface, but as an installation form, there is also a case where only the light-receiving glass 20 is exposed from the tunnel wall surface, and the fire detector main body is embedded and installed in the tunnel wall surface.

[0023] As described at the beginning, particularly when the inside of a tunnel is set as a fire monitoring area, dust is stirred up by passing vehicles, and the dust carried by the airflow generated in the tunnel drifts, making dust easily adhere to the surface of the convex light-receiving glass 20.

[0024] Therefore, a key technical feature of the fire detector according to this embodiment 1 is that it has a structure that makes it difficult for dust and other particles to adhere to the surface of the convex light-receiving glass 20. This technical feature will be explained in detail with reference to the drawings.

[0025] Figure 3 is an explanatory diagram showing the schematic configuration of a fire detector according to Embodiment 1 of the present disclosure. The fire detector according to Embodiment 1 shown in Figure 3, like the conventional fire detector shown in Figure 1, has a left flame detector 10L and a right flame detector 10R, which are light-receiving elements for fire detection, arranged inside a convex light-receiving glass 20.

[0026] However, in the fire detector according to this embodiment 1, a plurality of dimples 21 are formed on the surface of the convex light-receiving glass 20. By forming dimples 21 on the surface of the light-receiving glass 20, wind resistance can be reduced. As a result of being less susceptible to wind resistance, the surface of the light-receiving glass 20 is less likely to be affected by wind containing dirt, thereby reducing the adhesion of dust and other particles.

[0027] More specifically, the formation of the dimples 21 increases the frictional resistance on the surface of the light-receiving glass 20, while simultaneously decreasing the pressure resistance. This allows air to flow more easily backward along the light-receiving glass 20, better deflecting air containing dust and other particles, thus reducing the adhesion of dust and other particles.

[0028] Therefore, using Figure 4, the effects of forming the dimples 21 will be explained in detail from the viewpoint of frictional resistance and pressure resistance. Figure 4 is an explanatory diagram of the effects of forming dimples 21 on the surface of the light-receiving glass 20 in a fire detector according to Embodiment 1 of this disclosure.

[0029] In Figure 4, Figure 4(A) summarizes an explanatory diagram of a conventional fire detector without dimples 21, and Figure 4(B) summarizes an explanatory diagram of the fire detector according to this embodiment 1, in which dimples 21 are formed, showing a comparison of the differences between the two.

[0030] In particular, when a fire detector is installed in a nearly enclosed space such as a tunnel, an airflow is generated in the same direction as the vehicle traveling through the tunnel. The generated airflow collides with the surface of the convex-shaped light-receiving glass 20, creating air resistance, and flows along the surface of the light-receiving glass 20 from upwind to downwind.

[0031] Air resistance can be divided into two types: frictional resistance and pressure resistance. Frictional resistance: Air resistance due to friction between the airflow and the surface of the light-receiving glass 20. Pressure resistance: Air resistance caused by the separation of airflow from the surface of the light-receiving glass 20.

[0032] Here, airflow separation refers to the phenomenon in which, in a flow with a reverse pressure gradient (a flow where the pressure increases in the direction of flow), the boundary layer flow cannot resist the pressure, stops or reverses, and peels away from the surface of the light-receiving glass 20.

[0033] In a tunnel, frictional resistance is inevitable because air is constantly flowing. On the other hand, pressure resistance can be reduced by suppressing air separation. Therefore, in this embodiment 1, we considered a shape that would reduce the pressure resistance generated on the surface of the light-receiving glass 20.

[0034] One method for reducing the pressure resistance generated on the surface of the light-receiving glass 20 is to prevent the airflow on the surface of the light-receiving glass 20 from separating, or in other words, to prevent the flow from peeling off the surface of the light-receiving glass 20.

[0035] After various studies, it was found that the overall air resistance could be reduced by changing the surface shape of the light-receiving glass 20. Specifically, by forming multiple dimples 21 on the surface of the light-receiving glass 20 and making the surface rougher, air resistance was reduced compared to when there were no dimples 21.

[0036] This explains why forming dimples 21 on the surface of the light-receiving glass 20 to roughen the surface shape reduces air resistance. When the surface of the light-receiving glass 20 becomes rough, the airflow on the surface becomes turbulent rather than laminar.

[0037] The airflow on the surface becomes turbulent, and the resulting disturbance causes the faster flow on the outside of the boundary layer to mix with the slower flow near the surface of the light-receiving glass 20. As a result, energy exchange occurs between the fast and slow flows.

[0038] As a result of this energy exchange, the airflow flowing over the surface of the light-receiving glass 20 is less likely to decelerate, allowing it to flow along the surface for a longer period, and making boundary layer delamination less likely.

[0039] This phenomenon can be explained by comparing Figure 4(A) and Figure 4(B) as follows. Regarding energy exchange, the faster flow on the outside of the boundary layer and the slower flow near the surface of the light-receiving glass 20 mix, and energy exchange takes place between them. As a result, Figure 4(B) shows a more homogenized state of air vortices compared to Figure 4(A).

[0040] Regarding the delamination points, the delamination point PB in Figure 4(B) is closer to the installation surface 1 of the fire detector than the delamination point PA in Figure 4(A). This indicates that the formation of the dimple 21 causes delamination to occur closer to the base of the convex light-receiving glass 20, making it less prone to delamination.

[0041] Furthermore, due to the reduced likelihood of delamination through energy exchange, in Figure 4(B), compared to Figure 4(A), faster-moving air flows closer to the base of the light-receiving glass 20, and the velocity gradient becomes steeper. As a result, the frictional resistance is slightly greater in Figure 4(B) than in Figure 4(A). However, due to the effect of the dimples 21, the pressure resistance is smaller in Figure 4(B) than in Figure 4(A).

[0042] As a result, the total air resistance is smaller in Figure 4(B) than in Figure 4(A), and by adopting the light-receiving glass 20 in Figure 4(B) which has dimples 21, it is possible to realize a structure that can suppress the adhesion of dust and other particles to the surface of the light-receiving glass 20.

[0043] In other words, by forming the dimples 21, the frictional resistance of the surface of the light-receiving glass 20 increases slightly, but the pressure resistance is reduced, and the air is directed backward, making it possible to better deflect air containing dirt.

[0044] In Figure 4, as in Figure 2, there are cases where the fire detector is installed exposed to the tunnel wall and cases where the fire detector body is embedded in the tunnel wall, but in either case the airflow conditions are the same.

[0045] Finally, the shape of the dimples 21 will be described. Figure 5 is an explanatory diagram of the shape of the dimples formed on the light-receiving glass 20 of the fire detector according to Embodiment 1 of this disclosure. The upper part of Figure 5 shows two adjacent dimples 21 as enlarged views.

[0046] The shape of the dimples 21 formed on the surface of the light-receiving glass 20 can be defined by the following four parameters, as shown in the enlarged view of Figure 5. D: This value corresponds to the depth of the dimple and is defined as the distance from the surface of the light-receiving glass 20 to the bottom surface of the dimple 21.

[0047] L1: A value corresponding to the width of the dimple 21 on the surface of the light-receiving glass 20. L2: A value corresponding to the length on the surface of the light-receiving glass 20 between adjacent dimples 21. ΔL corresponds to L1 + L2 and is the pitch value of the adjacent dimple 21.

[0048] It is important to properly set these four parameters in order to reduce air resistance.

[0049] Furthermore, if fire detectors are installed in tunnels for a long period of time, dust and other debris may accumulate inside the dimples 21, potentially soiling the light-receiving glass 20. However, the light-receiving glass 20 is regularly cleaned to remove any dirt.

[0050] Therefore, it is appropriate to make the depth D of the dimple 21 shallow, and it is desirable that the depth D be smaller than the value of the opening L1. With such shallow dimples 21, even if dust accumulates, it is easy to remove the dust through cleaning.

[0051] Furthermore, the shape of the dimple 21 is not limited to a circle; even if a polygonal shape such as a hexagon or triangle is adopted, the effect of suppressing the adhesion of dust and other particles to the surface of the light-receiving glass 20 can be obtained. In addition, the shape of the dimple 21 may be an ellipse cut in half, which is the same shape as the light-receiving glass 20, or a shape with a gently curved surface, such as a part of a large circle that has been cut.

[0052] Furthermore, from the perspective of eliminating localized airflow turbulence and obtaining a stable effect, it is recommended to uniformly arrange the multiple dimples 21 on the surface of the light-receiving glass 20, similar to the dimples formed on the surface of a golf ball.

[0053] In particular, when fire detectors are installed inside tunnels, airflow tends to occur in a certain direction depending on the direction of vehicle travel. Therefore, in such installation environments, it is expected that the effect of further suppressing the adhesion of dust and other particles can be obtained by forming the dimples 21 on the surface of the light-receiving glass 20 uniformly along the direction of travel of vehicles traveling inside the tunnel.

[0054] As described above, according to Embodiment 1, dimples are formed on the surface of the light-receiving glass, intentionally making the surface shape rough. As a result, the air resistance of the air flowing over the surface can be reduced compared to when there are no dimples, allowing air to flow more smoothly over a long distance along the surface, and a structure that suppresses the adhesion of dust and other particles to the light-receiving glass surface can be easily realized.

[0055] In particular, when a fire detector is installed in an environment where air flows in a specific direction, such as inside a tunnel, dust and other particles contained in the air can pass more smoothly over the surface of the light-receiving glass with lower air resistance, thus suppressing the adhesion of dust and other particles to the light-receiving glass surface. As a result, the cleaning interval for the light-receiving glass surface can be extended, reducing the workload.

[0056] Furthermore, the same effect can be achieved with existing fire detectors by replacing the light-receiving glass, which does not have dimples, with light-receiving glass that does have dimples.

[0057] Furthermore, in addition to the fire detector described in Patent Document 1, which has a configuration that makes the rising angle of the light-receiving glass gentler, a configuration that further forms dimples can also be used, which can further suppress the adhesion of dust and other particles to the light-receiving glass surface. [Explanation of symbols]

[0058] 1 Installation surface, 10 Light-receiving elements, 10R Right-side flame detector (light-receiving element), 10L Left-side flame detector (light-receiving element), 20 Light-receiving glass, 21 Dimple, PA, PB Detachment point.

Claims

1. A fire detector in which a light-receiving element for fire detection is arranged inside a convex light-receiving glass, The light-receiving glass has dimples formed on its convex surface. Fire detector.

2. The light-receiving glass has the dimples uniformly formed on the convex surface of the light-receiving glass. The fire detector according to claim 1.

3. The light-receiving glass is configured such that, when the fire detector is installed in a tunnel which is a fire monitoring area, the dimples are uniformly formed along the direction of travel of vehicles traveling through the tunnel. The fire detector according to claim 1.

4. The dimples are provided on the light-receiving glass surface to create turbulent airflow, thereby increasing frictional resistance, which is air resistance due to friction between the airflow and the surface of the light-receiving glass, and decreasing pressure resistance, which is air resistance caused by the separation of the airflow from the surface of the light-receiving glass, thereby reducing the overall air resistance. The fire detector according to claim 3.

Images