阅读说明：本技术 具有用于从管道中采样流体的管道探测器的管道传感器及操作方法 (Pipeline sensor having a pipeline probe for sampling a fluid from a pipeline and method of operation ) 是由 尼古拉斯·默勒 马克·霍尔农 斯特凡·蒂勒 帕特里克·莱登贝里耶 斯特凡·科斯特纳 于 2020-05-19 设计创作，主要内容包括：用于从管道(10)中的主要流体流(Fm)中采样流体的管道探测器(20)限定了伸长的供应通道(21)和伸长的排出通道(22)。供应通道具有至少一个流入开口(23),所述至少一个流入开口用于将部分流(Fp)从主要流体流转移到供应通道中；排出通道具有至少一个流出开口,所述至少一个流出开口用于在部分流已经经过环境传感器(30)之后使部分流从排出通道返回到主要流体流中。管道探测器还包括至少一个补偿开口(26),所述至少一个补偿开口在位于供应通道和排出通道的封闭端和开口端之间的区域中连接供应通道和排出通道。通过存在补偿开口(26),喷射流(Fj)被产生,当管道探测器暴露于主要流体流(Fm)时,喷射流用于减小供应通道与排出通道之间的压差。(A conduit probe (20) for sampling fluid from a main fluid flow (Fm) in the conduit (10) defines an elongate supply passage (21) and an elongate discharge passage (22). The supply channel has at least one inflow opening (23) for diverting a partial flow (Fp) from the main fluid flow into the supply channel; the discharge channel has at least one outflow opening for returning the partial flow from the discharge channel into the main fluid flow after the partial flow has passed the environmental sensor (30). The duct detector also includes at least one compensating opening (26) connecting the supply and discharge passages in a region between the closed and open ends of the supply and discharge passages. By the presence of the compensation opening (26), a jet flow (Fj) is generated, which serves to reduce the pressure difference between the supply channel and the discharge channel when the pipe probe is exposed to the main fluid flow (Fm).)

1. A pipe probe (20) for sampling a fluid from a main fluid flow (Fm) in a pipe (10),

the duct probe (20) defining an elongated supply channel (21) and an elongated discharge channel (22), the supply channel (21) and the discharge channel (22) extending substantially along a longitudinal axis (L) of the duct probe (20),

each of the supply channel (21) and the discharge channel (22) having a closed end and an open end, the open end being configured for direct or indirect connection to an environmental sensor (30),

the supply channel (21) having at least one inflow opening (23) for transferring a partial flow (Fp) from the main fluid flow (Fm) into the supply channel (21), and the discharge channel (22) having at least one outflow opening (24) for returning the partial flow (Fp) from the discharge channel (22) into the main fluid flow (Fm) after the partial flow (Fp) has passed the environment sensor (30),

the duct probe (20) comprising at least one compensation channel (26) connecting the supply channel (21) and the discharge channel (22) in a region between the closed end and the open end of the supply channel (21) and the discharge channel (22), respectively, in order to reduce a pressure difference (dp) between the supply channel (21) and the discharge channel (22) when the duct probe is exposed to a main fluid flow (Fm),

wherein the inflow opening (23) and the compensation channel (26) are arranged and dimensioned such that a jet flow (Fj) passes through the inflow opening (23), which jet flow is directed towards the compensation channel (26) and is decelerated when passing through the compensation channel (26).

2. The pipe probe according to claim 1, wherein the inflow opening (23) and the compensation channel (26) are arranged and dimensioned: -inducing the jet flow (Fj) by accelerating a portion of the main fluid flow passing through the inflow opening (23).

3. The duct detector (20) of claim 1 or 2, wherein the inflow opening (23) and the compensation channel (26) are aligned along a common injection axis (N).

4. The pipeline sonde (20) according to any of the preceding claims, wherein the inflow opening (23) has a first cross-sectional area (A1) and the compensating channel (26) has a second cross-sectional area (A2), the second cross-sectional area (A2) being greater than the first cross-sectional area (A1).

5. The pipe probe (20) of claim 4,

wherein the inflow opening (23) has a first hydraulic diameter D1, wherein the compensating channel (26) has a second hydraulic diameter D2, and wherein a downstream end of the inflow opening (23) and an upstream end of the compensating channel (26) are spaced apart by a distance W,

wherein the opening angle α is defined by the following equation:

and wherein the opening angle a is in the range of 2 ° to 4 °.

6. A duct probe (20) according to any of the preceding claims, wherein the duct probe comprises a partition wall (25) separating the discharge channel (22) from the supply channel (21), and wherein the compensation channel (26) is formed by a compensation opening in the partition wall (25).

7. A pipeline sensor comprising:

the pipe probe (20) according to any one of the preceding claims; and

an environmental sensor (30) for detecting the environmental conditions,

wherein the environment sensor (30) comprises a measurement channel (33) and a sensing element (31) arranged inside or near the measurement channel (33), the measurement channel (33) being directly or indirectly connected to an open end of the supply channel (21) and an open end of the discharge channel (22).

8. The duct sensor according to claim 7, wherein the environmental sensor (30) is a particulate matter sensor.

9. The duct sensor according to claim 7 or 8, wherein the environmental sensor (30) comprises a fan (34).

10. A method of operating a pipeline sensor according to any of claims 7 to 9, the method comprising:

arranging a pipe probe (20) of the pipe sensor in a pipe (10), a longitudinal axis (L) of the pipe probe (20) extending across a main flow direction of the pipe (10);

generating a main fluid flow (Fm) through the pipe (10) in the main flow direction, thereby passing a jet flow (Fj) through an inflow opening (23), which jet flow is directed towards a compensation channel (26) and is decelerated as it passes through the compensation channel (26); and

transferring the partial flow (Fp) from the inflow opening (23) into the supply channel (21), passing the partial flow (Fp) through the measurement channel (33), past the sensing element (31), and passing the partial flow (Fp) through the discharge channel (22) to the outflow opening (24).

11. Method according to claim 10, wherein the jet flow (Fj) is induced by accelerating a portion of the main fluid flow passing through the inflow opening (23).

12. Method according to claim 10 or 11, wherein the jet flow (Fj) has a maximum velocity which exceeds the average velocity of the main fluid flow (Fm) without the duct detector (20).

13. The method according to any one of claims 10 to 12, wherein the environmental sensor (30) is a particulate matter sensor, and wherein the method comprises using the particulate matter sensor to determine the particulate concentration and/or size distribution in the partial stream.

14. The method of any one of claims 10 to 13, wherein the environmental sensor (30) comprises a fan (34), and wherein the partial flow (Fp) is maintained by the fan (34).

Technical Field

The present invention relates to a pipe probe for sampling a fluid from a main fluid flow in a pipe, to a pipe sensor equipped with such a pipe probe, and to a method of operating such a pipe sensor.

Prior Art

From the prior art, pipeline probes are known for diverting a partial flow from a main fluid flow in a pipeline, passing the partial flow to a sensing element arranged outside the pipeline, and returning the partial flow to the pipeline after it has passed the sensing element. The pipe probe typically has a tubular shape defining a longitudinal axis extending perpendicular to the main fluid flow in the pipe. The pipeline probe defines two channels: a supply channel for passing the partial flow from the conduit to a sensing element outside the conduit; and a discharge channel for returning a partial flow from the sensing element to the conduit. Each of the supply and discharge passages is typically closed at one end located inside the duct and open at the other end located outside the duct. The open end is in fluid communication with the sensing element. In order to divert the partial flow from the pipe into the supply channel, one or more inflow openings are provided in the wall of the supply channel. Typically, but not necessarily, these inflow openings face the fluid flow in the pipe. Similarly, in order to return the partial flow to the main fluid flow, one or more outflow openings are provided in the wall of the discharge channel.

Examples of duct probes of various shapes and configurations are disclosed in US 2006/0027353 a1, US 2008/0257011 a1, US 2013/0160571 a1, US 2013/0255357 a1, EP 2835592 a1 and DE 102014010719 a 1.

In operation, the duct detector is arranged in the duct such that the main fluid flow impinges transversely on and bypasses the duct detector. Due to Bernoulli/Venturi effect (Bernoulli/Venturi effect), the resulting deflection of the main fluid flow will typically result in a positive back pressure at the inflow opening and a negative pressure at the outflow opening. Thereby, a pressure difference is created between the supply channel and the discharge channel, the magnitude of the pressure difference depending on the flow rate of the main fluid flow in the pipe. This pressure difference will in turn drive the partial flow through the pipeline probe, the flow rate of which strongly depends on the flow rate of the main fluid flow.

In some applications, it is desirable to minimize the pressure differential between the supply and discharge passages, or at least minimize the dependence of the pressure differential on the flow rate of the primary fluid flow. In particular, if the sensing element employs a particle counter, this is true because variations in the flow rate of the partial flow inevitably lead to undesirable variations in the number of particles passing through the particulate matter sensor per unit time. It may therefore be desirable to keep variations in the pressure difference between the inflow opening and the outflow opening to a minimum.

US 2005/0097947 a1 discloses a duct detector which forms a first passageway extending from an air inlet to an air outlet. The second passageway extends around the diverter plate to bypass the first passageway. An airflow measuring element is disposed in the second passage for measuring a flow rate of air passing through the second passage. If the airflow entering the duct detector contains a dust or liquid substance, the dust or liquid substance passes through the first passage and is prevented from entering the second passage. Thereby preventing dirt or liquid material from contaminating the airflow measuring device in the second passage. In an embodiment, a step is formed at a point where the first passage and the second passage meet, thereby increasing a cross section of the first passage thereat. Therefore, the dust or liquid substance contained in the air flow is temporarily caught at the stepped portion. In another embodiment, the flow distribution plate has an inclined portion that protrudes into the first passage and is inclined toward the air outlet. In yet another embodiment, the flow distribution plate has an inclined portion that protrudes into the first passage and is inclined toward the air inlet. The inclined portion has a through hole.

EP 3258241 a2 discloses a particulate matter sensor device comprising a flow channel extending between an inflow opening and an outflow opening, a radiation source and a radiation detector. A flow conditioning device is provided for reducing deposition of particulate matter onto a radiation source, radiation detector, or a channel wall in close proximity thereto.

Disclosure of Invention

It is an object of the present invention to provide a duct detector exhibiting: a reduced pressure difference between the supply channel and the discharge channel in the presence of the main fluid flow and/or a reduced dependence of the pressure difference on the flow rate of the main fluid flow.

This object is achieved by a duct detector according to claim 1. Further embodiments of the invention are given in the dependent claims.

Accordingly, a pipeline probe for sampling fluid from a main fluid flow in a pipeline is provided. The pipe probe defines an elongated supply passage and an elongated discharge passage extending substantially along a longitudinal axis of the pipe probe. In operation, the longitudinal axis of the pipe probe will advantageously extend across the primary fluid flow, preferably perpendicular thereto. Each of the supply channel and the exhaust channel has a closed end and an open end, the open end configured for direct or indirect connection to an environmental sensor. The supply channel has at least one inflow opening, preferably formed in a lateral peripheral surface of the supply channel (the term "lateral" is used with respect to the longitudinal axis of the duct probe), for diverting a partial flow from the main fluid flow into the supply channel. Likewise, the discharge channel has at least one outflow opening, which is preferably formed in a lateral peripheral surface of the discharge channel, for returning the partial flow from the discharge channel into the main fluid flow after the partial flow has passed the environmental sensor. According to the invention, the duct probe comprises at least one compensation channel connecting the supply channel and the discharge channel in a region between the closed end and the open end of the supply channel and the discharge channel, respectively, in order to reduce the pressure difference between the supply channel and the discharge channel when the duct probe is exposed to the main fluid flow.

The inflow opening and the compensation channel are arranged and dimensioned: the jet is directed towards the compensation channel by passing the jet through the inflow opening. When the duct detector is exposed to the primary fluid flow, a jet flow is generated, the inflow opening facing the primary flow or being oriented in some other way with respect to the primary flow, such that a portion of the primary fluid flow will enter the supply channel through the inflow opening. The portion of the main fluid flow passing through the inflow opening is accelerated to form a jet. As the jet passes through the compensating channel, the jet is decelerated. In other words, the maximum flow rate of the jet flow is higher upstream of the compensation passage (i.e., on the supply passage side) than downstream of the compensation passage (i.e., on the discharge passage side). The deceleration causes a negative pressure difference between the upstream side and the downstream side of the compensation channel, which counteracts a positive pressure difference caused by the back pressure at the inflow opening and the negative pressure due to the bernoulli/venturi effect at the outflow opening. By suitably selecting the dimensions of the inflow opening and the compensation channel, the injection flow can be tailored such that the negative pressure difference compensates for the positive pressure difference to such an extent that both the value of the pressure difference generated between the supply channel and the discharge channel and the dependency of the pressure difference on the flow rate of the main fluid flow are greatly reduced.

In order to ensure that the jet is directed towards the compensation channel, the inflow opening and the compensation channel are preferably aligned along a common jet axis. The injection axis preferably extends across the longitudinal axis of the pipe probe, in particular, perpendicular to the longitudinal axis. In use, the ejection axis may advantageously be arranged along the direction of the main fluid flow. In some embodiments, the outflow openings are also arranged along the same injection axis. This may simplify the manufacture of the pipe probe.

In order to decelerate the jet as it passes through the compensation channel, the free cross-sectional area of the compensation channel is preferably larger than the free cross-sectional area of the inflow opening. In addition, it is preferred that the outflow opening has a free cross-sectional area which is larger than or equal to the free cross-sectional area of the compensation channel in order to avoid an excessive flow resistance at the outflow opening.

In particular, assuming that the inflow opening and the compensation channel have a circular cross-sectional shape, a first geometric diameter D1 may be defined for the inflow opening and a second geometric diameter D2 may be defined for the compensation opening. Assuming further that the downstream end of the inflow opening and the upstream end of the compensating opening are spaced apart by a distance W, the opening angle α can be defined by the following equation:

the above definition of the opening angle can easily be generalized to the case where the inlet opening and the compensating channel do not have a circular cross-sectional shape, by replacing the geometrical diameters D1, D2 of the inlet opening and the compensating channel with the corresponding hydraulic diameters of the inlet opening and the compensating channel, D being defined as D-4A/P, where a is the cross-sectional area and P is the circumference of the opening/channel. For a circular cross-section, the hydraulic diameter is the same as the geometric diameter. It is advantageous if the opening angle thus defined is in the range of 2 ° to 4 °. This finding is independent of the exact cross-sectional shape of the inflow openings and the compensating channels, at least as long as the aspect ratio of each opening or channel is not too large. In the context of the present disclosure, the term "aspect ratio" should be understood in relation to the ratio between the longest diameter dimension and the shortest diameter dimension of the clear cross-section of an opening or channel,the term "diameter dimension" relates to the distance between two points on opposite sides of the perimeter of the net section through which a straight line passes through the geometric center (centroid) of the net section. For example, under this definition of the term "aspect ratio", the aspect ratio of a circle is 1: 1; for a square, the aspect ratio isAnd the like. In particular, the above-described preferred range of opening angles of 2 ° to 4 ° is expected to be effective at least as long as the aspect ratio is lower than about 2.5:1, for example, for a rectangle whose ratio between the long side and the short side is lower than about 2:1, a trapezoid whose average length-to-height ratio is between about 1:2 and about 2:1, an ellipse whose ratio between the long axis and the short axis is lower than 2.5:1, or the like. Ideally, the cross-sectional area of the inflow opening and the cross-sectional area of the compensation channel are selected and oriented such that the cross-sectional area of the compensation channel completely covers the cross-sectional area of the inflow opening in a projection along the injection axis. For larger aspect ratios, different opening angles may be optimal.

In some embodiments, the compensation channel is formed by a compensation opening in a partition wall common to both the supply channel and the discharge channel. In particular, the duct probe may have a tubular shape, preferably a cylindrical shape, and the duct probe may comprise a straight, flat partition wall separating the discharge channel from the supply channel within the duct probe. In other embodiments, the compensation channels may be formed in a different manner, for example, if the channels are formed by separate conduits, the compensation channels may be formed by short pipes between the supply channel and the discharge channel.

The pipeline probe may be supplemented by an environmental sensor to form a complete pipeline sensor. The environmental sensor may comprise a measurement channel and a sensing element within or adjacent to the measurement channel, the measurement channel being directly or indirectly connected to the open ends of the supply channel and the discharge channel of the duct probe. In this way, the partial flow entering the supply channel through the inflow opening flows through the supply channel into the measurement channel, past the sensing element, and from the measurement channel through the discharge channel into the outflow opening. The connection between the pipe probe and the environmental sensor may be direct, for example by mounting the sensor housing of the environmental sensor directly on the pipe probe, or the connection between the pipe probe and the environmental sensor may be indirect, for example via a rigid or flexible tube.

In particular, the environmental sensor may be a particulate matter sensor. In order to generate the partial flow at a defined flow rate, the environmental sensor may comprise a fan.

A method of operating such a duct sensor, the method may comprise:

arranging a pipe probe in the pipe, a longitudinal axis of the pipe probe extending across a main flow direction of the pipe;

generating a primary fluid flow through the conduit in a primary flow direction, thereby directing the jet flow through the inflow opening towards the compensation channel; and

the partial flow is diverted from the inflow opening into the supply channel, passed through the measurement channel, past the sensing element, and passed through the discharge channel to the outflow opening.

In particular, the duct sensor is operated under such conditions that: as the jet passes through the compensating channel, the jet is decelerated, i.e. has a higher maximum velocity upstream of the compensating channel than downstream of the compensating channel, in order to effectively reduce the pressure difference between the supply channel and the discharge channel. The jet stream is generated by accelerating the fluid passing through the inflow opening. In particular, it is advantageous for the jet flow to have a maximum velocity in the supply channel downstream of the inflow opening and upstream of the compensation channel, which exceeds the average velocity of the main fluid flow at the same location that would occur without the duct probe.

Advantageously, the fluid of the main fluid flow is a compressible fluid. Preferably, the fluid is a gas, in particular the fluid is air or an aerosol, i.e. a suspension of fine solid particles or liquid droplets in a gas such as air.

As already discussed, the environmental sensor may be a particulate matter sensor, and the method may include using the particulate matter sensor to determine the particulate concentration and/or size distribution in the partial flow. However, the environmental sensor may also be any other type of sensor for determining at least one characteristic of the partial flow, such as a gas sensor for determining the composition and/or concentration of one or more analyte gases in the partial flow, a humidity sensor, a temperature sensor, etc.

The environmental sensor may include a fan, and the method may include maintaining the partial flow using the fan.

Drawings

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, which are for the purpose of illustrating the presently preferred embodiments of the invention and are not for the purpose of limiting the same. In the drawings, there is shown in the drawings,

figure 1 shows in a highly schematic way a longitudinal section of a duct sensor comprising a duct probe according to the prior art;

FIG. 2 shows a two-dimensional graph illustrating simulated pressure distributions inside and outside the pipe probe of FIG. 1;

FIG. 3 shows a graph illustrating the variation of the pressure differential between the supply and exhaust passages of the duct probe of FIG. 1 with the flow rate of the main fluid flow in the duct;

figure 4 shows, in a highly schematic manner, a longitudinal section through a duct sensor comprising a duct probe according to the invention;

FIG. 5 shows a diagram illustrating the relative sizes of the inflow opening, the compensation opening and the outflow opening;

FIG. 6 shows a two-dimensional graph illustrating simulated pressure distributions inside and outside the pipe probe of FIG. 4;

FIG. 7 shows a graph illustrating the variation of the pressure differential between the supply and exhaust passages of the duct probe of FIG. 4 with the flow rate of the main fluid flow in the duct;

figure 8 shows in a highly schematic manner a front view of a portion of a duct detector with two inflow openings of different sizes and two associated compensation openings;

figure 9 shows in a highly schematic manner a front view of a portion of a duct detector with a slit-shaped inflow opening and an associated slit-shaped compensation opening;

figure 10 shows in a highly schematic manner a cross-sectional view of a pipe probe having a cylindrical shape and having a partition wall which divides the interior of the pipe probe into a supply channel and a discharge channel; and

figure 11 shows in a highly schematic way a cross-sectional view of a duct detector with an oval outer boundary and an inner two separate ducts forming a supply channel and a discharge channel.

Detailed Description

Fig. 1 shows in a highly schematic manner and not to scale a pipe sensor comprising a pipe probe 20 according to the prior art.

The environmental sensor 30 includes a sensor element 31 housed in a sensor housing 32. The sensor housing 32 defines a measurement channel 33, the sensor element 31 being arranged in the measurement channel 33 or in the vicinity of the measurement channel 33.

The environmental sensor 30 is arranged outside the pipe 10 carrying the main fluid flow Fm. The duct 10 is defined by a duct wall 11. The elongated duct probe 20 extends from the sensor housing 32 through a probe opening in the duct wall 11 to the interior of the duct 10. The duct detector 20 defines a longitudinal axis L extending perpendicular to the primary fluid flow Fm. Inside the pipe probe 20, the following two parallel channels extend along the longitudinal axis L: a supply channel 21 and a discharge channel 22. These passages are separated by a dividing wall 25. Each channel is closed at its respective end inside the pipe 10 and open at its respective end connected to an environmental sensor 30 outside the pipe 10. A lateral inflow opening 23 is present in the circumferential side wall of the supply channel 21, facing the main fluid flow Fm. In the circumferential side wall of the discharge channel 22 there is a lateral outflow opening 24. The outflow opening 24 is arranged downstream of the inflow opening 23 with respect to the main fluid flow Fm, facing away from the main fluid flow Fm.

At its open end, the supply channel 21 leads to a measuring channel 33. The measuring channel 33 in turn leads to the discharge channel 22. The measuring channel 33 forms the only connection between the supply channel 21 and the discharge channel 22. In particular, the supply channel 21 and the discharge channel 22 are not connected anywhere along the length of the duct probe 20 between their closed and open ends, i.e. the separation wall 25 does not have any openings.

In operation, the main fluid flow Fm in the pipe 10 impinges transversely on the pipe probe. The main fluid flow Fm generates a positive back pressure at the inflow opening 23 and a negative pressure at the outflow opening 24 due to the venturi/bernoulli effect. The pressure difference which is generated between the inflow opening 23 and the outflow opening 24 depends on the flow rate of the main fluid flow Fm.

Due to the pressure difference, a partial flow Fp is generated by the pipeline sensor. Part of the flow enters the supply channel 21 through the inflow opening 23. The partial flow Fp flows upwards through the supply channel 21 into the measuring channel 33, past the sensor element 31 and downwards through the discharge channel 22 and then leaves the pipe probe 20 at the outflow opening 24. The sensor element 31 detects one or more properties of the partial flow Fp. The flow rate of the partial flow Fp strongly depends on the pressure difference between the supply channel 21 and the discharge channel 22, which in turn strongly depends on the flow rate of the main fluid flow Fm.

FIG. 2 shows simulated pressure distributions inside and outside the pipe probe 10. The data shown in the figure were generated by numerical simulation of fluid dynamics using the software comsolmutiphysics version 5.4. The following assumptions were made in the simulation: the duct 10 has a square cross-section with a clear width of 120mm and a height of 100 mm. The pipe probe 20 has a circular cross-section with an outer diameter of 15mm and a wall thickness of 1.5 mm. Inside the duct probe, a straight, flat partition wall 25 of thickness 1.5mm separates the supply channel 21 from the discharge channel 22. The length of the portion of the pipe probe 20 extending inside the pipe is 50 mm. The inflow opening 23 has a circular shape with a diameter of 2.0 mm. The centre of which is located at a distance of 30mm from the wall of the tube. Also, the outflow opening 24 has a circular shape with a diameter of 2.0 mm; the centre of which is also located at a distance of 30mm from the pipe wall. The fluid used for the simulation was air under standard conditions (1013hPa, 20 ℃). The main fluid flow Fm is assumed to have a uniform flow velocity distribution at the inlet of the pipe, wherein the flow velocity is 12 m/s. A k-epsilon (k-epsilon) turbulence model was used. It is assumed that the flow resistance of the ambient sensor is substantially infinite, resulting in a negligible flow of the partial flow Fp.

The simulation results in fig. 2 show that a considerable pressure difference dp exists between the supply channel 21 and the discharge channel 22.

The simulation is repeated for different flows of the main fluid flow Fm, the flow velocity at the inlet of the pipe being in the range between 0 and 12 m/s. Fig. 3 shows that the pressure difference dp, which continuously and monotonically rises with increasing flow rate and approximately follows a quadratic function, strongly depends on the flow rate v of the main fluid flow Fm in the pipe 10. At a flow velocity of 6m/s, the pressure difference was about 32 Pa. At a flow rate of 12m/s, the pressure difference was approximately 130 Pa.

Such a strong dependence of the pressure difference on the flow rate of the main fluid flow Fm may be undesirable. This is particularly true in applications where the environmental sensor 30 is a particulate matter sensor for determining the concentration and/or size distribution of particulate matter in the primary fluid flow. A known type of particulate matter sensor is used as a particle counter, comprising a radiation source and a radiation detector. A radiation source, usually a laser, generates radiation in the measurement zone. The radiation is scattered by the particles entering the measurement zone. A radiation detector, typically a photodetector, records a single scatter event from a single particle. From the frequency of the scattering events and the flow through the measurement zone, the number concentration of particles can be inferred. From the intensity of each scattering event, the size of each particle can be inferred. By combining these two quantities, a measure of the mass concentration of the particles can be obtained. Since flow determines the number density, it is desirable to closely control the flow through the environmental sensor 30. However, the presence of a rather large and strongly varying pressure difference between the supply channel 21 and the discharge channel 22 makes it difficult to control the flow rate.

Fig. 4 shows a duct sensor according to an embodiment of the invention in a highly schematic manner and not to scale. The general arrangement of the duct sensor is similar to the prior art duct sensor of figure 1. Furthermore, the duct sensor comprises an environmental sensor 30, the environmental sensor 30 comprising a sensor element 31 and a sensor housing 32 defining a measurement channel 33 for the partial flow Fp. In the present example, the environmental sensor 30 further comprises a fan 34, which fan 34 is used to actively maintain the partial flow Fp through the measurement channel 33. However, in other embodiments, the fan may be omitted. Furthermore, in the present example, the sensor element 31 is arranged in the measurement channel 33 in the following manner: the partial flow Fp passes through the sensor element 31. However, in other embodiments, the sensor element 31 may be arranged adjacent to the measurement channel 33 such that part of the flow flows over the sensor element 31, as in the embodiment of fig. 1.

As in the prior art embodiment of fig. 1, the supply channel 21 and the discharge channel 22 extend along their longitudinal axis L inside the duct probe 20, these channels being parallel to each other and separated by a straight, flat, elongated partition wall 25. As in the prior art embodiment of fig. 1, each channel is closed at its respective end located inside the pipe 10, and is open at its respective end connected to the sensor housing 30 outside the pipe 10. As in the prior art embodiment in fig. 1, a lateral inflow opening 23 is present in the circumferential side wall of the supply channel 21 facing the main fluid flow Fm, and a lateral outflow opening 24 is present in the circumferential side wall of the discharge channel 22 downstream of the inflow opening 23.

In contrast to the prior art embodiment in fig. 1, the compensation channel 26 is present between the supply channel 21 and the discharge channel 22 in the region between their respective closed and open ends. The compensation channel 26 is formed by a compensation opening in a partition wall 25, which partition wall 25 separates the supply channel 21 from the discharge channel 22. The inflow opening 23 and the compensating channel 26 are aligned along a common injection axis. The injection axis extends perpendicular to the longitudinal axis L of the duct detector in the flow direction of the main fluid flow Fm. In this example, the outflow opening 24 is also aligned with the injection axis.

Due to the presence of the compensation channel 26, a jet flow Fj is generated through the inflow opening 23, which jet flow is directed towards the compensation channel 26. As the jet passes through the compensating channel 26, the jet decelerates, creating a negative pressure differential between the supply channel 21 and the discharge channel 22. This negative pressure differential counteracts the positive pressure differential caused by the primary fluid flow Fm as it strikes the pipe detector 20 and deflects around the pipe detector 20. Thus, the jet flow Fj serves to reduce the pressure difference between the supply channel 21 and the discharge channel 22 that would exist without the compensation channel 26. At the same time, the injection flow Fj reduces the dependency of the pressure difference on the flow of the main fluid flow Fm.

Simulations were performed to determine the expected velocity profile inside and around the pipe probe as shown in figure 4. The same assumptions are made in the simulations described above in connection with fig. 2. The simulation shows that: the jet flow Fj accelerates significantly as it passes through the inflow opening 23 and decelerates again as it passes through the compensating channel 26. The maximum flow rate of the jet flow Fj is much greater in the supply channel 21 upstream of the compensation channel 26 than in the discharge channel 22 downstream of the compensation channel 26. The maximum flow rate of the jet flow Fj is also significantly greater than the average flow rate of the main fluid flow Fm that would occur at the same location and at the same total flow through the pipe without the pipe probe.

In order to ensure that the flow rate of the jet flow Fj is greater on the upstream side of the compensation channel 26 than on the downstream side of the compensation channel 26, the cross-sectional area of the compensation channel 26 is advantageously greater than the cross-sectional area of the inflow opening 23. In addition, in order to avoid the outflow opening forming a bottleneck with an excessive flow resistance, the cross-sectional area of the outflow opening 24 is advantageously greater than or equal to the cross-sectional area of the compensation channel 26. This is shown by way of example in fig. 5. In this example, it is assumed that the inflow opening 23, the compensation channel 26 and the outflow opening 24 have a circular shape. The inflow opening 23 and the outflow opening 24 are each formed in the circumferential wall 27 of the duct detector; the compensation passage 26 is formed in the partition wall 25. The diameter of the inflow opening 23 is designated D1, the diameter of the compensating channel 26 is designated D2, and the diameter of the outflow opening 24 is designated D3. The corresponding cross-sectional areas are designated a1, a2, and A3, respectively. The width of the supply channel 21 measured along the injection axis N between the inflow opening 23 and the compensation channel 26 is designated W. In the present example, the discharge channel 22 has the same width W between the compensation channel 26 and the outflow opening 24. In order to decelerate the jet stream as it passes through the compensating channel 26, the cross-sectional area of the compensating channel 26 is slightly larger than the cross-sectional area of the inflow opening 23, i.e. D2 > D1. In the present example, the cross-sectional area of the outflow opening 24 is the same as the cross-sectional area of the compensation channel 26, i.e. D3 — D2.

Generally, among other things, the parameters D1, D2, D3 and W, etc. may be adjusted to optimize the dependence of the pressure difference between the supply channel 21 and the discharge channel 22 on the flow rate of the main fluid flow Fm. In order to more easily quantify the difference between the size of the inflow opening 23 and the compensation channel 26, which is independent of the absolute dimensions, a dimensionless opening angle α can be introduced, which is defined by the following relation:

instead of using the geometrical diameters D1 and D2, corresponding hydraulic diameters may be used.

In order to evaluate the effect of the jet flow Fj on the pressure difference between the supply channel 21 and the discharge channel 22, a simulation of the pressure distribution inside and around the pipe probe in fig. 4 was performed, again using the same assumptions as described above in connection with the simulation shown in fig. 2. The opening angle a is varied and the dependence of the pressure difference between the supply channel 21 and the discharge channel 22 on the flow rate of the main fluid flow Fm upstream from the pipe probe is evaluated for each opening angle. It has been found that an optimum value of the opening angle alpha is (2.7 + -0.3) °, resulting in a minimum variation of the pressure difference of the flow velocity between 0 and 12 m/s. While this result is obtained for the particular detector size discussed above in connection with fig. 2, it is expected that the result will only weakly depend on the absolute size of the detector, the precise shape of the detector, or the shape of the opening, as long as these variations are within reasonable limits. Of course, different opening angles may be optimal for pipe probes of entirely different geometries or for openings of entirely different shapes (e.g., narrow slits with large aspect ratios).

Fig. 6 shows a two-dimensional graph showing the resulting pressure distribution at an optimum opening angle of 2.7 deg. for a flow velocity of 12 m/s. As expected, there was little change in the pressure distribution compared to the graph outside the pipe probe in fig. 2. However, the pressure in the inflow opening decreases sharply (from almost +100Pa to about-10 Pa) due to the jet flow Fj. The pressure in the supply passage 21 is reduced from about +100Pa to about-6 Pa. On the other hand, the pressure in the discharge channel 22 rises again from about-27 Pa to about-6 Pa, which is also caused by the jet flow Fj. The total pressure difference generated between the supply channel 21 and the discharge channel 22 is almost zero.

Fig. 7 shows: for an optimized opening angle of 2.7 °, the simulated pressure difference dp between the supply channel 21 and the discharge channel 22 is dependent on the flow rate of the main fluid flow Fm upstream from the duct detector. The pressure difference never exceeds 1.7Pa for flow velocities between 0 and 12m/s, has a maximum at flow velocities of about 6m/s, and approaches zero at flow velocities of 12 m/s. This is in contrast to the simulated pressure differential of the conventional duct detector in FIG. 3, which rises sharply with increasing flow velocity and exceeds 120Pa at a flow velocity of 12 m/s. These simulation results show that a large reduction of the pressure difference and a large reduction of the dependency of the pressure difference on the flow of the main fluid flow Fm can be achieved with the present invention.

Although simulations have been made for a single inflow opening 23, a single outflow opening 24 and a compensation channel 26 in the form of a single compensation opening, each of these openings having a circular shape, different numbers and geometries of these openings are conceivable. This is shown by way of example in fig. 8 and 9.

Fig. 8 shows that more than one set of inflow openings and compensating channels can be provided. The groups may have different sizes. Thereby, the dependency of the pressure difference on the flow rate of the main fluid flow Fm can be further optimized. In the example of fig. 8, a first jet flow is generated through the first inflow opening 23 and the first compensation channel 26. A second jet is generated through the second inflow opening 23 'and the second compensation channel 26'. Due to the different sizes of the inflow opening and the compensation channel, the negative pressure difference caused by each jet will be different for the two jets. By dimensioning the inflow opening and the compensation channel, the dependency of the pressure difference between the supply channel and the discharge channel on the flow rate of the main fluid flow Fm can be optimized. The outflow openings are not shown in fig. 8. Instead of providing separate outflow openings for each set of first and second inflow openings and compensation channel, it is conceivable to provide a single common outflow opening.

Fig. 9 shows that the inflow opening, the outflow opening and the compensation channel may each have a cross-sectional shape other than circular. In the present example, the cross-sectional shape of the inflow opening and the cross-sectional shape of the compensation channel are slit-like and trapezoidal, the cross-sectional area of the compensation channel completely covering the inflow opening in projection along the common ejection axis. By optimizing the shape and size of the inflow opening and the compensation channel, the dependency of the pressure difference between the supply channel and the discharge channel on the flow rate of the main fluid flow Fm can again be optimized.

Of course, many other shapes of the inflow opening and the compensation channel are conceivable.

Although the simulations in the above examples were performed for a cylindrical pipe probe having a straight, flat dividing wall, different probe designs may be used. This is shown in fig. 10 and 11. In the embodiment of fig. 10, the duct detector has a circular cross-section and a straight, flat partition wall 25, in which partition wall 25 a compensation channel 26 in the form of a simple compensation opening is formed. The partial flow Fp through the supply channel 21 and the discharge channel 22 is indicated by a point in the small circle, which indicates the flow direction out of the plane of the drawing, and a cross in the small circle, which indicates the flow direction into the plane of the drawing. The jet flow Fj is indicated by an arrow drawn with a dashed line. In the embodiment of fig. 11, the pipe probe has an elliptical cross-section. Two parallel conduits are arranged within the pipe probe, forming a supply channel 21 and a discharge channel 22. The compensating channel 26 is formed by a stub 28 between the conduits. Many other detector designs are conceivable, including designs with more than one supply channel and/or more than one discharge channel.

Although in the embodiment of fig. 4 the environment sensor 30 is directly connected to the open ends of the supply channel 21 and the discharge channel 22, it is also conceivable to connect the environment sensor 30 to the duct detector 20 via a rigid or flexible tube.

The present invention is particularly advantageous if the environmental sensor 30 is a particulate matter sensor for determining the concentration and/or size distribution of particulate matter in the main fluid flow. However, the environmental sensor 30 need not be a particulate matter sensor. In other embodiments, the environmental sensor may be a gas sensor, humidity sensor, temperature sensor, or the like for determining the composition and/or concentration of one or more analyte gases in the primary fluid flow.

The present invention makes it possible to closely control the flow through the environmental sensor 30, for example by using an integrated fan, without the need to compensate for the pressure differential inside the duct detector resulting from the primary fluid flow.

List of reference numerals

10 pipeline 32 sensor housing

11 pipe wall 33 measurement channel

20 duct detector 34 fan

21 supply channel Fm main fluid flow

22 discharge channel Fp partial flow

23, 23' inflow opening Fj jet

Longitudinal axis of 24, 24' outflow opening L

25 dividing wall N injection axis

26, 26' offset channel A1, A2, A3 cross-sectional area

27 circumferential wall D1, D2, D3 diameter

Width of 28 tubes W

30 environmental sensor alpha opening angle

31 sensing element