System and manipulation path for monitoring the flow profile at the inlet of a flow sensor

Abstract

The invention relates to a manipulation path (1) for monitoring the flow profile at the inlet of a flow sensor. The manipulation path (1) is designed to conduct a fluid measuring medium, and the manipulation path (1) has a first end region (110) and a second end region (120), between which a manipulation section (130) is located that is designed such that secondary flows are formed in the measuring medium as a result of the measuring medium flowing through the manipulation section (130). The invention also relates to two different variants of a system, each variant comprising a flow sensor (2) and the manipulation path (3) according to the invention.

Description

[0001] System and manipulation section for controlling the flow profile at the inlet of a flow sensor

[0002] The invention relates to a manipulation section for controlling the flow profile at the inlet of a flow sensor. Furthermore, the invention relates to two different variants of a system, each comprising a flow sensor and the manipulation section according to the invention.

[0003] Flow sensors are used to determine the flow rate or flow velocity of a measuring medium or fluid, such as a gas, gas mixture, or liquid. There are various types of flow sensors, such as thermal flow sensors, Coriolis flow sensors, ultrasonic flow sensors, microwave flow sensors, etc.

[0004] Thermal flow sensors, for example, utilize the fact that a (flowing) measuring medium transports heat away from a heated surface. Thermal flow sensors typically consist of several functional elements, usually at least one low-resistance heating element and one high-resistance resistance element that serves as a temperature sensor. Alternatively, thermal flow sensors are constructed with several low-resistance heating elements as a heater and a temperature sensor.

[0005] The performance of flow sensors, especially thermal flow sensors, can depend on the inlet conditions of the measuring medium. For example, it makes a difference whether the measuring medium flows straight into the flow sensor or at a 90° angle. Depending on the inlet conditions, this can lead to a significant change in the measurement signal, which can result in significant inaccuracies in the application.

[0006] There are only a few ways to prevent this. The following are known from the current state of the art: The inlet of the flow sensor, or to the flow sensor, is designed as a long section. This allows the flow profile to fully develop along the section. However, this requires a lot of space.

[0007] The inlet section, e.g., designed as an inlet pipe, can have "dents" in the walls that cause the flow profile to become turbulent. This solution is used, for example, in the OmniFIN HFK35 from GMH Group - Honsberg. The disadvantage of this method is that the signal noise increases significantly.

[0008] Both solutions are therefore impractical for many applications.

[0009] Based on this problem, the invention is based on the object of minimizing the inlet dependence of a flow sensor.

[0010] The object is achieved by a manipulation path according to claim 1, by a system according to claim 5 and by a system according to claim 7.

[0011] With regard to the manipulation section, this serves to control the flow profile at the inlet of a flow sensor, wherein the manipulation section is designed to guide a fluid measuring medium, wherein the

[0012] Manipulation section has a first end region and a second end region, wherein a manipulation section is located between the first end region and a second end region of the manipulation section, which manipulation section is designed such that secondary flows form in the measuring medium by flowing through the section with the measuring medium.

[0013] The manipulation section is designed to create secondary flows, at least in the area of ​​the manipulation section. Secondary flow is defined as an additional flow in the plane perpendicular to the main flow direction at low velocity. This results in the flow profile being calmed and developing largely independently of the flow velocity. This increases the performance of the flow sensor and its dynamic range. Furthermore, the flow sensor's inlet dependence is drastically reduced. The other disadvantages listed in the introductory part of the description are reduced or completely eliminated.

[0014] According to an advantageous embodiment of the manipulation path according to the invention, the manipulation path is tubular, i.e., in the shape of a tube. In principle, any material can be used for this purpose, for example, a plastic or a metal.

[0015] A particularly advantageous embodiment of the manipulation path according to the invention provides that the manipulation path is curved helically in the manipulation section, with at least one full turn. It has been found that the helical shape offers an ideal balance between minimal space requirements and high efficiency in generating secondary currents.

[0016] An advantageous embodiment of the manipulation section according to the invention provides that the manipulation section has a tube diameter and a helix diameter, wherein the ratio of the tube diameter to the helix diameter is greater than 0.01. Such a ratio leads to an increase in the critical Reynolds number by a factor of two.

[0017] Alternatively, other configurations of the manipulation section are also provided that generate sufficient secondary flows. For example, instead of the tube being bent helically, a tube insert, for example, of a helical design, can be inserted into the tubular manipulation section.

[0018] Regarding the system, this includes in a first variant:

[0019] - A flow sensor for detecting at least one parameter relating to the flow velocity of a fluid measuring medium;

[0020] - A manipulation section according to the invention, wherein the second end region of the inlet pipe is connected to the inlet of the thermal flow sensor. In the first variant, the manipulation section is located upstream of the flow sensor. In particular, it consists of two separate components that are connected to one another.

[0021] According to an embodiment of the first variant of the system according to the invention, the system further comprises a primary pipeline through which the measuring medium flows, wherein the manipulation section is connected to the pipeline at the first end region, wherein an output of the flow sensor is connected to the pipeline.

[0022] Regarding the system, this includes in a first variant:

[0023] - A flow sensor for detecting at least one parameter relating to the flow velocity of a fluid measuring medium;

[0024] - A manipulation section according to the invention, wherein the flow sensor is integrated in the manipulation section and wherein the flow sensor is arranged between the end of the manipulation section and the second end region.

[0025] In the second variant, the flow sensor is located in the manipulation section.

[0026] According to an embodiment of the second variant of the system according to the invention, the system further comprises a primary pipeline through which the measuring medium flows, wherein the manipulation section is connected to the pipeline at the first end region, and wherein the manipulation section is connected to the pipeline at the second end region.

[0027] For both variants, the flow sensor and the manipulation section can be configured to form a bypass to the primary pipeline. This means that the medium flow through the primary pipeline is uninterrupted and that the measured medium flows parallel to the primary pipeline through the manipulation section and the flow sensor.

[0028] Alternatively, it is provided that the primary pipeline ends at the first end area of ​​the manipulation section and at the second end area of ​​the manipulation section, or at the outlet of the flow sensor (depending on the variant of the system), so that there is no parallel medium flow and the measuring medium flows exclusively through the manipulation section and the flow sensor.

[0029] According to one embodiment of the first or second variant of the system according to the invention, the flow sensor is a thermal flow sensor. Various variants of thermal flow sensors with different modes of operation and designs are known from the prior art:

[0030] Calorimetric thermal flow sensors determine the flow rate of the fluid in a channel by measuring a temperature difference between two temperature sensors located downstream and upstream of a heating element. This takes advantage of the fact that the temperature difference is linear with the flow rate up to a certain point. This method is extensively described in the relevant literature.

[0031] Anemometric thermal flow sensors consist of at least one heating element, which is heated during flow measurement. As the measured medium flows around the heating element, heat is transferred into the measured medium, which changes with the flow velocity. By measuring the electrical parameters of the heating element, the flow velocity of the measured medium can be determined.

[0032] Such an anemometric thermal flow sensor is typically operated in one of the following two control modes:

[0033] In the “Constant-Current Anemometry” (CCA) control mode, a constant current is applied to the heating element. The flow of the measuring medium around it changes the resistance of the heating element and with it the voltage drop across the heating element, which represents the measurement signal. The “Constant-Voltage Anemometry” (CVA) control mode works in a similar way, in which the heating element is subjected to a constant voltage. In the “Constant-Temperature Anemometry (CTA)” control mode, the heating element is kept at an averagely constant temperature. Using this control mode, relatively high flow velocities can be measured. Depending on the flow velocity, more or less heat is carried away by the flowing measuring medium and accordingly more or less electrical power must be supplied to keep the temperature constant. This supplied electrical power is a measure of the flow velocity of the measuring medium.

[0034] However, the system according to the invention can also be operated with other types of thermal flow sensors for which a flow profile that is stable over the flow velocity is advantageous. For example, other types of flow sensors can also be used, such as Coriolis flow sensors, ultrasonic flow sensors, or microwave flow sensors.

[0035] The invention is explained in more detail with reference to the following figures.

[0036] Fig. 1: a schematic representation of a structure of a manipulation path according to the invention and its use in an application;

[0037] Fig. 2: Measured values ​​of a thermal flow sensor for different inlet conditions, without using a manipulation section according to the invention and with using a manipulation section according to the invention; and

[0038] Fig. 3: Measured values ​​of a thermal flow sensor at different flow rates of the measuring medium, without using a manipulation section according to the invention and with using a manipulation section according to the invention.

[0039] Fig. 1 depicts a setup intended to improve the flow dependence of the inlet of a flow sensor 2. A manipulation section 1 is used. This section has a manipulation section 130, which manipulates a flowing measuring medium such that the dependence of the flow profile of the measuring medium at the inlet of the flow sensor 2 is essentially decoupled from the flow velocity over a wide range of values. In this case, the flow sensor 2 is a thermal flow sensor. However, other types of flow sensors can also be advantageously used.

[0040] For this purpose, the flow sensor 2 is connected to the manipulation section 1.

[0041] Either the inlet of the thermal flow sensor 2 is connected to a second end region 120 of the manipulation section 1. Alternatively, the thermal flow sensor 2 is part of the manipulation section 1 or integrated into it. This manipulation section-flow sensor assembly is then connected to a primary pipeline 3 through which the measuring medium flows.

[0042] It can be provided that the manipulation section-flow sensor assembly forms a bypass to the primary pipeline 3. This means that the medium flow through the primary pipeline 3 is not interrupted and that the measuring medium flows parallel to the primary pipeline through the manipulation section 1 and the flow sensor 2.

[0043] Alternatively, it is provided that the primary pipeline 3 ends at the first end region of the manipulation section and at the second end region of the manipulation section, or at the outlet of the flow sensor (depending on the variant of the system), so that there is no parallel medium flow and the measuring medium flows exclusively through the manipulation section 1 and the flow sensor 2.

[0044] One solution for a design of the manipulation section 130 is a helical curvature, as shown in Fig. 1. Experimental investigations have shown that the inlet dependence of a flow sensor 2 with such an upstream manipulation section as the inlet section is massively reduced compared to conventional flow sensors.

[0045] Fig. 2 shows test data that was collected for this purpose. Diagrams (a) and (b) represent a curve of the current measured values ​​of flow sensor 2 (in mW, y-axis) over time (in seconds, x-axis). The flow rate of the measuring medium is kept constant. The inlet condition of the measuring medium in flow sensor 2 is changed several times over time. For this purpose, the end section of the pipeline is changed, which is directly connected to the flow sensor (diagram (a)) or to the manipulation section (according to Fig. 1 , diagram (b)). In the two time intervals “2” a lateral, “S”-shaped inlet is used. In time interval “3” an angled inlet with a 90” curve is used. In time interval “4” an “S”-shaped inlet from below is used. In time interval “X” the inlet is constantly changed manually.

[0046] Diagram (a) shows the measured values ​​of a flow sensor that is operated conventionally, i.e., connected to the primary pipeline 3 without the manipulation section 1 according to the invention. It is evident that the course of the end region of the primary pipeline 3 has a significant influence on the measured values ​​of the flow sensor 2, even if the flow velocity is not changed.

[0047] In diagram (b), the manipulation section 1 is located between the variable end section of the primary pipe 3 and the flow sensor 2, as shown in Fig. 1. There is no longer any apparent dependency between the design of the end section of the primary pipe 3 and the measured values ​​of the flow sensor. The measured values ​​of the flow sensor 2 are independent of the inlet conditions.

[0048] In addition to these findings, it was also observed experimentally that the signal noise of flow sensor 2 is reduced. This is due to the so-called secondary currents that form when the measuring medium flows into the manipulation section 130. This reduction in signal noise has a direct impact on the sensor performance, as it increases the sensitivity of flow sensor 2.

[0049] Furthermore, it was shown that the transition from laminar to turbulent flow can be massively shifted to higher flow rates. This can also be justified theoretically. The critical Reynolds number for a classical pipe flow is approximately 2300. For a helical shape, as shown in Fig. 1, the following formula applies: with ek denotes the critical Reynolds number at which a transition from laminar to turbulent flow occurs. D wdenotes the helix diameter, d the tube diameter and h the distance between the tubes.

[0050] For a helical design of the manipulation section 130 with a helix diameter of Dw = 30 mm, a pipe diameter d = 3.7 mm, and a distance between the pipes h = 4 mm, the formula results in a critical Reynolds number of 10,300. Thus, the laminar range is a factor of 4 higher than with a conventional (straight) inlet section. For flow sensor 2, this means that the measuring range can be increased by this factor. Advantageously, the ratio of pipe diameter d to helix diameter Dw is greater than 0.01—thus, the factor is at least 2.

[0051] Fig. 3 shows experimental investigations into the transition from laminar to turbulent flow. It shows the relationship between the sensor readings (in mW, y-axis) and the mass flow rate of the measured medium (in kg / h, x-axis). The upper curve (indicating higher readings) shows this relationship when using a conventional flow sensor without an intermediate manipulation section.

[0052] A transition from laminar to turbulent flow is evident at a mass flow rate of approximately 25 kg / h. The lower curve (representing lower measured values) shows this dependence with an interposed manipulation section 1, in the sense of the setup shown in Fig. 1. No clear transition is evident across the entire measurement range (up to 80 kg / h), which confirms the increase in the critical Reynolds number described above.

[0053] In summary, the use of a manipulation path 1 according to the invention in conjunction with a flow sensor 2 leads to the following advantages:

[0054] • The inlet dependence of the flow sensor is significantly reduced;

[0055] • The laminar flow area is increased;

[0056] • external noise is attenuated; • space-saving compared to previous solutions.

[0057] Other configurations of the manipulation section 130, apart from a

[0058] Helix, can be used. For example, instead of the

[0059] Manipulation section 130 is curved helically, a tube insert, for example designed in a screw shape, can be inserted into the tubular manipulation section 130.

[0060] List of reference symbols

[0061] 1 manipulation section

[0062] 110 first end area 120, 120' second end area

[0063] 130 Manipulation section

[0064] 2 Flow sensor primary pipeline

[0065] Pipe diameter Dw Helix diameter

Claims

Patent claims 1. Manipulation section (1) for checking the flow profile at the inlet of a flow sensor, wherein the manipulation section (1) is designed to guide a fluid measuring medium, wherein the manipulation section (1) has a first end region (110) and a second end region (120), wherein a manipulation section (130) is located between the first end region and a second end region (120) of the manipulation section (1), which manipulation section (130) is designed such that secondary flows are formed in the measuring medium by the measuring medium flowing through the manipulation section (130).

2. Manipulation section according to claim 1, wherein the manipulation section (1) is designed in a tubular form.

3. Manipulation section according to claim 2, wherein the manipulation section (1) is curved helically with at least one full turn in the manipulation section (130).

4. Manipulation section according to claim 3, wherein the manipulation section (1) has a pipe diameter (d) and a helical diameter (D). w ) exhibits, where the ratio of the pipe diameter to the helix diameter is greater than 0.

01.

5. System, comprehensive: - A flow sensor (2) for detecting at least one parameter relating to the flow velocity of a fluid measuring medium; - A manipulation section (1) according to at least one of claims 1 to 4, wherein the second end region (120) of the manipulation section (1) is connected to an inlet of the thermal flow sensor (2).

6. System according to claim 5, further comprising a primary pipeline (3) through which the measuring medium flows, wherein the manipulation section (1) is located at the first End area (110) is connected to the primary pipeline (3), wherein an output of the flow sensor (2) is connected to the primary pipeline (3).

7. System, comprehensive: - A flow sensor (2) for detecting at least one parameter relating to the flow velocity of a fluid measuring medium; - A manipulation section (1) according to at least one of claims 1 to 4, wherein the flow sensor (2) is integrated in the manipulation section (1) and wherein the flow sensor (2) is arranged between the end of the manipulation section (130) and the second end region (120).

8. System according to claim 7, further comprising a primary pipeline (3) through which the measuring medium flows, wherein the manipulation section (1) is connected to the primary pipeline (3) at the first end region (110), and wherein the manipulation section (1) is connected to the primary pipeline (3) at the second end region (120).

9. System according to one of claims 5 to 8, wherein the flow sensor (3) is a thermal flow sensor.

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