EP4396540A1

EP4396540A1 - Method for detecting bubbles or droplets of a first medium in a fluid second medium flowing through a measuring pipe

Info

Publication number: EP4396540A1
Application number: EP22762077.0A
Authority: EP
Inventors: Ralf Emanuel BERNHARDSGRÜTTER; Jürgen DORSCH; Christoph Hepp
Original assignee: Innovative Sensor Technology IST AG
Current assignee: Innovative Sensor Technology IST AG
Filing date: 2022-08-10
Publication date: 2024-07-10

Abstract

The invention comprises a method for detecting bubbles (BL) or droplets of a first medium (MD1) in a fluid second medium (MD2) flowing through a measuring pipe (MR), with a first heating element (HE1) being arranged on the measuring pipe (MR) at a first measuring point (MS1), a second heating element (HE2) being arranged on the measuring pipe (MR) at a second measuring point (MS2) and the second measuring point (MS2) being arranged at a distance from the first measuring point (MS1) in the direction of flow (FR), the method comprising: - heating the first heating element (HE1) and the second heating element (HE2) by means of electrical power, - simultaneously sensing the ambient temperature at the first measuring point (MS1) by means of a first temperature sensor (TS1) and the ambient temperature at the second measuring point (MS2) by means of a second temperature sensor (TS2), a first electrical measurement variable (U1) of the first temperature sensor (TS1) being determined to sense the ambient temperature at the first measuring point (MS1) and a second electrical measurement variable (U2) of the second temperature sensor (TS2) being determined to sense the ambient temperature at the second measuring point (MS2), - forming a difference (ΔU) between the first electrical measurement variable (U1) and the second electrical measurement variable (U2), and - comparing the absolute value of the difference (ΔU) with a reference threshold value (ΔU_Ref), the presence of a bubble (BL) or droplet being detected if the absolute value of the difference (ΔU) at least briefly exceeds the reference threshold value (ΔU_Ref), and the invention comprises a sensor arrangement designed to carry out the method according to the invention.

Description

Method for detecting bubbles or droplets of a first medium in a fluid second medium flowing through a measuring tube

The invention relates to a method for detecting bubbles or droplets of a first medium in a fluid second medium flowing through a measuring tube, a first heating element being arranged on the measuring tube at a first measuring point, a second heating element being arranged on the measuring tube at a second measuring point, wherein the second measuring point is arranged at a distance from the first measuring point in the direction of flow. Furthermore, the invention relates to a sensor arrangement for carrying out the method according to the invention.

Thermal flow sensors are known for determining a flow rate or the flow rate of a measurement medium or a fluid, for example a gas, gas mixture or a liquid. These use 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 a low-impedance heating element and a high-impedance resistance element, which serves as a temperature sensor. Alternatively, thermal flow sensors are constructed with several low-impedance heating elements as heaters and temperature sensors.

Calorimetric thermal flow sensors determine the flow or the flow rate of the fluid in a channel via a temperature difference between two temperature sensors, which are arranged downstream and upstream of a heating element. For this purpose, use is made of the fact that the temperature difference is linear to the flow or the flow rate up to a certain point. This process or method is extensively described in the relevant literature.

Anemometric thermal flow sensors consist of at least one heating element, which is heated during flow measurement. As the measuring medium flows around the heating element, heat is transported into the measuring medium, which changes with the flow rate. By measuring the electrical variables of the heating element, conclusions can be drawn about the flow rate of the measuring medium.

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

With the "Constant-Current Anemometry" (CCA) control mode, the heating element is subjected to a constant current. The flow of the measuring medium changes the resistance of the Heating element and thus the voltage drop across the heating element, which represents the measurement signal.

The "Constant-Voltage Anemometry" (CVA) control mode works in the same way, in which the heating element is subjected to a constant voltage.

With the "Constant-Temperature Anemometry (CTA)" control mode, the heating element is kept at a constant temperature on average. Relatively high flow velocities can be measured using this type of control. Depending on the flow rate, more or less heat is transported away by the flowing measuring medium and more or less electrical power has to be added accordingly in order to keep the temperature constant. This tracked electrical power is a measure of the flow rate of the measuring medium.

However, bubbles or droplets in the measurement medium can affect the validity and accuracy of the flow rate measurement. Various systems are available on the market today that are used to detect bubbles or droplets. These are based, for example, on ultrasonic measurement or on optical measurement.

The disadvantage of these systems is that they are additional components to be attached to or in the pipeline. In addition, (partially) transparent pipes must be used for the optical measurement, which excludes the use of metal pipes.

Proceeding from this problem, the invention is based on the object of providing an alternative possibility for detecting anomalies, in particular bubbles or drops, in a pipeline which overcomes the disadvantages mentioned above.

The object is achieved by a method according to claim 1 and by a sensor arrangement according to claim 4.

With regard to the method, it is provided that this serves to detect bubbles or droplets of a first medium in a fluid second medium flowing through a measuring tube, with a first heating element being arranged on the measuring tube at a first measuring point, with a second heating element being arranged on the measuring tube at a second measuring point is arranged, wherein the second measuring point is arranged at a distance from the first measuring point in the direction of flow, comprising:

heating the first heating element and the second heating element by means of electrical energy,

Simultaneous detection of the ambient temperature of the first measuring point by means of a first temperature sensor and the ambient temperature of the second measuring point by means of a second temperature sensor, wherein for detecting the Ambient temperature of the first measuring point, a first electrical measured variable of the first temperature sensor is determined, and a second electrical measured variable of the second temperature sensor is determined for detecting the ambient temperature of the second measuring point, forming a difference between the first electrical measured variable and the second electrical measured variable, and comparing the amount of the difference with a reference threshold value, the presence of a bubble or a droplet being detected if the amount of the difference exceeds the reference threshold value at least for a short time.

The method according to the invention makes it possible to detect bubbles or droplets of a first medium in a second medium on the basis of the thermal principle. Two heating elements are required for this. These can, for example, be part of an already installed thermal flow sensor.

The method enables detection independent of the flow rate of the second medium. Even flow velocities that change during the measurement do not affect the measurement, since the difference between the determined electrical measurement variables, which measurement variables allow a direct statement about the temperature present at the respective measuring point, is always formed. A changing flow rate has a direct effect on the ambient temperature at both measuring points, so that this change is canceled out by calculating the difference. This can be done analog or digital.

Physical phase interfaces are referred to as bubbles or droplets. A bubble is a gaseous body (first medium) within a liquid (second medium). A droplet is a liquid body (first medium) within a liquid (first medium) or a gas (second medium).

The ambient temperature of the measuring point is that temperature which is directly in the area adjacent to the respective temperature sensor. This is essentially determined by the first or second medium.

Advantageously, the dimension or size of the droplets or bubbles can be inferred from the magnitude of the amount of the difference. For this, however, the flow rate of the second medium should be known. According to an advantageous embodiment of the method according to the invention, it is provided that the first electrical measured variable is a first voltage drop across the first temperature sensor and/or a first current value flowing through the first temperature sensor, and the second electrical measured variable is a second voltage drop across the second temperature sensor and/or a second current value flowing through the second temperature sensor. Both physical measured variables are advantageously of the same type, for example voltage, current, etc. However, it is also possible for the two physical measured variables to correspond to different (analog) types and to be offset against one another by means of digitization.

According to an advantageous embodiment of the method according to the invention, it is provided that a time between a change in the first measured variable and a corresponding change in the second measured variable is recorded, with a flow rate of the bubble being determined on the basis of the recorded time and a known distance between the first measuring point and the second measuring point or of the droplet and/or the direction of flow of the fluid second medium or of the bubble or the droplet is determined. The flow speed of the fluid second medium can be derived from the flow speed of the bubble or the droplet. Since the measured variables do not change simultaneously, but depend on the point in time at which the bubble or droplet passed, it can be determined which measuring point the bubble or droplet passed first. The direction of flow of the fluid second medium, or of the bubble or of the droplet, can be derived from this.

With regard to the sensor arrangement, it is provided that it comprises a measuring tube, a first heating element, a second heating element, a first temperature sensor, a second temperature sensor and a control/evaluation unit, the control/evaluation unit being designed to use the first heating element, the second heating element, to control the first temperature sensor and the second temperature sensor in such a way that the method according to the invention is carried out. For example, a thermal flow sensor that has the required components can be used.

An advantageous embodiment of the sensor arrangement according to the invention provides that the first temperature sensor is operated as a first heating element, with the second temperature sensor being operated as a second heating element.

According to an advantageous embodiment of the sensor arrangement according to the invention, it is provided that the first heating element and the first temperature sensor are separate elements, and the second heating element and the second temperature sensor are separate elements. All or individual ones of these heating elements and temperature sensors can be arranged on a common substrate or several individual substrates, or alternatively be applied directly to the measuring tube, for example by means of thick-film or thin-film technology.

According to an advantageous embodiment of the sensor arrangement according to the invention, it is provided that the first heating element and the second heating element or the first temperature sensor and the second temperature sensor are PCT or NTC resistance elements, in particular consisting of platinum.

In the event that the heating elements and the temperature sensors are separate elements, heating elements can also be used which have a material with a temperature coefficient of 0 ppm/K, which satisfies the temperature dependency of the separate temperature sensors.

Alternatively, it is provided that the first temperature sensor and the second temperature sensor are thermocouples.

According to an advantageous embodiment of the sensor arrangement according to the invention, it is provided that the first temperature sensor is structurally identical to the second temperature sensor. Alternatively, the temperature sensors can also be constructed differently. In this case, however, the corresponding deviations and their metrological effects must be known and, if necessary, compensated for.

An advantageous embodiment of the sensor arrangement according to the invention provides that the first heating element is structurally identical to the second heating element. Alternatively, the heating elements can also be constructed differently. In this case, however, the corresponding deviations and their metrological effects must be known and, if necessary, compensated for.

An advantageous embodiment of the sensor arrangement according to the invention provides that the first temperature sensor and the second temperature sensor are arranged in a bridge circuit, with the first temperature sensor being connected in series with a first resistor and with the second temperature sensor being connected in series with a second resistor, with the first Resistor and the second resistor are identical.

Alternatively, both physical measured variables can be recorded separately and digitally (for example using an analog-to-digital converter) and the difference can then be formed digitally. According to an advantageous embodiment of the sensor arrangement according to the invention, it is provided that the measuring tube consists of an optically opaque, in particular metallic, material. In contrast to the established and known measurement methodology for detecting bubbles based on ultrasound, the sensor arrangement according to the invention and the method can also be used in metal measuring tubes or pipelines. Of course, in addition to metallic materials, other suitable materials or transparent materials can also be used for the measuring tube.

According to an advantageous embodiment of the sensor arrangement according to the invention, it is provided that the first heating element, the second heating element, the first temperature sensor and the second temperature sensor, or the first temperature sensor operated as the first heating element and the second temperature sensor operated as the second heating element, are arranged on the outer wall of the measuring tube are.

According to an advantageous alternative embodiment of the sensor arrangement according to the invention, it is provided that the first heating element, the second heating element, the first temperature sensor and the second temperature sensor, or the first temperature sensor operated as the first heating element and the second temperature sensor operated as the second heating element, are arranged inside the measuring tube are. Inside the measuring tube means that the second heating element, the first temperature sensor and the second temperature sensor, or the first temperature sensor operated as the first heating element and the second temperature sensor operated as the second heating element, for example, are applied to or attached to the inner wall of the measuring tube could be. Alternatively, it is also possible, for example, for the second heating element, the first temperature sensor and the second temperature sensor, or the first temperature sensor operated as the first heating element and the second temperature sensor operated as the second heating element, to be plugged into the measuring tube and, for example, to be offset from the inner wall of the measuring tube are.

Alternatively, the measuring points can also be designed differently - for example, the first measuring point (and the corresponding first heating element and/or the corresponding first temperature sensor) can be located outside of the measuring tube, while the second measuring point (and the corresponding second heating element and/or the corresponding second temperature sensor) is located inside the measuring tube, and vice versa.

The invention is explained in more detail with reference to the following figures. Show it

Fig. 1: a schematic representation of two exemplary applications of the invention sensor arrays;

2 shows a schematic circuit diagram to illustrate the measuring principle of the sensor arrangement according to the invention;

3: a graph, having a first course of the difference between the electrical measured variables; and

4: a further graph, having a second course of the difference in the electrical measured variables.

FIG. 1 shows two exemplary structures or applications of a sensor arrangement which are designed to carry out the method according to the invention.

1a) shows a metallic measuring tube MR, for example made of chromium steel, through which a fluid second medium MD2, for example water, flows in the direction of flow FR. To detect any bubbles BL in a second medium, for example air bubbles, a first temperature sensor TS1 is fitted on the outer wall of the measuring tube MR at a first measuring point MS1 and a second temperature sensor TS2 is fitted at a second measuring point MS2. The temperature sensors TS1, TS2 are two platinum elements (for example PT50), which are applied to a substrate using thin-film technology. As an alternative to platinum elements, thermocouples could also be used.

By introducing electrical current into the temperature sensors TS1, TS2, these can be used as heating elements HZ1, HZ2 for emitting electrical energy. It is therefore in each case a single element which can be operated as a temperature sensor and as a heating element.

Alternatively, it can be provided that the temperature sensors TS1, TS2 and the heating elements HZ1, HZ2 are individual elements, that is to say are attached separately from one another at the position of the respective measuring points MS1, MS2.

The heating elements HZ1, HZ2 or temperature sensors TS1, TS2 should be coupled to the second fluid medium MD2 as well as possible. Methods for attachment to the measuring tube and exemplary structures of the heating elements/temperature sensors to improve the heat transfer from the heating element HZ1, HZ2 to the second medium MD2, or from the second medium the temperature sensors TS1, TS2 are disclosed in DE 10 2016 116101 A1 or in DE 102018 130547 A1.

The distance between the two measuring points MS1, MS2 depends on the size of the heating elements HZ1, HZ2, the diameter of the measuring tube MR1 and the average bubble or droplet size to be expected. A symmetrical structure of the heating elements HZ1, HZ2 or the temperature sensors TS1, TS2 in terms of physical parameters (e.g. electrical resistance value) simplifies the activation of the sensor arrangement and the evaluation of the measured variables U1, U2.

1b) shows an alternative structure of the sensor arrangement according to the invention. Here the heating elements HZ1, HZ, or the temperature sensors TS1, TS2 (here either as a common element or as individual elements) are designed as rods or ceramic plates, possibly surrounded by a protective cover (Thermowell) and attached and contacted inside the measuring tube MR the second medium MD2 immediately. A high sensitivity is achieved in this exemplary embodiment. The disadvantage is that the temperature sensors TS1, TS2 or the heating elements HZ1, HZ2 could be damaged by contact with the second medium MD2 and/or could influence the flow of the second medium MD2, for example by generating turbulence.

To detect the bubbles BL, the two heating elements HZ1, HZ2 are supplied with electrical current. An exemplary circuit diagram for this is shown in FIG. 2 if the heating elements HZ1, HZ2 and the temperature sensors TS1, TS2 are each designed as a common element.

An electrical resistor R1, R2 is connected upstream of each of the heating elements/temperature sensors, resulting in a full bridge. When a supply voltage U_VS is applied, the heating elements HZ1, HZ2 emit heat to the respective immediate surroundings of the first measuring point MS1 and the second measuring point MS2 by being supplied with electrical current. It goes without saying for the person skilled in the art that other types of circuit measurements can also be used, for example half bridges or digital detection of the two physical measured variables.

Immediately or during the application of the electric current, the voltage U1, which is present in the voltage divider between the resistor R1 and the first temperature sensor TS1, and the voltage U2, which is present in the voltage divider between the resistor R1 and the first temperature sensor TS1, are recorded as electrical measured variables . The heat emitted by the heating elements HZ1, HZ2 is dissipated differently depending on the nature of the second medium MD2 and the flow rate, which means that (assuming a constant heating output, the respective temperature on the heating element HZ1, HZ2 and in the immediate vicinity of the heating element HZ1, HZ2 is different. The voltage across the temperature sensor TS1, TS2 thus changes, depending on the flow rate and the physical properties of the second medium MD2. If a bubble BL, consisting of the first measuring medium (in the present example, air) at a measuring point MS1, MS2 passes, the heat dissipation changes for a short time because the physical properties of the second measuring medium change for a short time.However, the same effect is achieved when the flow speed changes.

According to the invention, the difference AU between the voltage U1 and the voltage U2 is now formed and recorded. As a result, passing bubbles BL can be easily distinguished from a change in the flow velocity.

These phenomena are illustrated in FIG. 3 (change in the difference AU when a bubble passes the two measuring points MS1, MS2) and FIG. 4 (change in the flow velocity). Both figures show a graph based on real measurements, the ordinate of which represents the difference AU and the abscissa of which represents the course of time t. The curve of the recorded difference AU over time is shown in each case.

If there is a bubble BL in the second measuring medium MD2 (FIG. 3), the heat dissipation changes at a given point in time only at one of the heating elements HZ1, HZ2, since the measuring points MS1, MS2 are spatially separated. This means that the difference AU between the two voltages U1, U2 will change. Two peaks are shown in the time interval At, since the bubble first passes the first measuring point MS1 and then the second measuring point MS2. The second peak runs in the negative direction since the subtraction of the voltages U1 and U2 is not commutative.

In the event of a flow change (FIG. 4), the heat removal also changes, but this change takes place simultaneously at both measuring points MS1, MS2, ie the difference AU remains constant. The bubble detection method according to the invention is therefore independent of the flow. The method according to the invention can be applied to a large number of medium combinations (MD1<->MD2) and is not restricted exclusively to bubbles BL (in which the first medium is present in gaseous form). Droplets (the second medium is in liquid form, immiscible with the second medium ML2) can also be reliably detected. If bubbles BL or droplets occur regularly, the flow rate (time-of-flight) or flow direction FR can also be inferred (see FIG. 3). Knowing the distance d between the two

Measuring points MS1, MS2 and the measured time At between the two peaks applies to the flow velocity v: v = d/At.

A combination of a conventional thermal flow sensor (anemometric, calorimetric or time-of-flight), which usually has two heating elements HZ1, HZ2, with the method according to the invention is also possible. For example, such a thermal flow sensor measures the flow rate of the second medium MD2 in the measuring tube in a first measuring mode. The method according to the invention is carried out in a second measurement mode. The thermal flow sensor switches between the two measurement modes at regular intervals or alternately.

Reference List

BL blisters

FR flow direction

HE1 first heating element

HE2 second heating element

MD1 first media

MD2 second medium

MS1 first measuring point

MS2 second measuring point

R1 first resistor

R2 second resistor

TS1 first temperature sensor

TS2 second temperature sensor

U1 first electrical measured variable

U2 second electrical measurement variable

At recorded time between changes of the two

metrics

AU difference of the measured quantities

AU_Ref reference value

Claims

patent claims

1 . Method for detecting bubbles (BL) or droplets of a first medium (MD1) in a fluid second medium (MD2) flowing through a measuring tube (MR), wherein a first heating element (HE1) is installed on the measuring tube (MR) at a first measuring point (MS1) is arranged, wherein a second heating element (HE2) is arranged at a second measuring point (MS2) on the measuring tube (MR), the second measuring point (MS2) being arranged at a distance from the first measuring point (MS2) in the direction of flow (FR), comprising:

Heating the first heating element (HE1) and the second heating element (HE2) using electrical energy,

Simultaneous detection of the ambient temperature of the first measuring point (MS1) using a first temperature sensor (TS1) and the ambient temperature of the second measuring point (MS2) using a second temperature sensor (TS2), with a first electrical measured variable for detecting the ambient temperature of the first measuring point (MS1). (U1) of the first temperature sensor (TS1) is determined, and a second electrical measured variable (U2) of the second temperature sensor (TS2) is determined for detecting the ambient temperature of the second measuring point (MS2), forming a difference (AU) between the first electrical measurement variable (U1) and the second electrical measurement variable (U2), and

Comparing the amount of the difference (AU) with a reference threshold (AU_Ref), the presence of a bubble (BL) or a droplet being detected if the amount of the difference (AU) exceeds the reference threshold (AU_Ref) at least briefly.

2. The method according to claim 1, wherein the first electrical measured variable (U1) is a first voltage drop across the first temperature sensor (TS1) and/or a first current value flowing through the first temperature sensor (TS1), and the second electrical measured variable (U2 ) is a second voltage drop across the second temperature sensor (TS2) and/or a second current value flowing through the second temperature sensor (TS2).

3. The method of claim 1 or 2, wherein a time (At) between a change in the first measured variable (U1) and a corresponding change in the second measured variable (U2) is detected, using the detected time (At) and a known distance between the first measuring point (MS1) and the second measuring point (MS2) a flow rate of the bubble (BL) or the droplet and/or the direction of flow (FR) of the fluid second medium (MD2) and/or the bubble (BL) or the droplet is determined.

4. Sensor arrangement with a measuring tube (MR), a first heating element (HE1), a second heating element (HE2), a first temperature sensor (TS1), a second temperature sensor (TS2) and a control Z evaluation unit, the control Z evaluation unit designed for this purpose is to control the first heating element (HE1), the second heating element (HE2), the first temperature sensor (TS1) and the second temperature sensor (TS2) in such a way that the method according to at least one of Claims 1 to 3 is carried out.

5. Sensor arrangement according to claim 4, the first temperature sensor (TS1) is operated as a first heating element (HE1), and the second temperature sensor (TS2) is operated as a second heating element (HE2).

6. Sensor arrangement according to claim 4, wherein the first heating element (HE1) and the first temperature sensor (TS1) are separate elements, and wherein the second heating element (HE2) and the second temperature sensor (TS2) are separate elements.

7. Sensor element according to claim 5 or 6, wherein the first heating element (HE1) and the second heating element (HE2), or the first temperature sensor (TS1) and the second temperature sensor (TS2) are PCT or NTC resistance elements, in particular consisting of Platinum.

8. Sensor element according to claim 6, wherein the first temperature sensor (TS1) and the second temperature sensor (TS2) are thermocouples.

9. Sensor arrangement according to one of claims 6 to 8, wherein the first temperature sensor (TS1) is identical to the second temperature sensor (TS2).

10. Sensor arrangement according to at least one of claims 4 to 9, wherein the first heating element (HE1) is structurally identical to the second heating element (HE2).

11. Sensor arrangement according to at least one of claims 4 to 10, wherein the first temperature sensor (TS1) and the second temperature sensor (TS2) are arranged in a bridge circuit, wherein the first temperature sensor (TS1) is preceded by a first resistor (R1) in series and wherein the second temperature sensor (TS2) is preceded by a second resistor (R1), wherein the first resistor (R1) and the second resistor (R2) are in particular identical in construction.

12. Sensor arrangement according to at least one of claims 4 to 11, wherein the measuring tube (MR) consists of an optically opaque, in particular metallic, material. 14 Sensor arrangement according to at least one of claims 4 to 12, wherein the first heating element (HE1), the second heating element (HE2), the first temperature sensor (TS1) and the second temperature sensor (TS2), or as the first heating element (HE1) operated the first temperature sensor (TS1) and the second temperature sensor (TS2) operated as the second heating element (HE2) are arranged on the outer wall of the measuring tube (MR). Sensor arrangement according to at least one of Claims 4 to 13, wherein the first heating element (HE1), the second heating element (HE1), the first temperature sensor (TS1) and the second temperature sensor (TS2), or the first one operated as the first heating element (HE1). Temperature sensor (TS1) and as the second heating element (HE1) operated second temperature sensor (TS2) inside the measuring tube (MR) are arranged.