Heated flow wet steam humidity sensor and its measurement and calibration methods

Abstract

The application discloses a heated flow wet steam humidity sensor and a measuring method and a calibration method thereof, an outer pipe sleeve is connected to the outer wall of an inner pipe, a cavity is arranged between the inner wall of the outer pipe and the outer wall of the inner pipe, the cavity is communicated with the inside of the inner pipe through a balance hole, a first thermocouple array and a second thermocouple array are arranged in the cavity, a support body, a first rectifier plate, a first temperature sensing plate, a second rectifier plate and a second temperature sensing plate are sequentially arranged in the inner pipe along the flow direction of the airflow, a first thermocouple is arranged in the inlet section of the inner pipe, a heating body is arranged in the support body, a second thermocouple and a second pressure sensor are arranged on the first temperature sensing plate, a third thermocouple and a third pressure sensor are arranged on the second temperature sensing plate, the sensor and the measuring method and the calibration method thereof can realize the humidity measurement of the flowing wet steam and the calibration of the wet steam humidity sensor.

Description

Technical Field

[0001] This invention relates to a humidity sensor and its measurement and calibration methods, specifically to a heating-based flowing wet steam humidity sensor and its measurement and calibration methods. Background Technology

[0002] Wet steam is an important working fluid in the power, petrochemical and many other industrial production fields, and there is an urgent and widespread need for accurate measurement of the humidity of flowing wet steam.

[0003] The heating method is a way to measure the humidity of flowing wet steam. Its basic principle is to heat a certain flow rate of wet steam to a dry saturated or superheated state, and then measure its pressure and temperature to obtain the enthalpy value. Based on the steam flow rate, net heating amount, and changes in the steam's thermodynamic parameters before and after heating, the humidity of the wet steam can be calculated. The heating method has advantages such as simple measurement principle and high measurement accuracy. However, high measurement accuracy depends on accurately measuring the net heating amount and the average temperature of the steam at the flow cross-section, which presents many technical difficulties. Currently, industrial applications of heating method-based humidity sensors for flowing wet steam have not yet been realized.

[0004] Furthermore, the heating method for humidity measurement is an absolute measurement method; theoretically, its accuracy is only affected by the accuracy of temperature and pressure measurements. However, dimensional and assembly errors are unavoidable during the manufacturing process of sensors, requiring calibration and determination of their error range before use. However, the humidity of wet steam, the measured medium, changes with even the slightest heat exchange with the external environment. Therefore, there is no standard wet steam for calibration, making the calibration of wet steam humidity sensors difficult. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a humidity sensor for flowing wet steam using a heating method, as well as a measurement and calibration method thereof. This sensor, its measurement and calibration methods can realize the humidity measurement of flowing wet steam and the calibration of the wet steam humidity sensor.

[0006] To achieve the above objectives, the heating method flow wet steam humidity sensor of the present invention includes an outer tube, an inner tube, a support body, a first rectifier plate, a first temperature sensing plate, a second rectifier plate, and a second temperature sensing plate.

[0007] The inner tube has a combination of thick and thin walls. The outer tube is fitted onto the outer wall of the inner tube. A cavity is provided between the inner wall of the outer tube and the outer wall of the inner tube. The cavity is connected to the inside of the inner tube through a balance hole. A first thermocouple array and a second thermocouple array are installed in the cavity. A support body, a first rectifier plate, a first temperature sensing plate, a second rectifier plate, and a second temperature sensing plate are sequentially arranged inside the inner tube along the airflow direction. A first thermocouple is installed in the inlet section of the inner tube. A heating element is installed in the support body. A second thermocouple and a second pressure sensor are installed on the first temperature sensing plate. A third thermocouple and a third pressure sensor are installed on the second temperature sensing plate.

[0008] Furthermore, the support body is provided with a plurality of through holes, wherein each through hole is arranged along the axial direction, and the heating element is arranged in the through holes on the support body.

[0009] Furthermore, when the number of through holes is one, the cross-section of the through hole is an annular structure.

[0010] Furthermore, when there are multiple through holes, all through holes are distributed sequentially along the circumferential direction.

[0011] Furthermore, the first rectifier plate, the first temperature sensing plate, the second rectifier plate, and the second temperature sensing plate are all porous plates made of materials with high thermal conductivity.

[0012] Furthermore, the second pressure sensor is arranged coaxially with the second thermocouple.

[0013] Furthermore, the third pressure sensor is arranged coaxially with the third thermocouple.

[0014] Furthermore, the support body, heating body, first rectifier plate, and first temperature sensing plate constitute a heating section;

[0015] The space downstream of the first temperature sensing plate, along with the second rectifier plate and the second temperature sensing plate, constitutes the heat dissipation section.

[0016] The sensor humidity measurement method of the present invention includes the following steps:

[0017] 11) The humidity sensor for the flowing wet steam is placed in the wet steam to be measured. The wet steam enters the inner tube through the inlet section of the inner tube. The first thermocouple measures the temperature T1 of the wet steam. The wet steam flows through the heating element and is heated into superheated steam. The heating amount of the heating element is q2. The superheated steam flows through the first rectifier plate and then through the first temperature sensing plate. The second thermocouple installed on the first temperature sensing plate measures the temperature T2 of the superheated steam. At the same time, the second pressure sensor measures the pressure P2 of the superheated steam. The superheated steam continues to flow along the inner tube and dissipates heat to the outer tube. Then, the superheated steam flows through the second rectifier plate and the second temperature sensing plate. The third thermocouple installed on the second temperature sensing plate measures the temperature T3 of the superheated steam after the heat dissipation and the decrease in superheat. At the same time, the third pressure sensor measures the pressure P3 of the superheated steam after the heat dissipation and the decrease in superheat.

[0018] 12) Based on the heating amount q2 of the heating element and the heat dissipation q from the heating element to the outer tube. d2 The amount of heat dissipated by steam to the outer pipe, q d3 Calculate the humidity of the measured wet steam by taking the temperature T1 of the wet steam, the temperature T2 and pressure P2 of the superheated steam, and the temperatures T3 and P3 of the superheated steam with reduced superheat.

[0019] The calibration method for the heating-based flowing wet steam humidity sensor of the present invention includes the following steps:

[0020] 21) Superheated steam or humid air passes through a flow meter, the flow rate m of which is measured by the flow meter. The outlet of the flow meter is connected to the inlet of the humidity sensor for the heated steam flow via a connecting pipe. A pressure gauge is installed on the connecting pipe, and the pressure P1 of the incoming superheated steam or humid air is measured by the pressure gauge. The superheated steam or humid air enters the inner tube through the inlet section of the inner tube. The first thermocouple measures the temperature T1 of the superheated steam or humid air. The superheated steam or humid air is heated by the heating element, and the heating amount of the heating element is q2. The heated superheated steam or humid air is rectified by the first rectifier plate and then flows through the second rectifier plate. A temperature sensing plate is used. A second thermocouple mounted on the first temperature sensing plate measures the temperature T2 of the heated superheated steam or humid air, while a second pressure sensor measures the pressure P2 of the heated superheated steam or humid air. The superheated steam or humid air continues to flow along the inner tube and dissipates heat to the outer tube, causing the temperature of the superheated steam or humid air to decrease. Then it flows through a second rectifier plate and a second temperature sensing plate. A third thermocouple mounted on the second temperature sensing plate measures the temperature T3 of the superheated steam or humid air after the temperature decreases due to heat dissipation, while a third pressure sensor measures the pressure P3 of the superheated steam or humid air after the temperature decreases due to heat dissipation.

[0021] 22) Based on the heating amount q2 of the heating element and the heat dissipation q from the heating element to the outer tube. d2Calculate the flow rate m1 of the superheated steam or humid air in the heating section based on the temperature T1 and pressure P1 of the incoming superheated steam or humid air, and the temperature T2 and pressure P2 of the heated superheated steam or humid air; and calculate the heat dissipation q of the superheated steam or humid air to the outer pipe based on the heat dissipation q of the superheated steam or humid air. d3 Calculate the flow rate m2 of the superheated steam or humid air in the heat dissipation section based on the temperature T2 and pressure P2 of the superheated steam or humid air after heating, and the temperature T3 and pressure P3 of the superheated steam or humid air after cooling. Compare m with m1 and m2 to obtain the measurement error ε between the heating and heat dissipation sections. m1 and ε m2 Based on the measurement error ε of the heating section and the heat dissipation section m1 and ε m2 The error ε of wet steam humidity measurement is obtained. Y According to the error ε of the wet steam humidity measurement Y Calibrate the humidity sensor for the flow of wet steam using the heating method.

[0022] The present invention has the following beneficial effects:

[0023] The heating-based flowing wet steam humidity sensor, its measurement method, and calibration method described in this invention, in practical operation, incorporates a support body and a heating element, which significantly improves the heat transfer intensity of the steam while reducing the heating temperature of the heating element. This results in a sensor axial length of only a few centimeters, greatly expanding its application scenarios compared to existing sensors with an axial length of approximately 1 meter. Furthermore, the sensor exhibits advantages such as low failure rate, low thermal inertia, and short response time. Additionally, a cavity is formed between the inner and outer tubes, connected to the inner tube via a balance hole. The cavity is filled with superheated steam at a pressure of P3. On one hand, the thermal conductivity of the superheated steam is very low, and the natural convection heat transfer effect within the cavity is negligible, ensuring a sufficiently large temperature difference between the outer wall of the inner tube and the inner wall of the outer tube. On the other hand, the thermal conductivity of the superheated steam can be accurately calculated according to the IAPWS-IF97 international standard, ensuring the accuracy of heat dissipation measurement. Finally, this invention proposes the theoretical basis and implementation method for calibrating the sensor using superheated steam or humid air, providing a simple, convenient, and practical calibration method for heating-based flowing wet steam humidity sensors.

[0024] Furthermore, a porous plate made of a high thermal conductivity material is used as both the rectifier and the temperature sensing plate to solve the problem of accurately measuring the average temperature of steam flow with uneven temperature across the cross-section using a single temperature sensing element. When the steam with uneven temperature across the cross-section flows through the rectifier and temperature sensing plate, it undergoes bidirectional heat exchange. When the local temperature of the porous plate is higher than that of the steam, the porous plate transfers heat to the steam; conversely, the steam transfers heat to the porous plate. This makes the temperature across the cross-section of the steam flow more uniform after passing through the rectifier and temperature sensing plate. The temperature sensing plate material has a high thermal conductivity, resulting in minimal temperature differences at different locations, meaning it has an almost uniform temperature overall. This temperature is the average temperature of the steam across the cross-section. Therefore, a single temperature sensing element, such as a thermocouple, can be used to measure the average temperature of the steam across the entire cross-section by measuring the temperature of the temperature sensing plate. This not only simplifies the sensor design but also improves the measurement accuracy of the key parameter, steam temperature. Attached Figure Description

[0025] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0026] Figure 1 This is a schematic diagram of the structure of the present invention;

[0027] Figure 2 A schematic diagram of the cross-section of a support 3;

[0028] Figure 3 This is a schematic diagram of the cross-section of another type of support 3;

[0029] Figure 4 This is a schematic diagram of the cross-section of the rectifier plate / temperature sensing plate;

[0030] Figure 5 This is a schematic diagram for sensor calibration.

[0031] Among them, 1 is the outer tube, 2 is the inner tube, 3 is the support body, 4 is the heating body, 5 is the first thermocouple array, 6 is the first rectifier plate, 7 is the first temperature sensing plate, 8 is the second rectifier plate, 9 is the second temperature sensing plate, 10 is the second thermocouple array, 11 is the first thermocouple, 12 is the second thermocouple, 13 is the second pressure sensor, 14 is the third thermocouple, 15 is the third pressure sensor, and 16 is the balance hole. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0034] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0035] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0036] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0037] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0040] Example 1

[0041] refer to Figure 1 The heating method flow wet steam humidity sensor of the present invention includes an outer tube 1, an inner tube 2, a support body 3, a heating body 4, a first thermocouple array 5, a second thermocouple array 10, a first rectifier plate 6, a first temperature sensing plate 7, a second rectifier plate 8, a second temperature sensing plate 9, a first thermocouple 11, a second thermocouple 12, a second pressure sensor 13, a third thermocouple 14, a third pressure sensor 15, and a balance hole 16;

[0042] An outer tube 1 is fitted onto the outer wall of an inner tube 2. A cavity is provided between the inner wall of the outer tube 1 and the outer wall of the inner tube 2. A first thermocouple array 5 and a second thermocouple array 10 are installed in the cavity. A support body 3, a first rectifier plate 6, a first temperature sensing plate 7, a second rectifier plate 8, and a second temperature sensing plate 9 are sequentially arranged inside the inner tube 2 along the airflow direction. A first thermocouple 11 is installed in the inlet section of the inner tube 2. A heating element 4 is installed in the support body 3. A second thermocouple 12 and a second pressure sensor 13 are installed on the first temperature sensing plate 7. A third thermocouple 14 and a third pressure sensor 15 are installed on the second temperature sensing plate 9. The second pressure sensor 13 is coaxially arranged with the second thermocouple 12, and the third pressure sensor 15 is coaxially arranged with the third thermocouple 14.

[0043] It should be noted that the inner tube 2 has a combination of thick and thin walls, with the thickness of the thick and thin walls differing by several to tens of times. While meeting strength requirements, these walls also exhibit significantly different axial heat transfer characteristics. The inner tube 2 connects the sensor inlet section, heating section, heat dissipation section, and outlet section, each with a significantly different temperature. Therefore, the temperature of the inner tube 2 at each of these sections is also different, and heat inevitably transfers axially along the inner tube 2. This makes it difficult to accurately measure the net heating amount of the heating and heat dissipation sections. Previous heating-based humidity sensor designs mostly overcome this difficulty by extending the axial distance between the parts, but this also results in a long axial length of the sensor. In this invention, the inner tube 2 uses a combination of thick and thin walls, with the thickness of the thick and thin walls differing by several to tens of times. These two walls have significantly different axial heat transfer characteristics. The thin wall greatly increases the axial heat transfer resistance, approximately achieving thermal insulation between the sensor's heating and heat dissipation sections and the sensor's inlet and outlet sections. Under the compact space conditions inside the sensor, effective control of the axial heat transfer process is achieved, which is also an important design feature for significantly reducing the axial length of the sensor.

[0044] refer to Figure 2 and Figure 3 The support 3 is provided with a plurality of through holes, wherein each through hole is arranged along the axial direction and the flow area of ​​each through hole is greater than the cross-sectional area of ​​the inlet section of the inner tube 2. Preferably, there is one through hole and the cross-section of the through hole is an annular structure, or there are multiple through holes and all through holes are distributed sequentially along the circumference.

[0045] The heating element 4 adopts a spiral winding electric heating method. The heating element 4 is arranged in the through hole on the support body 3. The spiral winding direction of the heating element 4 is along the axial direction or perpendicular to the axial direction. The heating element 4 is in direct contact with the steam being measured to generate convective heat transfer. Figure 2 and Figure 3 The structure of the support 3 shown is for illustrative purposes only. All other design features of the support 3, which have a solid central portion along the axis, are within the scope of the claims of this invention.

[0046] refer to Figure 1 The inner tube 2 has a combination of thick and thin walls, with a difference of several times in wall thickness, resulting in significantly different heat transfer characteristics. Figure 1 The inner tube 2 shown is for illustrative purposes only. All other design features that utilize differences in tube wall thickness to control heat transfer characteristics are within the scope of the claims of this invention.

[0047] refer to Figure 4The first rectifier plate 6, the first temperature sensing plate 7, the second rectifier plate 8, and the second temperature sensing plate 9 are all porous plates made of high thermal conductivity materials. The first rectifier plate 6, the first temperature sensing plate 7, and the second thermocouple 12 constitute the first temperature measurement unit, and the third thermocouple 14, the second rectifier plate 8, and the second temperature sensing plate 9 constitute the second temperature measurement unit. The second thermocouple 12 is installed on the first temperature sensing plate 7, and the third thermocouple 14 is installed on the second temperature sensing plate 9. Figure 4 The cross-sectional shapes of the rectifier plate and the temperature sensing plate shown are for illustrative purposes only. All other design features that conform to the rectifier plate and the temperature sensing plate being porous plates made of materials with high thermal conductivity are within the scope of the claims of this invention.

[0048] A narrow cavity is formed between the outer tube 1 and the inner tube 2. This narrow cavity is connected to the interior of the inner tube 2 via a balance hole 16. The narrow cavity is filled with superheated steam at a pressure of P3. The heat dissipation q from the heating section to the outer tube 1 is measured using a first thermocouple array 5. d2 The amount of heat dissipation q from the heat dissipation section to the outer pipe 1 is measured using the second thermocouple array 10. d3 It should be noted that all design features that fill the space between the inner tube 2 and the outer tube 1 with superheated steam are within the scope of the claims of this invention.

[0049] Example 2

[0050] The sensor humidity measurement method of the present invention includes the following steps:

[0051] 11) The humidity sensor of the heating method flow wet steam is placed in the wet steam to be measured. The wet steam enters the inner tube 2 through the inlet section of the inner tube 2. The first thermocouple 11 measures the temperature T1 of the wet steam. The wet steam flows through the heating element 4 and is heated into superheated steam. The heating amount of the heating element 4 is q2. The superheated steam flows through the first rectifier plate 6 and then through the first temperature sensing plate 7. The second thermocouple 12 installed on the first temperature sensing plate 7 measures the temperature T2 of the superheated steam. At the same time, the second pressure sensor 13 measures the pressure P2 of the superheated steam. The superheated steam continues to flow along the inner tube 2 and dissipates heat to the outer tube 1. During the steam flow and heat dissipation process, the superheat of the steam decreases but remains positive. Then the superheated steam flows through the second rectifier plate 8 and the second temperature sensing plate 9. The third thermocouple 14 installed on the second temperature sensing plate 9 measures the temperature T3 of the superheated steam after the heat dissipation decreases. At the same time, the third pressure sensor 15 measures the pressure P3 of the superheated steam after the heat dissipation decreases.

[0052] 12) Based on the heating amount q2 of the heating element 4 and the heat dissipation q from the heating element 4 to the outer tube 1 d2 The amount of heat dissipated by steam to the outer pipe 1, q d3 Calculate the humidity of the measured wet steam by taking the temperature T1 of the wet steam, the temperature T2 and pressure P2 of the superheated steam, and the temperatures T3 and P3 of the superheated steam with reduced superheat.

[0053] The specific operation of step 12) is as follows:

[0054] 121) Calculate the steam flow rate m through the sensor;

[0055] A wet steam sample with a temperature of T1 enters the sensor and is heated to a superheated state by heating element 4. The state parameters after heating are: pressure P2, temperature T2, heating amount q2, and heat dissipation q. d2 The amount of heat dissipation from the steam in the heat dissipation section is q. d3 The state parameters of the superheated steam after heat dissipation are: pressure P3, temperature T3. According to the energy conservation equation, we get:

[0056]

[0057] Where h2 is the enthalpy of the superheated steam in the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located, which can be determined according to the formula for calculating the properties of water vapor based on pressure P2 and temperature T2; u2 is the flow velocity of the superheated steam in the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located; h3 is the enthalpy of the superheated steam in the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located, which can be determined according to the formula for calculating the properties of water vapor based on pressure P3 and temperature T3; u3 is the flow velocity of the superheated steam in the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located; q d3 The heat dissipation between the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located and the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located.

[0058] From equation (1), we get:

[0059]

[0060] According to the flow rate calculation formula, we get:

[0061] m=ρ2A2u2(3)

[0062] m=ρ3A3u3(4)

[0063] Where A2 is the flow area of ​​superheated steam in the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located, ρ2 is the density of superheated steam in the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located, A3 is the flow area of ​​superheated steam in the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located, and ρ3 is the density of superheated steam in the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located. Substituting equations (3) and (4) into equation (2), we get:

[0064]

[0065] From equation (5), we get:

[0066]

[0067] Solve equation (6) to obtain the steam flow rate m through the sensor. Then substitute the steam flow rate m into equation (3) to obtain the flow velocity u2 of the superheated steam at the cross section where the second thermocouple 12 and the second pressure sensor 13 are located.

[0068] 122) Calculate the humidity of the wet steam;

[0069] From the energy conservation equation, we get:

[0070]

[0071] Where h1 is the enthalpy of the wet steam at the cross-section where the first thermocouple 11 is located, u1 is the flow velocity of the wet steam at the cross-section where the first thermocouple 11 is located, q2 is the heating amount of the wet steam by the heating element 4, and q d2 The heat dissipation between the cross-section where the first thermocouple 11 is located and the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located is given by equation (7):

[0072]

[0073] According to the flow rate calculation formula, we get:

[0074] m=ρ1A1u1 (9)

[0075] Given m, u1 and h1 are determined by iterative method, and then the humidity of the wet steam being measured is determined by h1 and T1.

[0076] Example 3

[0077] refer to Figure 5 The calibration method for the heating-method flow wet steam humidity sensor of the present invention uses superheated steam or humid air to calibrate the sensor, and includes the following steps:

[0078] 21) Superheated steam or humid air flows through a flow meter, and the flow rate m of the superheated steam or humid air is measured by the flow meter. The outlet of the flow meter is connected to the inlet of the sensor through a connecting pipe. A pressure gauge is arranged on the connecting pipe, and the pressure P1 of the superheated steam or humid air flow is measured by the pressure gauge. The superheated steam or humid air enters the inner tube 2 through the inlet section of the inner tube 2. The first thermocouple 11 measures the temperature T1 of the superheated steam or humid air. The superheated steam or humid air flows through the heating element 4 and is heated. The heating amount of the heating element 4 is q2. After being heated, the superheated steam or humid air is rectified by the first rectifier plate 6 and then flows through the first temperature sensing plate 7. The second thermocouple 12 on the first temperature sensing plate 7 measures the temperature T2 of the heated superheated steam or humid air, while the second pressure sensor 13 measures the pressure P2 of the heated superheated steam or humid air. The superheated steam or humid air continues to flow along the inner pipe 2 and dissipates heat to the outer pipe 1, causing the temperature of the superheated steam or humid air to decrease. Then it flows through the second rectifier plate 8 and the second temperature sensing plate 9. The third thermocouple 14 installed on the second temperature sensing plate 9 measures the temperature T3 of the superheated steam or humid air after the temperature decreases due to heat dissipation, while the third pressure sensor 15 measures the pressure P3 of the superheated steam or humid air after the temperature decreases due to heat dissipation.

[0079] 22) Based on the heating amount q2 of the heating element 4 and the heat dissipation q from the heating element 4 to the outer tube 1 d2 Calculate the flow rate m1 of the superheated steam or humid air in the heating section based on the temperature T1 and pressure P1 of the incoming superheated steam or humid air, and the temperature T2 and pressure P2 of the heated superheated steam or humid air; and calculate the heat dissipation q of the superheated steam or humid air to the outer pipe 1. d3 Calculate the flow rate m2 of the superheated steam or humid air in the heat dissipation section based on the temperature T2 and pressure P2 of the superheated steam or humid air after heating, and the temperature T3 and pressure P3 of the superheated steam or humid air after cooling. Compare m with m1 and m2 to obtain the measurement error ε between the heating and heat dissipation sections. m1 and ε m2 Based on error analysis theory, the error ε in the measurement of wet steam humidity is obtained. Y .

[0080] The specific operation of step 22) is as follows:

[0081] 221) Calculate the flow rates m1 and m2 of the superheated steam or humid air flowing through the heating section and the heat dissipation section;

[0082] Superheated steam or humid air with pressure P1 and temperature T1 enters the sensor and is heated to a higher temperature in the heating section. The state parameters after heating are: pressure P2, temperature T2, heating amount q2, and heat dissipation q. d2 The heat dissipation of superheated steam or humid air in the heat dissipation section is q. d3The state parameters of the superheated steam or humid air after heat dissipation are: pressure P3, temperature T3. According to the energy conservation equation, for the heating section and the heat dissipation section respectively, we get:

[0083]

[0084] Where h1 is the enthalpy of the superheated steam or humid air at the cross-section where the first thermocouple 11 is located, which can be determined according to the formula for calculating the properties of water vapor or humid air based on the pressure P1 and temperature T1; u1 is the flow velocity of the superheated steam or humid air at the cross-section where the first thermocouple 11 is located; q2 is the amount of heating of the superheated steam or humid air by the heating element 4; q d2 h2 is the heat dissipation between the cross-section where the first thermocouple 11 is located and the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located; h2 is the enthalpy of superheated steam or humid air in the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located, which can be determined according to the formula for calculating the properties of water vapor or humid air based on pressure P2 and temperature T2; u2 is the flow velocity of superheated steam or humid air in the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located; h3 is the enthalpy of superheated steam or humid air in the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located, which can be determined according to the formula for calculating the properties of water vapor or humid air based on pressure P3 and temperature T3; u3 is the flow velocity of superheated steam or humid air in the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located; q d3 The heat dissipation between the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located and the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located.

[0085] From equations (10) and (11), we get:

[0086]

[0087] According to the flow rate calculation formula, we get:

[0088] m1=ρ1A1u1=ρ2A2u2(14)

[0089] m2=ρ2A2u2=ρ3A3u3(15)

[0090] Wherein, A1 is the flow area of ​​superheated steam or humid air in the cross-section where the first thermocouple 11 is located, ρ1 is the density of superheated steam or humid air in the cross-section where the first thermocouple 11 is located, A2 is the flow area of ​​superheated steam or humid air in the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located, ρ2 is the density of superheated steam or humid air in the cross-section where the second thermocouple 12 and the second pressure sensor 13 are located, A3 is the flow area of ​​superheated steam or humid air in the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located, and ρ3 is the density of superheated steam or humid air in the cross-section where the third thermocouple 14 and the third pressure sensor 15 are located.

[0091] Substituting equations (14) and (15) into equations (12) and (13) respectively, we get:

[0092]

[0093]

[0094] From equations (16) and (17), we get:

[0095]

[0096] Solve equations (18) and (19) respectively to obtain the flow rates m1 and m2 of the superheated steam or humid air flowing through the heating section and the heat dissipation section.

[0097] 222) Calibrate the sensor;

[0098] Due to measurement errors in the thermocouples and pressure sensors used, as well as dimensional and assembly errors in sensor manufacturing, the flow rates m1 and m2 of the heating section obtained according to the above steps will generally not be the same as the flow rate m measured by the flow meter used for calibration; that is, m1 ≠ m2 ≠ m. Under certain operating conditions, calibration coefficients α1 and α2 are introduced for the heating and heat dissipation sections respectively for calibration, so that after calibration, |m - m1| = ε m1 <ε,|m-m2|=ε m2 <ε, where ε m1 and ε m2 The flow measurement error of the heating and heat dissipation sections after calibration is ε, which is the maximum allowable error. The flow meter used for calibration should be a high-precision flow meter.

[0099] 223) Determine the measurement error of the sensor;

[0100] According to error analysis theory, when variable V is a function of several independent variables a, b, ..., i.e., V = V(a, b, ...), the error of variable V is:

[0101]

[0102] Where, ε V Let e ​​be the error of the variable V to be determined. a and e b The measurement error for each independent variable; and This is the error propagation coefficient.

[0103] To simplify the expression, let Q2 = q2 - q d2 To determine the net heating capacity of the heating section, we obtain the following from equation (10):

[0104]

[0105] According to error analysis theory, from equation (21), we get:

[0106]

[0107] From equation (10), we get:

[0108]

[0109] According to error analysis theory, from equation (23), we get:

[0110]

[0111] From equations (22) and (25), we get:

[0112]

[0113] in, To find the systematic error, The systematic error in measuring flow rate m1 is... To account for the measurement error of flow rate m1, during actual measurement, the sensor's heat dissipation section performs the flow measurement function, therefore... and The measurement error of the enthalpy h1 of water vapor at the sensor inlet section has been determined by the calibration process. Among them, c p The specific heat at constant pressure of water vapor. This is the measurement error of the inlet temperature;

[0114] Equation (26) can be written as:

[0115]

[0116] The following relationship exists between the enthalpy h1 and humidity Y of the wet steam at the sensor inlet:

[0117] h1=Yh1′+(1-Y)h1″(28)

[0118] Where h1′ and h1″ are the enthalpy of saturated water and saturated vapor, respectively, and further derived from error analysis theory, the humidity measurement error is obtained.

[0119] Following the above method, the humidity measurement error ε of the sensor can be accurately determined through the calibration process using superheated steam or humid air. Y .

[0120] This invention has the following characteristics:

[0121] Due to the following design features, the axial length of this invention is only a few centimeters, which greatly expands its application scenarios: 1) After the steam enters the sensor at high speed, the flow area of ​​the heating section increases significantly, the steam flow rate decreases significantly, and the heat exchange time with the heating body 4 increases significantly; 2) The heat exchange area of ​​the heating section increases significantly; 3) The heating body 4 directly undergoes forced convection heat exchange with the steam, the thermal resistance is greatly reduced, and the heat exchange intensity increases significantly.

[0122] In this invention, the inner tube 2 adopts a combination of thick and thin walls, with a difference of several times in wall thickness, thus having significantly different heat transfer characteristics, and realizing effective control of the heat transfer process under the compact space conditions inside the sensor.

[0123] This invention uses a porous plate made of a high thermal conductivity material as a rectifier and a temperature sensing plate. When the steam with uneven temperature on the cross-section flows through the rectifier and the temperature sensing plate, it undergoes bidirectional heat exchange, making the temperature on the steam cross-section more uniform. The temperature of the temperature sensing plate is equal to the average temperature of the steam on the cross-section. Therefore, a single temperature sensing element can be used to measure the average temperature of the steam on the entire cross-section by measuring the temperature of the temperature sensing plate. This not only simplifies the design of the sensor but also improves the measurement accuracy of the key parameter of steam temperature.

[0124] The present invention forms a narrow cavity between the inner tube 2 and the outer tube 1. The narrow cavity and the internal space of the inner tube 2 are connected through the balance hole 16. The narrow cavity is filled with superheated steam at a pressure of P3. Since the thermal conductivity of the superheated steam is very small and it is basically in a stagnant state, the natural convective heat transfer effect is negligible. This provides a sufficiently large temperature difference between the inner tube 2 and the outer tube 1 for measuring heat dissipation, thereby improving the measurement accuracy of this key parameter.

[0125] To address the lack of humid steam samples as calibration standards, this invention uses superheated steam or humid air to calibrate the sensor. Essentially, a humidity sensor measures the pressure and temperature changes of a flowing medium entering it under a certain net heating condition. The physical properties of the flowing medium, determined by pressure and temperature, can be accurately calculated according to relevant international standards. Therefore, the sensor's measurement accuracy depends only on the accuracy of the measurements of the net heating amount and the two state parameters of pressure and temperature, and is independent of whether the measured medium is humid steam. The heating-based humidity sensor proposed in this invention allows the heat dissipation section to obtain the steam flow rate entering the sensor by measuring the heat dissipation amount and the state parameters before and after superheated steam dissipation. For the heating section, by measuring the net heating amount and the state parameters of the steam before and after heating, when the humidity of the inlet steam is unknown, the humidity can be obtained from the flow rate measured in the heat dissipation section—this is the designed function of the humidity sensor. When the humidity of the inlet steam is known, for example, when the inlet is superheated steam with zero humidity, the steam flow rate can be obtained. Furthermore, when the inlet is humid air, both the heating and heat dissipation sections of the sensor can measure the flow rate of the humid air. In extreme cases, when the inlet is entirely water or other liquids with known properties, as long as the heating power of the heating element 4 is sufficiently large, the water or other liquid can be heated into superheated steam. Both the heating and cooling sections of the sensor can then measure two flow rates. Regardless of whether the inlet is wet steam, superheated steam, humid air, or other media, the type of parameter directly measured by the sensor remains consistent. The only difference lies in the different unknown quantities, which are then used to solve for humidity or flow rate using the thermal balance relationship. This invention uses superheated steam or humid air as the medium for sensor calibration. Based on error analysis theory, the error in wet steam humidity measurement can be accurately obtained. Addressing the current lack of wet steam samples as calibration standards, this invention provides a simple, convenient, and practical calibration method for heating-based flow wet steam humidity sensors.

[0126] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and disclosure of the invention. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0127] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

[0128] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A humidity sensor for flowing wet steam using a heating method, characterized in that, It includes an outer tube (1), an inner tube (2), a support body (3), a first rectifier plate (6), a first temperature sensing plate (7), a second rectifier plate (8), and a second temperature sensing plate (9); The inner tube (2) has a combination of thick and thin walls. The outer tube (1) is fitted onto the outer wall of the inner tube (2). A cavity is provided between the inner wall of the outer tube (1) and the outer wall of the inner tube (2). The cavity is connected to the interior of the inner tube (2) through a balance hole (16). A first thermocouple array (5) and a second thermocouple array (10) are installed in the cavity. The support body (3), the first rectifier plate (6), the first temperature sensing plate (7), the second rectifier plate (8), and the second temperature sensing plate (9) are arranged sequentially in the inner tube (2) along the airflow direction. A first thermocouple (11) is provided in the inlet section of the inner tube (2). A heating element (4) is provided in the support body (3). A second thermocouple (12) and a second pressure sensor (13) are installed on the first temperature sensing plate (7). A third thermocouple (14) and a third pressure sensor (15) are installed on the second temperature sensing plate (9). The support body (3) is provided with a plurality of through holes, wherein each through hole is arranged along the axial direction, and the heating element (4) is arranged in the through holes on the support body (3); The support (3), heating element (4), first rectifier plate (6) and first temperature sensing plate (7) constitute the heating section; The space downstream of the first temperature sensing plate (7), the second rectifier plate (8), and the second temperature sensing plate (9) constitute a heat dissipation section; The first rectifier plate (6), the first temperature sensing plate (7), the second rectifier plate (8) and the second temperature sensing plate (9) are all porous plates made of high thermal conductivity materials.

2. The heating-method flow wet steam humidity sensor according to claim 1, characterized in that, When the number of through holes is one, the cross-section of the through hole is an annular structure.

3. The heating-method flow wet steam humidity sensor according to claim 1, characterized in that, When there are multiple through holes, all through holes are distributed sequentially along the circumferential direction.

4. The heating-method flow wet steam humidity sensor according to claim 1, characterized in that, The second pressure sensor (13) is arranged coaxially with the second thermocouple (12).

5. The heating-method flow wet steam humidity sensor according to claim 1, characterized in that, The third pressure sensor (15) is arranged coaxially with the third thermocouple (14).

6. A sensor-based humidity measurement method, characterized in that, Includes the following steps: 11) The humidity sensor of the heating method for flowing wet steam according to any one of claims 1-5 is placed in the wet steam to be measured, and the wet steam enters the inner tube (2) through the inlet section of the inner tube (2); the first thermocouple (11) measures the temperature of the wet steam. The wet steam flows through the heating element (4) and is heated into superheated steam. The heating amount of the heating element (4) is... The superheated steam flows through the first rectifier plate (6) and then through the first temperature sensing plate (7). The second thermocouple (12) installed on the first temperature sensing plate (7) measures the temperature of the superheated steam. Meanwhile, the second pressure sensor (13) measures the pressure of the superheated steam. The superheated steam continues to flow along the inner pipe (2) and dissipates heat to the outer pipe (1). Then, the superheated steam flows through the second rectifier plate (8) and the second temperature sensing plate (9). The third thermocouple (14) installed on the second temperature sensing plate (9) measures the temperature of the superheated steam after the heat dissipation has decreased. Meanwhile, the third pressure sensor (15) measures the pressure of the superheated steam whose superheat has decreased after heat dissipation. ; 12) Based on the heating amount of the heating element (4) Heat dissipation from heating element (4) to outer tube (1) Heat dissipation of steam to the outer pipe (1) Temperature of wet steam The temperature of superheated steam and pressure The temperature of superheated steam with reduced superheat. and Calculate the humidity of the wet steam being measured.

7. A calibration method for a heating-based flow wet steam humidity sensor, characterized in that, Includes the following steps: 21) The flow rate of superheated steam or humid air passing through the flow meter. The flow meter outlet is connected to the inlet of the heating method wet steam humidity sensor according to any one of claims 1-5 via a connecting pipe. A pressure gauge is arranged on the connecting pipe to measure the pressure of the superheated steam or humid air flow. Superheated steam or humid air enters the inner tube (2) through the inlet section of the inner tube (2); the first thermocouple (11) measures the temperature of the superheated steam or humid air. Superheated steam or humid air is heated by flowing through the heating element (4), and the heating amount of the heating element (4) is... The heated superheated steam or humid air flows through the first rectifier plate (6) and then through the first temperature sensing plate (7). The second thermocouple (12) installed on the first temperature sensing plate (7) measures the temperature of the heated superheated steam or humid air. Meanwhile, the second pressure sensor (13) measures the pressure of the heated superheated steam or humid air. The superheated steam or humid air continues to flow along the inner pipe (2) and dissipates heat to the outer pipe (1), thus reducing the temperature of the superheated steam or humid air. Then it flows through the second rectifier plate (8) and the second temperature sensing plate (9), and the third thermocouple (14) installed on the second temperature sensing plate (9) measures the temperature of the superheated steam or humid air after the temperature decreases due to heat dissipation. Meanwhile, the third pressure sensor (15) measures the pressure of the superheated steam or humid air whose temperature drops after heat dissipation. ; 22) Based on the heating amount of the heating element (4) Heat dissipation from heating element (4) to outer tube (1) Temperature of superheated steam or humid air flow and pressure The temperature of the superheated steam or humid air after heating and pressure Calculate the flow rate of superheated steam or humid air in the heating section. Based on the amount of heat dissipated from superheated steam or humid air to the outer pipe (1) The temperature of the superheated steam or humid air after heating and pressure The temperature of superheated steam or humid air that decreases in temperature after heat dissipation and Calculate the flow rate of superheated steam or humid air in the heat dissipation section. ;contrast and , and The measurement errors of the heating section and the heat dissipation section are obtained. and Based on the measurement errors of the heating section and the heat dissipation section and The error in obtaining the humidity measurement of wet steam. According to the error in the measurement of the wet steam humidity Calibrate the humidity sensor for the flow of wet steam using the heating method.

Images