A centimeter-level flowing wet steam humidity sensor and its working method

Abstract

The present invention discloses a centimeter-level flowing wet steam humidity sensor and a working method thereof, comprising an outer tube, an inner tube, a thin-walled tube, a first support body, a first heating body, a second support body and a second support body; the outer tube is sleeved on the outer wall of the inner tube, a thin-walled tube is installed in the cavity between the inner tube and the outer tube, a first thermopile array and a second thermopile array are arranged on the thin-walled tube, the first support body and the second support body are nested in the inner wall of the inner tube, and the first heating body and the second heating body are respectively installed in the inner cavity of the first support body and the second support body; a first thermocouple, a second thermocouple and a third thermocouple are sequentially provided on the tube wall of the inner tube along the direction of steam flow, and a second pressure sensor and a third pressure sensor are provided on the tube wall of the inner tube. The sensor and the working method thereof can meet the needs of dynamic measurement.

Description

Technical Field

[0001] The invention relates to a sensor and a working method thereof, and in particular to a centimeter-level flowing wet steam humidity sensor and a working method thereof. Background Art

[0002] The exhaust humidity of wet steam turbines can reach 12%. This wet steam not only reduces turbine stage efficiency but also causes severe blade erosion, compromising both the unit's economic efficiency and safety. Accurately measuring the humidity of flowing wet steam is crucial to wet steam turbine operation. It helps quickly and accurately understand the efficiency of the turbine or wet steam stage, providing a basis for unit optimization and dehumidification structure design.

[0003] Thermodynamic method is a main method for measuring the humidity of flowing wet steam, including throttling method, condensation method, steam-air mixing method and heating method. The throttling method is to throttle the extracted wet steam sample with higher pressure to a lower steam pressure value in the throttling section, so that the steam state after throttling is in the superheated steam zone. The humidity of the steam can be calculated based on the principle that the enthalpy value before and after throttling remains unchanged. However, due to the restrictions of pressure reduction after throttling and ensuring that the steam after throttling is in a superheated state, it is not suitable for measuring wet steam in low pressure areas and with a humidity greater than 8%. The condensation method is to condense the extracted saturated steam sample into water in the condenser, and calculate the humidity of the wet steam based on the steam condensation heat absorbed by the cooling water. Although its structure is relatively simple, While simple, it has low accuracy and is not suitable for measuring exhaust humidity from condensing turbines. The steam-air mixing method involves mixing a wet steam sample with dry air introduced from outside in a mixing chamber under adiabatic conditions. The ratio is selected to ensure that the moisture content of the mixed air is unsaturated or superheated. The humidity of the wet steam sample is calculated based on the law of conservation of mass and energy. However, to ensure that the moisture content of the air at the mixing chamber outlet is not saturated, a large amount of hot air must be introduced. Therefore, when measuring the low-pressure area of a steam turbine, a large-capacity vacuum pump is required. The basic principle of the heating method is to heat a certain flow rate of wet steam to a dry saturated or superheated state. The enthalpy value is obtained by measuring its pressure and temperature. The humidity of the wet steam flow can be calculated based on the steam flow rate, the amount of heat added, and the changes in the thermodynamic parameters of the sample before and after heating. The heating method offers the advantages of a simple measurement principle and high accuracy.

[0004] Electric heating can be used to heat wet steam. Previous studies have proposed electric heating methods for flowing wet steam humidity sensors, all of which use a wet steam sample passing through a straight heating channel with a substantially constant flow area. Heat is transferred from the electric heating element through the channel wall and the water film attached to the inner wall to the wet steam flowing within the channel. However, the exhaust velocity of a condensing steam turbine reaches 80 to 120 m / s, meaning the wet steam being measured enters the humidity sensor at a very high flow rate. This limits the critical heating length required by the heat transfer intensity along the heat transfer path, resulting in an axial length of only about one meter for previous electric heating humidity sensors. This significantly restricts their applicable measurement applications. Furthermore, this excessive axial length results in high thermal inertia, making them unsuitable for dynamic measurements. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a centimeter-level flowing wet steam humidity sensor and a working method thereof, which can meet the needs of dynamic measurement.

[0006] To achieve the above-mentioned object, the centimeter-level flowing wet steam humidity sensor of the present invention comprises an outer tube, an inner tube, a thin-walled cylinder, a first support body, a first heating body, a second support body and a second support body;

[0007] The outer tube is sleeved on the outer wall of the inner tube, a thin-walled tube is installed in the cavity between the inner and outer tubes, a first thermopile array and a second thermopile array are arranged on the thin-walled tube, a first support body and a second support body are nested in the inner wall of the inner tube, and a first heating body and a second heating body are installed in the inner cavities of the first support body and the second support body respectively;

[0008] A first thermocouple, a second thermocouple and a third thermocouple are sequentially arranged on the wall of the inner tube along the direction of steam flow, and a second pressure sensor and a third pressure sensor are also arranged on the wall of the inner tube.

[0009] The first heating body is arranged in a spirally wound electric heating manner.

[0010] The second heating body is arranged in a spirally wound electric heating manner.

[0011] The second pressure sensor and the third pressure sensor are located at the same axial position as the second thermocouple and the third thermocouple, respectively.

[0012] The working method of the centimeter-level flowing wet steam humidity sensor of the present invention comprises the following steps:

[0013] 1) placing the centimeter-level flowing wet steam humidity sensor in the wet steam to be measured, the wet steam entering the inner tube through the inlet end of the inner tube, the first thermocouple detecting the temperature T1 of the wet steam, the wet steam flowing through the first heating body, heating the wet steam by the first heating body to convert the wet steam into superheated steam, the second thermocouple measuring the temperature T2 of the superheated steam, and the second pressure sensor measuring the pressure P2 of the superheated steam, then the superheated steam flowing through the second heating body to be heated again, increasing the superheat of the superheated steam, the third thermocouple measuring the temperature T3 of the superheated steam after the superheat is increased, and the third pressure sensor measuring the pressure P3 of the superheated steam after the superheat is increased, the amount of heating applied to the wet steam by the first heating body is q2, and the amount of heating applied to the superheated steam by the second heating body is q3;

[0014] 2) According to the heating amount q2 of the first heating body, the heating amount q3 of the second heating body, the heat dissipation q d2 , the heat dissipated by the second heating body to the environment q d3 The humidity of the measured wet steam is calculated based on the temperature T1 of the wet steam, the temperature T2 of the superheated steam, the pressure P2 of the superheated steam, the temperature T3 of the superheated steam after the superheat degree is increased after reheating, and the pressure P3 of the superheated steam after the superheat degree is increased after reheating.

[0015] The centimeter-level flowing wet steam humidity sensor is placed in the wet steam to be measured in the opposite direction of the flow.

[0016] The present invention has the following beneficial effects:

[0017] The centimeter-level flowing wet steam humidity sensor and its working method described in the present invention are based on a distributed heating method during specific operation, that is, a first thermopile array and a second thermopile array are arranged on a thin-walled tube, a first support body and a second support body are nested in the inner wall of the inner tube, and a first heating body and a second heating body are respectively installed in the inner cavity of the first support body and the second support body. Although the wet steam still enters the sensor at a speed of 80 to 120 m / s, the cross-sectional area of the heating section channel is significantly increased, the flow rate of the heating section is significantly reduced, the heat exchange time is significantly increased, and the heat exchange area of the heating section is significantly increased. In addition, forced convection heat exchange directly occurs between the heating body and the steam, and there is no other heat transfer link that generates thermal resistance. According to the basic principle of convection heat exchange, in order to achieve the required superheat, the required heating section length is greatly reduced. After calculation and actual testing, the overall length of the sensor can be shortened to the order of several centimeters. In addition, the present invention uses a thermopile array to measure heat dissipation, which greatly improves the measurement accuracy. It has a simple structure and high measurement accuracy. In particular, it has the characteristics of small size and a length of the order of several centimeters, so the thermal inertia is also small. It can be used for dynamic measurement or online measurement of humidity in confined spaces such as turbine interstages. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention.

[0019] Figure 2 Schematic cross-section of the support body.

[0020] Figure 3 A cross-sectional schematic diagram of another support body.

[0021] Figure 4 A cross-sectional schematic diagram of another support body.

[0022] Figure 5 A cross-sectional schematic diagram of another support body.

[0023] Among them, 1 is the outer tube, 2 is the inner tube, 3 is the thin-walled tube, 4 is the first support body, 5 is the first heating body, 6 is the second support body, 7 is the second heating body, 8 is the first thermocouple, 9 is the second pressure sensor, 10 is the second thermocouple, 11 is the third pressure sensor, 12 is the third thermocouple, 13 is the first thermopile array, and 14 is the second thermopile array. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only embodiments of a part of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0025] The accompanying drawings illustrate schematic diagrams of the structures of the disclosed embodiments of the present invention. These figures are not drawn to scale; for the purpose of clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0026] refer to Figure 1 The centimeter-level flowing wet steam humidity sensor of the present invention comprises an outer tube 1, an inner tube 2, a thin-walled tube 3, a first support 4, a first heating body 5, a second support 6 and a second support 6. The cross-section of the first support 4 and the second support 6 contains a plurality of isolated or fused heating and steam flow channels, such as Figures 2 to 5 As shown;

[0027] The outer tube 1 is sleeved on the outer wall of the inner tube 2. A thin-walled tube 3 is installed in the cavity between the inner tube 2 and the outer tube 1. A first thermopile array 13 and a second thermopile array 14 are arranged on the thin-walled tube 3, which are used to measure the heat dissipation q of the first heating body 5 and the second heating body 7 to the environment through the thin-walled tube 3. d2 and q d3 The first support body 4 and the second support body 6 are nested in the inner wall of the inner tube 2, and the first heating body 5 and the second heating body 7 adopt a spirally wound electric heating method and are installed in the inner cavity of the first support body 4 and the second support body 6 respectively.

[0028] A first thermocouple 8, a second thermocouple 10, and a third thermocouple 12 are sequentially arranged on the wall of the inner tube 2 along the direction of steam flow. These thermocouples are used to measure the temperature T1 of the wet steam being measured, the temperature T2 of the superheated steam after the first heating, and the temperature T3 of the superheated steam after the second heating. A second pressure sensor 9 and a third pressure sensor 11 are also arranged on the wall of the inner tube 2 to measure the pressure P2 of the superheated steam after the first heating and the pressure P3 of the superheated steam after the second heating, respectively. The second pressure sensor 9 and the third pressure sensor 11 are located at the same axial position as the second thermocouple 10 and the third thermocouple 12, respectively.

[0029] The working method of the centimeter-level flowing wet steam humidity sensor of the present invention comprises the following steps:

[0030] 1) The centimeter-level flow wet steam humidity sensor of the present invention is placed in the wet steam to be measured in the counter-flow direction. The wet steam enters the inner tube 2 through the inlet end of the inner tube 2. The first thermocouple 8 detects the temperature T1 of the wet steam. The wet steam flows through the first heating body 5, which heats the wet steam to convert it into superheated steam. The second thermocouple 10 measures the temperature T2 of the superheated steam. At the same time, the second pressure sensor 9 measures the pressure P2 of the superheated steam. The superheated steam then flows through the second heating body 7 to be heated again, thereby increasing the superheat of the superheated steam. The third thermocouple 12 measures the temperature T3 of the superheated steam after the superheat is increased. At the same time, the third pressure sensor 11 measures the pressure P3 of the superheated steam after the superheat is increased. The amount of heat applied to the wet steam by the first heating body 5 is q2, and the amount of heat applied to the superheated steam by the second heating body 7 is q3.

[0031] 2) According to the heating amount q2 of the first heating body 5, the heating amount q3 of the second heating body 7, the heat dissipation amount q d2 , the heat dissipation q of the second heating body 7 to the environment d3The humidity of the measured wet steam is calculated based on the temperature T1 of the wet steam, the temperature T2 of the superheated steam, the pressure P2 of the superheated steam, the temperature T3 of the superheated steam after the superheat degree is increased after reheating, and the pressure P3 of the superheated steam after the superheat degree is increased after reheating.

[0032] The specific operations of step 2) are:

[0033] 21) Calculate the steam flow rate m flowing through the sensor;

[0034] The temperature of the wet steam sample entering the sensor is T1, which is heated to the superheated state by the first heating body 5. The state parameters after heating are pressure P2 and temperature T2, the heating amount is q2, and the heat dissipation is q d2 ; The state parameters of the superheated steam after being heated again by the second heating body 7 are pressure P3 and temperature T3, the heating amount is q3, and the heat dissipation is q d3 , according to the energy conservation equation:

[0035]

[0036] Among them, h2 is the enthalpy of the superheated steam in the cross section where the second thermocouple 10 and the second pressure sensor 9 are located, which can be determined according to the water vapor property calculation formula based on the pressure P2 and the temperature T2, u2 is the flow velocity of the superheated steam in the cross section where the second thermocouple 10 and the second pressure sensor 9 are located, q3 is the heating amount of the second heating body 7, h3 is the enthalpy of the superheated steam in the cross section where the third thermocouple 12 and the third pressure sensor 11 are located, which can be determined according to the water vapor property calculation formula based on the pressure P3 and the temperature T3, u3 is the flow velocity of the superheated steam in the cross section where the third thermocouple 12 and the third pressure sensor 11 are located, q d3 It is the heat dissipation between the cross section where the second thermocouple 10 and the second pressure sensor 9 are located and the cross section where the third thermocouple 12 and the third pressure sensor 11 are located.

[0037] According to formula (1), we can get

[0038]

[0039] According to the mass conservation equation:

[0040] m=ρ2A2u2 (3)

[0041] m=ρ3A3u3 (4)

[0042] Wherein, A2 is the flow area of the superheated steam in the cross section where the second thermocouple 10 and the second pressure sensor 9 are located, ρ2 is the density of the superheated steam in the cross section where the second thermocouple 10 and the second pressure sensor 9 are located, A3 is the flow area of the superheated steam in the cross section where the third thermocouple 12 and the third pressure sensor 11 are located, ρ3 is the density of the superheated steam in the cross section where the third thermocouple 12 and the third pressure sensor 11 are located. Substituting equations (3) and (4) into equation (2), we get:

[0043]

[0044] From formula (5), we can get:

[0045]

[0046] Solve equation (6) to obtain the steam flow rate m flowing through the sensor, and then substitute the steam flow rate m into equation (3) to obtain the flow velocity u2 of the superheated steam in the cross section where the second thermocouple 10 and the second pressure sensor 9 are located;

[0047] 22) Calculate the humidity of wet steam

[0048] From the energy conservation equation we get:

[0049]

[0050] Among them, h1 is the enthalpy of the wet steam in the cross section where the first thermocouple 8 is located, u1 is the flow velocity of the wet steam in the cross section where the first thermocouple 8 is located, q2 is the heating amount of the wet steam by the first heating body 5, and q d2 is the heat dissipation between the cross section where the first thermocouple 8 is located and the cross section where the second thermocouple 10 and the second pressure sensor 9 are located. According to formula (7), we get:

[0051]

[0052] According to the mass conservation equation:

[0053] m=ρ1A1u1 (9)

[0054] Given m, use the iterative method to determine u1 and h1, and then use h1 and T1 to determine the humidity of the wet steam being measured.

[0055] It should be noted that the present invention has the following characteristics:

[0056] a) Based on a distributed heating method, the present invention overcomes the critical heating length limitation in the design of previous electric heating flowing wet steam humidity sensors, significantly reducing the length of the sensor's heating section, and reducing the overall sensor length from about 1 meter to less than 10 centimeters, thereby greatly expanding its scope of application. Furthermore, the present invention has the advantages of low thermal inertia and the ability to perform dynamic measurements.

[0057] b) The present invention is based on a distributed heating method, which is essentially equivalent to dividing the wet steam to be measured into several portions and heating each portion separately, thereby significantly increasing the heat exchange area between the steam and the heating body. At the same time, the steam flow rate is significantly reduced, and the heat exchange time between the steam and the heating body is correspondingly significantly increased. At the same time, the heating body directly undergoes forced convection heat exchange with the steam to be measured, minimizing the heat transfer link that generates heat exchange thermal resistance. Therefore, in order to achieve the required superheat, the heating temperature difference between the heating body and the steam can be significantly reduced, thereby avoiding the melting phenomenon caused by the excessive temperature of the heating body, reducing the failure probability of the sensor, and making it suitable for long-term online measurement.

[0058] c) The present invention uses a thermopile array arranged on the thin-walled tube 3 to measure the heat dissipation of the two heating bodies to the environment. According to the measurement principle of the thermopile, the temperature measurement accuracy and resolution can be improved by more than two orders of magnitude, thereby further improving the measurement accuracy of the sensor.

Claims

1. A centimeter-level flowing wet steam humidity sensor, characterized in that: It comprises an outer tube (1), an inner tube (2), a thin-walled tube (3), a first support body (4), a first heating body (5), a second support body (6) and a second heating body (7); The outer tube (1) is sleeved on the outer wall of the inner tube (2); a thin-walled tube (3) is installed in the cavity between the inner tube (2) and the outer tube (1); a first thermopile array (13) and a second thermopile array (14) are arranged on the thin-walled tube (3); a first support body (4) and a second support body (6) are nested in the inner wall of the inner tube (2); and a first heating body (5) and a second heating body (7) are installed in the inner cavities of the first support body (4) and the second support body (6), respectively. A first thermocouple (8), a second thermocouple (10), and a third thermocouple (12) are sequentially provided on the wall of the inner tube (2) along the direction of steam flow, and a second pressure sensor (9) and a third pressure sensor (11) are also provided on the wall of the inner tube (2); The first support body (4) and the second support body (6) are configured such that their cross sections include a plurality of isolated or fused heating and steam flow channels.

2. The centimeter-level flowing wet steam humidity sensor according to claim 1, characterized in that: The first heating body (5) is arranged in a spirally wound electric heating manner.

3. The centimeter-level flowing wet steam humidity sensor according to claim 1, characterized in that: The second heating body (7) is arranged in a spirally wound electric heating manner.

4. The centimeter-level flowing wet steam humidity sensor according to claim 1, characterized in that: The second pressure sensor (9) and the third pressure sensor (11) are respectively located at the same axial position as the second thermocouple (10) and the third thermocouple (12).

5. A method for operating the centimeter-level flowing wet steam humidity sensor according to claim 1, characterized in that: The following steps are involved: 1) The centimeter-level flowing wet steam humidity sensor is placed in the wet steam to be measured, and the wet steam enters the inner tube (2) through the inlet end of the inner tube (2). The first thermocouple (8) detects the temperature T1 of the wet steam. The wet steam flows through the first heating body (5), and the wet steam is heated by the first heating body (5) to become superheated steam. The second thermocouple (10) measures the temperature T2 of the superheated steam, and the second pressure sensor (9) measures the pressure P2 of the superheated steam. Then the superheated steam flows through the second heating body (7) to be heated again, so that the superheat of the superheated steam is increased. The temperature T3 of the superheated steam after the superheat is increased is measured by the third thermocouple (12), and the pressure P3 of the superheated steam after the superheat is increased is measured by the third pressure sensor (11). The heating amount of the wet steam by the first heating body (5) is q2, and the heating amount of the superheated steam by the second heating body (7) is q3; 2) According to the heating amount q2 of the first heating body (5), the heating amount q3 of the second heating body (7), the heat dissipation amount q d2 , the heat dissipated by the second heating body (7) to the environment q d3 The humidity of the measured wet steam is calculated based on the temperature T1 of the wet steam, the temperature T2 of the superheated steam, the pressure P2 of the superheated steam, the temperature T3 of the superheated steam after the superheat degree is increased after reheating, and the pressure P3 of the superheated steam after the superheat degree is increased after reheating.

6. The operating method of the centimeter-level flowing wet steam humidity sensor according to claim 5, characterized in that: The centimeter-level flowing wet steam humidity sensor is placed in the wet steam to be measured in the opposite direction of the flow.

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