Airflow humidity measurement method and sensor based on child-mother hot wire

Abstract

The application discloses a kind of airflow humidity measurement method and sensor based on child-parent hot wire.The sensor is composed of probe and control and measurement circuit, wherein, probe includes child hot wire and parent hot wire, child-parent hot wire is connected with control and measurement circuit, the current wet steam airflow velocity is derived by child hot wire measurement circuit in control and measurement circuit in the application, then the convection heat flow of parent hot wire is derived according to the wet steam airflow velocity, the total heat flow in parent hot wire is determined by parent hot wire measurement circuit in control and measurement circuit, and the total heat flow of parent hot wire is subtracted to obtain phase change heat flow, so as to determine the humidity of wet steam by combining current wet steam airflow velocity.The application can more accurately capture and measure micron and sub-micron scale droplets, so as to more accurately measure the humidity of spontaneously condensed steam.

Description

Technical Field

[0001] This invention relates to the field of liquid phase mass fraction measurement in gas-liquid two-phase flow, and particularly to a method and sensor for measuring airflow humidity based on a mother-daughter hot wire. Background Technology

[0002] Wet steam turbines, as the most important thermal prime movers, occupy an extremely important position in energy, power, and power engineering. Among them, the last few stages of high-power steam turbines in power plants, nuclear power turbines, and geothermal power plant turbines all or most of their stages operate under wet steam conditions, making wet steam problems very serious. The presence of wet steam affects steam turbines mainly in two ways: First, the non-equilibrium two-phase flow of wet steam during the steam condensation process generates wet steam losses. Data shows that a 1% decrease in stage efficiency results in approximately a 1% efficiency loss. Second, water droplets are formed during wet steam condensation. Some of these are primary droplets formed by spontaneous condensation of steam, while others are secondary droplets deposited on the blade surface and torn at the blade trailing edge, forming larger droplets. These secondary droplets carried by the wet steam erode and impact the blades, causing water erosion, and in severe cases, blade breakage. This not only causes economic losses but also threatens the safe operation of the steam turbine.

[0003] Measuring the humidity of wet steam flow is crucial for developing and evaluating the dehumidification efficiency and operational efficiency of steam turbines. Traditional airflow humidity measurement primarily relies on optical methods. However, current optical methods lack accuracy in measuring spontaneously condensed micron- and submicron-sized primary water droplets, which account for over 90% of the humidity. Therefore, there is currently a lack of sensors and measurement methods specifically designed for airflow humidity containing micron- and submicron-sized droplets. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the first objective of this invention is to provide an airflow humidity measurement sensor based on a mother-daughter hot wire. This sensor derives airflow humidity through convection and phase change heat transfer methods, enabling the measurement of airflow humidity at the micron and submicron levels. Furthermore, this sensor possesses advantages such as high measurement accuracy, compact structure, and strong anti-interference capability.

[0005] The second objective of this invention is to provide a method for measuring airflow humidity based on a mother-daughter hot wire.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] An airflow humidity measurement sensor based on a mother-daughter hot wire includes:

[0008] The probe includes two parallel female heating wires and a female heating wire, and a first metal fork to a fourth metal fork. One end of the first metal fork and the third metal fork is welded to one side of the female heating wire and the female heating wire, and one end of the second metal fork and the fourth metal fork is welded to the other side of the female heating wire and the female heating wire. The other ends of the first metal fork to the fourth metal fork are encapsulated by an insulating heat shield and expose the corresponding first to fourth connectors.

[0009] The control and measurement circuit includes a first Wheatstone bridge, a second Wheatstone bridge, a first servo amplifier, and a second servo amplifier. The first Wheatstone bridge includes a first resistor, a second resistor, a first variable resistor, and a female heating wire. The first connector of the female heating wire is connected to the first end of the first resistor and then to the first input terminal of the first servo amplifier. The second connector of the female heating wire is connected to the first end of the first variable resistor and then to the second output terminal of the first servo amplifier. The second resistor is connected to the second end of the first variable resistor and then to the second input terminal of the first servo amplifier. The second end of the first resistor is connected to the first end of the second resistor and then to the... The first output terminal of the first servo amplifier is connected; the second Wheatstone bridge includes a third resistor, a fourth resistor, a second variable resistor, and the sub-hot wire, wherein the connection method between the second Wheatstone bridge and the second servo amplifier is the same as the connection method between the first Wheatstone bridge and the first servo amplifier. The first Wheatstone bridge is used to measure the voltage difference between the main hot wire and the first variable resistor, and after being amplified by the first servo amplifier, the amplified voltage is used as the driving voltage of the first Wheatstone bridge; the second Wheatstone bridge is used to measure the voltage difference between the sub-hot wire and the second variable resistor, and after being amplified by the second servo amplifier, the amplified voltage is used as the driving voltage of the second Wheatstone bridge.

[0010] Optionally, the sub-heating wire is located in the wake region of the mother heating wire, and a preset distance is provided between the mother heating wire and the sub-heating wire. The preset distance is used to ensure that droplets in the wet steam flow will not collide with the sub-heating wire.

[0011] Optionally, the cross-sectional axis length of the mother heating wire and the daughter heating wire is determined according to the diameter of the droplets in the wet steam flow, and the cross-sectional axis length of the mother heating wire and the daughter heating wire is greater than the maximum droplet diameter.

[0012] Optionally, the surfaces of the mother heating wire and the daughter heating wire are provided with a hydrophilic material to give the surfaces of the mother heating wire and the daughter heating wire hydrophilic properties.

[0013] Optionally, the major axis of the mother heating wire cross section and the minor axis of the daughter heating wire cross section are perpendicular to the incoming flow direction of the wet steam gas flow.

[0014] Optionally, the end welding positions of the mother heating wire and the daughter heating wire are encapsulated with insulating and heat-insulating material to form a sleeve.

[0015] Optionally, the mother heating wire and the daughter heating wire are made of platinum-rhodium alloy.

[0016] Optionally, the insulating body is made of an insulating material, which is epoxy resin or ceramic.

[0017] To achieve the above objectives, a second aspect of the present invention provides a method for measuring airflow humidity based on a mother-daughter hot wire, applied to the aforementioned airflow humidity measurement sensor based on a mother-daughter hot wire, comprising:

[0018] Step S1: Place the airflow humidity measurement sensor in saturated dry steam with different incoming flow velocities and temperatures for calibration testing to obtain the correspondence between different incoming flow velocities and temperatures and the driving voltage of the sub-hot wire measurement circuit and the driving voltage of the main hot wire measurement circuit, respectively.

[0019] Step S2: Place the airflow humidity measurement sensor in the humid steam airflow, adjust the resistance value of the first variable resistor in the sub-hot wire measurement circuit until the driving voltage of the sub-hot wire measurement circuit is zero, and determine the resistance value of the sub-hot wire according to the resistance value of the first variable resistor, so as to determine the temperature of the humid steam airflow according to the resistance value of the sub-hot wire, and determine the speed of the humid steam airflow according to the temperature of the humid steam airflow and the driving voltage of the sub-hot wire measurement circuit;

[0020] Step S3: Obtain the driving voltage of the bus heating wire measuring circuit and determine the current of the bus heating wire so as to determine the wet steam power based on the driving voltage of the bus heating wire measuring circuit and the current of the bus heating wire.

[0021] Step S4: Based on the wet steam flow velocity and wet steam flow temperature in Step S2, and the correspondence between different incoming flow velocities, incoming flow temperatures and driving voltage of the main heating wire measuring circuit in Step S1, determine the driving voltage of saturated dry steam at the corresponding velocity and temperature and the corresponding dry steam thermal power.

[0022] Step S5: Calculate the difference between the wet steam power and the dry steam heat power to obtain the phase change heat power;

[0023] Step S6: Determine the latent heat of phase change of the wet steam gas flow at the current wet steam gas flow temperature, and calculate the mass flow rate of the droplets deposited on the mother hot wire based on the latent heat of phase change and the phase change heat power;

[0024] Step S7: Obtain the frontal area of ​​the main heating wire, and calculate the humidity of the wet steam based on the frontal area, the wet steam flow velocity, the wet steam flow temperature, and the mass flow rate.

[0025] Optionally, the mass flow rate of the droplets and the humidity of the wet vapor can be calculated using the following formulas:

[0026]

[0027]

[0028] Where ml is the mass flow rate of the droplet, P1l is the phase change heat power, L is the latent heat of phase change, h is the humidity of the wet steam, ρ is the steam density at the corresponding wet steam gas flow temperature, U is the wet steam gas flow velocity, and S is the frontal area.

[0029] This invention has at least the following technical effects:

[0030] 1. The airflow humidity measurement sensor of the present invention consists of a probe and a control and measurement circuit. The probe comprises two metal filaments resistant to high temperatures and oxidation, serving as a daughter heating wire and a mother heating wire. These two filaments are parallel to each other and perpendicular to the flow direction of the humid steam airflow. The control and measurement circuit enables the daughter and mother heating wires to be heated to a constant temperature by an electric current. This temperature is significantly higher than the temperature of the humid steam airflow. In this invention, both the daughter and mother heating wires are subjected to convective cooling by the humid steam airflow, and the convective heat flow rate in both the daughter and mother heating wires depends on the velocity of the humid steam airflow. Furthermore, the humid steam... The steam flow contains spontaneously condensed water droplets. These droplets collide with the high-temperature main heating wire and rapidly vaporize, creating a phase change cooling effect on the main heating wire. The phase change heat flow depends on the velocity and humidity of the wet steam flow. Because the secondary heating wire is located downstream of the main heating wire in the wake region, it ensures that water droplets in the wet steam flow will not collide with the secondary heating wire. This results in only convective heat flow on the secondary heating wire, which depends on the velocity of the wet steam flow. The main heating wire, in addition to generating convective heat flow corresponding to the velocity of the wet steam flow, also generates a phase change heat flow depending on the velocity and humidity of the wet steam flow. Therefore, this invention derives the current wet steam flow velocity through the secondary heating wire measurement circuit, then derives the convective heat flow of the main heating wire based on this velocity, determines the total heat flow in the main heating wire through the main heating wire measurement circuit, and subtracts the convective heat flow from the total heat flow to obtain the phase change heat flow. Finally, combining this with the current wet steam flow velocity, the humidity of the wet steam can be determined. This invention uses a thermodynamic method to measure airflow humidity, which can more accurately capture and measure droplets at the micron and submicron scales, thereby enabling more precise measurement of the humidity of spontaneously condensed steam.

[0031] 2. The probe of this invention has a small size, which provides higher spatial resolution for humidity measurement. In addition, the probe itself causes little disturbance to the flow field, and its measurement results can more accurately reflect the humidity of the actual airflow.

[0032] 3. The probe of this invention can deduce airflow humidity through only two voltage outputs, the data processing has low hardware requirements, and the sensor calibration process is also simpler.

[0033] 4. This invention can not only measure the humidity of wet steam, but also simultaneously obtain the velocity and temperature of wet steam.

[0034] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the probe structure provided in an embodiment of the present invention.

[0036] Figures 2-3 This is a schematic diagram of the control and measurement circuit provided in an embodiment of the present invention.

[0037] Figure 4 This is a flowchart of an airflow humidity measurement method based on a mother-daughter hot wire provided in an embodiment of the present invention. Detailed Implementation

[0038] The following describes this embodiment in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0039] The airflow humidity measurement method and sensor based on a mother-daughter hot wire according to this embodiment are described below with reference to the accompanying drawings. The airflow humidity measurement sensor of this embodiment includes a probe and control and measurement circuitry.

[0040] Figure 1 This is a schematic diagram of the probe structure provided in an embodiment of the present invention. Figure 1 As shown, the probe includes two parallel female heating wires 1 and female heating wires 2, and a first metal fork 3 to a fourth metal fork 6. One end of the first metal fork 3 and the third metal fork 5 is welded to one side of the female heating wire 1 and the female heating wire 2, and one end of the second metal fork 4 and the fourth metal fork 6 is welded to the other side of the female heating wire 1 and the female heating wire 2. The other ends of the first metal fork 3 to the fourth metal fork 6 are encapsulated by an insulating heat shield 7, exposing the corresponding first connector 8 to the fourth connector 11.

[0041] In this embodiment, the cross-sectional shape of the mother heating wire 1 and the daughter heating wire 2 is elliptical. The cross-sectional axis length is determined according to the diameter of the droplets in the wet steam gas flow. The cross-sectional axis length of the mother heating wire 1 and the daughter heating wire 2 is greater than the maximum droplet diameter. Specifically, for primary water droplets formed by spontaneous condensation, the cross-sectional axis length is selected between 3 micrometers and 10 micrometers. The effective length of the mother heating wire 1 and the daughter heating wire 2 is selected to be more than 20 times the cross-sectional axis length and less than 2 millimeters. Preferably, in this embodiment, the major axis length of the mother heating wire 1 and the daughter heating wire 2 is 5 micrometers, the minor axis length is 2.5 micrometers, and the total length of the mother heating wire 1 and the daughter heating wire 2 is 2 millimeters.

[0042] In this embodiment, the upstream metal filament is the mother heating wire 1, and the downstream metal filament is the daughter heating wire 2. The daughter heating wire 2 is located in the wake region of the mother heating wire 1. The preset distance between the axes of the mother heating wire 1 and the daughter heating wire 2 is maintained at 15 micrometers to ensure that the droplets in the wet steam flow will not collide with the daughter heating wire 2, so that only convective heat flow is generated on the daughter heating wire 2.

[0043] In this embodiment, the main heating wire 1 and the daughter heating wire 2 are perpendicular to the direction of the wet steam flow when they are working. The major axis of the cross-section of the main heating wire 1 is perpendicular to the direction of the incoming flow, which can ensure that the main heating wire 1 has the largest incoming flow area. The minor axis of the cross-section of the daughter heating wire 2 is perpendicular to the direction of the incoming flow, which can ensure that the daughter heating wire 2 has a larger convective heat transfer area.

[0044] It should be noted that the surfaces of the mother heating wire 1 and the daughter heating wire 2 may be coated with a hydrophilic material to give them hydrophilic properties, thereby ensuring that droplets impacting the mother heating wire 1 do not bounce back. In this embodiment, the materials of the mother heating wire 1 and the daughter heating wire 2 may be selected from platinum-rhodium alloys with high mechanical strength, high temperature resistance, oxidation resistance, and temperature coefficient of resistance, as well as weldability.

[0045] As described above, the ends of the mother heating wire 1 and the daughter heating wire 2 are welded to the first to fourth metal forks 3 to 6 with high conductivity. Each metal fork is made of hard copper alloy, and the end that contacts the mother heating wire 1 and the daughter heating wire 2 is arc-shaped to avoid leakage between the metal forks. The other end of each metal fork is encapsulated by an insulating heat shield 7 to ensure that the metal forks are insulated from each other, and the first to fourth connectors 8 to 11 that are connected to the control and measurement circuit are exposed. When encapsulating the metal forks, it is necessary to ensure that the mother heating wire 1 and the daughter heating wire 2 are in a pre-tensioned state between the metal forks, so as to ensure that the heating wires are minimally stretched and deformed in the airflow.

[0046] Furthermore, the end solder joints of the mother heating wire 1 and the daughter heating wire 2 can be encapsulated with insulating and heat-insulating material to form a first sleeve 12 and a second sleeve 13. In this embodiment, the sleeves ensure that the distance between the daughter heating wire 2 and the mother heating wire 1 remains constant. It should be noted that the heating wire segments within the first sleeve 12 and the second sleeve 13 in this embodiment do not participate in heat exchange. The axial lengths of the first sleeve 12 and the second sleeve 13 in this embodiment are each 0.5 mm, resulting in an effective length of 1 mm for the mother heating wire 1 and the daughter heating wire 2.

[0047] Preferably, the insulating and heat-insulating body 7 in this embodiment can be made of the insulating and heat-insulating material, which can be epoxy resin or ceramic.

[0048] Figure 2 and Figure 3 This is a schematic diagram of the control and measurement circuit provided in an embodiment of the present invention. Figure 2 and Figure 3 As shown, the control and measurement circuit includes a first Wheatstone bridge a1, a second Wheatstone bridge a2, a first servo amplifier b1, and a second servo amplifier b2. The first Wheatstone bridge a1 includes a first resistor 15, a second resistor 16, a first variable resistor 14, and a main heating wire 1. The first connector 8 of the main heating wire 1 is connected to the first end of the first resistor 15, and then to the first input terminal of the first servo amplifier b1. The second connector 9 of the main heating wire 1 is connected to the first end of the first variable resistor 14, and then to the second output terminal of the first servo amplifier b1. The second resistor 16 is connected to the second end of the first variable resistor 14, and then to the second input terminal of the first servo amplifier b1. The second end of the first resistor 15 is connected to the first end of the second resistor 16, and then to the first output terminal of the first servo amplifier b1. Figure 3 As shown, the second Wheatstone bridge a2 includes a third resistor 17, a fourth resistor 18, a second variable resistor 19, and a sub-hot wire 2. The connection method between the second Wheatstone bridge a2 and the second servo amplifier b2 is the same as the connection method between the first Wheatstone bridge a1 and the first servo amplifier b1.

[0049] Among them, the first resistor 15 and the second resistor 16 have the same resistance value, the third resistor 17 and the fourth resistor 18 have the same resistance value, and the current heating in the first Wheatstone bridge a1 and the second Wheatstone bridge a2 can raise the temperature of the mother and child hot wires, thereby causing the resistance of the hot wires to change.

[0050] In this embodiment, the first Wheatstone bridge a1 is used to measure the voltage difference between the main hot wire 1 and the first variable resistor 14. After being amplified by the first servo amplifier b1, the amplified voltage is used as the driving voltage V1 of the first Wheatstone bridge a1. In this embodiment, the second Wheatstone bridge a2 is used to measure the voltage difference between the sub-hot wire 2 and the second variable resistor 19. After being amplified by the second servo amplifier b2, the amplified voltage is used as the driving voltage V2 of the second Wheatstone bridge a2.

[0051] In this embodiment, the control and measurement circuit can automatically adjust the voltage on the hot wire so that the resistance of the hot wire approaches the voltage of the variable resistor, thereby making the temperature of the hot wire approach the temperature corresponding to the target resistance value, so as to achieve the goal of constant temperature of the hot wire.

[0052] Specifically, the resistance of the first variable resistor 14 in the main heating wire measurement circuit can be set to R1, which is equal to the resistance of the main heating wire 1 at 300℃. When the temperature of the main heating wire 1 is below 300℃, the real-time resistance R1r of the main heating wire 1 is less than R1. The voltage difference V1r between the main heating wire 1 and the first variable resistor 14 is proportional to the resistance value (R1-R1r). After the voltage difference V1r is amplified by r times by the first servo amplifier b1, it forms the driving voltage V1 = r*V1r. When there is no heat exchange between the main heating wire 1 and the environment, the main heating wire 1 will stop heating after being heated to 300℃. When the main heating wire 1 is cooled by the airflow, the main heating wire 1 will be continuously heated by the circuit to replenish the heat carried away by the airflow. When the temperature of the main heating wire 1 is stable, the convective heat transfer is equal to the current heating amount. Among them, the driving voltage r*V1r of the current corresponds one-to-one with the wet steam airflow velocity, and this correspondence needs to be experimentally calibrated.

[0053] Figure 4 This is a flowchart illustrating an embodiment of the airflow humidity measurement method based on a mother-daughter hot wire according to the present invention. Figure 4 As shown, the method includes:

[0054] Step S1: Place the airflow humidity measurement sensor in saturated dry steam with different inflow velocities and temperatures for calibration testing to obtain the correspondence between different inflow velocities and temperatures and the driving voltage of the sub-hot wire measurement circuit and the driving voltage of the main hot wire measurement circuit, respectively.

[0055] Step S2: Place the airflow humidity measurement sensor in the wet steam airflow, adjust the resistance value of the first variable resistor in the sub-hot wire measurement circuit until the driving voltage of the sub-hot wire measurement circuit is zero, and determine the resistance value of the sub-hot wire based on the resistance value of the first variable resistor, so as to determine the wet steam airflow temperature based on the resistance value of the sub-hot wire, and determine the wet steam airflow speed based on the wet steam airflow temperature and the driving voltage of the sub-hot wire measurement circuit.

[0056] In this embodiment, a weak driving voltage can also be applied, and then the actual resistance of the sub-heater can be measured to infer the temperature of the wet steam flow. Then, the current wet steam flow velocity can be calculated based on the driving voltage of the sub-heater measurement circuit and the wet steam flow temperature.

[0057] Step S3: Obtain the driving voltage of the bus heating wire measuring circuit and determine the current of the bus heating wire so as to determine the wet steam power based on the driving voltage of the bus heating wire measuring circuit and the current of the bus heating wire.

[0058] In this embodiment, the driving voltage V1 of the bus heating wire measurement circuit can be obtained, and the current I1 of the bus heating wire can be determined. Then, the wet steam power, i.e., the total heat power, can be determined according to the following formula:

[0059] P1 = V1·I1 2 (1)

[0060] Where P1 is the wet steam power.

[0061] Step S4: Based on the wet steam flow velocity and wet steam flow temperature in Step S2, and the correspondence between different incoming flow velocities, incoming flow temperatures and driving voltage of the main heating wire measuring circuit in Step S1, determine the driving voltage of saturated dry steam at the corresponding velocity and temperature and the corresponding dry steam thermal power.

[0062] Step S5: Calculate the difference between the wet steam power and the dry steam heat power to obtain the phase change heat power.

[0063] Step S6: Determine the latent heat of phase change of the wet steam gas flow at the current wet steam gas flow temperature, and calculate the mass flow rate of the droplets deposited on the mother hot wire based on the latent heat of phase change and the phase change heat power.

[0064] Step S7: Obtain the frontal area of ​​the main heating wire, and calculate the humidity of the wet steam based on the frontal area, wet steam flow velocity, wet steam flow temperature and mass flow rate.

[0065] In one embodiment of the present invention, the mass flow rate of the droplet and the humidity of the wet vapor can be calculated using the following formulas:

[0066]

[0067]

[0068] Where ml is the mass flow rate of the droplet, P1l is the phase change heat power, L is the latent heat of phase change, h is the humidity of the wet steam, ρ is the steam density at the corresponding wet steam gas flow temperature, U is the wet steam gas flow velocity, and S is the frontal area.

[0069] To separate the heat transfer caused by droplet impacts on the mother heating wire from the total heat transfer of the mother heating wire, this invention uses a sensor probe comprising two independent mother heating wires and a daughter heating wire. The mother and daughter heating wires are parallel to each other and perpendicular to the flow direction of the wet steam gas flow. The mother and daughter heating wires in this invention can be heated to a constant temperature by electric current, which is significantly higher than the temperature of the wet steam gas flow. The daughter heating wire is located in the wake region of the mother heating wire, and the spacing between the mother and daughter heating wires ensures that droplets in the wet steam gas flow cannot impact the daughter heating wire. Therefore, the daughter heating wire only experiences convective heat transfer with the wet steam, from which the wet steam flow velocity can be derived. The mother heating wire, on the other hand, experiences both convective heat transfer and phase change heat transfer caused by droplet impacts. Its convective heat transfer can be derived from the corresponding wet steam flow velocity, and the remaining phase change heat transfer can be obtained by subtracting the convective heat transfer from the total heat transfer. Thus, the mass flow rate of droplets impacting the mother heating wire can be derived from the phase change heat transfer, and the droplet mass fraction, i.e., the humidity of the wet steam, can be calculated.

[0070] In summary, this invention, through its thermodynamic method, can more accurately capture and measure droplets at the micron and submicron scales, thereby more accurately measuring the humidity of spontaneously condensed steam. The small probe size of this invention provides higher spatial resolution for humidity measurement, and the probe itself causes minimal disturbance to the flow field, resulting in measurement results that more accurately reflect the actual humidity of the airflow. Furthermore, the probe only requires two voltage outputs to derive airflow humidity, resulting in low hardware requirements for data processing and a simpler sensor calibration process. Finally, this invention can not only measure the humidity of wet steam but also simultaneously acquire its velocity and temperature.

[0071] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0072] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. An airflow humidity measurement sensor based on a mother-daughter hot wire, characterized in that, include: The probe includes two parallel female heating wires and a female heating wire, and a first metal fork to a fourth metal fork. One end of the first metal fork and the third metal fork is welded to one side of the female heating wire and the female heating wire, and one end of the second metal fork and the fourth metal fork is welded to the other side of the female heating wire and the female heating wire. The other ends of the first metal fork to the fourth metal fork are encapsulated by an insulating heat shield and expose the corresponding first to fourth connectors. The control and measurement circuit includes a first Wheatstone bridge, a second Wheatstone bridge, a first servo amplifier, and a second servo amplifier. The first Wheatstone bridge includes a first resistor, a second resistor, a first variable resistor, and a female heating wire. The first connector of the female heating wire is connected to the first end of the first resistor and then to the first input terminal of the first servo amplifier. The second connector of the female heating wire is connected to the first end of the first variable resistor and then to the second output terminal of the first servo amplifier. The second resistor is connected to the second end of the first variable resistor and then to the second input terminal of the first servo amplifier. The second end of the first resistor is connected to the first end of the second resistor and then to the... The first output terminal of the first servo amplifier is connected; the second Wheatstone bridge includes a third resistor, a fourth resistor, a second variable resistor, and the sub-hot wire, wherein the connection method between the second Wheatstone bridge and the second servo amplifier is the same as the connection method between the first Wheatstone bridge and the first servo amplifier. The first Wheatstone bridge is used to measure the voltage difference between the main hot wire and the first variable resistor, and after being amplified by the first servo amplifier, the amplified voltage is used as the driving voltage of the first Wheatstone bridge; the second Wheatstone bridge is used to measure the voltage difference between the sub-hot wire and the second variable resistor, and after being amplified by the second servo amplifier, the amplified voltage is used as the driving voltage of the second Wheatstone bridge; The sub-heating wire is located in the wake region of the main heating wire. A preset distance is provided between the main heating wire and the sub-heating wire. The preset distance is used to ensure that droplets in the wet steam flow will not collide with the sub-heating wire. The cross-sectional axis length of the mother heating wire and the daughter heating wire is determined according to the diameter of the droplets in the wet steam flow, and the cross-sectional axis length of the mother heating wire and the daughter heating wire is greater than the maximum droplet diameter.

2. The airflow humidity measurement sensor based on a mother-daughter hot wire as described in claim 1, characterized in that, The surfaces of the mother heating wire and the daughter heating wire are provided with a hydrophilic material to give the surfaces of the mother heating wire and the daughter heating wire hydrophilic properties.

3. The airflow humidity measurement sensor based on a mother-daughter hot wire as described in claim 2, characterized in that, The major axis of the mother heating wire cross section and the minor axis of the daughter heating wire cross section are perpendicular to the incoming flow direction of the wet steam gas flow.

4. The airflow humidity measurement sensor based on a mother-daughter hot wire as described in claim 3, characterized in that, The welding positions at the ends of the main heating wire and the sub-heating wire are encapsulated with insulating and heat-insulating material to form sleeves.

5. The airflow humidity measurement sensor based on a mother-daughter hot wire as described in claim 1, characterized in that, The mother heating wire and the daughter heating wire are made of platinum-rhodium alloy.

6. The airflow humidity measurement sensor based on a mother-daughter hot wire as described in claim 1, characterized in that, The insulating and heat-insulating body is made of insulating and heat-insulating material, which is epoxy resin or ceramic body.

7. A method for measuring airflow humidity based on a mother-daughter hot wire, applied to an airflow humidity measuring sensor based on a mother-daughter hot wire as described in any one of claims 1-6, characterized in that, include: Step S1: Place the airflow humidity measurement sensor in saturated dry steam with different incoming flow velocities and temperatures for calibration testing to obtain the correspondence between different incoming flow velocities and temperatures and the driving voltage of the sub-hot wire measurement circuit and the driving voltage of the main hot wire measurement circuit, respectively. Step S2: Place the airflow humidity measurement sensor in the humid steam airflow, adjust the resistance value of the first variable resistor in the sub-hot wire measurement circuit until the driving voltage of the sub-hot wire measurement circuit is zero, and determine the resistance value of the sub-hot wire according to the resistance value of the first variable resistor, so as to determine the temperature of the humid steam airflow according to the resistance value of the sub-hot wire, and determine the speed of the humid steam airflow according to the temperature of the humid steam airflow and the driving voltage of the sub-hot wire measurement circuit; Step S3: Obtain the driving voltage of the bus heating wire measuring circuit and determine the current of the bus heating wire so as to determine the wet steam power based on the driving voltage of the bus heating wire measuring circuit and the current of the bus heating wire. Step S4: Based on the wet steam flow velocity and wet steam flow temperature in Step S2, and the correspondence between different incoming flow velocities, incoming flow temperatures and driving voltage of the main heating wire measuring circuit in Step S1, determine the driving voltage of saturated dry steam at the corresponding velocity and temperature and the corresponding dry steam thermal power. Step S5: Calculate the difference between the wet steam power and the dry steam heat power to obtain the phase change heat power; Step S6: Determine the latent heat of phase change of the wet steam gas flow at the current wet steam gas flow temperature, and calculate the mass flow rate of the droplets deposited on the mother hot wire based on the latent heat of phase change and the phase change heat power; Step S7: Obtain the frontal area of ​​the main heating wire, and calculate the humidity of the wet steam based on the frontal area, the wet steam flow velocity, the wet steam flow temperature and the mass flow rate.

8. The airflow humidity measurement method based on mother-daughter hot wire as described in claim 7, characterized in that, The mass flow rate of the droplets and the humidity of the wet vapor were calculated using the following formulas: in, The mass flow rate of the droplet. For phase change heat power, For latent heat of phase transition, The humidity of wet steam. To correspond to the steam density at the temperature of the wet steam flow, The velocity of the wet steam flow. The area facing the airflow.

Images