Design method of hyperbolic cosine gap sensor and grid isolator for measuring water film thickness

Abstract

The present invention discloses a design method of a hyperbolic cosine gap sensor and a grid isolator for measuring the thickness of a water film, comprising a cylindrical cavity with openings at both ends and a microwave signal transmission interface in the middle, and a grid isolator is respectively arranged at both ends of the cylindrical cavity, and the grid isolator is composed of a middle straight metal strip and more than one pair of hyperbolic cosine metal strips symmetrically distributed about the middle straight metal strip, and one end of the hyperbolic cosine metal strips close to the port of the cylindrical cavity is connected to the cylindrical cavity. The present invention cooperates with a microwave signal processing circuit to realize microwave measurement of the thickness of water film and liquid film on the inner surface of cylindrical metal; the structure is simple, easy to use, has low requirements on the environment, and has high measurement accuracy; the grid isolator structure has a large opening, which can ensure good flow characteristics and accurate sampling; at the same time, the opening along the direction of the current density of the end face of the resonant cavity can ensure good electromagnetic performance and radiation performance.

Description

Technical Field

[0001] The invention relates to a design method of a resonant cavity sensor and a grid isolator for measuring the thickness of a water film, and in particular to a design method of a hyperbolic cosine gap sensor and a grid isolator for measuring the thickness of a water film, belonging to the field of testing technology. Background Art

[0002] The last few stages of large condensing steam turbines in conventional power plants and all stages of turbines in nuclear power plants operate under wet steam conditions. The humidity of steam directly affects the safety and economy of steam turbine operation. The increase in steam humidity will cause strong erosion and impact on the turbine blades, making the blades rough, pitted, and even causing the blades to twist and break, seriously threatening the safe operation of the turbine; at the same time, it will also reduce the thermal efficiency of the turbine. In geothermal power plants and nuclear power plants, the harm to the economy and safety of steam turbine generator sets caused by the appearance of saturated steam is particularly prominent. Therefore, the accurate measurement of the humidity of wet steam is of great significance to the long-term stability and life of the steam turbine.

[0003] Since the microwave resonant cavity perturbation method for measuring steam humidity was proposed in 2003, the microwave resonant cavity measurement of steam humidity has been widely studied. At present, the research in this field is mainly focused on steam humidity calibration and measurement accuracy improvement. The microwave perturbation method uses a microwave cylindrical resonant cavity as a humidity sensor. The operating frequency is in the microwave band. The equipment cost is not high and online measurement can be achieved. Compared with humidity measurement methods such as thermodynamics and optical measurement, the microwave perturbation method is more suitable for online measurement of steam humidity in steam turbines.

[0004] Since the microwave perturbation humidity sensor must be placed under the wet steam of the steam turbine for a long time, a layer of water film will be deposited on the inner wall of the resonance cavity. If the thickness of the water film deposited on the inner wall of the resonance cavity is 35μm, the humidity measurement deviation caused by ignoring the influence of the water film is 1.262%, so the accurate measurement of the water film thickness can improve the humidity measurement accuracy. In addition, the accurate measurement of the water film thickness is of great significance to automobile exhaust, skids, road conditions, sliding bearings, etc. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a design method of a hyperbolic cosine gap sensor and a grid isolator for measuring the thickness of a water film.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] Technical solution 1:

[0008] A hyperbolic cosine gap sensor for measuring water film thickness, comprising a resonant cavity body, a left-end wedge-shaped cylinder and a right-end wedge-shaped cylinder; the resonant cavity body is composed of a resonant cavity and a left grid isolator and a right grid isolator, the left and right ends of the resonant cavity are respectively connected to the left grid isolator and the right grid isolator, the left grid isolator and the right grid isolator have the same structure, both of which are composed of a straight middle metal strip and more than one hyperbolic cosine metal strip symmetrically distributed about the middle metal strip; the left end of the left end isolator is connected to the left end wedge-shaped cylinder, and the right end isolator is connected to the right end wedge-shaped cylinder; the side wall of the resonant cavity body is provided with a coupling mounting hole; the resonant cavity works at TE 111 mode.

[0009] The radius of the resonant cavity is 20.59 mm. The left and right grid isolators are composed of a middle metal strip and eight hyperbolic cosine metal strips symmetrically distributed on the left and right sides. The width of the metal strips is 1 mm. The x-axis passes through the center point of the circle and coincides with the direction of the middle metal strip. The y-axis is orthogonal to the x-axis. The four hyperbolic cosine metal strips along the positive direction of the y-axis pass through the points (0, 4.511), (0, 7.855), (0, 12.15), and (0, 16.9) respectively. The corresponding function equations are: y1 = 0.011cosh(x / 4) + 4.5, y2 = 0.055cosh(x / 4) + 7.8, y3 = 0.35cosh(x / 4) + 11.8, y4 = 2.1cosh(x / 4) + 14.8; the units are all mm. In the formula, x is the variable of the x-axis, and y1, y2, y3, and y4 are the variables of the y-axis.

[0010] The wall surface of the airflow inflow end of the left end wedge-shaped cylinder and the wall surface of the airflow outflow end of the right end wedge-shaped cylinder are both wedge-shaped structures.

[0011] The coupling mode of the resonant cavity body is coaxial line excitation.

[0012] Technical solution 2:

[0013] A design method for a grid isolator in a hyperbolic cosine gap sensor for measuring water film thickness according to a design technical solution 1, wherein the design method of the left-end grid isolator is the same as that of the right-end grid isolator, and the left-end grid isolator includes the following specific steps:

[0014] Step 1: Calculate the direction of the current density at the end of the resonant cavity: Set the x-axis through the center point of the left grid isolator and coincide with the direction of the middle metal strip, and set the y-axis to be orthogonal to the x-axis; J r is the radial component of the current density at the end face of the resonant cavity, is the tangential component of the current density at the end of the resonant cavity, J is the current density at the end of the resonant cavity; the current density at the end of the resonant cavity J and the radial component of the current density at the end of the resonant cavity J rThe tangent value of the angle θ1 is:

[0015]

[0016] In formula (1), J1 is the first-order Bessel function, and J1' is the first-order derivative of the first-order Bessel function;

[0017] Step 2: Position the hyperbolic cosine metal strips: Determine the position of the hyperbolic cosine metal strips according to the strength of the current density distribution on the end face of the resonant cavity. The distances from the intersection of the four pairs of hyperbolic cosine metal strips and the y-axis to the origin are 0.22R, 0.38R, 0.59R, and 0.82R, respectively, where R is the radius of the resonant cavity.

[0018] Step 3: Determine the shape of the hyperbolic cosine metal strip: fit the constants a, b, and c in the corresponding hyperbolic cosine function y=acosh(x / b)+c through the intersection points of each hyperbolic cosine metal strip and the y-axis in turn, so that the slope of any point (x, y) on the hyperbolic cosine function is the same as the direction of the current density at the corresponding point in formula (1).

[0019] The technical effects achieved by adopting the above technical solution are:

[0020] 1. The present invention cooperates with the microwave signal processing circuit to realize microwave measurement of the thickness of water film and liquid film on the inner surface of cylindrical metal;

[0021] 2. The present invention has a simple structure, low environmental requirements and high measurement accuracy;

[0022] 3. The grid isolator structure of the present invention has a larger opening, which can ensure good flow characteristics and accurate sampling; at the same time, the opening along the current density direction of the resonant cavity end face can ensure good electromagnetic performance and radiation performance. When the input power is 1w, the radiation can be as small as 0.01w. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0024] Figure 1 It is a schematic diagram of the structure of the present invention;

[0025] Figure 2 It is a schematic structural diagram of the left end wedge-shaped cylinder in Example 1 of the present invention;

[0026] Figure 3 It is a left side view of the left end wedge-shaped cylinder in Example 1 of the present invention;

[0027] Figure 4 is a schematic structural diagram of the left-end grid isolator in Example 1 of the present invention;

[0028] Figure 5It is a left side view of the left end grid isolator in Example 1 of the present invention;

[0029] Figure 6 is a schematic structural diagram of the resonant cavity body in Example 1 of the present invention;

[0030] Figure 7 is a left side view of the resonant cavity body in Example 1 of the present invention;

[0031] Among them: 1. left end wedge-shaped cylinder, 2. left end grid isolator, 3. resonant cavity body, 3-1, resonant cavity, 4. coupling component mounting hole, 5. right end grid isolator, 6. right end wedge-shaped cylinder. DETAILED DESCRIPTION

[0032] Embodiment 1:

[0033] A hyperbolic cosine gap sensor for measuring water film thickness comprises a resonant cavity body 3, a left-end wedge-shaped cylinder 1 and a right-end wedge-shaped cylinder 6; the resonant cavity body consists of a resonant cavity 3-1 and a left grid isolator 2 and a right grid isolator 5, the left and right ends of the resonant cavity 3-1 are respectively connected to the left grid isolator 2 and the right grid isolator 5, the left grid isolator 2 and the right grid isolator 5 have the same structure, and are both composed of 9 metal strips; the middle metal strip of the 9 metal strips is a straight line, and the remaining 8 hyperbolic cosine metal strips are symmetrically distributed about the middle metal strip; the left end of the left end isolator 2 is connected to the left end wedge-shaped cylinder 1, and the right end thereof is connected to the right end wedge-shaped cylinder 6; the side wall of the resonant cavity body 3 is provided with a coupling mounting hole 4.

[0034] The left-end grid isolator (2) and the right-end grid isolator (5) are both composed of a middle metal strip and four pairs of hyperbolic cosine metal strips symmetrically distributed on the left and right sides. The width of the metal strips is 1 mm. The x-axis passes through the center point of the circle and coincides with the direction of the middle metal strip. The y-axis is orthogonal to the x-axis. The four hyperbolic cosine metal strips along the positive direction of the y-axis pass through points (0, 4.511), (0, 7.855), (0, 12.15), and (0, 16.9) in sequence. Their function equations are: y1 = 0.011cosh(x / 4) + 4.5, y2 = 0.055cosh(x / 4) + 7.8, y3 = 0.35cosh(x / 4) + 11.8, y4 = 2.1cosh(x / 4) + 14.8; the units are all mm. In the formula, x is the variable of the x-axis, and y1, y2, y3, and y4 are the variables of the y-axis.

[0035] The airflow inflow end wall surface of the left end wedge-shaped cylinder 1 and the airflow outflow end wall surface of the right end wedge-shaped cylinder 6 are both wedge-shaped structures.

[0036] The coupling mode of the resonant cavity body 3 is coaxial line excitation.

[0037] The resonant cavity body 3, the left-end grid isolator 2, and the right-end grid isolator 5 are all made of the same material with a low expansion coefficient.

[0038] The resonant cavity 3-1 generally adopts a cylindrical resonant cavity that is easy to process. When the steam to be measured flows through the resonant cavity 3-1 at a high speed from the left end wedge-shaped cylinder 1 through the left end grid isolator 2, a layer of water film will form on the inner wall of the resonant cavity 3-1 over time. If the structure and size of the resonant cavity are constant, the resonant frequency will be different if the water film thickness is different. By monitoring the change of the resonant frequency of the resonant cavity, the water film thickness of the resonant cavity can be indirectly obtained.

[0039] At a certain pressure and temperature, the thickness of the water film is a function of the resonant frequency and the dielectric constant of the liquid film.

[0040] Due to TE 111 The mode has a radial electric field component and is the lowest mode, so the water film thickness has a strong correlation with the resonant frequency. Resonant cavity 3-1 works in TE 111 In this mode, the expressions of the various components of the end current density of the resonant cavity 3-1 are as follows:

[0041] Make the resonant cavity work at TE 111 In this mode, the radial component of the current density J at the end face of the resonant cavity r With tangential component The expression is as follows:

[0042]

[0043]

[0044] In the formula, k c1 =1.841 / R, R is the radius of the resonant cavity, H 111 is the amplitude of the magnetic field strength in the cavity, l is the length of the resonant cavity, r is the variable in the radial direction, z is the variable in the length direction, J1 and J1' are the first-order Bessel function and the first-order derivative of the first-order Bessel function, respectively.

[0045] J is the current density at the end of the resonant cavity, which specifies the current density J at the end of the resonant cavity at a certain point in the electromagnetic field and the radial component J of the current density at the end of the resonant cavity r The angle between them is θ1, then After simplification, the rectangular coordinate system equation is:

[0046]

[0047] Let P(x,y) be any point on the curve y(x), then the slope of point P is k=y'=tan(γ), y' is the derivative of y, γ is the angle between the tangent line of the curve y(x) at point P(x,y) and the x-axis. is the angle between the line connecting point P(x,y) and the center of the circle and the positive direction of the x-axis. To ensure that the electromagnetic field distribution is not affected after the installation of the hyperbolic cosine metal strip, the tangent direction of any point P(x,y) on the curve y(x) is the same as the direction of the current density on the end face of the resonant cavity at this point, that is, it satisfies,

[0048]

[0049] In the formula The angle between the current density at the end of the resonant cavity and its radial component after the hyperbolic cosine metal strip is added should be equal to the current density at the end of the resonant cavity J and the radial component of the current density at the end of the resonant cavity J r The angle between them is θ1.

[0050] Since the shape of the current density distribution at the end face of the resonant cavity is very similar to the curve of the hyperbolic cosine function, it is assumed that y = acosh (x / b) + c (a, b, c are all constants), and substituted into equations (6) and (7) respectively to obtain:

[0051]

[0052]

[0053] Use MATLAB to draw the function graph of tan(θ1) with respect to x and the function graph of tan(θ2) with respect to x. In this embodiment, considering that the radius of the resonant cavity is 20.59 mm, b is taken as 4. When a and c are set, the function graph of tan(θ1) with respect to x and the function graph of tan(θ2) with respect to x are exactly the same within the specified range of x, which proves that y=acosh(x / 4)+c is a curve that meets the requirements, and the tangent direction of any point on the curve is the same as the current density direction at this point. Because there are countless end face current density distribution lines of the resonant cavity 3-1, when a and c are taken at different values, they correspond to different end face current density distribution lines of the resonant cavity 3-1.

[0054] In this embodiment, the four hyperbolic cosine functions are y1=0.011cosh(x / 4)+4.5, y2=0.055cosh(x / 4)+7.8, y3=0.35cosh(x / 4)+11.8, and y4=2.1cosh(x / 4)+14.8. Substitute their a, b, and c values ​​into equations (6) and (7), respectively, and use MATLAB to plot the graphs of x with respect to tan(θ1) and tan(θ2), respectively. It is found that their function graphs are exactly the same within the specified range of x, which shows that TE 111 The current density distribution line at the end face of the resonant cavity of the mode can be described by a hyperbolic cosine function, and the general formula is y=acosh(x / b)+c.

[0055] The simulation results show that the curve drawn by the hyperbolic cosine function can completely coincide with the end current density distribution line of the resonant cavity 3-1, and the electromagnetic and radiation performances are very good after the slit is opened. When the input power is 1W, the radiation can be as small as 0.01W, which fully meets the design requirements.

[0056] The present invention proposes a resonant cavity sensor with a hyperbolic cosine slit structure for the first time, and combines it with a microwave perturbation method to make it work in TE 111 mode is used to measure the thickness of water film and liquid film in cylindrical resonant cavity. The above-mentioned grid isolator structure has a large opening and good flow characteristics, which can ensure accurate sampling; at the same time, it is proved through theoretical derivation that the hyperbolic cosine function is exactly the same as the distribution shape of the current density at the end of the resonant cavity, and the opening along the direction of the current density vector at the end of the resonant cavity also ensures its good electromagnetic performance and radiation performance. When the input power is 1w, the radiation can be as small as 0.01w. The present invention has a simple structure, is easy to use, and has low requirements on the environment. It can solve the problem of the current lack of a method for measuring the thickness of water film and liquid film on the inner surface of cylindrical metals, and can accurately measure the thickness of water film.

[0057] Embodiment 2:

[0058] A design method for a grid isolator in a hyperbolic cosine gap sensor for measuring water film thickness described in Design Example 1, wherein the design methods of the left-end grid isolator 2 and the right-end grid isolator 5 are the same, and the left-end grid isolator 2 includes the following specific steps:

[0059] Step 1: Calculate the direction of the current density at the end of the resonant cavity: Set the x-axis through the center point of the left grid isolator and coincide with the direction of the middle metal strip, and set the y-axis to be orthogonal to the x-axis; J r is the radial component of the current density at the end face of the resonant cavity, is the tangential component of the current density at the end face of the resonant cavity, J is the current density at the end face of the resonant cavity; the current density at the end face of the resonant cavity J and the radial component of the current density at the end face of the resonant cavity J r The tangent value of the angle θ1 is:

[0060]

[0061] In formula (1), J1 is the first-order Bessel function, and J1' is the first-order derivative of the first-order Bessel function;

[0062] Step 2: Position the hyperbolic cosine metal strips: Determine the position of the hyperbolic cosine metal strips according to the strength of the current density distribution on the end face of the resonant cavity. The distances from the intersection of the four pairs of hyperbolic cosine metal strips and the y-axis to the origin are 0.22R, 0.38R, 0.59R, and 0.82R, respectively, where R is the radius of the resonant cavity.

[0063] Step 3: Determine the shape of the hyperbolic cosine metal strip: fit the constants a, b, and c in the corresponding hyperbolic cosine function y=acosh(x / b)+c through the intersection points of each hyperbolic cosine metal strip and the y-axis in turn, so that the slope of any point (x, y) on the hyperbolic cosine function is the same as the direction of the current density at the corresponding point in formula (1).

[0064] In this embodiment, considering that the radius of the resonant cavity is 20.59 mm, b is first determined to be 4. The intersection of the function and the y-axis is a+c, so it must satisfy 0≤a+c≤20.59. By observing the simulated current density line, it is found that along the positive direction of the y-axis, the openings of the hyperbolic cosine lines are from large to small. Since the larger a is when c is determined, the smaller the opening, the a of the hyperbolic cosine line near the center is smaller, and the a of the hyperbolic cosine line near the edge is larger, but neither exceeds 2.5. Therefore, c can be determined first to determine the approximate position of the hyperbolic cosine line, and then the shape of the hyperbolic cosine line can be adjusted by adjusting a, and the hyperbolic cosine function can be completely overlapped with the simulated current density distribution line through optimization. Finally, the shape of each hyperbolic cosine metal strip in the left-end grid isolator 2 is obtained.

Claims

1. A hyperbolic cosine gap sensor for measuring water film thickness, characterized in that: The invention comprises a resonant cavity body (3), a left-end wedge-shaped cylinder (1) and a right-end wedge-shaped cylinder (6); the resonant cavity body (3) is composed of a resonant cavity (3-1), a left grid isolator (2) and a right grid isolator (5); the left and right ends of the resonant cavity (3-1) are respectively connected to the left grid isolator (2) and the right grid isolator (5); the left grid isolator (2) and the right grid isolator (5) have the same structure, both of which are composed of a straight middle metal strip and one or more pairs of hyperbolic cosine metal strips symmetrically distributed about the middle metal strip; the left end of the left isolator (2) is connected to the left wedge-shaped cylinder (1), and the right isolator (5) is connected to the right wedge-shaped cylinder (6); the side wall of the resonant cavity body (3) is provided with a coupling member mounting hole (4); the resonant cavity (3-1) works at TE 111 mode; the radius of the resonant cavity (3-1) is 20.59 mm, the left end grid isolator (2) and the right end grid isolator (5) are composed of a middle metal strip and four pairs of hyperbolic cosine metal strips symmetrically distributed on the left and right, and the width of the metal strips is 1 mm; the x-axis is the center point of the circle and coincides with the direction of the middle metal strip, the y-axis is orthogonal to the x-axis, and the four hyperbolic cosine metal strips along the positive direction of the y-axis pass through the points (0,4.511), (0,7.855), (0,12.15), (0,16.9), the corresponding function equations are: y1=0.011cosh(x / 4)+4.15, y2=0.055cosh(x / 4)+7.8, y3=0.35cosh(x / 4)+11.8, y4=2.1cosh(x234 / 4)+14.8; the unit is mm; where x is the variable of the x-axis, and y1, y2, y3, y4 are the variables of the y-axis.

2. The hyperbolic cosine gap sensor for measuring water film thickness according to claim 1, characterized in that: The wall surface of the airflow inflow end of the left-end wedge-shaped cylinder (1) and the wall surface of the airflow outflow end of the right-end wedge-shaped cylinder (6) are both wedge-shaped structures.

3. The hyperbolic cosine gap sensor for measuring water film thickness according to claim 1, characterized in that: The coupling mode of the resonant cavity body (3) is coaxial line excitation.

4. A method for designing a grid isolator in a hyperbolic cosine gap sensor for measuring water film thickness as claimed in claim 1, wherein the design methods of the left grid isolator (2) and the right grid isolator (5) are the same, and the left grid isolator (2) comprises the following specific steps: Step 1: Calculate the direction of the current density at the end face of the resonant cavity: Set the x-axis through the center point of the left end grid isolator (2) and coincide with the direction of the middle metal strip, and set the y-axis to be orthogonal to the x-axis; J r is the radial component of the current density r at the end face of the resonant cavity, is the tangential component of the current density at the end of the resonant cavity, J is the current density at the end of the resonant cavity; the current density at the end of the resonant cavity J and the radial component of the current density at the end of the resonant cavity J r The tangent value of the angle θ1 is: Where J is the first-order Bessel function, J' is the first-order derivative of the first-order Bessel function; Step 2: Position the hyperbolic cosine metal strips: Determine the position of the hyperbolic cosine metal strips according to the strength of the current density distribution on the end face of the resonant cavity. The distances from the intersection of the four pairs of hyperbolic cosine metal strips and the y-axis to the origin are 0.22R, 0.38R, 0.59R, and 0.82R, respectively, where R is the radius of the resonant cavity. Step 3: Determine the shape of the hyperbolic cosine metal strip: fit the constants a, b, and c in the corresponding hyperbolic cosine function y=acosh(x / b)+c through the intersection points of each hyperbolic cosine metal strip and the y-axis in turn, so that the slope of any point (x, y) on the hyperbolic cosine function is the same as the direction of the current density at the corresponding point in formula (1).

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