A method, system and device for multi-angle ultrasonic detection of heat exchange fouling thickness

Abstract

The present invention provides a method, system and device for multi-angle ultrasonic detection of heat exchange fouling thickness, belonging to the technical field of heat exchange fouling thickness detection. The invention first calculates the probe spacing corresponding to each oblique incident angle and adjusts the positions of the ultrasonic transmitting probe and the ultrasonic receiving probe, uses the ultrasonic transmitting probe to transmit longitudinal waves according to each oblique incident angle, and uses the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle; secondly, the multiple echoes corresponding to each oblique incident angle are screened; again, the ultrasonic transit time corresponding to each oblique incident angle is calculated based on the screened echoes; then, the dirt layer thickness corresponding to each oblique incident angle is calculated based on each oblique incident angle and the corresponding ultrasonic transit time; finally, the dirt layer thickness corresponding to each oblique incident angle is merged to obtain the average dirt layer thickness. The present invention obtains the dirt layer thickness based on multiple oblique incident angles and merges them, thereby improving the accuracy of heat exchange dirt layer thickness calculation.

Description

Technical Field

[0001] The invention belongs to the technical field of heat exchange fouling thickness detection, and in particular relates to a method, system and device for multi-angle ultrasonic detection of heat exchange fouling thickness. Background Art

[0002] Heat exchange equipment is widely used in the power, aerospace, chemical industry and other industries as well as in daily life. However, abnormal scaling in heat exchange equipment will directly lead to a decrease in heat exchange efficiency and may cause safety accidents. Therefore, it is of great significance to establish a real-time detection system for scale in heat exchange equipment.

[0003] At present, there are problems with heat exchange fouling thickness detection methods, such as difficulty in implementation and inability to be performed online. The more commonly used thermal detection methods that can be performed online also have disadvantages such as low reliability. Although the use of ultrasonic time-domain reflection method for fouling detection has the advantages of being simple to implement, accurate and reliable, and able to meet real-time detection needs, it is difficult to accurately obtain effective information due to the weak and fuzzy reflection information and complex interference caused by the texture characteristics and physical environment of the fouling object. In summary, how to develop a highly reliable heat exchange fouling detection method has become an urgent problem to be solved in this field. Summary of the invention

[0004] Based on the above technical problems, the present invention provides a method, system and device for multi-angle ultrasonic detection of heat exchange fouling thickness, which obtains the thickness of the fouling layer based on multiple oblique incident angles and merges them, thereby improving the accuracy of heat exchange fouling layer thickness calculation.

[0005] The present invention provides a multi-angle ultrasonic detection method for heat exchange fouling thickness, the method comprising:

[0006] Step S1: Calculate the probe spacing corresponding to each oblique incidence angle based on the repeated transmission coefficient corresponding to each key echo; the key echoes include pipe wall layer echoes and dirt layer echoes; the probe spacing is the distance between the ultrasonic transmitting probe and the ultrasonic receiving probe.

[0007] Step S2: adjusting the positions of the ultrasonic transmitting probe and the ultrasonic receiving probe according to the probe spacing corresponding to each oblique incident angle, using the ultrasonic transmitting probe to transmit longitudinal waves according to each oblique incident angle, and using the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle.

[0008] Step S3: screening the multiple echoes corresponding to the oblique incident angles to obtain the dirt layer echo and the pipe wall layer echo corresponding to the oblique incident angles.

[0009] Step S4: calculating the ultrasonic transit time corresponding to each oblique incident angle according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle.

[0010] Step S5: Calculate the dirt layer thickness corresponding to each oblique incident angle according to each oblique incident angle and the corresponding ultrasonic transit time.

[0011] Step S6: merging the dirt layer thicknesses corresponding to the oblique incident angles to obtain an average dirt layer thickness.

[0012] Optionally, the step of calculating the probe spacing corresponding to each oblique incidence angle based on the repeated transmission coefficient corresponding to each key echo comprises:

[0013] The refraction coefficient is calculated based on the normal acoustic impedance at oblique incidence; the refraction coefficient includes: a longitudinal wave reflection coefficient, a longitudinal wave refraction coefficient and a transverse wave refraction coefficient.

[0014] The repetitive transmission coefficient corresponding to each key echo is calculated according to the refraction coefficient.

[0015] The repetitive transmission coefficient corresponding to each key echo is used as the ordinate and the oblique incident angle is used as the abscissa, and a waveform diagram of the repetitive transmission coefficient corresponding to each key echo changing with the oblique incident angle is simulated and drawn.

[0016] The value range of the oblique incidence angle is determined according to the waveform diagram of the repeated transmission coefficient corresponding to each key echo changing with the oblique incidence angle.

[0017] A plurality of oblique incident angles are selected from the oblique incident angle value range.

[0018] The probe spacing corresponding to each oblique incident angle is determined using each oblique incident angle and the sound ray model.

[0019] Optionally, the steps of screening the multiple echoes corresponding to the oblique incidence angles to obtain the dirt layer echo and the pipe wall layer echo corresponding to the oblique incidence angles include:

[0020] The multiple echoes corresponding to the oblique incident angles are subjected to noise reduction processing to obtain multiple noise-reduced echoes corresponding to the oblique incident angles.

[0021] The improved chaotic spiral teaching and learning optimization algorithm is combined with the matching pursuit algorithm, and the echo features corresponding to each denoised echo are extracted based on multiple denoised echoes corresponding to each oblique incident angle.

[0022] As the oblique incident angles increase, according to the amplitude variation trend of the echo characteristics of multiple noise-reduced echoes, the theoretical signal is matched with each generated echo, the interference wave is eliminated, and the dirt layer echo and pipe wall layer echo corresponding to each oblique incident angle are obtained.

[0023] Optionally, the step of calculating the ultrasonic transit time corresponding to each oblique incident angle according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle comprises:

[0024] Envelopes are drawn respectively according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle, so as to obtain a first envelope and a second envelope corresponding to each oblique incident angle.

[0025] The first wave arrival time corresponding to each oblique incident angle is determined according to the first envelope line corresponding to each oblique incident angle, and the second wave arrival time corresponding to each oblique incident angle is determined according to the second envelope line corresponding to each oblique incident angle.

[0026] The ultrasonic transit time corresponding to each oblique incident angle is calculated according to the first wave arrival time and the second wave arrival time corresponding to each oblique incident angle.

[0027] Optionally, the thickness of the dirt layer corresponding to each oblique incident angle is calculated according to each oblique incident angle and the corresponding ultrasonic transit time, and the specific calculation formula is:

[0028]

[0029] Among them, x k represents the thickness of the dirt layer corresponding to the kth oblique incident angle, c1 represents the sound velocity of the ultrasonic wave in the ultrasonic water, c2 represents the sound velocity in the dirt layer, α k represents the kth oblique incident angle, ΔT k represents the ultrasonic transit time corresponding to the kth oblique incident angle.

[0030] Optionally, the dirt layer thicknesses corresponding to the oblique incident angles are merged to obtain an average dirt layer thickness, and the specific calculation formula is:

[0031] w k =e k exp(-λ(k-1)),k=1,2,…,n;

[0032]

[0033]

[0034] Among them, x k represents the dirt layer thickness corresponding to the kth oblique incident angle, represents the mean thickness of the dirt layer, n represents the total number of oblique incident angles, λ represents the exponential function attenuation coefficient, α k represents the kth oblique incident angle, e k and w k Both represent intermediate variables, η and μ represent weight coefficients selected according to working conditions.

[0035] The present invention also provides a multi-angle ultrasonic detection system for heat exchange fouling thickness, the system comprising:

[0036] The probe spacing calculation module is used to calculate the probe spacing corresponding to each oblique incidence angle based on the repeated transmission coefficient corresponding to each key echo; the key echoes include pipe wall layer echoes and dirt layer echoes; the probe spacing is the distance between the ultrasonic transmitting probe and the ultrasonic receiving probe.

[0037] The position adjustment module is used to adjust the positions of the ultrasonic transmitting probe and the ultrasonic receiving probe according to the probe spacing corresponding to each oblique incident angle, use the ultrasonic transmitting probe to transmit longitudinal waves according to each oblique incident angle, and use the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle.

[0038] The echo screening module is used to screen the multiple echoes corresponding to the oblique incident angles to obtain the dirt layer echo and the pipe wall layer echo corresponding to the oblique incident angles.

[0039] The ultrasonic transit time calculation module is used to calculate the ultrasonic transit time corresponding to each oblique incident angle according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle.

[0040] The dirt layer thickness calculation module is used to calculate the dirt layer thickness corresponding to each oblique incident angle according to each oblique incident angle and the corresponding ultrasonic transit time.

[0041] The dirt layer thickness fusion module is used to fuse the dirt layer thicknesses corresponding to the oblique incident angles to obtain an average dirt layer thickness.

[0042] Optionally, the probe spacing calculation module specifically includes:

[0043] The refraction coefficient calculation unit is used to calculate the refraction coefficient based on the normal acoustic impedance at oblique incidence; the refraction coefficient includes: longitudinal wave reflection coefficient, longitudinal wave refraction coefficient and transverse wave refraction coefficient.

[0044] The repetitive transmission coefficient calculation unit is used to calculate the repetitive transmission coefficient corresponding to each key echo according to the refraction coefficient.

[0045] The waveform diagram drawing unit is used to simulate and draw the waveform diagram of the repeated transmission coefficient corresponding to each key echo changing with the oblique incident angle, using the repeated transmission coefficient corresponding to each key echo as the ordinate and the oblique incident angle as the abscissa.

[0046] The oblique incidence angle value range determination unit is used to determine the oblique incidence angle value range according to the waveform diagram of the repeated transmission coefficient corresponding to each key echo changing with the oblique incidence angle.

[0047] The oblique incident angle selection unit is used to select multiple oblique incident angles from the oblique incident angle value range.

[0048] The probe spacing calculation unit is used to determine the probe spacing corresponding to each oblique incident angle by using each oblique incident angle and a sound ray model.

[0049] Optionally, the echo screening module specifically includes:

[0050] The noise reduction processing unit is used to perform noise reduction processing on the multiple echoes corresponding to each oblique incident angle to obtain multiple noise-reduced echoes corresponding to each oblique incident angle.

[0051] The echo feature extraction unit is used to combine the improved chaotic spiral teaching and learning optimization algorithm with the matching pursuit algorithm, and extract the echo features corresponding to each noise reduction echo based on multiple noise reduction echoes corresponding to each oblique incident angle.

[0052] The interference wave elimination unit is used to match the theoretical signal with each generated echo according to the amplitude change trend of the echo characteristics of multiple noise reduction echoes as the oblique incident angles increase, eliminate the interference waves, and obtain the dirt layer echo and pipe wall layer echo corresponding to each oblique incident angle.

[0053] The present invention also provides a multi-angle ultrasonic detection device for heat exchange fouling thickness, the device specifically comprising:

[0054] The ultrasonic transmitting probe is used to transmit longitudinal waves at various oblique incident angles.

[0055] The ultrasonic receiving probe is used to receive multiple echoes corresponding to each oblique incident angle.

[0056] The liquid cover for synchronously adjusting the angle and position of the probe is used for synchronously adjusting the oblique incident angle and position of the ultrasonic transmitting probe and the ultrasonic receiving probe.

[0057] The pulse transmitting and receiving device is connected to the ultrasonic transmitting probe and the ultrasonic receiving probe respectively, and is used to control the ultrasonic transmitting probe to transmit longitudinal waves and to control the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle.

[0058] The acquisition card is connected to the pulse transmitting and receiving device and is used to acquire multiple echo signals corresponding to each oblique incident angle.

[0059] The computer is connected to the acquisition card and is used to calculate the average value of the dirt layer thickness by using the above steps S3-S6, and is also used to calculate the probe spacing corresponding to each oblique incident angle by using the above step S1.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] The present invention utilizes multiple groups of oblique incident angles for ultrasonic detection, obtains multiple groups of ultrasonic transit time data, and then calculates the thickness of the dirt layer based on the multiple groups of ultrasonic transit time data, and fuses the multiple groups of dirt layer thicknesses. Compared with the vertically incident ultrasonic detection method, the measurement error caused by differences in material density, thickness, structure, etc. is reduced, and the measurement accuracy is improved.

[0062] The present invention calculates the probe spacing corresponding to each oblique incidence angle based on the repeated transmission coefficient corresponding to each key echo, so that the positions of the ultrasonic transmitting probe and the ultrasonic receiving probe can be adjusted according to the probe spacing corresponding to each oblique incidence angle, thereby improving the probability of the ultrasonic receiving probe accurately receiving the echo. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 A flow chart of a multi-angle ultrasonic detection method for heat exchange fouling thickness of the present invention;

[0064] Figure 2 It is a waveform diagram of the repeated transmission coefficient corresponding to each key echo of the present invention changing with the oblique incident angle;

[0065] Figure 3 Schematic diagram of the echo signal waveform corresponding to different incident angles of the present invention;

[0066] Figure 4 It is a schematic diagram of the overlap of each echo and the envelope line of the present invention;

[0067] Figure 5 This is a structural diagram of a multi-angle ultrasonic detection system for heat exchange fouling thickness of the present invention;

[0068] Figure 6 This is a structural diagram of a multi-angle ultrasonic detection device for heat exchange fouling thickness of the present invention;

[0069] Figure 7 It is a schematic diagram of the installation of a multi-angle ultrasonic detection device for heat exchange fouling thickness of the present invention;

[0070] in, Figures 1 to 7 The corresponding relationship between the reference numerals and component names in the figure is:

[0071] 1. Ultrasonic transmitting probe; 2. Ultrasonic receiving probe; 3. Liquid cover; 4. Pulse transmitting and receiving device; 5. Acquisition card; 6. Computer; 7. Pipe wall layer; 8. Dirt layer; 9. Water inlet; 10. Slide rail adjustment structure; 11. Water outlet. DETAILED DESCRIPTION

[0072] The present invention is further described below in conjunction with specific implementation cases and drawings, but the present invention is not limited to these embodiments.

[0073] Heat exchange pipe fouling refers to impurities deposited on the heat transfer surface inside the pipe of the heat exchange equipment, mainly calcium carbonate, which will affect the heat transfer efficiency and operation safety of the heat exchanger. Ultrasonic testing of heat exchange pipes generally adopts water immersion, so the medium experienced by the ultrasonic wave is the coupling layer (water), pipe layer (304 stainless steel), fouling layer (calcium carbonate), and material layer in the pipe (water / air). Since the thickness of the coupling layer and the pipe layer is known, the thickness to be measured is the fouling layer, so there are a total of four layers of media, and the detection layer is the third fouling layer.

[0074] At present, heat exchange fouling detection methods can be divided into two categories: thermal method and non-thermal method. Thermal method includes thermal resistance expression method and temperature difference expression method, while non-thermal method includes direct weighing method, thickness measurement method, pressure drop measurement method, microphotography method, radioactive technology, infrared absorption coefficient method, infrared spectroscopy analysis method, optical fiber method and ultrasonic detection method. Among them, thermal method is a method to describe the amount of fouling by using the difference in heat transfer coefficient of heat exchange equipment under clean and working conditions, while non-thermal method does not rely on the thermal properties of fouling for detection.

[0075] In thermal methods, the fouling thermal resistance method is a commonly used method, but the "induction period" will appear in the early stage of fouling, resulting in negative thermal resistance values, and the measurement process is relatively complicated and difficult to achieve. In comparison, the fouling temperature difference representation method is a more common method in industry, but due to the many and complex factors that affect the temperature change of the fluid in actual applications, the credibility of this method is insufficient, and its measured value is usually only used as a reference value for the amount of fouling.

[0076] Among non-thermal methods, traditional measurement methods such as direct weighing and thickness measurement methods often require the installation of dirt deposition plates, or the installation of specific detection devices on both sides of the heat exchange equipment and regular shutdown for offline detection, which cannot meet the needs of modern industrial detection. Radioactive technology, infrared absorption coefficient method and other methods make online dirt detection possible, but the preliminary preparations for the measurement are relatively complicated, and the measurement has high requirements for the environment and equipment, making it difficult to apply in industry. The fiber optic sensing method uses the intensity of optical fiber reflection or variable refraction light to measure the thickness of biological mucosa, and has the advantages of high sensitivity, but the range of dirt types and thickness that can be measured is currently narrow, and the interventional working method is susceptible to contamination, so more research is needed.

[0077] At present, ultrasonic fouling detection mainly includes two methods: time domain reflection method and guided wave method. The former is mainly used to measure membrane fouling, while the latter is mostly used for qualitative detection of dense and smooth layers of plates or tubes. At present, there are still few studies on the use of ultrasonic methods for the detection of rough and loose heat exchange fouling at home and abroad, and the relevant theories on the means and methods of obtaining information on ultrasonic detection of heat exchange fouling have not yet been perfected.

[0078] Ultrasonic time domain reflectometry is a technique that uses the pulse reflection of ultrasonic waves in different media to measure the thickness of objects. This technique can accurately measure almost any material. Its working principle is to calculate the thickness of the workpiece by presetting or measuring the sound velocity based on the proportional relationship between the transit time of ultrasonic waves and the thickness. Its main features are wide measurement range, small error, simple operation, and rapid measurement. It is widely used in product inspection and equipment safety operation inspection in various industrial sectors such as metallurgy, shipbuilding, machinery, chemical industry, and electric power. However, when actually detecting the thickness of heat exchange dirt, in some cases such as the dirt thickness is proportional to the wall thickness, the dirt structure is rough and loose, etc., the echo will be affected by aliasing and noise problems, reducing the reliability of the detection results.

[0079] In view of the above problems of the prior art, the purpose of the present invention is to provide a technology for measuring dirt thickness using multi-angle ultrasonic time domain reflection method. This technology can reduce the aliasing and noise effects of ultrasonic echoes as much as possible without destroying the detection object, and improve the reliability of measurement. The specific scheme is as follows:

[0080] like Figure 1 As shown, the present invention discloses a method for multi-angle ultrasonic detection of heat exchange fouling thickness, the method comprising:

[0081] Step S1: Calculate the probe spacing corresponding to each oblique incident angle based on the repeated transmission coefficient corresponding to each key echo.

[0082] Step S2: adjusting the positions of the ultrasonic transmitting probe and the ultrasonic receiving probe according to the probe spacing corresponding to each oblique incident angle, using the ultrasonic transmitting probe to transmit longitudinal waves according to each oblique incident angle, and using the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle.

[0083] Step S3: screening the multiple echoes corresponding to the oblique incident angles to obtain the dirt layer echo and the pipe wall layer echo corresponding to the oblique incident angles.

[0084] Step S4: calculating the ultrasonic transit time corresponding to each oblique incident angle according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle.

[0085] Step S5: Calculate the dirt layer thickness corresponding to each oblique incident angle according to each oblique incident angle and the corresponding ultrasonic transit time.

[0086] Step S6: merging the dirt layer thicknesses corresponding to the oblique incident angles to obtain an average dirt layer thickness.

[0087] The following is a detailed discussion of each step:

[0088] Step S1: Calculate the probe spacing corresponding to each oblique incidence angle based on the repeated transmission coefficient corresponding to each key echo; the probe spacing is the distance between the ultrasonic transmitting probe and the ultrasonic receiving probe; each key echo includes a pipe wall layer echo and a dirt layer echo; the echo generated at the interface between the pipe wall and the dirt medium is called a pipe wall layer echo, and the interface between the dirt and the medium inside the pipe is called a dirt layer echo. In this embodiment, step S1 uses a simulation method to calculate the probe spacing corresponding to each oblique incidence angle.

[0089] Step S1: Calculate the probe spacing corresponding to each oblique incident angle based on the repeated transmission coefficient corresponding to each key echo, specifically including:

[0090] Step S11: Calculate the reflection coefficient based on the normal acoustic impedance at oblique incidence; the reflection coefficient includes: longitudinal wave reflection coefficient, longitudinal wave refraction coefficient and transverse wave refraction coefficient, and the specific formula is:

[0091]

[0092]

[0093]

[0094] in, z 1L ,z 2L ,z 2T Both represent the normal acoustic impedance ratio at oblique incidence, c 1L represents the longitudinal wave velocity of medium 1, c 2L represents the longitudinal wave velocity of medium 2, c 2T represents the shear wave velocity of medium 2, α represents the incident angle of the longitudinal wave, β represents the refraction angle of the longitudinal wave, and β l represents the shear wave refraction angle, ρ1 represents the density of medium 1, ρ2 represents the density of medium 2, |r Φ | represents the longitudinal wave reflection coefficient, |t Φ | represents the longitudinal wave refraction coefficient, |t Ψ | represents the shear wave refraction coefficient.

[0095] In this embodiment, the medium includes a pipe wall layer, a dirt layer and a water immersion layer.

[0096] Step S12: Calculate the repetitive transmission coefficient corresponding to each key echo according to the refraction coefficient.

[0097] In this embodiment, different echoes are reflected and refracted at different times in the pipe wall layer and the dirt layer, so the calculated repeated transmission coefficients corresponding to the echoes are also different.

[0098] Step S13: using the repetitive transmission coefficient corresponding to each key echo as the ordinate and the oblique incident angle as the abscissa, a waveform diagram of the repetitive transmission coefficient corresponding to each key echo changing with the oblique incident angle is simulated and drawn.

[0099] Step S14: determining the value range of the oblique incident angle according to the waveform diagram of the repeated transmission coefficient corresponding to each key echo varying with the oblique incident angle.

[0100] Figure 2 Figure (a) in the figure mainly draws a waveform diagram of the repeated transmission coefficient corresponding to the pipe wall layer echo changing with the oblique incident angle. Figure 2 Figure (b) in the figure mainly draws a waveform diagram of the repeated transmission coefficient corresponding to the dirt layer echo changing with the oblique incident angle; Figure 2 It can be seen that as the oblique incident angle gradually increases to the first critical angle, the absolute value of the repeated transmission coefficient corresponding to the pipe wall layer echo gradually decreases, and decreases by about 10% when the oblique incident angle is 8°, and the repeated transmission coefficient corresponding to the dirt layer echo decreases by about 25% when the oblique incident angle is 8°. In order to ensure that the echo signal has sufficient signal-to-noise ratio and application value, the value range of the oblique incident angle is 0°~8°.

[0101] Step S15: Select multiple oblique incident angles from the oblique incident angle value range. In this embodiment, the results of 1°, 2°, and 3° are not much different from those of 0°, and the effect is obvious only after 5°, so the angles after 0° and 5° are used in the example. Therefore, a group of angles of 0°, 5°, 6°, and 7° are used for multi-angle detection, and the probe distance is determined according to the pipe wall thickness and the water immersion layer thickness.

[0102] Step S16: Determine the probe spacing corresponding to each oblique incident angle using each oblique incident angle and the sound ray model to ensure that the ultrasound can be normally acquired by the receiving probe after multiple reflections and refractions; the probe spacing is the distance between the ultrasound transmitting probe and the ultrasound receiving probe. In this embodiment, the sound ray model is a conventional model and is not the focus of the present invention.

[0103] Step S2: adjust the positions of the ultrasonic transmitting probe and the ultrasonic receiving probe according to the probe spacing corresponding to each oblique incident angle, use the ultrasonic transmitting probe to transmit longitudinal waves according to each oblique incident angle, and use the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle. The multiple echoes include the first echo of the pipe wall layer (also called the pipe wall layer echo), the first echo of the dirt layer (also called the dirt layer echo), the aliased echo, the second echo of the pipe wall layer and the shear wave echo of the pipe wall layer. The multiple echoes may also include aliased echoes formed by aliasing multiple echoes.

[0104] In the present invention, ultrasonic longitudinal waves are used for detection, and corresponding detection equipment is selected according to the specific conditions of the physical parameters of the detection object, including the frequency, size, coupling method with the detection material, transmission and receiving method of the probe; for example, in view of the thin wall and small diameter of a small-diameter thin-walled heat exchange pipe, a 10Mhz, 6-inch chip-sized ultrasonic water immersion longitudinal wave probe is selected, and a one-transmit-one-receive method is adopted.

[0105] Take the pipe wall thickness of 3mm and the dirt layer thickness of 1.1mm as an example. In this case, the dirt layer echo and the secondary echo of the pipe wall are aliased. The echo signal is as follows: Figure 3 As shown, (a) is the echo signal when the incident angle is 0°, (b) is the echo signal when the incident angle is 5°, (c) is the echo signal when the incident angle is 6°, and (d) is the echo signal when the incident angle is 7°. From left to right in Figure (a) are the primary echo of the pipe wall layer, the aliased echo composed of the dirt layer and the secondary echo of the pipe wall layer, and from left to right in Figures (b), (c), and (d) are the primary echo of the pipe wall layer, the shear wave echo of the pipe wall layer, and the dirt layer echo which is minimally affected by the secondary echo of the pipe wall.

[0106] Step S3: screening multiple echoes corresponding to each oblique incident angle to obtain the dirt layer echo and pipe wall layer echo corresponding to each oblique incident angle, specifically including:

[0107] Step S31: perform noise reduction processing on multiple echoes corresponding to each oblique incident angle to obtain multiple noise-reduced echoes corresponding to each oblique incident angle; the present invention preferably uses algorithms such as digital filtering to perform preliminary noise reduction on the signal, and other methods can also be used for initial noise reduction, which is selected according to actual needs.

[0108] Step S32: combining the improved chaotic spiral teaching and learning optimization algorithm with the matching pursuit algorithm, and extracting the echo features corresponding to each denoised echo based on multiple denoised echoes corresponding to each oblique incident angle; the echo features include amplitude, waveform and position.

[0109] The present invention proposes an improved Chaos Spiral Teaching Learning Based Optimization (CSTLBO) algorithm and combines it with matching pursuit to extract echo features from signal echoes. The matching pursuit is improved by the CSTLBO method and the algorithm is referred to as CSTLBO-MP to perform sparse decomposition and extraction of ultrasonic detection signals of heat exchange pipe fouling.

[0110] The specific steps of step S32 are as follows:

[0111] (1) Establishing an overcomplete atom dictionary

[0112] The Chirp overcomplete atom dictionary is established as the basis set D of sparse decomposition. The atom dictionary has five benchmark parameters for atomic scaling and translation operations, namely: s, u, ξ, θ and c.

[0113] (2) CSTLBO-MP algorithm initialization

[0114] The dimension of CSTLBO-MP is set to 5 dimensions, corresponding to the benchmark parameters in the overcomplete atom dictionary, and the value range of each benchmark parameter in the MP algorithm is set to the upper and lower limits of the space of each optimization dimension.

[0115] (3) CSTLBO-MP optimization goal setting

[0116] CSTLBO is used to perform the MP optimization operation on the above benchmark parameters in the continuous solution space. Since the better the matching pursuit is with the original signal F, the greater the inner product of the two is, the goal of CSTLBO optimization is to process the signal f i and the atomic d determined by the base parameters r The maximum value of the inner product, the formula of its fitness function objf is as follows:

[0117]

[0118] Among them, Γ is a 5-dimensional continuous solution space, and i is the number of sparse decomposition operations performed on the signal to be processed.

[0119] (4) CSTLBO-MP optimization process

[0120] Using the fitness function objf established in the previous stage and the signal to be processed f i Perform optimization operation and find the signal to be processed f through iteration i The best matching atom d i Benchmark parameters to complete signal feature extraction.

[0121] Among them, the specific steps of the improved chaotic spiral teaching and learning optimization algorithm (CSTLBO) are as follows:

[0122] 1) Teacher stage

[0123] The improved teacher stage is divided into two situations: one is the original student understanding and absorption state, and the other is the "spiral" state towards the average position of the population. These two states are determined by the value of p. The model formula is as follows:

[0124]

[0125] difference1=Tent h ×(X Teacher -T F XMean )

[0126] difference2=|X q,old -X Mean |

[0127] l=(a-1)×Tent h +1

[0128] Among them, X q,old and X q,new is the knowledge status of the qth student before and after the teacher’s teaching, X Mean is the average of all students’ knowledge, b is the spiral constant, a is a variable that decreases linearly from -1 to -2 as the number of iterations increases, and Tent h is the learning step of the student, p and Tent h Both are chaotic sequences that replace the role of random numbers, T F =round[1+rand(0,1)] is a teaching factor with a randomly selected value of 1 or 2, which reflects the teacher's teaching ability. Mean represents the average knowledge of the whole class, X Teacher Indicates that the best member X in this iteration Best The knowledge level of the student group is X Teacher Close, l represents the variable that controls the size of the spiral.

[0129] 2) Student stage

[0130] To improve learning ability, students can interact with other students randomly. The learning behavior between students can be expressed as follows:

[0131]

[0132] Among them, X q,old and X q,new are the knowledge status of the qth student before and after the teacher’s teaching, X q , X j For two randomly selected students, f(X q ) and f(X j ) is the performance level of the two students, and is actually the numerical value of the objective function for comparison. The efficiency of the improved TLBO algorithm has been greatly improved.

[0133] Get the best matching atom d i Then, calculate the system residual r i As the signal to be processed, continue to search for the best until i meets the required number of extractions. The process is shown in the following formula:

[0134] r i =fi -d i i=1,2,…,m

[0135]

[0136] Where m is the number of times the signal is sparsely decomposed.

[0137] (5) CSTLBO-MP sparse reconstruction process

[0138] Extract the most matching atom d from the feature repeated m times i The sparse reconstruction process can be realized by retaining and adding it to the last remaining residual to obtain the echo characteristics of each denoised echo.

[0139]

[0140] Among them, F′ represents the reconstructed signal and F represents the original signal.

[0141] The MP algorithm improved by the present invention based on CSTLBO greatly improves the problems of slow atomic search speed and low matching accuracy of the matching pursuit algorithm.

[0142] Step S33: As the oblique incident angles increase, according to the amplitude change trend of the echo characteristics of the multiple noise reduction echoes, the theoretical signal is matched with each generated echo, the interference wave is eliminated, and the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle are obtained; the present invention calls the waveform other than the dirt layer echo and the pipe wall layer echo an interference wave.

[0143] The present invention distinguishes and eliminates the interference of shear wave signals based on the two opposite amplitude change trend characteristics of increase and decrease produced by shear wave interference and interface reflection echo with the increase of incident angle; and as the angle increases, the dirt layer echo is gradually reduced by the influence of the secondary echo of the pipe wall, and its waveform gradually changes. The reliability of echo characteristics at each angle can also be analyzed by using the trend.

[0144] Step S4: Calculating the ultrasonic transit time corresponding to each oblique incident angle according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle, specifically including:

[0145] Step S41: drawing envelopes respectively according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle, and obtaining a first envelope and a second envelope corresponding to each oblique incident angle.

[0146] Step S42: Determine the first arrival time corresponding to each oblique incident angle according to the first envelope corresponding to each oblique incident angle, and determine the second arrival time corresponding to each oblique incident angle according to the second envelope corresponding to each oblique incident angle; specifically, the time at which the first envelope rises 5% or the amplitude point is located is called the first arrival time, and the time at which the second envelope rises 5% or the amplitude point is located is called the second arrival time, such as Figure 4 As shown, (a) is a schematic diagram of the overlap between the dirt layer echo and the first envelope line, and (b) is a schematic diagram of the overlap between the pipe wall layer echo and the second envelope line.

[0147] Step S43: Calculate the ultrasonic transit time corresponding to each oblique incident angle according to the first wave arrival time and the second wave arrival time corresponding to each oblique incident angle. The specific formula is:

[0148] ΔT k =t k2 -t k1 ;

[0149] Among them, t k1 represents the first wave arrival time corresponding to the kth oblique incidence angle, t k2 represents the second wave arrival time corresponding to the kth oblique incidence angle, ΔT k represents the ultrasonic transit time corresponding to the kth oblique incident angle.

[0150] like Figure 4 As shown in the figure, the letter 1 represents the envelope line, the letter 2 represents the echo line, the horizontal axis is the time point, and the arrival times of the two echoes correspond to the 265 and 1329 positions of the data points respectively, so the ultrasonic transit time corresponds to the data point interval of 1064, which corresponds to the real time of 1.06us.

[0151] Step S5: Calculate the dirt layer thickness corresponding to each oblique incident angle according to each oblique incident angle and the corresponding ultrasonic transit time. The specific calculation formula is:

[0152]

[0153] Among them, x k represents the thickness of the dirt layer corresponding to the kth oblique incident angle, c1 represents the sound velocity of the ultrasonic wave in the ultrasonic water, c2 represents the sound velocity in the dirt layer, α k represents the kth oblique incident angle, ΔT k represents the ultrasonic transit time corresponding to the kth oblique incident angle.

[0154] In order to avoid the influence of uncertain factors such as interference, a data fusion scheme for thickness measurement data at each angle is designed based on methods such as weighted average. The specific steps are as follows:

[0155] Step S6: The dirt layer thickness corresponding to each oblique incident angle is merged to obtain the average dirt layer thickness. The specific calculation formula is:

[0156] w k =e k exp(-λ(k-1)),k=1,2,…,n;

[0157]

[0158]

[0159] in, represents the mean thickness of the dirt layer, n represents the total number of oblique incident angles, λ represents the exponential function attenuation coefficient, η=0.9 and μ=0.004 represent the appropriate weight coefficients selected according to the working conditions, α k represents the kth oblique incidence angle.

[0160] The present invention uses a weighted average scheme to fuse the dirt layer thickness calculated at each angle to obtain the dirt thickness after data fusion (i.e., the mean dirt layer thickness). Since the reflection positions of the echoes of each layer are different, the influence of the uncertainty in detection and the aliasing problem between echoes are reduced. The result is closer to the actual dirt thickness value than the previous detection scheme, thereby improving the accuracy and stability of ultrasonic detection.

[0161] The technology proposed in the present invention for measuring heat exchange fouling thickness by using multi-angle ultrasonic incidence has the following effects compared with the prior art:

[0162] (1) The stability of the measurement results is improved: the present invention uses multiple groups of oblique incident angles for ultrasonic detection, and measures multiple groups of ultrasonic transit time data, and then calculates the thickness of the dirt layer based on the multiple groups of ultrasonic transit time data. Compared with the vertically incident ultrasonic detection method, the measurement error caused by differences in material density, thickness, structure, etc. can be reduced, thereby improving the stability of the measurement.

[0163] (2) Avoiding echo aliasing and noise influence: The present invention adopts oblique incidence for ultrasonic detection, which can avoid echo aliasing problems and noise influence in some cases, making the measurement result more accurate.

[0164] (3) Improved measurement efficiency: The measurement steps of the present invention are simple. It is only necessary to determine the oblique incidence angle and the distance between the ultrasonic probes according to the repeated transmission coefficient and the sound ray model, perform ultrasonic detection at different angles, and record the ultrasonic transit time and dirt thickness corresponding to each oblique incidence angle. The final average measured thickness is calculated through a data fusion scheme. The whole process is simple to operate and can improve the measurement efficiency.

[0165] (4) Reduced modification costs: Compared with existing material thickness measurement technologies, the multi-angle ultrasonic incident method adopted in the present invention does not require the addition of ultrasonic equipment. Instead, it only requires the addition of a mechanical structure for changing the incident angle on the basis of the existing ultrasonic equipment. This can achieve higher-precision measurements and minimize modification costs.

[0166] In summary, the technology of the present invention has the advantages of accurate measurement, high efficiency, low cost, etc., and has broad application prospects and promotion value.

[0167] Example 2

[0168] like Figure 5 As shown, the present invention also provides a multi-angle ultrasonic detection system for heat exchange fouling thickness, the system comprising:

[0169] The probe spacing calculation module 501 is used to calculate the probe spacing corresponding to each oblique incidence angle based on the repeated transmission coefficient corresponding to each key echo; the key echoes include pipe wall layer echoes and dirt layer echoes; the probe spacing is the distance between the ultrasonic transmitting probe and the ultrasonic receiving probe.

[0170] The position adjustment module 502 is used to adjust the positions of the ultrasonic transmitting probe and the ultrasonic receiving probe according to the probe spacing corresponding to each oblique incident angle, use the ultrasonic transmitting probe to transmit longitudinal waves according to each oblique incident angle, and use the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle.

[0171] The echo screening module 503 is used to screen the multiple echoes corresponding to the oblique incident angles to obtain the dirt layer echo and the pipe wall layer echo corresponding to the oblique incident angles.

[0172] The ultrasonic transit time calculation module 504 is used to calculate the ultrasonic transit time corresponding to each oblique incident angle according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle.

[0173] The dirt layer thickness calculation module 505 is used to calculate the dirt layer thickness corresponding to each oblique incident angle according to each oblique incident angle and the corresponding ultrasonic transit time.

[0174] The dirt layer thickness fusion module 506 is used to fuse the dirt layer thicknesses corresponding to the oblique incident angles to obtain a mean value of the dirt layer thicknesses.

[0175] As an optional implementation manner, the probe spacing calculation module 501 of the present invention specifically includes:

[0176] The refraction coefficient calculation unit is used to calculate the refraction coefficient based on the normal acoustic impedance at oblique incidence; the refraction coefficient includes: longitudinal wave reflection coefficient, longitudinal wave refraction coefficient and transverse wave refraction coefficient.

[0177] The repetitive transmission coefficient calculation unit is used to calculate the repetitive transmission coefficient corresponding to each key echo according to the refraction coefficient.

[0178] The waveform diagram drawing unit is used to simulate and draw the waveform diagram of the repeated transmission coefficient corresponding to each key echo changing with the oblique incident angle, using the repeated transmission coefficient corresponding to each key echo as the ordinate and the oblique incident angle as the abscissa.

[0179] The oblique incidence angle value range determination unit is used to determine the oblique incidence angle value range according to the waveform diagram of the repeated transmission coefficient corresponding to each key echo changing with the oblique incidence angle.

[0180] The oblique incident angle selection unit is used to select multiple oblique incident angles from the oblique incident angle value range.

[0181] The probe spacing calculation unit is used to determine the probe spacing corresponding to each oblique incident angle by using each oblique incident angle and a sound ray model.

[0182] As an optional implementation, the echo screening module 503 of the present invention specifically includes:

[0183] The noise reduction processing unit is used to perform noise reduction processing on the multiple echoes corresponding to each oblique incident angle to obtain multiple noise-reduced echoes corresponding to each oblique incident angle.

[0184] The echo feature extraction unit is used to combine the improved chaotic spiral teaching and learning optimization algorithm with the matching pursuit algorithm, and extract the echo features corresponding to each noise reduction echo based on multiple noise reduction echoes corresponding to each oblique incident angle.

[0185] The interference wave elimination unit is used to match the theoretical signal with each generated echo according to the amplitude change trend of the echo characteristics of multiple noise reduction echoes as the oblique incident angles increase, eliminate the interference waves, and obtain the dirt layer echo and pipe wall layer echo corresponding to each oblique incident angle.

[0186] As an optional implementation, the ultrasonic transit time calculation module 504 of the present invention specifically includes:

[0187] The envelope drawing unit is used to draw envelopes according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle, so as to obtain the first envelope and the second envelope corresponding to each oblique incident angle.

[0188] The wave arrival time determination module is used to determine the first wave arrival time corresponding to each oblique incident angle according to the first envelope line corresponding to each oblique incident angle, and to determine the second wave arrival time corresponding to each oblique incident angle according to the second envelope line corresponding to each oblique incident angle.

[0189] The ultrasonic transit time calculation unit is used to calculate the ultrasonic transit time corresponding to each oblique incident angle according to the first wave arrival time and the second wave arrival time corresponding to each oblique incident angle.

[0190] For details of the parts that are the same as those in Example 1, please refer to Example 1 and will not be discussed again.

[0191] Example 3

[0192] like Figure 6-7 As shown, the present invention also provides a multi-angle ultrasonic detection device for heat exchange dirt thickness, comprising: an ultrasonic transmitting probe 1, an ultrasonic receiving probe 2, a liquid cover 3 for synchronously adjusting the angle and position of the probe, a pulse transmitting and receiving device 4, an acquisition card 5 and a computer 6; the pulse transmitting and receiving device 4 is respectively connected to the ultrasonic transmitting probe 1 and the ultrasonic receiving probe 2, the acquisition card 5 is connected to the pulse transmitting and receiving device 4, and the computer 6 is connected to the acquisition card 5.

[0193] The ultrasonic transmitting probe 1 is used to transmit longitudinal waves according to each oblique incident angle. The ultrasonic receiving probe 2 is used to receive multiple echoes corresponding to each oblique incident angle. The liquid cover 3 for synchronously adjusting the probe angle and position is used to synchronously adjust the oblique incident angle and position of the ultrasonic transmitting probe 1 and the ultrasonic receiving probe 2. The pulse transmitting and receiving device 4 is used to control the ultrasonic transmitting probe 1 to transmit longitudinal waves and to control the ultrasonic receiving probe 2 to receive multiple echoes reflected after passing through the pipe wall layer 7 and the dirt layer 8 at each oblique incident angle. The acquisition card 5 is used to collect multiple echo signals corresponding to each oblique incident angle. The computer 6 is used to calculate the average thickness of the dirt layer 8 using the steps S3-S6 in Example 1, and is also used to calculate the probe spacing corresponding to each oblique incident angle using step S1 in Example 1.

[0194] In this embodiment, the liquid cover 3 for synchronously adjusting the angle and position of the probe includes two through holes, one of which is used to place the ultrasonic transmitting probe 1, and the other is used to place the ultrasonic receiving probe 2. A slide rail adjustment structure 10 is arranged between the two through holes, and a first spring is arranged on the side of the ultrasonic transmitting probe 1 away from the slide rail adjustment structure 10, and the first spring is respectively connected to the left bracket and the ultrasonic transmitting probe 1, and a second spring is arranged on the side of the ultrasonic receiving probe 2 away from the slide rail adjustment structure 10, and the second spring is respectively connected to the right bracket and the ultrasonic receiving probe 2; a water outlet 11 is arranged on the left bracket, and a water inlet 9 is arranged on the right bracket. In the present invention, the acquisition card is preferably a high-speed acquisition card.

[0195] When the incident angles of the ultrasonic transmitting probe 1 and the ultrasonic receiving probe 2 need to be adjusted, the slide rail adjustment structure is directly adjusted to drive the ultrasonic transmitting probe 1 and the ultrasonic receiving probe 2 to move, thereby achieving the adjustment of the incident angle and position.

[0196] The invention uses a manual or digital control device to drive the scale knob, and realizes the planned movement of the angle and spacing of the transmitting and receiving probes through the combination of an internal mechanical slide rail structure and an auxiliary spring. This device can reuse existing probe equipment to reduce costs to the greatest extent.

[0197] In this embodiment, both the ultrasonic transmitting probe 1 and the ultrasonic receiving probe 2 are water-immersed, so as to prevent the ultrasonic transmitting probe 1 and the ultrasonic receiving probe 2 from being immersed in water and then corroded. The present invention uses a 10Mhz, 6-inch wafer-sized water-immersed ultrasonic probe.

[0198] In the description of the present invention, the term "plurality" refers to two or more than two. Unless otherwise clearly defined, the orientation or positional relationship indicated by the terms "upper" and "lower" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention. The terms "connection", "installation", "fixation", etc. should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0199] In the description of the present invention, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In the present invention, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0200] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multi-angle ultrasonic detection method for heat exchange fouling thickness, characterized in that: The method comprises: Step S1: Calculate the probe spacing corresponding to each oblique incidence angle based on the repeated transmission coefficient corresponding to each key echo. The specific steps include: Calculate the refraction coefficient based on the normal acoustic impedance at oblique incidence; the refraction coefficient includes: longitudinal wave reflection coefficient, longitudinal wave refraction coefficient and transverse wave refraction coefficient; Calculate the repetitive transmission coefficient corresponding to each key echo according to the refraction coefficient; Taking the repeated transmission coefficient corresponding to each key echo as the ordinate and the oblique incident angle as the abscissa, a waveform diagram of the repeated transmission coefficient corresponding to each key echo changing with the oblique incident angle is simulated and drawn; Determine the value range of the oblique incidence angle according to the waveform diagram of the repeated transmission coefficient corresponding to each key echo changing with the oblique incidence angle; Selecting a plurality of oblique incident angles from the oblique incident angle value range; The probe spacing corresponding to each oblique incident angle is determined by using each oblique incident angle and the sound ray model; each key echo includes a pipe wall layer echo and a dirt layer echo; the probe spacing is the distance between the ultrasonic transmitting probe and the ultrasonic receiving probe; Step S2: adjusting the positions of the ultrasonic transmitting probe and the ultrasonic receiving probe according to the probe spacing corresponding to each oblique incident angle, using the ultrasonic transmitting probe to transmit longitudinal waves according to each oblique incident angle, and using the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle; Step S3: screening the multiple echoes corresponding to the oblique incident angles to obtain the dirt layer echo and the pipe wall layer echo corresponding to the oblique incident angles; Step S4: calculating the ultrasonic transit time corresponding to each oblique incident angle according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle; Step S5: Calculate the dirt layer thickness corresponding to each oblique incident angle according to each oblique incident angle and the corresponding ultrasonic transit time. The specific calculation formula is: ； in, represents the dirt layer thickness corresponding to the kth oblique incident angle, represents the speed of ultrasound in supersonic water, represents the speed of sound in the dirt layer, represents the kth oblique incident angle, represents the ultrasonic transit time corresponding to the kth oblique incident angle; Step S6: merging the dirt layer thicknesses corresponding to the oblique incident angles to obtain an average dirt layer thickness.

2. The multi-angle ultrasonic detection method for heat exchange fouling thickness according to claim 1 is characterized in that: The steps of screening the multiple echoes corresponding to the oblique incident angles to obtain the dirt layer echo and the pipe wall layer echo corresponding to the oblique incident angles include: Performing noise reduction processing on the multiple echoes corresponding to the oblique incident angles to obtain multiple noise-reduced echoes corresponding to the oblique incident angles; The improved chaotic spiral teaching and learning optimization algorithm is combined with the matching pursuit algorithm, and the echo features corresponding to each denoised echo are extracted based on multiple denoised echoes corresponding to each oblique incident angle. As the oblique incident angles increase, according to the amplitude variation trend of the echo characteristics of multiple noise-reduced echoes, the theoretical signal is matched with each generated echo, the interference wave is eliminated, and the dirt layer echo and pipe wall layer echo corresponding to each oblique incident angle are obtained.

3. The multi-angle ultrasonic detection method for heat exchange fouling thickness according to claim 1 is characterized in that: The specific steps of calculating the ultrasonic transit time corresponding to each oblique incident angle according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle include: Draw envelopes respectively according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle, and obtain a first envelope and a second envelope corresponding to each oblique incident angle; Determine the first wave arrival time corresponding to each oblique incident angle according to the first envelope line corresponding to each oblique incident angle, and determine the second wave arrival time corresponding to each oblique incident angle according to the second envelope line corresponding to each oblique incident angle; The ultrasonic transit time corresponding to each oblique incident angle is calculated according to the first wave arrival time and the second wave arrival time corresponding to each oblique incident angle.

4. The multi-angle ultrasonic detection method for heat exchange fouling thickness according to claim 1 is characterized in that: The dirt layer thickness corresponding to each oblique incident angle is merged to obtain the average dirt layer thickness. The specific calculation formula is: ； ； ； in, represents the dirt layer thickness corresponding to the kth oblique incident angle, represents the mean thickness of the dirt layer, n represents the total number of oblique incident angles, represents the exponential function decay coefficient, represents the kth oblique incident angle, and All represent intermediate variables. and Indicates the weight coefficient selected according to the working conditions.

5. A multi-angle ultrasonic detection system for heat exchange fouling thickness, characterized in that: The system comprises: The probe spacing calculation module is used to calculate the probe spacing corresponding to each oblique incidence angle based on the repeated transmission coefficient corresponding to each key echo. The probe spacing calculation module specifically includes: A refraction coefficient calculation unit, used to calculate the refraction coefficient based on the normal acoustic impedance ratio at oblique incidence; the refraction coefficient includes: a longitudinal wave reflection coefficient, a longitudinal wave refraction coefficient and a transverse wave refraction coefficient; A repeated transmission coefficient calculation unit, used for calculating the repeated transmission coefficient corresponding to each key echo according to the reflection coefficient; A waveform diagram drawing unit, used to simulate and draw a waveform diagram of the repeated transmission coefficient corresponding to each key echo changing with the oblique incident angle, using the repeated transmission coefficient corresponding to each key echo as the ordinate and the oblique incident angle as the abscissa; An oblique incidence angle value range determination unit, used to determine the oblique incidence angle value range according to a waveform diagram of the repeated transmission coefficient corresponding to each key echo varying with the oblique incidence angle; An oblique incident angle selection unit, used to select a plurality of oblique incident angles from the oblique incident angle value range; The probe spacing calculation unit is used to determine the probe spacing corresponding to each oblique incidence angle by using each oblique incidence angle and the sound ray model; each key echo includes a pipe wall layer echo and a dirt layer echo; the probe spacing is the distance between the ultrasonic transmitting probe and the ultrasonic receiving probe; A position adjustment module, used for adjusting the positions of the ultrasonic transmitting probe and the ultrasonic receiving probe according to the probe spacing corresponding to each oblique incident angle, using the ultrasonic transmitting probe to transmit longitudinal waves according to each oblique incident angle, and using the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle; An echo screening module, used for screening the multiple echoes corresponding to the oblique incident angles to obtain the dirt layer echo and the pipe wall layer echo corresponding to the oblique incident angles; An ultrasonic transit time calculation module, used to calculate the ultrasonic transit time corresponding to each oblique incident angle according to the dirt layer echo and the pipe wall layer echo corresponding to each oblique incident angle; The dirt layer thickness calculation module is used to calculate the dirt layer thickness corresponding to each oblique incident angle according to the oblique incident angles and the corresponding ultrasonic transit time. The specific calculation formula is: ； in, represents the dirt layer thickness corresponding to the kth oblique incident angle, represents the speed of ultrasound in supersonic water, represents the speed of sound in the dirt layer, represents the kth oblique incident angle, represents the ultrasonic transit time corresponding to the kth oblique incident angle; The dirt layer thickness fusion module is used to fuse the dirt layer thicknesses corresponding to the oblique incident angles to obtain an average dirt layer thickness.

6. A multi-angle ultrasonic detection system for heat exchange fouling thickness according to claim 5, characterized in that: The echo screening module specifically includes: A noise reduction processing unit, used for performing noise reduction processing on the multiple echoes corresponding to the oblique incident angles to obtain multiple noise-reduced echoes corresponding to the oblique incident angles; An echo feature extraction unit is used to combine the improved chaotic spiral teaching and learning optimization algorithm with the matching pursuit algorithm to extract echo features corresponding to each noise reduction echo based on multiple noise reduction echoes corresponding to each oblique incident angle; The interference wave elimination unit is used to match the theoretical signal with each generated echo according to the amplitude change trend of the echo characteristics of multiple noise reduction echoes as the oblique incident angles increase, eliminate the interference waves, and obtain the dirt layer echo and pipe wall layer echo corresponding to each oblique incident angle.

7. A multi-angle ultrasonic device for detecting heat exchange fouling thickness, characterized in that: The device specifically comprises: An ultrasonic transmitting probe, used for transmitting longitudinal waves at various oblique incident angles; An ultrasonic receiving probe, used for receiving multiple echoes corresponding to each oblique incident angle; A liquid cover for synchronously adjusting the angle and position of the probe, used for synchronously adjusting the oblique incident angle and position of the ultrasonic transmitting probe and the ultrasonic receiving probe; A pulse transmitting and receiving device, connected to the ultrasonic transmitting probe and the ultrasonic receiving probe respectively, for controlling the ultrasonic transmitting probe to transmit longitudinal waves and for controlling the ultrasonic receiving probe to receive multiple echoes corresponding to each oblique incident angle; An acquisition card, connected to the pulse transmitting and receiving device, for acquiring a plurality of echo signals corresponding to each oblique incident angle; A computer is connected to the acquisition card and is used to calculate the average thickness of the dirt layer using steps S3-S6 described in any one of claims 1-4, and is also used to calculate the probe spacing corresponding to each oblique incident angle using step S1 described in any one of claims 1-4.

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