CN110508566A - Surface descaling method based on multi-frequency leaky ultrasonic guided waves - Google Patents

Abstract

The invention relates to a surface descaling method based on multi-frequency ultrasonic guided waves, belonging to the technical field of descaling. The technical points of this method are as follows: For the fouling surface of the medium containing liquid load, the transducer module is placed at a position far from the liquid load fouling area, and the multi-frequency continuous excitation voltage signal is generated by the signal generating module, which is amplified by the signal amplifying module. In the transducer module, ultrasonic guided waves propagating along the structure are generated. When the guided wave propagates to the fouling area with liquid load, part of the energy leaks into the liquid, and the generated cavitation can effectively impact the fouling and achieve The purpose of removing scale. The invention utilizes the advantage of large ultrasonic guided wave coverage to realize remote on-line removal of scaling, the equipment to be cleaned does not need to be shut down or disassembled, and the multi-frequency excitation method can remove scaling more uniformly and effectively, thereby improving the removal rate. The method has high efficiency, wide range of action and no pollution to the environment.

Description

Surface descaling method based on multi-frequency leaky ultrasonic guided waves

technical field

The invention relates to a surface descaling method based on multi-frequency ultrasonic guided waves, belonging to the technical field of descaling.

Background technique

Industrial equipment in humid environments or fluid heat exchange areas, such as boilers, heat exchangers, circulating cooling water systems, and membrane filtration systems (seawater desalination), will always have foulant deposits on the heat transfer surfaces. Dirt usually accumulates on solid surfaces in contact with fluids and exists in the form of solid or ooze-like substances. Surface scaling will reduce the heat transfer coefficient of the equipment, resulting in a decrease in production capacity and an increase in production energy consumption. Moreover, if the dirt is not dealt with in time, it may also lead to mechanical failure of the equipment and unexpected shutdown, resulting in serious industrial accidents.

At present, the descaling methods for the surface of industrial equipment mainly include mechanical method, high-pressure water jet method, chemical method and ultrasonic method. The mechanical method mainly uses tools such as scrapers, milling cutters and wire brushes to remove scale. This method consumes a lot of human resources, requires equipment to stop production, cannot achieve online removal, and has blind spots for removal. The high-pressure water jet method uses the fluid kinetic energy generated by the high-pressure water flow to remove the scale on the surface. The main disadvantage of this method is that it will cause waste of water resources, and at the same time, it cannot achieve online scale removal; chemical methods use specific chemical reagents to chemically react with the scale. , so as to achieve the purpose of eliminating scaling, chemical descaling will damage the equipment, and may cause pollution to the environment. The ultrasonic method removes surface fouling based on the ultrasonic cavitation effect. In the traditional ultrasonic method, the object to be cleaned is immersed in a water tank containing cleaning liquid, the transducer is attached to the bottom of the water tank, the high-frequency vibration generated by the transducer enters the cleaning liquid, and the ultrasonic cavitation effect is generated to remove the scale on the surface of the object. . Therefore, the conventional ultrasonic method requires disassembly of the equipment, resulting in interruption of production, and this method has the disadvantage of a small removal range.

The surface descaling method based on multi-frequency ultrasonic guided waves can remove the internal fouling on the surface of industrial equipment online. The ultrasonic guided wave propagating in the solid medium of the equipment will partially leak into the liquid water carrier, and the resulting cavitation effect can effectively remove the surface dirt. This method can remove a wide range of fouling areas by taking advantage of the long propagation distance of ultrasonic guided waves, and at the same time, it can realize on-line operation. At the same time, multi-frequency excitation can improve the disadvantage of poor and uneven removal effect of single frequency, and improve the descaling efficiency.

SUMMARY OF THE INVENTION

The present invention proposes a surface descaling method based on multi-frequency ultrasonic guided waves, and the technical scheme is divided into the following steps:

For the medium fouling surface with liquid load, the transducer module is placed at a position far from the liquid load fouling area, and the multi-frequency continuous excitation voltage signal is generated by the signal generation module, which is amplified by the signal amplification module and acts on the transducer module. Ultrasonic guided waves propagating along the structure are generated. When the guided waves propagate to the fouling area with liquid load, part of the energy leaks into the liquid, and the generated cavitation can effectively impact the fouling and achieve the purpose of removing fouling.

The method for surface descaling based on multi-frequency ultrasonic guided waves is characterized in that the surface fouling is removed by utilizing the cavitation effect generated by the leaking ultrasonic guided waves in the medium liquid load.

The surface descaling method based on multi-frequency ultrasonic guided waves is characterized in that the excitation signal is a signal containing multiple frequency components, and the value of each frequency component is above 20KHz.

The signal generating module may be a multi-channel data acquisition card or an integrated signal generating module with a microprocessor as the core.

The amplifying module may use a high-frequency power amplifier or a high-voltage power operational amplifier.

The transducer module is composed of single or multiple piezoelectric transducers, and the core of the transducer is piezoelectric material, which can convert electrical energy into mechanical energy based on piezoelectric effect.

The method for surface descaling based on multi-frequency ultrasonic guided waves is characterized in that the method is suitable for removing the surface fouling of various structures including plate-like structures and tubular structures.

The invention belongs to the technical field of surface descaling, is suitable for removing dirt on the surface of a structure, and realizes remote online descaling by taking advantage of the large coverage distance of ultrasonic guided waves. The method can remove the scale more uniformly and effectively, and improve the removal rate. Compared with the traditional descaling method, the method has the advantages of high efficiency, large scope of action, and no pollution to the environment.

Description of drawings

Fig. 1 is the working schematic diagram of the method of the present invention;

Fig. 2 is the transducer used in the example;

Fig. 3 is the displacement-frequency characteristic curve diagram obtained from the test of the transducer by the scanning laser vibrometer;

In Figure 1, 1-signal generation module, 2-amplification module, 3-transducer, 4-guided wave, 5-structure surface, 6-leakage energy, 7-fouling, 8-cavitation effect, 9-liquid load ;

In Figure 2, 1-aluminum upper base, 2-piezoelectric ceramic sheet, 3-aluminum square base

Detailed ways

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

1. Frequency selection test

A single oblique-incidence transducer is used, as shown in Figure 2. The transducer, which consists of an aluminum square base and piezoelectric material, was first tested using a laser scanning vibrometer. The frequency sweep signal is generated by the signal generator and input to the oblique transducer, and the laser vibrometer is scanned and tested and FFT (fast Fourier transform) is performed to obtain the displacement and vibration characteristics of the transducer at different frequencies, and the displacement-frequency characteristics of the transducer. The curve is shown in Figure 3. According to the test results, the transducer has displacement peaks at frequencies of 22.789KHz, 38.125KHz and 44.437KHz respectively, and the transducer has good electro-acoustic conversion efficiency at the peak frequency. In order to improve the cavitation descaling effect, three frequencies of 22.879KHz, 38.125KHz and 44.437KHz were selected as the multi-frequency components of the descaling excitation signal.

2. Scale removal experiment

The experiment was divided into four groups, and the scale removal experiment was carried out on four stainless steel plates covered with calcium carbonate layers. Four stainless steel plates obtained calcium carbonate fouling layers under the same experimental conditions, and the lengths of the calcium carbonate fouling areas were all 18 cm.

The experiment is divided into four groups, and the specific technical process is as follows:

(1) Attach a single transducer to the surface of one end of the steel plate away from the scale layer with epoxy resin AB glue, and immerse the end of the steel plate with the scale layer into a water tank filled with water.

(2) The digital signal is generated by LabVIEW programming on the computer. The first three groups are single-frequency descaling experiments. The experimental excitation signal is shown in the following formula:

s(t)=A ₀ sin(2πft)

f is 22.789KHz or 38.125KHz or 44.437KHz, A ₀ is the amplified voltage amplitude.

The fourth group is the multi-frequency descaling experiment, and the experimental excitation signal is as follows:

s(t)=A ₀ (sin(2πf ₁ t)+sin(2πf ₂ t)+sin(2πf ₃ t))

f ₁ =22.789KHz, f ₂ =38.125KHz, f ₃ =44.437KHz, A ₀ is the amplified voltage amplitude. The peak frequencies of 22.789KHz, 38.125KHz, and 44.437KHz measured by the laser vibrometer are set as the multi-frequency components of the excitation signal.

(3) The digital signal generated on the computer is converted into an analog voltage signal through the digital-to-analog conversion of the NI USB6366 digital acquisition card (DAQ).

(4) The voltage signal output by the digital acquisition card is increased to 300V _pp through the HFVP-83A power amplifier,

(5) The amplified voltage signal is divided into two outputs, one output is connected to the transducer, the transducer converts the voltage signal into mechanical vibration based on the piezoelectric effect, and the other output is connected to the American Tektronix MDO3034 mixed domain oscilloscope to observe the waveform .

(6) The mechanical vibration of the transducer generates ultrasonic guided waves propagating in the medium, and the scaling on the surface of the medium is removed based on the cavitation effect.

Four sets of experiments of the above process were carried out on four steel plates with calcium carbonate scale layers attached. Except for the different excitation signals, the other processes are the same in the four sets of experiments. The excitation signals of the four sets of experiments are as follows:

The first group: s(t)=300sin(2π*22789*t)

The second group: s(t)=300sin(2π*38125*t)

The third group: s(t)=300sin(2π*44437*t)

The fourth group: s(t)=300(sin(2π*22789*t)+sin(2π*381258*t)+sin(2π*44437*t))

3. Experimental results

In order to quantitatively analyze the descaling effect, the removal rate R is introduced:

W _r is the total weight of fouling removed by the descaling experiment, and W _t is the total weight of fouling before the descaling experiment.

Table 1 Experimental descaling rate

It can be seen from Table 1 that the removal rate in the multi-frequency excitation descaling experiment is higher than that in the single-frequency experiment. The results show that multi-frequency excitation can improve the descaling effect. Therefore, the on-line surface descaling method based on the multi-frequency leaky ultrasonic guided wave proposed in the present invention can uniformly and effectively remove the scaling on the surface of the medium.

The above description is only one of the preferred embodiments of the present invention, and changes, modifications, substitutions and deformations to the embodiments of the present invention are within the protection scope of the present invention without departing from the principles of the present invention.

Claims (5)

1. a kind of surface descaling method based on multiple frequency ultrasonic guided wave, it is characterised in that the following steps are included:

For the medium fouling surface containing fluid load, transducer module is remotely from the position in fluid load fouling region, Multifrequency continuous pump voltage signal is generated by signal generating module, acts on transducer module after the amplification of signal amplification module, Generate the supersonic guide-wave propagated along structural body, when guided waves propagation to the fouling region for having fluid load, portion of energy is leaked to In liquid, the cavitation of generation can effectively Ground shock waves fouling, achieve the purpose that remove fouling.

2. the surface descaling method according to claim 1 based on multiple frequency ultrasonic guided wave, it is characterised in that super using leakage The cavitation effect that guided Waves generate in media fluid load is removed surface scale.

3. the surface descaling method according to claim 1 based on multiple frequency ultrasonic guided wave, it is characterised in that pumping signal is Signal containing multiple frequency components, and the value of each frequency component is in 20KHz or more.

4. signal generating module according to claim 1, can be multi-channel data acquisition board, it is also possible to micro process Device is that module occurs for the integrated signal of core.Amplification module can use high frequency power amplifier, can also use high-voltage power Operational amplifier.Transducer module is made of single or multiple PZT (piezoelectric transducer)s, and the core of energy converter is piezoelectric material, can Mechanical energy is converted electrical energy into based on piezoelectric effect.

5. the surface descaling method according to claim 1 based on multiple frequency ultrasonic guided wave, it is characterised in that this method is applicable in In the various structures body surface smut removal including plate structure and tubular structure.