Research On Fouling Detection Signal Processing Of Heat Exchange Tube With Ultrasonic Time-domain Reflectometry

Heat exchange equipment is widely used in metallurgy,electric power,chemical industry,aviation and other industrial production fields.As the heat exchanger operates,dirt will gradually form on the pipe wall.The presence of dirt will reduce the heat transfer efficiency of the heat exchanger,increase energy consumption,and affect the safety of the heat exchanger.Therefore,it is of great significance to study the fouling of heat exchanger.An important link in the fouling research of heat exchange equipment is to detect the fouling.At present,traditional fouling detection methods have some shortcomings,such as difficulty in implementation and inability to measure online.However,ultrasonic detection has attracted people's attention due to its non-destructive and easy to realize advantages.This paper studies the application of ultrasonic in dirt detection,and the main contents are as follows.In the ultrasonic testing of fouling in the heat exchange pipeline in the time domain,a de-noising method based on the improved VMD wavelet shrinkage threshold is proposed to de-noising the ultrasonic testing echo signal of fouling,which is caused by the serious modal mixing and large noise interference due to the complex composition and uneven surface of fouling.First using the method of VMD decomposition echo signal,in order to accurately judge the dominant mode noise,precision de-noising,calculate the autocorrelation function of the components in the value and draw the relevant characteristic curve,combined with different components of energy entropy,judgment and identify noise component,then using the method of wavelet threshold shrinkage handling noise leading mode,pick up the useful information,finally after reconstruction noise signal.In this paper,the simulation software is used to generate ultrasonic detection of fouling in heat exchange tube with different pipe materials,different SNR and different fouling thickness.Wavelet threshold denoising,CEEMD,VMD and the improved method in this paper are used to reduce the noise of the simulation signal respectively.The denoising effect of the above simulation experiments is compared and analyzed.The simulation results show that the method in this paper has a good denoising effect and can effectively avoid the mode aliasing phenomenon,which verifies the effectiveness of the method in this paper.In addition,based on the dynamic simulation test bench of heat exchange fouling,the experimental signal of ultrasonic detection of heat exchange fouling was obtained.The above four methods are used to test and analyze the experimental signals.The experimental results are consistent with the simulation results.The denoising effect of the proposed method is better than that of the wavelet global threshold,CEEMD and traditional VMD method.In this paper,by improving the noise reduction method,and using the simulation experiment and the actual experiment to verify the method,achieved the ideal signal noise reduction effect,verified the practicability and superiority of the method.