Research On Heat Exchange Bent Pipe Fouling Detection Technology With Ultrasonic Guided Waves

When conveying fluids in the pipeline,organic or inorganic substances will accumulate on the inner surface of the pipeline,and this kind of harmful substance accumulated over a long period of time is called fouling.Fouling exists in various industries such as chemical,petroleum,food,pharmaceutical,metallurgy,etc.Its existence will not only lead to the reduction of production capacity in the industrial production process and affect the economic efficiency,but also affect the safe operation of equipment and bring safety hazards.Therefore,the problem of fouling is of great concern to scholars from various countries,and accurate detection of fouling is the prerequisite and basis for taking effective measures to remove fouling.Accordingly,this paper adopts a combination of theoretical analysis,simulation,and testing experiments to carry out research on the fouling detection of heat exchanger bends by using ultrasonic guided waves,and the main work is as follows.Based on the theoretical basis of the ultrasonic guided wave,the displacement components and dispersion characteristics of different types of modes are discussed,and the guided wave mode suitable for detecting fouling of bends is selected.The dispersion equation of ultrasonic guided wave in the fouling pipe is calculated,the dispersion curve of the ultrasonic guided wave is plotted by GUIGUW software,and the corresponding mode is extracted to plot the fouling thickness-group velocity relationship,which provides theoretical guidance for the subsequent research.The best detection frequency interval is selected by the relationship graph of fouling thickness-group velocity,and the fouling detection method based on the ultrasonic guided wave is proposed to determine the fouling thickness of the bend by detecting the guided wave group velocity.Meanwhile,in order to study the universality of the detection method,the influence of the inner diameter and wall thickness on the dispersion characteristics of the guided wave mode and the frequency interval of the fouling thickness can be detected for the common sizes and tubes of the heat exchanger bend is studied.ANSYS finite element simulation software is used to numerically simulate the heat exchanger bend and analyze the influence of the change of detection spacing,a radius of curvature,and dirt thickness on the ultrasonic waveguide propagation characteristics,and calculate the group velocity of the waveguide mode at this moment according to the time of the mode arriving at the detection point obtained from the simulation.The simulated group velocity and the theoretical group velocity are compared and analyzed,and the simulation results show that the simulated group velocity is more consistent with the theoretical group velocity,and the trend of fouling thickness and group velocity is also consistent with the theoretical value,which initially verifies the feasibility of the selected detection method.Then simulate the liquid-filled fouling bend and the fouling bend with uneven fouling and carry out the research on the detection of fouling thickness based on ultrasonic guided wave under two different working conditions.The experimental system of ultrasonic wave-guided pipe detection is built to detect the heat exchanger bend.Considering the chance of detection and the error caused by the complex action of heat exchanger bend,pipe fouling,and wave-guided wave in the actual detection process,the experimental results obtained from the detection are processed by the method of multiple measurements to find the average value,and the error analysis is combined with the theoretical part.The experimental results are in high agreement with the theoretical results,which further proves the feasibility of the ultrasonic guided wave detection method of heat exchanger bend tube side fouling thickness.For the problem of serious interference and noise of the guided wave signal in the actual detection process,the noise reduction and mode extraction of the guided wave detection signal are performed by the forgetting factor variational modal method and the mutual correlation algorithm,so that the velocity value of the guided wave group can be obtained more accurately.