| Heat exchanger is the main equipment in HVAC, thermal energy engineering, chemical industry and other fields, these devices generally exist scaling phenomena in the operation, which leads to decrease the effect of heat transfer and influence the safety of equipment. At present, the conventional descaling method has the problem of high cost of maintenance, chemical waste, it is difficult to meet the production process requirements, ultrasonic cleaning technique is extended due to the advantages of the green environmental protection, low cost, obvious effect. But in the engineering application, the ultrasonic parameters matching and unreasonable transducer arrangement cause the loss of descaling efficiency, resulting in having no the descaling effect in heat exchanger area. Therefore, further study of ultrasonic descaling efficiency and range is very necessary.According to the study, the directivity of ultrasonic determines the scope of descaling, while sound intensity has certain influence on the descaling efficiency. In this paper, a non point source directivity function and the mathematical model of sound intensity are established on the basis of point sound source directivity function, making use of the MATLAB software simulation works out the distribution of ultrasonic directivity function under different frequency and transducer radius parameters, The relationship between ultrasonic sound intensity and transducer, ultrasonic frequency, radiation angle is also found. According to the simulation calculation, we can receive the following conclusions:(1) When the ultrasonic frequency is 28kHz, the greater the radius of the transducer, the smaller the distribution of the sound field, the sound field gradually gathered in the vertical direction to the transducer, when the transducer radius is 50mm, range of directivity of ultrasonic centre on center region of transducer.(2) Transducer radius is 30mm, the greater the frequency, the smaller the sound field distribution, when the frequency is 60kHz, ultrasonic directional range to a minimum.(3) Ultrasonic sound intensity is proportional to the square root of the power, and inversely proportional to the square of the distance traveled, the greater the power, the greater the sound intensity; the farther propagation distance, the sound intensity is smaller.(4) Ultrasonic frequency is 40kHz, with the transducer radius increases, sound intensity value gradually increases, the sound intensity value of other radiation angles is small, when the radius is 50mm, sound intensity at the vertical direction of the transducer reaches a maximum. When the transducer is fixed radius of 30mm, the frequency changes, the frequency of the sound intensity is similar to the influence of the radius of the transducer.In the paper, based on the theoretical research, the ultrasonic cleaning experiments are also carried out, based on experimental studies, make the following conclusions:(1) When the frequency is 20 kHz, the maximum range of cleaning, with increasing frequency, gradually narrowing the scope of descaling, concentrated near the vertical center of the transducer, the transducer radius of influence of the frequency range similar to cleaning. Descaling range affected law and sound field distribution simulation graphics transducer frequency and radius match.(2) At the center of the transducer, cleaning efficiency is the largest, as the angle spread to both sides, the cleaning efficiency decreases; when the frequency is 20kHz or radius of 15mm, the differences of the cleaning efficiency of various angles is less, about 50% to 60%, with increasing frequency, or the radius of the transducer, cleaning efficiency on both sides of is low and high cleaning efficiency at the center, reaching a maximum of 95.5%. Sound intensity graphics in simulation and experimental results is basically the same. |
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