At present, heat exchangers are widely used in industrial production processes, but fouling will lead to an increase in their energy consumption, and the application of ultrasonic can effectively reduce fouling. This study presents a crystallization fouling model under the action of ultrasonic, aimed at investigating the inhibitory effect of dual-frequency ultrasonic on CaCO3 fouling in heat exchanger tubes. Based on the constructed model, this study primarily compares the effects of single-frequency and dual-frequency ultrasonic, with a detailed analysis of the impact of pressure amplitude and frequency of the dual-frequency ultrasonic. The results indicate that dual-frequency ultrasonic at 20 + 40 kHz exhibits the fouling inhibition rate 19.9 % and 36.2 % higher than single-frequency ultrasonic at 20 kHz and 40 kHz, respectively. The fouling layer thickness under ultrasonic action increases progressively with tube length, while the wall shear force varies periodically over time. The average of wall shear force under dual-frequency ultrasonic action is higher than that under single-frequency. In the research range of dual-frequency ultrasonic, increasing pressure amplitude enhances its fouling inhibition effect. As pressure amplitude increases from 100 kPa to 250 kPa, the fouling inhibition rate rises by 21 %. An increase in frequency weakens the fouling inhibition effect. When the co-frequency increases from 30 + 30 kHz to 60 + 60 kHz, the fouling inhibition rate decreases by 19.9 %. When the different-frequency increased from 20 + 40 kHz to 50 + 70 kHz, the fouling inhibition rate decreased by 24.1 %. Additionally, the fouling inhibition rate at different-frequency ultrasonic is consistently higher than that at the co-frequency, indicating that different-frequency ultrasonic provides better inhibition. Furthermore, the fouling layer thickness decreases with increasing pressure amplitude and increases with frequency.
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