Thermal analysis and optimization of ultrasonic-assisted PCM with different ultrasonic frequencies

Excessive operating temperatures represent a major cause to malfunctions in electronic equipment. Developing high-efficiency thermal management systems is essential for maintaining the operational stability and safety of electronic devices. Ultrasonically driven paraffin thermal management features fast thermal response and great potential for high-efficiency thermal control in electronic devices. In this paper, physical and numerical models of the ultrasonic-assisted phase change material-based thermal management unit (PCM-TMU) are established for two typical scenarios: auxiliary thermal protection and dominant temperature control. The effects of ultrasonic frequency on melting characteristics of the PCM side and heat source side of the thermal management unit are investigated. Then flow characteristics and interaction mechanism between natural convection and ultrasonic flow under different ultrasonic frequencies and thermal boundaries are revealed. Furthermore, the dimensionless characteristic number L _u^⁎ is defined to characterize the direct influence range of ultrasonic, and an optimization criterion for the ultrasonic frequency of PCM-TMU for different types of heat sources is proposed. The results indicate that, compared with the no-ultrasonic case, ultrasonic actuation can significantly enhance heat absorption efficiency and reduce the overall equivalent thermal resistance. Notably, higher ultrasonic power consistently yields superior thermal management performance. For the auxiliary thermal protection scenario (constant temperature thermal boundary), at a fixed ultrasonic power, the ultrasonic frequency corresponding to L _u^⁎ = 1 achieves the maximum wall heat flux under high-power conditions (70 W < P _u < 120 W), while the maximum wall heat flux appears at L _u^⁎ = 0.5 for low-power conditions (10 W < P _u ≤ 70 W). For the dominant thermal control scenario (constant heat flux thermal boundary), at a fixed ultrasonic power, setting L _u^⁎ = 0.5 minimizes the peak wall temperature.