Experimental analysis of ultrasonic-assisted melting in phase change materials: role of transducer location

A latent heat thermal energy storage (LHTES) unit including lauric acid as a phase change material (PCM) is assessed for the PCM melting under different ultrasonic source locations, heat transfer fluid (HTF) inlet temperatures, and HTF flow rates. Ultrasonic vibrations are generated using 28 kHz piezoelectric transducers at 39 W and 48 W. The stored thermal energy increased to 475.4 kJ, indicating a 65.59% increase compared with the non-ultrasonic case. The ultrasonic source location noticeably influences PCM melting. The single-surface configuration produced the highest temperature (52.28 °C), liquid fraction (0.934), and stored energy (475.4 kJ). Results showed a clear disadvantage of the opposing-surface configuration, which produced the lowest temperature (49.20 °C), liquid fraction (0.728), and stored energy (402.4 kJ). The 1.37% difference in stored energy between the single-surface and orthogonal configurations remained within the experimental uncertainty of 4.49%. Regarding HTF inlet temperature, 70 °C was the only condition under which phase change was completed within 6 h whereas phase change remained incomplete at 50 and 60 °C. Although HTF flow rate had a marginal effect on the performance parameters investigated in most cases, increasing the HTF flow rate reduced the melting time from 396 to 342 min under the specific test conditions involving 48 W of ultrasonic power and 70 °C of HTF inlet temperature. The enhancement factor was below unity in all cases, indicating that ultrasonic application requires careful consideration. Consequently, ultrasonic vibration can improve melting rate and effective utilization of LHTES units, when the application strategy is optimized to maximize energy efficiency.