The effect of varying wall temperature on the influence of an ultrasonic field on the melting and freezing characteristics of a phase change material (PCM) is experimentally investigated in this study. A PCM with a melting temperature of 58.29 °C is placed inside a copper box with an ultrasonic transducer of 100 W positioned beneath it. During the melting tests, the temperature of the side walls is controlled within the range of 60-90°C, while for the freezing tests, it is maintained steadily between 10 and 40°C. Photos recorded with thermal and digital cameras are used to analyze the results. In the melting tests, it was found that an increase in wall temperature corresponds to a decrease in the efficiency of the ultrasonic field. While a wall temperature of 60°C resulted in a 26.15 % reduction in the PCM melting time with the application of the ultrasonic field, this reduction decreased to 10.26 % at a wall temperature of 90°C. In the solidification tests, it was established that applying an ultrasonic field reduces solidification time only at a temperature of 10°C (by 7.45 %), while at other temperatures, the solidification time increases with the application of the ultrasonic field, which is an unfavorable outcome.
