Effects of ultrasonic frequency and power on melting acceleration and energy storage performance of a lauric acid-based LHTES system

This experimental study explores how adjusting ultrasonic frequency and power affects the melting dynamics of the lauric acid, which is a suitable candidate for solar thermal energy storage, as a solution to the issue of long phase change duration in phase change material (PCM) integrated systems. The research specifically aims to quantify the ultrasonic frequency and power effects, indicate design parameters for future applications and fill the existing research gap in this field. The experimental rig designed consists of a latent heat thermal energy storage (LHTES) unit, ultrasonic transducers, an ultrasonic generator, a circulation bath, a data acquisition system, and thermocouples to measure the momentary changes in temperature of the PCM for 10 h of experimentation. Experiments were executed with constant heat transfer fluid inlet temperature (60 oC) and flow rate (6 L/min) to quantify the effects of 28 and 40 kHz ultrasonic frequencies and 30, 39, and 48 W ultrasonic powers on mass-averaged temperature, liquid fraction, and the amount of energy storage. After 10 h of experimentation at 48W, comparing 28 kHz to 40 kHz yielded stored energies of 434.7 kJ and 517.2 kJ (+18.98%), respectively. At 28 kHz, comparing 30 W to 48 W yielded stored energies of 325.5 kJ and 434.7 kJ (+33.55%). Additionally, 40 kHz–48W reduced thermal stratification by 3 °C relative to the reference. Results show that increasing the ultrasonic field parameters significantly accelerates the melting, provides for the effective use of the thermal energy storage potential of the PCM, and also helps to dampen the thermal stratification in the LHTES unit.