Evaluation of Acoustic Excitation on the Stability and Thermal Performance of Nanofluids

Nanofluids with magnetic nanoparticles have been proposed to enhance heat transfer and energy conversion. However, the performance of these fluids depends on suspension stability and thermal distribution under irradiation. Low-frequency acoustic excitation emerges as an active strategy to modulate mixing and heat transport in these systems. The objective of this research was to determine the effect of low-frequency acoustic excitation on suspension stability, radiative absorption, and thermal efficiency of nanofluids containing magnetite nanoparticles (Fe₃O₄) dispersed at 0.05, 0.25, and 0.5% v/v in an ethylene glycol–water mixture. The methodology included exposing the nanofluids to acoustic waves generated by a loudspeaker while irradiating them with visible and infrared light from a halogen lamp. Stability was assessed through transmittance measurements, and thermal evolution and energy conversion were characterized using the specific absorption rate (SAR) and the stored energy ratio (SER). A comparison was made between different nanoparticle concentrations and excitation conditions. The results demonstrated that acoustic excitation influenced the stability and thermal distribution of the fluid. The extent of these effects varied depending on concentration and experimental conditions. In particular, excitation reduced thermal stratification and increased homogenization in certain cases, whereas in others it did not yield significant improvements in thermal efficiency (SAR/SER). Finally, it is concluded that when used in conjunction with an acoustic excitation system, nanofluids can be utilized more effectively in thermal applications because the acoustic excitation system promotes more uniform temperature fields.