Combined enhancement of pool boiling heat transfer using a passive bubble-actuated vibrational spring and nanofluid

The high energy consumption of active vibration techniques limits their practicality for enhancing pool boiling heat transfer. This study presents a novel, entirely passive approach that harnesses the kinetic energy of departing bubbles to induce self-sustaining vibrations in an integrated spring mechanism. Twelve distinct spring configurations (varying in number: 3-6, and diameter: 3-6 mm) were experimentally evaluated on a copper surface to identify the optimal design using DI water. The top-performing configuration (5 springs, 3 mm diameter) was then tested with ethanol (70%) and a Fe₃O₄ nanofluid (0.1% vol). Results demonstrate a significant combined effect. The passive vibrator alone enhanced the heat transfer coefficient (HTC) by up to 26% in water by agitating the thermal boundary layer. When combined with the nanofluid, the HTC was enhanced by 55% compared to a plain surface, as nanoparticles increased nucleation site density and the bubble-induced vibrations amplified fluid mixing and nanoparticle dynamics. This energy-autonomous system achieves performance comparable to active methods without their associated cost and complexity, offering a highly scalable solution for thermal management systems in electronics and industrial applications.