Boiling enhancement through acoustically assisted bubble departure

Boiling has been extensively studied over the past several decades due to its critical role in thermal-fluidic systems for power generation and electronics thermal management. By exploiting the large latent heat, boiling offers exceptional heat dissipation rate and remarkable wall temperature uniformity for power-dense applications. Typically, boiling performance is characterized by two key parameters. The first one is the critical heat flux (CHF), which is the maximum heating power per unit area (aka heat flux) that can be removed from the heat transfer surface before burnout. The second parameter is the heat transfer coefficient (HTC), which is the measure of cooling efficiency often described by the heat flux per unit superheat (excess wall temperature above saturation). Conventional boiling enhancement strategies rely primarily on surface modifications that employ micro/nanostructuring and/or chemical functionalization, which are neither durable nor well suited to handling transient heating loads. In this work, we introduce robust ultrasonic acoustic waves as an externally imposed and dynamically tunable approach to actively manipulate bubble nucleation, growth, and departure during nucleate boiling for heat transfer gain. Experiments were conducted on smooth copper plates (heated area = 15 mm × 15 mm) using degassed pure ethanol (200 proof, purity > 99.9%). By systematically varying the acoustic pressure amplitude ( P inc = 0–460 kPa) and wave incidence angle ( α = 0°–90°), we identified an optimal forcing condition. The heat dissipation rate is maximum when P inc = 46 kPa at α = 45°, consistent with our COMSOL simulation. Under optimal forcing, the CHF increased from ≈ 45 W/cm 2 to ≈ 72 W/cm 2 . We attribute the ≈ 60% enhancement in CHF to expedited bubble departure as observed by ≈ 36% reduction in departure diameter and ≈ 100% increase in departure frequency. A physics-based framework that is grounded on the dimensionless Bond number, which compares buoyancy and capillary forces, and the acoustic-capillary pressure ratio, which quantifies acoustic forcing relative to interfacial stability, shows that moderate forcing enhances bubble growth and departure while excessive forcing initiates interfacial destabilization that leads to bubble coalescence. The experiments further reveal a non-monotonic effect of forcing amplitude on boiling wherein weak forcing provides limited benefits whereas excessive forcing impacts CHF unfavorably. Collectively, these results establish boiling enhancement through acoustically assisted bubble departure as a robust and tunable strategy for on-demand transient thermal management of power-dense electronic devices.