Boiling hysteresis governs pool-boiling inversion on structured surfaces

Pool boiling is ubiquitous and encountered daily across the globe. From cooking to cooling to power generation, pool boiling pervades our lives. In typical pool-boiling conditions, the wall superheat increases monotonically with heat flux. However, when boiling inversion occurs, the wall superheat decreases with increasing heat flux. This study, through optical visualization and pool-boiling characterization, shows that boiling inversion on structured surfaces is a spontaneous thermodynamic self-regulating process. Boiling inversion occurs near the onset of a boiling crisis under constant-heat-flux boundary conditions, where the system approaches its maximum heat dissipation capability, and is fundamentally driven by boiling hysteresis. Boiling hysteresis is accompanied by boiling-pattern transformation due to the activation of supplementary nucleation sites. A model is developed to characterize the behavioral regimes associated with spatial periodic boiling patterns on structured surfaces. The findings offer practical guidance for the design of enhanced pool-boiling surfaces.