Nonlinear heat transfer regimes and critical conditions of droplet impact on superheated surfaces

Efficient thermal management of superheated surfaces via fine water mist impingement is critical across numerous industrial applications, yet quantifying and optimizing the intricate heat-mass coupling remains a significant challenge. Here, we reveal and quantify a nonlinear cooling enhancement/suppression mechanism driven by the transient coupling of droplet kinetic energy, Leidenfrost vapor film evolution, and interfacial heat transfer. Through the numerical simulations incorporating an interface-confined phase change model, we rigorously elucidate the genesis of the M-shaped heat flux distribution. We mechanistically attribute this M-shape to non-uniform central vapor accumulation and pressure-gradient-driven radial transport, demonstrating its non-uniform suppression on local heat transfer. Crucially, we identify and quantitatively define “critical impact conditions”—encompassing critical droplet size and critical impact velocity—that effectively circumvent the profound inhibition of the Leidenfrost effect to maximize cooling efficiency. For instance, increasing impact velocity from 0.50 to 1.00 m/s leads to a remarkable 110.2% surge in total heat transfer, marking a fundamental transition from a low-efficiency (14.9% increase for 0.25–0.50 m/s) to high-efficiency cooling regime. The identification of this abrupt, stepwise enhancement, rather than a gradual trend, confirms the existence of a critical velocity threshold—the finding that fundamentally extends beyond parametric sensitivity analyses prevalent in the literature. This study provides unprecedented mechanistic insights into droplet-wall heat transfer and offers a novel parameter-based cooling strategy for precise enhancement and optimization of high-temperature cooling processes.