Impact of substrate wettability on Nucleate Boiling Heat Transfer in single and multiple bubble systems: a Direct Numerical Simulation analysis*

Phase-change phenomena, especially boiling, are critical in many industrial applications, including power generation plants and thermal management of micro-devices. These devices, noted for their high heat power density and dissipation rates, require sophisticated thermal management systems, essential for both space applications in microgravity and ground applications such as radar systems. Boiling stands out as an efficient cooling method to ensure their reliability.

In this study, we examine the transition from small-scale (O(1)) to large-scale (O(1000)) nucleation sites. We perform direct numerical simulations using our custom TPLS solver, which employs the diffuse-interface method to track the liquid-vapor interface evolution. This technique removes the stress singularity at the three-phase contact line, allowing for the imposition of a contact angle boundary condition to define surface wettability. This approach aids in understanding the impact of surface wettability on the nucleate boiling heat transfer coefficient (NBHTC), as well as bubble growth and departure.

We investigate how wettability affects the heat transfer coefficient, an indicator of energy efficiency, and the interaction between neighbouring nucleated bubbles. Our simulations are validated by in-house nucleate boiling experiments using FC72 on silicon surfaces. We show that hydrophilic substrates improve the NBHTC and assess the residual volumes after bubble departures. To further explore the relationship between nucleation, wettability, and micro-layer formation, we use an enhanced hybrid-pseudopotential lattice Boltzmann method.