The effect of dynamic wetting behavior on boiling heat transfer mechanisms during bubble growth and departure. (March 2022) - Allred, Taylor P.
Highlights: Simulation of diabatic bubble growth for hygrophilic, hygrophobic, and ambiphilic surfaces. Unique heat transfer behavior and promising performance of ambiphilic surfaces revealed. Minimizing receding contact angle mitigates vapor spreading, reduces departure time. Increasing advancing contact angle maximizes nucleation site density. Decreasing advancing contact angle maximizes microlayer heat transfer. Abstract: Decades of prior study has yet to fully disentangle the complex transport mechanisms that are attributed to highly effective heat transfer during boiling. Rational design of enhanced surfaces to maintain lower surface temperatures during boiling requires improved insight into the individual heat transfer processes and their dependence on surface characteristics. This study seeks to advance the understanding of the fundamental role that surface wettability plays in determining the relative contributions of different heat transfer mechanisms and on the overall heat transfer efficacy during bubble growth. Two-phase, diabatic simulations of single bubble growth considering interfacial phase change and a custom dynamic contact angle framework are employed to investigate how the distinct contact-line and bubble dynamics that are experienced on hygrophilic, hygrophobic, and ambiphilic surfaces impact heat transfer. The local surface temperature and heat flux profiles underneath the bubble are examined during the receding, pinning, and advancing stages of bubble growth to explore the dominant heat transfer modes at each stage. The results indicate that both hygrophilic and ambiphilic surfaces are promising candidates for the development of enhanced surfaces, but for different reasons related to microlayer heat transfer versus nucleation characteristics, respectively. Target ranges for the dynamic receding and advancing contact angles within each wettability regime are suggested to inform design of surfaces with tailored wettability that maximize performance. These findings indicate that the contact line dynamics play an important role in determining the heat transfer efficacy of a surface and provide a framework for the development of enhanced boiling surfaces.