Effect of confinement and heater surface inclination on pool boiling performance of patterned wettability surfaces

Boiling heat transfer is widely used in many practical applications due to its associated significantly high heat transfer coefficients (HTC). Several surface modification techniques are known to further improve heat transfer performance. Applications such as cooling of three-dimensional electronic stacks and portable electronic devices demand nucleate boiling in narrow gaps, often with inclined surfaces. In this regard, we experimentally investigated and compared the individual effects of confinement and orientation (horizontal and vertical) on the HTCs obtained during boiling on macroscale-patterned wettability surfaces with the baseline case of a homogeneous wettability bare surface. The baseline hydrophilic substrate was modified using macroscale hydrophobic dots with a sufficiently large pitch (greater than the bubble departure diameter, D<inf>b</inf>) to avoid lateral bubble coalescence on the modified patterned wettability surfaces. For confined pool boiling conditions, the modified surface always demonstrated a better HTC than the bare surface. Furthermore, the boiling heat transfer performance of the modified surface was independent of surface orientation. The results from this study provide insight into the performance of patterned wettability surfaces in a practical scenario of confined boiling in the narrow gaps and portable devices typically encountered in electronic cooling applications.