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

Abstract

Boiling heat transfer is widely used in many practical applications due to significantly high heat transfer coefficients (HTC) associated with it. Several surface modification techniques are known to further improve the heat transfer performance. Applications such as cooling of 3D electronic stacks and portable electronic devices demand nucleate boiling in narrow gaps and often with inclined surfaces. In this regard, we experimentally investigate and compare the individual effects of confinement and orientation (horizontal and vertical) on the HTC 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 to avoid lateral bubble coalescence on the modified patterned wettability surfaces. For confined pool boiling condition, modified surface always demonstrated better heat transfer coefficient than the bare surface. However, the relative HTC (?: a ratio of the difference between confined and unconfined HTC to the unconfined HTC) was higher for the bare surface than the modified surface at moderate and high heat fluxes. Also, the relative HTC for modified surface deteriorated (? < 0) at a comparatively lower heat flux than the bare surface. The boiling heat transfer performance of modified surface was independent of surface orientation. The results from this study provide an insight into the performance of patterned wettability surfaces in a practical scenario of confined boiling in narrow gaps and portable devices typically encountered in electronic cooling applications.