Enhanced pool boiling critical heat flux on tilted heating surfaces using columnar-post wicks

Abstract

The upper heat flux limit of nucleate pool-boiling heat transfer (NPHT), i.e., Critical Heat Flux (CHF), results in system burnouts in various energy and industrial applications, and the understandings of the tailored CHF mechanisms are crucial to develop robust thermal management systems. In various applications, the understandings of the tailored CHF mechanisms are essential for design flexibility and operation sustainability, but previous CHF tailoring studies focused on upward-facing heater orientation. This study examines the tailored hydrodynamic-instability using columnar post wick array to enhance CHF on tilted heater surfaces (with surface orientation θ = 60°–130°). Liquid supply enhances via the capillary flow through the post wicks, while the produced vapor efficiently escapes through pore space among the post wicks. The enhanced CHF are predicted using a modified interfacial lift-off CHF hydrodynamic model that relies on classical two-dimensional interfacial instability theory. On the tilted plain surface with the surface orientation from 60° to 130°, the model predicts the CHF, qCHF = 126.5 to 92.5 W/cm2 at the critical hydrodynamic instability wavelength, λcr = 9.2 to 12.7 mm, respectively, using water as a working fluid. The enhanced CHF is predicted at the surface orientations of θ = 90° and 120°, showing a maximum of 185% and 250% increase, respectively. The maximum enhancement occurs at the smallest columnar-post pitch distances, lp = 2.5 mm, where qCHF increases from 104 to 295 W/cm2 for θ = 90°, and from 89 to 313 W/cm2 for θ = 120°. The developed model will provide insights into the tailored hydrodynamic instability wavelength at tilted angle via engineered surface.