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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

ENHANCEMENT OF DRY-OUT HEAT FLUX IN NONUNIFORM VARIABLE-PERMEABILITY WICKING STRUCTURES

Get access (open in a dialog) DOI: 10.1615/IHTC16.bae.024136
pages 1017-1024

Sinopsis

Micro and nanostructured surfaces are commonly used to enhance fluid supply in thermal management, e.g., in thin film evaporation, flow boiling, and pool boiling. Capillary wicking within the structures passively supplies liquid to the evaporating interface where phase change occurs. In this work, we explored enhanced wicking for thin film evaporation in nonuniform structures by varying the geometry of a wicking pillar array in the direction of fluid propagation. Specifically, pillar pitch and diameter were varied along the wick in order to enhance performance (as opposed to uniform wicks used in previous studies). Constraints on the pitch and diameter were used in order to both ensure a feasible wick design that satisfied the criteria for imbibition and the validity of the used permeability relation. The nonuniform pillar array allowed the pressure drop to be minimized at each location by determining the best combination of pitch and diameter based on the relative liquid pressure at that location, leading to an increased dry-out heat flux. For example, an optimized uniform pillar array with a wicking length of 5 mm and a pillar height of 25 µm (diameter of 10 µm and pitch of 30 µm) had a dry-out heat flux of 61 W/cm2, whereas the nonuniform array designed in this work had a dry-out heat flux of 172 W/cm2. This modelling work demonstrates the potential of variable permeability wicking structures for enhanced thermal management systems, and shows that dry-out heat flux can be increased nearly 3x compared to uniform structures.