Enhancing heat transfer performance of a two-phase closed thermosyphon using a polymer-coated hydrophobic condenser

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A two-phase closed thermosyphon (TPCT) is a passive heat transfer device that transfers heat from one point to another by two-phase fluid circulation. Dropwise condensation on a hydrophobic surface, where discrete droplets grow on a condenser surface, promises higher condensation heat transfer coefficients (approximate to 40-70 kW/m(2).K) than conventional filmwise condensation. Recent researchers have investigated the effect of dropwise condensation on the heat transfer performance of a TPCT. However, their measured condenser heat transfer coefficients (<25 kW/m(2).K) were much lower than expected, and the heat transfer enhancement mechanism of a hydrophobic TPCT has not been investigated in depth. Here, we achieved a higher condenser heat transfer coefficient of similar to 66 kW/m(2)K in a TPCT using a polymer-based hydrophobic coating film and investigated the heat transfer enhancement mechanism by performing experiments and analytical models. A thin polymer film with an optimized thickness (approximate to 60 nm) was combined with adhesion promoter layers to achieve stable and high-performance dropwise condensation consisting of enhanced surface roughness and a coupling agent. The internal two-phase flow patterns and condensation behaviors were systematically evaluated for the heat transfer performance, which was compared to untreated bare and CuO nanostructured superhydmphobic surfaces. We revealed that rapid droplet removal and active re-nucleation on the polymer-coated hydrophobic surface in a TPCT led to 6 times higher condenser heat transfer coefficients and 68-74% smaller overall thermal resistance than those of the bare and superhydmphobic TPCTs. These results are helpful to understand the effect of dropwise condensation on the heat transfer performance of a TPCT and provide a direction for developing more efficient TPCTs.
Publisher
PERGAMON-ELSEVIER SCIENCE LTD
Issue Date
2021-09
Language
English
Article Type
Article
Citation

APPLIED THERMAL ENGINEERING, v.196, pp.117350

ISSN
1359-4311
DOI
10.1016/j.applthermaleng.2021.117350
URI
http://hdl.handle.net/10203/289761
Appears in Collection
ME-Journal Papers(저널논문)
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