Effect of Length Scales on the Boiling Enhancement of Structured Copper Surfaces

[+] Author and Article Information
Md Mahamudur Rahman

Drexel University 3141 Chestnut St., Philadelphia, PA, 19104, USA

Matthew McCarthy

Drexel University 3141 Chestnut St., Philadelphia, PA, 19104, USA

1Corresponding author.

ASME doi:10.1115/1.4036693 History: Received October 15, 2016; Revised December 16, 2016


While significant enhancements in pool boiling critical heat flux (CHF) and heat transfer coefficient (HTC) have been demonstrated using structured surfaces, fundamental questions remain about the nature of the enhancements and the role of structure length scale. This work presents a systematic investigation of structures from 100’s of nanometers to several millimeters . Specifically, copper substrates were fabricated with five different microchannel geometries and four different copper oxide nanostructured coatings. Additionally, twenty different multiscale structures were fabricated coinciding with each permutation of the various microchannels and nanostructures. The nanostructured coatings were observed to increase CHF via surface wicking, but decrease HTC due to the suppression of nucleation. The microchannels were observed to increase both CHF and HTC, generally outperforming the nanostructured coatings. The multiscale surfaces exhibited superior performance, with CHF and HTC values as high as 313 W/cm2 and 461 W/m2K, respectively. Most importantly, multiscale surfaces were observed to exhibit the individual enhancement mechanisms seen from each length scale, namely increased nucleation and bubble dynamics from the microchannels, and wicking- enhanced CHF form the nanostructures. Additionally, two of the surfaces tested here exhibited uncharacteristically high HTC values due to a decreasing wall superheat at increasing heat fluxes. While the potential mechanisms producing this counterintuitive behavior are discussed, further research is needed to definitively determine its cause.

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