Aluminum surface wettability changes by pool boiling of nanofluids

Abstract

Boiling of colloidal suspensions has been found to modify surface properties, which can lead to enhancements in heat transfer processes. In this paper, a systematic study of the surface modification after nanofluid boiling is reported. Aluminium substrates of different initial roughness were used to study the roughness effect on the wettability after boiling in various nanofluid concentrations, boiling durations and heat fluxes. Experimental results show that these parameters are significant to surface wettability changes. Extending boiling duration and increasing nanofluid concentration exhibits positive impact on the surface wettability enhancement, while roughness has a more complex influence. The mechanism of the wettability modification is revealed by microscopy and goniometry. It was found that the enhanced wettability on aluminium surfaces after boiling in Al2O3 nanoparticle aqueous suspensions is due to the growth of hydroxides and the deposition of particles during the boiling process, so both chemical and topographical modifications were caused by nanofluid boiling on aluminium surface. Scanning electron microscope (SEM) images demonstrate that, micro and nano multi-scale structures were introduced to the surface after the treatment, which contributes to the enhancement of wettability, and improves longevity. The good agreement of roughness factor obtained by atomic force microscopy (AFM) and water contact angle experiment indicates Wenzel wetting state on the surface.