Abstract
Nanofluids’ thermophysical properties and heat transfer performance has been investigated for many years, while research on their surface tension (ST) and wetting behavior is very limited. To assess nanofluids potential as industrial products, a complete picture is required to prove their performance in a specific application. Boiling heat transfer, microfluidics and drug development are among the applications where ST is a variable. ST of water-based ZnO nanofluids were measured in the presence and absence of direct ultrasonication. The experiments covered variation of ST with ZnO concentration (0.05–0.4 vol%), ultrasonication amplitude (40% and 100%) and duration. To the best of the authors’ knowledge, this is the first report of ST– ultrasonication process relation for a nanofluid. Results showed that after direct ultrasonication, nanofluids ST is strongly affected by the temperature raise, and in those cases relative ST may provide a clearer picture. A nano-film over individual and agglomerated nanoparticles spotted via TEM imaging was affected from the ultrasonication. Such a nano-film can play a key role in the anomalous thermal transport and wettability of nanofluids. Statistical analyses revealed that changes in ultrasonication amplitude resulted in a statistically significance difference on nanofluid ST and relative ST. Changes in nanoparticle concentration caused a significant difference on the nanofluid ST while the difference in relative ST was insignificant. Variation of ultrasonication duration caused significant variations on the relative ST while the difference in nanofluid ST was not significant. This work highlights that based on specific applications ST and other related features of any nanofluid can be adjusted employing proper ultrasonication conditions.
Highlights
Nanofluids has attracted immense attention from researchers worldwide [1] while their thermophysical properties and heat transfer performance has been under extensive research during the past decade
From the literature review presented in Introduction, it is deduced that statistical comparison of parameters effects is required to quantify whether surface tension (ST) or relative ST of nanofluids depend on a material or process variable
Before proceeding with ZnO-distilled water (DW) nanofluids ST measurements, the tensiometer was calibrated by per forming ST measurements of water droplets
Summary
Nanofluids has attracted immense attention from researchers worldwide [1] while their thermophysical properties and heat transfer performance has been under extensive research during the past decade. Such a high research interest is mainly due to the reported (earlier and current) improved thermophysical properties and heat transfer co efficients compared to base liquids with poor thermal characteristics, and for nanofluids potential in thermal management applications. Thermal properties have utmost importance for heat transfer applications, surface phenomena always play an important role for their outstanding properties. ST plays key role as a variable in numerous thermal techniques and applications
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