Experimental study on the dynamic wetting of dilute nanofluids

• Nanofluid dynamic wetting and parameter effects were studied experimentally.
• Bulk dissipations due to nanoparticle motions dominate the dynamic wetting.
• The individual effects of surface tensions and viscosities were examined.
• Diluted nanofluids exhibit Newtonian fluid dynamic wetting behaviors.

The attractive and tunable wetting behaviors extend the applications of nanofluids into many scientific and engineering areas; however, the corresponding mechanisms are not well understood. In this work, the time-dependent wetting radius and contact angle for various dilute nanofluid droplets were measured by the droplet spreading method. The effects of the nanoparticle material, loading and diameter, the base fluid, and the substrate material were examined. The results show that the adding of nanoparticles inhibits the dynamic wetting of nanofluids as compared with base fluids. The reduced spreading rate can be attributed to the increase in either surface tension or viscosity due to adding nanoparticles into the base fluid. It is interesting that once the effects of the surfaces tension and viscosity are both eliminated using the non-dimensional analysis, the wetting radius vs. spreading time (R–t) curves for all the nanofluid droplets overlap with each other. In addition, the spreading exponent fitted from the nanofluid dynamic wetting data is found to be very close to 0.1, which meets the prediction of the classical hydrodynamics model derived from the bulk viscous dissipation approach. Thus, the present results prove that the spreading of the dilute nanofluid droplets is dominated by the bulk dissipation rather than by the local dissipation at the moving contact line.

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