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Nanofluids dynamic viscosity evolution using high-frequency acoustic waves: application applied for droplet evaporation
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International audience. Many interests are shown on nanofluids as it's suitable for cooling applications. Knowing the physical properties of nanofluids such as viscosity plays a key role in practical heat transfer situations. The main goal of this work is to measure the dynamic viscosity of Gold nanofluids during sessile droplets evaporation, at ambient temperature, based on ultrasonic high-frequency acoustic waves (1 GHz). So, we have developed the high-frequency acoustic transducers, for longitudinal and shear waves, located at the bottom side of the silicon substrate. This method has access to characterize the liquid/solid interface (Droplet/Silicon). Due to viscoelastic losses (one of the causes of attenuation), the attenuation (attenuation in fluids about 220 dB/mm) of the sound energy produced by nanofluid generates a complex form for the mechanical impedance of the sessile droplet of nanofluid. The measured echoes diagram represented by amplitude and phase angle were obtained using a Network Analyzer. The complexity of the nanofluid for the shear signal wave has a direct relation between the attenuation and the viscosity and as a result, an online variation in the shear viscosity of a droplet contains 4% C-v gold nanoparticles were extracted throughout the evaporation process. At the same time, a new micromechanical model developed by FreeFem++ software was provided to compare the results obtained experimentally. This model has been validated to be used to calculate the viscosity of nanofluids.
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