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Experimental investigation of substrate roughness effects on high-acceleration film splitting

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Abstract

An experimental study is performed on high-acceleration separation of Newtonian liquid films trapped between two parallel plates. The test apparatus is capable of accelerating one plate at up to 325 m/s2 relative to a stationary substrate. Plates with average roughness up to 86 µm were studied. High-speed laser induced fluorescence (LIF) is used to determine the instantaneous film thickness distribution during the separation process. Two flow regimes exist in the film. As the gap between the substrates increases, a viscous fingering regime occurs along the perimeter of the wetted area, where air fingers grow radially inward. If the growth rate of those fingers is slow relative to the growth rate of the gap, a second regime exists in the center of the wetted region, in which cavitation bubbles emerge and grow. Once the two substrates are sufficiently separated, the liquid bridges connecting the two substrates break. At high accelerations, the separation ratio (the relative amount of fluid remaining on the moving substrate) is a nonlinear function of the surface roughness, liquid viscosity, and separation acceleration, and varies in the range between 35 and 55%. The separation ratio is strongly correlated with the relative areas of the fluid that are subject to viscous fingering and liquid cavitation. The LIF measurements show that the thickness of the residual layer remaining on each portion of the substrate depends on whether the substrate has been subject to viscous fingering or cavitation, and this observation explains qualitatively the measured differences in separation ratio.

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The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Funding

This study was supported by AstenJohnson Inc. and the Natural Sciences and Engineering Research Council of Canada (NSERC). This research was undertaken, in part, thanks to funding from the Canada Research Chairs program.

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AR developed the experimental apparatus and obtained and analyzed the experimental data. SG and BS were responsible for research supervision. All co-authors meaningfully contributed to manuscript writing and review prior to submission.

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Correspondence to Sheldon Green.

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Rostami, A., Stoeber, B. & Green, S. Experimental investigation of substrate roughness effects on high-acceleration film splitting. Exp Fluids 63, 176 (2022). https://doi.org/10.1007/s00348-022-03526-2

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  • DOI: https://doi.org/10.1007/s00348-022-03526-2

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