Experimentalists are limited in the amount of information they can derive from drop impact experiments on porous surfaces because of the short timescales involved and the normally opaque nature of porous materials. Numerical simulations can supplement experiments and provide researchers with previously unattainable information such as velocity and pressure profiles, and quantification of fluid volume flow rates into the pores. Ethanol drops, 2.0 mm in diameter, are impacted on a narrow gap at Weber numbers that match the impact of water drops, also 2.0 mm in diameter, on the same gap size in a previous study. The experiments show the ethanol drops cleaving at all Weber numbers tested, while the water drops completely enter the gap at low Weber numbers and only cleave at higher Weber numbers. A volume of fluid numerical model of the experiments is constructed in OpenFOAM and used to probe the interior of the drops during impact. For the water drop, a high-pressure region fills the drop during impact which continuously drives liquid into the gap. For the ethanol drops, the high-pressure region is smaller and quickly attenuates, which results in a near-zero vertical velocity at the entrance of the gap. Compared to water, the lower surface tension of ethanol causes these drops to spread further upon impact, recoil less, and overall have less liquid over the gap, which promotes cleaving. Against a superficial thought, when the penetration of liquids into porous materials is to be maximized, a higher surface tension liquid is therefore desirable.
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We would like to acknowledge and thank Joanna Kolodko, a summer undergraduate research student at the University of Toronto, for her contribution in conducting some of the ethanol droplet experiments. Dr. Manolia Andredaki, Dr. Anastasios Georgoulas, and Professor Marco Marengo would like to acknowledge that this research was partially funded through the European Space Agency (ESA MAP CORA projects ENCOM4, led by Prof. Davide Del Col, University of Padova, Italy, and WHISKIES, led by Dr. Carlo Iorio, ULB, Belgium). Professor Sanjeev Chandra and Dr. D. Jordan Bouchard would like to acknowledge financial support from the Natural Sciences and Engineering Council of Canada.
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