In situ observation and analysis of ultrasonic capillary effect in molten aluminium |
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| Institution: | 1. Brunel Centre for Advanced Solidification Technology, Brunel University, Uxbridge, London UB8 3PH, UK;2. Manchester X-ray Imaging Facility, University of Manchester, Manchester M13 9PL, UK;3. Research Complex at Harwell, Didcot OX11 0FA, UK;4. Laboratory of Hydraulics and Hydraulic Structures, Fluid Mechanics Division, Department of Civil Engineering, Democritus University of Thrace, Greece;1. Faculty of Electrical Engineering, University of Shahrood, Shahrood, 3619995161, Iran;2. Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GL, UK;3. School of Engineering and Design, Brunel University, Uxbridge, UB8 3PH, UK;1. School of Engineering & Computer Science, University of Hull, Hull, HU6 7RX, UK;2. Department of Engineering, University of Cambridge, CB2 1PZ, UK;3. ISIS Neutron Source, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, OX11 0QX, UK;4. Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, UK;5. Brunel Centre for Advanced Solidification Technology, Brunel University London, Uxbridge, London, UB8 3PH, UK;6. Diamond Light Source Ltd., Harwell Science & Innovation Campus, Didcot, OX11 0DE, UK;7. Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA |
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| Abstract: | An in situ synchrotron radiographic study of a molten Al–10 wt% Cu alloy under the influence of an external ultrasonic field was carried out using the Diamond-Manchester Branchline pink X-ray imaging at the Diamond Light Source in UK. A bespoke test rig was used, consisting of an acoustic transducer with a titanium sonotrode coupled with a PID-controlled resistance furnace. An ultrasonic frequency of 30 kHz, with a peak to peak amplitude at 140 microns, was used, producing a pressure output of 16.9 MPa at the radiation surface of the 1-mm diameter sonotrode.This allowed quantification of not only the cavitation bubble formation and collapse, but there was also evidence of the previously hypothesised ultrasonic capillary effect (UCE), providing the first direct observations of this phenomenon in a molten metallic alloy. This was achieved by quantifying the re-filling of a pre-existing groove in the shape of a tube (which acted as a micro-capillary channel) formed by the oxide envelope of the liquid sample. Analytical solutions of the flow suggest that the filling process, which took place in very small timescales, was related to micro-jetting from the collapsing cavitation bubbles. In addition, a secondary mechanism of liquid penetration through the groove, which is related with the density distribution of the oxides inside the groove, and practically to the filtration of aluminium melt from oxides, was revealed. The observation of the almost instantaneous re-filling of a micro-capillary channel with the metallic melt supports the hypothesised sono-capillary effect in technologically important liquids other than water, like metallic alloys with substantially higher surface tension and density. |
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| Keywords: | Sono-capillary Liquid metal Cavitation Micro jet Oxide Melt-filtration |
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