Abstract
Effective lubrication under extreme conditions such as high temperature is of considerable importance to ensure the reliability of a mechanical system. New lubricants that can endure high temperatures should be studied and employed as alternatives to traditional oil-based lubricant. In this paper, a thermocapillary model of a silicone-oil droplet is developed by solving the Navier–Stokes and energy equations to obtain the flow, pressure, and temperature fields. This is accomplished using a conservative microfluidic two-phase flow level set method designed to track the interface between two immiscible fluids. The numerical simulation accuracy is examined by comparing the numerical results with experimental results obtained for a silicone-oil droplet. Hence, the movement and deformation of molten silicon droplets on graphite and corundum are numerically simulated. The results show that a temperature gradient causes a tension gradient on the droplet surface, which in turn creates a thermocapillary vortex. As the vortex develops, the droplet migrates to the low-temperature zone. In the initial stage, the molten silicon droplet on the corundum substrate forms two opposite vortex cells, whereas two pairs of opposite vortices are formed in the silicone fluid on the graphite substrate. Multiple vortex cells gradually develop into a single vortex cell, and the migration velocity tends to be stable. The greater the basal temperature gradient, the stronger the internal thermocapillary convection of the molten silicon droplet has, which yields higher speeds.
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The authors appreciate the support from the Key Program of the National Natural Science Foundation of China (Grant No. 51335002) and Key support projects of strategic emerging industries in Jiangsu Province (Grant No. 2015-318).
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Tao SUN. He received his bachelor degree in mechanical engineering in 2014 from Changzhou University, Changzhou, China. After then, he was a master of Collaborative Innovation Center of Photovoltaic Science and Engineering at the same university. He will obtain his master degree of engineering in mechanical engineering at Changzhou University in June, 2017. His research interests include manufacture and equipment of new energy materials and devices.
Jianning DING. He received his Ph.D. degree in mechanical engineering from Tsinghua University, China, in 2001. He joined Jiangsu University between 1991–2007. He is a research fellow in City University of Hong Kong from 2002 to 2003. His current position is a professor and vice president of Changzhou University. He is the director of Center for low-dimensional materials, micro-nano devices and system, director of Jiangsu Collaborative innovation center of “Photovoltaic science and engineering” in 2011, director of Jiangsu Key Laboratory for Solar Cell Materials and Technology, the head of Science and Technology Innovation Team in Jiangsu Universities, and the chief scientist in the first level of young and middle-aged in “333 project” of Jiangsu province. His research areas cover the research of new energy materials, low-dimensional materials, micro-nano devices and system, and tribology. Above 500 academic papers and 6 books were published.
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Sun, T., Jiang, C., Ding, J. et al. Thermocapillary migration mechanism of molten silicon droplets on horizontal solid surfaces. Friction 6, 62–74 (2018). https://doi.org/10.1007/s40544-017-0163-9
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DOI: https://doi.org/10.1007/s40544-017-0163-9