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 studie...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.展开更多
A slow thermocapillary migration of a droplet at vanishingly small Reynolds and Marangoni numbers was theoretically investigated. A force on the droplet released in another liquid subjected to arbitrary configuration ...A slow thermocapillary migration of a droplet at vanishingly small Reynolds and Marangoni numbers was theoretically investigated. A force on the droplet released in another liquid subjected to arbitrary configuration of the gravitational field and an imposed thermal gradient for the case of constant liquid properties was derived using the general solutions given by Lamb. A solution to the migration was thereby obtained, which corresponds to the well-known YGB result as t →∞. In the case of variable physical properties with temperature, a nonlinear migration of the droplet was described by the dynamical equation of motion, and the numerical results were compared with available experimental data. The comparison exhibits a reasonable agreement between the theoretical prediction and the experimental results, which shows the dependence of physical properties on temperature is a primary cause of the continuous velocity variation in the thermocapillary droplet migration.展开更多
基金support from the Key Program of the National Natural Science Foundation of China(Grant No.51335002)support projects of strategic emerging industries in Jiangsu Province(Grant No.2015-318)
文摘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.
基金Project supported by the National Natural Science Foundation of China (Grant No: 10372060).
文摘A slow thermocapillary migration of a droplet at vanishingly small Reynolds and Marangoni numbers was theoretically investigated. A force on the droplet released in another liquid subjected to arbitrary configuration of the gravitational field and an imposed thermal gradient for the case of constant liquid properties was derived using the general solutions given by Lamb. A solution to the migration was thereby obtained, which corresponds to the well-known YGB result as t →∞. In the case of variable physical properties with temperature, a nonlinear migration of the droplet was described by the dynamical equation of motion, and the numerical results were compared with available experimental data. The comparison exhibits a reasonable agreement between the theoretical prediction and the experimental results, which shows the dependence of physical properties on temperature is a primary cause of the continuous velocity variation in the thermocapillary droplet migration.
