Wettability gradient in radial direction and evaporation rate gradient can cause droplet motion on a solid surface. Here a theoretical model is proposed. Besides, an equation of droplet velocity is derived on a solid surface. We consider the wettability and evaporation rate gradients are mainly caused by the chemical composition and surface roughness, only along the radial direction. Surface tension at the liquid-vapor interface is constant as it is assumed that the temperature does not change during the whole process. Thus, Marangoni effect induced by the liquid-vapor surface tension gradient is neglected. Besides, as droplet size is set as less than the capillary length (), the gravity effect is ignored as well. The velocity at the droplet center on a gradient surface along the radial direction is half of that along the x-direction. With the simulation of water droplet, the center velocity decreases with time and the droplet radius increases at the beginning part and then decreases.
Theoretical Model of Droplets Motions on Solid Surface With Radial Wettable and Evaporation Rate Gradients
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Yang, Y, Wu, Z, Chen, X, Sundén, B, & Huang, Y. "Theoretical Model of Droplets Motions on Solid Surface With Radial Wettable and Evaporation Rate Gradients." Proceedings of the ASME 2018 International Mechanical Engineering Congress and Exposition. Volume 8A: Heat Transfer and Thermal Engineering. Pittsburgh, Pennsylvania, USA. November 9–15, 2018. V08AT10A028. ASME. https://doi.org/10.1115/IMECE2018-87890
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