Scale Analysis of Thermal & Fluid Flow Induced by Thermocapillary Force During Laser Melting

• Main Authors: Jih-Sheng Yeh, 葉日昇
• Other Authors: P.S Wei
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/53805628502166121008

碩士 === 國立中山大學 === 機械與機電工程學系研究所 === 94 === In this study, shapes of the molten region and transport processes affected by thermocapillary convection in melting or welding pool irradiated by a low-power-density beam are determined from a scale analysis for the first time. A low-power-density-beam heating implies no deep and narrow cavity or keyhole taking place in the pool. A quantitative determination of the fusion zone shape is crucial due to its close relationship with the strength, microstructure, and mechanical properties of the fusion zone. In this work, the complicated flow pattern in the pool is influenced by an unknown shape of solid-liquid interface, and interactions between the free surface layer, corner regions, and boundary layer with phase transition on the solid-liquid interface. Since Prandtl number is much less than unity while Marangoni and Reynolds number can be more than in melting metals, an appropriate scaling mass, momentum, and energy transport subject to a force balance between viscous stress and surface tension gradient on the free surface account for distinct thermal and viscous boundary layers in these regions of different length, velocity, and temperature scales. The results find that shapes of the fusion zone, free surface velocity and temperature profiles are determined by Marangoni, Prandtl, beam power, Peclet, and Biot numbers, and solid-to-liquid thermal conductivity ratio. The predications agree with numerical computations.