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Heat transfer in a liquid droplet hanging at the tip of an electrode during arc welding

The motion of melted metal in a droplet hanging at the tip of an arc electrode during arc welding is considered. The motion is induced by a surface tension gradient due to the non-uniformly heated surface of the droplet. It is shown that the melt flow is confined within a narrow boundary layer. The thickness of this layer and the melt velocity within it are estimated. The influence of the metal motion on heat transfer in the droplet is considered. A simple formula for effective thermal conductivity, which takes into account thermocapillary convection, is obtained. Estimates show that, for conditions typical for arc welding, the effective coefficient of thermal conduction exceeds the normal value by approximately tenfold. Calculated heat fluxes agree with those obtained from the observed electrode melting rates.