Simulation of laser evaporation and plume

Results from a simultaneous simulation of laser-induced evaporation and plume formation are presented. The material model includes conduction heat transfer as well as melting and evaporation phase changes. The phase changes are modeled with kinetic and energy balance equations and the equation are solved in 1-dimension using finite differences. Transformations in the state of the vapor as it evolves across the Knudsen layer are modeled assuming strong evaporation with relatively small backpressure. The plume is modeled in a quasi-1-dimensional domain(which expands to match the focusing laser beam propogation path) use mass, energy and momentum conservation. Viscosity, ionization, laser beam absorption and radial conduction heat loss are considered in these relations. The transient behavior of established plumes is investigated using this simulation. It is found that, at surface power densities commonly associated with welding, the plume is not stable and convects away in the flow or evaporant. At low surface power densities (such as might occur on the tilted front wall of a keyhole), the vapor flow is slower and the simulation predicts that a stable plume might be established.