Evaporation Processes

Evaporation and low-pressure vapor phase transport play an important role in many processes, such as physical vapor deposition and hearth melting of metals. Opennovation has modeling expertise which can assist in the design and optimization of such processes, focused around vapor transport and multicomponent evaporation.

Vapor Transport in Physical Vapor Deposition

Thin film processes such as electron beam evaporation, sputtering, and pulsed laser deposition operate at a gas pressure where the mean free path of molecules between collisions is smaller than the chamber but too large to consider the gas a continuum. In this pressure range, a methodology called Direct Simulation Monte Carlo provides an efficient and accurate predictive model for gas flow and transport. In particular, modeling can calculate the extent of vapor plume focusing, which determines the thickness profile of deposited films.

References:

  1. A. Powell, P. Minson, G. Trapaga and U. Pal, "Mathematical Modeling of Vapor Plume Focusing in Electron Beam Evaporation," Metall. Mater. Trans. 32A:1959-1966 (2001).
  2. P. Minson, A. Powell and G. Trapaga, "Theory of Vapor Plume Focusing in Electron Beam Evaporation by the Direct Simulation Monte-Carlo Method," Proc. Conf. EBM&R State of the Art 1996, 126-137.

Multicomponent Evaporation

In processes involving liquids with multiple volatile compounds or elements, each component evaporates at a different rate. The strongly nonlinear temperature dependence of evaporation rate complicates this when the heat source is non-uniform or time-dependent, such as in electron beam processing of metals. Evaporation thus results in a composition change in the liquid which is often not evenly distributed, and can lead to quality issues in the product. Specialized codes modeling heat transfer through the surface can efficiently calculate the time-average evaporation rates of each component, and couple them with larger-scale codes for heat and mass transfer.

References:

  1. A. Powell, J. Van Den Avyle, B. Damkroger, J. Szekely and U. Pal, "Analysis of Multicomponent Evaporation in Electron Beam Melting and Refining of Titanium," Metall. Mater. Trans. 38B:1227-1239 (1997).
  2. A. Powell, J. Van Den Avyle and U. Pal, "Optimal Beam Pattern to Maximize Inclusion Residence Time in an Electron Beam Melting Hearth," Proc. AVS Vac. Metall. Conf. 78-84 (1997).
  3. A. Powell, J. Van Den Avyle, B. Damkroger and U. Pal, "Prospects for Titanium Alloy Composition Control by Electron Beam Scan Frequency Manipulation," Proc. Conf. EBM&R State of the Art 1996, 138-150.
  4. M. Miszkiel, R. Davis, J. Van Den Avyle and A. Powell, "Video Imaging and Thermal Mapping of the Molten Hearth in an Electron Beam Melting Furnace," Proc. Conf. EBM&R State of the Art 1995, 243-254.

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