Surface photovoltage ͑SPV͒ measurements are traditionally carried out under steady-state conditions to determine the minority carrier diffusion length. While this technique is very convenient for bulk wafer defect characterization, especially the detection of iron in boron-doped silicon wafers, it is poorly suited to characterize epitaxial layers that are typically much thinner than the minority carrier diffusion length. We have developed the theory for frequency-dependent SPV measurements and have verified this theory with experimental data. We consider the various recombination/generation components in the semiconductor and determine the dependence on photon flux density, optical absorption coefficient, doping density, recombination lifetime, and temperature. Epitaxial layers are usually measured with techniques that are sensitive to generation parameters confined to the reverse-biased space-charge region ͑scr͒. We show that optical excitation can be used for scr confined recombination measurements, but the resultant lifetime is an effective lifetime incorporating both scr and surface recombination, heavily influenced by surface recombination.
For simulations of liquid jets in crossflows, the primary atomization can be treated with the quadratic formula, which has been derived from integral form of conservation equations of mass and energy in our previous work. This formula relates the drop size with the local kinetic energy state, so that local velocity data from the volume-of-fluid simulation prior to the atomization can be used to determine the initial drop size. This initial drop size, along with appropriately sampled local gas velocities, are used as the initial conditions in the dispersed-phase simulation. This procedure has been performed on a coarse-grid platform, with good validation and comparison with available experimental data at realistic Reynolds and Weber numbers, representative of gas-turbine combustor flows. The computational procedure produces all the relevant spray characteristics: spatial distributions of drop size, velocities, and volume fluxes, along with global drop size distributions. The primary atomization module is based on the conservation principles, and is generalizable and implementable to any combustor geometries for accurate and efficient computations of spray flows.
Primary atomization is the key element in spray flow simulations. We have, in our previous work, used and validated the integral form of the conservation equations, leading to the "quadratic formula" for determination of the drop size during spray atomization in various geometry. A computational protocol has been developed where this formulation is adapted to existing computational frameworks for continuous and dispersed (droplet) liquid phase, for simulations of pressure-atomized sprays with and without swirl. In principle, this protocol can be applied to any spray geometry, with appropriate modifications in the atomization criterion. The pre-atomization continuous liquid motion (e.g. liquid column or sheet) is computed using volume-of-fluid (VOF) or similar methods, then the velocity data from this computation is input to the quadratic formula for determination of the local drop size. This initial drop size, along with the local liquid velocities from VOF, is then used in a Lagrangian tracking algorithm for the post-atomization dispersed droplet calculations. This protocol can be implemented on coarse-grid, time-averaged simulations of spray flows, and produces convincing results when compared with experimental data for pressure-atomized sprays with and without swirl. This approach is general, and can be adapted in any spray geometries for complete and efficient computations of spray flows.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.