Comparisons of Rational Engineering Correlations of Thermophoretically-Augmented Particle Mass Transfer With STAN5-Predictions for Developing Boundary Layers

Fouling (and corrosion) of gas turbine (GT) blading often results from the deposition of materials derived from inorganic impurities in the fuel and/or ingested air. When the depositing material is in the form of a submicron “aerosol” (dust or mist) it has been found that the rates of deposition on cooled surfaces can be augmented by some 100–1000-fold via the mechanism of thermophoresis (particle migration down a temperature gradient). For this reason, in earlier papers we reported the development of rational, yet simple, engineering correlations of thermophoretically-augmented particle transport across both laminar boundary layers (LBLs) and turbulent boundary layers (TBLs). While developed based on theoretical considerations, and numerical computations of self-similar LBLs and law-of-the-wall (Couette flow-like) TBLs, these mass transfer coefficient (St_m-) correlations, when applied locally, may also prove useful in making engineering mass transfer predictions for more complex geometries, including GT-blades. Pending additional controlled experiments, insight into the local applicability of these correlations can be gained by selected comparisons with numerical predictions for developing BLs. This paper reports on our a) modification of the code STAN5 to properly include thermophoretic mass transport, and b) examination of selected test cases of developing BLs which include variable properties, viscous dissipation, transition to turbulence and transpiration cooling. Under conditions representative of current and projected GT operation, local application of our St_m/St_m,o-correlations evidently provides accurate and economical engineering design predictions, especially for suspended particles characterized by Schmidt numbers outside of the heavy vapor range (say, Sc>10).