PREDICTION AND RATIONAL CORRELATION OF THERMOPHORETICALLY REDUCED PARTICLE MASS TRANSFER TO HOT SURFACES ACROSS LAMINAR OR TURBULENT FORCED-CONVECTION GAS BOUNDARY LAYERS†

Abstract

An approach originally developed to predict and correlate the thermophoretically-augmented submicron particle mass transfer rate to cold surfaces is shown here to account extremely well for the thermophoretically reduced particle mass transfer rate to “overheated” surfaces experiencing either a forced boundary layer (BL)-flow of laminar or turbulent dusty gas. This laminar BL/hot wall situation occurs, e.g., in hot surface/cold envelope chemical reactors used for growing epitaxial silicon layers from mainstreams containing, say, silane vapor and inadvertent submicron dust particles. “Thermo-phoretic blowing” is shown to produce effects on particle concentration BL-structure and wall mass transfer rates identical to those produced by real blowing (transpiration) through a porous wall. Indeed, a “blowing parameter additivity” relationship is proposed to account for the simultaneous effects of both phenomena should they be acting in concert (or in opposition). Exact numerical BL calculations covering the parameter ranges: l≤T _w/T _e6, (particle thermophoretic-/gas thermal- diffusivity ratios between )0·1 and 0·8 and particle Schmidt numbers between 10⁰ and 2 × 10³ are used to establish the validity of the basic forced convection mass transfer correlations for self-similar laminar BLs and law-of-the-wall turbulent BLs. This includes parametric combinations of immediate engineering interest for which the deposition rate is thermophoretically reduced by no less than 10-decades! The applicability of our correlations to developing BL-situations is then illustrated using a numerical example relevant to wet-steam turbine technology.