EROSION RATE PREDICTION AND CORRELATIONS TECHNIQUE FOR CERAMIC SURFACES EXPOSED TO HIGH-SPEED FLOWS OF ABRASIVE SUSPENSIONS

We describe a simple method to predict (based on available erosion yie ld data) erosion rates for cylindrical ceramic targets (e.g. circular tube coatings, leading edges of turbine blades, or the ceramic-lined t arget zone inside CFBC-cyclones) exposed to high-speed abrasive partic le-laden streams. Use is made of a convenient parameterization/extrapo lation of published laboratory results giving, in effect, average eros ion yields per particle impact (epsilon(p)) for particular planar cera mic target and projectile materials over a range of impact velocities, V-p, incidence angles, theta(i), and particle sizes, v(p). For a give n target/flow geometry we reduce the engineering problem of predicting absolute target erosion rates to that of multiplying a readily calcul ated characteristic erosion rate by the universal dimensionless erosio n rate. functions explicitly approximated here in the limit of impacts by particles large enough to be undeflected or slowed down by the loc al target gas flow. Our characteristic erosion rate is that which woul d be associated with the mainstream abrasive particle volume Aux if al l particles struck at normal incidence with the mainstream velocity, U . Dimensionless erasion rate results are cast in terms of the followin g four dimensionless parameters characterizing the erodent/ceramic tar get system of interest: sensitivity (exponent n) of erosion yield to p rojectile incident velocity; sensitivity (exponent,n appearing in (cos (m)(theta(i))) of erosion yield to angle of incidence theta(i); sensit ivity (exponent t) of erosion yield to projectile particle size (volum e, v(p)); and the reference erosion yield, epsilon(p,ref) (here, epsil on(p) is evaluated at V-p = 100 m s(-1), theta(1) = 0, and v(p) corres ponding to d(p) = 100 mu m). Based on our preliminary survey of availa ble erosion yield experimental data, we provide a table giving ''best- fit'' values of the four parameters: l, m, n, and epsilon(p,ref) requi red to complete a prediction of local and spatially-averaged erosion r ates according to our present formalism. For the latter, useful closed -form approximations are provided for convex or concave cylindrical ta rget geometries in the high Stokes number limit. Moreover, convenient correction factors are developed to account far a (Rosin-Rammler) part icle size distribution in the erodent mainstream, and mainstreams not perpendicular to the cylinder axis. The more general case of arbitrary (finite) Stokes numbers is outlined. Using two numerical examples (co nvex leading edge coating on a turbine stator blade, and concave secto r target zone in a CFBC-cyclone), we demonstrate that casting required erosion yield data in this suggested format greatly facilitates erosi on design calculations for ceramic targets (or coatings) exposed to hi gh-speed abrasive particle suspensions. Organizing empirical data in t his manner will also facilitate the longer range goal of correlating e ach of the above-mentioned parameters with independently measurable ph ysical properties of the participating materials.