Pergamon J. Aerosol Sci. Vol. 28, Suppl. 1, pp. $651-$652, 1997 ©1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain Pli:S0021-8502(97)00374-1 ~21-85cr~7 ,nT.~.~ HIGH STOKES NUMBER PARTICULATE DEPOSIT GROWTH DYNAMICS ON A CYLINDER IN CROSS-FLOW Margaritis Kostoglou and Athanasios G. Konstandopoulos ° Foundation for Research and Technology-Hellas Chemical Process Engineering Research Institute PO Box 361,Thermi 57001 Thessaloniki, Greece KEYWORDS Particle deposition, inertial impaction, interfacial dynamics, fouling INTRODUCTION Formation of particulate deposits is of interest to various engineering areas such as: fouling of surfaces exposed to the flow of ash-laden combustion gases, filtration and preparation of coatings in materials processing. Prediction and control of deposit growth rates, morphology and properties are essential in these processes e.g. for optimal powerplant maintenance planning in the former case, or for adjusting process conditions to achieve desired product specifications in the latter. Deposit accumulation on surfaces is a complex issue involving interrelations between particle properties, transport phenomena and particle-surface interactions. In such cases, the asymptotic solution of prototypical problems is an important step in our effort towards the understanding of the process. Accordingly, in the present work we address the problem of predicting the shape evolution of deposits created by high Stokes number inertial impaction of particles on a cylinder in cross-flow. METHODS Particle transport and deposition is assumed to be caused by momentum non-equilibrium (measured by the particle Stokes number, Stk) between the suspended particles and the host gas flow past a "distorted" cylinder with a growing deposit on it. By confining our attention to the limit of high-Stk we can to a first approximation uncouple particle transport to the surface from the dynamics of deposit growth. In this limit particles "travel" on linear trajectories starting far from the cylinder and reach the evolving deposit surface with little change of their velocity. Impact geometry (i.e. angle of incidence) is however determined by the local orientation of the evolving deposit "surface". Upon impact with the existing deposit on the cylinder, a particle may either stick or rebound, possibly undergo secondary collisions with the "rough" deposit surface and then either re-enter the gas stream or be re-deposited at a different location from the initial impact point. In addition, if its impact velocity is sufficiently high it may cause deposit erosion by re-entraining predeposited particles in the flow. An understanding of the complexity of these interactions has been gained through the use of 3-D, off-lattice, discrete particle dynamics simulations and continuum level interfacial growth dynamics computations [1-5] which have resulted in micromechanically-based dimensionless correlations for the local sticking fraction of impacting particles S (an exponentially decaying function of dimensionless impact velocity modulus, V, and angle, ~0), and the microstructure of the resulting deposits, including their porosity, e (an increasing function of t 0 and decreasing function of V~). Impact velocity v, is rendered dimensionless. (Vi = vi/v,,t) by dividing by the critical velocity for rebound, vent which is a material parameter depending in its simplest form on particle size, mechanical moduli and surface energies of incident and target particle (see e.g. [6]). Local deposit erosion fraction, E is presently calculated from dimensionless correlations of the "separable" form: E = fl V, nf(tp) (cf. [7]) for V~ above a certain threshold that signals the onset of erosion. *Corresponding author. Fax: + 30 31 980-180. E-mail: agk@aliakmon.cperi.forth.gr $651