Separation and Purification Technology 52 (2006) 126–135 The deposition morphology of Brownian particles onto a spherical collector You-Im Chang ∗ , Lee Rong-Shin, Cheng Wei-You Department of Chemical Engineering, Tunghai University, Taichung 40704, Taiwan, Republic of China Received 30 December 2005; received in revised form 27 March 2006; accepted 27 March 2006 Abstract The deposition morphology of particles onto a spherical collector is investigated by applying the Brownian dynamics simulation method in the present paper. The effect of various types of the total interaction energy curves of DLVO theory, and of the shadow area cast by those deposited particles, on the particles’ collection efficiencies are examined. The simulation results show that the collection efficiency is always higher when the particle’s Brownian motion behavior is taken into consideration. As the deposition location moves closer to the front stagnation point of the collector, the dendrites formed by those Brownian particles also contain more particles. The present simulation method successfully describes the amount of particles collected as well as the morphology of the deposits in a detailed step-by-step manner. © 2006 Elsevier B.V. All rights reserved. Keywords: Deposition; Morphology; Brownian particle; DLVO theory; Filtration 1. Introduction The importance of knowing the morphology of particle deposits is obvious in determining the collection efficiency of a fixed bed granular filter. Since the formation and growth of par- ticle deposits changes the surface characteristics of individual collectors continuously in a deep bed filter, hence the extent of particle deposition profoundly affects the rate of particle reten- tion and makes the filtration process become time dependent. Tien et al. [1] and Wang et al. [2] had outlined a direct approach for analyzing the deposition morphology of particles from a flowing suspension to a collector. In their approach, the particle deposition was examined by tracking the trajectories of individ- ual particles as they move toward the collector. Beizaie et al. [3] then executed this approach successfully with the establishment of a comprehensive simulation procedure. In their simulation, Wang et al. [2] had considered the deposition process as an inter- play of two basic concepts, the shadow effect caused by those deposited particles and the random distribution of particles in the suspension, which are intrinsic to all particles in a suspension flowing past a collector. The results of their study provide not ∗ Corresponding author. E-mail address: yichang@thu.edu.tw (Y.-I. Chang). only the deposition rate of entire filtration period but also rele- vant information on the geometry of the deposits formed time dependently. The simulation procedure can be found in detail elsewhere ([4], see Chapter 8 of Tien Chi’s book) and will be adopted in the present paper. The trajectory equations formulated by Wang et al. [2] and Beizaie et al. [3], which take into account the hydrodynamic and electrokinetic forces, were proven to be able to describe the deposition morphology of colloidal particles onto the collector surfaces. Since the Brownian diffusion force was not considered in those earlier works, the force balance equations established by their trajectory analyses were deterministic. However, if the Brownian diffusion forces are the dominant force of the deposi- tion process, the deterministic calculation of particle trajectory is no longer possible. Inclusion of these Brownian random forces in the Lagrangian type force balance equation leads to a Langevin type equation, which was solved successfully by Kanaoka et al. [5] in their simulation model of aerosol filtration. Their Brow- nian dynamics simulation method was proved useful when the inertia and long-range forces (i.e. van der Waals attraction and electrical double layer repulsion) are of the same order of the Brownian diffusion force [6,7]. Applying with this dynamics method, a stochastic procedure was established successfully in our previous papers to simulate the initial deposition rates of Brownian particles onto a spherical collector [8] and in the con- 1383-5866/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2006.03.030