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The advanced hybrid particulate collector (AHPC) is a highly promising and novel hybrid electrostatic filter technology that removes particles from flue gas. Perforated plates are used as collecting electrodes to attain better synergism between the electrostatic and bag zones. A laboratory-scale AHPC was built to investigate the dust collection performance of perforated plates with different percentages of open area (POA) and opening types. Particles were deposited on the front, flank, and back sides of the plate. Differences in cake packing density were observed at different locations. With the increase in POA, the collection efficiency of the front side decreases, whereas the collection efficiencies of the flank and back sides increase. The increase in the collection of the flank and back sides compensates for the decrease in the collection of the front side, which only changes slightly the total efficiency with the POA. The opening type exhibits minimal effect on total efficiency. A numerical method was established to simulate the dust collection process in the electrostatic zone. Simulation results indicate that the openings change the electric field near the plate and facilitate particle deposition on the flank and back sides, which result in the characteristics of collection efficiency. The difference in the cake structure results from the distribution of electric field strength on the plate surface. [ABSTRACT FROM AUTHOR]

Abstract: The impaction-sticking mechanism of fine particulates plays a significant role in a wide range of applications from dust separation devices, thin-film deposition techniques to the astrophysics science, but the underlying physics still remains unclear. In this paper, a discrete element method (DEM) approach is established to investigate the impaction-sticking process during the initial deposition of fine particles on a single fiber. Starting from the JKR adhesive contact theory, the DEM well predicts the measured trend of single-fiber capture efficiency as a function of Stokes number in the literature, by the proper considerations of key dissipation terms including the first-contact energy loss, the linear-dashpot damping and the rolling friction resistance. The increasing work of adhesion not only dramatically increases the peak value of single fiber efficiency, but also causes the peak to move towards a much higher Stokes number. The DEM predictions further clarify that the sticking probability depends on the adhesion parameter, rather than Stokes number. An empirical power law between sticking probability and adhesion parameter is drawn as h =0.0558⋅Ad5/3 (for Ad<5.65). Finally, by using both adhesion parameter for the sticking and Stokes number for the impaction, four distinct deposition patterns during the initial stage of single fiber filtration are identified. [Copyright &y& Elsevier]

Abstract: A JKR-based dynamic model, with energy dissipation through both irreversible snap-on/snap-off process and viscoelastic effect, is developed to simulate the dynamics of low-velocity normal impact of micro-sized particle with a flat surface. The first-contact energy loss because of the incompletely reversible, quasi-static loading/unloading is incorporated in the dissipation model. The damping forces corresponding to both the attractive and repulsive components of the JKR contact forces are introduced to account for the hysteresis related to material viscoelasticity. The predicted particle behaviors for the impacts with incident velocities below or above the critical velocity are discussed. The predictions of both the critical velocity and the variation of restitution coefficient vs. incident velocity are compared with experiments in literature where reasonable agreement is obtained. The dependence of restitution coefficient on incident velocity is analyzed. Finally, the model sensitivity analysis such as the effect of the damping coefficient variation is discussed. The work provides a solid basis for the development of discrete-element-method approach of micro-sized particulate system. [ABSTRACT FROM AUTHOR]

Abstract: A novel premixed swirl flame in stagnation point geometry is used to synthesize uniform, high-quality nanostructured TiO2 films at growth rates of 20–200nm/s in a single step. The roles of precursor concentration and substrate temperature in controlling film morphology and characteristics are investigated. Increasing precursor concentration, for a given substrate temperature, significantly increases the packing density of the nanoporous film. The specific surface area of the film is mainly dependent on substrate temperature, where two distinct regimes, i.e. in-flame-agglomeration at low temperature and on-substrate-sintering at high temperature, specify film properties. A simplified deposition model for the formation of the nanoporous film structure is proposed, correlating penetration distance of thermophoretically-driven Brownian particles into the film with the resultant morphology. The model predicts the packing density in excellent agreement with experiments, thereby clarifying the complex roles of precursor concentration and substrate temperature. Finally, increasing substrate temperature, at fixed precursor concentration, changes the packing density little, but considerably decreases specific surface area, as sintering becomes dominant among controlling mechanisms. [Copyright &y& Elsevier]

Abstract: In this paper, recent advances in the discrete-element method (DEM) for describing motion, deposition, agglomeration or aggregation of a large number of adhesive spherical particles immersed in fluid flows, termed as adhesive particulate flow, are reviewed. The constitutive equations together with the length and time scales of DEM are compared with those of other similar Lagrangian particle methods, e.g., molecular dynamics (MD), Brownian dynamics (BD), dissipative particle dynamics (DPD). The adhesive contact force and torque models in the presence of different adhesive effects are examined, including van der Waals force, ligand-receptor binding, liquid bridging force, interface adhesion, and sintering forces, all of which play an important role in DEM formulations for different types of adhesive particulate flow problems of interest in energy, combustion and environmental fluid mechanics problems. A summary of various kinds of particle-field interactions is presented, including fluid forces, electric field forces, acoustic force, and thermophoretic force. The computational method is illustrated by application to a series of examples involving capture of spherical particles by a fiber in a uniform upstream flow, examining the deposition/aggregation patterns of both mono-size and binary-size particles on the cylinder with and without the presence of electric field effects, which may be due either to charging of the cylinder or polarization of the particles. Particle capture problems of this sort are commonly encountered in filtration problems and ash-removal problems experienced in environmental and combustion applications, respectively. The article concludes with a discussion of remaining modeling challenges in development of discrete-element methods for adhesive particulate flow fields. [Copyright &y& Elsevier]