Sticking efficiency

Herbst and Dunbar" have investigated the effects of exit channel barriers on association reactions of type 43 and have shown that, depending on the size of the barrier, the efficiency of radiative association reactions as a function of N can be strongly curtailed. For example, at 10 K and a nonpolar neutral reactant, they found for a system with a well depth of 2 eV and an exothermic channel barrier of 1.0 eV, N = 130 atoms for 100% sticking efficiency, approximately 10 times the corresponding value of N in the absence of a competitive exothermic channel. 

Figure 7.6 Dependence of solid particle sticking efficiency for various surface treatments and substrate loading. From Turner and Hering, 1987.)...

Chemical Nature of Particles. The chemical nature of particle surfaces is an important aspect of the coagulation rate because it determines whether two particles will join to form a new, larger particle after a collision. The tendency of two particles to stick is expressed by using an experimentally determined parameter known as the collision efficiency factor, the sticking efficiency, or the stickiness, and denoted by the symbol a. It is usually thought of as the probability that two colliding particles will stick (31). 

The collision efficiency E(Dp,dp) is by definition equal to the ratio of the total number of collisions occurring between droplets and particles to the total number of particles in an area equal to the droplet s effective cross-sectional area. A value of E = 1 implies that all particles in the geometric volume swept out by a falling drop will be collected. Usually < 1, although E can exceed unity under certain conditions (charged particles). Experimental data suggest that all particles that hit a hydrometeor stick, and therefore, a sticking efficiency of unity is assumed. 

Sticking efficiency and coalescence upon collision are two factors that produce considerable uncertainty in the analysis of Brownian coagulation of ufp aerosols. 

As has been noted there is no viable theory for sticking efficiency. Coalescence may be assumed for liquid ufp, but the coagulation of solid ufp must generally lead to the formation of aggregates with highly variable morphology. 

Fig. 3.17. The dissociative charge transfer He+ + N2 —> N+ + He + N has been used to follow the time dependence of the nitrogen density in the trap at a temperature of 38K. The gas flow has been hold constant gas at 3 X 10 mbar Is. At the beginning of the experiment, the pumping speed of the cold clean surfaces maintains a rather low stationary density. With increasing time, saturation reduces the sticking efficiency.

Direct adhesion of particles to fibres can be explained with Deijaguin—Landau— Verwey—Overbeek (DLVO)" " theory for soft cell particles,and the adhesion of cell particles to the fibres may be quantified by using the attachment rate coefficient, att which is related to the collision efficiency, rj, and the sticking efficiency, , as follows... 

The sticking efficiency, a, is given according to the Interaction Force Boundary Layer... 

Multiscale descriptions of particle-droplet interactions in spray processing of composite particles are realized based on Multiphase Computational Fluid Dynamics (M-CFD) models, in which processes such as liquid atomization and particle-droplet mixing spray (macro-scale), particle-droplet collision (mesoscale), and particle penetration into droplet (micro-scale) are taken into account as shown in Fig. 18.52. Thereby, the incorporation efficiency and sticking efficiency of solid particles in matrix particles are correlated with the operatiOTi conditions and material properties. 

Fig. 18.65 Characteristic particle incorporation efficiency in droplet and sticking efficiency on droplet surface at different atomization process operation conditions and feeding conditions. 0 solid-liquid contact angle, AT melt superheat...

The other group of collisions will result in particle partial penetration according to the Re—We regime map. Since most of colhsions in this regime occur in the downstream spray flow, it is considered reasonable that most of the solid particles are likely to be captured by the droplet surface because of droplet solidification. The sticking efficiency of particulate reinforcements on the surface of MMC particles can be roughly described by the volume fraction of these particles to the droplet. 

Suitable process conditions for optimization of the particle incorporation/stick-ing efficiency may be derived from the M-CFD simulations. Figure 18.65 shows the calculated characteristic incorporation efficiency and sticking efficiency of TiC particles (0 = 90°) and SiC particles (0=152°) in Tin (Sn)-based composite... 

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