Deposition inertia

In order to understand the mechanism of inertia deposition of particles on the rising bubble, the particle inertia path 1 is introduced, which is defined as the distance the particle is able to pass in the presence of viscous resistance of the liquid of an initial velocity v . 

When St > 1, the inertia deposition is obviously possible, yet calculations have shown that it can also take place at St < 1 as long as St is not too small. This conclusion becomes apparent if it is considered that in a layer of thickness a the particle moves toward the surface not only due to inertia but also together with the liquid. The motion component of the particle normal to the bubble surface becomes zero at the surface of the bubble. Inertia deposition proves to be impossible if St is smaller than some critical value St . In the case of a potential flow regime and negligible particle size. Levin obtained (1961)... 

Levin (1961) has shown that inertia deposition of particles below a critical size, which corresponds to a critical Stokes number St = 1/12, is impossible. Regarding a finite size of particles, the collision is characterised by Sutherland s formula (10.11). Comparison of the results obtained from Sutherland s relation and by Levin enables to conclude that in the region of small St < St the approximation of the material point, accepted by Levin and useful at fairly big St, becomes unsuitable for Stsmall Stokes numbers were studied by Dukhin (1982 1983b) for particles of finite size. Under these conditions inertia forces retard microflotation. 

Many different techniques are available for flow measurement and for recording of respiratory functions or flow parameters in particular (e.g. [115,116]). However, not all methods are appropriate for measurement of inhalation flows, either because they have low frequency responses or they influence the shape of the inspiratory flow curve by a large volume or by the inertia of the measuring instrument (e.g. rotameters). They may also interfere with the aerosol cloud from the inhalation device during drug deposition studies. 

There is one reported brief study of ZnSe deposition using selenosulphate [136], Considering the understandable preference for using selenosulphate rather than selenourea for CdSe depositions in most cases (selenosulphate is more stable and simpler to make and to handle), it is surprising that this is not also the case for ZnSe. It is possible that this is simply a case of inertia i.e., most researchers follow essentially the same recipe (although the selenosulphate technique described here predated the other studies). 

Filtration is a physical separation whereby particles are removed from the fluid and retained by the filters. Three basic collection mechanisms involving fibers are inertial impaction, interception, and diffusion. In collection by inertial impaction, the particles with large inertia deviate from the gas streamlines around the fiber collector and collide with the fiber collector. In collection by interception, the particles with small inertia nearly follow the streamline around the fiber collector and are partially or completely immersed in the boundary layer region. Subsequently, the particle velocity decreases and the particles graze the barrier and stop on the surface of the collector. Collection by diffusion is very important for fine particles. In this collection mechanism, particles with a zig-zag Brownian motion in the immediate vicinity of the collector are collected on the surface of the collector. The efficiency of collection by diffusion increases with decreasing size of particles and suspension flow rate. There are also several other collection mechanisms such as gravitational sedimentation, induced electrostatic precipitation, and van der Waals deposition their contributions in filtration may also be important in some processes. 

For turbulence it is convenient to describe particle flux in terms of an eddy diffusion coefficient, similar to a molecular diffusion coefficient. Unlike a molecular diffusion coefficient, however, the eddy diffusion coefficient is not constant for a given temperature and particle mobility, but decreases as the eddy approaches a surface. As particles are moved closer and closer to a surface by turbulence, the magnitude of their fluctuations to and from that surface diminishes, finally reaching a point where molecular diffusion predominates. As a result, in turbulent deposition, turbulence establishes a uniform aerosol concentration that extends to somewhere within the viscous sublayer. Then molecular diffusion or particle inertia transports the particles the rest of the way to the surface. 

The probability of oropharyngeal deposition is determined more by droplet size than by velocity and density because the particle inertia is proportional to the density, velocity, and the square of the diameter. It, therefore, follows that oropharyngeal drug deposition is reduced and the respirable drug delivery is increased when MDI sprays are finely atomized and evaporate rapidly. Such MDI sprays are generally promoted by increasing the propellant vapor pressure and reducing the actuator spray nozzle diameter.f ... 

The principle of filtration combines many of the individual mechanisms of collection on which other methods are based. Thus, diffusion (Brownian motion), inertia, interception, charge, and sedimentation may all contribute to deposition of particles on filters. The inertial and interception effects are illustrated in Fig. 3. 

A large particle will follow a path deviating from the streamline as it approaches the fiber and will impinge on the fiber surface. If the particle follows a path approximately perpendicular to the fiber surface, it is deposited as a result of its inertia. Those particles that do not follow a path directly to the surface of the fiber but that enter the airstream passing within the distance equivalent to the radius of the particle from the fiber will be intercepted. It is only necessary for the surface of the particle to touch the fiber for capture to take place [29]. 

Electrostatic precipitators collect particles that may subsequently be examined by microscopy. The method precipitates particles according to the charge they carry. The aerosol is passed between two plates or surfaces across which is a large potential difference. Deposition occurs as a function of the ratio of the charge to the inertia (mass and velocity) of the particles [87]. The principle on which this method is based considers the motion of particles in planes directly perpendicular to and parallel to the plane of the condenser [88]. 

Other characteristics of particles that influence their deposition are density, charge, shape, solubility, and hygroscopicity. These play a secondary role to particle size. The density of the particle contributes to its mass and, thus, inertia [20,23]. Increasing density will result in increased, or more rapid, deposition of particles. Charge has a number of effects. First, particles may aggregate as... 

---