Impact, diameter parameter

These inertial effects become less important for particles with diameters less than 5 /rm and for low wind velocities, but for samplers attempting to collect particles above 5 p.m, the inlet design and flow rates become important parameters. In addition, the wind speed has a much greater impact on sampling errors associated with particles more than 5 fim in diameter (4). 

Researchers should be aware of, and account for, factors that can affect the performance of field studies with respect to precision, bias and possible error influences. The major factors affecting collectors, tracers and analytical approaches have been discussed elsewhere in this article. In summary, these are collection efficiency, stability and detection levels, respectively. Collection efficiency (or impaction parameter) for field samplers is related fo parficle/collector diameter and wind speed relationships, as summarized by the following equation developed by May and Clifford ... 

Because of the close similarity in shape of the profiles shown in Fig. 16-27 (as well as likely variations in parameters e.g., concentration-dependent surface diffusion coefficient), a controlling mechanism cannot be reliably determined from transition shape. If reliable correlations are not available and rate parameters cannot be measured in independent experiments, then particle diameters, velocities, and other factors should be varied and the observed impact considered in relation to the definitions of the numbers of transfer units. 

The impaction efficiency (17) for particles depends directly on the particle diameter (D), the flow velocity of the air (V), and the particle density (p) it varies inversely with the gas viscosity (p,) and with a parameter (Db) that is representative of the impactor s physical dimensions (e.g., the inlet nozzle diameter) and that is related to the curvature of the airstream. 

The stirrer diameter was introduced as the characteristic geometric parameter in the above case. This is reasonable. One can imagine how the mixing power would react to an increase of the vessel diameter D it is obvious that from a certain D on, there would be no influence but a small change of the stirrer diameter d would always have an impact. 

The impact, which the introduction of intermediate quantities can have on the relevance list, will be demonstrated in the following by one elegant example. Example 3 Mixing-Time Characteristics for Liquid Mixtures with Differences in Density and Viscosity. The mixing time 0 necessary to achieve a molecular homogeneity of a liquid mixture—normally measured by decolorizatiorr methods—depends, in material systems without differences in density and viscosity, on only four parameters stirrer diameter d, density p, kinematic viscosity v, rotational speed ti ... 

In gas phase chromatography, separations can be so complex that it is difficult to assess whether the temperature should be decreased or increased. The choice of the column, its length, its diameter, the choice of the stationary phase and of the phase ratio are all parameters that can have an impact on the separation. Furthermore, all of these parameters can affect each other. 

The probability of an inhaled particle being deposited by impaction is a function of the dimensionless Stokes number Stk, which relates particle properties (mass mP, diameter dP, and density, pP) to parameters of the airflow (air velocity vA, viscosity i)A, and airways radius rA) ... 

Liquid distribution may be an important parameter, as demonstrated in the HOC1 process, where different liquid distributors provided significantly different results (8). The initial contact of the liquid with the rotor influences the mass transfer performance of the RPB in gas continuous operations (15). Although the use of a packing support at the inside diameter of the rotor would be expected to impact this initial liquid contact with the rotor, experiments did not show any reduced mass transfer performance (36). 

Experiments on transfer of submicrometre radioactive particles to smooth surfaces (Wells Chamberlain, 1967 Chamberlain et al., 1984) have shown that the dependency of vg on D213 holds over many orders of magnitude of D. This means that the transport by Brownian diffusion becomes progressively less effective as the particle size increases. For example a particle of 0.1 pm diameter has a diffusivity of 6.8 x 10 10 m2 s 1, a factor 1.2 x 104 smaller than that of I2 vapour. Since D does not depend on the particle density, it is appropriate to discuss transport by Brownian motion in terms of the particle diameter. The aerodynamic diameter, dA, is equal to dppp2 where pp is the particle density in c.g.s. units (g cm-3) not SI units (kg m-3), and is the appropriate parameter for particles with dp> 1 pm, for which impaction and sedimentation are the mechanisms of deposition. 

Fig. 4.1.9 The deflection angle x 0n radians) as a function of the impact parameter b, for the collision between two hard spheres with the average diameter d.

Fig. 4.1.11 The deflection angle (in radians) of the scattered particle in a laboratory fixed coordinate system. The angle is given as a function of the impact parameter b, for the collision between two hard spheres A and B with the average diameter d. Particle B is initially at rest, and the five curves correspond to the mass ratios (mA/mn) 0, 0.5, 1, 1.5, and 2. The o at b = 0 and toa/tob = 1 indicates that the deflection angle is undefined in this case, since va = 0, that is, A is at rest after the collision.

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