Mobility diameter

The values of the aggregate mobility diameters shown in Fig. 9 are values measured by the Scanning Mobility Particle Sizer (SMPS). The data are consistent with a scaling relation of the form ... 

Fio. 9. Experimental measurements of CAST soot hydrodynamic resistance factor as a function of Peclet number and aggregate mobility diameter. The continuous lines are plotted using the scaling relation form Eqs. (8) and (9). 

Many aerosol materials have been used, and the aerosol material can be specifically chosen to minimize interference with the chemical separation being conducted. Widely used were KC1 aerosols which can easily be generated by sublimation of KC1 from a porcelain boat within a tube furnace. By choosing a temperature between 650°C and 670°C, specially tailored aerosols with a mean mobility diameter of about 100 nm and number concentrations of few times 106 particles/cm3 could be generated. The same technique could be applied to produce MoOj aerosols. Carbon aerosol particles of similar dimensions were generated by spark discharge between two carbon electrodes. 

Mobility diameter Differential mobility analyzer (DMA) Separation by differential mobility of charged particles in electric field +... 

Hygroscopic growth factor Increase of any aerosol property or phase change with increasing RH Light scattering, mobility diameter, etc. -h... 

The particle distribution graphs are done as commonly used in aerosol measurement the channel width, which represents particle diameter (dp) range, is plotted on a logarithmic scale against the total number concentration (TNC), that is calculated from the measured number of particles (dN) divided by the logarithm of the channel width (d og(dp)), where dp is the mobility diameter. 

The characteristic agglomerate sizes most often used are the mobility diameter, defined as the diameter of a sphere with the same friction coefficient as the agglomerate imdersimilar dynamic conditions, and the radius of gyration... 

In the free molecule range, the diameter of the sphere with the same projected area as the agglomerate is also importain. The relationships among the mobility diameter, ihe... 

Figure 8.12 Mobility diameter of agglomerates composed of 16-nm silver particles decreases as a result of in situ hearing at constant tentperaiure. (After Weber and Friediander, 1997b.)...

FIGURE 9.16 Ammonium sulfate particles with electrical mobility diameters of 200 and 322 nm (Zelenyuk et al. 2006). 

For larger particles or nanoparticle aggregates, SMPS measurements can be coupled with an aerodynamic particle sizer (APS). For spherical particles, it is easy to relate the measured diameters from the SMPS and APS because no corrections need to be made for shape and volume, but for irregularly shaped particles the APS reports an aerodynamic diameter. Da, by comparing the settling velocity to a spherical particle with a density of 1 g cm to compute the particle size. A volume equivalent diameter, D g, which is defined as the volume of a sphere with the same volume as a particle with an irregular shape, is used to relate the aerodynamic diameter from the APS with mobility diameter, D , from the SMPS (46) ... 

Mobility diameter The diameter of a sphere that has the same electrical mohility (velocity in an electric field) as the particle, droplet or bubble under study... 

In this section, we summarize the relationship between mobility diameter (d and volume equivalent diameter (d ), because the conversion of dme to dve is... 

The coupling between the radius of gyration and the mobility diameter is nontrivial the radius of gyration is a function of the geometric structure of the aggregate, whereas the mobility diameter is a function of the interaction between the aggregate and the carrier gas. The mechanical mobility of an aerosol particle is proportional to its radius... 

Using this method. Park et al. [81] analysed TEM images of diesel particles and showed that the projected area equivalent diameter nearly equals the mobility diameter in the mobility size range from 50 to 220 nm. Doubly charged particles and possible fragments were observed for the DMA-classified particles. The fractal dimension calculated from the TEM images of mobility-classified aggregates was 1.75. The... 

By using Equation (9.11) with the measured value of the fl actal dimension determined from mobility-mass measurements one obtains Az, = 1-87. The difference between the two values can be accounted for by experimental error and the assumption that the projected area diameter nearly equals the mobility diameter. 

In these correlations, is the void fraction of the soot deposit, the soot particle size, and 2 the mean free path of the fluid. Soot deposits are typically very low in density (50-150 g/1), equivalent to soot void fractions of 92-98 %, and have particles with an electrical mobility diameter in the range of 50-150 nm. As a result, the permeability of the soot layer is in the range of 10 m, more than two orders of magnitudes lower than the permeability of a clean wall. 

Fig. 20.14 Filtration efficiency as function of the mean pore size (left) and porosity (right). Note particle size is shown as electrical mobility diameter...

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