Mass median diameter

Pj = solids density (kg m" ) d = particle mass median diameter (m)... 

Mass median diameters determined by centrifugal sedimentation. 

Understanding particulate emissions, their formation and control, is another key issue in meeting the new particulate emission Hmits set by the new EURO emission standards. The particulate emissions formed in diesel engines have a mass median diameter of 0.05-1.0 gm. Particle consists of carbon with various HCs adsorbed on it including polyaromatic hydrocarbon (PAH) as well as nitro-PAH compounds. 

For several batches of the same catalyst with quite different mass median diameters, Gwyn found the exponent b to be constant, whereas the attrition constant Ka was found to decrease with mean particle size. Equation (1) is, therefore, valid for a particular size distribution only. Other... 

Depending on operation conditions and metal properties, the shapes of the atomized particles may be spheroidal, flaky, acicular, or irregular, but spherical shape is predominant. The spheroidal particles are coarse. For example, roller-atomized Sn particles exhibited a mass median diameter of 220 to 680 pm. The large particle sizes and highly irregular particle shapes suggested that the disintegration process may be arrested either by the premature solidification or by the formation of a thick, viscous oxide layer on the liquid surface. The particle size distributions were found to closely follow a log-normal pattern even for non-uniform particle shapes. 

Process parameters of primary importance include roll speed, differential roll speed, roll gap, metal flow rate, metal stream velocity, and melt superheat. The mass median diameter of particles diminishes exponentially as the roll speed increases. It is possible to obtain a smaller mass median diameter when one of the rolls is kept stationary rather than rotating the two rolls at the same speed. Metal flow rate seems to have a negligible effect on the mass median diameter. However, the mass median diameter increases with increasing metal stream velocity, suggesting that the relative velocity of the metal stream to the periphery of the rolls may be a fundamental variable controlling the mass median diameter. The size distribution is approximately constant for the conditions studied. 

The Laser-spin-atomized droplets are usually spherical, clean, and homogeneous in composition. A mass median diameter of 100 pm has been obtained for a Ni-Al-Mo alloy. Cooling rates are estimated to be in the order of magnitude of 105 °C/s. Similarly to other centrifugal atomization techniques, droplet properties (shape, size, cooling rate, etc.) are dependent on the rotation speed, ingot diameter, superheat, and material properties. 

The VEP-atomized particles are spherical. The mass median diameter of the particles ranges typically from 300 to 500 pm. Both the mass median diameter and size range of the particles reduce with decreasing wire diameter for a given vibration frequency. The narrowest particle size distribution is produced at the resonant... 

Wu, Ruff and Faethl249 made an extensive review of previous theories and correlations for droplet size after primary breakup, and performed an experimental study of primary breakup in the nearnozzle region for various relative velocities and various liquid properties. Their experimental measurements revealed that the droplet size distribution after primary breakup and prior to any secondary breakup satisfies Simmons universal root-normal distribution 264]. In this distribution, a straight line can be generated by plotting (Z)/MMD)°5 vs. cumulative volume of droplets on a normal-probability scale, where MMD is the mass median diameter of droplets. The slope of the straight line is specified by the ratio... 

A).5 (MMD) Mass median diameter 50% of total volume of droplets are of smaller diameters than this value V=50% Left-hand or right-hand side of Dpeak for q > or < 3.2584 MMD= (0.693) MMD -(o.evsf rfi 0 SMD v ( q J... 

In ultrasonic standing wave atomization, increasing the amplitude of the sonotrodes and/or the gas pressure reduces the mass median diameter of the droplets generated.[143]... 

Dunkley14871 analyzed droplet size data for gas-atomized Al, Fe, Cu-Al and Sn-Sb, and developed an empirical correlation between the specific gas consumption, SGC, and mass median diameter of droplets for various atomization gases, pressures, and atomizers ... 

Randall et al. (Rl) examined some 60 liquids with a buret-type atomizer and positive dc voltage. They also concluded that atomization could not be achieved if the resistivity was greater than 1010 fi cm and became much poorer if the resistivity was less than 10s SI cm. Increased viscosity resulted in a coarser spray, especially for viscosities above 20 cp. Measurements of size distribution are reported which indicate mass median diameters larger than 20 microns. An optimum voltage of 25-40 kV was found at which the mass median diameter was a minimum. They also ran limited tests with glass capillary atomizers (<200 microns i.d.) for which they estimated droplet sizes were less than 10 microns when atomization was achieved. They give a... 

The mass median diameter (MMD) is the most common descriptor of primary particle size and may be determined by sieving or centrifugal sedimentation. The volume median diameter, as determined by laser diffraction, may be used as an approximation of MMD, provided that the particle density is known and does not vary with size, and that the particle shape is near spherical. The MMD of a powder can be used as a predictor of aerodynamic diameter by Eq. (1),... 

In a study of 248 workers, no significant association was found between exposure to vapor concentrations of up to 0.42 mg/m (2.6-10 J,g mass median diameter) and symptoms of cough, phlegm, dyspnea, and wheezing. However, the FVC in the highest-exposure group was reduced compared with that of a low-exposure group. Repeated exposure of workers to unspecified sulfuric acid concentrations reportedly has caused chronic conjunctivitis, tracheobronchitis, stomatitis, and dermatitis. ... 

In Figure 2 we show the amount of Al, Fe, Sc, V, U, and Se in particles per log-size-interval of each impactor stage, per m of gas plotted against the mass median diameters (mmd) of Table I. Note that in choosing the mmd and log-size interval for the filter, we assumed that the submicrometer distribution is log-normal and that all of the mass on the filter is contained in particles of diameters between 0.01 and 0.07 Mm. These data suggest that the impactor intervals nicely bracket the accumulation mode that occurrs at 0.11 Mm. 

Mass median diameter. The uncertainties reported are the weighted means of the one-sigma uncertainties (from counting statistics) of the multiple photopeaks used in the analysis as described by Heft (17). 

Punte et al. I tested volunteers in a wind tunnel at an airspeed of 5 mph to establish CN tolerance time—the length of time a subject could remain in the CN-containing airstream. The tolerance time varied with the subject. CN aerosols were generated from acetone solutions and had a mass median diameter of about 0.6 ym. Such particles can reach and remain in the deep region of the respiratory tract. The immediate effects of such exposures were tingling of the nose ind rhinorrhea, burning of throat and eyes, lacrimation, and blurred vision. Some subjects suffered dyspnea. Mild conjunctivitis was observed, but this and the other symptoms passed rapidly when the subject left the wind tunnel. 

Inhalation toxicity Aerosol exposure (mass median diameter, 1.8 um) produced similar toxic signs In rats, mice, and guinea pigs. 

Table 9.11 shows the aerodynamic mass median diameter (MMD) for some typical inorganics that are common components of tropospheric particles. Also shown are the calculated crystal enrichment factors, EFcrusl. These are a measure of the enrichment of the element in the airborne particles compared to that expected for the earth s crust, using aluminum as the reference element. Thus EF,.rust for a particular element X is defined as... 

TABLE 9.11 Aerodynamic Mass Median Diameters of Tropospheric Particles Containing Various Elements Observed in a Number of Studies and Enrichment Factors 1... 

For control of flying insects with aerosols, research showed that there is an optimum particle size needed to obtain maximum kill. The size was determined through extensive research in wind tunnels (2) and Peet-Grady chambers in which the most nearly homogeneous sprays possible were used. For adult mosquitoes the optimum particle size was found to be between 10 and 15 microns mass median diameter and for adult houseflies between 15 and 20 microns. 

In treating some closed interiors with aerosols, it may be necessary to limit the time of application. In this case the particle size must be large enough to settle out in the time available. A 10- to 15-minute exposure time is the minimum for satisfactory results. An aerosol spray having a mass median diameter of 15 to 30 microns is sufficient for the short-exposure applications, but will not penetrate so completely as the smaller particle size. Furthermore, aerosols of this size must be released from more than one point if the radius of the area is more than 15 feet. When heat from thermal generators causes excess breakdown of the insecticide, equipment that produces larger particle sizes must be used. 

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