A rotary dust collector is a mechanical centrifugal separator provided with an internal rotor supplying a vortex.
In this paper, comparisons are made of the performance characteristics of rotary dust collectors with a tangential and an axial inlet. The pressure drop through the device of the axial inlet type is lower than that of the tangential inlet type, while little difference is observed in an increase of the pressure drop with the rotor speed between the both types. The critical particle size calculated through application of simplifying assumptions is nearly proportional to the specific particle size corresponding to the cumulative weight fraction of oversize particles taken equal to the measured collection efficiency. The particle size ratio is constant, independent of the gas flow rate and rotor speed, and it is also independent of the rotor diameter in case of the tangential inlet type. In case of the axial inlet type, however, the ratio depends on the rotor diameter.
In addition, the effect of the number of the rotor disks on the performance is compared for the rotors without bars on the periphery.

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By condensation method, aerosols of lead iodide were prepared, using carbon monoxide, nitrogen, or argon as carrier gas, the vapor of lead iodide being decomposed to yield iodine in oxygen-containing atmosphere; their weight concentrations were determined by a procedure like that in preceeding reports making use of chemical analysis, while their particle sizes were found through ultramicroscopy, in which the settling velocities of particles were measured.
The main findings are the following: (1) That both the weight concentration and the particle size go through a maximum with the rate of flow of the carrier gas. (2) That in carbon dioxide form aerosols of higher concentration, and in nitrogen and argon those of lower one; in carbon dioxide form aerosols of smaller size, and in nitrogen and argon those of larger one. (3) That the heat of vaporization of the melt of lead iodide is nearly 23kcal/mole, without distinction of carrier gas, in the range of temperature 360°-487°C. (4) That the circumstances under which highly monodisperse aerosols form are around 420°C-2l/min for carbon dioxide and 400°C-3l/min for nitrogen, the number concentrations being both of the order of magnitude of 10⁷ particles/cc.

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The particle size distribution of powdered xerogel of silica and alumina ground in ball mills were investigated experimentally.
The silica xerogel powder used as the feed material was prepared in an ordinary way, that is, after granular silica xerogels being quenched with water several times, the resulting crushed granules were ball milled and clasified into several particle size regions by standard mesh sives.
And then samples of powdered xerogels were prepared by rearranging the fractions of each size regions, one of which was the region of tracer powder, so that they would from a normal distribution in particle size. The tracer powder colored by methylviolet consisted the largest size region. As for the alumina xerogel, a commercial micro sphere powder was used as the sample without any pre-treatment.
Results obtained are as follows:
1) Several particle regions with a discrete size distribution were found in the ground products. From a behavier of the tracer xerogel, this pulverizing process was made clear to proceed consecutively while each region was stable aggregates and easy to transfer into a finer region from a larger region. This fact is quite unusual compered with a conventional monomodal, continuous size distribution in a usual material.
2) The unusual size distributions were not dependent on the grinding conditions, but also a property (a physical texture) of the feed xerogel powder.
3) The new silica xerogel particles formed by grinding were begun to crush after a certain induction period in a grinding process. From these experimental results, it was found that the particles were at the first stage strained by mechanical force, followed by breaking into a smaller one.
4) The fact that the bulkiness of the powders has changed periodically with the increase of the grinding time, is explained with the gap grading theory of product powder, in this case, consisted of the two main discrete sized particles.

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