Electrostatic Separation of Fine Particles in Vibrated Fluidized Beds
Very fine particles which cannot be fluidized by means of a flowing gas alone because of entrainment may be effectively individualized and retained in the bed through a combination of gas at low rate flow and mechanical vibrations of selected frequency and amplitude. A mixture of very fine particles may be fluidized and successfully separated and/or concentrated by means of electrostatic fields. Results are presented of a factorial experiment in which the conditions of temperature, humidity, and voltage were investigated for the separation of a (50-50 by weight) synthetic mixture of iron and glass powder of particle size ranging from 15-45¿m. A new and highly efficient particle collection mechanism is introduced, and mathematical models of the process are presented as part of the optimization work.
Influence of electric fields on friction electrification between metals and borosilicate glass
Abstract In a cylindrical geometry, electric fields were applied through the entire contact area between the sliding metal and the glass surface. The maximum electric charges developed on the metal were measured and plotted against the applied voltage producing the field. The metals were high-purity nickel and gold. The borosilicate glass was Pyrex, brand 7740. The experiments with nickel, which has a work function greater than that of the glass, were performed in 10 −7 mm Hg vacuum. The experiments with gold, with a work function smaller than that of glass, were carried out in air at atmospheric pressure. The results show that: 1. 1) There is both asymmetry and a reversed slope portion in the charge vs. voltage plot. 2. 2) For a certain range of reversing fields, the electric charge developed on the nickel is always negative and the charge on gold is always positive.
The electrostatic ignitibility of dust clouds and powders
The electrostatic ignitibilities of a number of varied substances in the form of dust clouds or powders have been determined under a variety of conditions; the work is divided into three pans. Results for dust clouds of magnesium, aluminium, ferro-manganese, zinc and silicon are given; under certain circumstances granular aluminium presents an electrostatic hazard of the same magnitude as magnesium. The minimum condenser energies required for the ignition of dust clouds of tetryl, acaroid resin, polymethyl methacrylate. sugar and flowers of sulphur are 0·012, 0·017, 0·5, 0·009 joules respectively; the effect on these ignitibilities of including a resistance in the discharge circuit aid of varying the size of the capacity is discussed. The electrostatic ignitibilities of guncotton and cordite in the dry state are 0·012 and 0·10 joules respectively. The effect of moisture content on the ignitibility of guncotton and the effect of panicle size, nitrogen content, and the size of the discharging capacity on the ignitibilities of nitrocellulose, guncotton and cordite is discussed.