Patent GB-403431-A (GB)
Title: An improved process and means for the production of ionisation
IPC: B03C3/66
Filed: 1932-06-09
Abstract: <PICT:0403431/III/1> In apparatus for the production of ionisation by means of electrodes separated by insulating materials, such as the dust precipitation apparatus described in Specification 394,050, an alternating voltage of such characteristics is applied to the electrodes that the potential drop across the insulating body, which may be regarded as a condenser dielectric, is decreased in relation to the potential drop at the electrodes producing the ionisation at the surface of the insulating material, due to the resistance of the dust layer which is deposited thereon.  The alternating voltage may be obtained from alternating current or from pulsating continuous current, and preferably charges or discharges the insulating body in a time which is short relative to the periodic time of the alternating voltage, the high velocity of charge in the voltage producing a field in the dust layer which is sufficient to cause ionisation of the gas.  Suitable forms of alternating voltage are those having a steep wave front which may be produced by suitable generators or discharge tubes and particularly those produced by surges, obtained for example by the discharge of a spark-gap. According to the arrangement shown in Fig. 4, illustrating a dust precipitating apparatus in which ionisation is produced by an alternating voltage applied to electrodes 13, 14 and 15 arranged on the surface or in the vicinity thereof of a sheet 12 of insulating material, and the dust is precipitated by means of another voltage, preferably direct, applied between the ioniser and electrodes 20 and 21 an alternating voltage with a steep wave front is produced by means of a spark-gap 32 interposed in the supply from a transformer 18. Protective resistances 36, 37 and 38 are provided to prevent damage to the transformers &c. by the surges.  The wave-form of the voltage may be varied by altering the relationship between the inductance and capacity of the circuit, the capacity of the ioniser, the length of conductor from the spark-gap to the ioniser, the protective resistances, the transformer leakage and by inserting a condenser 40, preferably large compared with the capacity of the ioniser, across the transformer.  The spark-gap is designed so that its capacity is small, but if the ioniser capacity is very small, a small condenser may be connected in parallel with the spark-gap.  The curvature of the spark-gap electrodes is preferably small to prevent glow discharge before the spark proper and to obtain a rapid collapse of the spark-gap resistance.  To prevent arcing, the electrodes may be ribbed or made of material of high conductivity, or the spark-gap may be cooled or immersed in oil or other dielectric liquid or in gas under high pressure.  Other suitable quenching devices may also be used.  The axis of the spark-gap is preferably horizontal so that the upward movement of the heated air tends to break any arc formed.  The electrodes may also be hollow and provided with holes at the point of production of the spark and a suitable fluid medium may be supplied through the openings under pressure or suction.  A number of spark-gaps may be connected in series to modify the steepness of the voltage surge.  A choke may be connected in parallel with the condenser 40 and the transformer winding to reduce the loading of the transformer or alter the phase relationship.  The apparatus may be applied to the production of chemical reactions between gases present at the ionising surface or between gases and substances flowing over or covering the surface of the insulating body.  The discharges may also clean insulating surfaces.