GB578783A - Improvements in apparatus for producing aerosols - Google Patents

Abstract

578,783. Spraying smoke screens, insecticides &c. BRITISH THOMSONHOUSTON CO., Ltd. March 22, 1944, No. 5386. Convention date, March 24, 1943. [Class 69 (iii)] The particles of an aerosol, e.g. a smoke screen, are made of optimum size, e.g. to give maximum opacity by imparting to the vaporized material a critical velocity. This is attained by raising the temperature and/or pressure of the vaporized material within a substantially enclosed chamber and blowing the vapour so formed into the atmosphere at lower temperature and at high velocity suitable to produce the suspension of particles of the desired size. In Fig. 1, fluid to be vaporized is supplied through the pipe 7 to the nozzle 6 forming a jet 5 of atomised fluid within a metal chamber 1. The chamber is heated by an (electric) heater 3 and, if desired, compressed air or gas is supplied through a pipe 9 which imparts the desired velocity to the. aerosol issuing' through the orifice 8. In another apparatus, Fig. 2 (or Fig. 4, not shown), a depth of fluid 11 to be atomised is maintained in the bottom of the chamber from a supply conduit 12 at constant pressure. The heater 10 vaporizes the liquid and the. tubular outlet 13 is heated by a controllable heater 15 to increase the temperature and pressure, or the pressure may be controlled by compressed air &c. through 16. In Fig. 3, the fluid from a nozzle 21 is blown by an air jet 22 into a channel 18 of a (copper) cylinder heated by gas flames 26. The velocity at the exit 19 may be controlled particularly by the air pressure at the air jets 22. In Fig. 5, a (flash) boiler 36 with a jet of combustible fluid 41 (propane) heats a pool 51 of aerosol fluid supplied from a valve 45, through a preheater coil 46, and passes through orifices in spaced diaphragms 48 in the tube 49 on a vapour heated inlet tube 50 to 51. The diaphragms 48 assist in breaking up the fluid. The vapour rises through the surrounding tube 52 to a vapour chamber 53 provided with an annular sump 54 for condensate which flows back down the tube 50 to the pool 51. An overflow 55 limits the level of condensate. A deflecting and condensing baffle 56 prevents the passage of large drops, the rest passing through an ejection nozzle 57. A valve 59 is provided to relieve pressure in the chamber 53 and a pressure gauge 60 is provided. The required size of particle may thus be obtained by using a nozzle of constant size and varying the quantity of weight of fluid evaporated per unit of time or vice versa. Tables on this basis are worked out. Increase in nozzle size may be effectively obtained by using small multiple nozzles a foot or more apart so that the jets do not merge until at least 2 ft. from the nozzles to allow the particles to complete their intended growth. In another arrangement (Fig. 6, not shown), the vaporized liquid passes up the central passage of a heated metallic cylinder with a blowing nozzle near the top of the passage to disseminate direct into the atmosphere. Such methods may be used to produce aerosols of insecticides over large areas or of smoke smudges to protect vegetation from frost &c. The particles may also be selected in size to form opaque smoke screens for military or naval purposes or to allow of infra-red photography.