Light Scattering by Dust Particles: Experimental Results

Abstract

The principle retained for our experimental investigation consists in generating a continuously flowing aerosol, a section of which is illuminated in order to study its scattering properties over the 0–180° interval of scattering angles. It can therefore be considered as a nephelometer whose key part is a fluidized — bed generator which receives a mixture of the dust to be studied (in the form of powder) and of “large” glass spheres having diameters of 100 to 200 μm. An air flow forces the mixture to “boll”, the collisions between the glass spheres desagglomerate the powder and the liberated dust particles are transported by the air flow. The fluidized bed is fed by an endless screw which continuously enrichs the mixture so as to compensate for the loss of transported particles. It can be shown that the operation of the generator is governed by a very simple equation which relates the ponderal concentrations of the mixture and the flow rates to the concentration of the aerosol. After a transitory phase of approximately 10 mn, the stationary regime given by the equation is reached and was experimentally shown to be remarkably stable. A nozzle concentrates the aerosol in a column having a diameter of 5 mm; it is then allowed to flow freely over a length of 20 mm before being taken over by a suction device.