Basic Studies on the Generation of Submicron Aerosol by Dautrebande Jet Generator

Abstract

In order to establish the method of experimental inhalation study of hazardous radioactive aerosol, including that of Pu compounds, studies have been made on a modified Dautrebande Aerosol Generator (Type D_30a), with regard to the relation between the concentration of dispersing solution and that of dispersed aerosol as well as its size characteristics for some inorganic salts (NaCl, SrCl₂, PrCl₃, Ce (NO₃)₃.)
Regardless of the difference of materials examined, the concentration of dispersed aerosol exactly depends on that of solution with linear relationship, when the flow rate of jet air is constant. The size distribution of dispersed aerosol is slightly diverged from the log-normal distribution, presumably because of the larger portion of the aerosol being cut off by the mechanism of generation and of other characteristics of the generator. Nevertheless, the mass median diameter of the solidified aerosol of a given salt directly measured on the cumulative mass distribution curve indicates linear relationship with cubic root of the concentration of solution of the salt. (Ce Nitrate is different, though.) The theoretical analysis of the case offers the following suggestions. Assuming that the total amount and size distribution of the mist at dispersion is always constant with one generator at the constant flow rate of air, regardless of kind and concentration of dispersing solution, the relation between MMD of the mist and that of corresponding solidified aerosol is expressed by the equation (D/2)³R=β(φ/2)ⁿ, since the mass of the salt included in a mist particle must be equal to that of the corresponding aerosol particle. Here D and φ are diameters of the mist and of the corresponding solidified particle, R being the concentration of the solution, while β is a constant related to the density of aerosol and n is a parameter related to the solidifying characteristics of aerosol. In case of chloride salts examined, n=3, indicating its solidifying tendency, equally applies to all directions. In case of Ce nitrate n seems to be less than 3 (about 2) that means that the solidifying tendency is different in some directions. Thus, in case of chloride salts, since D and β are constant for a given kind of solution, φ must be linearly proportional to ³√R. (In case of Ce Nitrate, approximately proportional to ²√R)
Therefore it is concluded that we can easily obtain radioactive submicron aerosol and control the concentration and size characteristics of the dispersed radioactive aerosol of a given salt (solidified by evaporation), within certain limitations, by changing the concentration and specific activity of the salt solution, with the generation technique.