High‐Temperature Evaporation Rates of Solid KBr and NH4Cl aerosol particles

Abstract

AbstractThe evaporation rates of particles of solid KBr or NH4Cl suspended in argon were studied under high‐temperature conditions behind incident shock waves. The mass‐transfer process during particle evaporation was observed by two optical techniques allowing the measurement of scattered light from a particle ensemble and also from individual particles. The scattered light flux signals were interpreted on the basis of the Mie theory, resulting in values for the time‐dependent particle size and for the refractive index of particle materials. The experiments were performed in the gas‐phase temperature ranges TG = 1070–1300K (KBr) and 525–650K (NH4Cl). The initial size of the suspended particles ranged between 0.6 and 1.0 μm. From the measured decrease in the particle size during the mass‐transfer process the evaporation coefficients of both materials were determined as a function of the gas‐phase temperature. They depend on the vapour pressure and the diffusion coefficient for vapour into gas. Typical parameters (àKBr, m) describing the diffusion coefficient of KBr vapour in argon and the vapour pressure of NH4Cl could be determined.