Heterogeneous freezing of single sulfuric acid solution droplets: laboratory experiments utilizing an acoustic levitator

[摘要] The heterogeneous freezing temperatures of single binary sulfuric acidsolution droplets were measured in dependency of acid concentration down totemperatures as low as -50°C. In order to avoid influence of supportingsubstrates on the freezing characteristics, a new technique has beendeveloped to suspend the droplet by means of an acoustic levitator. Thedroplets contained immersed particles of graphite, kaolin or montmorillonitein order to study the influence of the presence of such contamination on thefreezing temperature. The radii of the suspended droplets spanned the rangebetween 0.4 and 1.1mm and the concentration of the sulfuric acid solutionvaried between 5 and 14 weight percent. The presence of the particles in thesolution raises the freezing temperature with respect to homogeneousfreezing of these solution droplets. The pure solution droplets can besupercooled up to 40 degrees below the ice-acid solution thermodynamicequilibrium curve. Depending on the concentration of sulfuric acid and thenature of the impurity the polluted droplets froze between -11°C and-35°C. The new experimental set-up, combining a deep freezer with amovable ultrasonic levitator and suitable optics, proved to be a usefulapproach for such investigations on individual droplets.

[学科分类] 大气科学