Dresden 2011 – wissenschaftliches Programm

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UP: Fachverband Umweltphysik

UP 1: Poster Session

UP 1.6: Poster

Dienstag, 15. März 2011, 18:30–20:30, P2

Rain in the test tube? — •Jürgen Vollmer, Tobias Lapp, Martin Rohloff, Björn Hof, and Jan-Henrik Trösemeier — Max Planck Institute for Dynamics and Self-Organization, 37073 Göttingen

In clouds the adiabatic cooling drives uprising air across the cloud point and hence causes nucleation of cloud droplets which subsequently coarsen and eventually lead to rain. In clouds nucleation is due to seeds (mostly small salt particles) such that droplets have to grow from a submicrometer to millimeter scale.

Surprisingly similar scenarios lead to precipitation in binary liquid mixtures subjected to a shallow temperature ramp. In that case, however, critical nuclei are two orders of magnitude smaller, and gravity becomes noticeable when droplets have grown to a size of tens of microns. Consequently, the resulting “clouds” fit into test tubes with lateral dimensions of a few centimeters such that one can follow the evolution of the phase-separating mixtures for very long times under carefully controlled conditions. Upon slow cooling the mixtures repeatedly go through cycles of nucleation, coarsening and sedimentation.

We suggest a set of PDEs describing the evolution of the mixtures, and discuss its instability towards nucleation and convection. This approach also provides a minimal model explaining the arising of the repeated rain formation, and it allows us to discuss physical mechanisms leading to precipitation. The results are compared to detailed measurements. Similarities and differences to rain formation in clouds are discussed.