Marangoni instabilities in small circular containers under microgravity

Circular containers of various aspect ratios a with flat free upper liquid surfaces were heated from below under microgravity to generate the Marangoni instability (MI). We realized “liquid lateral sidewalls” for the containers to come near to the “slippery sidewalls” introduced by Rosenblat et al. (J Fluid Mech 120:91–122, 1982a) and Echebarría et al. (Physica D 99:487–502, 1997), henceforth referred to as RHD and EKP, respectively. The flow structure was visualized by aluminium flakes and recorded on videotape. The MI was clearly observed in all containers above a critical Marangoni number Ma ^c which depends on a. In the first microgravity experiment in a container with a=7.5, we found significant convective heat transport and reported a Nusselt number Nu=1.8 for Ma=4×Ma ^c . In a second microgravity experiment with containers with a=0.5, 0.75, 1.0, 1.5, 2.0, 4.0 and 5.0, various flow structures (azimuthal and radial wave numbers) were observed, depending on a and Ma. The observed scenario compares qualitatively well with the stability curves calculated by RHD and EKP. Frequent switching between modes (2,1) and (1,1) was observed in the container with a=2 at supercritical Ma that is exactly the case for which this behaviour was predicted by EKP for reduced gravity.