Thermocapillary bubble migration -Drop tower experiments-

Experiments on the thermocapillary bubble migration are presently carried out in the Drop Tower Bremen. After a heating period of about two hours, a sufficiently linear temperature gradient is established with paraffin liquids in a cavity. For the moment of drop of the capsule two bubbles with diameters of up to 2 mm are generated and the injection needles are retracted. During 4.74 s under strongly reduced gravity the speed of the bubble migration is observed with video camera, the temperature field by Pt 100 temperature gauges and the use of a differential interferometer. First experimental results with a liquid characterized by the Prandtl number Pr = 10 (n-decane) agree very well with theoretical data available both from literature as well as with numerical simulations. The correspoding Reynolds numbers are in the range between 20 < Re < 160. The experimental setup, the measuring technique and the evaluation method will be presented as well as comparison between experimental and theoretical results.