Inauguration of the Catapult Drop Tower - Bremen
16 Dec 2004Recently members of the PRODEX team visited the ZARM (Bremen) to participate in the inauguration of the only catapult drop tower in the world.
Catapult Details - Bremen Drop Tower
PRODEX is financing the project of Prof. Vedernikov (ULB, Brussels) to investigate aerosol particle motion in presence of temperature and concentration variations and uses the tower in its original configuration.
The project is focused on the investigation of the basic microscopic mechanisms of interaction between aerosol pollutant particles and hydrometeors (drops and snowflakes), particularly, attraction or repulsion forces arising between the particles in presence of temperature and concentration gradients, or phoretic forces.
Phoretic forces are of central interest in the scavenging of aerosol particles in clouds, when droplets and/or ice crystals grow or evaporate, and below cloud, during the fall of hydrometeors. During processes of evaporation or condensation of droplets or ice crystals temperature and water vapour gradient occur, and this determines movement of aerosol particles.
Theoretical and experimental analysis of the thermophoresis and diffusiophoresis in the transition region of Knudsen number (most interesting for the atmospheric processes) show high mismatching of the data. All these experiments were performed in the laboratory conditions where gravity highly perturbed these phenomena. As a matter of fact, in normal gravity it is not possible to study the phoretic effects alone, as in the case of thermophoresis particles move due to gravitation force and natural convection, and in the case of diffusiophoresis there is a continuous renewal of the vapor concentration. Only two groups from Japan and the Netherlands performed few experiments in microgravity conditions.
Their results, however, did not give the decisive conclusion most probably due to the low number of the experimental data. In 2000 and 2001 the joint team from the Microgravity Research Center (MRC, Université Libre de Bruxelles, Belgium) and the Institute for Science of the Atmosphere and Climate (ISAC-CNR, Bolgna, Italy) performed a series of experiments in the conditions of reduced gravity of the parabolic flights. In order to overcome the problem of low particle number we used the digital holographic velocimetry, which allowed increasing the observation volume by the decimal order of magnitude as compared to the traditional optical methods. The shortcoming of these experiments was in the presence of the velocity component lateral to the temperature gradient, which normally should be equal to zero and that should be attributed to relatively high microgravity perturbation in the parabolic flights where the residual gravity is about
The later problem is of no importance in the conditions of the drop tower where all the microgravity perturbations are of the order of
Advantages of making experiments in the drop tower
Technical support from the ZARM support company (assistance in assembling, cabling, tests, etc.; capsule control computer programming).
Possibility to use local university services and facilities including machinery works.
Nice working ambience in dealing with all the staff of the ZARM support center.