Posted April 18, 2000
With the help of an award-winning paper by co-investigators Carlos Coimbra and Roger Rangel, scientists will someday be able to use the three-dimensional light patterns of holography to see how bubbles and particles interact in microgravity conditions. The paper, which received the American Institute of Aeronautics and Astronautics’ Best Paper in Microgravity Science Award for 1999, forms the theoretical foundation for SHIVA, or Spaceflight Holography Investigation in a Virtual Apparatus. Principal Investigator James Trolinger, of MetroLaser Inc., in Irvine, California; Rangel, of the University of California, Irvine, Coimbra, of the University of Hawaii, and other members of the SHIVA team at Marshall Space Flight Center, will collect data using a unique holography-based diagnostics tool. They’ll use the instrument to understand the intricate, transient interaction between a single bubble or particle and its surrounding viscous fluid as well as bubble or particle interactions among themselves and the fluid. Findings from the experiment, which will be conducted on a space shuttle flight or on the International Space Station, will help scientists better understand the physics of most diffusion processes. For example, the bubbles in a glass of ginger ale on Earth travel quickly toward the top of the liquid because of buoyancy forces. In a microgravity environment, buoyancy forces are greatly reduced, so they have little influence on the motion of the bubbles. Recording the behavior of bubbles in this environment will allow SHIVA researchers to study in detail the motion and velocity history of the bubbles. What the researchers learn can be applied to manufacturing processes on Earth, where bubbles can cause defects if they remain in a molten material as it hardens.
The experiment will allow results obtained for particles 1-2 millimeters in size moving at fairly low frequencies (around 100 hertz) to be scaled down and applied to microparticles and nanoparticles in Brownian motion, the apparently erratic zigzag motion of microscopic particles that becomes more evident at raised temperatures, in less viscous fluid, or with a smaller particle size. The paths that the particles take become increasingly complicated as they enter the viscoelastic regime, which means that the path and velocity of a particle at any given moment depends on its entire path and all its previous velocities leading up to that moment. Scientists can determine where a particle will go and at what speed based on that information.
Coimbra and Rangel presented their paper, “Spherical Particle Motion in Unsteady Viscous Flows,” at the 37th Aerospace Science Meeting in January 2000.