MAGNETIC BUOYANCY FORCE ACTING ON BUBBLES IN NONCONDUCTING AND DIAMAGNETIC FLUIDS UNDER MICROGRAVITY

The magnetic buoyancy force acting on a bubble in a one-dimensional ma gnetic field can be represented as F = (chi(G) - chi(L))integral H(dH/ dx)dVol(B), where chi(G) and chi(L) are the volume magnetic susceptibi lities of the gas and liquid, respectively, and H is the magnetic fiel d strength. Since \chi(L)\ much greater than \chi(G)\ and most liquids are diamagnetic, this expression indicates that the magnetic buoyancy forces act in the direction of increasing magnetic field strength. Be cause the magnetic buoyancy force in a diamagnetic fluid is small, the motion of bubbles under normal gravity is difficult to study, but mic rogravity offers the possibility of detailed observations. Using a com pact permanent magnet under microgravity conditions, N-2 bubbles in pu re water (0.01 dyne s/cm(2)) and in a 69:31 glycerol/water mixture (0. 21 dyne s/cm(2)) were found to move in the direction of increasing H, and to be held stationary at the point of maximum H. The motion of the bubbles was also simulated with a theoretical model and was found to agree with measurements made under microgravity conditions. These resu lts indicate that magnetic buoyancy can be used to control bubble moti on. Since most fluids are diamagnetic, magnetic buoyancy can be used t o control bubbles in many fluidic devices used in space applications. (C) 1997 American Institute of Physics.