Physical modeling of the effect of shearing on the concentration profile in a shear cell

The effect of the action of shearing a column of molten gallium (Ga) doped germanium (Ge) on the gallium concentration field in a shear cell segment w as experimentally investigated using a physical model. A physical model is an experimental system that is different from the system of interest but co nnected by scaling relations. Water was used as the fluid in the physical m odel in place of the molten germanium, and methylene blue dye was used as a tracer in place of the gallium dopant to determine the extent of mixing. T wo adjacent cylindrical fluid segments in a capillary of a shear cell were studied with the physical model. These fluid segment dimensions were scaled by a factor of seven for the physical model, since the kinematic viscosity of water at 22.6 degrees C is seven times that of Ge at 950 degrees C. A s mall amount of mixing between adjacent segments was measured due to the ini tial fluid-fluid shear. The mass transfer between the top and bottom segmen ts of the physical model during the fluid-fluid shear was found to be less than 2% for all shear rates in the range 0.1-2.0 cm/s. The average mass tra nsfer between adjacent segments due to the fluid-fluid shear in that sheari ng range was 1.2%. (C) 1999 The Electrochemical Society. S0013-4651(98)10-0 77-0. All rights reserved.