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Flow Visualization of Low Prandtl Number Fluids using Electrochemical MeasurementsIt is well established that residual flows exist in contained liquid metal processes. In 1-g processing, buoyancy forces often drive these flows and their magnitudes can be substantial. It is also known that residual flows can exist during microgravity processing, and although greatly reduced in magnitude, they can influence the properties of the processed materials. Unfortunately, there are very few techniques to visualize flows in opaque, high temperature liquid metals, and those available are not easily adapted to flight investigation. In this study, a novel technique is developed that uses liquid tin as the model fluid and solid-state electrochemical cells constructed from Yttria-Stabilized Zirconia (YSZ) to establish and measure dissolved oxygen boundary conditions. The melt serves as a common electrode for each of the electrochemical cells in this design, while independent reference electrodes are maintained at the outside surfaces of the electrolyte. By constructing isolated electrochemical cells at various locations along the container walls, oxygen is introduced or extracted by imposing a known electrical potential or passing a given current between the melt and the reference electrode. This programmed titration then establishes a known oxygen concentration boundary condition at the selected electrolyte-melt interface. Using the other cells, the concentration of oxygen at the electrolyte-melt interface is also monitored by measuring the open-circuit potentials developed between the melt and reference electrodes. Thus the electrochemical cells serve to both establish boundary conditions for the passive tracer and sense its path. Rayleigh-Benard convection was used to validate the electrochemical approach to flow visualization. Thus, a numerical characterization of the second critical Rayleigh numbers in liquid tin was conducted for a variety of Cartesian aspect ratios. The extremely low Prandtl number of tin represents the lowest value studied numerically. Additionally, flow field oscillations are visualized and the effect of tilt on convecting systems is quantified. Experimental studies of the effect of convection in liquid tin are presented. Three geometries are studied: (1) double electrochemical cell with vertical concentration gradients; (2) double cell with horizontal concentration gradients; and (3) multiple cells with vertical temperature gradients. The first critical Rayleigh number transition is detected with geometry (1) and it is concluded that current measurements are not as affected by convection as EMF measurements. The system is compared with numerical simulations in geometry (2), and oscillating convection is detected with geometry (3).
Document ID
20030060519
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Crunkleton, D.
(Vanderbilt Univ. Nashville, TN, United States)
Anderson, T.
(Florida Univ. Gainesville, FL, United States)
Narayanan, R.
(Florida Univ. Gainesville, FL, United States)
Labrosse, G.
(Paris-Sud Univ. Orsay, France)
Date Acquired
August 21, 2013
Publication Date
February 1, 2003
Publication Information
Publication: 2002 Microgravity Materials Science Conference
Subject Category
Fluid Mechanics And Thermodynamics
Funding Number(s)
CONTRACT_GRANT: NAG8-1679
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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