On-line slurry viscosity and concentration measurement as a real-time waste stream characterization tool. 1998 annual progress report
'This project seeks to develop an on-line sensor to measure the viscosity of dense slurries. This report summarizes work after two years of a three year project. The flow behavior of slurries is important for many of the proposed unit operations to be used in the conveying and processing of tank wastes. One alternative for determining the rheological properties of such materials is to obtain samples and test them off-line using conventional rheometers. Such a protocol is not practical for a wide variety of wastes. Rather, it is the goal of this work to find on-line, in-process techniques for measurement. There are two systems that the authors have propose examining: (1) Nuclear magnetic resonance imaging (NMRI), and, (2) Ultrasonic Doppler Velocimetry. Central to both of these techniques is the measurement of velocity profiles in pipe flows. For the NMRI measurements, the presence of particles has two principal effects on the NMRI velocity profiles: a decrease in signal intensity and image blurring. Similar effects are observed in turbulent flows due to the local random fluctuations in the flow. This similarity has led us to turbulent flow using NMRI. The governing equations for the signal obtained by NMRI are the Bloch-Torrey equations. Previously, the author showed a relationship between turbulent fluctuations and spatial signal intensity variations, assuming isotropic turbulence. However, this assumption does not reflect the true nature of turbulence in a pipe flow where the turbulence is not isotropic. In the new work the Bloch-Torrey equations will be solved by first, time averaging and then employing a turbulence model for pipe flow. The purpose of the time averaging is to smooth the fluctuations of time scale smaller than that of NMRI data acquisition. After this work with single phase fluids, the authors shall undertake NMRI experiments of slurry flow. Various operational parameters will be optimized during the experiments to obtain velocity profile of the flow. Pressure drops will also be recorded to obtain shear stress distribution. Plot of shear stress versus the shear rate, obtained from the velocity profile, will yield the shear viscosity over a wide range of shear rate. The velocity images will also be analyzed to compare the effects of fluctuations with those of turbulent flow experiments For single phase fluids, the NMRI and the UDV work will be compared with measurements using LAV. In their LAV, flow apparatus, the working fluid, water, is gravity fed from a reservoir into a horizontal one inch Pyrex tube, 180 diameters in length. The system enables traverses of the optical probe in the horizontal and vertical directions, with a resolution of 200 micrometers. Radial distributions of the axial component of velocity were obtained at a location 150 diameters from the tube entrance. Measurements in the laminar regime indicate a precision of within one percent, as indicated by the root mean square fluctuations. In the turbulent regime, radial profiles of the mean and fluctuation velocities agree with literature values. In the laminar regime, symmetry of the radial velocity distribution was observed in the horizontal plane passing through the axis, but was not in general observed in the vertical plane passing through the axis. Further investigation revealed that the asymmetry was a result of buoyancy due to heat transfer between the working fluid and the surroundings, even though the pipe was not actively heated or cooled. Temperature differences as little as 1 degree Celsius were found to result in significant asymmetry. To have a reproducible result in the laminar regime, it was necessary to control the reservoir temperature to within 0.1 degree Celsius.'
- Research Organization:
- Univ. of California, Davis, CA (US)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM), Office of Science and Risk Policy
- OSTI ID:
- 13492
- Report Number(s):
- EMSP-54890-98; ON: DE00013492
- Country of Publication:
- United States
- Language:
- English
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