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Quick Look

Material and Flow Measurements Using Novel Magnetic Resonance
Analytical Technical Concept, 15-9121

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Principal Investigators
Qingwen Ni
J. Derwin King

Inclusive Dates: 01/28/99 - 05/28/99

Background - Nuclear magnetic resonance (NMR) sensors can directly acquire data from all hydrogen nuclei in gases, liquids, and solids. These data can provide rapid, nondestructive, and nonintrusive measurements of the properties, compositions, and flow of these materials. In multiphase flow systems, NMR offers a unique capability for providing real-time fluid physics data that are not directly available by other instrumentation technologies. For example, for a porous matrix of particles during melting, many models assume that the solid grains in a packed bed remain uniform, and the porosity is constant through the melting cycles. However, under flowing conditions, the size, shape, and packing (porosity) of the solid grains change spatially and temporally. Therefore, a real-time quantitative analysis of the actual phase changes is important to provide additional and more accurate information on the melting, both in gravity and in microgravity conditions. Simple pulsed NMR has the potential to provide such data.

Fourier transform (FT) analysis is widely and successfully used in NMR analytical laboratory experiments to provide frequency spectra and molecular analyses of materials. However, in using proton FT NMR to measure solid and liquid mixtures, it is impossible to distinguish and selectively measure the solid and liquid constituents in complex materials because the NMR spectral peak from solids is too broad and overlaps the liquid peak, for example, in ice-water mixtures (ice and water may have the same chemical shift). Here, the research team reports a new concept, inversion T2* relaxation spectrum, to separate the measured components in an ice-water mixture and in other solid-liquid mixtures. This novel concept, inversion T2* relaxation spectrum NMR, can particularly be applied to low-field, on-line measurements and provides useful solid-liquid data when even high-resolution FT NMR is not effective.

Approach - The approach for this quick-look project was: 1) develop a new measurement and data assessment concept--inversion T2* relaxation spectrum of NMR, 2) develop math algorithms to obtain the inversion T2* relaxation spectrum from NMR free-induction decay data, 3) apply this inversion T2* relaxation method under flowing conditions to study convective melting to determine the phase changes between the solid and the liquid, that is, the total unmelted solid mass, regardless of shape, as a function of time.

Accomplishments - An experimental NMR sensor was developed and used to investigate one- or two-dimensional melting of a packed bed for horizontal and vertical orientations during convective flow. The sample container consists of a 30-centimeter (12-inch ) length of rectangular glass tubing and a rectangular NMR sensor (radio frequency) coil wound on the surface of the glass tubing. The illustrations show inversion T2* spectra from the NMR free-induction decay signals of an ice-water mixture before and during the melting in a convective flow. The line broadening of the inversion T2* spectrum may be partially due to the magnetic field inhomogeneity. The integrated area of the ice and the water spectrum can be used to estimate the amount of existing ice and the amount of water passing through the packed zone at each test point during the melting. This NMR technique is a unique method to quantitatively determine the mass change of packed bed (ice) under similar experimental conditions, regardless of the uniformity of the ice during the convective melting. Using NMR combined with other techniques, a more accurate and complete characterization of the convective melting of granular porous media can be achieved. This study has demonstrated the capability and efficiency of hydrogen-transient NMR as a sensor for detecting ice mass changes and other properties during heat transfer in the porous media and for further studies of mathematical modeling of melting rates of the packed bed under nonthermal equilibrium convection. As a result of this project, a joint proposal for the NASA Microgravity Fluid Physics program was submitted, and a subcontract for Multiphase Complex Flow for NSF was awarded.

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The inversion T2* relaxation spectra obtained from the FID signal are shown with (A) ice before the melting and (B) ice during the melting

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