Moisture Transport in Unconsolidated Porous Media During Drying: Use of Nuclear Magnetic Resonance Imaging as an Experimental Probe

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This proposal presents a program of theoretical and experimental work directed toward a predictive theory of drying. The influence of local heterogeneities is incorporated into both the theoretical framework and the experimental measurements that were proposed. The theoretical analysis is based on the method of large-scale averaging and a closure scheme that incorporates the effect of local heterogeneities. The experimental studies make use of nuclear magnetic resonance imaging (NMRI) to both quantify the heterogeneities in a porous medium and to measure the local volume averaged saturation during drying. Determination of the spatial variation of the local volume averaged saturation will provide experimental values of the large-scale spatial deviation of the saturation. These in turn, will be compared with predictions from the closure calculations. The key feature of the method of large-scale averaging is the appearance of large-scale spatial deviations in the velocity and concentration, and the existence of a closure scheme that can predict these spatial deviations. In all previous studies of transport phenomena in porous media, theory and experiment have been compared in terms of measured and predicted effective transport coefficients. With the use of NMRI, the PI's are in a position to develop the comparison beyond the level of the effective transport coefficients and make a direct comparison between calculated and measured large-scale spatial deviations. The process of drying is of interest to a very wide range of engineering and scientific practitioners who are concerned with moisture transport in final or intermediate products. Some of these applications are given as follows: in agricultural products, paints and inks, wood, gels, soils, catalyst pellets, and foams. This investigation should permit a greater understanding of this important transport process.