The statistical approach to the thermal neutron radiography picture analysis is applied to evaluation of the experimental results obtained for drying of rectangular and cylindrical samples of granulated and rigid porous materials. We have shown that the time dependence of the standard deviation of image brightness reects the appearance and motion of the drying front observed during second period of the drying process. The results are discussed within a simple two-region model of the drying sample image.

No abstract

The application of modern digital neutron radiography in the study of the drying process in porous media is demonstrated with two simple examples of cylindrical and rectangular samples made of different materials. The statistical method of image analysis is presented and the standard deviation of grey scale values (referred to brightness) is shown to be a useful measure of receding drying front emergence. The motion of the drying front was analyzed and found neither linear nor proportional to the square root of time and was delineated with nonlinear functions different for each sample shape.

The changes in local temperature occurring during spontaneous imbibition of columnar samples of dry natural zeolite with water were studied. The temperature pulses of 20250 s duration and 340 • C amplitude were registered and correlated with the wetting front motion observed with neutron radiography. The amplitude of the pulses was shown to increase with increasing ambient temperature. The broadening of the temperature pulse with increasing distance from the water supplied end of the samples was observed. The amplitude and the pulse width were found to depend substantially on the drying temperature of the material. The observed eect was attributed to the heat of immersion released in the sample at the moving wetting front.

No abstract