Transient Thermal Phenomena during Spontaneous Water Migration in Zeolite Beds

The changes in local temperature occurring during spontaneous imbibition of columnar samples of dry natural zeolite with water were studied. The temperature pulses of 20-250 s duration and 3-40°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 effect was attributed to the heat of immersion released in the sample at the moving wetting front

zoladek.indd

Abstract. The results of the experiments on water migration in unsaturated beds of natural zeolite (clinoptilolite) performed with a dynamic neutron radiography technique are presented. It was found that the migration of water in zeolites is much slower than in quartz sand composed of the same size grains. The effect is attributed to the enormous grain surface roughness of the zeolite. The influence of gravity was found to be significant only for beds formed by the coarsest grains. It was found that the water imbibition rate increases with time in finest grain zeolite beds. The results show the difficulties of the classical theory of adhesion driven motion of the liquid in the single capillary as a model of water imbibition by zeolite beds

Dynamic neutron radiography studies of water migration in beds of natural zeolite

The results of the experiments on water migration in unsaturated beds of natural zeolite (clinoptilolite) performed with a dynamic neutron radiography technique are presented. It was found that the migration of water in zeolites is much slower than in quartz sand composed of the same size grains. The effect is attributed to the enormous grain surface roughness of the zeolite. The influence of gravity was found to be significant only for beds formed by the coarsest grains. It was found that the water imbibition rate increases with time in finest grain zeolite beds. The results show the difficulties of the classical theory of adhesion driven motion of the liquid in the single capillary as a model of water imbibition by zeolite beds

Studies on water transport in quasi two-dimensional porous systems using neutron radiography

The spontaneous wetting and drying of flat porous samples of linen, cotton and synthetic textiles were studied using dynamic neutron radiography (DNR). The progress of the wetting process of the media was delineated from the obtained neutron dynamical radiography images. The results of the investigation reveal a non-classical behaviour of kinetics of wicking of these materials. The character of the wetting kinetics is discussed in terms of the fractal character of the tortuosity of fabric capillaries

The Effect of Sodium Chloride on the Process of Drying of Porous Media

The high temperature drying process of corundum cylinders partially saturated with aqueous solutions of sodium chloride was investigated with neutron imaging technique accompanied with mass and temperature measurements. The statistical analysis of neutron images was applied in order to quantify the time evolution of the process. The substantial slowing down of drying with increasing salt concentration was found. This effect was attributed to increase of viscosity of the solution with increasing salt content as well as to the formation of an outer layer of NaCl on the sample surface

Neutron Radiography Studies of Water Self-Diffusion in Porous Medium

The results of neutron radiography studies on macroscopic self-diffusion of water confined within rigid porous material reveal the substantial reduction in diffusion constant in comparison to the diffusion in large volume. The studies performed in the 30-50°C temperature range on fired clay brick of 30% porosity show decrease in diffusion constant to approximately 17% of its value for free space and the Archie exponent is 1.4. The Arrhenius law was confirmed and the activation energy was found of the same value as in the water bulk

Effect of Gravitation on Water Migration in Granular Media

The results of the experiments on water migration in unsaturated granular media performed with dynamic neutron radiography technique are presented. It was found that the porosity of the medium did not determine the kinetics of the process in a marked way. The influence of gravity was found to be considerable for media like coarse sand and gravel, consisting of large grains. No effect of gravitation on the water migration in clay beds was observed. The results are discussed in terms of the classical Washburn-Bosanquet theory of adhesion driven motion of the liquid in a straight circular capillary under gravity. It was found that this theory provides only qualitative description of the water migration within granular media, and the viscous dissipation effects are greatly underestimated

Dynamic neutron radiography studies of drying of kaolin clay cylinders

The results of neutron radiography studies on convective drying of kaolin cylinders are presented. The sample shrinkage and loss of water during drying was easily observed on registered neutron radiograms. The saturation of the sample with water was estimated in terms of the neutron effective macroscopic cross-section. The results are comparable to those of gravimetric measurements and are discussed within the framework of simple theories of drying. The effect of the scattered neutrons is discussed in terms of the results of the MC simulations