longitudinal dispersion in nonuniform isotropic porous media

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Water in the column experiments and the capillary drainage
measurements comes under tensile stress. To minimize the formation of
bubbles in the fluid, all water used in these experiments 1S de-aerated
under vacuum for about 30 minutes. Since several hundred liters of
water are needed for the column experiments, a battery of 11, 19-1iter
glass jugs are connected in series to a vacuum line for de-aeration.
The de-aerated water 1S siphoned from the jugs into the supply
reservoirs to minimize air entrainment while transferring the water.
Procedures for the capillary drainage measurements follow those
given by Vomocil (1965). The Buchner funnel's porous disc is saturated
by submerging the funnel 1n de-aerated water overnight and then drawing
water through the funnel and tubing by using a vacuum pump. The
saturated Buchner funnel, tubing, and burette assembly are mounted
vertically as shown in Figure 4.8. Before putting sand into the sample
cylinder, the system is calibrated for any plate drainage or tubing
collapse by running through the entire series of suction heads and
noting the drainage into the burette. A 600-700g sample of the porous
medium 1S stirred into the de-aerated water to completely saturate the
sand. The sand and water mixture is then poured into the sample
cylinder in the Buchner funnel. The saturated sample 1S compacted by a
hand-held vibrator until the packing is at equilibrium. Excess water
is poured of the funnel while holding the sample in place. By lowering
the burette, a tension is applied to the sample and water drains into
the burette until equilibrium is reached. Due to the water draining
into the burette, the burette must be lowered as it fills to maintain a