Flow and transport experiments with unsaturated porous media can take prohibitively long time, because hydraulic conductivities decrease exponentially with decreasing water saturation. Experimental time can be shortened by using centrifuges. However, compelling evidence is needed to assure the applicability of centrifuges for studying colloid transport, as colloid filtration is affected by centrifugation. We determined the suitability of centrifuges to study colloid transport in porous media. We used filtration theory to predict the effect of particle density and flow rate on transport of colloids as affected by centrifugal accelerations. From filtration theory, a functional relation between centrifugal acceleration and pore water velocity and colloid density was derived, which allows us to predict at which acceleration colloid filtration will be dominated by sedimentation. For typical pore water velocities in the subsurface, it is expected that the filtration behavior of natural subsurface colloids will be impacted at centrifugal accelerations as low as 3 g.
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