Dual-deposition rates in colloid filtration caused by coupled heterogeneities in a colloidal population.

Colloidal deposition from an aqueous suspension, during its flow through saturated porous media, is of significance in many natural and man-made processes which lead to water purification. Colloid filtration theory (CFT), which was used to predict removal of homogeneous colloids, in the above systems, is based on a distance-invariant deposition rate. However, many authors over the past decade have reported data which suggest that more than one deposition rate is demonstrated by colloids naturally occurring in the environment on apparently homogeneous media.

Estimation of colloidal deposition from heterogeneous populations.

This paper reports a study of size-heterogeneous colloid filtration in a new bed using different types of colloids under different conditions of flow and solution chemistry. Depth-wise variation of the particle-size-distributions f(i)(x), and the total liquid-phase colloid concentration, C(x) are measured which are used to estimate the depth-wise variation of the liquid-phase concentration for each distinct section of the heterogeneous population, C(i)(x). It is observed that log C(i)(x) is linear with depth, for some systems, while it shows deviation from linearity, with the slope decreasing with depth, for others.

An agglomeration-based model for colloid filtration.

This paper develops a model for colloid filtration which accounts for the possibility of aggregation of the colloidal particles in the aqueous phase. Depth-wise variation of liquid-phase colloid concentration, C(x), is measured experimentally in the presence of monovalent cations at different concentrations and divalent cations, which confirm that log of C(x) deviates significantly from linearity for all of the above cases. It is also observed that in all systems showing significant removal, preaggregation of the colloids is observed, which confirms the correlation between aggregation of colloids with their retention in saturated porous media, which has been reported earlier.

Prediction of coupled menisci shapes by Young-Laplace equation and the resultant variability in capillary retention.

This paper shows how 2 coupled Young-Laplace equations can be solved to predict the shapes of two coupled menisci formed in a capillary system. Experiments are performed, which demonstrate that the equilibrium volume of liquid retained in a vertical capillary, can be variable, even when all the properties of the system are invariant. This variability in liquid retention also leads to different equilibrium shapes of the top and bottom menisci.

Limiting conditions for applying the spherical section assumption in contact angle estimation.

The shape of liquid drops on solid surfaces deviates from the spherical as tension decreases and gravity effects start affecting the drop shape. This paper attempts to define this deviation and estimates the dimensionless Eotvos number limits above which the deviation becomes "significant." The use of these limiting values can facilitate estimation of contact angle in the following manner.

Shape analysis based critical Eotvos numbers for buoyancy induced partial detachment of oil drops from hydrophilic surfaces.

Removal of oil drops from solid surfaces immersed in an aqueous medium is of interest in many applications. It has been shown that drop shape analysis can be used to predict conditions at which the stability limit of a lighter than water oil drop on a solid surface immersed in an aqueous bath is reached (Adv. Colloid Interface Sci.

Critical Eotvos numbers for buoyancy-induced oil drop detachment based on shape analysis.

Critical values of the Eotvos number, which is half the Bond number, above which buoyancy induced drop detachment occurs, are estimated based on force balance equations available in the literature [Colloids Surf. A: Physicochem. Eng.