Effect of turbulent and counter flow in front of moving air-water interfaces on glass attached colloids

Abstract

Abstract Hypothesis Advancing air in capillary channels causes disruption in the laminar parabolic flow pattern in saturated flow. The advancing motion of air generates flow cells in a head and behind the travelling air bubble, allowing creation of turbulent flow and counter flow. These disturbences in flow field create hydrodynamic forces which may to exceed the colloidal attachment forces. The collector-colloid interaction is affected by the chemical environment, hence colloid detachment due to the prementioned motions depends on the specif chemical conditions aswell.

Experiment In the study, colloids with diameter 1, 5, and 15μm, dissolved in solutions with pH 5,6,7,8 were introduced into an angular pore channel to let them retain at the surface of the glass channel. Various experiments were conducted to research the effect of surface rougness in additions to the chemical forces on colloid stability. For theseting the surface roughness the experiment used a near smooth surface of the glass capillary channel with impirties smaller than the used colloid size. Chemical forcing was tested using 15μm colloids under a changing chemical enviroment. A systematic method was used for the attachement process where after injection of a specific pore volume, an air bubble was introduced into the pore channel at four different air-water interface velocities. Using confocal microscope, experiminetal observations of colloidal motion was recorded and data processed using NIS-elements software (Nikon).

Findings Our experimental observation showed that neither of tubulent motion or counter flow was able to overcome the attacment force keeping colloids attached to the glass walls. Hydrodynamic force calculation however indicated a possibility that attachement might be overcome on a smooth glass surface. Impurtities on the collector surface caused increase of mechanical straining to be sufficient, and thereby obstructing colloidal movement. Thus, removal of colloids by the prementioned motions are highly unlikely to occur in natural conditions. The auxillary expeiments showed that interfacial forces are the dominant detachment mechanism and surface roughness is a key parameter in colloid stability.