Effect of turbulent flow condition on streaming potential measurement using cylindrical cells

Streaming potentials are useful guides for investigating the electric behavior of colloids. They are not well-defined as a concept and, in particular, the location of their generation has not been clearly identified, although they are easy to measure. Traditionally, a laminar flow has been required for measurement; however, adjacent to a wall, there should be a fixed layer where the stationary or laminar flow condition is maintained. The flow outside of the fixed layer should then not necessarily be the laminar flow.In this study, hydrodynamic conditions were analyzed using cylindrical cells of the simplest shape. In addition, the possibility of the streaming potential measurement in the turbulent flow was discussed.Observations from the experiments in this study are summarized below:(1)Assuming that there is a layer in which the shear stress is constant near the wall in the turbulent tube flow and that the structures of the electric double layer in the turbulent and laminar flows are the same, the Helmholtz–Smolukowsky equation can be applied in both flow conditions and can express the relation between the flow generation and streaming potential.(2)Hydrodynamic formulas macroscopically treating fluids can accurately express the bulk flow (turbulent core region); however, they cannot precisely express the fluid flow near the wall on the order of Å (whether laminar or turbulent).(3)Zeta-potentials can be measured in the turbulent flow using the streaming potential measurement method.