Experimental and Analytical Investigations of the Relative and Interactive Effects of Physicochemical Fluid Characteristics on the Incipient Motion of Granular Particles Under Laminar Flow Conditions
Open Access
- Author:
- Adams, Benjamin T.
- Graduate Program:
- Civil Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 16, 2016
- Committee Members:
- Ming Xiao, Dissertation Advisor/Co-Advisor
Ming Xiao, Committee Chair/Co-Chair
Tong Qiu, Committee Member
Shimin Liu, Committee Member
Zuleima T Karpyn, Outside Member
Patrick Joseph Fox, Program Head/Chair - Keywords:
- soil erosion
incipient motion
pH
ionic strength
viscosity
laminar
granular - Abstract:
- This dissertation first presents the evolutionary development of an experimental methodology for studying the relative and interactive effects of three physicochemical fluid characteristics (viscosity, pH, and ionic strength) on the incipient motion of granular particles under laminar flow conditions. Critical flow velocity was used to quantify the relative erosive capacity of the test fluids and a major goal throughout the research was to decrease the variability in its experimental quantification. This goal guided four phases of evolutionary developments in the methodological and analytical design and implementation. A statistical design of experiments, the response surface methodology (RSM), was used to guide the design and implementation of 20 test fluids with various levels of the three fluid characteristics. Incipient motion of a highly spherical glass bead positioned atop a specially designed and manufactured support pocket within a flow cell was observed using a microscope video camera. The critical flow velocity was quantified for seven repeat trials for each of the 20 test fluids. Regression analyses were conducted on the results to generate a statistical model to describe the relative effects of the three factors and their interactions. An analytical study was then conducted to provide a theoretical explanation of the experimental observations. The main conclusions are as follows: (1) viscosity, pH, and their two-way interaction were determined to be the factors most influential on critical velocity and viscosity was shown to be of greater influence than pH; ionic strength was found to be of little impact; (2) viscosity and pH interacted such that when pH was higher (at 10.5) the viscosity had greater influence than when the pH was lower (at 3.5); (3) at a viscosity of approximately 0.007 g/cm·s, critical velocity remained relatively unchanged throughout the range of pH (3.5 to 10.5); (4) for viscosities greater than 0.007 g/cm·s, critical velocity decreased with an increase in pH while for viscosities less than 0.007 g/cm·s, the effect of pH on critical velocity reversed; (5) at pH values from 3.5 to 10.5, critical velocity consistently decreased as viscosity increased; (6) both electrostatic and van der Waals forces are strongly dependent on the separation distance between two particles; (7) as pH increases and zeta potential decreases, the electrostatic force (repulsion) between a test particle and a bed of particles increases and the test particle is more likely to be mobilized, i.e., the critical flow velocity decreases; (8) as ionic strength increases, the repulsive electrostatic force generally decreases and could cause the net surface force on the test particle to change from repulsion to attraction. Thus, the test particle becomes less likely to be mobilized, i.e., critical flow velocity increases; (9) as zeta potential decreases from -10 mV to -40 mV, the electrostatic force increases by one order of magnitude and becomes more significant when compared with the van der Waals force. However, the trend of electrostatic force variation with ionic strength remains unchanged; (10) as pH increases, the electrostatic force increases, and ionic strength has a greater effect on the mobilization of particles; (11) changes in fluid temperature between 0°C and 50°C do not significantly affect the electrostatic force with various ionic strength and zeta potential.