This is an analytical study on electrohydrodynamic flow through a microchannel, of which the wall is micropatterned with a periodic array of longitudinal or transverse slip-stick stripes with different wall potentials. The flow is driven by steady or time-oscillating hydrodynamic and electric forcings. Four models are presented to study flow in a parallel-plate channel or in a circular channel, where, in each case, the forcings can be steady or oscillating with time of the same frequency. Using the methods of eigenfunction expansion and point collocation, the electric potential and velocity fields are determined by solving the linearized Poisson-Boltzmann equation and the Stokes equation subject to the mixed no-slip or partial-slip boundary conditions. The Onsager reciprocity relations for the fluid and current fluxes are deduced. Attention is paid to some particular kinds of stripe patterns, with a view to revisit and to generalize the theoretical limits made in previous studies on electrokinetic flow over an inhomogeneously slipping surface. In the first part of this thesis, electrohydrodynamic flow through a micropatterned parallel-plate channel is considered. We present a formal proof of the symmetry of the Onsager relations as well as more general results for arbitrary channel height, electric double layer (EDL) thickness, oscillation frequency and also partial-slip length. In the steady-flow regime, when a surface is not 100% uniformly slipping but has a small fraction of area being covered by no-slip slots, the electroosmotic flow (EOF) enhancement can be appreciable reduced. When the EDL is not very thin or the uncharged regions are partial-slipping, there will be a finite inhibition effect on the EOF. Further in the oscillatory-flow regime, we show that, for uniformly charged walls, the effective slip length obtained from the hydrodynamic problem can still be used directly in the EOF as if the wall were uniformly slipping. The presence of uncharged perfectly-slipping stripes will always have a decreasing effect on the EOF, unlike the steady case where it gives no enhancement to the EOF in the thin EDL limit. Furthermore, we confirm the presence of a threshold frequency beyond which the flow will experience significant reduction in magnitude of the tidal volume. Slipping area fraction of the wall and wall potential are shown to have distinct effects on this threshold frequency and the flow response. In the second part, electrohydrodynamic flow through a micropatterned circular channel is considered. Some remarks for EOF in a parallel-plate channel are also applicable to the present problem. Our focus is placed on the effects of the pattern pitch on the flow. When the wall is uniformly charged, the adverse effect on the EOF enhancement due to a small area fraction of no-slip slots can be amplified if the pitch decreases. When the slipping regions are uncharged, reducing the pitch will lead to a greater deviation from the Helmholtz-Smoluchowski limit in the steady-flow regime, yet this effect will be reversed for oscillatory flow. With oppositely charged slipping regions, a net reversed flow is possible, even when the wall is on the average electro-positive. The flow morphology is found to be subject to the combined influence of the geometry of the channel and the electrohydrodynamic properties of the wall. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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A need exists for developing a drying technique for heat-sensitive materials as the conventional heat-based drying methods often produce changes in their physico-chemical properties. This thesis presents a non-thermal electrohydrodynamic (EHD) drying technique that may be used to dry both heat-sensitive and viscous materials. A single point-to-plate EHD system was used in de-watering sugar solutions and glycerin-water mixtures having viscosity between 2 and 22 mPa s. The EHD and forced air (2.5 m s-1) each produced 3 to 5 times higher evaporation rate than the control, which was at ambient temperature and relative humidity. The vapor flux decreased considerably and quadratically compared with the control as viscosity increased, and the dehydration kinetics was linear regardless of viscosity. Agar gels showed a linear relationship between vapor flux and time, and EHD was effective in drying at sub-zero temperatures. The agar temperature during drying was significantly below the ambient, indicating evaporative and entropic cooling.

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Drying is an energy intensive process. The conventional heat-based drying methods often produce changes in the physico-chemical properties of products. A newly developed electrohydrodynamic (EHD) drying technique may be much less destructive to these heat-sensitive materials. This thesis presents comparative analyses of product deterioration in EHD-dried whey proteins, using electrophoresis, differential scanning calorimetry (DSC), and color measurements. Gel electrophoresis showed the disappearance of bands and reduction in band intensities depending upon the temperature of the oven in which the whey protein was dried. The thermograms of the differential scanning calorimeter varied considerably as the temperature of oven-drier increased. EHD, air-drying, and their combination showed no significant change in the electrophoretograms and thermograms compared with the native protein. Color measurements also indicated no significant change in color of EHD-dried whey protein whereas oven-drying produced darker colors from the original. These results allowed us to conclude that physico-chemical properties of whey protein remained intact after drying with EHD.

The distillation of sea water is of importance for the future demands for potable water and other uses in the world. A novel technique, based on electrohydrodynamic (EHD) principles, was used in this realm to desalinate artificial sea water of 3.3% (w/V) concentration. A single point corona electrode was operated at a potential of 5.3 kV (maximum output current 0.3 mA), and was installed one cm over the surface of sea water. The flux of air ions was about 3.0 $ times$ 10$ sp{12}$ cm$ sp{-2}$ s$ sp{-1}$ which produced an average electric wind of 1.72 m s$ sp{-1}$ at the sea water surface. Space charge from a corona electrode generated forces in the media to enhance the evaporation rate by about a factor of three compared with a control freely evaporating sea water. Water vapour was condensed and the condensate's purity was evaluated by chemical and physical analyses. Electrical conductivity and pH of the EHD distillate were found to be 14 $ mu$S cm$ sp{-1}$ and 5.5, respectively. In the absence of Joule heating, the energy required for EHD-distillation was comparable to the latent heat of vaporization of 2.3 $ times$ 10$ sp3$ kJ kg$ sp{-1}$ for water. The steady-state temperature of EHD solution was below that of the corresponding unventilated freely evaporating sea water. Electric wind caused by the ionic drag is considered to be the principal driving force for the enhancement.

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Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xiii, 246 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 131-133).

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