Oscar Bautista - Academia.edu (original) (raw)

Papers by Oscar Bautista

Micromachines, 2021

In this paper, the combined effect of the fluid rheology, finite-sized ions, and slippage toward ... more In this paper, the combined effect of the fluid rheology, finite-sized ions, and slippage toward augmenting a non-reacting solute’s mass transport due to an oscillatory electroosmotic flow (OEOF) is determined. Bikerman’s model is used to include the finite-sized ions (steric effects) in the original Poisson-Boltzmann (PB) equation. The volume fraction of ions quantifies the steric effects in the modified Poisson-Boltzmann (MPB) equation to predict the electrical potential and the ion concentration close to the charged microchannel walls. The hydrodynamics is affected by slippage, in which the slip length was used as an index for wall hydrophobicity. A conventional finite difference scheme was used to solve the momentum and species transport equations in the lubrication limit together with the MPB equation. The results suggest that the combined slippage and steric effects promote the best conditions to enhance the mass transport of species in about 90% compared with no steric effect...

The Oscillatory electroosmotic flow (OEOF) in power law fluids through a microchannel i... more The Oscillatory electroosmotic flow (OEOF) in power law fluids through a microchannel is studied numerically. A time-dependent external electric field (AC) is suddenly imposed at the ends of the microchannel which induces the fluid motion. The continuity and momentum equations in the x and y direction for the flow field were simplified in the limit of the lubrication approximation theory (LAT), and then solved using a numerical scheme. The solution of the electric potential is based on the Debye-H¨uckel approximation which suggest that the surface potential is small,say, smaller than 0.025V and for a symmetric (z : z) electrolyte. Our results suggest that the velocity profiles across the channel-width are controlled by the following dimensionless parameters: the angular Reynolds number, Reω, the electrokinetic parameter, ¯κ, defined as the ratio of the ch...

World Congress on Mechanical, Chemical, and Material Engineering, 2018

Journal of Applied Fluid Mechanics, 2018

In this study, the isothermal electroosmotic flow of two immiscible electrical conducting fluids ... more In this study, the isothermal electroosmotic flow of two immiscible electrical conducting fluids within a uniform circular microcapillary was theoretically examined. It was assumed that an annular layer of liquid adjacent to the inside wall of the capillary exists, and this in turn surrounds the inner flow of a second liquid. The theoretical analysis was performed by using the linearized Poisson-Boltzmann equations, and the momentum equations for both fluids were analytically solved. The interface between the two fluids was considered uniform, hypothesis which is only valid for very small values of the capillary number, and shear and Maxwell stresses were considered as the boundary condition. In addition, a zeta potential difference and a charge density jump were assumed at the interface. In this manner, the electroosmotic pumping is governed by the previous interfacial effects, a situation that has not previously been considered in the specialized literature. The simplified equations were nondimensionalized, and analytical solutions were determined to describe the electric potential distribution and flow field in both the fluids. The solution shows the strong influence of several dimensionless parameters, such as μr, εr, w  ,   and sf Q , and 1,2  , on the volumetric flow. The parameters represent the ratio of viscosity, the ratio of electric permittivity of both fluids, the dimensionless zeta potential of the microcapillary wall, the dimensionless charge density jump and charge density between both fluids, and the electrokinetic parameters, respectively.

Physics of Fluids, 2018

In this work, non-linear Joule heating effects induced on an electroosmotic flow with patterned s... more In this work, non-linear Joule heating effects induced on an electroosmotic flow with patterned surface charges driven inside of a slit microchannel are analyzed. Here, the movement of the fluid is controlled by placing electro-thermal forces, which are induced through an imposed longitudinal electric field, E0, and the wall electric potential generated by electrodes inserted along the surface of the microchannel wall. For this analysis, the physical properties of the fluid are included as known functions, which depend on the temperature. Therefore, in order to determine the flow, temperature, and electric potential fields together with their simultaneous interactions, the governing equations have to be solved in a coupled manner. For a strong Joule heating, the non-isothermal flow regime reveals that with the presence of thermal gradients, the local electro-thermal and viscous forces, F¯χ and F¯v,χ, are affected in a sensible manner, which results in changes in the flow pattern cau...

Physics of Fluids, 2017

The effective dispersion coefficient of a neutral solute in the combined electroosmotic (EO) and ... more The effective dispersion coefficient of a neutral solute in the combined electroosmotic (EO) and magnetohydrodynamic (MHD)-driven flow of a Newtonian fluid through a parallel flat plate microchannel is studied. The walls of the microchannel are assumed to have modulated and low zeta potentials that vary slowly in the axial direction in a sinusoidal manner. The flow field required to obtain the dispersion coefficient is solved using the lubrication approximation theory. The solution of the electrical potential is based on the Debye-Hückel approximation for a symmetric (Z:Z) electrolyte solution. The EO and MHD effects, together with the variations in the zeta potentials of the walls, are observed to notably modify the axial distribution of the effective dispersion coefficient. The problem is formulated for two cases of the zeta potential function. Note that the dispersion coefficient primarily depends on the Hartmann number, on the ratio of the half height of the microchannel to the ...

Micromachines, 2017

In this work, a non-isothermal electroosmotic flow of two immiscible fluids within a uniform micr... more In this work, a non-isothermal electroosmotic flow of two immiscible fluids within a uniform microcapillary is theoretically studied. It is considered that there is an annular layer of a non-Newtonian liquid, whose behavior follows the power-law model, adjacent to the inside wall of the capillary, which in turn surrounds an inner flow of a second conducting liquid that is driven by electroosmosis. The inner fluid flow exerts an interfacial force, dragging the annular fluid due to shear and Maxwell stresses at the interface between the two fluids. Because the Joule heating effect may be present in electroosmotic flow (EOF), temperature gradients can appear along the microcapillary, making the viscosity coefficients of both fluids and the electrical conductivity of the inner fluid temperature dependent. The above makes the variables of the flow field in both fluids, velocity, pressure, temperature and electric fields, coupled. An additional complexity of the mathematical model that describes the electroosmotic flow is the nonlinear character due to the rheological behavior of the surrounding fluid. Therefore, based on the lubrication theory approximation, the governing equations are nondimensionalized and simplified, and an asymptotic solution is determined using a regular perturbation technique by considering that the perturbation parameter is associated with changes in the viscosity by temperature effects. The principal results showed that the parameters that notably influence the flow field are the power-law index, an electrokinetic parameter (the ratio between the radius of the microchannel and the Debye length) and the competition between the consistency index of the non-Newtonian fluid and the viscosity of the conducting fluid. Additionally, the heat that is dissipated trough the external surface of the microchannel and the sensitivity of the viscosity to temperature changes play important roles, which modify the flow field.

Non-isothermal flow of a variable viscosity non-Newtonian fluid between a pair of counter-rotatin... more Non-isothermal flow of a variable viscosity non-Newtonian fluid between a pair of counter-rotating cylinders with equal speed and equal size rolls is analyzed to study theoretically the effect of viscous dissipation on the exiting sheet thickness for the power law plastic fluid model. A regular perturbation method based on the lubrication approximation theory is used to uncouple the momentum and the energy equations to provide numerical results of the effects of temperature profiles on the final sheet thickness. The heat transfer analysis of Calendering Non-Newtonian fluids is an important area on polymer processing. Here, we are interested in studying the heat transfer phenomena on calendering Non-Newtonian process using the power law model. This model, takes into account the effects of temperature on the consistency index, also the viscous dissipation. In this study the important parameters are the Nahme-Griffith number as a perturbation parameter, this one relates the temperature...

Journal of Porous Media, 2015

In this work we treat theoretically the conjugate film-condensation process on a vertical fin emb... more In this work we treat theoretically the conjugate film-condensation process on a vertical fin embedded in a homogeneous porous medium filled with a saturated vapor. The presence of the solid matrix results in the ocurrence of a two-phase flow region governed by gravity and capillarity. In order to predict the influence of surface tension on the condensed thickness, an overall energy balance in the liquid, the two-phase region and through the fin was conducted. Therefore, the conservation equations of mass, momentum and energy for the condensed film, together with the energy equation in the fin are reduced to a nonlinear system of two differential equations containing five dimensionless numbers: the Bond number, Bo; the Jakob number, Ja; the Rayleigh number Ra; a conjugate heat transfer parameter, α, which represents the competition between the heat conducted by the fin in the longitudinal direction and the heat conducted through the condensate film, and the aspect ratio of the fin, e. Using the limit of Ja ≪ 1 with Ra ≫ 1, and finite values of Bo, together with the boundary layer approximation for the film condensation process, the nondimensional heat transfer or Nusselt number and the overall mass flow rates of the condensed fluid have been obtained as functions of the involved dimensionless parameters.

Journal of Applied Mathematics, 2015

We obtain asymptotic formulas for the reflection/transmission coefficients of linear long water w... more We obtain asymptotic formulas for the reflection/transmission coefficients of linear long water waves, propagating in a harbor composed of a tapered and slender region connected to uniform inlet and outlet regions. The region with variable character obeys a power-law. The governing equations are presented in dimensionless form. The reflection/transmission coefficients are obtained for the limit of the parameterκ2≪1, which corresponds to a wavelength shorter than the characteristic horizontal length of the harbor. The asymptotic formulas consider those cases when the geometry of the harbor can be variable in width and depth: linear or parabolic among other transitions or a combination of these geometries. For harbors with nonlinear transitions, the parabolic geometry is less reflective than the other cases. The reflection coefficient for linear transitions just presents an oscillatory behavior. We can infer that the deducted formulas provide as first approximation a practical referen...

ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels: Parts A and B, 2010

In this work we solve numerically the conjugated heat transfer problem of a non-Newtonian fluid a... more In this work we solve numerically the conjugated heat transfer problem of a non-Newtonian fluid and solid walls in a microchannel under the influence of pressure and electro-osmotic forces. The velocity field is determined taking into account a hydrodynamically fully-developed flow and a constitutive relation based in a viscoelastic rheological model with a simplified Phan-Thien Tanner fluid. The numerical process results in solid and fluid temperature distributions. Is shown the influence of nondimensional parameters involved in the analysis on the conjugated heat transfer problem: an indicator of viscoelastic behavior, the Peclet number, a normalized power generation term being the ratio of heat flow from the external wall to the Joule heating, a conjugation term which determines the basic heat transfer regimes between fluid and solid sections in the microchannel. For the flow field: the ratio of pressure forces to the electro-osmotic forces acts on flow as a drag reducer and drag...

The Open Ocean Engineering Journal, 2009

In the present work, we have studied the performance of an open compression chamber with compress... more In the present work, we have studied the performance of an open compression chamber with compressed air and driven by an oscillating water column. Recognizing the existence of a free-surface for the water column, the interface position between the trapped-air and water volume-together with the motion of the column-, is described by a non-linear energy equation that reflects the main dynamic characteristics. The above governing equation is posed in dimensionless form and solved by conventional numerical methods. In addition, a theoretical approximation of the first order in to predict the resonant frequency of the oscillatory system is derived to complete the analysis. The numerical results of the above governing equation serve us to estimate the dimensionless work done by the oscillating water column as a function of three dimensionless parameters: a characteristic Froude number, , and two equivalent quasi-geometric parameters, and , defined below. The predictions show that the influence of the geometry and the involved physical parameters exert a great influence on work generation into the air-chamber.

Computational Methods and Experimental Measurements XV, 2011

In this work, we have theoretically re-visited the capillary rise process into a circular tube fo... more In this work, we have theoretically re-visited the capillary rise process into a circular tube for very short time scales, retaining in this manner, the physical influence of the inertial effects. We use the boundary-layer technique or matched asymptotic expansion procedure in order to treat this singular problem by identifying two appropriate time scales: one short time scale related with inertial effects, , and the other, , the large scale which is basically associated with imbibition effects. Considering that the well-known Washburn's law was derived by neglecting the inertial effects, the corresponding solution has a singular behavior for short times, which is reflected by an infinite mass flow rate. Then, for this purpose we derive a zero-order solution which is enough to avoid the singular behavior of the solution. In this manner, the Washburn's solution represents only the external solution only valid for the large time scale. The above analytical result is compared with a numerical solution including the case when the contact angle between the meniscus and the inner surface of the capillary tube becomes a dynamic contact angle. On the other hand, the presence of inertial effects can induce oscillations of the imbibition front which are controlled by the dynamic contact angle. Therefore, in the present work we predict a global asymptotic formula for the temporal evolution of the height of the liquid. In order to show the importance of the inertial terms, we present this evolution for different values of the dimensionless parameters involved in the analysis.

International Journal of Thermal Sciences, 2005

In this paper, we treat the unsteady entropy generation rate due to an instantaneous internal hea... more In this paper, we treat the unsteady entropy generation rate due to an instantaneous internal heat generation in a solid slab. Following the basic ideas developed by Bejan [Heat Transfer, Wiley, 1993], we conduct a multiple-scale analysis identifying the "early" and "late" regimes to derive, in a very simple way, the nondimensional unsteady temperature profile for small values of the Biot number, Bi. In consequence, the nondimensional spatial average entropy generation rate per unit volume, Φ and the corresponding average steady-state entropy generation rate, Ψ , were evaluated for different values of the nondimensional heat generation parameter β. This parameter represents physically the ratio of the temperature of the solid slab (due to the internal heat generation) to the fluid temperature. We show that for the assumed values of this parameter β, the nondimensional temperature and entropy generation rate variables present a very sensible dependence between both parameters, indicating a direct relationship between the basic heat transfer mechanics: heat conduction, heat convection and internal heat generation.

Applied Ocean Research, 2011

A singular perturbation analysis based on the WKB technique to study the hydrodynamic performance... more A singular perturbation analysis based on the WKB technique to study the hydrodynamic performance of periodic ocean waves that are incident on an open parabolic channel of constant depth is proposed. We derive a linear model to predict the propagation of the long ocean waves into the channel. In this manner, the spatial distribution for the surface elevation of the ocean waves inside the channel as a function of two dimensionless parameters, namely, a kinematical parameter, κ and a geometrical parameter ε, is governed by a second-order ordinary differential equation. The kinematical parameter κ denotes the ratio of the potential head, due to gravity, to the kinetic head of the ocean waves along the longitudinal axis of the parabolic channel. Meanwhile, ε is a dimensionless geometrical parameter that represents a characteristic ratio of the parabolic channel. Using matching conditions, simple expressions for the reflection and transmission coefficients are obtained.

Applied Mathematical Modelling, 2013

ABSTRACT An analysis of calendering for an incompressible Newtonian fluid flow, with pressure-dep... more ABSTRACT An analysis of calendering for an incompressible Newtonian fluid flow, with pressure-dependent viscosity is studied theoretically under assumptions of isothermal conditions. We predict the influence of pressure-dependent viscosity on the exiting sheet thickness of the sheet of fluid from the gap. The dimensionless mass and momentum balance equations, which are based on lubrication theory, were solved for the velocity and pressure fields by using perturbation techniques, where the exiting sheet thickness represents an eigenvalue of the mathematical problem. When the above variables were obtained, the dimensionless exiting sheet thickness was determined by considering the influence of the pressure variations in the calendering process. Moreover, quantities of engineering interest are also calculated, which include the cylinder-separating force and power required to drive both cylinders in terms of the geometrical and kinematical parameters of the system. The results show that the inclusion of pressure-dependent viscosity effect increases the leave-off distance and consequently the dimensionless exiting sheet thickness in comparison with the case of pressure-independent viscosity.

International Journal of Thermal Sciences, 2011

Applied Mathematical Modelling, 2010