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In this paper, numerical simulation of flow field in three types of standard new design cyclone separators namely 1D2Dn, 1D3Dn and 2D2Dn are investigated. In these standard cyclones, the length of cylindrical top part of the body is equal to 1, 1 and 2 times of the body diameter, respectively; and the length of the cylindrical bottom part is 2, 3 and 2 times of the body diameter. The new design cyclone is based on the idea of improving cyclone collection efficiency and pressure drop by increasing the vortex length. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). Results show that among the three standard new design cyclones, cyclone 2D2Dn has the highest efficiency followed by 1D3Dn one with about only 2% lower efficiency. Cyclone 1D2Dn possesses the lowest efficiency among all. Similarly, the highest pressure drop occurs in cyclone 2D2Dn. Cyclones 1D3Dn and 1D2Dn followed 2D2Dn one with a marked difference of about 20%. In result section, the details of the flow field including velocity, pressure contours, turbulence, velocity vectors and particle trajectory will be presented.

Long fiber-reinforced composite materials consist of continuous fibers with high strength and modulus embedded in either a thermoset or thermoplastic matrix. The resulting composite material provides a combination of properties that cannot be achieved with either of the constituents acting alone. In composite structures, fibers are the primary load-carrying element, whereas the matrix transfers stress to and between the fibers while protecting them from adverse environmental conditions and mechanical damages. While thermosetting matrices provide a high level of protection against water permeation, exposure to moisture may still be significant in certain thermoplastics. Therefore, the effect of moisture on the reinforcing elements and the degradation rate may be considerable. The presented study investigated the effects of environmental aging conditions on different commercially available continuous fibers, i.e., glass fiber, carbon fiber, and basalt fiber. The fibers were soaked in water at room and elevated temperature to investigate the degradation mechanisms and, ultimately, the mechanical performance of the fibers. Mechanical testing was performed with wet fibers and dried fibers after aging. In addition, scanning electron microscopy was employed to explore the responsible mechanism for fiber degradation by environmental aging.

A systematic study on the formation of thin liquid films (TLFs) of n-dodecane, as an intervening liquid phase in aqueous surfactant solution, was performed using a modified 3D-printed Scheludko-cell (MSC). The formation and stability of TLFs are electrically detected using the current density-voltage (J-Ψ) characteristics of the system, and it is confirmed by in-situ visualization of TLFs. The conductivity of the TLFs is measured using the J-Ψ curve and resistors in a series model of the system. The induced conductivity of the film is measured for different concentrations of potassium chloride (KCl) and sodium dodecyl sulfate (SDS) aqueous solutions. We monitored an increase in TLF conductivity due to the accumulation of inorganic hydrophilic ions like (K+ or Cl−) and adsorption of amphiphilic anion of dodecyl sulfate to the interface. The higher rate of increase in the TLF conductivity in the case of SDS is attributed to the ability of amphiphilic ions to pass through a so-called unscreened potential in the vicinity of oil-aqueous solution interface leading to an unscreenable potential at the boundary of the TLF. The predicted adsorption time-scale of surfactants using the MSC cell in ionic liquid (IL) phase, at O/W interface, is found to be in good agreement with the dynamic interfacial tension test results.

Deformation of thin viscous liquid films exposed to a transverse thermal gradient results in Bénard–Marangoni instability, which would lead to the formation of micro- and nano-sized features. Linear and nonlinear analyses are performed to investigate the thermally induced pattern formation in shear thinning and shear thickening liquid films. The so-called thin film (TF) equation is re-derived to include viscosity variations using the power-law (PL) model. The characteristic wavelength for the growth of instabilities is found using a linear stability analysis of the PL-TF equation. A finite-difference-based discretization scheme and adaptive time step solver are used to solve the PL-TF equation for the nonlinear numerical model. The results show that the rheological property affects the timescale of the process and the size and final shape of the formed features. The fastest growth pillar reaching the top substrate in a shear thickening fluid is shorter than both the shear thinning and the Newtonian fluid cases. Moreover, morphological changes between patterns of shear thinning and shear thickening fluids are correlated with local viscosity variations. The number of formed pillars considerably increases with the increasing flow behavior index. The existing model also predicts the formation of pillars and bicontinuous structures at very low and high filling ratios.

Creating well-ordered, submicron-sized pillars have been stated as main limitation for electrically induced patterning of nanofilms (thickness 100 nm) [1] . In our previous works, it was shown that the aspect ratio of formed nanopillars was increased to about 0.35 when thermocapillary induced instabilities (Thermally Induced Patterning, TIP) is combined with electrodynamics instabilities (Electrically Induced Patterning, EIP). However, further reduction of pillar size resulted in a coarse and randomly distributed pillars [2] , [3] . Here, the reflowing of initially prepatterned nanofilms are examined in the EIP and combined EIP-TIP process to create a well-ordered and high aspect ratio nanopillar arrays without sacrificing the fidelity of the final structure. The long-wave approximation is used to simplify the governing equations and boundary conditions leading to a fourth order nonlinear partial differential equation called thin film equation that describes the spatio-temporal evolution of the interface. The mechanism of pattern reflowing is discussed for both linear (initial) and nonlinear (long-term) deformations in EIP and EIP-TIP process. The optimum initial pattern width, height and the center-to-center distance is found based on the characteristic wavelength for growth of instabilities predicted by linear stability analysis and nonlinear simulation results.

Hydrogel-facilitated phase separation (HFPS) has recently been applied to make microstructured porous membranes by modified phase separation processes. In HFPS, a soft lithographically patterned hydrogel mold is used as a water content source that initiates the phase separation process in membrane fabrication. However, after each membrane casting, the hydrogel content changes due to the diffusion of organic solvent into the hydrogel from the original membrane solution. The absorption of solvent into the hydrogel mold limits the continuous use of the mold in repeated membrane casts. In this study, we investigated a simple treatment process for hydrogel mold recovery, consisting of warm and cold treatment steps to provide solvent extraction without changing the hydrogel mold integrity. The best recovery result was 96%, which was obtained by placing the hydrogel in a warm water bath (50 &deg, C) for 10 min followed by immersing in a cold bath (23 &deg, C) for 4 min and finally 4 min drying in air. This recovery was attributed to nearly complete solvent extraction without any deformation of the hydrogel structure. The reusability of hydrogel can assist in the development of a continuous membrane fabrication process using HFPS.

Electrohydrodynamic (EHD) and thermocapillary (TC) forces are used to destabilize the interface of ultra-thin liquid films and create submicron sized features. EHD instabilities result from normal component of Maxwell stress while the TC induces shear stress to the interface. In this study the accuracy of linear stability (LS) analysis for the prediction of final structures which undergo non-linear stages during pattern evolution are investigated by using new normalizing factors. Then the reason for the deviation between LS analysis and non-linear simulation results are discussed. It is found that despite the positive effect of TC in reducing the structure sizes compared to the EHD case, it causes lateral movement of pillars which results in faster coarsening in later stages of pattern formation. To control the movement of patterns and create well-ordered features, non-uniform electrostatic and TC induced instabilities of the film are examined by using ridge and square block shaped electrodes.

Microporous membranes are permeable substrates primarily used for wastewater treatment and desalination. The lab-fabricated and commercial polyethersulfone (PES) microporous membranes are characterized for permeability by filtration test, cross-section thickness by SEM images, surface roughness by AFM data, and hydrophilicity by dynamic contact angle measurements. The choice of membranes of different nominal pore sizes ensures a diverse range of imbibition time scale. The hydrodynamic permeability of these membranes is calculated based on the cross-section thickness and its resistance, which is obtained from filtration test. A lubrication-based mathematical model using precursor film approximation is used to study the behavior of droplet spreading and imbibition on the membrane surface. The theoretical disjoining pressure is also shown to be related to its numerical value obtained from the mathematical model, in the case of apolar and polar interactions. The effective permeability obtained by validating the numerical predictions with contact angle experiments, is then matched to hydrodynamic permeability by introduction of lubrication ratio at the equilibrium stage.

This study focuses on a detailed analysis of thermally induced Benard convection, thermocapillary instability, and interfacial deformation of a nanofilm. The dynamics, instability, and morphological evolution of a thin liquid film investigated using a volume of fluid (VOF) numerical scheme that incorporates the Marangoni stress to model the gas–liquid interface deformation. The results obtained from VOF are then compared with those of the “thin-film” model in many cases to find an accurate model for predicting the characteristic wavelength for the growth of instabilities. We also present a correlation to predict the relation between the characteristic wavelength found by VOF numerical results and the analytical linear stability analysis predictions. This is followed by examining the protrusion width and the distance between the protrusions on the structures’ final shape and interface evolution time. Finally, linear theoretical relations for the formation of secondary pillars are presented based on the width of protrusions, their separation distance, and the inverse filling ratio. The results show that the number of pillars increases when the width and distance between two protrusions are greater than a critical value.

To improve the electrically assisted patterning process and create smaller sized features with the higher active surface area, the combined thermocapillary-electrohydrodynamic (TC-EHD) instability of liquid nanofilms is considered. First, the 3-D thin film equation is rederived for nonisothermal films and then the influential factors on the dynamics and stability of thin liquid film are found using linear stability (LS) analysis. Nonlinear studies are also conducted to investigate the long-time evolution of the interface using an in-house developed Fortran code employing high order finite difference and adaptive time step solver for the spatial and time derivatives. The number density of pillars (columnar raised structure) formed in 1 μm(2) area is significantly increased compared to the EHD base-case and nanosized pillars are created due to the thermocapillary effects. Relative interface area increases of up to 18% due to this pattern miniaturization are realized. It is also found that increase in the thermal conductivity ratio of layers changes the mechanism of pattern formation resulting in nonuniform and randomly distributed micro pillars being generated.

An analytical solution is developed for the unsteady flow of fluid through a parallel rotating plate microchannel, under the influence of electrokinetic force using the Debye–Huckel (DH) approximation. Transient Navier–Stokes equations are solved exactly in terms of the cosine Fourier series using the separation of variables method. The effects of frame rotation frequency and electroosmotic force on the fluid velocity and the flow rate distributions are investigated. The rotating system is found to have a damped oscillatory behavior. It is found that the period and the decay rate of the oscillations are independent of the DH parameter (κ). A time dependent structure of the boundary layer is observed at higher rotational frequencies. Furthermore, the rotation is shown to generate a secondary flow and a parameter is defined (β(t)) to examine the ratio of the flow in the y and x directions. It showed that both the angular velocity and the Debye–Huckel parameters are influential on the induced transient secondary flow in the y direction. At high values of the Debye–Huckel parameter and the rotation parameter the flow rates in the x and y directions are found to be identical. The analytical solution results are found to be in good agreement with the numerical method results and previously published work in this field.

The underlying mechanism of thermal induced patterning is investigated using a numerical phase-field model. Research on the subject has been mostly restricted to lubrication approximation, which is only valid for the cases that the initial film thickness is smaller than the characteristic wavelength of induced instabilities. Since the long-wave approximation is no longer valid in the later stages of pattern evolution, we employed the full governing equations of fluid flow and the thermally induced Marangoni effect to track the interface between the polymer film and the air bounding layer. Conducting a systematic study on the impact of influential parameters, we found that an increase in the temperature gradient, thermal conductivity ratio, and initial thickness of the thin film resulted in shorter processing time and faster pattern formation. Additionally, the contact angle between the polymer film and the bounding plates showed a significant effect on the shape of created features. Compared to the reported experimental observation by Dietzel and Troian [“Mechanism for spontaneous growth of nanopillar arrays in ultrathin films subject to a thermal gradient,” J. Appl. Phys. 108, 074308 (2010)], our numerical modeling provided a more accurate prediction of the characteristic wavelength against the linearized model currently used in the literature. The numerical findings in this study provide valuable insight into thermal-induced patterning, which can be a useful guide for future experimental works.

The dynamics, instability, and pattern formation of thermally triggered thin liquid films are investigated numerically under a long-wave limit approximation. To determine the mechanisms responsible for instability growth and pattern formation in confined heated nanofilms, acoustic phonon (AP) and thermocapillary (TC) models are examined using both linear and nonlinear analyses. Under uniform heating conditions, both AP and TC models predict the formation of raised columnar structures (pillars) and bicontinuous structures for very low and high filling ratios defined as the ratio of the initial film thickness to the plate separation distance, ${D}^{\ensuremath{-}1}$. A transition threshold is observed when $D\ensuremath{\approx}2.5$. However, the TC model predicts smaller features for larger $D$, whereas the opposite prediction applies for the AP model. Under spatially variable cooling conditions involving a patterned top plate, both TC and AP models exhibit similar predictions: pillars form under the top plate protrusions. When the heating is spatially variable, the lower plate is patterned; the AP model predicts pillar formation above ridges, whereas the TC model predicts pillar formation above the valleys.

In this study, an analytical model is provided to describe the filling dynamics of a capillary filled with a viscous fluid containing spinning particles. The aim is to demonstrate the effect of angular momentum on the capillary filling dynamics of molecular fluids which has not been explored before. The presence of spinning particles generates additional coefficients of viscosity, namely, spin viscosity and vortex viscosity, which couples rotational and translational movements. Three different time stages have been noticed during the capillary filling phenomenon: inertia force dominated, visco-inertial, and viscous-dominated regions. The last two regions are found to be mainly affected by the spinning particles. An increase in the spin and vortex viscosities is found to increase the viscous force and thus reduce the front position of the moving liquid. The results of this study are validated using the literature no-angular-momentum (NAM) base-case results and an excellent agreement is observed.

The influence of electrostatic heterogeneity on the electric-field-induced destabilization of thin ionic liquid (IL) films is investigated to control spatial ordering and to reduce the lateral dimension of structures forming on the films. Commonly used perfect dielectric (PD) films are replaced with ionic conductive films to reduce the lateral length scales to a sub-micron level in the EHD pattering process. The 3-D spatiotemporal evolution of a thin IL film interface under homogenous and heterogeneous electric fields is numerically simulated. Finite differences in the spatial directions using an adaptive time step ODE solver are used to solve the 2-D nonlinear thin film equation. The validity of our simulation technique is determined from close agreement between the simulation results of a PD film and the experimental results in the literature. Replacing the flat electrode with the patterned one is found to result in more compact and well-ordered structures particularly when an electrode with square block protrusions is used. This is attributed to better control of the characteristic spatial lengths by applying a heterogeneous electric field by patterned electrodes. The structure size in PD films is reduced by a factor of 4 when they are replaced with IL films, which results in nano-sized features with well-ordered patterns over the domain.

In the electrohydrodynamic (EHD) patterning process, electrostatic destabilization of the air-polymer interface results in micro- and nano-size patterns in the form of raised formations called pillars. The polymer film in this process is typically assumed to behave like a perfect dielectric (PD) or leaky dielectric (LD). In this study, an electrostatic model is developed for the patterning of an ionic liquid (IL) polymer film. The IL model has a finite diffuse electric layer which overcomes the shortcoming of assuming infinitesimally large and small electric diffuse layers inherent in the PD and LD models respectively. The process of pattern formation is then numerically simulated by solving the weakly nonlinear thin film equation using finite difference with pseudo-staggered discretization and an adaptive time step. Initially, the pillar formation process in IL films is observed to be the same as that in PD films. Pillars initially form at random locations and their cross-section increases with time as the contact line expands on the top electrode. After the initial growth, for the same applied voltage and initial film thickness, the number of pillars on IL films is found to be significantly higher than that in PD films. The total number of pillars formed in 1 μm(2) area of the domain in an IL film is almost 5 times more than that in a similar PD film for the conditions simulated. In addition, the pillar structure size in IL films is observed to be more sensitive to initial film thickness compared to PD films.

The effect of electrostatic force on the dynamics, morphological evolution, and drainage time of ultrathin liquid bilayers (100 nm) are investigated for perfect dielectric-perfect dielectric (PD-PD) and ionic liquid-perfect dielectric (IL-PD) bilayers. The weakly nonlinear "thin film" equation is solved numerically to obtain spatiotemporal evolution of the liquid-liquid interface responses to transverse electric field. In order to predict the electrostatic component of conjoining/disjoining pressure acting on the interface for IL-PD bilayers, an analytical model is developed using the nonlinear Poisson-Boltzmann equation. It is found that IL-PD bilayers with electric permittivity ratio of layers (lower to top), εr, greater than one remain stable under an applied electric field. An extensive numerical study is carried out to generate a map based on εr and the initial mean thickness of the lower layer. This map is used to predict the formation of various structures on PD-PD bilayer interface and provides a baseline for unstable IL-PD bilayers. The use of an ionic liquid (IL) layer is found to reduce the size of the structures, but results in polydispersed and disordered pillars spread over the domain. The numerical predictions follow similar trend of experimental observation of Lau and Russel. (Lau, C. Y.; Russel, W. B. Fundamental Limitations on Ordered Electrohydrodynamic Patterning; Macromolecules 2011, 44, 7746-7751).

Spatiotemporal evolution of liquid-liquid interface leading to dewetting and pattern formation is investigated for thin liquid bilayeres subjected to the long range electrostatic force and the short range van der Waals forces. Based on the 2D weakly non-linear thin film equation three dimensional structure evolution is numerically simulated. A combined finite difference for the spatial dimensions and an adaptive time step ODE solver is used to solve the governing equation. For initially non-wetting surfaces, the stabilizing effects of viscosity and interfacial tension and the destabilizing effect of the Hamaker constant are investigated. Electrostatic interaction is calculated analytically for both perfect dielectric-perfect dielectric and ionic conductive-perfect dielectric bilayers. Ionic conductive-perfect dielectric bilayers based on the electric permittivity ratio of layers are found to be stabilized or deformed in response to the applied external electric field.Copyright © 2014 by ASME

The present article encompasses the laminar ascending flow and combined mixed (free and forced) convective-radiative heat transfer within symmetrically heated vertical parallel plates. Radiative heat transfer between two opposite walls is considered and the gas is assumed as gray, absorbing, emitting and scattering. Elliptic governing equations for the case of buoyancy assisted flow are solved numerically employing a home-made CFD code based on the finite volume method. The radiative transfer equation is solved using the discrete ordinates method, adopting its S6 quadrature scheme. The influence of two important radiative parameters, namely, wall emissivity and scattering albedo, while the extinction coefficient is either constant or not, on the occurrence of flow reversal, fanning friction coefficient, flow and thermal fields, is investigated. Present results show that the occurrence of reversed flow enhances both heat transfer and the fanning friction coefficient, and the radiation mode amplifies heat transfer, while reducing the fanning friction coefficient. As wall emissivity increases from 0 to 1, effects of radiation on flow and thermal fields rise. However, there is no linear relationship for the whole range of ε. As scattering albedo varies between 0 and 0.75, radiation effects on flow and thermal fields for the constant and variable extinction coefficient are entirely opposite.