Gabriel Ascanio

A virtual finite element model for centered and eccentric mixer configurations

An implementation of the virtual finite element method with unstructured grids for the modeling of laminar flow in eccentric mixers is presented. The effect of the meshing strategy on the quality of the computed flow field is first carefully investigated with a centered impeller. It is shown that both the number of elements in the vicinity of the impeller and the number of kinematics constraints imposed in the virtual finite element formulation control the computational accuracy. The method is then applied to the case of an eccentric mixer provided with a Rushton turbine showing the capabilities of the proposed approach.

Forward deformable roll coating at high speed with Newtonian fluids

The flow of Newtonian fluids through the deformable nip of a high speed roll coater was experimentally studied. A digital video system was used for the observation of the formation, elongation and break-up of fluid filaments at the exit of the nip and to investigate how misting droplets are ejected to the surroundings. The pressure profile in the nip was obtained by a miniaturized piezoelectric transducer mounted on one of the coater rolls. Experimental results show that both film splitting and air entrainment into the nip can be responsible for misting occurrence when a low load is applied between the rolls. When a high load is applied, misting can be eliminated and a periodic flow is generated in the nip gap.

Cost-effective flow-through nanohole array-based biosensing platform for the label-free detection of uropathogenic E. coli in real time

Rapid, inexpensive and sensitive detection of uropathogenic Escherichia coli (UPEC), a common cause of ascending urinary tract infections (UTIs) including cystitis and pyelonephritis, is critical given the increasing number of cases and its recurrence worldwide. In this paper, we present a label-free nanoplasmonic sensing platform, built with off-the-shelf optical and electronic components, which can detect intact UPEC at concentrations lower than the physiological limit for UTI diagnosis, in real time. The sensing platform consists of a red LED light source, lens assembly, CMOS detector, Raspberry Pi interface in conjugation with a metallic flow-through nanohole array-based sensor. Detection is achieved exploiting nanoplasmonic phenomena from the nanohole arrays through surface plasmon resonance imaging (SPRi) technique. The platform has a bulk sensitivity of 212 pixel intensity unit (PIU)/refractive index unit (RIU), and a resolution in the order of 10-6 RIU. We demonstrate capture and detection of UPEC with a detection limit of ~100 CFU/ml - a concentration well below the threshold limit for UTI diagnosis in clinical samples. We also demonstrate detection of UPEC in spiked human urine samples for two different concentrations of bacteria. This work is particularly relevant for point-of-care applications, especially for regions around the world where accessibility to medical facilities is heavily dependent upon economy, and availability.

THE EFFECT OF THICKENER ON THE RHEOLOGY OF COATING COLORS

The effect of type and amount of thickener on the shear and extensional rheological properties of paper coating colors was studied. A coarse delaminated kaolin clay was used as pigment and either a carboxy methylcellulose (CMC) or an associative gum was used as thickener. The shear properties were evaluated with a stress controlled rheometer and the extensional properties were obtained at high strain rates using an orifice flow meter. The apparent extensional viscosity was compared to the shear viscosity in terms of the Trouton ratio, which was shown to exceed considerably the theoretical value of 3 expected for Newtonian fluids. Suspensions formulated with the associative gum exhibited more pronounced strain hardening at high strain rates than those prepared with CMC.

Viscous Filament Fragmentation in a Turbulent Flow Inside a Stirred Tank

The present work describes the dispersion process of a viscous fluid in water in a cylindrical vessel agitated at Re = 24,000. The formation of viscous filaments and other amorphous structures in turbulent conditions produced in the early stage, before oil drops saturate the continuous phase, is shown. The oil-phase evolution is followed with high-speed video recordings and compared with the flow pattern produce in the liquid bulk. The effects of four kinds of perturbations are identified: intermittences in the radial velocity, turbulent fluctuations, rotation, and the stretching. As a consequence, the viscous-phase experiences instabilities that include random deformation, elongation, hairpin filaments formation, folding, and fragmentation. In the final part of this study, a mechanism describing the drop size reduction has been proposed.

Extensional Properties of Coating Colors at High Strain Rates

Paper coating fluids also called colors are concentrated aqueous suspensions composed mainly of mineral pigments, thickeners, binders and dispersing agents. They are applied onto moving paper web for improving the optical and printing properties. Roll coating is one of the most used technologies for paper coating, however jet coating is currently a promising technology for high-speed processes. Coating colors are submitted to high strain rates in both roll or jet coaters, therefore the extensional viscosity plays a major role in the process. An orifice flowmeter was used for measuring the extensional properties of complex rheology fluids such as coating colors. The principle of this flowmeter is based on the relationship between pressure drop and the flow rate of fluid passing through a small orifice. The flowmeter was firstly calibrated in terms of a dimensionless Euler number as a function of the Reynolds number with Newtonian fluids. The calibration curve was then used to determine the apparent extensional viscosity of coating colors. Results of extensional properties of paper coating colors are presented and compared to shear viscosity. The ratio of extensional to shear viscosity (Trouton ratio) for some coating colors was shown to exceed considerably the theoretical value of 3 expected for Newtonian fluids.Copyright

Mixing Enhancement of Non-Newtonian Fluids Using Unconventional Configurations

Dynamic perturbations and off-centered single impeller configurations have been investigated to reduce mixing time with shear thinning fluids. The use of a color-decolorization technique based on a fast acid-base reaction allowed to measure mixing times and to reveal the presence of both segregated and dead zones. A statistical design approach has been used to evaluate the effect of the impeller position as well as the dynamic conditions and their interactions. Mixing times and flow patterns for shear thinning fluids were presented and compared to conventional operating modes. Homogenization was significantly enhanced when a radial flow impeller was used under both off-centered and dynamic perturbation conditions. In the case of an axial flow impeller, a combination of a large axial displacement with long clockwise times and short counter-clockwise times gave better mixing times.Copyright

Building a three-dimensional model of the upper gastrointestinal tract for computer simulations of swallowing

We aimed to provide realistic three-dimensional (3D) models to be used in numerical simulations of peristaltic flow in patients exhibiting difficulty in swallowing, also known as dysphagia. To this end, a 3D model of the upper gastrointestinal tract was built from the color cryosection images of the Visible Human Project dataset. Regional color heterogeneities were corrected by centering local histograms of the image difference between slices. A voxel-based model was generated by stacking contours from the color images. A triangle mesh was built, smoothed and simplified. Visualization tools were developed for browsing the model at different stages and for virtual endoscopy navigation. As result, a computer model of the esophagus and the stomach was obtained, mainly for modeling swallowing disorders. A central-axis curve was also obtained for virtual navigation and to replicate conditions relevant to swallowing disorders modeling. We show renderings of the model and discuss its use for simulating swallowing as a function of bolus rheological properties. The information obtained from simulation studies with our model could be useful for physicians in selecting the correct nutritional emulsions for patients with dysphagia.

Flow-through nanohole array based sensor implemented on analogue smartphone components

Mobile communications have massively populated the consumer electronics market over the past few years and it is now ubiquitous, providing a timeless opportunity for the development of smartphone-based technologies as point-of-care (POC) diagnosis tools1 . The expectation for a fully integrated smartphone-based sensor that enables applications such as environmental monitoring, explosive detection and biomedical analysis has increased among the scientific community in the past few years2,3. The commercialization forecast for smartphone-based sensing technologies is very promising, but reliable, miniature and cost-effective sensing platforms that can adapt to portable electronics in still under development. In this work, we present an integrated sensing platform based on flow-through metallic nanohole arrays. The nanohole arrays are 260 nm in diameter and 520 nm in pitch, fabricated using Focused Ion Beam (FIB) lithography. A white LED resembling a smartphone flash LED serves as light source to excite surface plasmons and the signal is recorded via a Complementary Metal-Oxide-Semiconductor (CMOS) module. The sensing abilities of the integrated sensing platform is demonstrated for the detection of (i) changes in bulk refractive index (RI), (ii) real-time monitoring of surface modification by receptor-analyte system of streptavidin-biotin.

Numerical Analysis of Peristaltic Flow Through the Pharyngeal Duct

This work was aimed to study numerically the food bolus flow through the pharynx. Using a 2D geometry obtained elsewhere, a three-dimensional code has been developed for the study exclusively of the fluid inside the pharynx considering a non-Newtonian fluid. Three-dimensional geometries of the pharynx at ten different instants using high-order polynomials were generated. For any time range investigated, the shape of the pharynx was introduced into a Cartesian grid by using the technique of immersed boundaries and three-dimensional interpolations. The geometry evolved within this grid and the equations of fluid mechanics were numerically solved. The effect of the pharyngeal walls on the fluid was modeled from the theory of elastic membranes. Flow fields in terms of the axial velocity, pressure, shear rate and viscosity were obtained.Copyright