# Manuel A. AlvesUniversity of Porto | UP · Departamento de Engenharia Química

Manuel A. Alves

PhD

## About

208

Publications

36,815

Reads

**How we measure 'reads'**

A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more

5,976

Citations

Citations since 2016

Introduction

Additional affiliations

May 2004 - present

September 1995 - present

## Publications

Publications (208)

This work addresses the conjugate heat transfer of a simplified PTT fluid flowing past an unbounded sphere in the Stokes regime (Re = 0.01). The problem is numerically solved with the finite-volume method assuming axisymmetry, absence of natural convection and constant physical properties. The sphere generates heat at a constant and uniform rate, a...

This work presents new semi-analytical solutions for the combined fully developed electro-osmotic pressure-driven flow in microchannels of viscoelastic fluids, described by the generalised Phan-Thien–Tanner model (gPTT) recently proposed by Ferrás et al. (Journal of Non-Newtonian Fluid Mechanics, 269:88–99, 2019). This generalised version of the PT...

Complex fluids exist in nature and are continually engineered for specific applications involving the addition of macromolecules to a solvent, among other means. This imparts viscoelasticity to the fluid, a property responsible for various flow instabilities and major modifications to the fluid dynamics. Recent developments in the numerical methods...

We employ a state-of-the-art microfabrication technique (selective laser-induced etching) to fabricate a set of axisymmetric microfluidic geometries featuring a 4:1 contraction followed by a 1:4 downstream expansion in the radial dimension. Three devices are fabricated: the first has a sudden contraction followed by a sudden expansion, the second f...

In this work, we reveal the flow dynamics of Vitreous Humour (VH) gel and liquid phases during saccadic movements of the eye, considering the biofluids viscoelastic character as well as realistic eye chamber geometry and taking into account the saccade profile. We quantify the differences in the flow dynamics of VH gel and liquid phases using visco...

Electro-elastic instabilities in electro-osmotic contraction/expansion flows (EOF) of viscoelastic fluids are experimentally investigated in this work. Several microchannel configurations are used, including the cases with hyperbolic-shaped contractions followed by an abrupt expansion, or abrupt contractions followed by a hyperbolic-shaped expansio...

This work addresses the conjugate heat transfer of a simplified PTT fluid flowing past an unbounded sphere in the Stokes regime ($Re = 0.01$). The problem is numerically solved with the finite-volume method assuming axial symmetry, absence of natural convection and constant physical properties. The sphere generates heat at a constant and uniform ra...

In this work, we present a systematic numerical investigation of the 1:4 planar expansion creeping flow under the influence of slip boundary conditions for Newtonian and viscoelastic fluids, the latter modeled by the simplified Phan–Thien–Tanner constitutive model. The linear and nonlinear Navier slip laws were considered with the dimensionless sli...

The capillary thinning dynamics can be considered one of the fingerprints of extensionally-dominated viscoelastic flows. Notably, the rheological behavior of complex fluids in extensional flow has been investigated in different rheometric devices, as for instance in the Capillary Breakup Extensional Rheometer (CaBER), the Dripping-onto-Substrate (D...

This book presents the proceedings of IBEREO 2019. This conference addresses the most recent trends in rheology with a special emphasis on both basic science and industrial applications. Papers presented cover different perspectives, like experimental, theoretical and numerical. Topics include Microfluidics and microrheology, Food, Cosmetics and Ph...

Microfluidic contraction devices have been proposed for extensional rheometry measurements, in particular as a useful method for determining the extensional viscosity of low elasticity solutions. The first commercially available “Extensional Viscometer-Rheometer-On-a-Chip ” (e-VROC TM ), developed by Rheosense, is a hyperbolically-shaped contractio...

The flows of two semi-dilute surfactant solutions (CTAB and CPyCl) through several micro contractions/expansions are experimentally investigated, following an extensive rheological characterization in both shear and extensional flows. The shear rheology of the solutions shows strong shear thinning and shear banding, whereas Small Amplitude Oscillat...

The accuracy and stability of implicit CFD codes are frequently impaired by the decoupling between variables, which can ultimately lead to numerical divergence. Coupled solvers, which solve all the governing equations simultaneously, have the potential to fix this problem. In this work, we report the implementation of coupled solvers for transient...

Evaluating the effectiveness of teaching and learning core knowledge outcomes and professional skills is a highly challenging task that has not yet been satisfactorily addressed at higher education level. The iTeach European project consortium developed a framework for assessing the effectiveness of various pedagogical methodologies in chemical eng...

The accuracy and stability of implicit CFD codes is frequently impaired by the decoupling between variables, which can ultimately lead to numerical divergence. Coupled solvers, which solve all the governing equations simultaneously, have the potential to fix this problem. In this work, we report the implementation of coupled-solvers for transient a...

Secondary flows are ubiquitous in channel flows, where small velocity components perpendicular to the main velocity appear due to the complexity of the channel geometry and/or that of the flow itself such as from inertial or non-Newtonian effects. We investigate here the inertialess secondary flow of viscoelastic fluids in curved microchannels of r...

We simulate the isothermal, incompressible, time-dependent flow of Boger fluids, using the FENE-CR constitutive model, in the optimized shape cross-slot extensional rheometer [Haward et al., Phys. Rev. Lett. 109, 128301 (2012)]. We uncover a family of predominantly elastic instabilities resulting from the interaction of stationary asymmetric and ti...

Secondary flows are ubiquitous in channel flows, where small velocity components perpendicular to the main velocity appear due to the complexity of the channel geometry and/or that of the flow itself such as from inertial or non-Newtonian effects, etc. We investigate here the inertialess secondary flow of viscoelastic fluids in curved microchannels...

We present a methodology for the shape optimization of flow-focusing devices with the purpose of creating a wide region of homogeneous extensional flow, characterized by a uniform strain-rate along the centerline of the devices. The numerical routines employed include an optimizer, a finite-volume solver, and a mesh generator operating on geometrie...

Purely-elastic flow instabilities have been extensively investigated in pressure-driven systems, but little attention has been paid to electrically-driven systems. This work attempts to fill this gap by investigating the electroosmotic flow of viscoelastic fluids in cross-slot and flow-focusing micro-devices, with a special focus on the onset of el...

We present an investigation of the rheological behavior of whole human blood under uniaxial extensional flow. For that purpose, capillary breakup experiments were carried out by combining the slow retraction method, high-speed imaging techniques, and an immiscible oil bath. The use of the oil bath was aimed at reducing liquid loss by evaporation an...

In this work, we study the implementation of electrically-driven flow (EDF) models in the finite-volume framework of $\text{OpenFOAM}^\circledR$. The Poisson-Nernst-Planck model is used for the transport of charged species and it is coupled to the Navier-Stokes equations, governing the fluid flow. In addition, the Poisson-Boltzmann and Debye-H\"uck...

A simplified method, successfully tested previously for flow in circular pipes, is used in this work to estimate the friction factor and Nusselt number in fully-developed laminar flow between parallel plates of non-Newtonian fluids. Both constant wall temperature and constant wall heat flux cases are considered. The methodology was tested using sev...

We experimentally investigate the dynamics of viscoelastic fluid flows in cross-slot microgeometries under creeping flow conditions. We focus on the unsteady flow regime observed at high Weissenberg numbers (Wi) with the purpose of understanding the underlying flow signature of elastic turbulence. The effects of the device aspect ratio and fluid rh...

We present an Eulerian free-surface flow solver for incompressible pseudoplastic and viscoelastic non-Newtonian fluids. The free-surface flow solver is based on the streamfunction flow formulation and the volume-of-fluid method. The streamfunction solver computes the vector potential of a solenoidal velocity field, which ensures by construction the...

Saccadic eye movements are rapid movements that allow the eye to rapidly refixate from one object to another. These movements are considered the most important in inducing fluid motion in the eye. Vitreous humour (VH) is the fluid that fills the eyeball and is a complex, gel‐like viscoelastic fluid. VH liquefies with age, leading to the appearance...

In this work, we investigate the behavior of dilute and semidilute polymer solutions flowing in a microfluidic flow focusing device, in which an inlet stream is stretched by two balanced lateral streams. By varying the flow rates in the inlet and lateral channels and their ratio, several types of flow transitions are observed and the resulting velo...

The vitreous humour (VH) is a complex biofluid that occupies a large portion of the eyeball between the lens and the retina, and exhibits non-Newtonian rheological properties that are key for its function in the eye. It is often possible to distinguish two different phases in VH, known as liquid and gel phases (Sebag J Eye 1: 254–262, 1987). In thi...

Supplementary Information

Supplementary Information

Supplementary Information

Supplementary Information

The characterization of the extensional rheology of polymeric solutions is important in several applications and industrial processes. Filament stretching and capillary breakup rheometers have been developed to characterize the extensional properties of polymeric solutions, mostly for high-viscosity fluids. However, for low concentration polymer so...

In this work, we explore two methods to simultaneously measure the electroosmotic mobility in microchannels and the electrophoretic mobility of micron-sized tracer particles. The first method is based on imposing a pulsed electric field, which allows to isolate electrophoresis and electroosmosis at the startup and shutdown of the pulse, respectivel...

In this work, we modify the viscoelastic solver available in the OpenFOAM® toolbox (Favero et al., 2010), in order to improve its stability for differential-type constitutive equations. The Oldroyd-B constitutive equation is solved using the log-conformation approach and the high-resolution schemes used to discretize the convective terms are handle...

A multi-disciplinary pilot-scale setup was assembled with the purpose of studying coupled mass transport and chemical reaction phenomena during coke combustion in a fluidized bed. Such experimental work has been integrated in the program of a laboratory course (4th year) of the Integrated Master in Chemical Engineering at FEUP (Faculty of Engineeri...

In this paper, we present numerical solutions of the Oldroyd-B fluid flowing through a 4:1 planar contraction, for Weissenberg numbers (Wi) up to 20. The incompressible viscoelastic flows are simulated with the streamfunction–log-conformation methodology. The log-conformation representation guarantees by construction the positive-definiteness of th...

In this work, we present a series of solutions for combined electro-osmotic and pressure-driven flows of viscoelastic fluids in microchannels. The solutions are semi-analytical, a feature made possible by the use of the Debye–Hückel approximation for the electrokinetic fields, thus restricted to cases with small electric double-layers, in which the...

We present results of a numerical investigation of the low Reynolds number flow of viscoelastic fluids, described by the Oldroyd-B model, in a 2D cross-slot channel with a main inlet flow and two periodic in-phase and out-of-phase forcings imposed on the opposing lateral inlets. Several types of flow transition are reported that depend on the ampli...

We determine both experimentally and numerically the onset of elastic flow instabilities in viscoelastic polymer solutions with different levels of shear thinning. Previous experiments realized in microfluidic serpentine channels using dilute polymeric solutions showed that the onset of elastic instabilities strongly depends on the channel curvatur...

In this work, we optimise microfluidic converging/diverging geometries in order to produce constant strain-rates along the centreline of the flow, for performing studies under homogeneous extension. The design is examined for both two-dimensional and three-dimensional flows where the effects of aspect ratio and dimensionless contraction length are...

We examine fluid flow through cross-slot devices with various depth to width ratios α. At low Reynolds number, Re, flow is symmetric and a sharp boundary exists between the two incoming fluid streams. Above an α-dependent critical value, Rec(α), a steady symmetry-breaking bifurcation occurs and a spiral vortex structure develops. Order parameters c...

The lid-driven cavity flow is a well-known benchmark problem for the validation of new numerical methods and techniques. In experimental and numerical studies with viscoelastic fluids in such lid-driven flows, purely-elastic instabilities have been shown to appear even at very low Reynolds numbers. A finite-volume viscoelastic code, using the log-c...

We present a numerical study of a stabilization method for computing confined and free-surface flows of highly elastic viscoelastic fluids. In this approach, the constitutive equation based on the conformation tensor, which is used to define the viscoelastic model, is modified introducing an evolution equation for the square-root conformation tenso...

Significant progress has been made over the years on the topic of hemorheology, not only in terms of the development of more accurate and sophisticated techniques, but also in terms of understanding the phenomena associated with blood components, their interactions and impact upon blood properties. The rheological properties of blood are strongly d...

In this work, we perform creeping-flow simulations of upper-convected Maxwell and simplified Phan-Thien–Tanner fluids to study the purely-elastic steady bifurcation and transition to time-dependent flow in three-dimensional planar cross-slots. By analysing the flow in geometries with aspect ratios ranging from the near Hele-Shaw flow like limit, up...

We present an experimental investigation of viscoelastic fluid flow in a cross-slot microgeometry under low Reynolds number flow conditions. By using several viscoelastic fluids, we investigate the effects of the microchannel bounding walls and the polymer solution concentration on the flow patterns. We demonstrate that for concentrated polymer sol...

Experimental measurements and numerical simulations are made on fluid flow
through cross-slot devices with a range of aspect (depth:width) ratios, 0.4 <
alpha < 3.87. For low Reynolds numbers Re, the flow is symmetric and a sharp
boundary exists between fluid streams entering the cross-slot from opposite
directions. Above an alpha-dependent critica...

This work completes a previous study (Cruz et al., in J Heat Transf 134:091703, 2012) by evaluating the performance of the simplified method proposed therein for calculating the Nusselt number for laminar flow of non-Newtonian fluids in pipes with constant wall temperature. The methodology was tested using the Herschel-Bulkley, Bingham, Casson and...

Comparison of computational times of GPU parallelized finite volume viscoelastic flow code relative to the original code.

Resumo — Este artigo trata do estudo numérico de um fenómeno de bifurcação matemática que ocorre para escoamento de um fluido viscoelástico numa geometria que consiste na ju nção de 2 canais planos. O interesse será analisar o comportamento do escoamento na zona do cruzamento dos canais e verificar se a simetria da geometria conduz, como seria intu...

Resumo — Neste estudo p rocedeu-se à simulação do escoamento de fluidos viscoelásticos, como é o caso do sangue, numa bifurcação de 90º, com o objectivo de estudar o seu comportamento com a variação da elasticidade do fluido , para diferentes razões entre a viscosidade do solvente e a viscosidade total. Pretendeu-se observar a variação do tamanho e...

This work presents a technique and develops an apparatus that allows the application of homogeneous external magnetic fields (parallel or perpendicular to the deformation axis) to a fluid sample undergoing extensional flow kinematics while measuring the filament thinning using the commercial version of the capillary breakup extensional rheometer (H...

It is well known that, beyond a critical aspect-ratio-dependent Reynolds number, the flow in a three-dimensional T-channel junction, i.e. two-opposing planar channel streams joining and turning through 90 degrees, can break symmetry. For the case of two square cross-section inlets and an outlet arm of equal area (i.e. aspect ratio of two) this bifu...

In this work we propose the cross-slot geometry as a candidate for a numerical benchmark flow problem for viscoelastic fluids. Extensive data of quantified accuracy is provided, obtained via Richardson extrapolation to the limit of infinite refinement using results for three different mesh resolutions, for the upperconvected Maxwell, Oldroyd-B and...

Many artificial and natural fluids contain macromolecules, particles or droplets that impart complex flow behaviour to the fluid. This complex behaviour results in a non-linear relationship between stress and deformation standing in between Newton’s law of viscosity for an ideal viscous liquid and Hooke’s law for an ideal elastic material. Such non...

This work provides analytical and numerical solutions for the linear, quadratic and exponential Phan-Thien - Tanner (PTT) viscoelastic models, for axial and helical annular fully-developed flow under no slip and slip boundary conditions, the latter given by the linear and nonlinear Navier slip laws. The rheology of the three of the PTT variants mod...

This work investigates the steady-state slip flow of viscoelastic fluids in hydrophobic two-dimensional microchannels under the combined influence of electro-osmotic and pressure gradient forcings with symmetric or asymmetric zeta potentials at the walls. The Debye–Hückel approximation for weak potential is assumed, and the simplified Phan-Thien-Ta...