Paulo R. de Souza Mendes | Pontifícia Universidade Católica do Rio de Janeiro (original) (raw)

Papers by Paulo R. de Souza Mendes

Chemical Engineering Science, Dec 1, 2021

Abstract An emulsion may be classified as a colloidal system depending on the scale analyzed. Sta... more Abstract An emulsion may be classified as a colloidal system depending on the scale analyzed. State parameters (e.g. temperature, volume fraction and osmotic pressure) determine whether the system is regarded as in a liquid-like, liquid/solid-like or solid-like phase. The transition threshold between different phases has been separately observed from thermodynamic and rheological viewpoints. For the case in which the system is under free particle motion regime (van der Waals forces, Brownian motion, depletion, etc.), we obtained a relationship between the rheological behavior and the thermodynamic state. The thermodynamic analysis is based on the McMillan-Mayer theory, and binodal curves were determined with a perturbation theory. It was that liquid-like phases behave as Newtonian, while liquid/solid-like and solid-like phases possess a non-Newtonian rheological behavior. Water-in-crude oil emulsions were used in the experiments. We studied the effect of volume fraction ( φ = 20 % and 30 % ), temperature (T = 60 ° C, 40 ° C, 25 ° C), and mean size diameter ( d p = 6.4 μ m, 5.34 μ m, and 4.22 μ m). The transition line from the liquid-like to the liquid-solid phase moves with volume fraction, temperature, monolayer thickness and particle diameter, consistently with the rheology results.

Physics of Fluids, Apr 1, 2023

We conduct nonlinear simulations to investigate the radial growth of viscous fingers in a Hele–Sh... more We conduct nonlinear simulations to investigate the radial growth of viscous fingers in a Hele–Shaw cell by performing a wide parametric study on the two dimensionless parameters that govern the dynamics. These are the viscosity contrast, A, and the effective surface tension, B, which compares the influence of surface tension with the injection rate that drives instability. It is well known that the surface tension between the fluids has a stabilizing influence on pattern formation leading to slower fingering growth and a reduced number of fingers. Moreover, the current results show that, for fixed A values, larger values of the effective surface tension lead to the formation of fingering patterns that are similar to each other. As such, the calculated interfacial shapes are larger and take longer to develop. Furthermore, the calculated shapes offer a visually striking portrait of instability evolution, and comparison to our experimental measurements highlights the close resemblance between the two with a few discrepancies pointed out. Finally, we observe how changes to the initial nearly circular interface affect both the morphology of viscous fingers and the timescale for pattern formation.

Journal of Petroleum Science and Engineering, Jul 1, 2019

We propose a constitutive model to describe the rheological behavior of oil well cement pastes. T... more We propose a constitutive model to describe the rheological behavior of oil well cement pastes. The model is capable of predicting time dependence and irreversibility caused by the continuous hydration process that occurs in oil well cement pastes during cementing operations. The model is developed for a specific cement paste according to a recently proposed method [1], with a modification to accommodate cement setting predictive capability. The fluidity (reciprocal of viscosity) is directly employed to indicate the structuring level of the microstructure. The model relies on the results of several rheological experiments to determine the nature and parameter values of novel material functions that arise in the model development. The material function that carries the cement setting information is the yield stress function, which turns out to be an exponentially increasing function of time. Except for minor differences observed at low shear rates, good agreement is observed between the data and the model predictions.

Journal of Petroleum Science and Engineering, Mar 1, 2019

An experimental study of the flow of yield stress materials was conducted. The main goal was to u... more An experimental study of the flow of yield stress materials was conducted. The main goal was to understand the relationship between the minimum axial pressure gradient required for the onset of motion and the rheological properties. The sought-for application is the startup flow of waxy crude oils in subsea pipelines. We examined two types of yield stress materials, namely a non-thixotropic acrylic polymer solution and a layered silicate suspension which presents thixotropic properties. We observed that for both materials the measured minimum axial pressure gradient was in good agreement with the prediction of a simple force balance. On the other hand, a puzzling fact is observed in the oil industry, namely that the just mentioned force balance result grossly overestimates the minimum axial pressure gradient for the case of gelled waxy crude oils. One often evoked explanation is the thixotropic behavior of the gelled crude, but the present results serve to falsify it.

Journal of Petroleum Science and Engineering, Nov 1, 2017

The performance of protocols usually employed for the rheological characterization of oil well ce... more The performance of protocols usually employed for the rheological characterization of oil well cement slurries is investigated. To this end two cement slurries were employed, namely Paste A and Paste B. The API procedure is addressed and a modication to it is investigated. Flow curves are determined with the aid of a rotational rheometer using three dierent methods (ramp up/down, ramp down, and minimum-viscosity). The API procedure yielded ow curves that signicantly overestimate (Paste A) or underestimate (Paste B) the viscosity throughout the whole range of shear rate. The deviations become particularly dramatic in the low end of this range and for Paste B, clearly because the steady state is not attained due to a thixotropic behavior. The investigated modication to the API procedure resulted in ow curves similar to the ones based on the minimum-viscosity method.

Journal of Rheology, Sep 1, 2020

We introduce a constitutive model to describe the rheological behavior of gelled waxy crude oil. ... more We introduce a constitutive model to describe the rheological behavior of gelled waxy crude oil. The irreversible time-dependence effects were experimentally characterized and incorporated into the model. The model is developed with basis on the data of standard rheological tests to determine the parameters of novel material functions that arise in the model development procedure, namely, flow curve, destruction, and construction tests. The fluidity is directly employed as the indicator of the structuring level of the material. Good agreement is observed between the model predictions and the data, corroborating its potential as a useful tool in the study of start-up flows of gelled crudes in pipelines.

Journal of The Brazilian Society of Mechanical Sciences and Engineering, Jun 1, 2008

The displacement of a fluid by liquid injection occurs in some practical applications like oil re... more The displacement of a fluid by liquid injection occurs in some practical applications like oil recovery in porous media and cementation of drilling wells. The dimensionless numbers that govern this problem are the capillary number, Reynolds number and viscosity ratio. An overview of selected oil recovery processes shows that hydrolyzed polyacrilamide and bio-polymers, as xanthan gun, are commonly pumped into oil reservoir in order to aid oil recovery. These materials are non-Newtonian, presenting high viscoelastic effects. The fractional mass deposited on the tube wall and the shape of the interface on liquid-liquid displacement of two Newtonian materials was studied previously by Soares et al. (2005). The goal of the present work is to conduct an experimental investigation analyzing viscoelastic effects on the fractional coverage and on the shape of the interface for both: a polymer displacing a Newtonian liquid and a Newtonian liquid displacing a polymer.

Physics of Fluids, Nov 1, 2022

The growth of viscous fingers in the radial displacement of a yield strength material confined be... more The growth of viscous fingers in the radial displacement of a yield strength material confined between the plates of a Hele–Shaw cell is investigated. The apparatus is filled with an aqueous solution of Carbopol® before air is injected to start the displacement process. In addition to striking fingering patterns, we identify unyielded residuals of the Carbopol solution arrested on the plates' surfaces with the assistance of digital mobile microscopes placed above the top plate. These unyielded residuals are subjected to slip conditions on the surface walls and appear in different forms. The experimental observations are correlated with the wall slip behavior detected in rheometric measurements, i.e., observed in the flow curve for shear rates below a critical value. This correlation provides an estimate of a critical propagating radius beyond which shear rates drop to values lower than the critical one, and the influence of wall slip becomes significant. We observe that these residuals are uniformly distributed and appear as thin films where the radii are smaller than the critical value and the wall slip is minimum. However, in locations where the radii are larger than the critical one, the residuals turn into isolated blobs of different sizes, which may propagate in a stick-slip motion radially downstream inside the air fingers. In addition, we observe that the morphology of residuals depends on the gap width between the plates, the injection rate of the invading air, the yield strength of the Carpobol solution, and the wettability conditions of the surface walls.

Journal of Non-newtonian Fluid Mechanics, Aug 1, 2016

Fundamental understanding of flow of suspensions is key in many different areas such as bioengine... more Fundamental understanding of flow of suspensions is key in many different areas such as bioengineering, oil, food, pharmaceutical and cosmetic industries. Two important phenomena may occur in the flow of particle suspensions. The first is associated with the relaxation process of particles towards a rest state after the flow is stopped that leads to shear-sensitive viscosity. The second is associated with particle-particle interaction that leads to shear-induced particle migration. The intensity of each of these effects is directly associated with particle size and imposed deformation rate. The available analyses are usually limited to one of these phenomena. A common approach is to consider that the suspension viscosity varies with shear rate, using a viscosity function to describe this dependency, and that the particle concentration is uniform throughout the flow. Most of the studies that consider shear-induced particle migration assume that the viscosity varies only with the local particle concentration and is not a function of shear rate. The range of validity and accuracy of these two approaches is not well understood. In this work, we analyze the fully developed flow of particle suspensions in a tube using different flow models to evaluate the effect of both particle migration and shear dependent viscosity. The results show that, at certain conditions, accurate predictions on the flow rate-pressure gradient relation can only be made by considering both phenomena in a fully coupled, non-linear flow model.

Journal of Non-Newtonian Fluid Mechanics

Proceedings of the 26th International Congress of Mechanical Engineering, 2021

Displacement of a liquid in a capillary tube by gas injection occurs in many situations, like enh... more Displacement of a liquid in a capillary tube by gas injection occurs in many situations, like enhanced oil recovery, coating of catalytic converters and gas-assisted injection molding. Generally the liquid being displaced is a polymeric solution or dispersion, that are not Newtonian. Viscoelastic forces alter the force balance in various parts of the flow and consenquently change the amount of liquid left attached to the capillary wall. In order to model the effect of the rheological properties in this important flow, the mechanical behavior of the flowing liquid has to be well described by an appropriate constitutive model. Here, the Oldroyd-B differential constitutive equation that approximate viscoelastic behavior of dilute polymer solutions was used, together with momentum and continuity equation, to model the two-dimensional free surface flow near the gas-liquid interface. The equation system was solved with the Finite Element Method. The resulting non-linear system of algebrai...

Journal of Fluids Engineering, 2004

Circular Couette flow of inelastic shear-thinning materials in annuli is examined. The curved str... more Circular Couette flow of inelastic shear-thinning materials in annuli is examined. The curved streamlines of the circular Couette flow can cause a centrifugal instability leading to toroidal vortices, well known as Taylor vortices. The presence of these vortices changes the hydrodynamic and heat transfer characteristics of the processes at which this type of flow occurs. Therefore, it is quite important to be able to predict the onset of instability. Most of the available theoretical and experimental analyses are for Newtonian and viscoelastic (dilute polymeric solutions) liquids. In this work, the effect of the shear-thinning behavior of high concentration suspensions on the onset of the Taylor vortices is determined theoretically by solving the conservation equations, constructing the solution path as the inner cylinder speed rises and searching for the critical conditions. This procedure avoids the need for a stability analysis of the flow and the solution of an eigenproblem. The...

Fluids Engineering, 2003

ABSTRACT Displacement of a liquid in a capillary tube by gas injection occurs in many situations,... more ABSTRACT Displacement of a liquid in a capillary tube by gas injection occurs in many situations, like enhanced oil recovery, coating of catalytic converters and gas-assisted injection molding. Generally the liquid being displaced is a polymeric solution or dispersion, that are not Newtonian. Viscoelastic forces alter the force balance in various parts of the flow and consequently change the amount of liquid left attached to the capillary wall. In order to model the effect of the rheological properties in this important flow, the mechanical behavior of the flowing liquid has to be well described by an appropriate constitutive model. Here, the Oldroyd-B differential constitutive equation that approximate viscoelastic behavior of dilute polymer solutions was used, together with momentum and continuity equation, to model the two-dimensional free surface flow near the gas-liquid interface. The equation system was solved with the Finite Element Method. The resulting nonlinear system of algebraic equations was solved by Newton’s method. The results show the effect of the viscoelastic character of the liquid on the free surface shape and the film thickness attached to the capillary wall.

Procceedings of the 19th Brazilian Congress of Thermal Sciences and Engineering, 2022

Journal of Non-newtonian Fluid Mechanics, Nov 1, 2018

A phenomenological constitutive model that accounts for thixotropy, viscoelasticity and yielding ... more A phenomenological constitutive model that accounts for thixotropy, viscoelasticity and yielding behavior is presented. It uses the fluidity to specify the microscopic state. The model is composed of two differential equations, one tensorial equation that relates the stress to the rate of strain and one scalar evolution equation for the fluidity. The equation for stress is a modified version of the Oldroyd-B model in which the relaxation and retardation times are functions of the fluidity. In contrast to the existing phenomenological models for thixotropic materials, the evolution equation that describes the microscopic state only involves material functions that are directly measurable by means of standard rheological tests.

Current Opinion in Colloid and Interface Science, Oct 1, 2019

Time-dependent yield stress materials abound in nature and in industrial processes. Examples incl... more Time-dependent yield stress materials abound in nature and in industrial processes. Examples include clays, light metal alloys, paints and inks, adhesives, gelled waxy crude oils, drilling muds, fresh cement pastes, food products, biological fluids, ferrofluids, some lubricants, gypsum paste, and many other slurries, emulsions, suspensions and foams. In this paper we describe the main features of time-dependent yield stress materials, present recent developments and applications, and discuss a number of important issues regarding the physics that govern the mechanical behavior of these complex materials. Finally we discuss some recently developed experimental methods that are suitable to the rheological characterization of time-dependent yield stress materials.

Science Talks, Jun 1, 2022