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Munoz-Sanchez B.N.,University of Seville | Silva S.F.,Polytechnic Institute of Bragança | Pinho D.,Polytechnic Institute of Bragança | Vega E.J.,University of Extremadura | And 2 more authors.
Biomicrofluidics | Year: 2016

Polydimethylsiloxane (PDMS), due to its remarkable properties, is one of the most widely used polymers in many industrial and medical applications. In this work, a technique based on a flow focusing technique is used to produce PDMS spherical particles with sizes of a few microns. PDMS precursor is injected through a hypodermic needle to form a film/reservoir over the needle's outer surface. This film flows towards the needle tip until a liquid ligament is steadily ejected thanks to the action of a coflowing viscous liquid stream. The outcome is a capillary jet which breaks up into PDMS precursor droplets due to the growth of capillary waves producing a micrometer emulsion. The PDMS liquid droplets in the solution are thermally cured into solid microparticles. The size distribution of the particles is analyzed before and after curing, showing an acceptable degree of monodispersity. The PDMS liquid droplets suffer shrinkage while curing. These microparticles can be used in very varied technological fields, such as biomedicine, biotechnology, pharmacy, and industrial engineering. © 2016 AIP Publishing LLC.

Bento D.,Polytechnic Institute of Bragança | Lima R.,CEFT | Lima R.,University of Minho | Miranda J.M.,CEFT
Micro and Nanosystems | Year: 2015

Traditional grid-based numerical methods, such as finite volume method (FVM), are not suitable to simulate multiphase biofluids (such as blood) at the microscale level. Alternatively, meshfree Lagrangian methods can deal with two or more finely dispersed phases moving relatively to each other. The Moving Particle Semi-Implicit Method (MPS), used in this study, is a deterministic particle method based on a Lagrangian technique to simulate incompressible flows. The advantages of particle methods over traditional grid-based numerical methods have motivated several researchers to implement them into a wide range of studies in computational biomicrofluidics. The main aim of this paper is to evaluate the accuracy of the MPS method by comparing it with numerical simulations performed by an FVM. Hence, simulations of a Newtonian fluid flowing through a constriction were performed for both methods. For the MPS, a section of the channel of 30*11.5*11.5 μm was simulated using periodic boundary conditions. The obtained results have provided indications that, if the initial particle distance is sufficiently small, the MPS method can calculate accurately velocity profiles in the proposed channel. © 2015 Bentham Science Publishers.

Yaginuma T.,ESTiG | Pereira A.I.,ESTiG | Rodrigues P.J.,ESTiG | Lima R.,ESTiG | And 3 more authors.
Computational Vision and Medical Image Processing, Proceedings of VipIMAGE 2011 - 3rd ECCOMAS Thematic Conference on Computational Vision and Medical Image Processing | Year: 2012

The present study aims to assess the deformability of Red Blood Cells (RBCs) under extensionally dominated microfluidic flows using an image based technique. For this purpose, a microchannel having a hyperbolic shaped-contraction was used and the images were captured by a standard high-speed microscopy system. The images acquired display RBCs with various light intensity levels and image analysis was used to quantify the Deformation Index (DI) of the RBCs considering these light intensity differences. Additionally, the velocities of different intensity-level RBCs flowing along the centerline of the channel were measured using particle tracking velocimetry. The preliminary results at two different flow rates reveal a highly deformable nature of RBCs when submitted to strong extensional flows. It was also observed that the low intensity cells exhibit a slightly higher velocity than intermediate intensity cells, which we attribute to the cells being located in different planes. © 2012 Taylor & Francis Group.

Alves M.A.,CEFT | Baptista A.,Rua Dr. Roberto Frias | Coelho P.M.,CEFT
Heat and Mass Transfer/Waerme- und Stoffuebertragung | Year: 2015

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 Carreau-Yasuda generalized Newtonian models, and also the simplified form of the Phan-Thien–Tanner viscoelastic model. The error of the approximate methodology is below 3 %, except for yield stress fluids, for which the maximum error increases to 7.4 % for the cases analyzed, which cover a wide range of shear viscosity curves. An explicit expression of Nusselt number for Casson fluids is also presented. © 2015, Springer-Verlag Berlin Heidelberg.

Dhinakaran S.,CEFT | Afonso A.M.,CEFT | Alves M.A.,CEFT | Pinho F.T.,CEFT
Journal of Colloid and Interface Science | Year: 2010

The electro-osmotic flow of a viscoelastic fluid between parallel plates is investigated analytically. The rheology of the fluid is described by the Phan-Thien-Tanner model. This model uses the Gordon-Schowalter convected derivative, which leads to a non-zero second normal stress difference in pure shear flow. A nonlinear Poisson-Boltzmann equation governing the electrical double-layer field and a body force generated by the applied electrical potential field are included in the analysis. Results are presented for the velocity and stress component profiles in the microchannel for different parametric values that characterize this flow. Equations for the critical shear rates and maximum electrical potential that can be applied to maintain a steady fully developed flow are derived and discussed. © 2010 Elsevier Inc. All rights reserved.

Falcao D.S.,CEFT | Oliveira V.B.,CEFT | Rangel C.M.,National Laboratory of Energy and Geology | Pinto A.M.F.R.,CEFT
Renewable and Sustainable Energy Reviews | Year: 2014

Fuel cells have unique technological attributes: efficiency, minimization of moving parts and low emissions. The Direct Methanol Fuel Cell (DMFC) has attracted much attention due to its potential applications as a power source for transportation and portable electronic devices. With the advance of micromachining technologies, miniaturization of power sources became one of the trends of evolution of research in this area. Based on the advantages of the scaling laws, miniaturization promises higher efficiency and performance of power generating devices, so, MicroDMFC is an emergent technology. There has been a growing interest in the development of this type of micro cells in the last years, resulting both in experimental studies (operating conditions, cell design and new materials) and in modeling studies. Despite the increase in the knowledge acquired, many challenges are still to be reached. This paper provides a detailed comprehensive review both on fundamental and technological aspects of micro-direct methanol fuel cells. Special attention is devoted to systematization of published results on experimental area since to date and also to a special section dedicated to modeling studies. © 2014 Published by Elsevier Ltd.

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