We experimentally study the time evolution of the distance between two identical spheres settling... more We experimentally study the time evolution of the distance between two identical spheres settling down in polyacrylamide shear-thinning solutions in mixtures of water and glycerin. In order to analyze the behavior of the spheres under different rheological conditions, we varied the concentration of the polymer and glycerin. To examine the influence of wall effects, the experiments were performed in two containers of different size. We found that depending on the fluids' rheological properties, two different regimes are revealed for the same diluted polymer. In one of them (I), the separation between the spheres grows in time if the initial separation S i is beyond a critical distance S c , while the separation decreases for an initial distance shorter than S c. In the second observed regime (II), the spheres aggregate if S i < S c while they remain unchanged in their separation if S i > S c , i.e., repulsion is not detected. The transition from one to another regime can be produced at constant polymer concentration by changing the solvent viscosity η s. In our experiments this shift has been done modifying the glycerin-water proportion. Although these two behaviors were reported in previous works for different viscoelastic fluids, a result that we show is that both regimes can be observed for the same polymer. The elusive regime I, in which far-field repulsion is exhibited, is of particular interest since it has been previously reported only by Riddle et al. [J. Non-Newtonian Fluid Mech. 2, 23 (1997)]. Thus, our results confirm that this behavior is also feasible.
International Journal of Heat and Mass Transfer, Feb 1, 2016
Abstract In this paper we analyse, numerically and experimentally, the laminar reactive flow in a... more Abstract In this paper we analyse, numerically and experimentally, the laminar reactive flow in a cylindrical cavity with a rotating end wall. A basic solution is initially in the cavity and an acid solution is introduced at very low velocity through the center of the stationary endwall when the flow in the cavity is at the steady state. The effect of the different flow structures obtained at different Reynolds numbers on the irreversible fast acid–base neutralization is measured with a simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) technique and simulated numerically with a finite volume code. The observed flow structure, the recirculation bubbles in the vortex breakdown regions as well as the numerical velocity profiles are in agreement with the measurements and with previous studies. The range of measured concentrations is limited to regions where the molar fraction of the base (xB) is larger than 0.57. The comparison between the experimental and numerical contours of concentration of base solution at Re = 1000 and 1500 are in general agreement. At larger Reynolds numbers (Re = 1700, 2000 and 2300), the experimental and numerical contours of concentration of base solution inside the vortex breakdown bubbles differ because of the relatively large concentration of product (i.e. xB
Journal of Industrial and Engineering Chemistry, Apr 1, 2018
The numerical prediction of mass transfer rates of gas components within the liquid phase in a st... more The numerical prediction of mass transfer rates of gas components within the liquid phase in a stirred two-phase flow reactor is presented. Experiments have been conducted to determine the flow regime and the number and sizes of the bubbles formed under different conditions. The dynamic field of the twophase flow was obtained through numerical simulations. Bubbles with the experimentally measured diameter were released from the free surface and tracked numerically to compute the particle Reynolds number, which is used to determine the mass transfer rates. The unbaffled reactor provides mass transfer rates 30% larger than the baffled reactor for the bubbly flow. Mass transfer rates drop about 65% when the emulsion is formed. Therefore, above the critical rotation rate at which the emulsion forms for the unbaffled reactor, the baffled configuration provides larger mass transfer rates. The results indicate that even for the most unfavorable case mass transfer is not the limiting step, as 90% of the equilibrium concentration is reached in 10 s.
Several methods are available for measuring the fluid movement in experimental setups. One of the... more Several methods are available for measuring the fluid movement in experimental setups. One of the most used technique is the particle image velocimetry (PIV). This is an optical technique that indirectly measures the fluid velocity by measuring the displacement of some small particles that seeds the fluid. To obtain the velocity field, the zone of interest of the experimental setup is illuminated twice with a laser beam. Two consecutive images are obtained and the displacement of the particles can be calculated. Knowing the time difference between both images allow to compute the velocity. Appropriate flow seeding is particularly critical in PIV. Particles that follow the flow accordingly and scatter enough light must be used in order to obtain accurate velocity field of the flow. Therefore, particles should be as small as possible in order to ensure good tracking of the fluid motion and they should not be too small, since they will not scatter enough light.
The aim of this paper was to evaluate the potential of using near-infrared (NIR) spectroscopy and... more The aim of this paper was to evaluate the potential of using near-infrared (NIR) spectroscopy and multivariate analysis as a rapid tool to non-destructively determine the presence of surface treatments applied to cork stoppers. Density and dimensions of 6 closure varieties were characterized and the extraction force was measured on those produced for still wines. Cork stoppers were also analyzed using hand-held NIR and Raman spectrometers. Soft independent modelling of class analogy (SIMCA) models showed significant differences among treated and untreated samples, linked to components of the coating agents applied (silicone and paraffin). SIMCA model's classification performance was tested and high sensitivity (93.33 %) and specificity (100 %) values were obtained. Partial least squares regression (PLSR) model accurately predicted the extraction forces measured with low standard error of prediction (SEP = 4.0 daN). Our results are promising for the future application of this technology in cork industry, reducing time and economic losses.
Journal of Industrial and Engineering Chemistry, 2018
The numerical prediction of mass transfer rates of gas components within the liquid phase in a st... more The numerical prediction of mass transfer rates of gas components within the liquid phase in a stirred two-phase flow reactor is presented. Experiments have been conducted to determine the flow regime and the number and sizes of the bubbles formed under different conditions. The dynamic field of the twophase flow was obtained through numerical simulations. Bubbles with the experimentally measured diameter were released from the free surface and tracked numerically to compute the particle Reynolds number, which is used to determine the mass transfer rates. The unbaffled reactor provides mass transfer rates 30% larger than the baffled reactor for the bubbly flow. Mass transfer rates drop about 65% when the emulsion is formed. Therefore, above the critical rotation rate at which the emulsion forms for the unbaffled reactor, the baffled configuration provides larger mass transfer rates. The results indicate that even for the most unfavorable case mass transfer is not the limiting step, as 90% of the equilibrium concentration is reached in 10 s.
We experimentally study the time evolution of the distance between two identical spheres settling... more We experimentally study the time evolution of the distance between two identical spheres settling down in polyacrylamide shear-thinning solutions in mixtures of water and glycerin. In order to analyze the behavior of the spheres under different rheological conditions, we varied the concentration of the polymer and glycerin. To examine the influence of wall effects, the experiments were performed in two containers of different size. We found that depending on the fluids' rheological properties, two different regimes are revealed for the same diluted polymer. In one of them (I), the separation between the spheres grows in time if the initial separation S i is beyond a critical distance S c , while the separation decreases for an initial distance shorter than S c. In the second observed regime (II), the spheres aggregate if S i < S c while they remain unchanged in their separation if S i > S c , i.e., repulsion is not detected. The transition from one to another regime can be produced at constant polymer concentration by changing the solvent viscosity η s. In our experiments this shift has been done modifying the glycerin-water proportion. Although these two behaviors were reported in previous works for different viscoelastic fluids, a result that we show is that both regimes can be observed for the same polymer. The elusive regime I, in which far-field repulsion is exhibited, is of particular interest since it has been previously reported only by Riddle et al. [J. Non-Newtonian Fluid Mech. 2, 23 (1997)]. Thus, our results confirm that this behavior is also feasible.
Appropriate flow seeding is particularly critical with in the particle image velocimetry (PIV) te... more Appropriate flow seeding is particularly critical with in the particle image velocimetry (PIV) technique that indirectly measures the displacement from the particle velocity instead of fluid velocity. Particles that follow the flow accordingly and scatter enough light must be used in order to obtain accurate velocity field of the flow. Therefore, particles should be as small as possible in order to ensure good tracking of the fluid motion and they should not be too small, since they will not scatter enough light. The microparticles can be obtained from approximately 20 nm to around 50 µm in a controlled manner with ability increasing their light scattering behavior by fluorescein imbedding so that they gain the light scattering property. Alginate microparticles as flow seeding fulfill all the requirements that are recommended for the velocity measurements in PIV. These spherical microparticles offer the advantage of being environmentally friendly, excellent seeding properties and very simple production ability. They can be obtained as small as possible while increasing its scattering behavior by adding fluorescein into them. Additionally, they can be perfectly used as flow seeding in gas and several liquid flows with matching densities.
The reactive and laminar flow in a cylindrical cavity with a rotating end wall is analysed experi... more The reactive and laminar flow in a cylindrical cavity with a rotating end wall is analysed experimentally, using Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF), and numerically using the commercial code Ansys Fluent. The cavity is initially filled with a basic solution and the acid solution is introduced through a small inlet at the bottom wall. The experimental emergence of the vortex breakdown for an aspect ratio H/R = 2, that occurs at Re = 1500 has been compared with previous studies. The numerically predicted velocity profiles are in agreement with the measurements. The measured product concentration is limited in regions where the molar fraction of the base (x B) is larger than 0.57, because the response of the fluorescence light is linear in this range. The simultaneous combination of PIV and PLIF has been performed with success. The separation of PIV and PLIF signals has been possible by means of physical and computational filters. In simultaneous PIV and PLIF experiments, the PIV results are comparable with the previous results obtained using only the PIV technique. Also, the experimental contours of concentration obtained with PLIF, are in general agreement with the numerical predictions.
International Journal of Heat and Mass Transfer, 2016
Abstract In this paper we analyse, numerically and experimentally, the laminar reactive flow in a... more Abstract In this paper we analyse, numerically and experimentally, the laminar reactive flow in a cylindrical cavity with a rotating end wall. A basic solution is initially in the cavity and an acid solution is introduced at very low velocity through the center of the stationary endwall when the flow in the cavity is at the steady state. The effect of the different flow structures obtained at different Reynolds numbers on the irreversible fast acid–base neutralization is measured with a simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) technique and simulated numerically with a finite volume code. The observed flow structure, the recirculation bubbles in the vortex breakdown regions as well as the numerical velocity profiles are in agreement with the measurements and with previous studies. The range of measured concentrations is limited to regions where the molar fraction of the base (xB) is larger than 0.57. The comparison between the experimental and numerical contours of concentration of base solution at Re = 1000 and 1500 are in general agreement. At larger Reynolds numbers (Re = 1700, 2000 and 2300), the experimental and numerical contours of concentration of base solution inside the vortex breakdown bubbles differ because of the relatively large concentration of product (i.e. xB
Appropriate flow seeding is particularly critical with in the particle image velocimetry (PIV) te... more Appropriate flow seeding is particularly critical with in the particle image velocimetry (PIV) technique that indirectly measures the displacement from the particle velocity instead of fluid velocity. Particles that follow the flow accordingly and scatter enough light must be used in order to obtain accurate velocity field of the flow. Therefore, particles should be as small as possible in order to ensure good tracking of the fluid motion and they should not be too small, since they will not scatter enough light. The microparticles can be obtained from approximately 20 nm to around 50 µm in a controlled manner with ability increasing their light scattering behavior by fluorescein imbedding so that they gain the light scattering property. Alginate microparticles as flow seeding fulfill all the requirements that are recommended for the velocity measurements in PIV. These spherical microparticles offer the advantage of being environmentally friendly, excellent seeding properties and very simple production ability. They can be obtained as small as possible while increasing its scattering behavior by adding fluorescein into them. Additionally, they can be perfectly used as flow seeding in gas and several liquid flows with matching densities.
This study analyzes experimentally the deposition of magnetic beads on the walls of a square micr... more This study analyzes experimentally the deposition of magnetic beads on the walls of a square microchannel by the action of a nearby cubical magnet. The deposition has been studied for different magnetic bead sizes, flow rates, magnetic conditions and with solutions of magnetic and non-magnetic particles. Images of the time evolution of the deposition under the different conditions have been analyzed to determine the spatial distribution of the accumulation and the growth rate of the depositions. It has been found that the way in which the magnetic beads are deposited on the walls of the microchannel depends strongly on their size and the magnetic configuration. The accumulation of the major part of particles is on the wall closest to the magnet and, depending on the size of the particles, near the magnet leading and trailing edges or near the center of the magnet. The experiments with magnetic and non-magnetic particles revealed the screening effect of the non-magnetic particles on ...
The effect of fixed cylindrical rods located at the centerline axis on vortex breakdown (VB) is s... more The effect of fixed cylindrical rods located at the centerline axis on vortex breakdown (VB) is studied experimentally and numerically. We find that the VB is enhanced for very small values of the rod radius $d$, while it is suppressed for values of $d$ beyond a critical value. In order to characterize this effect, the critical Reynolds number for the appearance of vortex breakdown as a function of the radius of the fixed rods and the different aspect ratios was accurately determined, using digital particle image velocimetry. The numerical and experimental results are compared showing an excellent agreement. In addition, a simple model in order to show that this effect also appears in open pipe flows is presented in the appendix.
Alginate microparticles as flow seeding fulfil all the requirements that are recommended for the ... more Alginate microparticles as flow seeding fulfil all the requirements that are recommended for the velocity measurements in Particle Image Velocimetry (PIV). These spherical microparticles offer the advantage of being environmentally friendly, having excellent seeding properties and they can be produced via a very simple process. In the present study, the performances of alginate microparticles functionalised with a fluorescent dye, Rhodamine B (RhB), for PIV have been studied. The efficacy of fluorescence is appreciated in a number of PIV applications since it can boost the signal-to-noise ratio. Alginate microparticles functionalised with RhB have high emission efficiency, desirable match with fluid density and controlled size. The study of the particles behaviour in strong acid and basic solutions and ammonia is also included. This type of particles can be used for measurements with PIV and Planar Laser Induced Fluorescence (PLIF) simultaneously, including acid-base reactions.
The main,objective of this work,is to study velocity fields in complex,domains,like those encount... more The main,objective of this work,is to study velocity fields in complex,domains,like those encountered in computers or other electronics refrigerated systems with printed circuit board (PCB). Particle Image Velocimetry (PIV) has been used to obtain thevelocity field in a simplified model of a PCB. Previous
ABSTRACT The heat transfer analysis and temperature distribution inside printed circuit board (PC... more ABSTRACT The heat transfer analysis and temperature distribution inside printed circuit board (PCB) enclosures for different geometries was investigated in this paper. Herein, the computational fluid dynamic (CFD) solver caffa3d.MB was employed to simulate the 3D incompressible Navier-Stokes equations. The numerical method uses a spatial discretization based on block-structured, nonorthogonal body fitted grids. Numerical simulations for two different PCB geometry configurations are analysed using eight Reynolds numbers. The temperature field is practically the same above the plate encasing the PCB, differences appear below the plate. While analysing the plane just below for the open geometry the main consideration is the presence of a hot zone. The greater heat transfer is obtained in the top channel for both geometries. In turn, in the bottom channel the heat transfer is greater in the closed geometry than the open one. The calculating results show that the cooling of the PCB is more efficient for the closed geometry. Keywords: electrical enclosure, caffa3d.MB, numerical simulation, heat transfer.
We experimentally study the time evolution of the distance between two identical spheres settling... more We experimentally study the time evolution of the distance between two identical spheres settling down in polyacrylamide shear-thinning solutions in mixtures of water and glycerin. In order to analyze the behavior of the spheres under different rheological conditions, we varied the concentration of the polymer and glycerin. To examine the influence of wall effects, the experiments were performed in two containers of different size. We found that depending on the fluids' rheological properties, two different regimes are revealed for the same diluted polymer. In one of them (I), the separation between the spheres grows in time if the initial separation S i is beyond a critical distance S c , while the separation decreases for an initial distance shorter than S c. In the second observed regime (II), the spheres aggregate if S i < S c while they remain unchanged in their separation if S i > S c , i.e., repulsion is not detected. The transition from one to another regime can be produced at constant polymer concentration by changing the solvent viscosity η s. In our experiments this shift has been done modifying the glycerin-water proportion. Although these two behaviors were reported in previous works for different viscoelastic fluids, a result that we show is that both regimes can be observed for the same polymer. The elusive regime I, in which far-field repulsion is exhibited, is of particular interest since it has been previously reported only by Riddle et al. [J. Non-Newtonian Fluid Mech. 2, 23 (1997)]. Thus, our results confirm that this behavior is also feasible.
International Journal of Heat and Mass Transfer, Feb 1, 2016
Abstract In this paper we analyse, numerically and experimentally, the laminar reactive flow in a... more Abstract In this paper we analyse, numerically and experimentally, the laminar reactive flow in a cylindrical cavity with a rotating end wall. A basic solution is initially in the cavity and an acid solution is introduced at very low velocity through the center of the stationary endwall when the flow in the cavity is at the steady state. The effect of the different flow structures obtained at different Reynolds numbers on the irreversible fast acid–base neutralization is measured with a simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) technique and simulated numerically with a finite volume code. The observed flow structure, the recirculation bubbles in the vortex breakdown regions as well as the numerical velocity profiles are in agreement with the measurements and with previous studies. The range of measured concentrations is limited to regions where the molar fraction of the base (xB) is larger than 0.57. The comparison between the experimental and numerical contours of concentration of base solution at Re = 1000 and 1500 are in general agreement. At larger Reynolds numbers (Re = 1700, 2000 and 2300), the experimental and numerical contours of concentration of base solution inside the vortex breakdown bubbles differ because of the relatively large concentration of product (i.e. xB
Journal of Industrial and Engineering Chemistry, Apr 1, 2018
The numerical prediction of mass transfer rates of gas components within the liquid phase in a st... more The numerical prediction of mass transfer rates of gas components within the liquid phase in a stirred two-phase flow reactor is presented. Experiments have been conducted to determine the flow regime and the number and sizes of the bubbles formed under different conditions. The dynamic field of the twophase flow was obtained through numerical simulations. Bubbles with the experimentally measured diameter were released from the free surface and tracked numerically to compute the particle Reynolds number, which is used to determine the mass transfer rates. The unbaffled reactor provides mass transfer rates 30% larger than the baffled reactor for the bubbly flow. Mass transfer rates drop about 65% when the emulsion is formed. Therefore, above the critical rotation rate at which the emulsion forms for the unbaffled reactor, the baffled configuration provides larger mass transfer rates. The results indicate that even for the most unfavorable case mass transfer is not the limiting step, as 90% of the equilibrium concentration is reached in 10 s.
Several methods are available for measuring the fluid movement in experimental setups. One of the... more Several methods are available for measuring the fluid movement in experimental setups. One of the most used technique is the particle image velocimetry (PIV). This is an optical technique that indirectly measures the fluid velocity by measuring the displacement of some small particles that seeds the fluid. To obtain the velocity field, the zone of interest of the experimental setup is illuminated twice with a laser beam. Two consecutive images are obtained and the displacement of the particles can be calculated. Knowing the time difference between both images allow to compute the velocity. Appropriate flow seeding is particularly critical in PIV. Particles that follow the flow accordingly and scatter enough light must be used in order to obtain accurate velocity field of the flow. Therefore, particles should be as small as possible in order to ensure good tracking of the fluid motion and they should not be too small, since they will not scatter enough light.
The aim of this paper was to evaluate the potential of using near-infrared (NIR) spectroscopy and... more The aim of this paper was to evaluate the potential of using near-infrared (NIR) spectroscopy and multivariate analysis as a rapid tool to non-destructively determine the presence of surface treatments applied to cork stoppers. Density and dimensions of 6 closure varieties were characterized and the extraction force was measured on those produced for still wines. Cork stoppers were also analyzed using hand-held NIR and Raman spectrometers. Soft independent modelling of class analogy (SIMCA) models showed significant differences among treated and untreated samples, linked to components of the coating agents applied (silicone and paraffin). SIMCA model's classification performance was tested and high sensitivity (93.33 %) and specificity (100 %) values were obtained. Partial least squares regression (PLSR) model accurately predicted the extraction forces measured with low standard error of prediction (SEP = 4.0 daN). Our results are promising for the future application of this technology in cork industry, reducing time and economic losses.
Journal of Industrial and Engineering Chemistry, 2018
The numerical prediction of mass transfer rates of gas components within the liquid phase in a st... more The numerical prediction of mass transfer rates of gas components within the liquid phase in a stirred two-phase flow reactor is presented. Experiments have been conducted to determine the flow regime and the number and sizes of the bubbles formed under different conditions. The dynamic field of the twophase flow was obtained through numerical simulations. Bubbles with the experimentally measured diameter were released from the free surface and tracked numerically to compute the particle Reynolds number, which is used to determine the mass transfer rates. The unbaffled reactor provides mass transfer rates 30% larger than the baffled reactor for the bubbly flow. Mass transfer rates drop about 65% when the emulsion is formed. Therefore, above the critical rotation rate at which the emulsion forms for the unbaffled reactor, the baffled configuration provides larger mass transfer rates. The results indicate that even for the most unfavorable case mass transfer is not the limiting step, as 90% of the equilibrium concentration is reached in 10 s.
We experimentally study the time evolution of the distance between two identical spheres settling... more We experimentally study the time evolution of the distance between two identical spheres settling down in polyacrylamide shear-thinning solutions in mixtures of water and glycerin. In order to analyze the behavior of the spheres under different rheological conditions, we varied the concentration of the polymer and glycerin. To examine the influence of wall effects, the experiments were performed in two containers of different size. We found that depending on the fluids' rheological properties, two different regimes are revealed for the same diluted polymer. In one of them (I), the separation between the spheres grows in time if the initial separation S i is beyond a critical distance S c , while the separation decreases for an initial distance shorter than S c. In the second observed regime (II), the spheres aggregate if S i < S c while they remain unchanged in their separation if S i > S c , i.e., repulsion is not detected. The transition from one to another regime can be produced at constant polymer concentration by changing the solvent viscosity η s. In our experiments this shift has been done modifying the glycerin-water proportion. Although these two behaviors were reported in previous works for different viscoelastic fluids, a result that we show is that both regimes can be observed for the same polymer. The elusive regime I, in which far-field repulsion is exhibited, is of particular interest since it has been previously reported only by Riddle et al. [J. Non-Newtonian Fluid Mech. 2, 23 (1997)]. Thus, our results confirm that this behavior is also feasible.
Appropriate flow seeding is particularly critical with in the particle image velocimetry (PIV) te... more Appropriate flow seeding is particularly critical with in the particle image velocimetry (PIV) technique that indirectly measures the displacement from the particle velocity instead of fluid velocity. Particles that follow the flow accordingly and scatter enough light must be used in order to obtain accurate velocity field of the flow. Therefore, particles should be as small as possible in order to ensure good tracking of the fluid motion and they should not be too small, since they will not scatter enough light. The microparticles can be obtained from approximately 20 nm to around 50 µm in a controlled manner with ability increasing their light scattering behavior by fluorescein imbedding so that they gain the light scattering property. Alginate microparticles as flow seeding fulfill all the requirements that are recommended for the velocity measurements in PIV. These spherical microparticles offer the advantage of being environmentally friendly, excellent seeding properties and very simple production ability. They can be obtained as small as possible while increasing its scattering behavior by adding fluorescein into them. Additionally, they can be perfectly used as flow seeding in gas and several liquid flows with matching densities.
The reactive and laminar flow in a cylindrical cavity with a rotating end wall is analysed experi... more The reactive and laminar flow in a cylindrical cavity with a rotating end wall is analysed experimentally, using Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF), and numerically using the commercial code Ansys Fluent. The cavity is initially filled with a basic solution and the acid solution is introduced through a small inlet at the bottom wall. The experimental emergence of the vortex breakdown for an aspect ratio H/R = 2, that occurs at Re = 1500 has been compared with previous studies. The numerically predicted velocity profiles are in agreement with the measurements. The measured product concentration is limited in regions where the molar fraction of the base (x B) is larger than 0.57, because the response of the fluorescence light is linear in this range. The simultaneous combination of PIV and PLIF has been performed with success. The separation of PIV and PLIF signals has been possible by means of physical and computational filters. In simultaneous PIV and PLIF experiments, the PIV results are comparable with the previous results obtained using only the PIV technique. Also, the experimental contours of concentration obtained with PLIF, are in general agreement with the numerical predictions.
International Journal of Heat and Mass Transfer, 2016
Abstract In this paper we analyse, numerically and experimentally, the laminar reactive flow in a... more Abstract In this paper we analyse, numerically and experimentally, the laminar reactive flow in a cylindrical cavity with a rotating end wall. A basic solution is initially in the cavity and an acid solution is introduced at very low velocity through the center of the stationary endwall when the flow in the cavity is at the steady state. The effect of the different flow structures obtained at different Reynolds numbers on the irreversible fast acid–base neutralization is measured with a simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) technique and simulated numerically with a finite volume code. The observed flow structure, the recirculation bubbles in the vortex breakdown regions as well as the numerical velocity profiles are in agreement with the measurements and with previous studies. The range of measured concentrations is limited to regions where the molar fraction of the base (xB) is larger than 0.57. The comparison between the experimental and numerical contours of concentration of base solution at Re = 1000 and 1500 are in general agreement. At larger Reynolds numbers (Re = 1700, 2000 and 2300), the experimental and numerical contours of concentration of base solution inside the vortex breakdown bubbles differ because of the relatively large concentration of product (i.e. xB
Appropriate flow seeding is particularly critical with in the particle image velocimetry (PIV) te... more Appropriate flow seeding is particularly critical with in the particle image velocimetry (PIV) technique that indirectly measures the displacement from the particle velocity instead of fluid velocity. Particles that follow the flow accordingly and scatter enough light must be used in order to obtain accurate velocity field of the flow. Therefore, particles should be as small as possible in order to ensure good tracking of the fluid motion and they should not be too small, since they will not scatter enough light. The microparticles can be obtained from approximately 20 nm to around 50 µm in a controlled manner with ability increasing their light scattering behavior by fluorescein imbedding so that they gain the light scattering property. Alginate microparticles as flow seeding fulfill all the requirements that are recommended for the velocity measurements in PIV. These spherical microparticles offer the advantage of being environmentally friendly, excellent seeding properties and very simple production ability. They can be obtained as small as possible while increasing its scattering behavior by adding fluorescein into them. Additionally, they can be perfectly used as flow seeding in gas and several liquid flows with matching densities.
This study analyzes experimentally the deposition of magnetic beads on the walls of a square micr... more This study analyzes experimentally the deposition of magnetic beads on the walls of a square microchannel by the action of a nearby cubical magnet. The deposition has been studied for different magnetic bead sizes, flow rates, magnetic conditions and with solutions of magnetic and non-magnetic particles. Images of the time evolution of the deposition under the different conditions have been analyzed to determine the spatial distribution of the accumulation and the growth rate of the depositions. It has been found that the way in which the magnetic beads are deposited on the walls of the microchannel depends strongly on their size and the magnetic configuration. The accumulation of the major part of particles is on the wall closest to the magnet and, depending on the size of the particles, near the magnet leading and trailing edges or near the center of the magnet. The experiments with magnetic and non-magnetic particles revealed the screening effect of the non-magnetic particles on ...
The effect of fixed cylindrical rods located at the centerline axis on vortex breakdown (VB) is s... more The effect of fixed cylindrical rods located at the centerline axis on vortex breakdown (VB) is studied experimentally and numerically. We find that the VB is enhanced for very small values of the rod radius $d$, while it is suppressed for values of $d$ beyond a critical value. In order to characterize this effect, the critical Reynolds number for the appearance of vortex breakdown as a function of the radius of the fixed rods and the different aspect ratios was accurately determined, using digital particle image velocimetry. The numerical and experimental results are compared showing an excellent agreement. In addition, a simple model in order to show that this effect also appears in open pipe flows is presented in the appendix.
Alginate microparticles as flow seeding fulfil all the requirements that are recommended for the ... more Alginate microparticles as flow seeding fulfil all the requirements that are recommended for the velocity measurements in Particle Image Velocimetry (PIV). These spherical microparticles offer the advantage of being environmentally friendly, having excellent seeding properties and they can be produced via a very simple process. In the present study, the performances of alginate microparticles functionalised with a fluorescent dye, Rhodamine B (RhB), for PIV have been studied. The efficacy of fluorescence is appreciated in a number of PIV applications since it can boost the signal-to-noise ratio. Alginate microparticles functionalised with RhB have high emission efficiency, desirable match with fluid density and controlled size. The study of the particles behaviour in strong acid and basic solutions and ammonia is also included. This type of particles can be used for measurements with PIV and Planar Laser Induced Fluorescence (PLIF) simultaneously, including acid-base reactions.
The main,objective of this work,is to study velocity fields in complex,domains,like those encount... more The main,objective of this work,is to study velocity fields in complex,domains,like those encountered in computers or other electronics refrigerated systems with printed circuit board (PCB). Particle Image Velocimetry (PIV) has been used to obtain thevelocity field in a simplified model of a PCB. Previous
ABSTRACT The heat transfer analysis and temperature distribution inside printed circuit board (PC... more ABSTRACT The heat transfer analysis and temperature distribution inside printed circuit board (PCB) enclosures for different geometries was investigated in this paper. Herein, the computational fluid dynamic (CFD) solver caffa3d.MB was employed to simulate the 3D incompressible Navier-Stokes equations. The numerical method uses a spatial discretization based on block-structured, nonorthogonal body fitted grids. Numerical simulations for two different PCB geometry configurations are analysed using eight Reynolds numbers. The temperature field is practically the same above the plate encasing the PCB, differences appear below the plate. While analysing the plane just below for the open geometry the main consideration is the presence of a hot zone. The greater heat transfer is obtained in the top channel for both geometries. In turn, in the bottom channel the heat transfer is greater in the closed geometry than the open one. The calculating results show that the cooling of the PCB is more efficient for the closed geometry. Keywords: electrical enclosure, caffa3d.MB, numerical simulation, heat transfer.
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Papers by Sylvana Varela