WO2013087966A1 - Use of alginates in particle image velocimetry and method for measuring the velocity of a fluid - Google Patents

Use of alginates in particle image velocimetry and method for measuring the velocity of a fluid Download PDF

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Publication number
WO2013087966A1
WO2013087966A1 PCT/ES2012/070867 ES2012070867W WO2013087966A1 WO 2013087966 A1 WO2013087966 A1 WO 2013087966A1 ES 2012070867 W ES2012070867 W ES 2012070867W WO 2013087966 A1 WO2013087966 A1 WO 2013087966A1
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particles
alginate
fluid
tracer
piv
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PCT/ES2012/070867
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Spanish (es)
French (fr)
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Nihal ERTÜRK DÜZGÜN
Antonio VERNET PEÑA
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Universitat Rovira I Virgili
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Publication of WO2013087966A1 publication Critical patent/WO2013087966A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
    • G01P5/18—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance
    • G01P5/22—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance using auto-correlation or cross-correlation detection means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/85—Investigating moving fluids or granular solids

Definitions

  • the present invention relates to particle image velocimetry ⁇ partióle image velocimetry, or PIV), and in particular to the use of a new type of tracer particles in PIV.
  • Velocity imaging by particle imaging is a widely used technique that consists of sowing a fluid (liquid or gas) with tracer particles to directly measure particle displacement and thus determine fluid velocity.
  • the tracer particles should be as small as possible to ensure a good flow path. However, they should not be too small, because in that case they would not reflect enough light.
  • the tracer particles of the fluid are illuminated at least twice in a short period of time with a laser in a plane of the flow. It is assumed that the tracer particles move at the fluid velocity between each of the illuminations. The light reflected by the particles is recorded in a single image or in a sequence of images. Then the displacement of the particles between each of the illuminations is determined by analyzing the PIV images. This is an indirect technique because it measures the speed of the particles instead of the speed of the fluid, so the properties must be checked mechanical flow of the particles to avoid significant discrepancies between the flow of the fluid and that of the particles.
  • the tracer particles most used in research with PIV are polystyrene, aluminum, glass microspheres, different oils and air bubbles.
  • the intensity of the image obtained from the particles is directly proportional to their ability to reflect the light. Therefore, it is more effective and economical to increase the intensity of the image by a correct selection of particles rather than by the use of a higher power laser.
  • Patent application US5124071 describes the tracer particles for use in PIV.
  • the proposed microscopic particles are composed of an acrylic resin (methacrylate) and its diameter ranges between 10 and 30 microns.
  • a special chamber is required for the generation of these particles, which complicates their production.
  • these particles are not appropriate for certain applications, such as experimental analysis of flow dynamics in systems containing metal parts in contact, since the interaction of rigid particles with the contact between metals would damage the system.
  • the invention solves the problems set forth in the previous section through the use of alginate particles in particle image velocimetry (PIV).
  • the invention proposes a method for measuring the velocity of a fluid by sowing tracer particles in the fluid and recording the light they reflect at two different times and where the tracer particles are alginate particles.
  • the diameter of the alginate particles preferably ranges between 0.2 and 30 microns and optionally an embedded fluorescent dye such as fluorescein can be applied.
  • the use of alginate particles with fluorescent dye improves contrast with any fluid in applications in those that green laser is used to illuminate the particles and that these reflect the light.
  • Alginate particles can be produced in the form of a sphere with exact diameters such as 0.2 ⁇ , 1 ⁇ , 5 ⁇ , 10 ⁇ or higher. Thanks to their spherical shape and an adequate diameter, alginate particles have a good fluidity (monitoring the fluid in which they are immersed). In general, it is important that the particles have a spherical shape due to their known interactions with fluids and the visual response to illumination. The particles are very suitable for systems with metallic parts in contact with each other or rotating, since they do not damage the systems because their structure is soft and jelly-like. In addition, alginates are neither toxic nor harmful to the environment and, being porous, their density can be matched to that of the fluid so that the flow monitoring is carried out more effectively.
  • Figure 1 Graph showing the size distribution of alginate particles and air bubbles as a percentage of the number of particles of each size compared to the total number of particles.
  • Figure 2 Graph showing the response time of different tracer particles of 5 ⁇ in diameter in an accelerating water flow.
  • Figure 3 Photograph of spherical alginate particles used in the present invention.
  • Figure 4 Graph showing the displacement errors derived from the use of air bubbles and alginate particles in the analysis speed measurements of a gear pump with different number of phase average images.
  • Alginate is a natural and non-toxic polysaccharide present in all species of brown algae. Chemically, alginate is a linear copolymer consisting of junctions (1-4) of ⁇ -D-mannuronic acid and ⁇ -L-guluronic acid. Generally, alginate microspheres are produced by one of two known methods: (i) by dripping an aqueous alginate solution in a solution of calcium salts, or (ii) by emulsification, gently stirring. The particles produced by method (i) are usually larger (more than 1 mm in diameter) and the production of smaller particles requires a special device that can have disadvantages such as its high cost and potential for obstruction. Method (ii) has recently been extended to the field of nanotechnology.
  • alginate microspheres by internal emulsification / gelation also has several advantages. Encapsulation in alginate spheres is considered a safe system, Simple and economical that has good mechanical stability. In internal gelation, calcium ions are distributed homogeneously in the alginate solution, so the diffusion of protons to the pregelled drops induces gelation from the surface, and creates homogeneous drops. In addition, the low shear of internal gelation protects fragile encapsulants. Applications in the biological and food industries can also be considered, since this procedure does not require the use of toxic reagents or solvents. This method allows the efficient production of large quantities of micro and nanospheres of small and controlled diameter. The particles produced by internal gelation are more porous than those produced by external gelation, which are not suitable for food and biomedical applications. This disadvantage can become an advantage if these particles are used in a PIV system.
  • the internal emulsification / gelation method is preferred, which is made possible by the formation of a water / oil emulsion whose drops are stabilized by the use of surfactants.
  • an ultrasonic probe is used to agitate and detach the particles. 50 g of aqueous solution with a concentration of 3% sodium alginate is stirred for 6 hours with a magnetic stirrer at 900 rpm.
  • the type of alginate used is the sodium salt of low viscosity alginic acid from brown algae.
  • 0.2 g of fluorescein is added to the solution and stirring is continued at the same rate for 2 hours.
  • This aqueous solution is dispersed in 75 g of isooctane containing 1.7 g of SPAN 85 using a magnetic stirrer at 1600 rpm and an ultrasonic probe at a power of 60 with a frequency of 0.5 for 10 minutes.
  • Another solution containing 0.9 g of TWEEN 85 in 6 g of isooctane is added to the emulsion and stirred with the magnetic stirrer and the ultrasonic probe at the same rate for 5 minutes.
  • aqueous solution with a concentration of 10% calcium chloride and allow to react for 20 minutes while stirring at 1600 rpm to allow ionotropic gelation of the particles. Then, the solution is subjected to an ultrasonic bath and stirred for 30 minutes. Before collecting the particles, the emulsion is diluted with 500 ml of distilled water to reduce the possibility of the spheres sticking to each other if they come into contact and to slow down the gelation process. After dilution, the solution is allowed to settle and then the emulsion particles are separated. The particles are subjected to a liquid filtrate with the aid of a syringe filter of 5 ⁇ pore size, or less, as a separation process.
  • These particles can be used as tracer particles in the analysis of water flows.
  • PIV such as analyzing gas flows
  • the particles using the magnetic stirrer to a maximum temperature of 60 Q C to obtain dry microparticles are dried.
  • a solid filtrate can be applied with the aid of an agitator to obtain the particles having the appropriate diameter ready to be used as tracer particles in different areas of application of PIV.
  • alginate particles with a diameter of nanometers containing fluorescein can be produced.
  • the fluorescein with which the alginate particles are stained allows the tracer particles of the PIV system to reflect a large amount of light.
  • the particles concentrate and retain a large amount of fluorescein thanks to the absorption and diffusion properties of alginate particles.
  • the PIV technique takes advantage of these particle properties and uses them effectively in flow systems to obtain clear digital images.
  • the elasticity of alginate particles can be controlled by adjusting the parameters during the production process. To obtain more rigid alginate particles, more calcium chloride and / or isooctane solvent can be added.
  • the particles produced in the manner indicated are particularly suitable for analyzing external gear pumps.
  • alginate particles 10 microns and for air bubbles is 100 ⁇ .
  • alginate particles larger than 10 ⁇ were also detected, although in a very small percentage of the total objects measured.
  • air bubbles 32% had a size of 100 ⁇ , which indicates that, under equal conditions, alginate particles are more suitable for the gear pump system due to a size distribution of smaller particles, with a maximum peak near 10 ⁇ .
  • the production process can be optimized to increase the percentage of alginate particles of
  • Up is the velocity of the particle
  • U is the velocity of the fluid
  • r s is the relaxation time given by: (Equation 2) where d p is the diameter of the particle and ⁇ is the dynamic viscosity of the fluid.
  • T S is an indicator of the ability of a particle of a certain size and density to respond to fluid acceleration.
  • the response of a particle to a step is useful for measuring the tendency of a particle to reach equilibrium velocity with the fluid.
  • Figure 2 shows the result of the response time of different particles with constant diameters of 5 ⁇ before a strong acceleration in a water flow.
  • the alginate particles were the fastest of the three types of particles at any given time, which means that the alginate particles are the ones that cooperate most with the movement of the observed fluid.
  • the images of alginate particles obtained by scanning electron microscopy show three-dimensional spherical shapes with different size distribution between 0.2 and 30 microns. Note that the system has not been subject to the filtering process, so that with the appropriate filtering particles of homogeneous size can easily be produced.
  • the PIV technique benefits from spherical alginate particles having a homogeneous size distribution and using them effectively in flow systems to obtain sharp digital images.
  • Figure 4 shows a comparison of the total errors of alginate particles and air bubbles by adding the mean bias and the mean square root of the errors.
  • These errors are displacement errors that can be observed in the PIV data analysis of the gear pump model.
  • PIV data analysis is performed by studying the correlation between the 32x32 pixel question windows in which the images are divided. In order to analyze the flow in detail, we reduced the interrogation windows to 32x32 pixels since this size is best suited for the analysis of turbulent flows on a small scale. The data is obtained from the reading of the PIV analysis of the external gear pump.
  • the offset error is shown by comparing a variety of phase average images and the pixel offset error.
  • the graph indicates that, when alginate particles are used, the displacement error is much smaller by 10 orders of magnitude, which suggests that measurements with PIV are more accurate when alginate particles are used than when air bubbles are used. This is possible thanks to its smaller diameter, which allows increasing the number of particles present in the same image window.

Abstract

A particle image velocimetry method for measuring the velocity of a fluid by means of seeding the fluid with tracer particles and recording the light reflected at two different moments in time, wherein the tracer particles are particles of alginate. This method may be used in systems with metal parts in contact with one another, since no damage will be caused thereto. The particles are spherical and, furthermore, non-toxic and non-harmful to the environment; moreover, as the particles are porous, the density thereof may be matched easily with that of the fluid for effective monitoring thereof.

Description

USO DE ALGINATOS EN VELOCIMETRIA POR IMAGENES DE PARTÍCULAS Y PROCEDIMIENTO PARA MEDIR LA VELOCIDAD DE UN USE OF ALGINATES AT SPEED BY PARTICLE IMAGES AND PROCEDURE TO MEASURE THE SPEED OF A
FLUIDO FLUID
D E S C R I P C I O N D E S C R I P C I O N
CAMPO TECNICO DE LA INVENCION TECHNICAL FIELD OF THE INVENTION
La presente invención se refiere a la velocimetría por imágenes de partículas {partióle image velocimetry, o PIV), y en particular al uso de un nuevo tipo de partículas trazadoras en PIV. The present invention relates to particle image velocimetry {partióle image velocimetry, or PIV), and in particular to the use of a new type of tracer particles in PIV.
ESTADO DE LA TECNICA STATE OF THE TECHNIQUE
La velocimetría por imágenes de partículas es una técnica ampliamente utilizada que consiste en sembrar un fluido (líquido o gas) con partículas trazadoras para medir directamente el desplazamiento de las partículas y determinar así la velocidad del fluido. Las partículas trazadoras deben tener el menor tamaño posible para asegurar un buen trazado del flujo. Sin embargo, no deben ser demasiado pequeñas, porque en ese caso no reflejarían suficiente luz. Las partículas trazadoras del fluido se iluminan al menos dos veces en un corto intervalo de tiempo con un láser en un plano del flujo. Se asume que las partículas trazadoras se desplazan a la velocidad del fluido entre cada una de las iluminaciones. La luz que reflejan las partículas se registra en una única imagen o en una secuencia de imágenes. Después se determina el desplazamiento de las partículas entre cada una de las iluminaciones mediante el análisis de las imágenes PIV. Se trata de una técnica indirecta porque mide la velocidad de las partículas en lugar de la velocidad del fluido, por lo que deberán comprobarse las propiedades mecánicas del flujo de las partículas para evitar discrepancias significativas entre el flujo del fluido y el de las partículas. Velocity imaging by particle imaging is a widely used technique that consists of sowing a fluid (liquid or gas) with tracer particles to directly measure particle displacement and thus determine fluid velocity. The tracer particles should be as small as possible to ensure a good flow path. However, they should not be too small, because in that case they would not reflect enough light. The tracer particles of the fluid are illuminated at least twice in a short period of time with a laser in a plane of the flow. It is assumed that the tracer particles move at the fluid velocity between each of the illuminations. The light reflected by the particles is recorded in a single image or in a sequence of images. Then the displacement of the particles between each of the illuminations is determined by analyzing the PIV images. This is an indirect technique because it measures the speed of the particles instead of the speed of the fluid, so the properties must be checked mechanical flow of the particles to avoid significant discrepancies between the flow of the fluid and that of the particles.
Las partículas trazadoras más usadas en investigación con PIV son el poliestireno, el aluminio, las microesferas de cristal, diferentes aceites y burbujas de aire. La intensidad de la imagen que se obtiene de las partículas es directamente proporcional a su capacidad para reflejar la luz. Por lo tanto, resulta más efectivo y económico aumentar la intensidad de la imagen mediante una correcta selección de partículas antes que mediante el uso de un láser de mayor potencia.  The tracer particles most used in research with PIV are polystyrene, aluminum, glass microspheres, different oils and air bubbles. The intensity of the image obtained from the particles is directly proportional to their ability to reflect the light. Therefore, it is more effective and economical to increase the intensity of the image by a correct selection of particles rather than by the use of a higher power laser.
La solicitud de patente US5124071 describe las partículas trazadoras para uso en PIV. Las partículas microscópicas propuestas se componen de una resina acrílica (metacrilato) y su diámetro oscila entre los 10 y los 30 micrones. Para la generación de estas partículas se requiere una cámara especial, lo que complica su producción. Además, estas partículas no son apropiadas para ciertas aplicaciones, como el análisis experimental de dinámicas de flujo en sistemas que contienen partes metálicas en contacto, puesto que la interacción de las partículas rígidas con el contacto entre metales dañaría el sistema. OBJETO DE LA INVENCIÓN Patent application US5124071 describes the tracer particles for use in PIV. The proposed microscopic particles are composed of an acrylic resin (methacrylate) and its diameter ranges between 10 and 30 microns. A special chamber is required for the generation of these particles, which complicates their production. In addition, these particles are not appropriate for certain applications, such as experimental analysis of flow dynamics in systems containing metal parts in contact, since the interaction of rigid particles with the contact between metals would damage the system. OBJECT OF THE INVENTION
La invención solventa los problemas expuestos en la sección anterior mediante el uso de partículas de alginato en velocimetría por imágenes de partículas (PIV). En particular, la invención propone un procedimiento para medir la velocidad de un fluido mediante el sembrado de partículas trazadoras en el fluido y el registro de la luz que reflejan en dos momentos diferentes y donde las partículas trazadoras son partículas de alginato. El diámetro de las partículas de alginato oscila preferiblemente entre 0,2 y 30 micrones y opcionalmente se les puede aplicar un tinte fluorescente embebido como la fluoresceína. El uso de partículas de alginato con tinte fluorescente mejora el contraste con cualquier fluido en las aplicaciones en las que se use láser verde para iluminar las partículas y que estas reflejen la luz. The invention solves the problems set forth in the previous section through the use of alginate particles in particle image velocimetry (PIV). In particular, the invention proposes a method for measuring the velocity of a fluid by sowing tracer particles in the fluid and recording the light they reflect at two different times and where the tracer particles are alginate particles. The diameter of the alginate particles preferably ranges between 0.2 and 30 microns and optionally an embedded fluorescent dye such as fluorescein can be applied. The use of alginate particles with fluorescent dye improves contrast with any fluid in applications in those that green laser is used to illuminate the particles and that these reflect the light.
Las partículas de alginato pueden producirse en forma de esfera con diámetros exactos como 0,2 μιη, 1 μιη, 5 μιη, 10 μιη o superiores. Gracias a su forma esférica y a un diámetro adecuado, las partículas de alginato presentan una buena fluidez (seguimiento del fluido en el que se encuentran inmersas). En general, es importante que las partículas tengan forma esférica debido a sus conocidas interacciones con fluidos y a la respuesta visual a la iluminación. Las partículas son muy apropiadas para los sistemas con partes metálicas en contacto entre sí o giratorias, ya que no dañan los sistemas porque su estructura es blanda y gelatinosa. Además, los alginatos no son tóxicos ni perjudiciales para el medio ambiente y, al ser porosos, se puede igualar su densidad a la del fluido para que el seguimiento del flujo se realice con mayor eficacia. Alginate particles can be produced in the form of a sphere with exact diameters such as 0.2 μιη, 1 μιη, 5 μιη, 10 μιη or higher. Thanks to their spherical shape and an adequate diameter, alginate particles have a good fluidity (monitoring the fluid in which they are immersed). In general, it is important that the particles have a spherical shape due to their known interactions with fluids and the visual response to illumination. The particles are very suitable for systems with metallic parts in contact with each other or rotating, since they do not damage the systems because their structure is soft and jelly-like. In addition, alginates are neither toxic nor harmful to the environment and, being porous, their density can be matched to that of the fluid so that the flow monitoring is carried out more effectively.
BREVE DESCRIPCIÓN DE LAS FIGURAS BRIEF DESCRIPTION OF THE FIGURES
Las figuras adjuntas tienen por objeto completar la descripción y facilitar la comprensión de la invención. Las mismas ilustran una puesta en práctica preferente de la invención pero no deben interpretarse como una restricción al alcance de la invención, sino simplemente como un ejemplo de la forma que podría adoptar la misma. Se incluyen las siguientes figuras: The attached figures are intended to complete the description and facilitate the understanding of the invention. They illustrate a preferred implementation of the invention but should not be construed as a restriction on the scope of the invention, but simply as an example of the form it could take. The following figures are included:
Figura 1 : gráfico que muestra la distribución por tamaño de las partículas de alginato y de las burbujas de aire como un porcentaje del número de partículas de cada tamaño comparado con el número total de partículas. Figure 1: Graph showing the size distribution of alginate particles and air bubbles as a percentage of the number of particles of each size compared to the total number of particles.
Figura 2: gráfico que muestra el tiempo de respuesta de distintas partículas trazadoras de 5 μιη de diámetro en un flujo de agua en aceleración. Figura 3: fotografía de las partículas esféricas de alginato usadas en la presente invención. Figure 2: Graph showing the response time of different tracer particles of 5 μιη in diameter in an accelerating water flow. Figure 3: Photograph of spherical alginate particles used in the present invention.
Figura 4: gráfico que muestra los errores de desplazamiento derivados del uso de burbujas de aire y de partículas de alginato en las mediciones de velocidad del análisis de una bomba de engranajes con diferente número de imágenes de promedio de fase. Figure 4: Graph showing the displacement errors derived from the use of air bubbles and alginate particles in the analysis speed measurements of a gear pump with different number of phase average images.
DESCRIPCION DETALLADA DE LA INVENCIÓN DETAILED DESCRIPTION OF THE INVENTION
El alginato es un polisacárido natural y no tóxico presente en todas las especies de algas pardas. Químicamente, el alginato es un copolímero lineal consistente en uniones (1 -4) de ácido β-D-manurónico y ácido a-L- gulurónico. Generalmente, las microesferas de alginato se producen mediante uno de los dos métodos conocidos: (i) por goteo de una solución acuosa de alginato en una solución de sales cálcicas, o (ii) por emulsificación, agitando suavemente. Las partículas producidas con el método (i) suelen ser más grandes (más de 1 mm de diámetro) y la producción de partículas más pequeñas requiere de un dispositivo especial que puede presentar desventajas como su alto coste y potencial de obstrucción. El método (ii) se ha extendido recientemente al campo de la nanotecnología. Las pruebas experimentales indican que se han producido con éxito nanopartículas de alginato gracias a la creación de las condiciones ideales para la formulación. Para el método de la presente invención, se han escogido partículas con un diámetro de entre 0,2 y 30 micrones. La emulsificación/gelificación interna es un procedimiento adecuado y económico para la producción de microesferas de alginato de ese tamaño. Alginate is a natural and non-toxic polysaccharide present in all species of brown algae. Chemically, alginate is a linear copolymer consisting of junctions (1-4) of β-D-mannuronic acid and α-L-guluronic acid. Generally, alginate microspheres are produced by one of two known methods: (i) by dripping an aqueous alginate solution in a solution of calcium salts, or (ii) by emulsification, gently stirring. The particles produced by method (i) are usually larger (more than 1 mm in diameter) and the production of smaller particles requires a special device that can have disadvantages such as its high cost and potential for obstruction. Method (ii) has recently been extended to the field of nanotechnology. Experimental tests indicate that alginate nanoparticles have been successfully produced thanks to the creation of the ideal conditions for formulation. For the method of the present invention, particles with a diameter between 0.2 and 30 microns have been chosen. Internal emulsification / gelation is a suitable and economical process for the production of alginate microspheres of that size.
La producción de microesferas de alginato mediante emulsificación/gelificación interna presenta además varias ventajas. La encapsulación en esferas de alginato se considera un sistema seguro, sencillo y económico que presenta una buena estabilidad mecánica. En la gelificación interna, los iones calcio se distribuyen homogéneamente en la solución de alginato, por lo que la difusión de protones hacia las gotas pregelificadas induce la gelificación desde la superficie, y crea gotas homogéneas. Además, el bajo cizallamiento de la gelificación interna protege los encapsulantes frágiles. También se pueden considerar aplicaciones en las industrias biológica y alimentaria, ya que este procedimiento no requiere el uso de reactivos ni solventes tóxicos. Este método permite la producción eficiente de grandes cantidades de micro y nanoesferas de diámetro pequeño y controlado. Las partículas producidas por gelificación interna son más porosas que las producidas por gelificación externa, que no son apropiadas para aplicaciones alimentarias y biomédicas. Esta desventaja puede convertirse en ventaja si se usan estas partículas en un sistema PIV. The production of alginate microspheres by internal emulsification / gelation also has several advantages. Encapsulation in alginate spheres is considered a safe system, Simple and economical that has good mechanical stability. In internal gelation, calcium ions are distributed homogeneously in the alginate solution, so the diffusion of protons to the pregelled drops induces gelation from the surface, and creates homogeneous drops. In addition, the low shear of internal gelation protects fragile encapsulants. Applications in the biological and food industries can also be considered, since this procedure does not require the use of toxic reagents or solvents. This method allows the efficient production of large quantities of micro and nanospheres of small and controlled diameter. The particles produced by internal gelation are more porous than those produced by external gelation, which are not suitable for food and biomedical applications. This disadvantage can become an advantage if these particles are used in a PIV system.
Por lo tanto, para producir microesferas de gel de alginato se prefiere el método de la emulsificación/gelificación interna, que es posible gracias a la formación de una emulsión agua/aceite cuyas gotas se estabilizan mediante el uso de surfactantes. Para producir partículas más pequeñas, típicamente con un diámetro inferior a 10 μιη, se usa una sonda ultrasónica para agitar y desprender las partículas. Se agitan 50 g de solución acuosa con una concentración del 3% de alginato de sodio durante 6 horas con un agitador magnético a 900 rpm. El tipo de alginato que se usa es la sal sódica del ácido algínico de baja viscosidad, procedente de algas pardas. Según el tipo de láser, como en el caso del láser verde que se usa en PIV, se añaden a la solución 0,2 g de fluoresceína y se sigue agitando a la misma velocidad durante 2 horas. Esta solución acuosa se dispersa en 75 g de isooctano que contiene 1 ,7 g de SPAN 85 usando un agitador magnético a 1600 rpm y una sonda ultrasónica a una potencia de 60 con una frecuencia de 0,5 durante 10 minutos. Se añade a la emulsión otra solución que contiene 0,9 g de TWEEN 85 en 6 g de isooctano y se agita con el agitador magnético y la sonda ultrasónica a la misma velocidad durante 5 minutos. Entonces se añaden 20 g de solución acuosa con una concentración del 10% de cloruro cálcico y se deja reaccionar durante 20 minutos mientras se agita a 1600 rpm para permitir la gelificación ionotrópica de las partículas. Después, se somete la solución a un baño de ultrasonidos y se agita durante 30 minutos. Antes de recoger las partículas, se diluye la emulsión con 500 mi de agua destilada para reducir la posibilidad de que las esferas se peguen unas a otras si entran en contacto y para ralentizar el proceso de gelificación. Tras la dilución, se deja que solución se asiente y luego se separan las partículas de la emulsión. Las partículas se someten a un filtrado líquido con ayuda de un filtro de jeringa de 5 μιη de tamaño de poro, o menos, como proceso de separación. Estas partículas se pueden usar como partículas trazadoras en el análisis de flujos de agua. Para otras aplicaciones de PIV, como el análisis de flujos de gas, se secan las partículas utilizando el agitador magnético a una temperatura máxima de 60 QC para obtener micropartículas secas. Por último, se puede aplicar un filtrado sólido con ayuda de un agitador para obtener las partículas que tengan el diámetro adecuado listas para ser usadas como partículas trazadoras en diferentes áreas de aplicación de PIV. Therefore, to produce alginate gel microspheres, the internal emulsification / gelation method is preferred, which is made possible by the formation of a water / oil emulsion whose drops are stabilized by the use of surfactants. To produce smaller particles, typically with a diameter less than 10 μιη, an ultrasonic probe is used to agitate and detach the particles. 50 g of aqueous solution with a concentration of 3% sodium alginate is stirred for 6 hours with a magnetic stirrer at 900 rpm. The type of alginate used is the sodium salt of low viscosity alginic acid from brown algae. Depending on the type of laser, as in the case of the green laser used in PIV, 0.2 g of fluorescein is added to the solution and stirring is continued at the same rate for 2 hours. This aqueous solution is dispersed in 75 g of isooctane containing 1.7 g of SPAN 85 using a magnetic stirrer at 1600 rpm and an ultrasonic probe at a power of 60 with a frequency of 0.5 for 10 minutes. Another solution containing 0.9 g of TWEEN 85 in 6 g of isooctane is added to the emulsion and stirred with the magnetic stirrer and the ultrasonic probe at the same rate for 5 minutes. Then add 20 g of aqueous solution with a concentration of 10% calcium chloride and allow to react for 20 minutes while stirring at 1600 rpm to allow ionotropic gelation of the particles. Then, the solution is subjected to an ultrasonic bath and stirred for 30 minutes. Before collecting the particles, the emulsion is diluted with 500 ml of distilled water to reduce the possibility of the spheres sticking to each other if they come into contact and to slow down the gelation process. After dilution, the solution is allowed to settle and then the emulsion particles are separated. The particles are subjected to a liquid filtrate with the aid of a syringe filter of 5 μιη pore size, or less, as a separation process. These particles can be used as tracer particles in the analysis of water flows. For other applications PIV, such as analyzing gas flows, the particles using the magnetic stirrer to a maximum temperature of 60 Q C to obtain dry microparticles are dried. Finally, a solid filtrate can be applied with the aid of an agitator to obtain the particles having the appropriate diameter ready to be used as tracer particles in different areas of application of PIV.
Mediante el uso de un dispositivo ultrasónico durante el proceso de producción se pueden producir partículas de alginato con un diámetro de nanómetros que contengan fluoresceína. La fluoresceína con la que se tiñen las partículas de alginato permite que las partículas trazadoras del sistema PIV reflejen gran cantidad de luz. Las partículas concentran y retienen gran cantidad de fluoresceína gracias a las propiedades de absorción y difusión de las partículas de alginato. La técnica PIV aprovecha estas propiedades de las partículas y las usa eficazmente en los sistemas de flujos para obtener imágenes digitales nítidas. La elasticidad de las partículas de alginato se puede controlar mediante el ajuste de los parámetros durante el proceso de producción. Para obtener partículas de alginato más rígidas, se puede añadir más cloruro de calcio y/o solvente isooctano. Las partículas producidas de la forma indicada son particularmente adecuadas para analizar bombas de engranajes externos. Hasta ahora, en ese análisis se usaban burbujas de aire como partículas trazadoras, para no dañar los engranajes. Sin embargo, resulta muy difícil controlar el diámetro de las burbujas de aire. El uso de micropartículas de alginato como partículas trazadoras cumple con los requisitos de PIV para este sistema concreto de bomba de engranajes, ya que siguen el flujo del líquido que se use para el análisis sin dañar los engranajes. Para el caso de un proceso de producción de esferas de alginato de 10 μιη, se registraron dos imágenes PIV, en las que se usaron burbujas de aire y partículas de alginato como partículas trazadoras, en las mismas condiciones del campo de flujo de la bomba de engranajes externos. Las imágenes PIV se analizaron para medir y comparar la distribución por tamaño de partículas (PSD, por sus siglas en inglés) de los dos tipos de partículas trazadoras, como se muestra en la Figura 1 . Se ha constatado que el tamaño teóricamente óptimo para las partículas de alginato es 10 micrones y para las burbujas de aire es 100 μιη. En el análisis se detectaron también partículas de alginato mayores de 10 μιη, aunque en un porcentaje muy pequeño del total de objetos medidos. En el caso de las burbujas de aire, el 32% tenía un tamaño de 100 μιη, lo que indica que, en condiciones de igualdad, las partículas de alginato son más adecuadas para el sistema de bomba de engranajes debido a una distribución por tamaño de partículas menor, con un pico máximo cercano a 10 μιη. El proceso de producción puede optimizarse para aumentar el porcentaje de partículas de alginato deBy using an ultrasonic device during the production process, alginate particles with a diameter of nanometers containing fluorescein can be produced. The fluorescein with which the alginate particles are stained allows the tracer particles of the PIV system to reflect a large amount of light. The particles concentrate and retain a large amount of fluorescein thanks to the absorption and diffusion properties of alginate particles. The PIV technique takes advantage of these particle properties and uses them effectively in flow systems to obtain clear digital images. The elasticity of alginate particles can be controlled by adjusting the parameters during the production process. To obtain more rigid alginate particles, more calcium chloride and / or isooctane solvent can be added. The particles produced in the manner indicated are particularly suitable for analyzing external gear pumps. Until now, in that analysis air bubbles were used as tracer particles, so as not to damage the gears. However, it is very difficult to control the diameter of the air bubbles. The use of alginate microparticles as tracer particles meets the requirements of PIV for this particular gear pump system, since they follow the flow of the liquid used for analysis without damaging the gears. In the case of a production process of alginate spheres of 10 μιη, two PIV images were recorded, in which air bubbles and alginate particles were used as tracer particles, under the same conditions of the flow field of the pump external gears PIV images were analyzed to measure and compare the particle size distribution (PSD) of the two types of tracer particles, as shown in Figure 1. It has been found that the theoretically optimal size for alginate particles is 10 microns and for air bubbles is 100 μιη. In the analysis, alginate particles larger than 10 μιη were also detected, although in a very small percentage of the total objects measured. In the case of air bubbles, 32% had a size of 100 μιη, which indicates that, under equal conditions, alginate particles are more suitable for the gear pump system due to a size distribution of smaller particles, with a maximum peak near 10 μιη. The production process can be optimized to increase the percentage of alginate particles of
10 micrones. 10 microns
La influencia de las fuerzas gravitatorias cuando la densidad del fluido de trabajo es diferente de la densidad de las partículas trazadoras es una fuente primordial de error en PIV. Aunque puede pasarse por alto en muchas situaciones prácticas, el comportamiento de las partículas en aceleración se deriva de la Ley de Stokes (Ecuación 1 ). The influence of gravitational forces when the density of the working fluid is different from the density of the tracer particles is a primary source of error in PIV. Although it can be overlooked in many practical situations, the behavior of accelerating particles is derived from Stokes's Law (Equation 1).
(Ecuación 1 )
Figure imgf000009_0001
(Equation 1)
Figure imgf000009_0001
Up es la velocidad de la partícula, U es la velocidad del fluido y rs es el tiempo de relajación dado por:
Figure imgf000009_0002
(Ecuación 2) donde dp es el diámetro de la partícula y μ es la viscosidad dinámica del fluido. TS es un indicador de la capacidad de una partícula de cierto tamaño y densidad para responder ante la aceleración del fluido. Up is the velocity of the particle, U is the velocity of the fluid and r s is the relaxation time given by:
Figure imgf000009_0002
(Equation 2) where d p is the diameter of the particle and μ is the dynamic viscosity of the fluid. T S is an indicator of the ability of a particle of a certain size and density to respond to fluid acceleration.
La respuesta de una partícula a un escalón resulta útil para medir la tendencia de una partícula para alcanzar la velocidad de equilibrio con el fluido. La Figura 2 muestra el resultado del tiempo de respuesta de diferentes partículas con diámetros constantes de 5 μιη ante una aceleración fuerte en un flujo de agua. Las partículas de alginato fueron las más rápidas de los tres tipos de partículas en un momento dado, lo que significa que las partículas de alginato son las que más cooperan con el movimiento del fluido observado. The response of a particle to a step is useful for measuring the tendency of a particle to reach equilibrium velocity with the fluid. Figure 2 shows the result of the response time of different particles with constant diameters of 5 μιη before a strong acceleration in a water flow. The alginate particles were the fastest of the three types of particles at any given time, which means that the alginate particles are the ones that cooperate most with the movement of the observed fluid.
Como puede verse en la Figura 3, las imágenes de partículas de alginato obtenidas mediante microscopía electrónica de barrido ambiental (MEBA, o ESEM por su siglas en inglés) muestran formas esféricas tridimensionales con diferente distribución por tamaño de entre 0,2 y 30 micrones. Nótese que el sistema no ha sido objeto del proceso de filtrado, por lo que con el filtrado adecuado se pueden producir fácilmente partículas de tamaño homogéneo. La técnica PIV se beneficia de que las partículas esféricas de alginato tengan una distribución por tamaño homogénea y las usa eficazmente en los sistemas de flujos para obtener imágenes digitales nítidas. As can be seen in Figure 3, the images of alginate particles obtained by scanning electron microscopy (MEBA, or ESEM) show three-dimensional spherical shapes with different size distribution between 0.2 and 30 microns. Note that the system has not been subject to the filtering process, so that with the appropriate filtering particles of homogeneous size can easily be produced. The PIV technique benefits from spherical alginate particles having a homogeneous size distribution and using them effectively in flow systems to obtain sharp digital images.
La Figura 4 muestra una comparativa del total de errores de las partículas de alginato y las burbujas de aire al sumar el sesgo medio y la raíz cuadrada media de los errores. Estos errores son errores de desplazamiento que pueden observarse en el análisis de datos PIV del modelo de la bomba de engranajes. El análisis de datos PIV se realiza mediante el estudio de la correlación entre las ventanas de interrogación de 32x32 pixeles en que se dividen las imágenes. Para poder analizar el flujo en detalle, redujimos las ventanas de interrogación a 32x32 pixeles ya que este tamaño es el más adecuado para el análisis de flujos turbulentos a pequeña escala. Los datos se obtienen de la lectura del análisis PIV de la bomba de engranajes externos. El error de desplazamiento se muestra mediante la comparación de una variedad de imágenes de promedio de fase y el error de desplazamiento en pixeles. El gráfico indica que, cuando se usan partículas de alginato, el error de desplazamiento es mucho menor en 10 órdenes de magnitud, lo que sugiere que las mediciones con PIV son más exactas cuando se usan partículas de alginato que cuando se usan burbujas de aire. Esto es posible gracias a su menor diámetro, que permite incrementar el número de partículas presentes en una misma ventana de la imagen. Figure 4 shows a comparison of the total errors of alginate particles and air bubbles by adding the mean bias and the mean square root of the errors. These errors are displacement errors that can be observed in the PIV data analysis of the gear pump model. PIV data analysis is performed by studying the correlation between the 32x32 pixel question windows in which the images are divided. In order to analyze the flow in detail, we reduced the interrogation windows to 32x32 pixels since this size is best suited for the analysis of turbulent flows on a small scale. The data is obtained from the reading of the PIV analysis of the external gear pump. The offset error is shown by comparing a variety of phase average images and the pixel offset error. The graph indicates that, when alginate particles are used, the displacement error is much smaller by 10 orders of magnitude, which suggests that measurements with PIV are more accurate when alginate particles are used than when air bubbles are used. This is possible thanks to its smaller diameter, which allows increasing the number of particles present in the same image window.

Claims

REIVINDICACIONES
1 . - Procedimiento para medir la velocidad de un fluido mediante el sembrado de partículas trazadoras en el fluido y el registro de la luz que reflejan en dos instantes diferentes caracterizado porque las partículas trazadoras son partículas de alginato. one . - Procedure for measuring the speed of a fluid by sowing tracer particles in the fluid and recording the light they reflect in two different moments characterized in that the tracer particles are alginate particles.
2. - Procedimiento según reivindicación 1 caracterizado porque las partículas de alginato son esencialmente esféricas, con un diámetro de entre 0,2 y 30 micrones. 2. - Method according to claim 1 characterized in that the alginate particles are essentially spherical, with a diameter of between 0.2 and 30 microns.
3. - Procedimiento según la reivindicación 2 caracterizados porque las partículas de alginato se componen de sal sódica del ácido algínico de baja viscosidad, procedente de algas pardas. 3. - Method according to claim 2 characterized in that the alginate particles are composed of sodium salt of low viscosity alginic acid, from brown algae.
4. - Procedimiento según cualquiera de las reivindicaciones anteriores caracterizado porque al menos algunas de las partículas de alginato se tiñen con fluoresceína. 4. - Method according to any of the preceding claims characterized in that at least some of the alginate particles are stained with fluorescein.
5. - Procedimiento según la reivindicación 4 caracterizado porque las partículas de alginato se iluminan mediante un láser verde para que reflejen la luz. 5. - Method according to claim 4 characterized in that the alginate particles are illuminated by a green laser to reflect the light.
6.- Procedimiento según cualquiera de las reivindicaciones anteriores caracterizado porque las partículas de alginato se producen mediante un proceso de gelificación interna. 6. Method according to any of the preceding claims characterized in that the alginate particles are produced by an internal gelation process.
7.- Uso de partículas de alginato en velocimetría por imágenes de partículas. 7.- Use of alginate particles in velocimetry by particle images.
PCT/ES2012/070867 2011-12-15 2012-12-14 Use of alginates in particle image velocimetry and method for measuring the velocity of a fluid WO2013087966A1 (en)

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US5124071A (en) * 1990-09-20 1992-06-23 Joseph Katz Microscopic particles containing imbedded fluorescent dyes and use thereof in particle-image velocimetry

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US5124071A (en) * 1990-09-20 1992-06-23 Joseph Katz Microscopic particles containing imbedded fluorescent dyes and use thereof in particle-image velocimetry

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Title
BIN YANG ET AL.: "PIV measurements of two phase velocity fields in aeolian sedimenttransport using fluorescent tracer particles.", MEASUREMENT, vol. 44, no. 4, 7 January 2011 (2011-01-07), pages 708 - 716, XP028183166, DOI: doi:10.1016/j.measurement.2011.01.007 *

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