Ricard González-Cinca

Polytechnic University of Catalonia, Barcelona, Catalonia, Spain

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Publications (26)19.01 Total impact

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    ABSTRACT: We perform a characterization of a recently reported microbubble injector in conditions relevant to microgravity. Injection of bubbles is based on the generation of a slug flow in a capillary T-junction, whose operation is robust to changes in the gravity level. We address questions regarding the performance under different working regimes. In particular, we focus on the regimes found within a large range of gas and liquid injection flow rates. The injection performance is characterized by measuring bubble generation frequency. We propose curves obtained empirically for the behavior of generation frequency and crossover between regimes.
    09/2014;
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    F Suñol, R González-Cinca
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    ABSTRACT: The droplet dynamics and collisions after a liquid jet breakup have been experimentally studied in low gravity conditions. An experimental setup was designed in order to be used at the I.N.T.A. Drop Tower, which allows for 2.1 seconds of microgravity. The dynamics of distilled water jets injected into a rectangular tank was recorded by means of a high-speed video camera. Observations of the droplet trajectories showed a conical shape of the liquid jet caused by droplet collisions just after detachment from the liquid jet. The detached droplets initially follow straight paths at constant velocity in the direction of injection. Deviation of these trajectories is a consequence of the collision between two droplets with an impact parameter slightly different from zero. The collision between two droplets can give rise to coalescence or bouncing between droplets depending on the droplet velocity difference and impact parameter. At low values of the relative velocity, the collision leads to coalescence between droplets, while at higher values the collision results in bouncing between droplets.
    Journal of Physics Conference Series 12/2011; 327(1):012026.
  • Francesc Suñol, Ricard González-Cinca
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    ABSTRACT: The impingement of bubbly jets in distilled water and ethanol has been experimentally studied on ground. An experimental apparatus for the study of jet impingement on ground and in microgravity has been designed. The opposed-jet configuration with changeable orientation is used in order to study which is the better disposition to achieve an efficient mixing process. The impact angle between jets that can be changed from 0° (frontal collision) up to 90° (perpendicular collision). The impinging jets are introduced into a test tank full of liquid by means of two bubble injectors. The bubble generation method, insensitive to gravity level for low Bond numbers, is based on the creation of a slug flow inside a T-junction of capillary tubes of 0.7 mm of diameter. Bubble velocities at the injector outlet and generation frequencies can be controlled by changing gas and liquid flow rates. Individual bubble properties and coalescence events, as well as the whole jet structure are analyzed from the images recorded by a high speed camera. Bubble velocities are compared with the velocity field of a single-phase jet. Rate of coalescence between bubbles is found higher in ethanol than in water, creating a higher dispersion in bubble sizes. KeywordsJet impingement–Bubbly jet–Two-phase flow–Jet mixing
    Microgravity - Science and Technology 01/2011; 23(2):151-158. · 0.59 Impact Factor
  • Francesc Suñol, Ricard González-Cinca
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    ABSTRACT: The rise, bouncing and coalescence processes of millimetric gas bubbles impacting at a free surface were studied experimentally. Single air bubbles were released from a syringe into a methacrylate tank filled with ethanol. The position and shape of the bubbles were measured from the images recorded by means of a high-speed camera. Bubbles with equivalent diameters de<0.47 mm rise until they touch the free surface and coalesce with it immediately. In contrast, bubbles with equivalent diameters de≥0.47 mm bounce repeatedly before the coalescence with the free surface occurs. We present results on the bubble terminal velocities, drag forces, and shape of the bubble during its steady rise before coalescence takes place. The oscillatory behavior of the bubble shape after the collision is described, and the position and velocities of bubbles during the bouncing process are analyzed. The motion of the bubble after the first bounce is found to be very similar to that of a damped oscillator. Bouncing time increases with bubble size, and so does the height of the bounce.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects. 01/2010;
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    Francesc Suñol, Ricard González-Cinca
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    ABSTRACT: The structure of two colliding water jets containing small gas bubbles is studied experimentally. The effects of the separation distance between jets, as well as the orientation angle, on the spatial distribution of bubbles have been considered. Results on the global structure of the final jet and bubble properties have been obtained using a high-speed video camera, and measurements of the positions of coalescence events are presented. Jets are introduced through inclined pipes (with a diameter of 0.7 mm) into a large water tank to avoid wall effects. Inclination angle has been changed from 0° to 45° with respect to the horizontal, resulting in a 0° up to 90° impact angle between jets. Generation of bubbles is controlled by a T-junction device where a regular slug-flow is created prior to injection. Bubble sizes have been measured, and a mean diameter of around 1 mm has been obtained using high values of the liquid flow rate. In the studied range of separation distances between the bubbly jets, a more homogeneous dispersion of bubbles is created as the distance between jets is decreased and the momentum flux of each jet is increased. Higher numbers of coalescences are observed when using smaller distance between jets, and the obtained measurements revealed that the number of bubble coalescence events is reduced significantly using high values of liquid flow rates.
    International Journal of Multiphase Flow. 01/2010;
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    ABSTRACT: We perform a characterization of a recently reported minibubbles (bubbles with a diameter of the order of 10−3 m) generator in microgravity related conditions. Generation of bubbles is based on the generation of a slug flow in a capillary T-junction, whose operation is robust to changes in the gravity level. We address questions regarding the performance under different working regimes. In particular, we focus on the regimes found within a large range of gas and liquid injection flow rates. The injection performance is characterized by measuring bubble generation frequency. We propose curves obtained empirically for the behaviour of generation frequency and crossover between regimes.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects. 01/2010;
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    F. Suñol, O. Maldonado, R. Pino, R. González-Cinca
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    ABSTRACT: A new experimental setup for the study of bubble coalescence and bubble jet interactions in microgravity conditions is presented. The section consists of a cavity full of liquid containing two bubble injectors whose separation distance and relative orientation angle can be controlled. Injection of bubbles is based on the generation of a slug flow in a capillary T-junction, which allows a control of bubble size and velocity by means of liquid and gas flow rates. Individual and collective behaviour of bubbles injected in the cavity has been studied. On ground results on the individual trajectories, maximum distance reached, and the delimitation between turbulence and buoyancy regions are presented. The influence on these results of the inclination angle of one injector with respect to gravity has also been considered. A good knowledge of bubble jets behaviour in microgravity will enhance the development of space technologies based on two-phase systems.
    Microgravity - Science and Technology 12/2008; 21(1):95-99. · 0.59 Impact Factor
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    Ricard González-Cinca, Eduard Santamaria, J. Luis A. Yebra
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    ABSTRACT: This article describes an innovative methodology for teaching an undergraduate course on Computational Science, with a particular emphasis in Computational Fluid Dynamics (CFD), and the experiences derived from its implementation. The main activities taking place during this course are: development by students of a training project on a topic in materials science, development of a larger CFD project, and an introduction to a CFD commercial package. Projects are carried out by groups of students and are assigned from a set of different available possibilities. Project development consists in the implementation in code of the corresponding mathematical models and a graphical interface which permits the visualization of the results derived from the numerical resolution of the models. The main innovative aspects of the methodology are the use of Project Based Learning combined with the participation of lecturers from different areas of expertise. Other innovative issues include the opportunity for students to practice skills such as report writing, doing oral presentations, the use of English (a foreign language for them) and the use of Linux as the development environment.
    06/2008: pages 735-744;
  • Pere Bruna, Daniel Crespo, Ricard González-Cinca, Eloi Pineda
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    ABSTRACT: Calorimetric data of primary crystallization is usually interpreted in the framework of the Kolmogorov [Dokl. Akad. Nauk SSSR 1, 355 (1937)] , Johnson and Mehl [Trans. AIME 135, 416 (1939)] , and Avrami [J. Chem. Phys. 7, 1103 (1939) ; 8, 212 (1940) ; 9, 177 (1941)] (KJMA) theory. However, while the KJMA theory assumes random nucleation and exhaustion of space by direct impingement, primary crystallization is usually driven by diffusion-controlled growth with soft impingement between the growing crystallites. This results in a stop of the growth before the space is fully crystallized and induces nonrandom nucleation. In this work, phase-field simulations are used to check the validity of different kinetic models for describing primary crystallization kinetics. The results show that KJMA theory provides a good approximation to the soft-impingement and nonrandom nucleation effects. Moreover, these effects are not responsible of the slowing down of the kinetics found experimentally in the primary crystallization of glasses.
    Journal of Applied Physics 09/2006; 100(5):054907-054907-11. · 2.21 Impact Factor
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    R González-Cinca, Y Couder, A Hernández-Machado
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    ABSTRACT: The development of side-branching in solidifying dendrites in a regime of large values of the Peclet number is studied by means of a phase-field model. We have compared our numerical results with experiments of the preceding paper and we obtain good qualitative agreement. The growth rate of each side branch shows a power-law behavior from the early stages of its life. From their birth, branches which finally succeed in the competition process of side-branching development have a greater growth exponent than branches which are stopped. Coarsening of branches is entirely defined by their geometrical position relative to their dominant neighbors. The winner branches escape from the diffusive field of the main dendrite and become independent dendrites.
    Physical Review E 06/2005; 71(5 Pt 1):051601. · 2.31 Impact Factor
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    Y Couder, J Maurer, R González-Cinca, A Hernández-Machado
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    ABSTRACT: The dynamics of growth of dendrites' side branches is investigated experimentally during the crystallization of solutions of ammonium bromide in a quasi-two-dimensional cell. Two regimes are observed. At small values of the Peclet number a self-affine fractal forms. In this regime it is known that the mean lateral front grows as t(0.5). Here the length of each individual branch is shown to grow (before being screened off) with a power-law behavior t (alpha(n)). The value of the exponent alpha(n) (0.5< or = alpha(n) < or =1) is determined from the start by the strength of the initial disturbance. Coarsening then takes place, when the branches of small alpha(n) are screened off by their neighbors. The corresponding decay of the growth of a weak branch is exponential and defined by its geometrical position relative to its dominant neighbors. These results show that the branch structure results from a deterministic growth of initially random disturbances. At large values of the Peclet number, the faster of the side branches escape and become independent dendrites. The global structure then covers a finite fraction of the two-dimensional space. The crossover between the two regimes and the spacing of these independent branches are characterized.
    Physical Review E 03/2005; 71(3 Pt 1):031602. · 2.31 Impact Factor
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    R González-Cinca, L Ramírez-Piscina
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    ABSTRACT: We present a numerical study of sidebranching of a solidifying dendrite by means of a phase-field model. Special attention is paid to the regions far from the tip of the dendrite, where linear theories are no longer valid. Two regions have been distinguished outside the linear region: a first one in which sidebranching is in a competition process and a second one further down where branches behave as independent of each other. The shape of the dendrite and integral parameters characterizing the whole dendrite (contour length and area of the dendrite) have been computed and related to the characteristic tip radius for both surface tension and kinetic dominated dendrites. Conclusions about the different behaviors observed and comparison with available experiments and theoretical predictions are presented.
    Physical Review E 12/2004; 70(5 Pt 1):051612. · 2.31 Impact Factor
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    ABSTRACT: In this paper we study the sidebranching development of solidifying dendrites both experimentally and by numerical integration of a phase-field model with a noise term. Our results support the idea that sidebranching is originated through the selective amplification of natural noise at the tip. The initial stages turn to be of crucial importance in the selection of the final noisy shape. However, our results suggest that after the stochastic initial disturbance, a deterministic mechanism dominates the growth and screening-off process of sidebranching.
    Proc SPIE 05/2004;
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    ABSTRACT: The phase-field method is reviewed from the general perspective of converting a free boundary problem into a set of coupled partial differential equations. Its main advantage is that it avoids front tracking by using phase fields to locate the fronts. These fields interpolate between different constant values in each bulk phase through diffuse interfaces of finite thickness. In solidification, the phase fields can be understood as order parameters, and the model is often derived to dynamically minimise a free energy functional. However, this is not a necessary requirement, and both derivations involving a free energy (basic solidification model) and not (first viscous fingering model) are worked out. In any case, the model is required to reproduce the original free boundary problem in the limit of vanishing interface thickness. This limit and its higher order corrections, important to make quantitative contact between simulations and experiments, are discussed for both examples. Applications to fluctuations in solidification, the growth of liquid crystal mesophases, and viscous fingering in Hele-Shaw cells are presented.
    06/2003;
  • R González-Cinca
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    ABSTRACT: The complete shape of dendrites grown in regimes of high undercooling has been studied by means of a phase-field model. The integral parameters surface area and contour length have been used to characterize the dendrite. The dependence on the undercooling of the behaviour of both parameters gives some insight in the role played by the radius of the tip as a length scale. It is found that in regimes dominated by kinetics, lengths far from the tip cannot be scaled by the tip radius. This is significantly different to what has been previously observed in experiments and simulations of dendrites mainly determined by surface tension.
    Physica A: Statistical Mechanics and its Applications 01/2002; · 1.68 Impact Factor
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    ABSTRACT: We have studied sidebranching induced by fluctuations in dendritic growth. The amplitude of sidebranching induced by internal (equilibrium) concentration fluctuations in the case of solidification with solutal diffusion is computed. This amplitude turns out to be significantly smaller than values reported in previous experiments. The effects of other possible sources of fluctuations (of an external origin) are examined by introducing nonconserved noise in a phase-field model. This reproduces the characteristics of sidebranching found in experiments. Results also show that sidebranching induced by external noise is qualitatively similar to that of internal noise, and it is only distinguished by its amplitude.
    Physical Review E 06/2001; 63(5 Pt 1):051602. · 2.31 Impact Factor
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    ABSTRACT: An anisotropic heat diffusion coefficient is introduced in order to study some interfacial growth phenomena. This anisotropy has been incorporated in a phase field model which has been studied numerically to reproduce some fundamental solidification situations (needle crystal growth) as well as the dynamics of a nematic–smectic-B interface. As a general result, we find that dendrites grow faster in the lower heat diffusion direction. Simulation results are compared with experiments with remarkable qualitative agreement.
    Journal of Crystal Growth 10/1998; · 1.55 Impact Factor
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    ABSTRACT: An anisotropic heat diffusion coefficient is introduced in order to study some interfacial growth phenomena. This anisotropy has been incorporated in a phase field model which has been studied numerically to reproduce some fundamental solidification situations (needle crystal growth) as well as the dynamics of a nematic–smectic-B interface. As a general result, we find that dendrites grow faster in the lower heat diffusion direction. Simulation results are compared with experiments with remarkable qualitative agreement.
    Journal of Crystal Growth - J CRYST GROWTH. 01/1998; 193(4):712-719.
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    ABSTRACT: Remarkable differences in the shape of the nematic-smectic-B interface in a quasi-two-dimensional geometry have been experimentally observed in three liquid crystals of very similar molecular structure, i.e., neighboring members of a homologous series. In the thermal equilibrium of the two mesophases a faceted rectanglelike shape was observed with considerably different shape anisotropies for the three homologs. Various morphologies such as dendritic, dendriticlike, and faceted shapes of the rapidly growing smectic-B germ were also observed for the three substances. Experimental results were compared with computer simulations based on the phase field model. The pattern forming behavior of a binary mixture of two homologs was also studied.
    Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 09/1996; 54(2):1574-1583.
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    ABSTRACT: We present numerical simulations directed at the description of smectic-B germs growing into the supercooled nematic phase for two different liquid crystalline substances. The simulations are done by means of a phase-field model appropriate to study strong anisotropy and also faceted interfaces. The most important ingredient is the angle-dependent surface energy, but kinetic effects are also relevant. The simulations reproduce qualitatively a rich variety of morphologies observed in the experiments for different value of undercooling, extending from the faceted equilibrium shape to fully developed dendrites.
    Physica D Nonlinear Phenomena 01/1996; · 1.67 Impact Factor

Publication Stats

111 Citations
19.01 Total Impact Points

Institutions

  • 1996–2011
    • Polytechnic University of Catalonia
      • Department of Applied Physics (FA)
      Barcelona, Catalonia, Spain
    • Universitat Oberta de Catalunya
      • Department of Applied Physics
      Barcino, Catalonia, Spain
  • 2005
    • Ecole Normale Supérieure de Paris
      • Laboratoire de Physique Statistique
      Paris, Ile-de-France, France