DISPERSIONS

Author: CALVO BERNAD ESTEBAN.
Year: 2004.
University: ZARAGOZA [www.unizar.es].
Place of defense: CENTRO POLITÉCNICO SUPERIOR.
Place of preparation: CENTRO POLITÉCNICO SUPERIOR.

Summary: This paper conducts a study of a jet biphasic aire-partículas sound generated by a convergent nozzle and forced acoustically. Forced interest lies in increasing the radial dispersion experienced by the dispersed phase. The particles are employed glass microspheres whose size allows exploring the mid range of numbers Stokes (St. -- 1). The forced takes place with a sinusoidal signal with the frequency that induces greater disruption of jet gas phase. The reason employed mass is low, so that the particles induce a weak disturbance in the continuous phase (gas). The characterization of the flow has been carried out through the art optical Anemometría of Delay Doppler (PDAs), which allows the measurement of speed and the diameter of individual particles interns for a small region of space or volume measurement. Prior to the experimental characterization, there has been a systematic and comprehensive review of the art PDA focused primarily on rebuilding the statistics of the dispersed phase space from the measures gross acquired by ADP. Reconstruction methods have also been extended to obtaining the velocimetría of a fluid. Moreover, the methods of reconstruction have been adapted to the case of a flow almost cyclical, as studied in this thesis. The purpose is to correct biases in the measurement of the phase velocimetría gas by strong inhomogeneidad of plotters caused by the forced acoustic. The characterization of the experimental jet has been carried out with three different configurations: jet biphasic (gas and particles) is not forced, jet phase (air only) and forced biphasic forced jet, which is the main purpose of this study. The first two configurations are benchmarks compared to the third to evaluate the effect of forced and the addition of particle flow. The measure has been acquired over the whole cycle of forced, which allows a detailed description of the estrucuturación jet over the cycle. The experimental results shown include times of the speed of both phases (gas and particles), and concentration of the dispersed phase flow in overall statistics as conditional gap. The estrucuturación in the cycle of forced been quantified through the modulation parameters and consistency defined ad hoc. This set of data, statistics corrected, are very useful as a verification codes computational simulation. The results show as the jet is strongly affected by the forced acoustic. The gas flow is almost cyclical in the area closest to the nozzle for, downstream, losing its structure and degenerate into a turbulent conventional jet. Their structures are well captured and quantified through the conditional statistical gap along the entire cycle of forced. The estrucuturación air, in turn, is organizing the movement of particles, generating strong inhomogeidades in the distribution of the particles. In particular, the measures detect and quantify the formation of aggregates thrust high concentration of particles, as well as cross projections. There has been a delay in the structuring of the particles with respect to the air due to inertia. Also the structure of the dispersed phase degenerates later that the gas, again by inertial effects. On the other hand, since the cross projections are an efficient mechanism of particle dispersion, they are quantified by size classes both in geometry and in extension. It gets further development of the projections associated with the smaller particles injected, fewer Stokes. The flow measures local particles are used for measuring the radial dispersion of particles by scattering parameters. It compares the cases not forced and forced to end 8 of zo 3a9 na disturbed by the forced acoustic, which allows users to view the overall effect on the forced dispersal radio. Here, a quantitative manner, as the forced dispersal radio noise increases. Likewise, smaller particles injected Stokes presented a greater dispersion.

Author: Maldonado Valderrama Julia.
Year: 2005.
University: GRANADA [www.ugr.es].
Place of defense: Facultad de Ciencias, Universidad de Granada.
Place of preparation: Universidad de granada.

Summary: The formulation of new food products (foods with low-fat, semi-processed or instant foods, baby foods or diets hospital, sparkling drinks with a low alcohol content or creams containing a large ethanol, etc.). Optimization or traditional products , is conditional on fisico - químicas knowledge of the characteristics of its components. An important focus of foodstuffs dispersions are complex, such as emulsions (liquid-liquid systems) and foams (systems líquido-gas). However, the development of such dispersions is dependent on the presence of surfactant protein and low molecular weight, which by their nature anfifílica focus on interfaces líquido-fluido. In this way, proteins and / or surfactants in the interfaces, are molecular barriers that stabilize these dispersions and favor their formation. Thus, the study of the structure and behavior of

Author: LÓPEZ LÓPEZ JOSÉ MANUEL.
Year: 2005.
University: GRANADA [www.ugr.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACUTLAD DE CIENCIAS - UNIVERSIDAD DE GRANADA.

Summary: The thesis focuses on the processes heteroagregación in colloidal dispersions bicomponentes, whose particles are all of equal size but with opposite electric charges. It is a phenomenon essential for the synthesis of nanocomposite materials, large industrial interest. It has studied the rates of both aggregation and kinetic behavior, depending on two variables: (ion) (electrolyte concentration of median) and x (particulate fraction of each species). The thesis twofold complementary experimental and simulation. The pilot study is based on light scattering by individual aggregates, SCLS, which enables us to determine the size distribution of aggregates, CSD, without recourse to a model for its structure. Other techniques have been used to a lesser extent (nefelometría, mobility electroforética ..). The study by simulation uses two types of simulations of dynamic Browniana, BDS: 1, BDS-contact rules for interactions between particles short range. 2-BDS with interactions DLVO-HHF, for other cases. Finally, the thesis has been completed with other numerical methods, highlighting an algorithm for solving the stochastic equation coagulation. The main points of the work are: 1-selection and characterization of test systems and adapting the device SCLS. 2-A measure of the rate of formation of dimers, both kS (constant kinetic effective) (k) AB (constant kinetic absolute), compared with (ion). KS found that takes 1 - Securities DLCA for (ion) high. 2-Half of that value for intermediate (ion). 3-values much higher for very low (ion). We have found a good agreement with our measures to compare the theoretical predictions of the theory DLVO-HHF and with the simulations with interactions. 3-Determination of schemes heteroagregación in symmetric systems. The CSD has been measured as a function of time and concentration of electrolyte, and has been compared with those obtained by BDS and numerical solutions of the equation of coagulation. It has established the existence of three different regimes Aggregation: Aggregation limited by diffusion (DLCA) to high concentrations of electrolyte; aggregation binary limited by diffusion (BDLCA) to intermediate concentrations, and aggregation headed by attraction (ADCA) to low (ion) . In the latter case, we found a rapid disappearance of dimers or "discrimination of dimers." In all cases, the agreement experiment / simulation is excellent. 4-Study dependence on x heteroagregación asymmetric regime BDLCA using BDS outside network. A short time has proved the validity of the approximation HHF. A long time has been found that there is a critical proportion xc such that, for x greater xc aggregation continues until it forms a single aggregate, while for x xc some minor additions remain stable. In addition, for values of x near xc is very atypical behavior: the concentration of certain oligomers reaches maximum two different time scales ( "two-hump effect"). We must emphasize that this behavior was not found earlier. Finally, we have developed a five-stage model that accounts for these effects.