Electroviscous Effects in Stationary Solid Phase Suspensions

El flujo a través de medios porosos es un tema de interés en diferentes campos de investigación como la medicina, la ingeniería y la ciencia. La aparición espontánea de distribución iónica en la interfase sólido-líquido da lugar a una reducción del caudal, lo que generalmente se denomina efecto electroviscoso. Sin embargo, esto debe diferenciarse en dos efectos más específicos, el efecto primario debido a la distorsión de las nubes iónicas y el efecto secundario debido a la superposición de las nubes iónicas. No siempre se han realizado con claridad trabajos teóricos y experimentales para separar ambos efectos. En su lugar, se han agrupado globalmente. El propósito de esta revisión es revisar la bibliografía teórica y experimental sobre el efecto electroviscoso en suspensiones en fase sólida estacionaria (tapones porosos, membranas, microcanales, capilares). Las principales conclusiones de esta breve revisión son: (i) cuando las nubes iónicas son relativamente pequeñas, es posible aceptar que sólo el efecto primario es la causa del aumento aparente de la viscosidad de la fase líquida cuando se la fuerza a fluir relativa a la fase sólida estacionaria; (ii) aunque la teoría predice un máximo para la variación del efecto electroviscoso general frente al tamaño relativo de la nube iónica, se ha observado experimentalmente, pero no se ha razonado adecuadamente, que su existencia depende del tipo de sal; y (iii) es necesario justificar por qué, si el fluido es no newtoniano, los parámetros electrocinéticos dominan las características del flujo debido a los altos gradientes de presión, pero los parámetros reológicos son más determinantes cuando el flujo es generado por bajos gradientes de presión. (i) cuando las nubes iónicas son relativamente pequeñas, es posible aceptar que solo el efecto primario es la causa del aumento aparente de la viscosidad de la fase líquida cuando se la fuerza a fluir con respecto a la fase sólida estacionaria; (...)Partial funding for open access charge: Universidad de Málag

Rheological behaviour of fruit and milk-based smoothies

Two of the most important food attributes for today´s fast-moving lifestyle are convenience and healthiness [1-2]. Fast-moving lifestyle specifically affects to elderly people, who are prone to bad-nutrition due to their dental status reducing the consumption of fruits and vegetables [3]. Smoothies are blended beverages, and good examples of convenient and healthy foods for helping to reduce this problem. So, they are gaining increasing market leverage in the beverage sector. Texture and rheological behaviour of foods can determine their acceptability. Therefore, added to nutritious features, smoothies must also account with outstanding mechanical properties. Stability of the products is also a main quality, which can be gained adding a small amount of stabiliser to beverage formulations. But, to avoid opposite effects, stabilisers addition should ameliorate the product texture.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Temperature and particle concentration influence on the complex viscous behavior of a hydrophilic fumed silica suspension

Shear-thinning behavior (decrease of the apparent steady viscosity with shear) due to breaking of weak particle flocs and posterior alignment of individual particles in layers parallel to the flow direction is usually observed before the appearance of the shear-thickening behavior (increase of the apparent steady viscosity with shear). The shear-thickening behavior is mainly due to the dominant role played by hydrodynamic over Brownian and colloidal forces at relatively high shear. As a rule, the onset of shear-thickening behavior and the maximum viscosity value appear at lower shear rates when solid concentration increases, and temperature decreases. However, the influence of solid concentration and temperature on shear stress characteristic values have received less attention despite being the shear stress the true cause of microstructure changes that can provoke the appearance of the shear-thickening behaviour. A recently published empirical equation for the shear stress dependence of the steady viscosity of shear thickening fluids [T. Shende, V.J. Niasar, M. Babaei, J. Mol. Liq. 325 (2021) 115220] has been used for fitting experimental data (MARSIII, Thermo-Haake, Germany) of a hydrophilic fumed silica suspension (A200 (Evonik, Germany) in PPG400 (Sigma-Aldrich, Germany)). The influence of temperature (10,\ 30,\ 50,\ 70\degc) and solid concentration (10,\ 15,\ 20,\ 25%\ wt) on the shear-thickening behavior has been monitored recording their influence on the model parameters.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Electrorheological behaviour of flour/olive oil dough

• Changes in flow properties upon the application of an electrical field can be evaluated using of electrorheological techniques. • The fact that it had shown successful to reduce the fat content [1] has aimed us to explore potential benefits resulting from the wide use of this technique in food science. • It was claimed long time ago that the integration of this technique in food processing should translate into the development of new products [2]. • A study on the influence of the solid content and temperature on the steady viscous flow electrorheological behavior of wheat flour/olive oil dough has been made. • The overall conclusion is that this system is electrorheological positive, i.e. the yield stress increases with the electric field.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Rheological study of the aggregation state of alumina nanofluids

Se adjunta una comunicación, aunque se han publicado tres comunicaciones más.The presence of alumina solid particles in aqueous phase induces a change in the viscosity of the suspension from Newtonian to non- Newtonian flow. Besides, the presence of solid particles is adequate for the use as a heat exchanger fluid. The effect of nanoparticle size on thermal properties of nanofluids is still today a question, which is far from being answered. In this respect, the results reported in the literature are contradictory [1], probably due to the formation of aggregates when particles are dispersed in the liquid phase. Regarding to the nanoparticle shape influence in thermal conductivity, cylinders and spheres have been considered as the more effective in heat transfer. Spherical nanoparticles of alumina, which is one of the most investigated nanofluid, dispersed in water were used in this study. TEM images showed a mean average diameter of 50 nm. However, DLS measurements showed monodispersed particles of 260 nm. Very recently [2], the relationship between shear rheology and aggregation state of suspensions has been reviewed. Mechanical and physical properties of the resultant materials depend on shape, size and size distribution, which are considered determining parameters in the formation of particle aggregates. The steady shear flow (figure 1) has shown that these clusters, when they are at rest, are formed by highly branched aggregates that erode when shear rate increases, until a suspension of individual particles is achieved. These results are in good agreement with the intrinsic viscosity obtained by Money and Krieger-Dougherty models. In both cases, these values are far from the 2.5 corresponding to spherical particles. The temperature effects were also taken into account.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Activation energy in particle suspensions

Assuming that the molar activation energy in a fluid is interpreted as a measure of the potential energy barrier required for the molecular movement [1], the viscosity of a fluid depends on the actual size of the molecules, and the presence of solid particles in a suspension increases the dissipation of energy when the system flows, therefore it is expected that the viscosity of the suspension is higher than that of the pure solvent at a given temperature. The dependence of the viscosity of some silica/glycol suspensions with the temperature can be fitted using an empirical function analogous to the Arrhenius equation, ln⁡η=E/RT-ln⁡C, where η is the viscosity, C is a system-dependent constant, E is the molar activation energy for the viscous flow, T is the absolute temperature and R is the gas universal constant. When the temperature of the suspension decreases two effects are observed. First, larger aggregates of particles are formed due to the reduction of the thermal agitation and, second, the number of links among the molecules of the liquid phase increases. These two effects give place to a higher increase in the viscosity with the temperature compared to the pure solvent. Assuming that a higher viscosity value is due to a smaller free volume available for the molecular movement, and taking into account that the free suspension volume is limited only to the liquid fraction [2], it should be expected that the viscosity of the suspension is less sensitive to temperature than that of the pure solvent. In this work the dependence on the temperature of the viscosity values of the silica/glycol suspensions is compared to that of the liquid media. The results have shown a lower activation energy when the solid volume fraction increases, which has been explained with a scheme that assumes that the particle links are less sensitive to thermal energy absorption than the joining bonds among the solvent molecules. Our conclusion is that, for a given mechanical energy applied to the system, the thermal energy absorbed by the system is mainly used in the rupture of bonds between the solvent molecules. This study can be useful to understand the mechanisms that govern the differences in the activation energy values found between samples of foods, in which many factors are connected with sample composition [3]. [1] Briscoe B, Luckham P, Zhu S. Rheological properties of poly (ethylene oxide) aqueous solutions. J Appl Polym Sci 70 (1998) 419-429. [2] Shenoy AV. Rheology of filled polymer systems. Kluwer Acad Pub, 1999, The Netherlands. [3] Alvarez MD, Canet W. Time-independent and time-dependent rheological characterization of vegetable-based infant purees. J Food Eng 114 (2013) 449-464.Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tech

Using Natural Raw Materials and CEM Approach for the Design of Andean Volcanic Self-Compacting Concretes

La actividad volcánica es característica de las zonas sísmicas. En consecuencia, el material volcánico forma parte del paisaje en lugares donde los terremotos son fenómenos naturales comunes. Dado que los residuos volcánicos (VW) muestran actividad puzolánica, la sustitución del cemento Portland (PC) manufacturado por VW es claramente una opción deseable no solo desde el punto de vista económico sino también para reducir las emisiones de CO 2huella dactilar. Por lo tanto, diseñar hormigones con cementos Portland volcánicos (VPC) contribuye claramente a una producción de cemento más limpia. Las actividades de construcción y edificación en zonas sísmicas necesitan utilizar un tipo específico de hormigón: hormigón autocompactante (SCC). El desafío en el que nos enfocamos fue el diseño de SCC usando VPC. El comportamiento de flujo de SCC se caracteriza por un límite elástico bajo, una viscosidad plástica alta y un comportamiento de espesamiento por cizallamiento a cizallamiento alto. Sin embargo, obtener estas sorprendentes propiedades del hormigón no es fácil con los ensayos de flujo de hormigón tradicionales (cono de Abrams, etc.). Además, estos métodos son muy costosos en términos de tiempo y material. Una alternativa que nos permite utilizar la reometría absoluta y que ha sido poco explorada consiste en la sustitución del hormigón por un mortero equivalente. En este estudio se utilizó el denominado mortero equivalente de hormigón (CEM) para obtener formulaciones de HAC con VPC. Las pruebas de minicono confirmaron la ausencia de mezcla en algunas formulaciones de CEM seleccionadas según el cumplimiento de los criterios para SCC. De las respectivas formulaciones del CEM se infirieron tres propuestas concretas. Se adaptaron al estándar europeo SCC según el ensayo de apertura de conos de Abrams.Partial funding for open access charge: Universidad de Málag

Experimental assessment of thermal and rheological properties of coconut oil-silica as green additives in drilling performance based on minimum quantity of cutting fluids

Conventional metal working fluids are prepared from petroleum based mineral oils with toxic, carcinogenic, non- biodegradable and unsustainable additives, which can cause serious environmental contamination and health risks to operators. Formulations with non-toxic emulsifiers and natural additives such as vegetable oils are currently being considered for further development and use of non-toxic tribological products. This study is concerned with the thermal and flow properties of a cutting fluid (taladrine, T) mixed with a phase change material (PCM) coconut oil (CO) in a proportion of 1:9 (CO-0.1T) and hydrophilic silica in 0.01, 0.03 and 0.05 vol fractions. The thermal properties were evaluated by differential scanning calorimetry (DSC) and thermal conductivity measurements while the flow properties were assessed by viscosity temperature curves. The addition of solid particles has demonstrated an enhancement of the thermal conductivities with small differences in the latent heat. The microstructure of the suspensions was established from the DSC cooling dynamic ther- mogram and the rheological measurements. These results were confirmed by the images of optical polarized microscopy in which plate-like needles were observed. The suspension of 0.03 silica in CO-0.1T demonstrated an adequate gel strength and produced a reduction of 11 ◦C in drilling performance. A Minimum Quantity of Cutting Fluid (MQCF) of 2 g as an alternative for dry machining and flood cooling. It also prevented evaporative loss and removed metal chips, as a high viscosity complex fluid. In this work the use of phase change materials filled with solid particles as a way of sustainable eco-friendly toxic waste removal in drilling was justified.Funding for open access charge: Universidad de Málag

Thermophysical and flow properties of coconut oil with silica fumed nanoparticles

This work is concerned with the rheological and thermal study of silica fumed dispersed in coconut oil. The dispersed phase behave as a non newtonian fluid during the phase change. The addition of nanoparticles complicates considerably the flow behaviour of the system. Therefore, a very thoughtful study of the flow and thermal properties with temperature when silica particles are added must be carried out.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Rheological behavior of a commercial milk-based sauce

• The acceptation of semisolid foods by consumers is greatly determined by their rheological properties. • Sauces are semisolid foods and, in general, show viscoplastic and shear-thinning viscous flow behaviours. On the other hand, viscoelastic properties are specifically significant in the handling and quality control tasks. • As temperature changes cause alterations in physical and chemical properties of food components, which influence in texture, stability, taste, etc., a better understanding of the influence of this parameter on milk-based sauces would allow improve product quality.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech