Microstructure and mechanical properties of grains of silica nanofluids dried in an acoustic levitator

The microstructure and mechanical properties of spray-dried grains are key factors in many applications. In this work single droplets of silica nanofluids were dried in an acoustic levitator under different experimental conditions of solid mass fraction, pH value, salt concentration, drying temperature and initial droplet volume. ANOVA method was used to determine their influence on the final grain diameter, the shell thickness and the mechanical strength. The solid content and the droplet volume are the variables that exert an influence on these three properties. In addition, the mechanical strength is influenced by the pH value. The maximum packing fraction of the particles inside the shell was obtained by modeling the viscosity data with the Quemada equation. The packing fraction was then used to calculate the shell thickness. The internal microstructure of the grains was observed by SEM and the shell thickness was measured. Experimental and calculated results show good agreemen

Characterization of silica–water nanofluids dispersed with an ultrasound probe: A study of their physical properties and stability

The stability and agglomeration state of nanofluids are key parameters for their use in different applications. Silica nanofluids were prepared by dispersing the nanoparticles in distilled water using an ultrasonic probe, which has proved to be the most effective system and gives the best results when compared with previous works. Results were obtained concerning the influence of the solid content, pH and salt concentration on the zeta potential, electrical double layer, viscosity, elastic and viscous moduli, particle size and light backscattering. Measurement of all these properties provides information about the colloidal state of nanofluids. The most important variable is the solid content. Despite the agglomeration due to high concentration, nanofluids with low viscosity and behaving like liquid were prepared at 20% of mass load thanks to the good dispersion achieved with the ultrasonic treatment. The pH of the medium can be used to control the stability, since the nanofluids are more stable under basic conditions far from the isoelectric point (IEP) and settle at pH = 2. Therefore, stable nanofluids for at least 48 h, with high solid content, can be prepared at high pH value (pH > 7) due to the electrostatic repulsion between particles

El proceso de secado por atomización: formación de gránulos y cinética de secado de gotas

Spray drying is a unit operation very common in many industrial processes. For each particular application, the resulting granulated material must possess determined properties that depend on the conditions in which the spray drying processing has been carried out, and whose dependence must be known in order to optimize the quality of the material obtained. The large number of variables that influence on the processes of matter and energy transfer and on the formation of granular material has required a detailed analysis of the drying process. Over the years there have been many studies on the spray drying processing of all kind of materials and the influence of process variables on the drying kinetics of the granulated material properties obtained. This article lists the most important works published for both the spray drying processing and the drying of individual droplets, as well as studies aimed at modeling the drying kinetics of drops.El proceso de secado por atomización es una operación unitaria que interviene en numerosas aplicaciones industriales. Para cada aplicación en concreto, el material granulado resultante debe poseer unas propiedades determinadas que dependen de las condiciones en las que se lleve a cabo el secado por atomización, y cuya dependencia debe conocerse para así optimizar la calidad del material obtenido. El gran número de variables que influyen en los procesos de transferencia de materia y energía que tienen lugar, y en la formación del material granulado, han hecho necesario el análisis en detalle del proceso de secado. A lo largo de los años han sido muchos los estudios realizados sobre el secado por atomización y la influencia de las variables del proceso en la cinética de secado y las propiedades del material granulado obtenido, para todo tipo de materiales. En este artículo se recogen los trabajos más importantes publicados correspondientes tanto al secado por atomización como al secado de gotas individuales, así como los estudios cuyo objetivo es el modelado de la cinética de secado de gotas

Estudio de caso sobre la implementación de la política de gestión de riesgo de desastres en una municipalidad, Lambayeque 2023

La presente investigación tuvo como objetivo conocer cómo se implementa la Política Nacional de la Gestión del Riesgo de Desastres de una Municipalidad de Lambayeque. El estudio fue de enfoque cualitativo, método inductivo y de tipo básico, el diseño de investigación usado fue el estudio de caso intrínseco. La Municipalidad Distrital de Íllimo fue el organismo estudiado para conocer la implementación de la Política; siendo la técnica aplicada la entrevista cuya cantidad se calculó aplicando una muestra no probabilística de tipo intencional, conteniendo 16 preguntas que fueron aplicadas a 20 trabajadores que conforman el Grupo de Trabajo para la Gestión del Riesgo de Desastres. Como resultado, cinco coeficientes de co-ocurrencia presentaron valores de 0.73, 0.72, 0.60, 0.43 y 0.34; y responden a 10 códigos asociados en 5 pares y que resultaron con los coeficientes de co-ocurrencia más altos, estos están dentro de las subcategorías de Comprensión del Riesgo de Desastres, Gobernanza de la Gestión del Riesgo, Gestión municipal del Riesgo de Desastres en la, Respuesta ante las emergencias y Recuperación de las emergencias. Esta investigación concluye que, el objetivo general planteado se cumplió; dado que los códigos que presentaron coeficiente de co-ocurrencia confirman lo establecido en cinco de seis categorías

Modeling of Drying Curves of Silica Nanofluid Droplets Dried in an Acoustic Levitator Using the Reaction Engineering Approach (REA) Model

The use of nanoparticles has become of great interest in different industrial applications. The spray drying of nanofluids forms nanostructured grains, preserving the nanoparticle properties. In this work, individual droplets of silica nanofluids were dried in an acoustic levitator. Tests were carried out under different experimental conditions to study the influence of the variables on the drying process. The drying curves were experimentally obtained and an REA model was used to obtain the theoretical curves and the correlations for the activation energy. The critical moisture content theoretically obtained was used to predict the grain diameter

Influence of Particle Size on the Drying Kinetics of Single Droplets Containing Mixtures of Nanoparticles and Microparticles: Modeling and Pilot-Scale Validation

The particle size of the primary particles is an important parameter influencing the drying behavior of droplets. In this work, the influence of particle size on the drying kinetics and grain properties was analyzed for droplets containing silica nanoparticles, microparticles, and mixtures of the two. The presence of microparticles was found to increase the drying rate and shrinkage of the droplet. The drying curves were modeled using a reaction engineering approach (REA) model. Finally, different suspensions were dried in a pilot-scale spray dryer in order to prove the influence of the particle size obtained in the levitator tests

The Effect of Surface Modification of Silica Microfillers in an Epoxy Matrix on the Thermo-mechanical Properties

Thermo-mechanical and mechanical studies were carried out on silica filled epoxy composites. The effects of the filler with and without surfacemodification were studied. Silica particles were incorporated into the polymer matrix: (i) as received and (ii) surface treated with aminosilane coupling agents, namely 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). The epoxy matrix consisted of poly (bisphenol A-co-epichlorohydrin) glycidyl end-capped (DGEBA) resin cured with ethylenediamine (EDA). The relaxation temperatures assigned to the glass transition temperatures (Tg) of the composites revealed that the filler both with and without surface treatment greatly affects the polymer network structure. It seems that on filling the epoxy-amine reactive mixture with silica a stoichiometric change in the epoxy/amine mixture occurs, which causes a decrease in the Tg. However, no significant differences were found for the different surface treatments. Assuming the systems were homogeneous a pseudo-fractional free volume was calculated from the superposition in the slow dynamics regime and good correlations between this parameter with the type of surface treatment and with the yield stress were found.Authors gratefully acknowledge projects Nanoter (MAT2001347), Interfases (S-0505/MAT/0227) and MEC, Acciones Integradas (HH2006-0007) for financial support. Furthermore, the authors acknowledge the Universidad Carlos III de Madrid and the Universidad del País Vasco/Euskal Herriko Unibertsitatea for sup-porting Dr. J. González-Benito at the Departamento de Ingeniería Química y del M. Ambiente

El manejo de conflicto laboral y su relación con la productividad de las empresas comerciales del distrito de San Martín de Porres, 2022

La indagación se ejecutó con el objeto de demostrar cómo se relaciona el manejo de conflicto laboral con la productividad de las entidades comerciales en San Martín de Porres, 2022. Ante ello, se usó bibliografía primaria y secundaria confiable, las cuales se extrajeron de repositorios, revistas indexadas y artículos científicos relacionados con el tema. El método empleado fue de tipo básica, mediante una perspectiva descriptiva, cuantitativa y correlacional; además, de tener un constructo no empírico con un corte transversal. La muestra se compuso por 385 empresas del distrito de San Martín de Porres, a la cual se le efectuó un cuestionario de 20 preguntas. Asimismo, el cuestionario fue aprobado por especialistas en la materia, cuyo nivel de confiabilidad fue del 88,5 %. Además, para analizar la data, se ejecutó el análisis numérico descriptivo mediante cuadros y figuras y el análisis numérico inferencial mediante la correlación de Spearman. De la prueba no paramétrica de Spearman, se determinó un coeficiente de 0, 925 entre las variables de indagación, concluyéndose así que predomina una significativa relación fuerte entre el manejo de conflicto laboral y la productividad de las entidades comerciales del distrito de San Martín de Porres, 2022.The investigation was conducted to demonstrate how the management of labor conflict is related to the productivity of commercial entities in San Martín de Porres, 2022. In view of this, reliable primary and secondary bibliography was used, which were extracted from repositories, indexed journals and scientific articles related to the subject. The method used was basic, through a descriptive, quantitative and correlational perspective; in addition, to have a non-empirical construct with a cross section. The sample was made up of 385 companies from the San Martín de Porres district, to which a 20-question questionnaire was applied. Likewise, the questionnaire was approved by specialists in the field, whose reliability level was 88.5%. In addition, to analyze the data, the descriptive numerical analysis was carried out through tables and figures and the inferential numerical analysis through Spearman's correlation. From Spearman's non-parametric test, a coefficient of 0.925 was determined between the inquiry variables, thus concluding that a significant strong relationship prevails between the management of labor conflict and the productivity of commercial entities in the district of San Martín de Porres, 2022