Jesús Javier Jiménez-Galea

The correlation between microstructure, rheology, and tribological behavior in silica-based nanofluids dispersed in vegetable oils was investigated. Nanofluids containing 3 vol.% hydrophilic silica in coconut oil (CO), CO with 10 vol.% of Taladrine (CO-10Tal) and the 50CO-50SO mixture of CO and sunflower oil (SO) were characterized using tribometry, rheometry, and thermal analysis. Friction-velocity curves revealed two lubrication regimes, boundary and mixed lubrication, which were interpreted using a semi-logarithmic model. The slope parameter was identified as a measure of shear-induced activation of lubrication mechanisms. Results showed that lubrication mechanisms evolved from tribofilm-dominated behavior with particle-assisted sliding to mobility-controlled regimes involving rolling and dynamic third-body layers. Rheological measurements indicated the fragmentation and restructuring of fractal aggregates. The intrinsic viscosity and maximum packing fraction provided quantitative descriptors of aggregate structure. The CO-10Tal nanofluid exhibited large, open aggregates with high intrinsic viscosity and strong shear sensitivity, resulting in higher friction at low velocity and rapid friction reduction at bigger velocities. The 50CO-50SO colloid displayed compact aggregates, enhanced dispersion, and superior tribological performance due to increased particle mobility. The results demonstrated that shear-induced microstructural evolution controlled frictional behavior. This work provided a unified framework linking aggregation, rheology, and nanolubrication mechanisms in bio-based systems.

Industrial heritage movable assets, particularly the traditional machining tools used in manufacturing processes, are facing an increasing risk of disappearing due to the continuous advances in technology. Innovations in industry have progressively displaced many of these manual tools, making them obsolete or irrelevant in current manufacturing processes, remaining only for artisanal work. In this context, manual vertical drilling presses, which have played a crucial role in manufacturing for decades, are being displaced by more advanced machining tools, which incorporate technologies such as Computer Numerical Control (CNC). This work focuses on the development of a manual vertical drill press digital model, in order to virtually recreate its operation and structure. The software used to develop the model was SolidWorks (version 2024). This model aims not only to preserve a historically significant machine but also to serve as an educational resource, illustrating drilling operations before modern technologies emerged. Reconstructing them in 3D enhances the study and understanding of their mechanics and utility, ensuring access to technical knowledge and preserving their legacy in a digitalized world.

Industrial heritage movable assets, particularly the traditional machining tools used in manufacturing processes, are facing an increasing risk of disappearing due to the con-tinuous advance of technology. Innovations in industry have progressively displaced many of these manual tools, making them obsolete or irrelevant in current manufacturing processes, remaining only for artisanal work. In this context, manual vertical drilling presses, which have played a crucial role in manufacturing for decades, are being dis-placed by more advanced machining tools, which incorporates, technologies such as Computer Numerical Control (CNC). This work focuses on the development of a manual vertical drill press digital model, in order to virtually recreate its operation and structure. The software used to develop the model was SolidWorks. This model aims not only to preserve a historically significant machine but also to serve as an educational resource, illustrating drilling operations before modern technologies emerged. Reconstructing them in 3D enhances the study and understanding of their mechanics and utility, ensuring access to technical knowledge and preserving their legacy in a digitalized world.

Phase change materials (PCMs) have the advantage of using the latent thermal heat as energy storage. Coconut oil (CO) has attracted much attention as PCM due to its high stability against oxidation. Although the viscosity of CO-based dispersions has extensively been studied, little research has been performed on time-dependent flow behaviors. In this work, the rheological properties of fumed silica dispersed in CO at fractions of 1, 2, 3, and 4 vol.% were investigated. All suspensions showed shear-thinning behavior, which became more Newtonian at temperatures above the phase change. The 3 and 4 vol.% suspensions showed gel-like microstructures. The thixotropic properties of the 3 vol.% suspension at 30 °C and 35 °C were mainly studied through stepwise changes in the shear rate. The results were consistent with thixotropic behavior, with a complete recovery of the microstructure. The sweep frequency of this sample demonstrated the dominance of the elastic modulus at both temperatures. Therefore, a thixoelastic nature of this gel could be inferred. This gel-like material flowed under high stress, providing superior thermal damping capabilities compared to conventional fluids. A reduction of 8.65 °C was confirmed after 30 min. of the laptop power supply operation.

Phase change materials (PCM) as liquid phase have the advantage of using the latent thermal heat as energy storage. Coconut oil (CO) has attracted much attention as PCM due to its high stability against oxidation. The addition of fumed silica has exhibited superior performance in thickening, thixotropy, sag resistance, reinforcement, and caking resistance. Although viscosity of CO-based dispersions has extensively been studied, few research has been done on time-dependent flow be-haviors. In this work, the rheological properties of fumed silica dispersed in CO at fractions of 1, 2, 3, and 4 vol.% were investigated. All suspensions showed shear-thinning behavior, which became more Newtonian at temperatures above the phase change. The 3 and 4 vol. % suspensions showed gel-like microstructures. The thixotropic properties of the 3 vol.% suspension at 30 °C and 35 °C were mainly studied through stepwise changes in shear rate. The results were consistent with thixotropic behavior with a complete recovery of the microstructure. The sweep frequency of this sample demonstrated the dominance of the elastic modulus at both temperatures. Therefore, a thixoelastic nature of this gel could be inferred.

Virgin coconut oil (VCO) is an edible vegetable oil that is eco-friendly, biodegradable, and sustainable, with high thermal and chemical stability as a phase change material (PCM). In this work, VCO filled with fumed silica A200 nanoparticles was tested as a cutting fluid in drilling processes. Silica concentrations ranging from 1 to 4 vol% were analyzed. Thermal properties were evaluated by differential scanning calorimetry (DSC) and thermal conductivity measurements at different temperatures and concentrations. Thermal conductivity showed an enhancement with the addition of silica powder and reduced with increasing temperature. Based on thermal and flow properties, VCO-3A200 was found to be the optimal concentration. The thermal images of this nanofluid taken after 60 s of drilling exhibited a reduction of 12 °C with respect to the dry process. The friction coefficient versus shear rate was also measured. With 8% VCO, a reduction in the friction coefficient of 8% compared to the dry test was achieved. The addition of 3 vol% of silica to the base oil reduced the friction coefficient by 16% compared to the dry test. The use of fumed silica dispersed in VCO has proven to be a sustainable, recyclable, and environmentally friendly refrigerant and lubricant cutting fluid.

La iniciativa y la proactividad del alumnado de Ingeniería durante el desarrollo de las clases teóricas es normalmente muy limitada, al contrario que en las prácticas de laboratorio donde muestra más interés. Se constata un aumento del abandono en las carreras de ingeniería y una disminución de matriculados y este estudio tiene como finalidad analizar cuantitativamente el impacto de una herramienta de evaluación 360 grados encuestada en la evaluación de prácticas en estudiantes de ingeniería industrial. Se pretenden lograr varios objetivos: por un lado, implicar al estudiante en el proceso de evaluación y, por otro, conocer su grado de satisfacción con este tipo de evaluación, así como su opinión sobre la ponderación justa. Se Sigue una metodología basada en la aplicación de la evaluación 360 grados y un diseño de encuesta con 23 preguntas. Las etapas del proceso de evaluación 360 grados fueron tres: co- (entre estudiantes), auto- (por el propio estudiante) y hetero-evaluación (por el docente). Se diseñó un cuestionario, validado mediante análisis factorial confirmatorio, y se procedió al análisis de las respuestas en base a 4 agrupaciones seleccionadas: dos asignaturas de primeros y últimos cursos, modalidad de evaluación, sexo (hombre o mujer) y ciclo (Grado o Máster). También se ha analizado la mejor ponderación en la calificación final para cada evaluador, proponiéndose como óptimos los valores 50%-30%-20% para la hetero-, co- y autoevaluación, respectivamente. Los resultados muestran un elevado grado de satisfacción por parte de los grupos analizados a través de la encuesta y adecuada maduración del estudiante.

The number of students enrolled in engineering studies in Spain is in decline, mainly due to the difficulty in passing the subjects, whose factors may be linked to the science-related content of the subject, a very demanding evaluation system or a lack of active participation of students. The main objective of this study is to provide the student with a 360-degree feedback tool and a survey, from which lecturers can extract the degree of satisfaction of students in its application in a standardized way in scientific-technological activities of BSc/MSc in industrial engineering to quantify learning and motivation. The involvement of students in the assessment process was carried out in three phases: peer-assessment (among students), self-assessment (student himself) and hetero-assessment (teaching staff). After that, a survey was designed, which was validated through confirmatory factor analysis. Ninety-nine percent of the students valued this evaluation experience very positively with respect to the objectivity of the criteria used in the methodology and the material provided by the teaching staff. The fact that only 37.5% of the students considered this experience very favorable for their learning and self-training shows the importance of the teaching staff in their learning process and suggests a need to find complementary improvements to this evaluation system in industrial engineering degrees.

The addition of nanoparticles to liquid media can improve thermomechanical properties of dispersants. This ability gives rise to the development of multiple applications of nanofluids (NF) in branches so different as electronic and photonic devices or cosmetic industry. Logically, these applications require a good control of heat transfer and flow properties. Moreover, if we consider the necessity to optimize industrial processes in which NF take part, it is necessary to obtain possible relationships between both physical mechanisms. Specifically, in this work, a study about thermal conductivity and rheological behavior of fumed silica suspensions in polypropylene glycol (PPG400) and polyethylene glycol (PEG200) was performed. The study of these two suspensions is interesting because the flow behaviors are very dissimilar (while the fumed silica in PEG200 suspension is viscoplastic, the fumed silica in PPG400 suspension shows shear-thickening behavior between two shear-thinning regions), despite the addition of fumed silica producing similar enhancement of the relative thermal conductivity in both liquid phases. The more outstanding contribution of this work lies in the combination of rheological and conductivity measurements to deepen in the understanding of the heat transfer phenomenon in NF. The combination of rheological together with thermal conductivity measurements have permitted establishing the mechanisms of liquid layering and aggregate formation as the more relevant in the heat transfer of these silica fumed suspensions.