In real-life mechanical engineering applications, it is often complex to achieve an optimal multi-objective design, because of the costs related to fabrication and test of different prototypes. For this reason, the use of computational tools is a recommended practice. In this work, the design of an efficient mixing mechanical device composed of a rectangular pillar confined in a microchannel is aided by machine learning techniques (addressed as machine learning-aided design optimization, MLADO, proposed in this work). A random forest classifier is trained to predict which geometric configuration may lead to vortex shedding. Later, a multi-objective optimization problem is investigated, which consists of minimizing the required pumping power and maximizing the mixing efficiency under some design constrains. If extra training data are desired for surrogates, the random forest classifier can be used to predict whether it is worthy or not to simulate the new configuration, avoiding to run irrelevant computational intensive cases and accelerating the data-driven process. The resulting optimal designs from using the NSGA-II genetic algorithm on the surrogates are simulated, and their performance is shown. The optimal geometric configurations, even for very unfavorable mixing conditions and a medium-low Reynolds number of 200, give a maximum mixing efficiency of around 50% at very low pumping power cost in a short channel, outperforming existing devices in the literature. The MLADO framework followed in this work can be easily extendable and automated for other similar design processes in mechanical engineering at any scale, by including shape parameterization strategies.

In recent years, additive manufacturing has gained importance in a wide range of research applications such as medicine, biotechnology, engineering, etc. It has become one of the most innovative and high-performance manufacturing technologies of the moment. This review aims to show and discuss the characteristics of different existing additive manufacturing technologies for the construction of micromixers, which are devices used to mix two or more fluids at microscale. The present manuscript discusses all the choices to be made throughout the printing life cycle of a micromixer in order to achieve a high-quality microdevice. Resolution, precision, materials, and price, amongst other relevant characteristics, are discussed and reviewed in detail for each printing technology. Key information, suggestions, and future prospects are provided for manufacturing of micromixing machines based on the results from this review.

Numerical modeling of turbulent impinging swirling jets involve complex flow physics that make their computation still very challenging. Thus, the literature on computational modeling of these nanofluid jets is really scarce, with most works on laminar impinging nanofluid jets or turbulent swirling/non-swirling air or water-only jets. In this paper a computational analysis of different configurations in the application of ${\mathrm{A}\mathrm{l}}_2{\mathrm{O}}_3$ nanoparticles to submerged high-Reynolds turbulent jet flows for cooling purposes is developed. Six volume fractions have been investigated ( $\varphi =0,2,4,6,8$ and $10\mathrm{\%}$, which correspond to a Prandtl number of the nanofluid within the range $P{r}_{nf}\in [7,14.4]$) along with two nozzle-to-plate distances ( $H/D=2$ and 4) and several swirl numbers ( $S=0$, $0.16$, $0.27$, $0.45$, $0.77$ and $0.83$). The jet regime is fixed at a Reynolds number $Re=\mathrm{35,000}$. The computational study shows that the application of nanoparticles enhances forced convection for all the simulations carried out. However, the influence of swirl number and nozzle-to-plate distance is not that clear. Variations cause different effects on the performance. For instance, to vary the swirl intensity at large nozzle-to-plate separation has different effect than in short separations. Also, some ranges of variation of swirl may enhance heat transfer whilst others may worsen it.

Heat exchangers are widely used in many mechanical, electronic, and bioengineering applications at macro and microscale. Among these, the use of heat exchangers consisting of a single fluid passing through a set of geometries at different temperatures and two flows in T-shape channels have been extensively studied. However, the application of heat exchangers for thermal mixing over a geometry leading to vortex shedding has not been investigated. This numerical work aims to analyse and characterise a heat exchanger for microscale application, which consists of two laminar fluids at different temperature that impinge orthogonally onto a rectangular structure and generate vortex shedding mechanics that enhance thermal mixing. This work is novel in various aspects. This is the first work of its kind on heat transfer between two fluids (same fluid, different temperature) enhanced by vortex shedding mechanics. Additionally, this research fully characterise the underlying vortex mechanics by accounting all geometry and flow regime parameters (longitudinal aspect ratio, blockage ratio and Reynolds number), opposite to the existing works in the literature, which usually vary and analyse blockage ratio or longitudinal aspect ratio only. A relevant advantage of this heat exchanger is that represents a low-Reynolds passive device, not requiring additional energy nor moving elements to enhance thermal mixing. This allows its use especially at microscale, for instance in biomedical/biomechanical and microelectronic applications.

Insect-proof screens are a frequent passive method to restrict the entrance of insects into greenhouses. However, the installation of these screens also has a negative effect on natural ventilation, which is reflected in the turbulence and velocity of the airflow inside the greenhouse. The turbulent characteristics of airflow through an insect-proof screen installed in the greenhouse windows have not been studied thoroughly in the literature. The present work focuses on the use of two simultaneous 3D sonic anemometers to study the impact of the use of a 13 × 30 threads·cm⁻² insect-proof screen on the turbulence properties of the micro and microscale airflow turbulence. Four tests have been carried out in windward-oriented side windows of a Mediterranean greenhouse. Results demonstrate that the approach of using two simultaneous 3D sonic anemometers for the first time allows one to observe that the effect is different for the three components of the velocity vector field, and there is a strong connection between the simultaneous conditions inside and outside of the greenhouse. Useful information and data on the effect of using a 13 × 30 threads·cm⁻² insect-proof screen are also provided. To give details on the impact of screens in the turbulent properties of ventilation is essential for any commercial distribution, as well as providing important data in the design and development of more efficient insect-proof screens.

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.