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- Fluid flow and structural numerical analysis of a cerebral aneurysm modelPublication . Souza, Maria Sabrina; Souza, Andrews Victor Almeida; Carvalho, Violeta Meneses; Teixeira, Senhorinha F.C.F.; Fernandes, Carla S.; Lima, Rui A.; Ribeiro, J.E.Intracranial aneurysms (IA) are dilations of the cerebral arteries and, in most cases, have no symptoms. However, it is a very serious pathology, with a high mortality rate after rupture. Several studies have been focused only on the hemodynamics of the flow within the IA. However, besides the effect of the flow, the development and rupture of the IA are also associated with a combination of other factors such as the wall mechanical behavior. Thus, the objective of this work was to analyze, in addition to the flow behavior, the biomechanical behavior of the aneurysm wall. For this, CFD simulations were performed for different Reynolds numbers (1, 100, 500 and 1000) and for two different rheological models (Newtonian and Carreau). Subsequently, the pressure values of the fluid simulations were exported to the structural simulations in order to qualitatively observe the deformations, strains, normal stresses and shear stress generated in the channel wall. For the structural simulations, a hyperelastic constitutive model (5-parameter Mooney–Rivlin) was used. The results show that with the increase in the Reynolds number (Re), the recirculation phenomenon is more pronounced, which is not seen for Re = 1. The higher the Re, the higher the strain, displacement, normal and shear stresses values.
- Manufacture wing models to analyze air fluid flow in wind tunnel using a 3D printerPublication . Ariati, Ronaldo; Rocha, João; Ribeiro, J.E.Aerodynamics is a field that is very present in our daily lives, but we are unaware of it. One of the best examples of this is our car, which was not designed at random. This study of aerodynamics has been very important in recent years in several areas, namely motor racing and aeronautics, which is so useful for us when we want to travel. This study consists of developing prototypes of aircraft wings for wind tunnel simulation and numerical simulations due to the high demand to be able to better develop cars, aircraft, and all means involving aerodynamics. The prototypes were created using the SolidWorks CAD software, and additive printing was done in a 3D printer using PLA filament.
- Polydimethylsiloxane composites characterization and its applications: a reviewPublication . Ariati, Ronaldo; Sales, Flaminio; Souza, Andrews Victor Almeida; Lima, Rui A.; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is one of the most promising elastomers due its remarkable pro-prieties such as good thermal stability, biocompatibility corrosion resistance, flexibility, low cost, ease of use, chemically inertia, hyperplastic characteristics, and gas permeability. Thus, it can be used in areas like microfluidic systems, biomedical devices, electronic components, membranes for filtering and pervaporation, sensors and coatings. Although pure PDMS has low mechanical properties, such as low modulus of elasticity and strength, it can be improved by mixing the PDMS with other polymers and by adding particles or reinforcements. Fiber-reinforced PDMS has proved to be a good alternative to manufacture flexible displays, batteries, wearable devices, tac-tile sensors, and energy harvesting systems. PDMS and particulates are often used in the sepa-ration of liquids from wastewater by means of porosity followed by hydrophobicity. Waxes as beeswax and paraffin have proved to be materials capable of improving properties such as hy-drophobic, corrosion resistance, thermal and optical properties of PDMS. Finally, blended with polymers such as poly (vinyl chloride-co-vinyl acetate), PDMS became a highly efficient alterna-tive for separation membrane applications. However, to the best of our knowledge there are few works dedicated to the review and comparison of different PDMS composites. Hence, this review will be focused in PDMS composites, their respective applications, and properties. Generally, it will be discussed the combination of elastomer with fibers, particles, waxes, polymers, and others; aiming to be a review able to demonstrate the wide applications of this material and how tailored characteristics can be reached for custom applications.
- Low-cost multifunctional vacuum chamber for manufacturing PDMS based compositesPublication . Ariati, Ronaldo; Sales, Flaminio C.P.; Noronha, Verônica Teixeira; Lima, Rui A.; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is one of the best known elastomers and has been used in several areas of activity, due to its excellent characteristics and properties, such as biocompatibility, flexibility, optical transparency and chemical stability. Furthermore, PDMS modified with other materials promotes the desired changes to broaden its range of applications in various fields of science. However, the heating, mixing and degassing steps of the manufacturing process have not received much attention in recent years when it comes to blending with solid materials. For instance, PDMS has been extensively studied in combination with waxes, which are frequently in a solid state at room temperature and as a result the interaction and manufacturing process are extremely complex and can compromise the desired material. Thus, in this work it is proposed a multifunctional vacuum chamber (MVC) with the aim to improve and accelerate the manufacturing process of PDMS composites combined with additives, blends and different kinds of solid materials. The MVC developed in this work allows to control the mixing speed parameters, temperature control and internal pressure. In addition, it is a low cost equipment and can be used for other possible modifications with different materials and processes with the ability to control those parameters. As a result, samples fabricated by using the MVC can achieve a time improvement over 133% at the heating and mixing step and approximately 200% at the last degassing step. Regarding the complete manufacturing process, it is possible to achieve an improvement over 150%, when compared with the conventional manufacturing process. When compared to maximum tensile strength, specimens manufactured using the MVC have shown a 39% and 65% improvement in maximum strain. The samples have also shown a 9% improvement in transparency at room temperature and 12% at a temperature of about 75 C. It should be noted that the proposed MVC can be used for other blends and manufacturing processes where it is desirable to control the temperature, agitation speed and pressure.
- Composite material of PDMS with interchangeable transmittance: study of optical, mechanical properties and wettabilityPublication . Sales, Flaminio; Souza, Andrews; Ariati, Ronaldo; Noronha, Verônica Teixeira; Giovanetti, Elder Gulick; Lima, Rui A.; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is a polymer that has attracted the attention of researchers due to its unique properties such as transparency, biocompatibility, high flexibility, and physical and chemical stability. In addition, PDMS modification and combination with other materials can expand its range of applications. For instance, the ability to perform superhydrophobic coating allows for the manufacture of lenses. However, many of these processes are complex and expensive. One of the most promising modifications, which consists of the development of an interchangeable coating, capable of changing its optical characteristics according to some stimuli, has been underexplored. Thus, we report an experimental study of the mechanical and optical properties and wettability of pure PDMS and of two PDMS composites with the addition of 1% paraffin or beeswax using a gravity casting process. The composites’ tensile strength and hardness were lower when compared with pure PDMS. However, the contact angle was increased, reaching the highest values when using the paraffin additive. Additionally, these composites have shown interesting results for the spectrophotometry tests, i.e., the material changed its optical characteristics when heated, going from opaque at room temperature to transparent, with transmittance around 75%, at 70 °C. As a result, these materials have great potential for use in smart devices, such as sensors, due to its ability to change its transparency at high temperatures.
- Product development and industrial processingPublication . Ribeiro, Luís Frölén; Ribeiro, J.E.; Costa, Carlos Casimiro da; Duarte, António; Andrade, Carlos A.R.; Svinth, Arne; Madsen, John; Thomsen, Morten; Smidstrup, Kent; Carsten, John JacobsenThis article aims at presenting a teaching experiment where the same course is taught simultaneously in two countries, Portugal at the Polytechnic Institute of Bragança (IPB) and Denmark, at Lillebaelt Academy (EAL). Project Based Learning (PBL) underlies the applied methodology. As the project is still in its initial phase it is too premature to delve into a conclusive and thus critical approach. Nonetheless, we will highlight the course methodological procedures and objectives as well as the educational gains to the students and to the two institutions involved.
- Green synthesis of nanoparticles from olive oil waste for environmental and health applications: A reviewPublication . Afonso, Inês Santos; Cardoso, Beatriz D.; Nobrega, Glauco; Minas, Graça; Ribeiro, J.E.; Lima, Rui A.Environmental degradation is a growing concern, driving researchers to explore eco-friendly nanoparticle (NP) synthesis, for diverse applications. Within this context, the employment of olive oil waste (OOW) as a green source for the synthesis of NPs has emerged as a viable alternative to conventional techniques. The olive industry has a significant impact in the Mediterranean region, and alongside it, comes the OOW, where most of it cannot be left untreated. In the present review, a comprehensive overview of the NPs’ green synthesis derived from OOW and its potential applications in both environmental and health areas have been assessed, outlining its major challenges and potential outcomes for future research. Both principles and methods of green NPs synthesis were also explored, focusing on the unique properties of OOW as an effective agent for reduction and stabilization, as well as the characterization techniques used for characterizing the synthesized NPs. The OOW-derived NPs can have a wide variety of environmental applications including water purification, pollutant degradation, and remediation of contaminated environments. In the health field, the OOW applications include drug delivery systems, antimicrobial activity and cancer therapy. These OOW NPs have been successfully used as efficient drug delivery vehicles to cancer cells, enhancing treatment outcomes and potentially minimizing side effects. However, it is imperative to point out the importance of performing in-depth toxicity assessments, particularly at higher concentrations of NPs.
- Experimental evaluation of green nanofluids in heat exchanger made oF PDMSPublication . Nobrega, Glauco; Souza, Reinaldo Rodrigues de; Cardoso, Beatriz D.; Afonso, Inês Santos; Pereira, José Eduardo; Cardoso, Elaine; Moita, Ana S.; Ribeiro, J.E.; Lima, Rui A.Conventional methods for synthesizing metallic nanoparticles face challenges such as instability and environmental concerns. Therefore, new, simpler, and more eco-friendly methods are being explored. In this context, the study reports a green synthesis process to produce magnetic iron oxide nanoparticles using an aqueous extract of the alga Chlorella vulgaris. This process leverages natural resources to create a sustainable nanofluid known as green nanofluid. To evaluate the characteristics of this nanofluid, experimental measurements of wettability, viscosity, thermal conductivity, and qualitative stability analysis were conducted. An experimental setup consisting of a heat exchanger made of polydimethylsiloxane (PDMS) was used to assess the thermal performance and the results were compared to theoretical equations and numerical simulation. Additionally, thermographic imaging of temperature gradients as the fluids passed over the heated surface of the serpentine channel were made. The main findings confirmed that the nanofluid was more stable than that obtained by traditional methods and had a more uniform temperature distribution over the heat exchanger. The higher concentration exhibited superior thermal performance compared to DI-Water. Moreover, the green nanofluid was used at a weight concentration of 0.1 wt%, provided thermal performance results of nearly 4.5% superior to those estimated by the numerical model and 6.4% higher than those experimentally obtained with the base fluid, respectively. Finally, the results obtained for the nanofluid also showed an average increase of around 5% in the viscosity of the base fluid, with a more significant sedimentation at a concentration of 0.1 wt%.
- Conventional and recent advances of vegetable oils as metalworking fluids (MWFs): a reviewPublication . Afonso, Inês Santos; Nobrega, Glauco; Lima, Rui A.; Gomes, José R.; Ribeiro, J.E.Vegetable oils have been used as metalworking fluids (MWFs) for many years, particularly in small-scale metalworking operations and in industries where environmental regulations are strict. Before the development of modern MWFs, vegetable oils were one of the most common lubricants used for metalworking tools. The use of vegetable oils can be traced back to ancient civilizations such as Egypt, Greece, and Rome, where olive oil was commonly used to lubricate metal tools and weapons. Today, vegetable oils are used as MWFs in a variety of applications. They are often combined with additives or nanoparticles to enhance their performance, such as improving the lubricity, cooling properties, and stability of the oil, as well as reducing friction and wear on the cutting tool. Additives, such as antioxidants, anti-wear agents, and extreme pressure (EP) additives, can be used to improve the performance of vegetable oils as cutting fluids. Compared to standard MWFs, vegetable oils are generally more biodegradable and environmentally friendly, and can be more cost-effective. However, MWFs may offer superior performance in certain areas, such as lubrication and cooling. Ultimately, the choice of MWFs will depend on the specific requirements of the metalworking operation and the balance between performance, cost, and environmental considerations. As the demand for sustainability and environmental responsibility continues, the use of vegetable oils as MWFs is likely to become even more popular in the future. Overall, vegetable oils offer a viable and potentially attractive alternative to standard MWFs in certain applications. This review highlights both conventional and most recent advances in vegetal oils frequently used as lubricant fluids in manufacturing processes.
- Cooling performance of an acrylic serpentine with a rectangular cross sectionPublication . Nobrega, Glauco; Barbosa, F.M.; Soares, Filipe de Almeida da Silva; Ralha, R.; Souza, Reinaldo Rodrigues de; Ribeiro, J.E.; Moita, Ana S.; Lima, Rui A.In recent years, photovoltaic panels have been established as one of the main sources of electricity considered to be clean. Its efficiency and lifetime are greatly influenced by the operating temperature. Active cooling using cylindrical copper serpentines is one of the most common methods for many systems. However, due to the cylindrical geometry of the tubes, the contact with the plate is a point and its area tends to be zero. In this way, serpentines that provide a bigger contact area between the heat removal system and the solar panel board are desired. Serpentines manufactured by machining acrylic plates in CNC milling machines allow the construction of a channel with a rectangular cross-section with a considerable area of contact between the channel and the plate. The obtained results show that there was a significant improvement in the heat exchange between the plate and the thermofluid when the acrylic serpentine with a rectangular section was used.