Microelectromechanical Systems Research Unit

Funder

Organizational Unit

Publications

Control of the dimensional variation adjusting the thermal drying cycle of abrasive composites with incorporated PLA

Publication . Costa, Sharlane; Marques, F.D.P.; Pereira, Mário J.; Ribeiro, J.E.; Soares, Delfim

In composite production, during the thermal drying cycle (T<100ºC), size variation of the composite material occurs due to thermal expansion and water elimination. However, when incorporating PLA components, produced by additive manufacturing, into the abrasive composite, the dimensional variation of the set is very large due to the higher polymer thermal expansion. During this stage, this composite, still in the green state, could not have the sufficient mechanical strength to withstand dimensional variations. These can result in crack formation. Therefore, the proper thermal cycle is a critical step. To define the convenient heating rate during the drying of composites with a PLA piece, thermomechanical analyzes were conducted. Three different heating ramps were tested, 0.1, 0.5, and 2.0 ºC/min in the most critical phase of dimensional change (up to 60 ºC), after this temperature the heating continues at 2 ºC/min. The results indicate that the slower the heating rate, the higher the absorption of the polymer's expansion by the composite. In the slower heating rate (0.1 ºC/min) it was possible to minimize the dimensional variation of the samples by more than 94%.

2022Conference object

Open access

Experimental Investigation of Green Nanofluids: Assessment of Wettability, Viscosity and Thermal Conductivity

Publication . Nobrega, Glauco Tapijara Vallicelli; Cardoso, Beatriz D.; Barbosa, Filipe; Pinho, Diana; Abreu, Cristiano; Souza, Reinaldo Rodrigues de; Moita, Ana S.; Ribeiro, J.E.; Lima, Rui A.

Metallic nanoparticles are a type of nanomaterial synthesized from metallic precursors. Due to their unique physiochemical, electrical, and optical properties, metallic nanoparticles are widely studied and applied in various areas such as medicine, electronics, and heat transfer systems. However, conventional synthesis methods to produce metallic nanoparticles face challenges such as instability and environmental concerns, prompting the exploration of greener synthesis methods. Green synthesis uses natural resources like plants and algae as reducing agents, offering a more environmentally friendly approach for the synthesis of metallic nanoparticles. These green-synthesized metallic nanoparticles can enhance heat transfer by becoming part of nanofluids (NFs), which are colloidal mixtures of NPs in a fluid base. NFs, employed for heat transfer. As a result, it is essential to characterize the NFs regarding wettability, viscosity, and thermal conductivity. The results of the spectrophotometer confirmed the green synthesis of NPs, and it was observed that the increase in NP concentration impacted the contact angle, improving the ability to wet. The thermal conductivity is also modified, with an improvement of 11.3% compared to distilled water, without a significant increase in fluid viscosity.

2024Conference object

Restricted access

Advances in Microfluidic Systems and Numerical Modeling in Biomedical Applications: A Review

Publication . Ferreira, Mariana; Carvalho, Violeta Meneses; Ribeiro, J.E.; Lima, Rui A.; Teixeira, Senhorinha F.C.F.; Pinho, Diana

The evolution in the biomedical engineering field boosts innovative technologies, with microfluidic systems standing out as transformative tools in disease diagnosis, treatment, and monitoring. Numerical simulation has emerged as a tool of increasing importance for better understanding and predicting fluid-flow behavior in microscale devices. This review explores fabrication techniques and common materials of microfluidic devices, focusing on soft lithography and additive manufacturing. Microfluidic systems applications, including nucleic acid amplification and protein synthesis, as well as point-of-care diagnostics, DNA analysis, cell cultures, and organ-on-a-chip models (e.g., lung-, brain-, liver-, and tumor-on-a-chip), are discussed. Recent studies have applied computational tools such as ANSYS Fluent 2024 software to numerically simulate the flow behavior. Outside of the study cases, this work reports fundamental aspects of microfluidic simulations, including fluid flow, mass transport, mixing, and diffusion, and highlights the emergent field of organ-on-a-chip simulations. Additionally, it takes into account the application of geometries to improve the mixing of samples, as well as surface wettability modification. In conclusion, the present review summarizes the most relevant contributions of microfluidic systems and their numerical modeling to biomedical engineering.

2024Journal article

Open access

Influence of micro-textures on cutting insert heat dissipation

Publication . Rosas, José; Lopes, Hernani; Guimarães, Bruno; Piloto, P.A.G.; Miranda, Georgina; Silva, Filipe S.; Paiva, Olga C.

Metal machining is one of the most important manufacturing processes in today’s pro- duction sector. The tools used in machining have been developed over the years to improve their performance, by reducing the cutting forces, the friction coefficient, and the heat generated during the cutting process. Several cooling systems have emerged as an effective way to remove the excessive heat generated from the chip-tool contact region. In recent years, the introduction of nano and micro-textures on the surface of tools has allowed to further improve their overall performance. However, there is not sufficient scientific data to clearly show how surface texturing can contribute to the reduction of tool temperature and identify its mechanisms. Therefore, this work proposes an experimental setup to study the tool surface characteristics’ impact on the heat transfer rate from the tools’ surface to the cooling fluid. Firstly, a numerical model is developed to mimic the heat energy flow from the tool. Next, the design variables were adjusted to get a linear system response and to achieve a fast steady-state thermal condition. Finally, the experimental device was implemented based on the optimized numerical model. A good agreement was obtained between the experimental tests and numerical simulations, validating the concept and the implementation of the experimental setup. A square grid pattern of 100 μm × 100 μm with grooves depths of 50, 100, and 150 μm was introduced on cutting insert surfaces by laser ablation. The experimental results show that there is a linear increase in heat transfer rate with the depth of the grooves relatively to a standard surface, with an increase of 3.77% for the depth of 150 μm. This is associated with the increase of the contact area with the coolant, the generation of greater fluid turbulence near the surface, and the enhancement of the surface wettability.

2022Journal article

Open access

A New Grinding Wheel Design with a 3D Internal Cooling Structure System

Publication . Costa, Sharlane; Capela, Paulina; Souza, Maria S.; Gomes, José R.; Carvalho, Luís; Pereira, Mário J.; Soares, Delfim

This work discusses challenges in conventional grinding wheels: heat-induced tool wear and workpiece thermal damage. While textured abrasive wheels improve heat dissipation, the current surface-only methods, such as those based on laser and machining, have high renewal costs. The proposed manufacturing technology introduces an innovative 3D cooling channel structure throughout the wheel, enabling various channel geometries for specific abrasive wheel applications. The production steps were designed to accommodate the conventional pressing and sintering phases. During pressing, a 3D organic structure was included in the green body. A drying cycle eliminated all present fluids, and a sintering one burnt away the structure, revealing channels in the final product. Key parameters, such as binder type/content and heating rate, were optimized for reproducibility and scalability. Wear tests showed a huge efficiency increase (>100%) in performance and durability compared of this system to conventional wheels. Hexagonal channel structures decreased the wear rates by 64%, displaying superior wear resistance. Comprehensive CFD simulations evaluated the coolant flow through the cooling channels. This new design methodology for three-dimensionally structured grinding wheels innovates the operation configuration by delivering the coolant directly where it is needed. It allows for increasing the overall efficiency by optimizing cooling, reducing tool wear, and enhancing manufacturing precision. This 3D channel structure eliminates the need for reconditioning, thus lowering the operation costs.

2024Journal article

Open access