A carregar...
Projeto de investigação
Sem título
Financiador
Autores
Publicações
Instability of a Moving Bogie
Publication . Dimitrovová, Zuzana; DEC - Departamento de Engenharia Civil; MDPI - Multidisciplinary Digital Publishing Institute
This paper analyzes vibrations induced by a moving bogie passing through a single-layer railway track model. The emphasis is placed on the possibility of unstable behavior in the subcritical velocity range. All results are presented in dimensionless form to encompass a wide range of possible scenarios. The results are obtained semi-analytically, however, the only numerical step involves solving the roots of polynomial expressions. No numerical integration is used, allowing for the straightforward solution of completely undamped scenarios, as damping is not required for numerical stability. The vibration shapes are presented in the time domain in closed form. It is concluded that increased foundation damping worsens the situation. However, in general, the risk of instability in the subcritical velocity range for a moving bogie is lower than that of two moving masses, particularly for higher mass moments of inertia of the bogie bar and primary suspension damping. The study also examines how the results change when a Timoshenko-Rayleigh beam is considered instead of an Euler-Bernoulli beam. Although some cases may appear academic, it is demonstrated that instability in the supercritical velocity range cannot be assumed to be guaranteed.
Enhancing the efficiency of Brown 24 pigment production through continuous microwave heating in conveyor belt and rotary kiln systems
Publication . Ramos, Pedro A.V.; Albuquerque, Duarte M.S.; Pereira, José C.F.; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; DEMI - Departamento de Engenharia Mecânica e Industrial; Faculdade de Ciências e Tecnologia (FCT); Elsevier Science B.V., Amsterdam.
In energy intensive industries, the continuous production with microwave technology presents several challenges in achieving high energy efficiency and heating uniformity. In the ceramic pigments sector, the Brown 24 is the ideal candidate for this study due to its susceptibility to thermal runaways and its high temperature to reach total conversion, higher than 1000 K. By another hand, most literature related to this field focus on static systems while ignoring the continuous ones which are required by the industry. A coupled model that integrates thermal, electromagnetic and chemical phenomena within an energy system was implemented in COMSOL Multiphysics. Additionally, a MATLAB controller was employed to dynamically adjust the cavity length through a moving plunger, which maximizes the electrical efficiency. The required power is also managed to guarantee a total chemical conversion of the material. The proposed optimization methodology reduces computational costs, and it is applicable to any continuous microwave system processing moving solid materials. In this work, two microwave configurations were optimized. The first one, based on a conveyor belt, achieved a global efficiency close to 70%. While the second one, based on a rotary kiln, achieved a global efficiency of 85% and a production rate of 4.66 kg/h, significantly outperforming a previous study by factors of 1.57 and 2.06, respectively. These findings show the potential for substantial improvements in continuous microwave systems.
Electrodialytic lithium extraction from secondary resources
Publication . Almeida, Joana; Gouveia, Joana R.; Ribeiro, Inês S.; Pires, Carolina; Mateus, Eduardo P.; Ribeiro, Alexandra B.; CENSE - Centro de Investigação em Ambiente e Sustentabilidade; Elsevier BV
In transportation, large-scale electrification, particularly through lithium-ion batteries, is expected to drive significant emissions reductions while simultaneously increasing global lithium demand. However, the limited availability of lithium, compounded by geopolitical constraints, poses risks to the energy transition, namely in the European Union. Adopting circular economy models offers a sustainable approach to increase resource recovery. The present research aims to assess the potential of the electrodialytic process for lithium recovery from wastewater generated during lithium-ion battery recycling and aluminium-lithium alloy dust processing, as well as related environmental and economic impacts. Bench-scale experiments were conducted using two-compartment electrodialytic reactors, operated at 50 mA, 100 mA and 200 mA with a cation-exchange membrane interposed. Tests were performed over 24 h, 48 h and 72 h. Lithium recovery reached 91.54 % from the aluminium-lithium alloy dust and 97.23 % from the wastewater of lithium-ion battery recycling. The cradle-to-gate life cycle assessment resulted in 0.26 kg of CO2 eq/g Li global warming impacts for wastewater of lithium-ion battery recycling, and 46.40 kg of CO2 eq/g Li for aluminium-lithium alloy dust. Material flow cost accounting showed lower recovery costs for wastewater (0.36 €/g Li versus 129.26 €/g Li). Energy consumption in the reactor is the primary hotspot, where optimizing energy and time efficiency could reduce environmental and economic impacts.
Design of magnetic kappa-carrageenan-collagen bioinks for 3D bioprinting
Publication . Almeida, Duarte; Küppers, Freya; Gusmão, Afonso; Manjua, Ana C.; Ferreira, Catarina F.R.; Portugal, Carla A.M.; Silva, João C.; Sanjuan-Alberte, Paola; Ferreira, Frederico Castelo; LAQV@REQUIMTE; DQ - Departamento de Química; Springer
Bioprinting approaches are of great promise for tissue engineering applications as they allow the fabrication of constructs able to mimic native tissues’ mechanical and topographical features. Additional control over cells fate can be enhanced using stimuli-responsive materials, requiring the development of novel bioinks for this purpose. In this study, bioinks comprising κ-carrageenan, collagen, and magnetic nanoparticles were designed for 3D bioprinting applications. The characterization of this material was performed, where mechanical compressive tests yielded Young’s moduli ranging from 8.25 to 18.4 kPa. Rheological assessments also revealed the shear-thinning behavior of the bioinks and a temperature-dependent gelation. The capability of these bioinks to produce 3D constructs by extrusion bioprinting was established through the printability evaluation and the development of complex structures, supporting the viability and proliferation of mesenchymal stromal cells (MSCs). Finally, as proof-of-concept, it was observed that the secretome of bioprinted MSCs stimulated with an external magnetic field of 80 mT was able to increase the number of tubes formed by human umbilical vein endothelial cells.
Experimental Evidence of Efficient Phononic-Based Vibration Isolators for Mechanical Applications
Publication . Policarpo, Hugo Filipe Diniz; Almeida, Raquel A.B.; Neves, Miguel M.; Maia, Nuno M.M.; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; MDPI - Multidisciplinary Digital Publishing Institute
Even though the design of vibration isolators is well-established for many engineering applications, their efficiency in wide and multiple frequency ranges is still a challenge. In these cases, the use of Phononic-Based Vibration Isolators (PBVIs) may be advantageous as they present different Attenuation Regions (ARs) in which the elastic waves are strongly attenuated. Therefore, the present paper is devoted to the experimental evaluation, in terms of force transmissibility, of different types of supporting devices tested on a load mass and a motor of a Hermetic Compressor (HC). Those devices are the original Helical Coil Spring (HS) that equips the HC, the PBVI, and the Combined Structure (CS) which is composed of a PBVI combined in series with the HS. Results evidentiate the capability of the CSs to isolate vibrations, where the PBVI contributes with its ARs, thus operating as a “filter” in specific frequency ranges, while the HSs maintain the flexibility of the CSs, which is advantageous for impact-loads and/or transient-case scenarios. Hence, the capability, relevance and impact that these PBVIs present for force transmissibility reduction applications is highlighted here, which should capture the attention of and motivate the industry, e.g., producers of isolation systems, since it has wide-ranging engineering applications.
Unidades organizacionais
Descrição
Palavras-chave
Contribuidores
Financiadores
Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
Concurso de avaliação no âmbito do Programa Plurianual de Financiamento de Unidades de I&D (2017/2018) - Financiamento Base
Número da atribuição
UIDB/50022/2020