FE - DEM | Documentos por Auto-Depósito
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- 3D and transient numerical modeling of door opening and closing processes and its influence on thermal performance of cold roomsPublication . Carneiro, Rui; Gaspar, Pedro Dinis; Silva, Pedro Dinho daThis paper presents the comparison of three-dimensional and transient CFD modelling of the opening and closing processes of hinged and sliding doors and its influence on the thermal performance of cold rooms. A species transport model is used to model a tracer gas. The air infiltration through the door opening is determined by the tracer gas concentration decay technique. The prediction of air temperature and velocity fields in the cold room as function of external air temperature allows quantifying the increase of the air infiltration rate and consequently of the average air temperature inside the cold room. When the hinged door is used, the formation of vortices during the opening movement promotes a larger and faster thermal interaction between the two contiguous air masses. The air infiltration during the sliding door opening/closing is 20% lower than for a hinged door. Consequently, the average air temperature inside the cold room is 17% lower. The air infiltration rate was numerically predicted and compared with analytical models’ results. The numerical model predicts closely the air infiltration rate for each door type. Moreover, the transient CFD modelling extends the results of the analytical models allowing the analysis of the influence of door opening and closing processes on the air temperature and velocity fields.
- 3D transient CFD modeling of sliding door operation and its influence on the thermal performance of cold roomsPublication . Carneiro, Rui; Gaspar, Pedro Dinis; Silva, Pedro Dinho daThe need of rationalize energy consumption in agrifood industry has fasten the development of methodologies to improve the thermal and energy performances of cold rooms. This paper presents a 3D transient Computational Fluid Dynamics (CFD) modelling of a cold room to evaluate the air infiltration rate through sliding doors. A species transport model is used for modelling the tracer concentration decay technique. Numerical predictions indicate that air temperature difference between spaces affects the air infiltration. For this case study, the infiltration rate increases 0.012 m3 s-1 per K of air temperature difference. The knowledge about the evolution of air infiltration during door opening/closing times allows to draw some conclusions about its influence on the air conditions inside the cold room, as well as to suggest best practices and simple technical improvements that can minimize air infiltration, and consequently improve thermal performance and energy consumption rationalization.
- Accounting for temperature-dependent properties in viscoelastic duct flowsPublication . Nóbrega, J. M.; Pinho, Fernando; Oliveira, Paulo J.; Carneiro, OlgaA numerical and theoretical study is conducted to evaluate the effect of temperature-dependent properties on the hydrodynamic and thermal characteristics of viscoelastic fluid flow. The rheological constitutive equation of the fluid under consideration follows a common form of the PTT model, which embodies both influences of elasticity and shearthinning in viscosity. A large number of simulations were carried out for a developing channel flow with an imposed constant wall temperature by varying the parameters controlling elasticity (Weissenberg number) and viscous dissipation (Brinkman number). The resulting Nusselt number and friction factor were determined from the numerical results, for both conditions of constant and temperature-dependent properties. The properties that were allowed to vary with temperature were the viscosity, thermal conductivity, specific heat and relaxation time of the PTT model. From the results it was possible to determine how the usual correlations for Nu and Cf have to be modified, following the property-correction method, in order to represent variable-property flow of this viscoelastic fluid. An alternative method to account for variable properties, based on the definition of an equivalent temperature to be used with the constant property Nu and Cf expressions, is also proposed and shown to be less sensitive to the influence of viscous dissipation. The corrections are highly non-linear and strongly depend on eWe2 and Br especially when viscous dissipation is weak.
- Acquisition of multiple physiological parameters during physical exercisePublication . Felizardo, Virginie; Gaspar, Pedro Dinis; Garcia, Nuno M.; Reis, VMThis paper describes the experimental method focused on the acquisition of various physiological parameters during different effort levels of physical exercise like walking and running at several velocities. The study involved 57 young and adult people, 43 male and 14 female (24,37±5,96 years), from which 48 were soldiers belonging to the Infantry Regiment n.° 13 (RI13) of the Portuguese Army and 9 were teachers or college students of Sport Sciences, physically active but not competitive. The experimental measures provide a set of information that offers insight about the health status and physical performance of the subjects during exercise. This experimental method procedure is suited for the acquisition of physiological parameters with both the wireless physiological data acquisition systems such as the bioPlux and the respiratory analyzer gas systems such as Cosmed K4b2.The data was collected to allow the definition of a model that will be used to estimate the energy expenditure of a subject using a wireless physiological data acquisition system, which is much more comfortable and suitable to monitor physical exercise in everyday use than the standard method that makes use of a respiratory gas analysis system.
- Active and intelligent packaging - Principles of operation, characteristics and applicationsPublication . Rato, Nuno; Gaspar, Pedro DinisFood preservation is a topic increasingly being discussed due to market needs, where food from all over the world is required under the best chemical and physical conditions, with minimal waste. Active packaging is defined as the deliberate addition of some components to enhance the properties of the packaging. The various types of active packaging are oxygen scavengers, carbon dioxide emitters and absorbers, ethylene absorbers, ethanol emitters, moisture absorbers, and antimicrobial agents. Smart packaging includes indicators that provide information on product quality and safety over time, such as packaging history, inside and outside atmosphere, oxygen levels, among others. Given the demands on food safety and quality as well as product traceability, there is an exponential increase in the development, production and use of active and intelligent packaging.
- Active Learning “Factory of Boxes” in the Teaching-Learning Processes in Engineering and EntrepreneurshipPublication . Silva, Ricardo; Garcez, Ana; Gomes, Maria; Morais, António; Lima, Tânia M.; Santos, Fernando Charrua; Franco, Mário"Factory of Boxes” is an Active Learning (AL) where concepts related to Industrial Engineering, Mechanics, Mechatronics, Electrotechnics and Entrepreneurial Management can be cultivated. The interconnection of these concepts offers the possibility of developing occupational related skills in the most diverse areas of knowledge. It is the use of AL, simulating the method of a factory which produces cardboard boxes in different layouts and production systems, namely: (a) Classic Taylorist-Fordist Model; (b) Positions’ Enrichment Volvo Model; (c) cell production Toyota Model; and (d) automated line Taylorist-Fordist Classic Model. Data collection was based on observation, counting and recording production in a simulated test at two Universities (UFPB – Brazil and UBI – Portugal) involving master students in Industrial Engineering. The data were analysed from the aspects of productivity and cycle-time. The results showed: (a) It is an economically viable AL since it uses low-cost materials (except for simulating with automated posts which requires some investment) and (b) the Classic Model has the highest cycle-time and the Toyota Model has higher productivity, although these results derive from simulations with a teaching-learning aim and cannot be generalized. With the involvement of students-apprentices, knowledge was absorbed through layout-sharing and analysis of work organisation models’ dynamics, involving activities using Engineering, Industrial Management and Entrepreneurship tools and concepts.
- Adaptive multiresolution approach for two-dimensional PDE'sPublication . Santos, J. C.; Cruz, P.; Alves, M. A.; Oliveira, Paulo J.; Magalhães, F.D.; Mendes, AdélioA multiresolution adaptive approach for the solution of two-dimensional partial differential equations (PDEs) is presented. This methodology is a multidimensional extension of that presented in a previous work [Comput. Methods Appl. Mech. Engrg. 191 (2002) 3909]. The method proposed is unconditionally stable, by incorporating convection differencing schemes with the TVD property, and the grid is dynamically adapted so that higher spatial resolution is automatically allocated to domain regions where strong gradients are observed. The two desired properties of any PDE solver, stability and accuracy, are therefore retained. Numerical results for four test problems are presented which serve to demonstrate the robustness and cost effectiveness of the method.
- Advanced CaZrO3-MgO Ceramic Compositions for High Responsability ApplicationsPublication . Nunes-Pereira, João; Pereira Silva, A; Pena, Pilar; Baudin, CarmenThe development of new advanced materials for harsh environment operation conditions, such as high temperature, wear and severe erosion and corrosion, is of growing interest, namely for transport and energy industries, due to the ecological and energetic current concerns on a global scale. Particularly, in aerospace industry the increase of working temperature of engines and turbines combined with weight reduction will give rise to higher thrust and lower fuel consumption and consequently less emissions. [...]
- Advancements in High-Frequency Antenna Design: Integrating Photonic Crystals for Next-Generation Communication TechnologiesPublication . Bagheri, Nila; Velez, Fernando J.; Peha, JonCentral to this study is the introduction of a pioneering photonic crystal-based microstrip patch antenna array with high gain. Engineered to meet the demands of evolving wireless communication technologies, this novel antenna system leverages Photonic Band Gap (PBG) structures. A fractal microstrip patch antenna, operating within the E-W-F band, is designed and simulated using the High-Frequency Structure Simulation (HFSS) software. With an operational frequency spanning 60.15 GHz to 120 GHz and a resonant band at 64.80 GHz, the antenna achieves a peak gain of 10.50 dBi within the obtained bandwidth. In this study, we selected Rogers RT/Duroid 5880 as the substrate material for our antenna, capitalizing on its unique properties to achieve superior functionality in high-frequency applications. One of the advantages of RT/Duroid 5880 is its exceptionally low dielectric constant (Ɛr = 2.2). This property is paramount for high-frequency antennas, as a lower dielectric constant facilitates improved signal propagation characteristics. The result is reduced signal loss and enhanced impedance matching, contributing to the overall efficiency of the antenna. The mechanical machinability of RT/Duroid substrates, including RT/Duroid 5880, adds another layer of advantage. The material can be easily cut, sheared, and machined to shape, streamlining the manufacturing process, and allowing for precise customization of the antenna design. In addition, by creating air hole in substrate reduce the dielectric constant, the introduction of air holes can decrease the effective dielectric constant of the material. As a lower dielectric constant results in a slower wave propagation speed, a reduction wavelength and a more compact antenna design may result. The presence of air holes or a photonic crystal structure can modify the electromagnetic properties of the substrate, potentially leading to enhanced bandwidth characteristics of broadband antennas.
- Agregados leves impregnados por imersão com materiais de mudança de fase e selagem superficial por molhagem com revestimentos à prova de águaPublication . Gomes, João Castro; Kheradmand, Mohammad; Zoorob, Salah; Silva, Pedro Dinho da; Azenha, Miguel; Aguiar, JoséA presente invenção está relacionada com a obtenção e método de preparação de agregados leves, impregnados com materiais de mudança de fase e impermeabilizados superficialmente. a presente invenção aplica-se, por exemplo, em misturas para pavimentos de modo a permitir atrasar o processo deformação de gelo na sua superfície. esta invenção abrange diferentes agregados leves e apresenta um método de impregnação por imersão em materiais de mudança de fase, sendo a impermeabilização da superfície feita por molhagem, com revestimentos à prova de água. as principais vantagens da presente invenção são a sua aplicação a diferentes tipos de agregados leves e, do método de impregnação dos agregados leves consistir na sua imersão, sem recorrer à utilização de vácuo e, a selagem da superfície dos agregados impregnados ser obtida por molhagem, sem utilização de vácuo, em soluções correntes, correntemente existentes no mercado, de revestimentos à prova de água.