Engenharia Mecânica
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/23
Navegar
16 resultados
Resultados da Pesquisa
Artigo de evento 3 Citação(ões) na Scopus The effect of altitude and intensity of physical activity on the exergy efficiency of respiratory system(2013-07-16) HENRIQUES, I. B.; Carlos Mady; Cyro Albuquerque; YANAGIHARA, J. I.; OLIVEIRA JUNIOR, S.The effect of altitude on exercise performance of lowlanders has long been discussed, but it is still unclear whether the performance reduction is related to inefficiency of the respiratory system, tissues or both. In the present work, exergy analysis was applied to the human body in order to compare its exergy efficiency under basal conditions and during physical activity at sea level and high altitudes for different periods of acclimatization. Two control volumes were analyzed: the respiratory system, which comprises the lungs and the airways, and the human body as a whole. In the first control volume, the exergy rates and flow rates are associated with the venous blood and the inspired air in the inlet and the arterial blood and expired air in the outlet. An internal exergy variation due to the exergy metabolism of the lung, an exergy transfer rate associated with the metabolism of the lung and the power performed by the respiratory muscles were also taken into account. Analyzing the second control volume, the exergy transferred rate to the environment due to the heat losses by convection and radiation were considered, as well as the exergy flow rate associated with respiration and transpiration. The temperatures of different parts of the body and the heat losses to the environment were obtained from a heat transfer model of the human body. The data concerning gas and blood flows were obtained from a model of the respiratory system. The last one was modified based on medical literature to simulate the response to physical activity at high altitude for different periods of acclimatization, from the first moment that the body is exposed to a high altitude environment to three months of acclimatization. The results obtained indicated that the respiratory system exergy efficiency is reduced at high altitudes and under physical activity, while the exergy efficiency of the body increases for both parameters. Concerning the acclimatization period, its influence was more pronounced in the respiratory system. It was possible to observe a decrease in the exergy efficiency of the respiratory system in the first two days. From this moment on, the efficiency increased continuously until the twentieth day, when it is stabilized and remains constant.Artigo de evento 2 Citação(ões) na Scopus The effect of carbon monoxide in the exergy behavior of lungs(2017-07-02) CENZI, J. R.; HENRIQUES, I. B.; Cyro Albuquerque; YANAGIHARA, J. I.; OLIVEIRA, S.; Carlos Mady© 2017 IMEKOThe present work evaluates the impact of carbon monoxide inhalation in the human lungs exergy behaviour for different levels of intoxications and altitude. It is significant because this substance is one of the most common air pollutants in cities and an increasing in the destroyed exergy can be associated with a reduction in lifespan. Moreover, an evaluation of the severity as a function of the city height may intensify the hazard associated with carbon monoxide. In order to evaluate these consequences, a carbon monoxide transportation model obtained in literature was used to calculate the concentrations of oxygen, carbon monoxide and carbon dioxide in the different respiratory system tissues. With the purpose to better evaluate the different levels of carbon monoxide intoxication and hemoglobin concentration (which is a function of acclimatization time) it was proposed an exergy efficiency for the lungs. From this model, it was possible to conclude that a higher level of intoxication is associated to lower exergy efficiency values. Higher hemoglobin levels when associated to carbon monoxide intoxication also results in lower efficiencies.Artigo de evento 0 Citação(ões) na Scopus Exergy analysis of the body efficiency during aerobic activities(2018-06-17) IGARASHI, T. L.; SPANGHERO, G. M.; FERNANDES, T. L.; HERNANDEZ, A. J.; Carlos Mady; Cyro Albuquerque© 2018 University of Minho. All rights reserved.The First and Second Law of Thermodynamic were applied to the human body in order to evaluate the quality of the energy conversion process during muscle activity. Such an implementation represents an important issue in the exergy analysis of the body, because there is a difficulty in literature to evaluate the performed power in some activities. To this aim, the exergy analysis was applied to an aerobic activity (treadmill running test) to evaluate the efficiency of energy conversion process in the body and cells. Physiological and test data such as, oxygen consumption, carbon dioxide production, skin temperature, treadmill velocity, air temperature, relative humidity, were measured. Different methods to calculate the performed power were studied and the results compared with the First Law of Thermodynamics concerning to evaluate the accuracy of equations. From the Second Law of Thermodynamics point of view it was obtained similar, yet complementary results. Some methods resulted in efficiency around 10% others close to the maximum possible performed work, which is the exergy released in ATP hydrolysis (around 50 to 60%).Artigo de evento 0 Citação(ões) na Scopus Simulation of respiratory gas exchange in the placenta(2018-06-17) CENZI, J.; Cyro Albuquerque; Carlos Mady© 2018 University of Minho. All rights reserved.This work evaluates the gas exchange between a fetus circulatory system and the mother’s, which occurs in the placenta. Oxygen, carbon dioxide and carbon monoxide transport were analyzed. Carbon monoxide is one of the most common air pollutants in cities and it has a significant impact in physiological conditions even in low concentration. These effects are particularly prejudicial for pregnant women, fetus and newborn babies. A carbon monoxide transportation model, from literature, is adapted to simulate a pregnant woman. The respiratory gas exchange in the placenta is modeled, so it is possible to evaluate the concentration of the different gases. In this way, it is possible to assess carbon monoxide concentration in fetus and evaluate its effects. Exergy analysis are performed for both mother’s and fetus’ respiratory systems, in other to compare it to the respiratory system of a male adult. It is possible to verify that the fetus was more affected by CO poisoning than the adults, although it HbCO rate is significantly reduced compared to maternal’s.Artigo de evento 0 Citação(ões) na Scopus Analysis of an absorption refrigeration system for air-conditioning of a microbus(2018-06-17) RANIERI, M. A.; MANIERI, G.; Carlos Mady; Cyro Albuquerque© 2018 University of Minho. All rights reserved.The present work evaluates the possibility of recovering cooling and exhaust systems energy of an internal combustion engine as an energy source input for an absorption refrigeration cycle. From experimental data of the cooling and exhaust systems of an urban microbus under various loading and rotation conditions, simulations of a lithium bromide absorption cycle were performed. The performance of the absorption cycle was obtained in each condition of use of the vehicle: warm-up, city and road route. The results showed that the cooling capacity was 0.97 kW during the initial phase of warming-up, reaching 7.01 kW in road route. In the city condition, which is the main application of the micro-bus studied, 4.17 kW of cooling capacity was found, which represents 78.9% of the cooling capacity in vehicles of this category.Artigo de evento 0 Citação(ões) na Scopus Efficiency trade-offs in the Brazilian passenger vehicle fleet(2021-06-28) MOSQUIM, R. F.; Carlos Mady© ECOS 2021 - 34th International Conference on Efficency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems.Transportation energy demand in Brazil increases despite vehicles improving technologically. Models calculating possible avoided emissions can benefit from the estimation between vehicle attribute trade-offs and technological progress. A regression analysis with year-fixed effects was carried for 1,656 models in the passenger vehicle fleet in Brazil from 2004 to 2020. Weight and aerodynamic drag had the main effect on fuel economy. Parameters related to power, such as displacement, horsepower, torque and acceleration, impacted as well. Hybrids had positive effects, but its diffusion in Brazil is likely to be slow. Fuel economy could have been 20.9% to 23.4% higher in the period if all technological progress were expended on better fuel economy, as opposed to the 12.1% actually realized. This gap is an important aspect that should not be neglected in scenario-building.Artigo de evento 0 Citação(ões) na Scopus Assessment of Different More Electric and Hybrid-Electric Configurations for Long-Range Multi-Engine Aircraft(2021-06-28) GIMENEZ, F. R.; Carlos Mady; HENRIQUES, I. B.© ECOS 2021 - 34th International Conference on Efficency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems.This work intends to assess the characteristics, penalties, gains, and challenges through the Electrification and Hybridization process for long-range aircraft. A system, engines and mission level analysis was created focusing on a Thermodynamics and financial approach. A conventional reference aircraft was compared with enhanced more electric and hybrid-electric versions of itself. These new models may carry batteries, which supply the aircraft systems and/or engines, or not. State-of-the-art propulsion and systems’ architecture were also implemented within the cutting-edge airplanes. A full factorial analysis was conducted to vary the batteries’ energy density and the hybridization ratio for the hybrid configurations. A typical mission profile was developed to match the boundary conditions in all cases. Hybrid powertrains confirmed superior behavior than any other cases. The least efficient hybrid configuration, with intermediate battery choices, reduced 10.7% the fuel consumption upon the conventional aircraft and 1.0% facing the battery powered more electric option. Moreover, both baseline models were also surpassed by the worst midway-battery hybrid airplane by 3.6% and 1.0% in overall mission exergy efficiency. Notwithstanding the markets’ actual low battery density, long-range hybrid-electric aircraft will take substantial time to become viable. Nevertheless, only after a significant period, the use of hybrid-electric aircraft will be economically feasible. In the end, preliminary well-to-wake CO2 emissions analysis was developed in all cases for different electricity mix scenarios to observe the environmental impact and viability of the conventional and state-of-the-art configurations.Artigo de evento 0 Citação(ões) na Scopus Exergy analysis as a tool for the rational use of energy in an average house and everyday personal habits(2021-06-28) PEREIRA, M. T. R. M.; Carlos Mady© ECOS 2021 - 34th International Conference on Efficency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems.This article focuses on studying the exergy efficiency of an average household as an appropriate guideline for decision-making concerning technologies and habits in the context of the Brazilian energy matrix and other economic sectors. The exergy behavior is evaluated as a function of the household’s electric appliances and the need for essential services and consumption of everyday items, e.g., food and water. The methods involve evaluating the inputs and outputs to a control volume surrounding the house. As inputs, food, electricity, and fuels were considered, whereas outputs include discharges to the environment in the form of sewage and liquids and urban solid residues. The results show an overall exergy efficiency of 15% for the household, and that the demand for transportation is the most relevant hotspot in both exergy and environmental terms.- Assessment of different more-electric and hybrid-electric configurations for long-range multi-engine aircraft(2023-03-15) GIMENEZ, F. R.; Carlos Mady; HENRIQUES, I. B.© 2023 Elsevier LtdIn this study, the characteristics, penalties, gains, and challenges in the electrification and hybridization process for long-range aircraft were investigated. A system and mission analysis was conducted on thermodynamics and cost. A reference aircraft was compared with other more-electric and hybrid-electric versions of the same type. These latter versions may carry batteries to supply the aircraft system and/or engine. A state-of-the-art propulsion and system architecture were also implemented in these innovative aircraft. A full factorial analysis was conducted to vary the battery energy density and the hybridization ratio for the hybrid configurations. A typical mission profile was developed to match the boundary conditions in all cases. The hybrid powertrains were confirmed in our results as exhibiting superior behavior compared to those of the other cases. The least efficient hybrid configuration, which employed an intermediate battery choice, reduced fuel consumption by 10.7% in the conventional aircraft and by 1% in the battery-powered more-electric type. Moreover, both baseline models were surpassed by the worst intermediate-battery hybrid aircraft by 3.6% and 1% in terms of overall mission exergy efficiency. Considering the actual low density of batteries available on the market, long-range hybrid-electric aircraft will require substantial time to become viable.
- Adressing Energy Demand and Climate Change through the Second Law of Thermodynamics and LCA towards a Rational Use of Energy in Brazilian Households(2022-10-25) PEREIRA, M. T. R. M.; CARVALHO, M.; Carlos Mady© 2022 by the authors.This study focuses on a typical Brazilian household through the lens of sustainable development, regarding energy demand and GHG emissions. The analysis encompasses both the direct and indirect energy, exergy consumption, and GHG emissions (quantified by life cycle assessment) associated with the usual routine of a household. The household is modeled as a thermodynamic system to evaluate inputs (food, electricity, fuels for transportation) and outputs (solid and liquid residues). The hypothesis is that each input and output contains CO (Formula presented.) emissions and exergy derived from its physical-chemical characteristics or production chains. Each household appliance is modeled and tested as a function of external parameters. The contribution of several industries was obtained to the total GHG emissions and exergy flows entering and exiting the household (e.g., fuels for transportation, food, gas, electricity, wastewater treatment, solid waste). It was verified that urban transportation was the flow with the highest GHG and exergy intensity, ranging between 1.49 and 7.53 kgCO (Formula presented.) /day and achieving 94.7 MJ/day, almost five times higher than the calculated exergy demand due to electricity. The second largest flow in GHG emissions was food due to the characteristics of the production chains, ranging from 1.6 to 4.75 kgCO (Formula presented.) /day, depending on the adopted diet. On the other hand, the electricity presented low GHG emissions due to the main energy sources used to generate electricity, only 0.52 kgCO (Formula presented.) /day. Moreover, the chemical exergy of the solid waste was 9.7 MJ/day, and is not irrelevant compared to the other flows, representing an interesting improvement opportunity as it is entirely wasted in the baseline scenario.