Artigos
URI permanente para esta coleçãohttps://repositorio.fei.edu.br/handle/FEI/799
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Resultados da Pesquisa
- Comparison among exergy analysis methods applied to a human body thermal model(2022-01-15) RIBEIRO, T. J. D. S.; Carlos Mady© 2021 Elsevier LtdOver the past decades, thermodynamics concepts applied to biological systems, such as the human body, have aided in explaining their functioning. The first law of thermodynamics is primarily used — from the prime research that assessed the body surface area and the temperature distribution in members to the thermal comfort conditions with Fanger methods. The second law of thermodynamics may provide new insights to this discussion because it considers the internal irreversibilities of human metabolisms to the external communications with the environment. In this study, we compared three methods to evaluate the exergy behavior of the human body with an aim to determine the thermal comfort conditions. This is defined as 30oC and 50% of relative humidity. All methods indicated equivalent points of thermal comfort conditions, thus raising the question of how to apply the exergy analysis in similar reasoning for the three models. Therefore, a distinguishing feature of this study concerns the additional contributions when applying the exergy analysis in the same human thermal model. Furthermore, we attempted to compare and suggest connections or adjustments for each method to pave the way for the realization of a unified exergy model of the human body in the future.
- The effect of carbon monoxide on the exergy behavior of the lungs(2018-12-05) CENZI, J. R.; Cyro Albuquerque; Carlos Mady© 2018 by the authors.The present work evaluates the impact of carbon monoxide (CO) inhalation on the human lung’s exergy behavior by considering different levels of intoxication and amounts of hemoglobin. Its impact is significant because CO is one of the most common air pollutants in cities and an increase in destroyed exergy may be correlated with lifespan reduction or the malfunctioning of certain human organs. An evaluation of the severity of intoxication as a function of city altitude may intensify the hazard associated with carbon monoxide. A computational model of human lungs obtained from the literature was used to calculate the concentrations of oxygen (O2), carbon monoxide (CO), and carbon dioxide (CO2) in the respiratory system. With the purpose of better evaluating the different levels of CO intoxication and hemoglobin concentration (which is a function of acclimatization time and some pathologies, such as anemia), a model calculating exergy efficiency for the lungs was proposed. From this model, it was possible to conclude that a higher level of intoxication is associated with lower exergy efficiency values. When associated with carbon monoxide intoxication, higher hemoglobin levels also result in lower efficiency. Eventually, a comparison between previous studies and the current study was carried out, regarding the method employed to calculate the exergy destroyed in the lungs, considering not only gas transport, but also hemoglobin concentration and its reaction with the gases from a second law perspective.
- Phenomenological and thermodynamic model of gas exchanges in the placenta during pregnancy: A case study of intoxication of carbon monoxide(2019-11-05) CENZI, J. R.; Cyro Albuquerque; MADY, C. E. K.© 2019 by the authors. Licensee MDPI, Basel, Switzerland.The present work simulates the transport of oxygen, carbon dioxide, and carbon monoxide between a fetus’s circulatory system and the mother’s. The organ responsible for this exchange is the placenta. Carbon monoxide is a common air pollutant, and it impacts the physiological conditions even in low concentration. The impacts of carbon monoxide are especially dangerous for pregnant women, fetuses, and newborn babies. A model of carbon monoxide transport, from the literature, is modified to simulate a pregnant woman (original model was a male), therefore changing some parameters to express the adjusted respiratory system. It was considered the gas exchange in the placenta, to evaluate the concentration of these different gases in the fetus arterial and venous blood. Three methods of the exergy analysis are implemented for both mother and fetus respiratory systems, aiming at the comparison with the respiratory system of a male adult. The destroyed exergy of the literature did not have the same trend as the models proposed in this article, taking into consideration the hemoglobin reactions. In contrast, the entropy generation associated only with the diffusion transport phenomena was one order of magnitude lower than the other methods. The placenta destroyed exergy rate is significantly higher compared to the irreversibilities of the mother’s respiratory system. One possible explanation is the fact that the placenta has other physiological functions than gas transportation.
- Exergy efficiency on incremental stationary bicycle test: A new indicator of exercise performance?(2019-12-01) MADY, C. E. K.; IGARASHI, T. L.; Cyro Albuquerque; SANTOS-SILVA, P. R.; FERNANDWS, A. J.; HERNANDEZ, A. J.© 2019, The Brazilian Society of Mechanical Sciences and Engineering.The first and second laws of the thermodynamics were applied to the human body to evaluate the performance of subjects under different training levels. Ten cyclists were evaluated in the stationary bicycle with the indirect calorimetry analysis to obtain the metabolism on an energy and exergy basis. A distinguishing feature of this article is the evaluation of the exergy efficiency of the body with the knowledge of the real performed power and the internal temperature (measured tympanic temperature and calculated esophagus temperature). Regarding the skin temperature, an infrared camera was used to measure different parts of the body. Therefore, the phenomenological behavior of the body was assessed and used as a basis to apply the exergy analysis. Results indicate that the destroyed exergy can be an indicator of performance when compared with maximum oxygen consumption. Nevertheless, more experiments must be carried out to proper state if there is a correlation. Eventually, the exergy efficiency was calculated for all subjects, and its value was around 23 to 28%.
- Energy and exergy analysis of an absorption and mechanical system for a dehumidification unit in a gelatin factory(2021-04-05) LIMA, L. S.; Carlos Mady© 2020 by the authors.In this paper, an energy and exergy analysis is applied to the air dehumidification unit of a liquid desiccant system in an industrial gelatin conveyor dryer. The working fluid is a binary solution of lithium chloride (LiCl) in water. Dry air is used in order to decrease the amount of liquid in the gelatin. Therefore, the environmental air must have its absolute humidity reduced from about 12 g/kg to the project target, which is 5 g/kg. The process is a cycle using an absorption desiccant unit (LiCl in water), where the weak solution absorbs water vapor from the air. In the regenerator, condensation of the solution (desorption) from the moist air occurs. As a result, the steam consumption of the desorber and electrical power used for the vapor compression chiller (with ammonia, NH3, as working fluid) are the primary sources of cost for the factory. To improve the plant’s energy and exergy behaviors, the process is evaluated using a mathematical model of the system processes. In addition, we evaluate the substitution of the vapor compression chiller by an absorption unit (lithium bromide (LiBr) in water). The performance indicators of the compression vapor systems showed the best results. Even when using the condenser’s energy to pre-heat the solution, the installed system proved to be more effective.
- Exergy analysis of the human body to assess thermal comfort conditions: Comparison of the thermal responses of males and females(2021-06-05) MOLLIET, D. S.; Carlos Mady© 2021 The Author(s).Males and females share the same physiological transportation systems and phenomenological mechanism to exchange heat and mass with the environment. Nevertheless, a literature review shows that they have significantly distinctive anatomies, metabolic rates, and hormonal cycles, all of which influence individual comfort conditions. Moreover, how to obtain thermal environments that suit everyone's thermal comfort conditions remains unclear. Therefore, computational models were proposed to compare thermal behaviors in different environments for two males (one dressed in a suit and the other in lighter clothing) and two females with the same office clothing (in the luteal and follicular phases). Exergy indicators were compared with traditional indices used to assess thermal comfort in air conditioning environments. The minimum points of destroyed exergy had similar occurrences to PMV=0 and PPD=5%. The environmental temperature in which the exergy minimums occurred varied by approximately 5% compared to traditional energy indices. It was concluded that females demand higher comfort temperatures than men. Women's comfort temperatures in the luteal phase were similar to men in lighter clothing and lower during the follicular phase. Higher environmental temperatures respecting the use lightweight clothing implies a lower energy expenditure, with a reduction of electricity by approximately 22%.
- Exergy efficiency on incremental stationary bicycle test: A new indicator of exercise performance?(2019-11-16) MADY, CARLOS EDUARDO KEUTENEDJIAN; IGARASHI, TATIANE LIE; Cyro Albuquerque; SANTOS-SILVA, PAULO ROBERTO; FERNANDES, TIAGO LAZZARETTI; HERNANDEZ, ARNALDO JOSEThe frst and second laws of the thermodynamics were applied to the human body to evaluate the performance of subjects under diferent training levels. Ten cyclists were evaluated in the stationary bicycle with the indirect calorimetry analysis to obtain the metabolism on an energy and exergy basis. A distinguishing feature of this article is the evaluation of the exergy efciency of the body with the knowledge of the real performed power and the internal temperature (measured tympanic temperature and calculated esophagus temperature). Regarding the skin temperature, an infrared camera was used to measure diferent parts of the body. Therefore, the phenomenological behavior of the body was assessed and used as a basis to apply the exergy analysis. Results indicate that the destroyed exergy can be an indicator of performance when compared with maximum oxygen consumption. Nevertheless, more experiments must be carried out to proper state if there is a correlation. Eventually, the exergy efciency was calculated for all subjects, and its value was around 23 to 28%.
- Phenomenological and Thermodynamic Model of Gas Exchanges in the Placenta during Pregnancy: A Case Study of Intoxication of Carbon Monoxide(2019-10-19) CENZI, JULIANA RANGEL; Cyro Albuquerque; MADY, KEUTENEDJIAN CARLOS EDUARDOThe present work simulates the transport of oxygen, carbon dioxide, and carbon monoxide between a fetus’s circulatory system and the mother’s. The organ responsible for this exchange is the placenta. Carbon monoxide is a common air pollutant, and it impacts the physiological conditions even in low concentration. The impacts of carbon monoxide are especially dangerous for pregnant women, fetuses, and newborn babies. A model of carbon monoxide transport, from the literature, is modified to simulate a pregnant woman (original model was a male), therefore changing some parameters to express the adjusted respiratory system. It was considered the gas exchange in the placenta, to evaluate the concentration of these different gases in the fetus arterial and venous blood. Three methods of the exergy analysis are implemented for both mother and fetus respiratory systems, aiming at the comparison with the respiratory system of a male adult. The destroyed exergy of the literature did not have the same trend as the models proposed in this article, taking into consideration the hemoglobin reactions. In contrast, the entropy generation associated only with the diffusion transport phenomena was one order of magnitude lower than the other methods. The placenta destroyed exergy rate is significantly higher compared to the irreversibilities of the mother’s respiratory system. One possible explanation is the fact that the placenta has other physiological functions than gas transportation.
- Exergy analysis of the musculoskeletal system efficiency during aerobic and anaerobic activities(2018) Spanghero G.M.; Albuquerque C.; Fernandes T.L.; Hernandez A.J.; Mady C.E.K.© 2018 by the authors.The first and second laws of thermodynamics were applied to the human body in order to evaluate the quality of the energy conversion during muscle activity. Such an implementation represents an important issue in the exergy analysis of the body, because there is a difficulty in the literature in evaluating the performed power in some activities. Hence, to have the performed work as an input in the exergy model, two types of exercises were evaluated: weight lifting and aerobic exercise on a stationary bicycle. To this aim, we performed a study of the aerobic and anaerobic reactions in the muscle cells, aiming at predicting the metabolic efficiency and muscle efficiency during exercises. Physiological data such as oxygen consumption, carbon dioxide production, skin and internal temperatures and performed power were measured. Results indicated that the exergy efficiency was around 4% in the weight lifting, whereas it could reach values as high as 30% for aerobic exercises. It has been shown that the stationary bicycle is a more adequate test for first correlations between exergy and performance indices.
- The effect of altitude and intensity of physical activity on the exergy efficiency of respiratory system(2014) Henriques I.B.; Mady C.E.K.; Albuquerque Neto C.; Yanagihara J.I.; Oliveira 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, body 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: respiratory system and human body as a whole. Data concerning mass and energy balances of the body and respiratory system were obtained from models available in the literature, which were modified based on medical literature to simulate the responses to physical activity at high altitude for different periods of acclimatization. The results indicated that the respiratory system exergy efficiency is reduced at high altitudes and under physical activity, while exergy efficiency of the body increases for both parameters, which may indicate that the discomfort reported at high altitudes is mostly related to the respiratory system than to the other ones. Concerning the acclimatization period, its influence was more pronounced on the respiratory system.