Photospheric properties and fundamental parameters of M dwarfs

M dwarfs are an important source of information when studying and probing the lower end of the Hertzsprung-Russell (HR) diagram, down to the hydrogen-burning limit. Being the most numerous and oldest stars in the galaxy, they carry fundamental information on its chemical history. The presence of molecules in their atmospheres, along with various condensed species, complicates our understanding of their physical properties and thus makes the determination of their fundamental stellar parameters more challenging and difficult. The aim of this study is to perform a detailed spectroscopic analysis of the high-resolution H-band spectra of M dwarfs in order to determine their fundamental stellar parameters and to validate atmospheric models. The present study will also help us to understand various processes, including dust formation and depletion of metals onto dust grains in M dwarf atmospheres. The high spectral resolution also provides a unique opportunity to constrain other chemical and physical processes that occur in a cool atmosphere The high-resolution APOGEE spectra of M dwarfs, covering the entire H-band, provide a unique opportunity to measure their fundamental parameters. We have performed a detailed spectral synthesis by comparing these high-resolution H-band spectra to that of the most recent BT-settl model and have obtained fundamental parameters such as effective temperature, surface gravity, and metallicity (Teff, log g and [Fe/H]) respectively.Comment: 15 pages, 10 figures, accepted for publication in A&

A review of biomass thermal analysis, kinetics and product distribution for combustion modeling: from the micro to macro perspective

Driven by its accessibility, extensive availability, and growing environmental consciousness, solid biomass has emerged as a viable alternative to enhance the diversity of renewable energy sources for electricity generation. To understand the phenomena involved in solid biomass conversion, it is necessary not only to understand the stages of the biomass combustion process but also to understand specifically the kinetics of the reaction and the release of the volatiles. The present work presents an overview of the existing literature on several topics related to the biomass combustion process, its characterization, as well as strategies to develop simple and effective models to describe biomass conversion with a view to the future development of numerical simulation models. Since the focus of most of the investigations is the development of a numerical model, a summary and identification of the different model assumptions and problems involved in thermal analysis experiments are presented. This literature review establishes the significance and credibility of the research, providing the main concepts and assumptions with a critique on their validity. Hence, this work provides specific contributions from a multi-scale perspective which can further be extended to provide insights into the design and optimization of biomass combustion technologies, such as boilers and furnaces.This work was supported by the Portuguese Foundation for Science and Technology (FCT) within the R&D Units Project Scope UIDB/00319/2020 (ALGORITMI), and R&D Units Project Scope UIDP/04077/2020 (MEtRICs)

Numerical modeling and optimization of an air handling unit

Concerns about the efficiency of Heating, Ventilating, and Air Conditioning systems, including Air Handling Units (AHUs), started in the last century due to the energy crisis. Thenceforth, important improvements on the AHUs performance have emerged. Among the various improvements, the control of the AHUs and the redesign of the fans are the most important ones. Although, with increasingly demanding energy efficiency requirements, other constructive solutions must be investigated. Therefore, the objective of this work is to investigate, using a computational fluid dynamics (CFD) tool, the fluid flow inside an AHU and to analyze different constructive solutions in order to improve the AHU performance. The numerical model provided a reasonable agreement with the experimental results in terms of air flow rate, despite the assumed simplifications. Regarding the constructive solution concept, the CFD results for the two different flow control units (FCUs) showed improvements in terms of fan static pressure rise. Under real conditions, improvements of 15.1% when compared with the case without the FCU were obtained. Nevertheless, it was concluded that the axial component of the air velocity, at the fan exit, can have a determinant impact on the FCU viability. Finally, an improved FCU geometry, with a new body shape, which resulted in an additional improvement of 6.1% in the fan static pressure rise.The second author would like to express his gratitude for the support given by FCT through the Grant SFRH/BD/130588/2017

A CFD study of a pMDI plume spray

Uncorrected proofAsthma is an inflammatory chronic disease characterized by airway obstructions disorders. The treatment is usually done by inhalation therapy, in which pressurized metered-dose inhalers (pMDIs) are preferred devices. The objective of this paper is to characterize and simulate a pMDI spray plume by introducing realistic factors through a computational fluid dynamics (CFD) study. Numerical simulations were performed with Fluent® software, by using a three-dimensional “testbox” for room environment representation. A salbutamol/HFA-134a formulation was used for characterization, whose properties taken as input for the CFD simulations. Spray droplets were considered to be composed by ethanol, salbutamol and HFA-134a. Propellant evaporation was taken into consideration, as well as, drag coefficient correction. Results showed an air temperature drop of 3.3 °C near the nozzle. Also, an increase in air velocity of 3.27 m/s was noticed. The CFD results seem to be in good agreement with Dunbar (1997) data on particle average velocity along the axial distance from the nozzle.National Funds-Portuguese Foundation for Science and Technology, under Strategic Project PEst-C/EME/UI4077/2011 and PEst-OE/EME/299UI0252/201

Design of an inlet track of a small I.C. engine for swirl enhancement

The purpose of this project was to re-design the inlet port of a small Internal Combustion Engine in order to enhance the production of turbulence by swirl. A good swirl promotes fast combustion and improves the efficiency. A small internal combustion engine was designed to be part of a very efficient vehicle to enter a consumption marathon. The engine should run at low speeds, in order to have low mechanical losses but the combustion should be fast, enabling good combustion efficiency. Therefore high turbulence should be produced prior to combustion within the cylinder, so swirl was induced by the inlet channel within the cylinder head. To perform this task the help of three software programs is required, Solid Works, Gambit and Fluent. The first was required to produce the CAD-geometry. To build the geometry it is important to bear in mind that there are some restrictions for casting and fuel injection. In the next step, Gambit meshes the geometry in the design by using a volume mesh. At last; Fluent calculates the flow within the engine by using a suitable turbulence model. Initially the current geometry was tested and proved to create low swirl, so the geometry was changed several times until reaching a good result in terms of generated swirl. The tests include just steady flow, where the air enters the inlet port and leaves the bottom of the cylinder continuously. The flow within the cylinder is examined at specific sections, namely at various heights of the cylinder (horizontal sections) and pathlines are also evaluated. The flow is calculated for various valve lifts at a specific engine condition.Fundação para a Ciência e a Tecnologia (FCT) - POCI/EME/59186/2004MIT Portugal Program - MIT-Pt/EDAM-SMS/0030/200

On Exact and Approximate Solutions for Hard Problems: An Alternative Look

We discuss in an informal, general audience style the da Costa-Doria conjecture about the independence of the P = NP hypothesis and try to briefly assess its impact on practical situations in economics. The paper concludes with a discussion of the Coppe-Cosenza procedure, which is an approximate, partly heuristic algorithm for allocation problems.P vs. NP , allocation problem, assignment problem, traveling salesman, exact solution for NP problems, approximate solutions for NP problems, undecidability, incompleteness

Influence of arterial mechanical properties on carotid blood flow: comparison of CFD and FSI studies

Carotid artery blood flow is studied to compare models with rigid and elastic walls. Considering a patient-specific geometry and transient boundary conditions. In the case of rigid walls, only the fluid (blood) behavior is considered, in a typical Computational Fluid Dynamics study. With the elastic walls, the reciprocal influence of both fluid and solid (blood and artery) are taken into account, constituting a Fluid-Structure Interaction study. Further more, the study of the influence of mechanical properties of the artery, which become stiffer with the progression of atherosclerosis, on blood flow is also presented, an innovative approach relative to the work done in this field. Results show that the carotid sinus is the preferential zone to develop atherosclerosis, given its low values of Time-Averaged Wall Shear Stress. Additionally, it is fundamental to consider the arterial wall as elastic bodies, given that the rigid model overestimates the flow velocity and Wall Shear Stress. On the different mechanical properties of the vessel, its influence is minimal in the Time-Averaged Wall Shear Stress profiles. However, given the results of the displacement and velocity profiles, their inclusion in blood flow simulations in stenosed arteries should be considered.This work was supported by FEDER funds through the COMPETE program with the reference project PTDC/SEM-TEC/3827/2014. Additionally, this work is supported by FCT with the reference projects UID/EEA/04436/2019, UID/CEC/00319/2019 and UID/EMS/04077/2019

Project-based learning in a mechanical engineering course: A new proposal based on student's views

The evolution of learning in higher education is nowadays evident. Several discussions and studies have been performed about new methodologies that can disrupt the way the classes are taught in universities. In this context, Project-Based Learning (PBL) is the most emphasized. In the Mechanical Engineering course at the University of Minho (UM), the Integration Project (IP) courses apply a PBL methodology, being these classes the differentiating element of the Integrated Master in Mechanical Engineering (IMME) compared with other Portuguese universities. However, even if the innovative aspect of this approach is recognized nationally, the opinions between students and Professors, about the structure and organization of this class, are still divided. In that sense, this work presents a new proposal for the IP courses in which the opinion of students and successful models implemented in international universities are considered. This study analyses the best PBL methodologies implemented in Engineering courses and presents a PBL model actually implemented at the IMME. This information is combined with the student's views obtained from a survey conducted at the Department of Mechanical Engineering (DEM), regarding the actual PBL model. Through this study, a new proposal for the IP courses is presented. This proposal intends to provide an effective answer to the necessity of the students, using successful tools and methodologies to improve the teaching and learning process in the IMME course. Through this proposal, it is expected to increase the learning process and motivation of the students making them better prepared for a productive profession.The first author would like to express her gratitude for the support given by the Portuguese Foundation for Science and Technology (FCT) and the MIT Portugal Program. This work has been supported by FCT - Fundacao para a Ciencia e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020 (ALGORITMI Center) and R&D Units Project Scope UIDP/04077/2020 (METRICS Center)

Exergy efficiency optimization for gas turbine based cogeneration systems

Energy degradation can be calculated by the quantification of entropy and loss of work and is a common approach in power plant performance analysis. Information about the location, amount and sourc es of system deficiencies are determined by the exergy analysis, which quantifies the exergy destruction. Micro - gas turbines are prime movers that are ideally suited for cogeneration applications due to their flexibility in providing stable and reliable power. This paper presents an exergy analysis by means of a numerical simulation of a regenerative micro - gas turbine for cogeneration applications . The main objective is to study the best configuration of each system component , considering the minimization of the system irreversibilities . Each component of the system was evaluated considering the quantitative exergy balance . Subsequently the optimization procedure was applied to the mathematical model that describes the full system. The rate of irreversibility, efficiency and flaws are highlighted for each system component and for the whole system. The effect of turbine inlet temperature change on plant exergy destruction was also evaluated . The results disclose that considerable exergy destruction occurs in the combustion chamber. Also, it was revealed that the exergy efficiency is expressively dependent on the changes of the turbine inlet temperature and increases with the latter .The authors would like to express their acknowledgments for the support given by the Portuguese F01mdation for Science and Technology (FCT) through the PhD grant SFRH/BD/62287/2009. This work was financed by National Funds-Portuguese Foundation for Science and Technology, under Strategic Project and PEst-OE/EME/UI0252/2011 and also the PEst-C/EME/UI4077/2011