13,043 research outputs found
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)
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
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
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
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&
In-cylinder swirl analysis of different strategies on over-expanded cyclies
Innovative series hybrid vehicles have a small Internal Combustion Engine used as a “range extender”. This
engine should work at steady conditions whenever is running. Therefore its development is quite different from engines
intended to be driven (unsteady working conditions, such as accelerations). For thıs applicatıon the engine
development seeks optimisation on a specified speed/load condition.
Previous work proved the concept of over-expansion, as a mean to enhance thermal efficiency of spark ignition
engines, even beyond the efficiency of common Diesel engines. There are two ways of performing over-expansion
through variation of inlet valve timing: early inlet valve closure (EIVC) and late inlet valve closure (LIVC).
To further enhance efficiency, these engines should work with lean or extra lean mixtures. which are very sensitive to
in-cylinder charge motion. In order to improve fast burning rates at lean conditions one should optimise turbulence at
the end of the compression stroke.
A small engine geometry and mesh was created in GAMBIT and later FLUENT was used to perform calculations of the
in-cylinder fluid dynamics during intake and compression strokes.
These calculations were performed with both described over-expanded valve strategies. The results are compared with
engine performance data using the same strategies.Fundação para a Ciência e a Tecnologia (FCT) - (SFRH / BPD / 48189 / 2008), POCI/EME/59186/2004, POCI/ENR/59168/2004MIT Portugal Program - MIT-Pt/EDAMSMS/0030/2008
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