534 research outputs found
Optimização de aproveitamento de condensados em sistemas energéticos
Mestrado em Engenharia MecânicaNos últimos anos tem-se assistindo a um aumento do consumo de energia devido ao desenvolvimento socioeconómico dos países e ao aumento da população global. De forma a auxiliar o aumento do consumo de energia têm se
desenvolvido técnicas de análise com o objectivo principal de optimizar os consumos energéticos nos processos produtivos.
Inicialmente dois métodos de análise e optimização de redes térmicas são analisadas e comparadas. Estas análises, Pinch e Termoecnómica, revelaram
grandes potencialidades na obtenção de melhorias, sendo a pinch a metodologia seleccionada para implementação no caso de estudo, por se
tratar de uma área com alguma carência de especialistas e de implementação sistemática, o que facilita na busca por melhorias.
Neste trabalho é realizada uma análise de eficiência energética a uma rede de fluidos térmicos real através da tecnologia pinch. Este tipo de análise permite a definição de metas que motivam o projectista na pesquisa por melhores soluções de recuperação de energia entre as correntes de processo.
As metas inicialmente calculadas pela tecnologia pinch são ultrapassadas devido ao máximo aproveitamento dos permutadores existentes que permitem o aumento da temperatura de uma determinada corrente para além do seu
ponto pinch.
Com a implementação desta metodologia foi possível a obtenção de duas situações de melhoria que revelam o potencial deste tipo de análise ao se
constatar que não existe apenas uma situação óptima, podendo optar-se por propostas com melhores resultados a nível energético ou económico.
No caso de estudo foi possível obter reduções na ordem de 1010 kg/h de vapor o que implica uma redução 17% do consumo anual de vapor. A redução na factura energética anual é de aproximadamente 98.000,00. Para a obtenção destas reduções é necessária a aquisição de permutadores de calor com tempo de retorno de investimento entre 2 e 3 meses o que torna as duas
situações muito atractivas.
Nas duas situações propostas obteve-se reduções de cerca de 8% do consumo específico da instalação em estudo podendo esta cumprir os novos planos de racionalização (SGCIE) e obter os benefícios fiscais conseguidos pelo cumprimento destes.
ABSTRACT: In recent years an increase of the energy consumption was verified, this is caused by the socio-economic development of the countries and the increase of global population. In order to assist the increase of energy consumption, techniques were developed to optimize these consumptions in productive processes.
Initially two methods of analysis and optimization of thermal systems were analyzed and compared. These analyzes, Pinch and Thermoeconomic had
disclosed great potentialities in the attainment of improvements, Pinch methodology was the selected one to implement in the study case, it was
chosen because it’s an area with a lack of specialists and the possibility of systematic implementation.
In this work is made an analysis of energetic efficiency to a real thermal fluid net through the Pinch technology. This type of analysis allows the
definition of targets that motivate the developer in the research for better solutions of energy recovery in process chains.
The initially calculated energy targets by pinch technology were exceeded because of the maximum exploitation of the existing exchangers that allow the increase of temperature in a current beyond its point pinch By implementing this methodology it was possible to obtain two
improvement situations, what reveal the potential of Pinch analysis, being possible to find several proposals of performing with great results at energetic or economic level.
In study case it was achieved reductions in the order of 1010kg/h of steam, which implies a 17% reduction in the annual consumption. The reduction in annual energy bill is approximately € 98,000.00. To obtain these reductions, the company must acquire heat exchangers, which the return of investment is between 2 and 3 months, that makes the proposes very attractive.
In this two proposals situations, one obtained reductions close to 8% of the specific consumption of installation in study being able to fulfill the new plans of rationalization (SGCIE) and obtaining tax benefits by the fulfilment of these
Desenvolvimento e caracterização de nanofluidos para intensificação de transferência de calor
Doutoramento em Engenharia MecânicaA desmaterialização da economia é um dos caminhos para a promoção do
desenvolvimento sustentável na medida em que elimina ou reduz a utilização
de recursos naturais, fazendo mais com menos. A intensificação dos
processos tecnológicos é uma forma de desmaterializar a economia. Sistemas
mais compactos e mais eficientes consomem menos recursos. No caso
concreto dos sistemas envolvendo processo de troca de calor, a intensificação
resulta na redução da área de permuta e da quantidade de fluido de trabalho, o
que para além de outra vantagem que possa apresentar decorrentes da
miniaturização, é um contributo inegável para a sustentabilidade da sociedade
através do desenvolvimento científico e tecnológico.
O desenvolvimento de nanofluidos surge no sentido de dar resposta a estes
tipo de desafios da sociedade moderna, contribuindo para a inovação de
produtos e sistemas, dando resposta a problemas colocados ao nível das
ciências de base. A literatura é unânime na identificação do seu potencial
como fluidos de permuta, dada a sua elevada condutividade, no entanto a falta
de rigor subjacente às técnicas de preparação dos mesmos, assim como de
um conhecimento sistemático das suas propriedades físicas suportado por
modelos físico-matemáticos devidamente validados levam a que a
operacionalização industrial esteja longe de ser concretizável.
Neste trabalho, estudou-se de forma sistemática a condutividade térmica de
nanofluidos de base aquosa aditivados com nanotubos de carbono, tendo em
vista a identificação dos mecanismos físicos responsáveis pela condução de
calor no fluido e o desenvolvimento de um modelo geral que permita com
segurança determinar esta propriedade com o rigor requerido ao nível da
engenharia. Para o efeito apresentam-se métodos para uma preparação
rigorosa e reprodutível deste tipo de nanofluido assim como das metodologias
consideradas mais importantes para a aferição da sua estabilidade,
assegurando deste modo o rigor da técnica da sua produção. A estabilidade
coloidal é estabelecida de forma rigorosa tendo em conta parâmetros
quantificáveis como a ausência de aglomeração, a separação de fases e a
deterioração da morfologia das nanopartículas.
Uma vez assegurado o método de preparação dos nanofluídos, realizou-se
uma análise paramétrica conducente a uma base de dados obtidos
experimentalmente que inclui a visão central e globalizante da influência
relativa dos diferentes fatores de controlo com impacto nas propriedades
termofísicas. De entre as propriedades termofísicas, este estudo deu particular
ênfase à condutividade térmica, sendo os fatores de controlo selecionados os
seguintes: fluido base, temperatura, tamanho da partícula e concentração de
nanopartículas. Experimentalmente, verificou-se que de entre os fatores de
controlo estudados, os que maior influência detêm sobre a condutividade
térmica do nanofluido, são o tamanho e concentração das nanopartículas.
Com a segurança conferida por uma base de dados sólida e com o
conhecimento acerca da contribuição relativa de cada fator de controlo no
processo de transferência de calor, desenvolveu-se e validou-se um modelo
físico-matemático com um caracter generalista, que permitirá determinar com
segurança a condutividade térmica de nanofluidos.The economy dematerialization is a means to promote sustainable
development as it eliminates or reduces the use of natural resources. Hence,
the intensification of technological processes is a way to dematerialize the
economy. More compact and efficient systems require fewer resources. In what
concerns technological systems involving heat exchange processes,
intensification results in the reduction of the exchanging area and amount of
working fluid, which in addition to other advantages inherent to systems’
miniaturization, is a direct contribution of the scientific and technological
development to a more sustainable society.
The development of nanofluids is a response to such challenges of
contemporary society, contributing to the innovation of products and systems
by solving fundamental questions raised at the level of basic sciences. The
available literature is unanimous identifying nanofluids potential as an
engineering thermal fluid due to their thermo-physical properties, namely a high
thermal conductivity. However, the lack of rigorous preparation techniques as
well as of a systematic knowledge of their thermo-physical properties,
supported by validated physical-mathematical models, are serious constrains to
their use in engineering applications.
In this work, the thermal conductivity of carbon nanotubes, water based
nanofluids were systematically studied. The governing physical mechanisms
for heat conduction in the nanofluid were established as the basic condition for
the development of a general model able to securely determine this property
with the precision required in engineering applications. For this purpose the
methodologies to correctly prepare such nanofluids in a reproducible way as
well as to measure their long term stability are presented. The colloidal stability
is accurately established and quantified taking into account parameters such as
the absence of agglomeration, separation of phases and deterioration of the
morphology of the nanoparticles.
A parametric analysis was developed through appropriate DOE methodologies
in order to build a comprehensive data base of the nanofluid physical properties
as a function of control factors, previously identified variables considered to
have the greatest impact on the variability of thermo-physical properties.
Among the latter, this work gives particular attention to the acquisition of
thermal conductivity data against the selected control factors: base fluid,
temperature, size and concentration of nanoparticles. It was verified
experimentally that amongst these control factors, those that hold the greatest
influence on the thermal conductivity of the nanofluid are the size and
concentration of nanoparticles.
A solid database and the awareness about the relative contribution of each
mechanism controlling the heat transfer process in nanofluids successfully
supported the development and validation of a general physical-mathematical
model to determine the thermal conductivity of nanofluids
MAMMALS IN PORTUGAL : A data set of terrestrial, volant, and marine mammal occurrences in P ortugal
Mammals are threatened worldwide, with 26% of all species being includedin the IUCN threatened categories. This overall pattern is primarily associatedwith habitat loss or degradation, and human persecution for terrestrial mam-mals, and pollution, open net fishing, climate change, and prey depletion formarine mammals. Mammals play a key role in maintaining ecosystems func-tionality and resilience, and therefore information on their distribution is cru-cial to delineate and support conservation actions. MAMMALS INPORTUGAL is a publicly available data set compiling unpublishedgeoreferenced occurrence records of 92 terrestrial, volant, and marine mam-mals in mainland Portugal and archipelagos of the Azores and Madeira thatincludes 105,026 data entries between 1873 and 2021 (72% of the data occur-ring in 2000 and 2021). The methods used to collect the data were: live obser-vations/captures (43%), sign surveys (35%), camera trapping (16%),bioacoustics surveys (4%) and radiotracking, and inquiries that represent lessthan 1% of the records. The data set includes 13 types of records: (1) burrowsjsoil moundsjtunnel, (2) capture, (3) colony, (4) dead animaljhairjskullsjjaws, (5) genetic confirmation, (6) inquiries, (7) observation of live animal (8),observation in shelters, (9) photo trappingjvideo, (10) predators dietjpelletsjpine cones/nuts, (11) scatjtrackjditch, (12) telemetry and (13) vocalizationjecholocation. The spatial uncertainty of most records ranges between 0 and100 m (76%). Rodentia (n=31,573) has the highest number of records followedby Chiroptera (n=18,857), Carnivora (n=18,594), Lagomorpha (n=17,496),Cetartiodactyla (n=11,568) and Eulipotyphla (n=7008). The data setincludes records of species classified by the IUCN as threatened(e.g.,Oryctolagus cuniculus[n=12,159],Monachus monachus[n=1,512],andLynx pardinus[n=197]). We believe that this data set may stimulate thepublication of other European countries data sets that would certainly contrib-ute to ecology and conservation-related research, and therefore assisting onthe development of more accurate and tailored conservation managementstrategies for each species. There are no copyright restrictions; please cite thisdata paper when the data are used in publications.info:eu-repo/semantics/publishedVersio
Multidifferential study of identified charged hadron distributions in -tagged jets in proton-proton collisions at 13 TeV
Jet fragmentation functions are measured for the first time in proton-proton
collisions for charged pions, kaons, and protons within jets recoiling against
a boson. The charged-hadron distributions are studied longitudinally and
transversely to the jet direction for jets with transverse momentum 20 GeV and in the pseudorapidity range . The
data sample was collected with the LHCb experiment at a center-of-mass energy
of 13 TeV, corresponding to an integrated luminosity of 1.64 fb. Triple
differential distributions as a function of the hadron longitudinal momentum
fraction, hadron transverse momentum, and jet transverse momentum are also
measured for the first time. This helps constrain transverse-momentum-dependent
fragmentation functions. Differences in the shapes and magnitudes of the
measured distributions for the different hadron species provide insights into
the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any
supplementary material and additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb
public pages
Study of the decay
The decay is studied
in proton-proton collisions at a center-of-mass energy of TeV
using data corresponding to an integrated luminosity of 5
collected by the LHCb experiment. In the system, the
state observed at the BaBar and Belle experiments is
resolved into two narrower states, and ,
whose masses and widths are measured to be where the first uncertainties are statistical and the second
systematic. The results are consistent with a previous LHCb measurement using a
prompt sample. Evidence of a new
state is found with a local significance of , whose mass and width
are measured to be and , respectively. In addition, evidence of a new decay mode
is found with a significance of
. The relative branching fraction of with respect to the
decay is measured to be , where the first
uncertainty is statistical, the second systematic and the third originates from
the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb
public pages
Measurement of the ratios of branching fractions and
The ratios of branching fractions
and are measured, assuming isospin symmetry, using a
sample of proton-proton collision data corresponding to 3.0 fb of
integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The
tau lepton is identified in the decay mode
. The measured values are
and
, where the first uncertainty is
statistical and the second is systematic. The correlation between these
measurements is . Results are consistent with the current average
of these quantities and are at a combined 1.9 standard deviations from the
predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb
public pages
Mammals in Portugal: a data set of terrestrial, volant, and marine mammal occurrences in Portugal
Mammals are threatened worldwide, with ~26% of all species being included in the IUCN threatened categories. This overall pattern is primarily associated with habitat loss or degradation, and human persecution for terrestrial mammals, and pollution, open net fishing, climate change, and prey depletion for marine mammals. Mammals play a key role in maintaining ecosystems functionality and resilience, and therefore information on their distribution is crucial to delineate and support conservation actions. MAMMALS IN PORTUGAL is a publicly available data set compiling unpublished georeferenced occurrence records of 92 terrestrial, volant, and marine mammals in mainland Portugal and archipelagos of the Azores and Madeira that includes 105,026 data entries between 1873 and 2021 (72% of the data occurring in 2000 and 2021). The methods used to collect the data were: live observations/captures (43%), sign surveys (35%), camera trapping (16%), bioacoustics surveys (4%) and radiotracking, and inquiries that represent less than 1% of the records. The data set includes 13 types of records: (1) burrows | soil mounds | tunnel, (2) capture, (3) colony, (4) dead animal | hair | skulls | jaws, (5) genetic confirmation, (6) inquiries, (7) observation of live animal (8), observation in shelters, (9) photo trapping | video, (10) predators diet | pellets | pine cones/nuts, (11) scat | track | ditch, (12) telemetry and (13) vocalization | echolocation. The spatial uncertainty of most records ranges between 0 and 100 m (76%). Rodentia (n =31,573) has the highest number of records followed by Chiroptera (n = 18,857), Carnivora (n = 18,594), Lagomorpha (n = 17,496), Cetartiodactyla (n = 11,568) and Eulipotyphla (n = 7008). The data set includes records of species classified by the IUCN as threatened (e.g., Oryctolagus cuniculus [n = 12,159], Monachus monachus [n = 1,512], and Lynx pardinus [n = 197]). We believe that this data set may stimulate the publication of other European countries data sets that would certainly contribute to ecology and conservation-related research, and therefore assisting on the development of more accurate and tailored conservation management strategies for each species. There are no copyright restrictions; please cite this data paper when the data are used in publications
Determination of quantum numbers for several excited charmed mesons observed in B- -> D*(+)pi(-) pi(-) decays
A four-body amplitude analysis of the B − → D * + π − π − decay is performed, where fractions and relative phases of the various resonances contributing to the decay are measured. Several quasi-model-independent analyses are performed aimed at searching for the presence of new states and establishing the quantum numbers of previously observed charmed meson resonances. In particular the resonance parameters and quantum numbers are determined for the D 1 ( 2420 ) , D 1 ( 2430 ) , D 0 ( 2550 ) , D ∗ 1 ( 2600 ) , D 2 ( 2740 ) and D ∗ 3 ( 2750 ) states. The mixing between the D 1 ( 2420 ) and D 1 ( 2430 ) resonances is studied and the mixing parameters are measured. The dataset corresponds to an integrated luminosity of 4.7 fb − 1 , collected in proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV with the LHCb detector
Updated measurement of decay-time-dependent CP asymmetries in D-0 -> K+ K- and D-0 -> pi(+)pi(-) decays
A search for decay-time-dependent charge-parity (CP) asymmetry in D0 \u2192 K+ K 12 and D0 \u2192 \u3c0+ \u3c0 12 decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4 fb^ 121. The D0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutral D meson at production. The asymmetries in the effective decay widths of D0 and anti-D0 mesons are determined to be A_\u393(K+ K 12) = ( 124.3 \ub1 3.6 \ub1 0.5)
7 10^ 124 and A_\u393(\u3c0+ \u3c0 12) = (2.2 \ub1 7.0 \ub1 0.8)
7 10^ 124 , where the uncertainties are statistical and systematic, respectively. The results are consistent with CP symmetry and, when combined with previous LHCb results, yield A_\u393(K+ K 12) = ( 124.4 \ub1 2.3 \ub1 0.6)
7 10^ 124 and A_\u393(\u3c0+ \u3c0 12) = (2.5 \ub1 4.3 \ub1 0.7)
7 10^ 124
Updated measurement of decay-time-dependent CP asymmetries in D-0 -> K+ K- and D-0 -> pi(+)pi(-) decays
A search for decay-time-dependent charge-parity (CP) asymmetry in D-0 -> K+ K- and D-0 -> pi(+)pi(-) eff decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4 fb(-1). The D-0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutral D meson at production. The asymmetries in the effective decay widths of D-0 and (D) over bar (0) mesons are determined to be A(Gamma)(K+ K-) = (-4.3 +/- 3.6 +/- 0.5) x 10(-4) and A(Gamma) (K+ K- ) = (2.2 +/- 7.0 +/- 0.8) x 10(-4), where the uncertainties are statistical and systematic, respectively. The results are consistent with CP symmetry and, when combined with previous LHCb results, yield A(Gamma) (K+ K-) = (-4.4 +/- 2.3 +/- 0.6) x 10(-4) and A(Gamma) (pi(+)pi(-))= (2.5 +/- 4.3 +/- 0.7) x 10(-4)
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