1,886 research outputs found
Brayton technology for Concentrated Solar Power plants: Comparative analysis of central tower plants and parabolic dish farms
[EN]Concentrated solar power plants intend to be key in the pool of renewable energy production technologies in the next future because of their versatility and high efficiency. In this work a comparative study between two promising technologies is developed. A central tower receiver surrounded by a heliostat field and a farm of parabolic dishes, both coupled to a hybrid Brayton cycle, are considered. Two power scales are surveyed (between 5 and 20 MW) at three different locations with quite different latitudes (between Sahara desert and medium European latitudes) and meteorological conditions. A modelling scheme developed by our group that allows to obtain the expected thermodynamic and thermo-economic plant records is applied. Key indicators like efficiency, net generated energy, levelized cost of electricity, and specific plant investment are calculated and analysed. Variability of natural gas prices and also land cost uncertainty are reflected on levelized cost of electricity range. Among the plants compared, minimum values are found within the interval [135–163] USD/MWh for central towers at the highest power considered and southern latitudes. In addition, the area needed for the installation of the plants and the influence of CO
taxes is also analysed. Displayed cashflows show larger investment costs for central tower than for dish farms. Finally, those systems are put into the context of other concentrated solar power, other renewable, like wind or photovoltaic, and other conventional power plants.PC_TCUE18-20P_010.
Universidad de Salamanca and Banco de Santande
Designing the physical metallurgy of a bainitic microalloyed steel with a dilatometer
During the past decade, medium carbon microalloyed steels have become increasingly important in the automotive sector. These steels are especially suitable for automobile components such as connecting rods, crankshafts and wheel hubs. Their mechanical properties are generally adequate in most cases although their toughnesses are consistently low. High toughness can be obtained in medium carbon microalloyed bainitic steel (38MnV7) after a careful control of the chemistry and heat thermal treatment. An specific chemical composition of a 38MnV7 steel has been developed, providing impact energies after Charpy-V tests at room temperature as high as 40J (the steel in bainitic state). Present work is oriented to an optimization of the above chemical composition by control of the Transformation Time Temperature (TTT) curves as well as the Precipitation Time Temperatures (PTT) curves of the present microallying elements. To attain this purpose six different casting were prepared, ranging the chemical composition as follows %C: 0.35-0.46, %Mn: 1.33-1.84, %V: 0.066-0.14% and %Ti: 0.010- 0.025. To appropriate design the thermal cycle, TTT curves were determined for each steel at two austenitization conditions, in order to promote fine and large initial grain sizes.. PTT curves were determined by the stress relaxation technique, a method which can be also be used to derive recrystrallization kinetics. All curves, TTT and PTT curves where derived by using a quenching dilatometer Bahr DIL805A/D.
While the TTT curves were obtained in a classical way, the relaxation test consist in sample austenization followed by cooling down to the testing temperature. After a short stabilization period of 10s, samples are deformed to different strain levels and then relaxed, i.e. deformation is kept constant and the variation of the stress with the time is recorded. The different deformation levels are selected to evaluate the effect of deformation on precipitation characteristics. The relaxation curves under these conditions gave information about the kinetics of precipitation when there is no plastic deformation and, thus, generation of dislocations involved. Results are finally discussed in terms of the chemical composition, initial microstructure and precipitates interaction.Peer Reviewe
Malnutrition as cause and consequence of sensory distorsiones
La malnutrición es una enfermedad provocada por un
exceso o defecto en el consumo o aprovechamiento de los
nutrientes. Habitualmente, se utiliza este término para
referirse a la desnutrición, es decir, a un trastorno derivado
del déficit de algún macro y o micronutrientes.
Las alteraciones quimiosensoriales pueden reducir de
forma importante la alimentación en el individuo, por lo
que es importante verificar que el aporte de nutrientes y, de
forma concreta, de algunos micronutrientes, sea suficiente,
ya que alguno de ellos, como el zinc, desempeñan un papel
primordial en las alteraciones del gusto y del olfato.
Además, el paciente malnutrido o con una alimentación
que excluya gran número de alimentos, tiene mayor
riesgo de presentar déficits de dichos micronutrientes.
Diversas enfermedades, tanto agudas como crónicas, se
asocian a alteraciones de la percepción sensorial, y pueden
llegar a afectar a más del 50% de las personas mayores de
65 años. Los efectos provocados por los fármacos y algunos
tratamientos como la quimioterapia y la radioterapia, juegan
también un papel muy importante en la distorsión sensorial
y en la incidencia de malnutriciónMalnutrition is a pathological condition caused by an
excess or deficiency in the consumption or the use of the
nutrients. Usually this term refers to a lack of adequate
nourishment, a disorder resulting from a deficiency of
some macro and/or micronutrients.
Chemo-sensory alterations can significantly reduce
food choice and intake, so it is very important to verify
that the supply of nutrients and specifically of some
micronutrients are sufficient. Some of them, such as
“zinc”, play a very important role in alterations in the
sense of taste and smell.
In addition malnutrition patients or a poorly-balanced
diet or faulty utilization of foods have increased the risk
of deficiencies in these micronutrients.
Several types of diseases, both acute and chronic ones,
are associated with sensory perception and can affect
more than 50% of people over 65 years old. The effects
caused by drugs and some treatments such as chemotherapy
and radiation therapy play an important role in sensory
distortion and the incidence of malnutritio
Coefficient of performance at maximum figure of merit and its bounds for low-dissipation Carnot-like refrigerators
The figure of merit for refrigerators performing finite-time Carnot-like
cycles between two reservoirs at temperature and () is
optimized. It is found that the coefficient of performance at maximum figure of
merit is bounded between 0 and for the
low-dissipation refrigerators, where is the
Carnot coefficient of performance for reversible refrigerators. These bounds
can be reached for extremely asymmetric low-dissipation cases when the ratio
between the dissipation constants of the processes in contact with the cold and
hot reservoirs approaches to zero or infinity, respectively. The observed
coefficients of performance for real refrigerators are located in the region
between the lower and upper bounds, which is in good agreement with our
theoretical estimation.Comment: 5 journal pages, 3 figure
Aqueous phase reforming of starch wastewater over Pt and Pt-based bimetallic catalysts for green hydrogen production
This work analyses the application of aqueous phase reforming (APR) for green hydrogen production from starch industry wastewater. This work reports for the first time on the direct conversion of a high molecular weight biomass polymer contained in wastewater in contrast to low molecular weight substrates mainly reported in the literature. The potential of this type of feedstock was evaluated by varying the starch source (rice, potato, sweet potato and cassava) and the type of catalyst (carbon supported Pt, PtRu, PtPd, PtRe and PtRh catalysts). In APR experiments at 220 °C with synthetic wastewater, PtRu/C and Pt/C catalysts achieved the highest H2 yield values, around 51 mmol H2 per g of organic carbon in the initial wastewater, close to 2.6 times higher than that reported in the literature of brewery wastewater, a promising substrate. The lack of free aldehyde or keto groups due to glycosidic bonds between glucose units in starch results in higher conversion to gas and H2 production compared to APR of glucose. This fact shows that APR has more feedstock flexibility than that previously reported for light compounds. In the experiments with real wastewaters, the organic matter removal was influenced largely by the starch source: the best APR performance (28.5 mmol H2 gTOCi−1) was obtained for rice processing wastewater, which is characterized by the highest starch concentration and the lowest protein content. Poor performance was observed in the APR of potato processing wastewater, probably due to catalyst deactivation caused by protein fractio
Pumped heat energy storage with liquid media: Thermodynamic assessment by a transcritical Rankine-like model
[EN]A pumped heat energy storage (PHES) system based on a Rankine cycle for supercritical working fluids, such
as carbon dioxide and ammonia, accounting for the irreversible latent and sensible heat transfers between
the working fluid and the storage liquid medium, as water or thermal oil, is analyzed. The model also
includes several parameters such as pressure losses, heat exchanger efficiencies, and isentropic efficiencies of
the compressor, pump, and expansion devices (such as turbines and valves), that take into account the main
internal and external losses and heat leak to the environment. The model allows for the calculation of specific
energy, the heat pump performance coefficient, heat engine efficiency, and overall round-trip efficiency, as well
as the temperatures of the working fluid and reservoirs. A zero-dimensional model is also used to determine
the time dependence of heat leak in the tanks. The main results show that this technology could achieve
round trip efficiency values in the order of 50–70%. Irreversibilities in compression and expansion appears
as the most influential energy losses factor. The time effect of the ambient conditions on the tanks has been
analyzed for a wet subtropical climate but it seems that the ambient conditions have no major influence on the
performance of the system. In addition, explicit numerical results and temperature–entropy plots are presented
for two representative systems as carbon dioxide-water and ammonia-thermal oil to take into account the main
values in an operating condition
Resorcinolic Lipids from Yucatecan Propolis
Propolis is a material produced by bees from a combination of plant exudates and wax, used to fill out cracks in the beehive and to defend against intruders and pathogenic microorganisms; it is recognized for its many biological activities and its chemical composition depends on the botanical sources close to the beehive. The objective of this investigation was to isolate and identify metabolites with antioxidant activity present in a propolis sample collected in Yucatan, Mexico. Purification of the bioactive metabolites was carried out using argentation chromatography, while the combination of 1H nuclear magnetic resonance (NMR), laser desorption ionization (LDI), gas chromatography-mass spectrometry (GC-MS) and biosynthetic origin data allowed their identification as resorcinolic lipids. Finally, the resin of Mangifera indica was identified as the botanical source of these metabolite
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