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1.
Experiments were conducted in a full‐scale physical model of a delta‐shaped, four‐strand tundish to study the effect of flow modifiers on tundish performance. Two different types of flow modifiers were studied; an existing flow‐modifier and a turbulence‐inhibitor. Their effects were quantified by measuring residence times of fluid in the tundish and residual ratios of inclusions. Although the Turbulence‐Inhibitor appeared to be more effective in guiding flows than the flow‐modifier, the latter gave the longer average residence times and smaller residence time differences between the inner and outer nozzles, which resulted in a higher residual ratio of inclusions. 相似文献
2.
Ennio M. Palmeira Débora L.A. Melo Isac P. Moraes-Filho 《Geotextiles and Geomembranes》2019,47(4):566-576
Nonwoven geotextiles have been used as filters in geotechnical and geoenvironmental works for half a century. They are easy to install and can be specified to meet the requirements for proper filter performance. There are situations where a geotextile filter may be subjected to tensile loads, which may alter relevant filter properties, such as its filtration opening size. Examples of such situations are silty fence applications, geotextile separators, geotextile tubes and geotextiles under embankments on soft soils. This paper investigates the effects of tensile strains on geotextile pore dimensions. A special equipment and testing technique allowed tests to be carried out on geotextile specimens subjected to tension and confinement. The results obtained showed that the variation in filtration opening size depends on the type of strain state the geotextile is subjected, under which the geotextile pore diameter may remain rather constant or increase significantly. However, confinement reduces the geotextile filtration opening size independent on the strain mobilised. An upper bound for the filtration opening size of strained nonwoven geotextiles is introduced and was satisfactory for the geotextile products tested. 相似文献
3.
Dynamic wetting and heat transfer at the initiation of aluminum solidification on copper substrates 总被引:1,自引:0,他引:1
Dominique Bouchard Sébastien Leboeuf Jean-Paul Nadeau Roderick I. L. Guthrie Mihaiela Isac 《Journal of Materials Science》2009,44(8):1923-1933
Dynamic wetting and heat transfer during the start of solidification were studied with the help of molten aluminum droplets
falling from a crucible onto a copper substrate. A high-speed camera captured the change in the spreading droplet’s geometry,
while thermocouple, inserted inside the substrate, allowed a heat transfer analysis to be performed. Droplet spreading factors
and interfacial heat fluxes were then used to, respectively, characterize dynamic wetting and heat transfer for the various
experimental conditions explored. These were: (1) effects of chemical composition of the aluminum alloy, (2) initial temperature
of the substrate, (3) surface roughness of the substrate, and (4) composition of the gaseous atmosphere. The experiments were
all carried out in gaseous atmospheres containing oxygen in sufficient amount to form oxide skins at the surface of the droplets
and the substrates. The results showed instances where an improvement in the dynamic wetting was accompanied by an increase
in heat transfer during the early stages of solidification but this was not systematic. In these cases where a positive correlation
was not observed, it was postulated this was caused by factors such as variations in the oxidation at the surface of the substrates
and the droplets as well as gas trapped at the interface between the droplets and the substrates.
Sébastien Leboeuf formerly with the Aluminum Technology Centre and McGill University. 相似文献
4.
Kinnor Chattopadhyay Mainul Hasan Mihaiela Isac Roderick I.L. Guthrie 《Metallurgical and Materials Transactions B》2010,41(1):225-233
Inert gas shrouding practices were simulated using a full-scale, four-strand water model of a 12-tone, delta-shaped tundish.
Compressed air was aspirated into the ladle shroud to model volumetric flow rates that range between 2 and 10 pct of steel
entry flows. Bubble trajectories, slag layer movements, and flow fields, were visualized. Flow fields were visualized using
particle image velocimetry (PIV). A numerical model also was developed using discrete phase modeling (DPM) along with the
standard k-ε turbulence model with two-way turbulence coupling. Predicted flow fields and bubble trajectories corresponded with the
water model experiments. 相似文献
5.
Instantaneous interfacial heat fluxes during the 4 to 8 m/min casting of carbon steels in a twin-roll caster 总被引:2,自引:0,他引:2
R. P. Tavares M. Isac F. G. Hamel R. I. L. Guthrie 《Metallurgical and Materials Transactions B》2001,32(1):55-67
Instantaneous heat fluxes between the roll and the solidifying metal were evaluated in a pilot twinroll caster, producing
strips of low-carbon steels. This evaluation was based on the solution of an inverse heat-transfer problem, using temperature
readings of thermocouples inserted at various locations in the roll sleeve. The response times of the thermocouples were determined
and used to correct measured temperatures. The variation of the instantaneous heat fluxes with time of contact between the
roll and the melt presented two distinct types of behavior, one exhibiting a single peak and other a double peak, depending
on the casting conditions. These different patterns were interpreted in terms of the variation of the metallostatic pressure,
solidification shrinkage, thermal expansion of the rolls, and characteristics of the solid shell. Predictions of the amounts
of heat extracted by the roll and secondary dendrite arm spacings (SDAS) in the strips, based on the calculated heat fluxes,
were in reasonable agreement with experimental values. This also demonstrated that the level of correction applied to the
thermocouple readings was appropriate. 相似文献
6.
7.
Rosalin Abraham Soosy Kuryan Jayakumari Isac Ajesh K. Zacharia Sabu Thomas 《应用聚合物科学杂志》2011,120(4):2233-2241
Electrical impedance measurements are carried out on high temperature superconducting ceramic Yttrium Barium Copper Oxide (YBCO)–Polystyrene (PS) composite materials, in which superconducting particles are embedded in polystyrene matrix. The results of impedance versus frequency (100 Hz–13 MHz), phase angle versus temperature for volume percentage of superconductor (0–40%) are presented. No marked transition in phase angle is observed when the material goes through the superconducting transition temperature of the filler. The dielectric constant and losses increase with increasing YBCO content. However the increase in losses is modest and the excellent dielectric properties of the composites are not adversely affected. The system conforms to Clausius‐Mossotti equation. Dipole moment of YBCO particles and polarizability of the composites are calculated using the Clausius‐Mossotti approaches. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
8.
Maria Eliza de Castro Moreira Rosemary Gualberto Fonseca Alvarenga Pereira Danielle Ferreira Dias Vanessa Silva Gontijo Fabiana Cardoso Vilela Gabriel de Oliveira Isac de Moraes Alexandre Giusti-Paiva Marcelo Henrique dos Santos 《Journal of Functional Foods》2013,5(1):466-474
Green coffee contains a large quantity and variety of polyphenols and flavonoids. The roasting affects the composition of the polyphenols in coffee, due to the formation of compounds generated by Maillard reaction, which can have anti-inflammatory or antioxidant potential. The anti-inflammatory and antioxidant effects of aqueous extracts of green (AGCa) and roasted (ARCa) coffee beans were investigated in animal models and using a DPPH radical scavenging test. In the formalin test the extracts reduced licking activity only in the late phase. The inhibitory values of oedema at 3 h post-carrageenan were 53% and 74% for 100 and 300 mg/kg of the AGCa extract and 36% for ARCa (300 mg/kg). Leukocyte recruitment into the peritoneal cavity was inhibited by the extracts. The antioxidant activities of the extracts were higher than the reference antioxidants, ascorbic acid and butylated hydroxytoluene. These results indicate that coffee extracts exhibit anti-inflammatory and antioxidant properties. 相似文献
9.
R. I. L. Guthrie M. Isac J. S. Kim R. P. Tavares 《Metallurgical and Materials Transactions B》2000,31(5):1031-1047
Using implanted thermocouples, and an inverse heat-transfer technique, heat fluxes and associated heat-transfer coefficients
during the solidification of steel in a pilot scale 0.6-m-diameter twin roll caster, whose copper contact surfaces had been
treated with a propriety coating, were measured. It was found that heat fluxes during initial contact of liquid steel with
the rolls were low, rising to maximum values of about 5 to 6 MW per square meter halfway down the sump of liquid steel, but
then diminishing toward zero as the strip approached the roll nip. These results corresponded to roll speeds of some 7 m/min,
strip thicknesses of 7 mm, and a roll separating force of 20 kN. For higher speeds and thinner strip, a secondary peak in
the heat flux was observed. Associated microstructures revealed acicular ferrite, large prior austenite grains, and secondary
dendrite arm spacings in keeping with measurements.
In parallel experiments simulating a single belt horizontal caster, heat fluxes from strips of various aluminum alloys to
coated and uncoated steel and copper substrates were measured. Under these conditions, peak heat fluxes were recorded during
the period of initial contact, and depending on the coating characteristics, these reduced to a lower plateau before declining,
or continuously decreased toward zero, corresponding to complete solidification of the strip.
A theoretical analysis of the maximum heat-transfer rates that can be expected given perfect thermal contact of metal with
the rolls, and its moderations by gas films, and substrate coatings illustrates the dominant role of the gas film and the
need for dynamic heat flux measurements for quantitative modeling of fluid flows and solidification phenomena in thin strip
casting operations. A model for air gap formation is proposed, based on viscous laminar flows within the gas films. Predicted
thicknesses are in reasonable accord with those deduced on the basis of heat flux measurements.
This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney,
Australia, under the joint sponsorship of ISS and TMS. 相似文献
10.
Praseodymium barium molybdate (PBM) single crystals grown by gel method, reveal multiple and isolated octahedral bipyramidal
crystals as well as spherulites of PBM at different depths from the surface inside the gel. Oscillation X-ray diffraction
pattern of the sample reveals that PBM is single crystalline in nature. Infrared absorption spectrum confirms the presence
of molybdate (MoO4)2− ions in PBM, while the thermogravimetric analysis shows that PBM loses molybdenum oxide component around 420°C. Energy dispersive
X-ray analysis establishes the presence of Pr, Ba and Mo in the sample. X-ray photoelectron spectroscopic studies of PBM establish
the presence of Pr, Ba and Mo in their respective oxide states. An empirical structure has been proposed on the basis of these
findings. The implications are discussed. 相似文献