•The CHF experiments were constructed on the one-dimensional full-height facility with 1:1 height ratio of each modeled section to the prototypic counterpart for the IVR strategy of CAP1400.•The ...prototypic SA508-III surface is aged in the temperature of the containment during the normal operating.•After aging, the roughness and wettability are changed with aging time and finally stable, Ra2.6 and 48°, respectively. The porous structure has been observed.•The CHF on the aged surface and the stability of the oxide layer are studied. CHF is enhanced by the aged surface. The oxide layer is not stable and further oxidized by water. After the first experiments, CHF decreases slightly in the second and third experiments.
Critical Heat Flux (CHF) plays an important role in the nuclear power plant safety strategy both during normal operation and under accident conditions. During normal operation, the outside wall is exposed to high-temperature environment. The surface is oxidized by air, which is so-called “aged surface”. To specify the characteristics of aged surface and the effect on CHF, the specimen aging experiments and flow boiling experiments under External Reactor Vessel Cooling (ERVC) were conducted. The results of specimen aging experiments show that surface characteristics get steady after 500 h aging and the oxide layer is the Fe-Fe2O3-Fe3O4 mixture. After aging, the surface gets rougher and has better hydrophily. In the flow boiling experiments, characteristics of heat transfer and CHF are studied. Heat transfer is enhanced by extended surface area and increased nucleation sites at lower angle. The influence of capillary suction is not obvious and the enhancement of CHF is limited. As the inclination angle increases, the departure of bubbles is more frequent and capillary suction is dominant to assist liquid supply into the liquid sublayer and delay the boiling process. At higher angle, CHF is more obviously enhanced but heat transfer gets worse. Overall, CHF of RPV outer wall is increased after surface aging, and it is beneficial to improving the safety margin of IVR mitigation measures.
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•Surface superheat increases during long-term operation in water and salt solutions.•Nucleation activity drops due to wetting, surface chemistry and topography changes.•Boiling curve ...stability is an uncertain indication of surface’s long-term operation.•Aging mechanisms found in water appear in solutions with lower relative importance.•Laser-texturing improves resistance to boiling-induced degradation by up to tenfold.
Long-term boiling stability marks an important and often overlooked characteristic when engineering advanced interfaces for efficient phase-change heat removal. This study presents long-term pool boiling on functionalized smooth and laser-textured copper interfaces in de-ionized water and in an aqueous solution of calcium sulphate. Each surface was exposed to nucleate boiling for several hundred hours and wettability, morphology and surface chemistry were evaluated prior to and after each test. In addition, consecutive pool boiling curves were recorded on all samples. Our findings indicate an increase of wall superheat on all samples, caused by added thermal resistance in the salt solution and by diminished nucleation activity in water. The latter resulted from spatially non-uniform and interconnected mechanisms of wettability transition towards hydrophilicity, surface chemistry changes and topography deformation. These mechanisms also appeared in salt solutions, where their relative importance compared to dominant influence of scaling was linked to crystallization-mitigative ability of the interface. In both liquids, laser-textured surfaces exhibited up to an order of magnitude lower degradation rates. Our results also emphasize the importance of evaluation times of several days to accurately gauge boiling-induced changes to the surface and the ambiguity of evaluating the latter through boiling curve stability.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Elevated tropospheric ozone concentrations are associated with increased morbidity and mortality. Indoor ozone chemistry affects human exposure to ozone and reaction products that also may adversely ...affect health and comfort. Reactive uptake of ozone has been characterized for many building materials; however, scant information is available on how diurnal variation of ambient ozone influences ozone reaction with indoor surfaces. The primary objective of this study is to investigate ozone-surface reactions in response to a diurnally varying ozone exposure for three common building materials: ceiling tile, painted drywall, and carpet tile. A secondary objective is to examine the effects of air temperature and humidity. A third goal is to explore how conditioning of materials in an occupied office building might influence subsequent ozone-surface reactions. Experiments were performed at bench-scale with inlet ozone concentrations varied to simulate daytime (ozone elevated) and nighttime (ozone-free in these experiments) periods. To simulate office conditions, experiments were conducted at two temperatures (22 °C and 28 °C) and three relative humidity values (25%, 50%, 75%). Effects of indoor surface exposures were examined by placing material samples in an occupied office and repeating bench-scale characterization after exposure periods of 1 and 2 months. Deposition velocities were observed to be highest during the initial hour of ozone exposure with slow decrease in the subsequent hours of simulated daytime conditions. Daily-average ozone reaction probabilities for fresh materials are in the respective ranges of (1.7–2.7) × 10−5, (2.8–4.7) × 10−5, and (3.0–4.5) × 10−5 for ceiling tile, painted drywall, and carpet tile. The reaction probability decreases by 7%–47% across the three test materials after two 8-h periods of ozone exposure. Measurements with the samples from an occupied office reveal that deposition velocity can decrease or increase with time. Influence of temperature and humidity on ozone-surface reactivity was not strong.
•We examine ozone reaction with indoor surfaces considering diurnal ozone variation.•Ozone deposition velocities are highest during the initial hour of ozone exposure.•Surface-ozone reaction probability can decrease or increase in the occupied space.•Influence of temperature and humidity on ozone-surface reactivity is moderate.
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•Aging of untreated and enhanced boiling surfaces is underreported.•Two surfaces are exposed to water and pool boiling for eight days.•Untreated surface exhibits two-stage aging with ...increased final performance.•Laser-textured surface exhibits stable behavior with slight HTC degradation.•Universal prediction of the effect of aging on boiling performance is not possible.
Despite its importance for practical applications, investigation of aging of enhanced boiling heat transfer surfaces, which occurs during exposure to the boiling process, is often neglected. This study explores the boiling-induced aging behavior of an untreated and a laser-textured copper boiling surface during an eight-day testing period under pool boiling conditions using saturated water at atmospheric pressure. During the test, approx. 40–50 h of intermittent boiling operation were simulated. Boiling curve measurements are used to quantify boiling performance and measurements during steady state operation periods are used to analyze the heat transfer coefficient variations. SEM imaging, contact angle measurements and Raman spectroscopy are used to analyze the surface morphology, chemistry and wettability before and after exposure to hot water and boiling. The results show that no universal prediction of aging effects is possible. A distinct two-stage aging behavior resulting in increased performance was observed on the reference surface, while the boiling performance of the laser-textured surface changed very little during the test. The results also indicate that functionalized surfaces, which might primarily rely on surface microtopography for boiling enhancement, are presumably less prone to boiling behavior changes resulting from oxidation since slight changes in surface wettability will only have a minor effect on the overall boiling performance. Furthermore, evaluation of long-term performance of enhanced surfaces is necessary since their aging behavior differs from untreated surfaces.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Artificial and natural weathering treatments have been shown to influence the chemical and physical properties of wood and wood-based materials, e.g. moisture content, density, composition and ...coloration. Changes in color caused by natural and artificial sources of ultraviolet radiation (UV) are an important topic to be studied in wood, and have been addressed in this work for eight strength classes of timber species (hardwoods and softwoods). Color measurements were carried out according to ABNT NBR 7190:1997 normative document by the CIE-L*a*b* (CIELAB) system, with L* representing lightness, and a* and b*, red/green and yellow/blue coordinates, respectively. For the samples studied herein, a* and b* approached zero after exposure to artificial UV radiation, when a gray tonality was noticed in dark-colored surfaces. Naturally weathered samples, on the other hand, responded more effectively to long-term UV exposure (360 days) for all color-space parameters, both hardwoods and softwoods. This implies that effects of air pollution and other degradation-aging factors need to be considered. Results of statistical analysis also contributed to quantify changes in color after artificial and natural weathering treatments.
•Considerable changes in color caused by natural and artificial UV sources.•Complete analysis of changes in color for eight strength classes of timbers.•Natural, long-term aging caused changes in all color-space parameters in woods.•Changes in color distinguish weathered softwoods and hardwoods from certified forests.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Fresh two-dimensional molybdenum disulfide (MoS
2
) absorbs the hydrocarbon contaminations in the ambient air and makes surface aging. To understand how the surface aging influences the interactions ...between MoS
2
and biomolecules is important in the biomedical applications. Here, employing all-atom molecular dynamics simulations, we investigated the interactions of the fresh and aged MoS
2
nanosheets with the lipid membranes of different components. Our results demonstrate that both the fresh and aged MoS
2
nanosheets can spontaneously insert into the bilayer membranes. However, the fresh MoS
2
nanosheet displays significantly stronger interaction and then has a larger penetration depth than the aged counterpart, regardless of the lipid components. The calculations of potential mean forces through the umbrella sampling further confirm that the insertion of fresh MoS
2
into the lipid membranes is more energetically favorable. Moreover, we found that the fresh MoS
2
nanosheet can cause a larger damage to the integrity of lipid membranes than the aged one. This work provides insightful understandings of the surface-aging-dependent interactions of the MoS
2
nanosheets with biomembranes, which could facilitate the design of novel MoS
2
-based nanodevices with advanced surface properties.
An inductively-coupled H2O vapor plasma was used to modify the surface of polycarbonate and polyethylene terephthalate track-etched membranes with the goal of permanently increasing the ...hydrophilicity of the membrane surfaces. Contact angle measurements on freshly treated and aged samples confirmed the wettability of the membrane surfaces was significantly improved by plasma treatment. X-ray photoelectron spectroscopy and scanning electron microscopy analyses revealed increased oxygen incorporation onto the surface of the membranes, without any damage to the surface or pore structure. Contact angle measurements on a membrane treated in a stacked assembly suggest the plasma effectively modified the entire pore cross section. Plasma treatment also increased water flux through the membranes, with results from plasma modified membranes matching those from commercially available hydrophilic membranes (treated with wetting agent). Mechanisms for the observed modification are discussed in terms of OH and O radicals implanting oxygen functionality into the polymers.
► The surfaces of track-etched membranes were modified using H2O vapor plasmas. ► The entire membrane cross section was undamaged and became permanently hydrophilic. ► Modified membranes have significantly higher water flux than untreated membranes. ► Modification occurs via substantial oxygen incorporation in the treated membranes. ► Mechanisms for observed changes in membrane composition and performance are given.
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The use of active components in biomaterials improves the properties of existing ones and makes it possible to obtain new devices with antibacterial properties that prevent infections after ...implantation, thus guaranteeing the success of the implant. In this work, cetyltrimethylammonium bromide (CTAB) and magnesium particles were incorporated into polylactic acid (PLA) films to assess the extent to which progressive aging of the new surfaces resists bacterial colonization processes. For this purpose, the films' surface was characterized by contact angle measurements, ToF-SIMS and AFM, and adhesion, viability and biofilm growth of
bacteria on these films were also evaluated. The results show that the inclusion of Mg and CTAB in PLA films changes their surface properties both before and after aging and also modifies bacterial adhesion on the polymer. Complete bactericidal activity is exhibited on non-degraded films and films with CTAB. This antibacterial behavior is maintained after degradation for three months in the case of films containing a higher amount of CTAB.
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► Exposure of Li
x
Ni
1/3Mn
1/3Co
1/3O
2 to humidity delithiates a surface layer 10
nm thick. ► It is independent of the time of exposure (
t
>
few min) and of the cation disorder. ► It is associated ...to the formation of LiOH and Li
2CO
3 impurities at the surface. ► Lamellar compounds are more sensitive to humidity than olivines.
LiNi
1/3Mn
1/3Co
1/3O
2 compound was successfully synthesized by the co-precipitation method. The effect of H
2O on LiNi
1/3Mn
1/3Co
1/3O
2 in humid atmosphere was investigated by structural, magnetic and electrochemical analysis, and Raman spectroscopy. The consequence is that immersion of LiNi
1/3Mn
1/3Co
1/3O
2 to H
2O and exposure of LiNi
1/3Mn
1/3Co
1/3O
2 to humid atmosphere (ambient atmosphere, 20
°C, 50% relative humidity) led to a rapid attack that manifests itself by the delithiation of the surface layer of the particles and the concomitant formation of LiOH and Li
2 CO
3 at the surface. This aging process occurred during the first few minutes, then it is saturated, and the thickness of the surface layer at saturation is 10
nm. After aging, an initial discharge capacity of 139
mAh/g was delivered at 1C-rate in the cut-off voltage of 3.0–4.3
V. About 95% of its initial capacity was retained after 30 cycles.
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LiNi1/3Mn1/3Co1/3O2 compound was successfully synthesized by the co-precipitation method. The effect of H2O on LiNi1/3Mn1/3Co1/3O2 in humid atmosphere was investigated by structural, magnetic and ...electrochemical analysis, and Raman spectroscopy. The consequence is that immersion of LiNi1/3Mn1/3Co1/3O2 to H2O and exposure of LiNi1/3Mn1/3Co1/3O2 to humid atmosphere (ambient atmosphere, 20 °C, 50% relative humidity) led to a rapid attack that manifests itself by the delithiation of the surface layer of the particles and the concomitant formation of LiOH and Li2 CO3 at the surface. This aging process occurred during the first few minutes, then it is saturated, and the thickness of the surface layer at saturation is 10 nm. After aging, an initial discharge capacity of 139 mAh/g was delivered at 1 C-rate in the cut-off voltage of 3.0-4.3 V. About 95% of its initial capacity was retained after 30 cycles.
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