In this paper, we present a theoretical study aimed at investigating the rate-limiting factors in thin-film evaporative heat transfer processes, considering the finite-rate evaporation kinetics. The ...problems of evaporation of a flat thin-film in either pure vapours or vapour-inert-gas mixtures are analysed based on the non-dimensionalised macroscopic transport equations for continuum fluids, coupled with out-of-equilibrium kinetic boundary conditions. Both the full numerical solutions and asymptotic analytical solutions at slow evaporation limit are provided and applied to analyse thin water film evaporation. Existing solutions, assuming negligible heat transfer in the gas domain, or negligible temperature jump across the non-equilibrium kinetic layer, or more boldly a thermodynamically equilibrial interface (i.e. its temperature is at the saturation temperature), can be fully recovered from the more general solutions presented here. Our results show that while these assumptions hold in special cases, they can lead to significant errors in many conditions, especially when the film thickness δ is reduced to a few micrometers or thinner. We show that the conventional views that the rate-limiting factors in thin-film evaporative heat transfer is either the heat diffusion through the liquid film or the mass transfer in the gas domain only apply to thick film (i.e. δ≫λ where λ is the mean free path in the vapour phase). As δ decreases to a few micrometer or smaller (more precisely when the Knudsen number Kn increases beyond O(1) in an pure vapour environment or when the kinetic Peclet number Pe is reduced below O(1) in inert gases), the interfacial thermal resistance due to the evaporation kinetics can be on the same orders of magnitude as the thermal resistance in the liquid film. The analysis also allow us to compare the heat transfer processes during the evaporation of a thin-film in pure vapours to those in inert gases, providing deeper insight into the effectiveness of various strategies for exploring the evaporation process in practical thermal management.
•Analysis of thin-film evaporation counting for finite-rate evaporation kinetics.•Provision of both dimensionless numerical and analytical asymptotic solutions.•Significant thermal resistance due to kinetics observed in micrometers or thinner films.•Limitations and conditions for existing assumptions to hold are identified.
Context.
The chemical composition of the Sun is a fundamental yardstick in astronomy, relative to which essentially all cosmic objects are referenced. As such, having accurate knowledge of the solar ...elemental abundances is crucial for an extremely broad range of topics.
Aims.
We reassess the solar abundances of all 83 long-lived elements, using highly realistic solar modelling and state-of-the-art spectroscopic analysis techniques coupled with the best available atomic data and observations.
Methods.
The basis for our solar spectroscopic analysis is a three-dimensional (3D) radiative-hydrodynamical model of the solar surface convection and atmosphere, which reproduces the full arsenal of key observational diagnostics. New complete and comprehensive 3D spectral line formation calculations taking into account of departures from local thermodynamic equilibrium (non-LTE) are presented for Na, Mg, K, Ca, and Fe using comprehensive model atoms with reliable radiative and collisional data. Our newly derived abundances for C, N, and O are based on a 3D non-LTE analysis of permitted and forbidden atomic lines as well as 3D LTE calculations for a total of 879 molecular transitions of CH, C
2
, CO, NH, CN, and OH. Previous 3D-based calculations for another 50 elements are re-evaluated based on updated atomic data, a stringent selection of lines, improved consideration of blends, and new non-LTE calculations available in the literature. For elements where spectroscopic determinations of the quiet Sun are not possible, the recommended solar abundances are revisited based on complementary methods, including helioseismology (He), solar wind data from the Genesis sample return mission (noble gases), sunspot observations (four elements), and measurements of the most primitive meteorites (15 elements).
Results.
Our new improved analysis confirms the relatively low solar abundances of C, N, and O obtained in our previous 3D-based studies: log
ϵ
C
= 8.46 ± 0.04, log
ϵ
N
= 7.83 ± 0.07, and log
ϵ
O
= 8.69 ± 0.04. Excellent agreement between all available atomic and molecular indicators is achieved for C and O, but for N the atomic lines imply a lower abundance than for the molecular transitions for unknown reasons. The revised solar abundances for the other elements also typically agree well with our previously recommended values, with only Li, F, Ne, Mg, Cl, Kr, Rb, Rh, Ba, W, Ir, and Pb differing by more than 0.05 dex. The here-advocated present-day photospheric metal mass fraction is only slightly higher than our previous value, mainly due to the revised Ne abundance from Genesis solar wind measurements:
X
surface
= 0.7438 ± 0.0054,
Y
surface
= 0.2423 ± 0.0054,
Z
surface
= 0.0139 ± 0.0006, and
Z
surface
/
X
surface
= 0.0187 ± 0.0009. Overall, the solar abundances agree well with those of CI chondritic meteorites, but we identify a correlation with condensation temperature such that moderately volatile elements are enhanced by ≈0.04 dex in the CI chondrites and refractory elements possibly depleted by ≈0.02 dex, conflicting with conventional wisdom of the past half-century. Instead, the solar chemical composition more closely resembles that of the fine-grained matrix of CM chondrites with the expected exception of the highly volatile elements.
Conclusions.
Updated present-day solar photospheric and proto-solar abundances are presented for 83 elements, including for all long-lived isotopes. The so-called solar modelling problem – a persistent discrepancy between helioseismology and solar interior models constructed with a low solar metallicity similar to that advocated here – remains intact with our revised solar abundances, suggesting shortcomings with the computed opacities and/or treatment of mixing below the convection zone in existing standard solar models. The uncovered trend between the solar and CI chondritic abundances with condensation temperature is not yet understood but is likely imprinted by planet formation, especially since a similar trend of opposite sign is observed between the Sun and solar twins.
An experimental investigation on the explosion characteristics of hydrogen-air mixtures diluted with inert gases (Ar, N2, CO2) was carried out in a cylinder chamber at room temperature (298 K) ...sub-atmospheric pressures (40 kPa, 60 kPa, 80 kPa, 100 kPa). Based on the pressure history recording, some explosion parameters, e.g., maximum explosion pressure (Pmax), maximum rate of pressure rise ((dp/dt)max), deflagration index (KG) and combustion duration (θ) were derived. Effects of initial pressure (P0), equivalence ratio (φ) and dilution fraction (Z%) on these explosion indices were discussed. The results show that with the increase of initial pressure, the maximum explosion pressure, maximum rate of pressure increase and deflagration index increase monotonously while the combustion duration decrease. The diluent effect on these parameters is increased in the order of Ar, N2 and CO2. Linear correlations Pmax/P0=f(Z), Pmax=f(P0) and (dp/dt)max=f(P0) were found. In addition, the heat loss to the walls during the explosion propagation was estimated on the basis of the difference between the adiabatic and experimental measured pressure. The energy loss increases with the increase of initial pressure and specific heat of the dilutions.
•Effects of dilutions on explosion behaviors of hydrogen-air are studied at reduced pressure.•Explosion indices are derived from the experiment and analyzed.•Heat loss to walls during the explosion propagation is estimated.
A new type of supramolecular chemosensor based on the polyoxometalate (POM) Na
DyW
O
(DyW
) and the block copolymer poly(ethylene oxide-
,
-dimethylaminoethyl methacrylate) (PEO
-
-PDMAEMA
) is ...reported. By taking advantage of the CO
sensitivity of PDMAEMA blocks to protonate the neutral tertiary amino groups, CO
can induce the electrostatic coassembly of anionic DyW
with protonated PDMAEMA blocks, and consequently trigger the luminescence chromism of DyW
due to the change in the microenvironment of Dy
. The hybrid complex in dilute aqueous solution is very sensitive to CO
content and shows rapid responsiveness in luminescence. The luminescence intensity of the DyW
/PEO-
-PDMAEMA complex increases linearly with an increasing amount of dissolved CO
, which permits the qualitative and quantitative detection of CO
. The complex solution also shows good selectivity for CO
, with good interference tolerance of CO, N
, HCl, H
O and SO
. The supramolecular chemosensor can be recycled through disassembly of the hybrid complex by simply purging with inert gases to remove CO
.
The inhibitory effects of CO2, N2 and Ar on TiH2 dust explosion had been experimentally studied. The results showed that the inhibitory effects of the three inert gases on the flame morphology, ...propagation velocity and temperature of TiH2 dust explosion were in the order of CO2 > N2 > Ar under the same oxygen concentration. CO2 accelerated the cooling and extinguishing processes of the incomplete burning particles to inhibit the further dehydrogenation and combustion reactions of TiH2 particles. N2 reacted with TiH2 particles and form ternary Ti-O-N solutions on its surface to hinder the binding progress of TiH2 and O2. In the process of Ar dilution, OH radical was adsorbed on the surface of TiH2-x to enhance its surface reactivity. N2 and CO2 mainly inhibited the explosion of TiH2 dust cloud through dilution of O2, cooling and chemical reactions, whereas Ar mainly played the roles of diluting O2 and cooling.
Display omitted
•Inhibition effects of typical inert gases on TiH2 dust explosion was studied.•Colorimetric pyrometer was used to study the inhibition of TiH2 dust explosion.•Compositions of combustion residues were analyzed to reveal the reaction processes.•Inhibition mechanisms of inert gases on gas-solid phases of TiH2 dust were analyzed.
Construction of functional synthetic systems that can reversibly bind and transport the most biologically important gaseous molecules, oxygen and nitric oxide (NO), remains a contemporary challenge. ...Myoglobin and nitrophorin perform these respective tasks employing a protein‐embedded heme center where one axial iron site is occupied by a histidine residue and the other is available for small molecule ligation, structural features that are extremely difficult to mimic in protein‐free environments. Indeed, the hitherto reported designs rely on sophisticated multistep syntheses for limiting access to one of the two axial coordination sites in small molecules. We have shown previously that binuclear Ga(III) and Al(III) corroles have available axial sites, and now report a redox‐active binuclear Fe(III) corrole, (1‐Fe)2, in which each (corrolato)Fe(III) center is 5‐coordinate, with one axial site occupied by an imidazole from the other corrole. The binuclear structure is further stabilized by attractive forces between the corrole π systems. Reaction of NO with (1‐Fe)2 affords mononuclear iron nitrosyls, and of functional relevance, the reaction is reversible: nitric oxide is released upon purging the nitrosyls with inert gases, thereby restoring (1‐Fe)2 in solutions or films.
Strong attractive interactions between corrole subunits drive the release of nitric oxide from iron(III) nitrosyls, mimicking nitrophorin function.
In the monolayer limit, transition metal dichalcogenides become direct-bandgap, light-emitting semiconductors. The quantum yield of light emission is low and extremely sensitive to the substrate ...used, while the underlying physics remains elusive. In this work, we report over 100 times modulation of light emission efficiency of these two-dimensional semiconductors by physical adsorption of O2 and/or H2O molecules, while inert gases do not cause such effect. The O2 and/or H2O pressure acts quantitatively as an instantaneously reversible “molecular gating” force, providing orders of magnitude broader control of carrier density and light emission than conventional electric field gating. Physi-sorbed O2 and/or H2O molecules electronically deplete n-type materials such as MoS2 and MoSe2, which weakens electrostatic screening that would otherwise destabilize excitons, leading to the drastic enhancement in photoluminescence. In p-type materials such as WSe2, the molecular physisorption results in the opposite effect. Unique and universal in two-dimensional semiconductors, the effect offers a new mechanism for modulating electronic interactions and implementing optical devices.
When lithium-ion batteries undergo thermal runaway in a confined space, the released gases and/or vapors or dust particles can lead to an explosion. An 8L cylindrical experimental vessel was ...constructed to study the inert effect of inert gases on battery-vented gas (BVG) in a confined vessel. Firstly, the inhibition effect and inert mechanism of CO2 and N2 on BVG explosion were analyzed by experiments and simulation software. The results show that the inert effect of CO2 on the BVG is significantly better than that of N2. This is because CO2 is not only better than N2 in physical explosion inhibition, but also participates in the chemical reaction. Secondly, the effect of the release of high-pressure CO2 gas on the explosion of the BVG in a closed container was simulated, showing that when the BVG is near the lower explosive limit, the CO2 jet will significantly increase the rate of explosion pressure rise of the BVG. This suggests that the inhibition effect of the CO2 jet is not as good as in premixed conditions. Finally, it is found that the inhibition effect of CO2 on the hybrid explosion is better than that of CO2 jet on the BVG. Since CO2 makes oxygen insufficient, leading to a reduction in the amount of graphite dust burned. The graphite dust and CO2 have a synergistic inhibition effect on the hybrid explosion. The above findings can provide a reference for the lithium-ion battery explosion inhibition method in the process industry.
•Experimental and theoretical analyses of the inhibition effects of CO2 and N2 on BVG explosion were conducted.•The synergistic effect of CO2 and turbulence on BVG explosion was studied.•The effect of CO2 on the hybrid explosion of BVG and graphite dusts was investigated.
A direct look at halogen bonds Neaton, Jeffrey B.
Science (American Association for the Advancement of Science),
10/2017, Volume:
358, Issue:
6360
Journal Article
Peer reviewed
High-resolution images of halogen-containing molecules reveal unusual bonding patterns
The halogen group elements (F, Cl, Br, I, and At) are, in the words of the late Oliver Sacks, “the absolute ...opposite of the inert gases” (
1
). They are highly electronegative, that is, they strongly attract electrons, making them extremely reactive and even toxic. As a constituent atom in a molecule or complex, halogens therefore tend to be negatively charged. Yet, halogen atoms in molecules can attract other negatively charged species via a noncovalent interaction known as halogen bonding. Somewhat analogous to a hydrogen bond, the halogen bond (
2
) arises from an emergent electrophilic region on a molecule's constituent halogen atom, allowing it to attract a net negatively charged species on the same molecule or on a neighboring molecule (
3
). On page 206 of this issue, Han
et al.
report images of halogen bonding at atomic resolution (
4
).
An experimental and computational investigation has been conducted on the determination of the flammability limits of the multi-component NCA (Nickel, Cobalt, and aluminum) battery vent gas (BVG) ...blended with an inert gas (CO2, H2O, and N2), and on the understanding of associated limit phenomena in general. The simulation results based on detailed chemical kinetics and transport properties agree well with the experimental data from low to high inert gas ratios for both lean and rich limits. In addition, when the inert gas ratio is very high, an absolute limit state exists, at which the lean and rich limits merge, and beyond which flame propagation is not possible. The combustible regime increases in the order of CO2, H2O and N2. The effects of each inert gas on the flame temperature, laminar flame speed, flame broadening, diffusion and radiation are identified and investigated. Furthermore, a linear growth law of the normalized sensitivity with the dominant chain termination reaction rate to the chain branching reaction rate was found near the lean flammability limit. Based on first principle concept of competition between the dominant chain branching and termination reactions, the criterion of a unified flammability exponent is extended to the current multi-component mixture system. This outcome yields useful insight into the fundamental processes of flammability limits, and scrutinizes the heat loss and chain termination effects of flammability limits. Results of this study provide guidance for hazard mitigation and fire suppression for the thermal runaway of lithium-ion batteries.
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